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Sample records for comparative first-principles study

  1. Comparative study of Ti and Ni clusters from first principles

    Energy Technology Data Exchange (ETDEWEB)

    Lee, B; Lee, G W

    2007-08-20

    Icosahedral clusters in Ti and Ni are studied with first-principles density functional calculations. We find significant distortion on the Ti icosahedron caused by the strong interaction between surface atoms on the icosahedron but not between the center atom and surface atoms, whereas no such distortion is observed on Ni clusters. In addition, distortion becomes more severe when atoms are added to the Ti13 cluster resulting in short bonds. Such distorted icosahedra having short bonds are essentially to explain the structure factor of Ti liquid obtained in experiment.

  2. Comparative first-principles study of clean-surface properties of metals

    Science.gov (United States)

    Patra, Abhirup; Sun, Jianwei; Perdew, John P.

    Metal surfaces are widely used in different applications from nano-devices to heterogeneous catalysis. Clean-surface properties such as the surface energy, work function and interlayer spacing importantly determine the behavior of metal surfaces. Prior work has been done to understand these properties using high-level methods including the local density approximation (LDA) and the generalized gradient approximation (PBE). In this work, we study (111) (100) and (110) surfaces of Pt, Pd, Cu, Al, Au, Ag, Rh and Ru by extrapolation from a finite number of layers. These surfaces are studied using SCAN, a new member of the computationally-efficient meta-GGA family of density functionals. We have compared the performance of SCAN and three other standard density functionals - LDA, PBE and PBEsol - to available experimental results. We find that the performance of the general-purpose SCAN is at the level of the more-specialized PBEsol, giving accurate metallic properties. Ref: Jianwei Sun, Adrienn Ruzsinszky, John P Perdew, Strongly Constrained and Appropriately Normed Semilocal Density Functional, Physical Review Letters115 (3), 036402 (2015). Supported by NSF under DMR-1305135, CNS-09-5884, and by DOE under DE-SC0012575, DE-AC02-05CH11231.

  3. Theoretical investigation of manganese adsorption on graphene and graphane: A first-principles comparative study

    Energy Technology Data Exchange (ETDEWEB)

    AlZahrani, A.Z., E-mail: azalzahrani@kau.edu.sa [Physics department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589 (Saudi Arabia)

    2012-03-15

    Within the framework of spin-polarized generalized gradient approximation ({sigma}GGA) of the density functional theory (DFT) and pseudopotential method, the structural, magnetic, and electronic properties of graphene and graphane upon the adsorption of manganese atoms have been theoretically investigated. In contrast to the recent results (New J. Phys. 12, 063020 (2010)), Mn atom has been found to be adsorbed on a hollow-site configuration and no appreciable indication to substitute one of the C atoms of the graphene sheet. Unlike the recent results on Mn-doped graphane (Carbon 48, 3901 (2010)), the Mn adatom prefers to adsorb on the top of a carbon atom, forming a bridge with the uppermost hydrogen atoms. The magnetic moment of the Mn-doped graphene is found to be larger than that of the Mn-doped graphane. The structural parameters and electronic properties of both Mn-doped graphene and Mn-doped graphane are determined and compared with the available data.

  4. Study on Co-doped ZnO comparatively by first-principles calculations and relevant experiments

    Science.gov (United States)

    Su, Y. L.; Zhang, Q. Y.; Zhou, N.; Ma, C. Y.; Liu, X. Z.; Zhao, J. J.

    2017-01-01

    Co-doped ZnO was studied using first-principles methods with comparison to experimental results taken from epitaxial Zn1-xCoxO (x 0.05) films. Density of Co2+ ions was determined using absorption spectra for the first time, and then a definite correlation between metallic Co clusters and the magnetism of the ZnCoO films was proved and the average number of Co atoms in the metallic Co clusters was estimated to be less than 200 using a superparamagnetic model. First-principles calculations of ZnCoO alloys and the relevant problems were discussed by comparing the electronic structures with absorption spectra and the results calculated by Tanabe-Sugano theory. U correction was proved to be necessary for calculating the band-gap energy of ZnCoO alloys, but other optical properties related to Co2+ ions are incorrect and the conclusion for magnetic properties is ambiguous due to uncertainty of the calculated highly localized states, which are in pressing for solution in study of material properties relevant to electronic structure.

  5. First-principles calculations of structural, electronic, vibrational, and magnetic properties of C-60 and C48N12 : A comparative study

    NARCIS (Netherlands)

    Xie, RH; Bryant, GW; Jensen, L; Smith, VH

    2003-01-01

    The structural, electronic, vibrational, and magnetic properties of the C48N12 azafullerene and C-60 are comparatively studied from the first-principles calculations. Full geometrical optimization and Mulliken charge analysis are performed. Electronic structure calculations of C48N12 show that the

  6. Thermal Conductivity of Wurtzite Zinc-Oxide from First-Principles Lattice Dynamics--a Comparative Study with Gallium Nitride.

    Science.gov (United States)

    Wu, Xufei; Lee, Jonghoon; Varshney, Vikas; Wohlwend, Jennifer L; Roy, Ajit K; Luo, Tengfei

    2016-03-01

    Wurtzite Zinc-Oxide (w-ZnO) is a wide bandgap semiconductor that holds promise in power electronics applications, where heat dissipation is of critical importance. However, large discrepancies exist in the literature on the thermal conductivity of w-ZnO. In this paper, we determine the thermal conductivity of w-ZnO using first-principles lattice dynamics and compare it to that of wurtzite Gallium-Nitride (w-GaN)--another important wide bandgap semiconductor with the same crystal structure and similar atomic masses as w-ZnO. However, the thermal conductivity values show large differences (400 W/mK of w-GaN vs. 50 W/mK of w-ZnO at room temperature). It is found that the much lower thermal conductivity of ZnO originates from the smaller phonon group velocities, larger three-phonon scattering phase space and larger anharmonicity. Compared to w-GaN, w-ZnO has a smaller frequency gap in phonon dispersion, which is responsible for the stronger anharmonic phonon scattering, and the weaker interatomic bonds in w-ZnO leads to smaller phonon group velocities. The thermal conductivity of w-ZnO also shows strong size effect with nano-sized grains or structures. The results from this work help identify the cause of large discrepancies in w-ZnO thermal conductivity and will provide in-depth understanding of phonon dynamics for the design of w-ZnO-based electronics.

  7. First principles studies on anatase surfaces

    Science.gov (United States)

    Selcuk, Sencer

    TiO2 is one of the most widely studied metal oxides from both the fundamental and the technological points of view. A variety of applications have already been developed in the fields of energy production, environmental remediation, and electronics. Still, it is considered to have a high potential for further improvement and continues to be of great interest. This thesis describes our theoretical studies on the structural and electronic properties of anatase surfaces, and their (photo)chemical behavior. Recently much attention has been focused on anatase crystals synthesized by hydrofluoric acid assisted methods. These crystals exhibit a high percentage of {001} facets, generally considered to be highly reactive. We used first principles methods to investigate the structure of these facets, which is not yet well understood. Our results suggest that (001) surfaces exhibit the bulk-terminated structure when in contact with concentrated HF solutions. However, 1x4-reconstructed surfaces, as observed in UHV, become always more stable at the typical temperatures used to clean the as-prepared crystals in experiments. Since the reconstructed surfaces are only weakly reactive, we predict that synthetic anatase crystals with dominant {001} facets should not exhibit enhanced photocatalytic activity. Understanding how defects in solids interact with external electric fields is important for technological applications such as memristor devices. We studied the influence of an external electric field on the formation energies and diffusion barriers of the surface and the subsurface oxygen vacancies at the anatase (101) surface from first principles. Our results show that the applied field can have a significant influence on the relative stabilities of these defects, whereas the effect on the subsurface-to-surface defect migration is found to be relatively minor. Charge carriers play a key role in the transport properties and the surface chemistry of TiO2. Understanding their

  8. First principles study of magnetism in nanographenes

    CERN Document Server

    Jiang, De-en; Dai, Sheng

    2007-01-01

    Magnetism in nanographenes (also know as polycyclic aromatic hydrocarbons, or PAHs) are studied with first principles density functional calculations. We find that an antiferromagnetic (AFM) phase appears as the PAH reaches a certain size. This AFM phase in PAHs has the same origin as the one in infinitely long zigzag-edged graphene nanoribbons, namely, from the localized electronic state at the zigzag edge. The smallest PAH still having an AFM ground state is identified. With increased length of the zigzag edge, PAHs approach an infinitely long ribbon in terms of (1) the energetic ordering and difference among the AFM, ferromagnetic (FM), and nonmagnetic (NM) phases and (2) the average local magnetic moment at the zigzag edges. These PAHs serve as ideal targets for chemical synthesis of nanographenes that possess magnetic properties. Moreover, our calculations support the interpretation that experimentally observed magnetism in activated carbon fibers originates from the zigzag edges of the nanographenes.

  9. A Comparative Study of Elastic Constants of NiTi and NiAl Alloys from First-Principle Calculations

    Institute of Scientific and Technical Information of China (English)

    Jianmin Lu; Qingmiao Hu; Rui Yang

    2009-01-01

    To investigate the origin of the strong dependence of martensitic transformation temperature on composition,the elastic properties of high temperature B2 phases of both NiTi and NiAl were calculated by a first-principle method, the exact-muffin orbital method within coherent potential approximation. In the composition range of 50-56 at. pct Ni of NiTi and 60-70 at. pct Ni of NiAI in which martensitic transformation occurs, non-basalplane shear modulus c44 increases with increasing Ni content, while basal-plane shear modulus c' decreases.In the above composition ranges however the transformation temperature of NiAI increases with increasing Ni content while that of NiTi decreases from experimental observation. The softening of c' is experimentally observed only in NiAl, and the decrease of c' with increasing Ni content is responsible for the increase of transformation temperature. The result of the present work demonstrates that, besides c', c44 also influences the martensitic transformation of NiTi and plays quite important a role.

  10. A first-principles DFT study of UN bulk and (001) surface: comparative LCAO and PW calculations.

    Science.gov (United States)

    Evarestov, R A; Bandura, A V; Losev, M V; Kotomin, E A; Zhukovskii, Yu F; Bocharov, D

    2008-10-01

    LCAO and PW DFT calculations of the lattice constant, bulk modulus, cohesive energy, charge distribution, band structure, and DOS for UN single crystal are analyzed. It is demonstrated that a choice of the uranium atom relativistic effective core potentials considerably affects the band structure and magnetic structure at low temperatures. All calculations indicate mixed metallic-covalent chemical bonding in UN crystal with U5f states near the Fermi level. On the basis of the experience accumulated in UN bulk simulations, we compare the atomic and electronic structure as well as the formation energy for UN(001) surface calculated on slabs of different thickness using both DFT approaches.

  11. First-principles study of transition metal carbides

    Science.gov (United States)

    Connétable, Damien

    2016-12-01

    This study investigates the physical properties of transition metal carbides compounds associated with the Nb-C, Ti-C, Mo-C and W-C alloys systems using first-principles calculations. The ground-state properties (lattice parameters, cohesive energies and magnetism) were analyzed and compared to the experimental and theoretical literature. The simulations are in excellent agreement with experimental findings concerning atomic positions and structures. Elastic properties, computed using a finite-differences approach, are then discussed in detail. To complete the work, their lattice dynamics properties (phonon spectra) were investigated. These results serve to establish that some structures, which are mechanically stable, are dynamically unstable.

  12. First-principles study of point defects in thorium carbide

    Science.gov (United States)

    Pérez Daroca, D.; Jaroszewicz, S.; Llois, A. M.; Mosca, H. O.

    2014-11-01

    Thorium-based materials are currently being investigated in relation with their potential utilization in Generation-IV reactors as nuclear fuels. One of the most important issues to be studied is their behavior under irradiation. A first approach to this goal is the study of point defects. By means of first-principles calculations within the framework of density functional theory, we study the stability and formation energies of vacancies, interstitials and Frenkel pairs in thorium carbide. We find that C isolated vacancies are the most likely defects, while C interstitials are energetically favored as compared to Th ones. These kind of results for ThC, to the best authors' knowledge, have not been obtained previously, neither experimentally, nor theoretically. For this reason, we compare with results on other compounds with the same NaCl-type structure.

  13. First-principles study of point defects in thorium carbide

    Energy Technology Data Exchange (ETDEWEB)

    Pérez Daroca, D., E-mail: pdaroca@tandar.cnea.gov.ar [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, (1033) Buenos Aires (Argentina); Jaroszewicz, S. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM-CNEA, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Llois, A.M. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, (1033) Buenos Aires (Argentina); Mosca, H.O. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM-CNEA, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina)

    2014-11-15

    Thorium-based materials are currently being investigated in relation with their potential utilization in Generation-IV reactors as nuclear fuels. One of the most important issues to be studied is their behavior under irradiation. A first approach to this goal is the study of point defects. By means of first-principles calculations within the framework of density functional theory, we study the stability and formation energies of vacancies, interstitials and Frenkel pairs in thorium carbide. We find that C isolated vacancies are the most likely defects, while C interstitials are energetically favored as compared to Th ones. These kind of results for ThC, to the best authors’ knowledge, have not been obtained previously, neither experimentally, nor theoretically. For this reason, we compare with results on other compounds with the same NaCl-type structure.

  14. A comparative first-principles study of the structural and electronic properties of the liquid Li-Si and Li-Ge alloys.

    Science.gov (United States)

    Chiang, Han-Hsin; Kuo, Chin-Lung

    2017-02-14

    We have performed a comparative first-principles study on the structural and electronic properties of the liquid Li1-xSix and Li1-xGex alloys over a range of composition from x = 0.09 to 0.50. Our calculations showed that Si and Ge atoms can exhibit very distinct local bonding characteristics as they were alloyed with the Li atoms in the liquid state, where Si atoms tended to form a variety of covalent bonding configurations while Ge atoms predominantly appeared as the isolated anions in the liquid alloys. These differences in bonding characteristics were reflected in their electronic density of states, in which the liquid Li1-xGex alloys have a lower degree of s-p hybridization with narrower distributions of the 3s and 3p states than the liquid Li1-xSix alloys. Our calculations also showed that the optical conductivities of these two liquid alloys can undergo a transition from the Drude-like metallic nature to the semiconductor-like character as the Si/Ge content increases from 0.09 to 0.22. However, as the Si/Ge content further increases to 0.50, the liquid Li1-xGex alloys may transit to exhibit the Drude-like metallic nature, while the liquid Li1-xSix alloys can still hold the semiconductor-like character. Moreover, our calculations revealed that the dc conductivities of these liquid alloys are predominantly determined by the number of total electronic states at the Fermi level. As the liquid Li1-xSix alloys are within the composition range between 0.20 and 0.50, the increment of the states at the Fermi level with increasing the Si content is nearly identical to the amount of the Li states decreased, leading to an almost unchanged number of total electronic states at the Fermi level. However, since Ge atoms do not favor forming covalent bonding in the liquid alloys to keep the Fermi level at a minimum of the density of states, the liquid Li1-xGex alloys would have more electronic states at the Fermi level and thereby higher dc conductivities than the liquid Li1

  15. Comparative study of the absorption spectrum of Li 2CaSiO 4:Cr 4+: First-principles fully relativistic and crystal field calculations

    Science.gov (United States)

    Brik, M. G.; Ogasawara, K.

    2007-11-01

    Systematic analysis of the energy level scheme and ground state absorption of the Cr4+ ion in Li2CaSiO4 crystal was performed using the exchange charge model of the crystal field [B.Z. Malkin, in: A.A. Kaplyanskii, B.M. Macfarlane (Eds.), Spectroscopy of Solids Containing Rare-earth Ions, North-Holland, Amsterdam, 1987, pp. 33-50] and recently developed first-principles approach to the analysis of the absorption spectra of impurity ions in crystals based on the discrete variational multielectron (DVME) method [K. Ogasawara, T. Iwata, Y. Koyama, T. Ishii, I. Tanaka, H. Adachi, Phys. Rev. B 64 (2001) 115413]. Using the former method, the values of parameters of crystal field acting on the Cr4+ ion valence electrons were calculated using the Li2CaSiO4 crystal structure data. Energy levels of the Cr4+ ion obtained after diagonalizing the crystal field Hamiltonian are in good agreement with those obtained from the experimental spectra. The latter method is based on the numerical solution of the Dirac equation; therefore, all relativistic effects are automatically considered. As a result, energy level scheme of Cr4+ and its absorption spectra in both polarizations were calculated, assigned and compared with experimental data; energy of the lowest charge transfer transition was evaluated and compared with theoretical predictions for the CrO44- complex available in the literature. The main features of the experimental spectra shape are reproduced well by the calculations. By performing analysis of the molecular orbitals (MO) population, it was shown that the covalent effects play an important role in formation of the spectral properties of Cr4+ ion in the considered crystal.

  16. Diffusion in thorium carbide: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Pérez Daroca, D., E-mail: pdaroca@tandar.cnea.gov.ar [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650, San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, 1025, Buenos Aires (Argentina); Llois, A.M. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650, San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, 1025, Buenos Aires (Argentina); Mosca, H.O. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650, San Martín, Buenos Aires (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM–CNEA, Av. General Paz 1499, 1650, San Martín, Buenos Aires (Argentina)

    2015-12-15

    The prediction of the behavior of Th compounds under irradiation is an important issue for the upcoming Generation-IV nuclear reactors. The study of self-diffusion and hetero-diffusion is a central key to fulfill this goal. As a first approach, we obtained, by means of first-principles methods, migration and activation energies of Th and C atoms self-diffusion and diffusion of He atoms in ThC. We also calculate diffusion coefficients as a function of temperature. - Highlights: • Diffusion in thorium carbide by means of first-principles calculations is studied. • The most favorable migration event is a C atom moving through a C-vacancy aided path. • Calculated C atoms diffusion coefficients agree very well with the experimental data. • For He, the energetically most favorable migration path is through Th-vacancies.

  17. Comparative studies of band structures for biaxial (100)-, (110)-, and (111)-strained GeSn: A first-principles calculation with GGA+U approach

    Science.gov (United States)

    Huang, Wenqi; Cheng, Buwen; Xue, Chunlai; Liu, Zhi

    2015-10-01

    Experiments and calculations performed in previous studies indicate that compressive strain will increase (100)-strained GeSn's need for Sn to realize a direct bandgap when it is pseudomorphically grown on Ge buffers. To eliminate this negative effect, we systematically investigate the band structures of biaxial (100)-, (110)-, and (111)-strained GeSn using a first-principle calculation combined with supercell models and the GGA+U approach. This method has proven to be efficient and accurate for calculating the properties of GeSn. The calculated lattice constants and elastic constants of Ge and Sn are in good agreement with the experimental results. The crossover value of Sn concentration which is required to change the bandgap of unstrained GeSn from indirect to direct is found to be 8.5%, which is very close to the recent experimental result of 9%. The calculated bandgaps of strained GeSn show that the moving rate of the Γ valley is higher than those of the L and X valleys in (100)- and (110)-strained GeSn. However, the moving rate of the L valley is higher than those of Γ and X valleys in (111)-strained GeSn. Tensile strain has a positive effect on the transition of (100)- and (110)-strained GeSn, changing the bandgap from indirect to direct, whereas compressive strain has a positive effect for (111)-strained GeSn. The use of the (111) orientation can reduce GeSn's need for Sn and greatly increase the energy difference between the L valley and Γ valley. Thus, for strained GeSn grown on Ge buffers, the (111) orientation is a good choice to take advantage of compressive strain.

  18. Diffusion in thorium carbide: A first-principles study

    Science.gov (United States)

    Pérez Daroca, D.; Llois, A. M.; Mosca, H. O.

    2015-12-01

    The prediction of the behavior of Th compounds under irradiation is an important issue for the upcoming Generation-IV nuclear reactors. The study of self-diffusion and hetero-diffusion is a central key to fulfill this goal. As a first approach, we obtained, by means of first-principles methods, migration and activation energies of Th and C atoms self-diffusion and diffusion of He atoms in ThC. We also calculate diffusion coefficients as a function of temperature.

  19. Transition metal doped arsenene: A first-principles study

    Science.gov (United States)

    Sun, Minglei; Wang, Sake; Du, Yanhui; Yu, Jin; Tang, Wencheng

    2016-12-01

    Using first-principles calculations, we investigate the structural, electronic, and magnetic properties of 3d transition metal (TM) atoms substitutional doping of an arsenene monolayer. Based on the binding energy, the TM-substituted arsenene systems were found to be robust. Magnetic states were obtained for Ti, V, Cr, Mn and Fe doping. More importantly, a half-metallic state resulted from Ti and Mn doping, while the spin-polarized semiconducting state occurred with V, Cr and Fe doping. Our studies demonstrated the potential applications of TM-substituted arsenene for spintronics and magnetic storage devices.

  20. Oxygen in the Earth's core a first principles study

    CERN Document Server

    Alfè, D; Gillan, M J; Alfe`, Dario; Gillan, Michael J.

    1998-01-01

    First principles electronic structure calculations based on density functional theory have been used to study the thermodynamic, structural and transport properties of solid solutions and liquid alloys of iron and oxygen at Earth's core conditions. Aims of the work are to determine the oxygen concentration needed to account for the inferred density in the outer core, to probe the stability of the liquid against phase separation, to interpret the bonding in the liquid, and to find out whether the viscosity differs significantly from that of pure liquid iron at the same conditions. It is shown that the required concentration of oxygen is in the region 25-30 mol percent, and evidence is presented for phase stability at these conditions. The Fe-O bonding is partly ionic, but with a strong covalent component. The viscosity is lower than that of pure liquid iron at Earth's core conditions. It is shown that earlier first-principles calculations indicating very large enthalpies of formation of solid solutions may nee...

  1. Hydrogen storage in LiH: A first principle study

    Science.gov (United States)

    Banger, Suman; Nayak, Vikas; Verma, U. P.

    2014-04-01

    First principles calculations have been performed on the Lithium hydride (LiH) using the full potential linearized augmented plane wave (FP-LAPW) method within the framework of density functional theory. We have extended our calculations for LiH+2H and LiH+6H in NaCl structure. The structural stability of three compounds have been studied. It is found that LiH with 6 added Hydrogen atoms is most stable. The obtained results for LiH are in good agreement with reported experimental data. Electronic structures of three compounds are also studied. Out of three the energy band gap in LiH is ˜3.0 eV and LiH+2H and LiH+6H are metallic.

  2. Point defects in thorium nitride: A first-principles study

    Science.gov (United States)

    Pérez Daroca, D.; Llois, A. M.; Mosca, H. O.

    2016-11-01

    Thorium and its compounds (carbides and nitrides) are being investigated as possible materials to be used as nuclear fuels for Generation-IV reactors. As a first step in the research of these materials under irradiation, we study the formation energies and stability of point defects in thorium nitride by means of first-principles calculations within the framework of density functional theory. We focus on vacancies, interstitials, Frenkel pairs and Schottky defects. We found that N and Th vacancies have almost the same formation energy and that the most energetically favorable defects of all studied in this work are N interstitials. These kind of results for ThN, to the best authors' knowledge, have not been obtained previously, neither experimentally, nor theoretically.

  3. Hydrogen storage in LiH: A first principle study

    Energy Technology Data Exchange (ETDEWEB)

    Banger, Suman, E-mail: sumanphy28@gmail.com; Nayak, Vikas, E-mail: sumanphy28@gmail.com; Verma, U. P., E-mail: sumanphy28@gmail.com [School of Studies in Physics, Jiwaji University, Gwalior-474011 (India)

    2014-04-24

    First principles calculations have been performed on the Lithium hydride (LiH) using the full potential linearized augmented plane wave (FP-LAPW) method within the framework of density functional theory. We have extended our calculations for LiH+2H and LiH+6H in NaCl structure. The structural stability of three compounds have been studied. It is found that LiH with 6 added Hydrogen atoms is most stable. The obtained results for LiH are in good agreement with reported experimental data. Electronic structures of three compounds are also studied. Out of three the energy band gap in LiH is ∼3.0 eV and LiH+2H and LiH+6H are metallic.

  4. First Principles Studies of ABO3 Perovskite Surfaces and Nanostructures

    Science.gov (United States)

    Pilania, Ghanshyam

    Perovskite-type complex oxides, with general formula ABO 3, constitute one of the most prominent classes of metal oxides which finds key applications in diverse technological fields. In recent years, properties of perovskites at reduced dimensions have aroused considerable interest. However, a complete atomic-level understanding of various phenomena is yet to emerge. To fully exploit the materials opportunities provided by nano-structured perovskites, it is important to characterize and understand their bulk and near-surface electronic structure along with the electric, magnetic, elastic and chemical properties of these materials in the nano-regime, where surface and interface effects naturally play a dominant role. In this thesis, state-of-the-art first principles computations are employed to systematically study properties of one- and two-dimensional perovskite systems which are of direct technological significance. Specifically, our bifocal study targets (1) polarization behavior and dielectric response of ABO3 ferroelectric nanowires, and (2) oxygen chemistry relevant for catalytic properties of ABO3 surfaces. In the first strand, we identify presence of novel closure or vortex-like polarization domains in PbTIO3 and BaTiO3 ferroelectric nanowires and explore ways to control the polarization configurations by means of strain and surface chemistry in these prototypical model systems. The intrinsic tendency towards vortex polarization at reduced dimensions and the underlying driving forces are discussed and previously unknown strain induced phase transitions are identified. Furthermore, to compute the dielectric permittivity of nanostructures, a new multiscale model is developed and applied to the PbTiO3 nanowires with conventional and vortex-like polarization configurations. The second part of the work undertaken in this thesis is comprised of a number of ab initio surface studies, targeted to investigate the effects of surface terminations, prevailing chemical

  5. First-principles studies of atomic dynamics in tetrahedrite thermoelectrics

    Science.gov (United States)

    Li, Junchao; Zhu, Mengze; Abernathy, Douglas L.; Ke, Xianglin; Morelli, Donald T.; Lai, Wei

    2016-10-01

    Cu12Sb4S13-based tetrahedrites are high-performance thermoelectrics that contain earth-abundant and environmentally friendly elements. At present, the mechanistic understanding of their low lattice thermal conductivity (applies first-principles molecular dynamics simulations, along with inelastic neutron scattering (INS) experiments, to study the incoherent and coherent atomic dynamics in Cu10.5NiZn0.5Sb4S13, in order to deepen our insight into mechanisms of anomalous dynamic behavior and low lattice thermal conductivity in tetrahedrites. Our study of incoherent dynamics reveals the anomalous "phonon softening upon cooling" behavior commonly observed in inelastic neutron scattering data. By examining the dynamic Cu-Sb distances inside the Sb[CuS3]Sb cage, we ascribe softening to the decreased anharmonic "rattling" of Cu in the cage. On the other hand, our study of coherent dynamics reveals that acoustic modes are confined in a small region of dynamic scattering space, which we hypothesize leads to a minimum phonon mean free path. By assuming a Debye model, we obtain a lattice minimum thermal conductivity value consistent with experiments. We believe this study furthers our understanding of the atomic dynamics of tetrahedrite thermoelectrics and will more generally help shed light on the origin of intrinsically low lattice thermal conductivity in these and other structurally similar materials.

  6. First-principles studies of atomic dynamics in tetrahedrite thermoelectrics

    Directory of Open Access Journals (Sweden)

    Junchao Li

    2016-10-01

    Full Text Available Cu12Sb4S13-based tetrahedrites are high-performance thermoelectrics that contain earth-abundant and environmentally friendly elements. At present, the mechanistic understanding of their low lattice thermal conductivity (<1 W m−1 K−1 at 300 K remains limited. This work applies first-principles molecular dynamics simulations, along with inelastic neutron scattering (INS experiments, to study the incoherent and coherent atomic dynamics in Cu10.5NiZn0.5Sb4S13, in order to deepen our insight into mechanisms of anomalous dynamic behavior and low lattice thermal conductivity in tetrahedrites. Our study of incoherent dynamics reveals the anomalous “phonon softening upon cooling” behavior commonly observed in inelastic neutron scattering data. By examining the dynamic Cu-Sb distances inside the Sb[CuS3]Sb cage, we ascribe softening to the decreased anharmonic “rattling” of Cu in the cage. On the other hand, our study of coherent dynamics reveals that acoustic modes are confined in a small region of dynamic scattering space, which we hypothesize leads to a minimum phonon mean free path. By assuming a Debye model, we obtain a lattice minimum thermal conductivity value consistent with experiments. We believe this study furthers our understanding of the atomic dynamics of tetrahedrite thermoelectrics and will more generally help shed light on the origin of intrinsically low lattice thermal conductivity in these and other structurally similar materials.

  7. First principles study of lithium insertion in bulk silicon

    KAUST Repository

    Wan, Wenhui

    2010-09-23

    Si is an important anode material for the next generation of Li ion batteries. Here the energetics and dynamics of Li atoms in bulk Si have been studied at different Li concentrations on the basis of first principles calculations. It is found that Li prefers to occupy an interstitial site as a shallow donor rather than a substitutional site. The most stable position is the tetrahedral (Td) site. The diffusion of a Li atom in the Si lattice is through a Td-Hex-Td trajectory, where the Hex site is the hexagonal transition site with an energy barrier of 0.58 eV. We have also systematically studied the local structural transition of a LixSi alloy with x varying from 0 to 0.25. At low doping concentration (x = 0-0.125), Li atoms prefer to be separated from each other, resulting in a homogeneous doping distribution. Starting from x = 0.125, Li atoms tend to form clusters induced by a lattice distortion with frequent breaking and reforming of Si-Si bonds. When x ≥ 0.1875, Li atoms will break some Si-Si bonds permanently, which results in dangling bonds. These dangling bonds create negatively charged zones, which is the main driving force for Li atom clustering at high doping concentration. © 2010 IOP Publishing Ltd.

  8. First Principle simulations of electrochemical interfaces - a DFT study

    DEFF Research Database (Denmark)

    Ahmed, Rizwan

    for the whole system to qualify as a proper electrochemical interface. I have also contributed to the model, which accounts for pH in the first principle electrode-electrolyte interface simulations. This is an important step forward, since electrochemical reaction rate and barrier for charge transfer can......In this thesis, I have looked beyond the computational hydrogen electrode (CHE) model, and focused on the first principle simulations which treats the electrode-electrolyte interfaces explicitly. Since obtaining a realistic electrode-electrolyte interface was difficult, I aimed to address various...... challenges regarding first principle electrochemical interface modeling in order to bridge the gap between the model interface used in simulations and real catalyst at operating conditions. Atomic scale insight for the processes and reactions that occur at the electrochemical interface presents a challenge...

  9. First-principle studies on the Li-Te system

    Science.gov (United States)

    Wang, Youchun; Tian, Fubo; Li, Da; Duan, Defang; Liu, Yunxian; Liu, Bingbing; Zhou, Qiang; Cui, Tian

    2017-01-01

    First-principle evolutionary calculation was performed to search for all probable stable lithium tellurium compounds. In addition to the well-known structures of Fm-3m Li2Te and Pnma Li2Te, several novel structures, including those of P4/nmm Li2Te, Imma Li8Te2, and C2/m Li9Te2, were determined under high pressure. The transformation sequence of Li2Te induced by pressure was presented as follows. The phase transition occurred at 7.5 GPa while transforming from Fm-3m phase to Pnma structure, then transformed to P4/nmm phase at 14 GPa. P4/nmm Li2Te can remain stable at least up to 140 GPa. Li8Te2 and Li9Te2 were stable at 8-120 GPa and 80-120 GPa, respectively. Interestingly, Li8Te2 and Li9Te2 were predicted to be metallic under high pressure, Li2Te would metalize on compression. P4/nmm Li2Te is likely a super ionic conductor due to the special characteristic. Metallic P4/nmm Li2Te may be a candidate mixed conductor material under extreme pressure. Charge transfer was studied using Bader charge analysis. Charge transferred from Li to Te, and the relative debilitated ionicity between Li and Te atoms existed at high pressure.

  10. O deficient LaAlO3/SrTiO3(110) and (001) superlattices under hydrostatic pressure: a comparative first principles study

    KAUST Repository

    Albar, Arwa

    2017-03-17

    We compare the electronic properties of O deficient LaAlO3/SrTiO3 superlattices oriented along the (001) and (110) directions, taking into account the effect of hydrostatic compression and tension. Interfacial O vacancies turn out to be less likely in the case of the (110) orientation, with compression (tension) reducing (enhancing) the energy cost for both orientations. The presence of O vacancies results in the formation of a two-dimensional electron gas, for which we observe a distinct spatial pattern of carrier density that depends strongly on the amount of applied pressure. We clarify the interrelation between structural features and the properties of this electron gas (confinement, carrier density, and mobility).

  11. Electron field emission in nanostructures: A first-principles study

    Science.gov (United States)

    Driscoll, Joseph Andrew

    The objective of this work was to study electron field emission from several nanostructures using a first-principles framework. The systems studied were carbon nanowires, graphene nanoribbons, and nanotubes of varying composition. These particular structures were chosen because they have recently been identified as showing novel physical phenomena, as well as having tremendous industrial applications. We examined the field emission under a variety of conditions, including laser illumination and the presence of adsorbates. The goal was to explore how these conditions affect the field emission performance. In addition to the calculations, this dissertation has presented computational developments by the author that allowed these demanding calculations to be performed. There are many possible choices for basis when performing an electronic structure calculation. Examples are plane waves, atomic orbitals, and real-space grids. The best choice of basis depends on the structure of the system being analyzed and the physical processes involved (e.g., laser illumination). For this reason, it was important to conduct rigorous tests of basis set performance, in terms of accuracy and computational efficiency. There are no existing benchmark calculations for field emission, but transport calculations for nanostructures are similar, and so provide a useful reference for evaluating the performance of various basis sets. Based on the results, for the purposes of studying a non-periodic nanostructure under field emission conditions, we decided to use a real-space grid basis which incorporates the Lagrange function approach. Once a basis was chosen, in this case a real-space grid, the issue of boundary conditions arose. The problem is that with a non-periodic system, field emitted electron density can experience non-physical reflections from the boundaries of the calculation volume, leading to inaccuracies. To prevent this issue, we used complex absorbing potentials (CAPs) to absorb

  12. A first-principles comparative study of lithium, sodium, and magnesium storage in pure and gallium-doped germanium: Competition between interstitial and substitutional sites

    Science.gov (United States)

    Legrain, Fleur; Manzhos, Sergei

    2017-01-01

    Thermodynamics and kinetics of Li, Na, and Mg storage in Ge are studied ab initio. The most stable configurations can consist of tetrahedral, substitutional, or a combination of the two types of sites. In the dilute limit, Li and Na prefer interstitial, while Mg prefers substitutional sites. At higher concentrations of Li, Na, and Mg, there is a combination of interstitial and substitutional sites. This is an important finding, as most previous ab initio studies of alloying type electrode materials ignored substitutional sites. Insertion energies computed at dilute concentration (x = 1/64) show that Na and Mg insertion are not thermodynamically favored in Ge vs. the formation of bulk Na and Mg, as opposed to Li insertion which is favored. We investigate the effect of p-doping of Ge (with Ga) on the thermodynamics and find that it considerably lowers the defect formation energies associated with the insertion of Li/Na/Mg at tetrahedral sites. On the other hand, the energetics associated with Li/Na/Mg insertion at substitutional sites are not significantly affected. In addition, we compute the migration energy barriers for Li/Na/Mg diffusion between two tetrahedral sites (0.38/0.79/0.66 eV), between two substitutional sites (0.77/0.93/1.83 eV), and between two sites of different types (2.15/1.75/0.85 eV).

  13. Transport and first-principles study of novel thermoelectric materials

    Science.gov (United States)

    Chi, Hang

    Thermoelectric materials can recover waste industrial heat and convert it to electricity as well as provide efficient local cooling of electronic devices. The efficiency of such environmentally responsible and exceptionally reliable solid state energy conversion is determined by the dimensionless figure-of-merit ZT = alpha2 sigmaT/kappa, where alpha is the Seebeck coefficient, sigma is the electrical conductivity, kappa is the thermal conductivity, and T is the absolute temperature. The goal of the thesis is to (i) illustrate the physics to achieve high ZT of advanced thermoelectric materials and (ii) explore fundamental structure and transport properties in novel condensed matter systems, via an approach combining comprehensive experimental techniques and state-of-the-art first-principles simulation methods. Thermo-galvanomagnetic transport coefficients are derived from Onsager's reciprocal relations and evaluated via solving Boltzmann transport equation using Fermi-Dirac statistics, under the relaxation time approximation. Such understanding provides insights on enhancing ZT through two physically intuitive and very effective routes: (i) improving power factor PF = alpha2sigma; and (ii) reducing thermal conductivity kappa, as demonstrated in the cases of Mg2Si1-xSnx solid solution and Ge/Te double substituted skutterudites CoSb3(1-x)Ge1.5x Te1.5x, respectively. Motivated by recent theoretical predictions of enhanced thermoelectric performance in highly mismatched alloys, ZnTe:N molecular beam epitaxy (MBE) films deposited on GaAs (100) substrates are carefully examined, which leads to a surprising discovery of significant phonon-drag thermopower (reaching 1-2 mV/K-1) at ~13 K. Further systematic study in Bi2Te3 MBE thin films grown on sapphire (0001) and/or BaF2 (111) substrates, reveal that the peak of phonon drag can be tuned by the choice of substrates with different Debye temperatures. Moreover, the detailed transport and structure studies of Bi2-xTl xTe3

  14. Oxygen reduction activity on perovskite oxide surfaces: a comparative first-principle study of LaMnO$_3$, LaFeO$_3$ and LaCrO$_3$

    CERN Document Server

    Wang, Yan

    2012-01-01

    The understanding of oxygen reduction reaction (ORR) activity on perovskite oxide surfaces is essential for promising future fuel cell applications. We report a comparative study of ORR mechanisms on La$B$O$_3$ ($B$=Mn, Fe, Cr) surfaces by first-principles calculations based on density functional theory (DFT). Results obtained from varied DFT methods such as generalized gradient approximation(GGA), GGA+$U$ and the hybrid Hartree-Fock density functional method are reported for comparative purposes. We find that the results calculated from hybrid-functional method suggest that the order of ORR activity is LaMnO$_3$ $>$ LaCrO$_3$ $>$ LaFeO$_3$, which is in better agreement with recent experimental results (Suntivich \\textit{et al.}, Nature Chemistry 3, 546 (2011)) than those using the GGA or GGA+$U$ method.

  15. First-principle study of nanostructures of functionalized graphene

    Indian Academy of Sciences (India)

    Naveen Kumar; Jyoti Dhar Sharma; P K Ahluwalia

    2014-06-01

    We present first-principle calculations of 2D nanostructures of graphene functionalized with hydrogen and fluorine, respectively, in chair conformation. The partial density of states, band structure, binding energy and transverse displacement of C atoms due to functionalization (buckling) have been calculated within the framework of density functional theory as implemented in the SIESTA code. The variation in band gap and binding energy per add atom have been plotted against the number of add atoms, as the number of add atoms are incremented one by one. In all, 37 nanostructures with 18C atoms, 3 × 3 × 1 (i.e., the unit cell is repeated three times along -axis and three times along -axis) supercell, have been studied. The variation in C–C, C–H and C–F bond lengths and transverse displacement of C atoms (due to increase in add atoms) have been tabulated. A large amount of buckling is observed in the carbon lattice, 0.0053–0.7487 Å, due to hydrogenation and 0.0002–0.5379 Å, due to fluorination. As the number of add atoms (hydrogen or fluorine) is increased, a variation in the band gap is observed around the Fermi energy, resulting in change in behaviour of nanostructure from conductor to semiconductor/insulator. The binding energy per add atom increases with the increase in the number of add atoms. The nanostructures with 18C+18H and 18C+18F have maximum band gap of 4.98 eV and 3.64 eV, respectively, and binding energy per add atom –3.7562 eV and –3.3507 eV, respectively. Thus, these nanostructures are stable and are wide band-gap semiconductors, whereas the nanostructures with 18C+2H, 18C+4H, 18C+4F, 18C+8F, 18C+10F and 18C+10H atoms are small band-gap semiconductors with the band gap lying between 0.14 eV and 1.72 eV. Fluorine being more electronegative than hydrogen, the impact of electronegativity on band gap, binding energy and bond length is visible. It is also clear that it is possible to tune the electronic properties of functionalized

  16. First principles pharmacokinetic modeling: A quantitative study on Cyclosporin

    DEFF Research Database (Denmark)

    Mošat', Andrej; Lueshen, Eric; Heitzig, Martina

    2013-01-01

    renal and hepatic clearances, elimination half-life, and mass transfer coefficients, to establish drug biodistribution dynamics in all organs and tissues. This multi-scale model satisfies first principles and conservation of mass, species and momentum.Prediction of organ drug bioaccumulation...... as a function of cardiac output, physiology, pathology or administration route may be possible with the proposed PBPK framework. Successful application of our model-based drug development method may lead to more efficient preclinical trials, accelerated knowledge gain from animal experiments, and shortened time-to-market...

  17. Hadron phenomenology from first-principle QCD studies

    CERN Document Server

    Papavassiliou, J

    2016-01-01

    The form of the kernel that controls the dynamics of the Bethe-Salpeter equations is essential for obtaining quantitatively accurate predictions for the observable properties of hadrons. In the present work we briefly review the basic physical concepts and field-theoretic techniques employed in a first-principle derivation of a universal (process-independent) component of this kernel. This "top-down" approach combines nonperturbative ingredients obtained from lattice simulations and Dyson-Schwinger equations, and furnishes a renormalization-group invariant quark-gluon interaction strength, which is in excellent agreement with the corresponding quantity obtained from a systematic "bottom-up" treatment, where bound-state data are fitted within a well-defined truncation scheme.

  18. Electronic Structures of Silicene Doped with Galium: First Principle study

    Directory of Open Access Journals (Sweden)

    Pamungkas Mauludi Ariesto

    2015-01-01

    Full Text Available Following the success of graphene which possesses unique and superior properties, 2D material other than graphene become centre of interest of material scientists.Silicene, which has the same crystal structure as graphene but consist of silicon atoms rather than carbon become intriguing material due to domination of silicon as main material of electronic component. It is common to enhance electronic properties of semiconductor by adding dopant atoms. The electronic properties of Silicene doped with Gallium are investigated using first principle calculation based on density functional theory (DFT.Ga doping changes character of silicene from semimetal to conductor except silicene with Ga doping on S-site (Ga atom substitutes one Si atom which lead to semiconductor.

  19. A Comparative Study of Structural Stability and Mechanical and Optical Properties of Fluorapatite (Ca5(PO4)3F) and Lithium Disilicate (Li2Si2O5) Components Forming Dental Glass-Ceramics: First Principles Study

    Science.gov (United States)

    Biskri, Z. E.; Rached, H.; Bouchear, M.; Rached, D.; Aida, M. S.

    2016-10-01

    The aim of this paper is a comparative study of structural stability and mechanical and optical properties of fluorapatite (FA) (Ca5(PO4)3F) and lithium disilicate (LD) (Li2Si2O5), using the first principles pseudopotential method based on density functional theory (DFT) within the generalized gradient approximation (GGA). The stability of fluorapatite and lithium disilicate compounds has been evaluated on the basis of their formation enthalpies. The results show that fluorapatite is more energetically stable than lithium disilicate. The independent elastic constants and related mechanical properties, including bulk modulus ( B), shear modulus ( G), Young's modulus ( E) and Poisson's ratio ( ν) as well as the Vickers hardness ( H v), have been calculated for fluorapatite compound and compared with other theoretical and experimental results. The obtained values of the shear modulus, Young's modulus and Vickers hardness are smaller in comparison with those of lithium disilicate compound, implying that lithium disilicate is more rigid than fluorapatite. The brittle and ductile properties were also discussed using B/ G ratio and Poisson's ratio. Optical properties such as refractive index n( ω), extinction coefficient k( ω), absorption coefficient α( ω) and optical reflectivity R( ω) have been determined from the calculations of the complex dielectric function ɛ( ω), and interpreted on the basis of the electronic structures of both compounds. The calculated values of static dielectric constant ɛ 1(0) and static refractive index n(0) show that the Li2Si2O5 compound has larger values compared to those of the Ca5(PO4)3F compound. The results of the extinction coefficient show that Li2Si2O5 compound exhibits a much stronger ultraviolet absorption. According to the absorption and reflectivity spectra, we inferred that both compounds are theoretically the best visible and infrared transparent materials.

  20. Predicted boron-carbide compounds: a first-principles study.

    Science.gov (United States)

    Wang, De Yu; Yan, Qian; Wang, Bing; Wang, Yuan Xu; Yang, Jueming; Yang, Gui

    2014-06-14

    By using developed particle swarm optimization algorithm on crystal structural prediction, we have explored the possible crystal structures of B-C system. Their structures, stability, elastic properties, electronic structure, and chemical bonding have been investigated by first-principles calculations with density functional theory. The results show that all the predicted structures are mechanically and dynamically stable. An analysis of calculated enthalpy with pressure indicates that increasing of boron content will increase the stability of boron carbides under low pressure. Moreover, the boron carbides with rich carbon content become more stable under high pressure. The negative formation energy of predicted B5C indicates its high stability. The density of states of B5C show that it is p-type semiconducting. The calculated theoretical Vickers hardnesses of B-C exceed 40 GPa except B4C, BC, and BC4, indicating they are potential superhard materials. An analysis of Debye temperature and electronic localization function provides further understanding chemical and physical properties of boron carbide.

  1. A first principle study of band structure of III-nitride compounds

    Energy Technology Data Exchange (ETDEWEB)

    Ahmed, Rashid [Centre for High Energy Physics University of the Punjab, Lahore-54590 (Pakistan)]. E-mail: rasofi@hotmail.com; Akbarzadeh, H. [Department of Physics, Isfahan University of Technology, 841546 Isfahan (Iran, Islamic Republic of); Fazal-e-Aleem [Centre for High Energy Physics University of the Punjab, Lahore-54590 (Pakistan)

    2005-12-15

    The band structure of both phases, zinc-blende and wurtzite, of aluminum nitride, indium nitride and gallium nitride has been studied using computational methods. The study has been done using first principle full-potential linearized augmented plane wave (FP-LAPW) method, within the framework of density functional theory (DFT). For the exchange correlation potential, generalized gradient approximation (GGA) and an alternative form of GGA proposed by Engel and Vosko (GGA-EV) have been used. Results obtained for band structure of these compounds have been compared with experimental results as well as other first principle computations. Our results show a significant improvement over other theoretical work and are closer to the experimental data.

  2. First Principles Study of Electron Tunneling through Ice

    KAUST Repository

    Cucinotta, Clotilde S.

    2012-10-25

    With the aim of understanding electrochemical scanning tunnel microscopy experiments in an aqueous environment, we investigate electron transport through ice in the coherent limit. This is done by using the nonequilibrium Greens functions method, implemented within density functional theory, in the self-interaction corrected local density approximation. In particular, we explore different ice structures and different Au electrode surface orientations. By comparing the decay coefficient for different thicknesses to the ice complex band structure, we find that the electron transport occurs via tunneling with almost one-dimensional character. The slow decay of the current with the ice thickness is largely due to the small effective mass of the conduction electrons. Furthermore, we find that the calculated tunneling decay coefficients at the Fermi energy are not sensitive to the structural details of the junctions and are at the upper end of the experimental range for liquid water. This suggests that linear response transport measurements are not capable of distinguishing between different ordered ice structures. However, we also demonstrate that a finite bias measurement may be capable of sorting polar from nonpolar interfaces due to the asymmetry of the current-voltage curves for polar interfaces. © 2012 American Chemical Society.

  3. First principles study of aromatic molecules on Copper substrates

    Science.gov (United States)

    Ferretti, Andrea; Calzolari, Arrigo; di Felice, Rosa; Ruini, Alice; Molinari, Elisa

    2009-03-01

    Conjugated molecules and oligomers have attracted large attention in the last years due to their interesting electronic and transport properties. The interaction of these molecules with metallic surfaces is attractive both for the properties of the metal-organic interface and for the possibility of tuning the crystal structure of the films using the surface as a template. In the present work we focus on an ab initio investigation based on density functional theory of pentacene adsorbed on Copper surface. We also compare with the case of the DPDI molecule adsorbed on the same substrate. We address structural and electronic properties, and we relate our results to experimental data, STM, XSW, and angle resolved photoemission spectroscopy in particular. Our theoretical findings show a flat adsorption geometry for both pentacene and DPDI molecules. For what concerns the electronic structure, a strong rehybridization of the molecular electron states is found in the range of the occupied π states. These results lead to an interpretation of the adsorption mechanism of pentacene in terms of a coupling intermediate between the physi- and the chemi-sorption regimes.

  4. First-principles study on dielectric function of isolated and bundled carbon nanotubes

    Science.gov (United States)

    Yang, J. Y.; Liu, L. H.; Tan, J. Y.

    2015-06-01

    The dielectric function fundamentally determines the thermal radiative properties of nanomaterials. In this work, the first-principles method is applied to investigate the finite temperature dielectric function of isolated and bundled single-walled carbon nanotubes in the visible-ultraviolet spectral range without empirical models. The effects of diameter, intertube interactions and temperature on dielectric functions are discussed. The calculated extraordinary dielectric functions of four isolated (5,5), (6,6), (7,7) and (8,8) armchair nanotubes with different diameters are compared to study the diameter effect. It shows that the locations of absorption peaks of dielectric functions consistently shift to lower energy with increasing diameter. To analyze the influence of non-local intertube interactions, the dielectric functions of bundled (6,6) armchair nanotubes with varying intertube distance are calculated within the van der Waals theory. As nanotubes bundle together, the intertube interactions become strong and the absorption peaks enhance. The temperature effect is included into computing dielectric function of isolated (5,0) zigzag nanotubes via first-principles molecular dynamics method. It observes that the dominant absorption peak shifts to lower energy as temperature increases from 0 to 600 K. To interpret the temperature influence, the temperature perturbed density of states is presented.

  5. First principles study of the electron density distribution in a pair of bare metallic electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Chun-Lan [Suzhou University of Science and Technology, School of Mathematics and Physics, Suzhou (China); Chen, Yu-Chang; Nghiem, Diu; Tseng, Allen; Huang, Pao-Chieh [National Chiao Tung University, Department of Electrophysics, Hsinchu (China)

    2011-07-15

    Self-consistent calculations of electron density distribution from first principles for a series of semi-infinite metals show that the electron density almost drops to zero at 8.5 a.u. away from a metal surface. The electron densities in a series of bimetallic-electrode systems with a distance between the two electrodes of 21.7 a.u. are further investigated. Spin-polarized calculations of electron density for nonmagnetic and magnetic bimetallic-electrode systems are compared. Our work is helpful for first principles investigation of spin-dependent metal-molecule-metal tunneling junctions. (orig.)

  6. First-principles study of transition-metal nitrides as diffusion barriers against Al

    Energy Technology Data Exchange (ETDEWEB)

    Mei, Zhi-Gang, E-mail: zmei@anl.gov; Yacout, Abdellatif M.; Kim, Yeon Soo; Hofman, Gerard; Stan, Marius

    2016-04-01

    Using density-functional theory based first-principles calculations we provided a comparative study of the diffusion barrier properties of TiN, ZrN, and HfN against Al for U–Mo dispersion fuel applications. We firstly examined the thermodynamic stability of these transition-metal nitrides with Al. The calculated heats of reaction show that both TiN and ZrN are thermodynamically unstable diffusion barrier materials, which might be decomposed by Al at relatively high temperatures. As a comparison, HfN is a stable diffusion barrier material for Al. To evaluate the kinetic stability of these nitride systems against Al diffusion, we investigated the diffusion mechanisms of Al in TiN, ZrN and HfN using atomic scale simulations. The effect of non-stoichiometry on the defect formation and Al migration was systematically studied.

  7. Strength and bonding nature of superhard Z-carbon from first-principle study

    Directory of Open Access Journals (Sweden)

    Jiaqian Qin

    2012-06-01

    Full Text Available Z-carbon is a candidate structure proposed recently for the cold-compressed phase of carbon. We have studied the mechanical properties of Z-carbon by performing the first-principles density functional calculations. The single-crystal elastic constants calculations show that Z-carbon is mechanically stable. The predicted bulk and shear moduli of Z-carbon are comparable to diamond and cubic BN, suggesting that Z-carbon can be a superhard material. We also obtained the ideal tensile and shear strengths for Z-carbon through deformation from the elastic regime to structural instability. The failure modes under tensile deformation were explored carefully based on the calculated charge density distribution and bonding evolution.

  8. Titanium Trisulfide Monolayer as a Potential Thermoelectric Material: A First-Principles-Based Boltzmann Transport Study.

    Science.gov (United States)

    Zhang, Jie; Liu, Xiaolin; Wen, Yanwei; Shi, Lu; Chen, Rong; Liu, Huijun; Shan, Bin

    2017-01-25

    Good electronic transport capacity and low lattice thermal conductivity are beneficial for thermoelectric applications. In this study, the potential use as a thermoelectric material for the recently synthesized two-dimensional TiS3 monolayer is explored by applying first-principles method combined with Boltzmann transport theory. Our work demonstrates that carrier transport in the TiS3 sheet is orientation-dependent, caused by the difference in charge density distribution at band edges. Due to a variety of Ti-S bonds with longer lengths, we find that the TiS3 monolayer shows thermal conductivity much lower compared with that of transition-metal dichalcogenides such as MoS2. Combined with a high power factor along the y-direction, a considerable n-type ZT value (3.1) can be achieved at moderate carrier concentration, suggesting that the TiS3 monolayer is a good candidate for thermoelectric applications.

  9. Elastic stability and optical property under pressure of TiN phases: by first principles study

    Science.gov (United States)

    Eslam, Farzaneh Ghafari; Boochani, Arash; Babaeipour, Manuchehr; Khodadadi, Jabbar

    2017-06-01

    The electronic and optical properties of the rock-salt, CsCl-type, zinc-blende and wurtzite phases of TiN have been calculated by First-Principles study for relaxed and under pressure conditions. Calculations are based on the density functional theory and full potential augmented plane waves method by Generalized Gradient Approximation. The optical transitions in zero pressure are derived from the density of states and dielectric function. In addition, various optical characters, such as reflectivity, refraction and extinction indices, under positive and negative pressures are compared and contrasted. It is found that all mentioned phases of TiN are elastically stable and exhibit a rising trend in their plasmonic frequencies by increasing the pressure imposed on.

  10. Experimental and first principle studies on electronic structure of BaTiO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Sagdeo, Archna, E-mail: archnaj@rrcat.gov.in; Ghosh, Haranath, E-mail: archnaj@rrcat.gov.in; Chakrabarti, Aparna, E-mail: archnaj@rrcat.gov.in; Kamal, C., E-mail: archnaj@rrcat.gov.in; Ganguli, Tapas, E-mail: archnaj@rrcat.gov.in; Deb, S. K. [Indus Synchrotrons Utilization Division, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India); Phase, D. M. [IUC-DAEF, University Campus, Khandwa Road, Indore-452017 (India)

    2014-04-24

    We have carried out photoemission experiments to obtain valence band spectra of various crystallographic symmetries of BaTiO{sub 3} system which arise as a function of temperature. We also present results of a detailed first principle study of these symmetries of BaTiO{sub 3} using generalized gradient approximation for the exchange-correlation potential. Here we present theoretical results of density of states obtained from DFT based simulations to compare with the experimental valence band spectra. Further, we also perform calculations using post density functional approaches like GGA + U method as well as non-local hybrid exchange-correlation potentials like PBE0, B3LYP, HSE in order to understand the extent of effect of correlation on band gaps of different available crystallographic symmetries (5 in number) of BaTiO{sub 3}.

  11. First-principles study of point-defect production in Si and SiC

    Energy Technology Data Exchange (ETDEWEB)

    Windl, W.; Lenosky, T.J.; Kress, J.D.; Voter, A.F.

    1998-03-01

    The authors have calculated the displacement-threshold energy E(d) for point-defect production in Si and SiC using empirical potentials, tight-binding, and first-principles methods. They show that -- depending on the knock-on direction -- 64-atom simulation cells can be sufficient to allow a nearly finite-size-effect-free calculation, thus making the use of first-principles methods possible. They use molecular dynamics (MD) techniques and propose the use of a sudden approximation which agrees reasonably well with the MD results for selected directions and which allows estimates of Ed without employing an MD simulation and the use of computationally demanding first-principles methods. Comparing the results with experiment, the authors find the full self-consistent first-principles method in conjunction with the sudden approximation to be a reliable and easy method to predict E{sub d}. Furthermore, they have examined the temperature dependence of E{sub d} for C in SiC and found it to be negligible.

  12. Intrinsic defects and dopants in LiNH2 : a first-principles study

    NARCIS (Netherlands)

    Hazrati, E.; Brocks, G.; Buurman, B.; de Groot, R. A.; de Wijs, G. A.

    2011-01-01

    The lithium amide (LiNH2) + lithium hydride (LiH) system is one of the most attractive light-weight materials options for hydrogen storage. Its dehydrogenation involves mass transport in the bulk (amide) crystal through lattice defects. We present a first-principles study of native point defects and

  13. First-principles study of the interaction and charge transfer between graphene and metals

    NARCIS (Netherlands)

    Khomyakov, Petr; Giovannetti, G.; Rusu, P.C.; Brocks, G.; van den Brink, J.; Kelly, Paul J.

    2009-01-01

    Measuring the transport of electrons through a graphene sheet necessarily involves contacting it with metal electrodes. We study the adsorption of graphene on metal substrates using first-principles calculations at the level of density-functional theory. The bonding of graphene to Al, Ag, Cu, Au,

  14. Stability of Sb-Te layered structures: First-principles study

    NARCIS (Netherlands)

    Govaerts, K.; Sluiter, M.H.F.; Partoens, B.; Lamoen, D.

    2012-01-01

    Using an effective one-dimensional cluster expansion in combination with first-principles electronic structure calculations we have studied the energetics and electronic properties of Sb-Te layered systems. For a Te concentration between 0 and 60 at. % an almost continuous series of metastable

  15. First-principle studies of electronic structure and magnetic excitations in FeSe monolayer

    Science.gov (United States)

    Bazhirov, Timur; Cohen, Marvin L.

    2013-03-01

    Recent experimental advances made it possible to study single-layered superconducting systems of iron-based compounds. The results show evidence of significant enhancement of superconducting properties compared to the bulk case. We use first-principle pseudopotential density functional theory techniques and the local spin-density approximation to study the electronic properties of an FeSe monolayer in different spin configurations. The results show that the experimental shape of the Fermi surface is best described by a checkerboard antiferromagnetic (AFM) spin arrangement. To explore the underlying pairing mechanism, we study the evolution of the non-magnetic to the AFM-ordered structures under constrained magnetization, and we estimate the electronic coupling to magnetic excitations involving transfer and increase of iron magnetic moments and compare it to the electron-phonon coupling. Finally, we simulate the substrate-induced interaction by using uniform charge doping and show that the latter can lead to an increase in the density of states at the Fermi level and possibly produce higher superconducting transition temperatures. This work was supported by NSF grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at Lawrence Berkeley National Laboratory's NERSC facility

  16. Grain growth in U-7Mo alloy: A combined first-principles and phase field study

    Science.gov (United States)

    Mei, Zhi-Gang; Liang, Linyun; Kim, Yeon Soo; Wiencek, Tom; O'Hare, Edward; Yacout, Abdellatif M.; Hofman, Gerard; Anitescu, Mihai

    2016-05-01

    Grain size is an important factor in controlling the swelling behavior in irradiated U-Mo dispersion fuels. Increasing the grain size in U-Mo fuel particles by heat treatment is believed to delay the fuel swelling at high fission density. In this work, a multiscale simulation approach combining first-principles calculation and phase field modeling is used to investigate the grain growth behavior in U-7Mo alloy. The density functional theory based first-principles calculations were used to predict the material properties of U-7Mo alloy. The obtained grain boundary energies were then adopted as an input parameter for mesoscale phase field simulations. The effects of annealing temperature, annealing time and initial grain structures of fuel particles on the grain growth in U-7Mo alloy were examined. The predicted grain growth rate compares well with the empirical correlation derived from experiments.

  17. First principles study of nanostructured TiS2 electrodes for Na and Mg ion storage

    Science.gov (United States)

    Li, S. N.; Liu, J. B.; Liu, B. X.

    2016-07-01

    The development of competitive Na- and Mg-ion batteries (NIBs and MIBs) with performance comparable to Li-ion batteries is hindered by the major challenge of finding advanced electrode materials. In this work, nanostructured TiS2 electrodes including nanosheets, nanoribbons and nanotubes are shown by first principles calculations to achieve improved Na and Mg ion diffusion as compared with the bulk phase. Comparative studies between Li, Na, and Mg reveal that the diffusion kinetics of Na ions would especially benefit from the nanostructure design of TiS2. More specifically, the Na ion diffusivity turns out to be considerably higher than Li ion diffusivity, which is opposite to that observed in bulk TiS2. However, in the case of Mg ions, fast diffusion is still beyond attainment since a relatively high degree of interaction is expected between Mg and the S atoms. Edge-induced modifications of diffusion properties appear in both Na and Mg ions, while the mobility of Li ions along the ribbon edges may not be as appealing. Effects of the curvature of nanotubes on the adsorption strength and ion conductivity are also explored. Our results highlight the nanostructure design as a rich playground for exploring electrodes in NIBs and MIBs.

  18. Lithium ion adsorption and diffusion on black phosphorene nanotube: A first-principles study

    Science.gov (United States)

    Cao, Jin; Shi, Jing; Hu, Yinquan; Wu, Musheng; Ouyang, Chuying; Xu, Bo

    2017-01-01

    Li ion storage performance of the single-walled black phosphorene nanotube (PNT), which is considered as potential anode materials for high-performance Li-ion batteries (LIBs), is studied from first-principles calculations. The Li ion adsorption, diffusion and structural evolution of the one-dimensional armchair type PNT (aPNT) upon Li intercalation on the inside (in-PNT) and outside (out-PNT) surfaces were explored, comparing with that of the two-dimensional phosphorene (Psheet). A maximum Li storage capacity (at the intercalated state of Li22P44) is evaluated to be 432 mAh/g. It is also shown that the in-PNT system has higher adsorption energy and lower Li diffusion energy barrier compared with that of the Psheet and the out-PNT systems. The reason on why the better Li storage performance of the in-PNT is also studied from charge distribution and transfer analysis. These results suggest that PNT can be served as potential anode material for LIBs.

  19. First-principles insights into f magnetism: A case study on some magnetic pyrochlores

    Science.gov (United States)

    Deilynazar, Najmeh; Khorasani, Elham; Alaei, Mojtaba; Javad Hashemifar, S.

    2015-11-01

    First-principles calculations are performed to investigate f magnetism in A2Ti2O7 (A=Eu, Gd, Tb, Dy, Ho, Er, Yb) magnetic pyrochlore oxides. The Hubbard U parameter and the relativistic spin orbit correction are applied for a more accurate description of the electronic structure of the systems. It is argued that the main obstacle for the first-principles study of these systems is the multi-minima solutions of their electronic configuration. Among the studied pyrochlores, Gd2Ti2O7 shows the least multi-minima problem. The crystal electric field theory is applied for phenomenological comparison of the calculated spin and orbital moments with the experimental data.

  20. First-principles study of structural and bonding properties of vanadium carbide and niobium carbide

    Science.gov (United States)

    Joshi, K. B.; Paliwal, U.

    2009-11-01

    An ab initio linear combination of atomic orbitals method founded on density functional theory is applied to study the structural and bonding properties of vanadium carbide and niobium carbide. We present structural properties, namely, first-principles total energies, equilibrium lattice constants, bulk moduli and their pressure derivatives, together with the x-ray structure factors. Two generalized correction schemes—P86 and PW92—are applied to treat correlation. P86 gives a favourable ground state compared with the PW92. The computed equilibrium lattice constants and bulk moduli of the two compounds are compared with available experimental data. The x-ray structure factors for a few reflection planes are also reported. Comparison with experiment could be done only for niobium carbide. More refined measurements on x-ray structure factors for both compounds are required. We also present the autocorrelation functions derived from the ground-state momentum density. The electronic behaviour and bonding properties are discussed in terms of absolute and anisotropies in the directional autocorrelation functions. Our findings on structural and bonding parameters are well in accordance with the experimental data.

  1. First-principles study of structural and bonding properties of vanadium carbide and niobium carbide

    Energy Technology Data Exchange (ETDEWEB)

    Joshi, K B; Paliwal, U [Department of Physics, University College of Science, M L Sukhadia University, Udaipur - 313001 (India)], E-mail: k_joshi@yahoo.com

    2009-11-15

    An ab initio linear combination of atomic orbitals method founded on density functional theory is applied to study the structural and bonding properties of vanadium carbide and niobium carbide. We present structural properties, namely, first-principles total energies, equilibrium lattice constants, bulk moduli and their pressure derivatives, together with the x-ray structure factors. Two generalized correction schemes-P86 and PW92-are applied to treat correlation. P86 gives a favourable ground state compared with the PW92. The computed equilibrium lattice constants and bulk moduli of the two compounds are compared with available experimental data. The x-ray structure factors for a few reflection planes are also reported. Comparison with experiment could be done only for niobium carbide. More refined measurements on x-ray structure factors for both compounds are required. We also present the autocorrelation functions derived from the ground-state momentum density. The electronic behaviour and bonding properties are discussed in terms of absolute and anisotropies in the directional autocorrelation functions. Our findings on structural and bonding parameters are well in accordance with the experimental data.

  2. First-principles study of the interaction and charge transfer between graphene and metals

    OpenAIRE

    Khomyakov, P.A.; Giovannetti, G.; Rusu, P. C.; Brocks, G.; Brink, J.G.J. van den; Kelly, P. J.

    2009-01-01

    Measuring the transport of electrons through a graphene sheet necessarily involves contacting it with metal electrodes. We study the adsorption of graphene on metal substrates using first-principles calculations at the level of density functional theory. The bonding of graphene to Al, Ag, Cu, Au and Pt(111) surfaces is so weak that its unique "ultrarelativistic" electronic structure is preserved. The interaction does, however, lead to a charge transfer that shifts the Fermi level by up to 0.5...

  3. Adsorption of CO molecules on doped graphene: A first-principles study

    OpenAIRE

    Weidong Wang; Yuxiang Zhang; Cuili Shen; Yang Chai

    2016-01-01

    As a typical kinds of toxic gases, CO plays an important role in environmental monitoring, control of chemical processes, space missions, agricultural and medical applications. Graphene is considered a potential candidate of gases sensor, so the adsorption of CO molecules on various graphene, including pristine graphene, Nitrogen-doped graphene (N-doped graphene) and Aluminum-doped graphene (Al-doped graphene), are studied by using first-principles calculations. The optimal configurations, ad...

  4. First principles total energy study of NbCr{sub 2} + V Laves phase ternary system

    Energy Technology Data Exchange (ETDEWEB)

    Ormeci, A. [Koc Univ., Istanbul (Turkey); Chen, S.P.; Wills, J.M.; Albers, R.C. [Los Alamos National Lab., NM (United States)

    1999-04-01

    The C15 NbCr{sub 2} + V Laves phase ternary system is studied by using a first-principles, self-consistent, full-potential total energy method. Equilibrium lattice parameters, cohesive energies, density of states and formation energies of substitutional defects are calculated. Results of all these calculations show that in the C15 NbCr{sub 2} + V compounds, V atoms substitute Cr atoms only.

  5. First-principles study of electron transport through monatomic Al and Na wires

    DEFF Research Database (Denmark)

    Kobayashi, Nobuhiko; Brandbyge, Mads; Tsukada, Masaru

    2000-01-01

    We present first-principles calculations of electron transport, in particular, the conduction channels of monatomic Al and Na atom wires bridged between metallic jellium electrodes. The electronic structures are calculated by the first-principles recursion-transfer matrix method, and the conduction...... channels are investigated using the eigenchannel decomposition (ECD) of the conductance, the local density of states (LDOS), and the current density. The ECD is different from the conventional decomposition of atomic orbitals, and the study of decomposed electronic structures is shown to be effective...... in clarifying the details of transport through atomic wires. We show channel transmissions, channel resolved LDOS, and channel resolved current density, and elucidate the number of conduction channels, the relation between atomic orbitals and the channels, and their dependency on the geometry of the atomic wire...

  6. Novel two-dimensional silicon and germanium allotropes: a first-principles study

    Science.gov (United States)

    Gimbert, Florian; Lee, Chi-Cheng; Friedlein, Rainer; Fleurence, Antoine; Yamada-Takamura, Yukiko; Ozaki, Taisuke

    2014-03-01

    Graphene has been extensively studied but its integration into Si-based device technologies is difficult. It has been recently predicted by first-principles calculations that freestanding silicene and germanene, the counterparts of graphene made of Si and Ge atoms respectively, have graphene-like electronic structure with a low buckled structure. So far, the models predicted by first-principles calculations were not able to describe completely the experimental results. These difficulties tend to suggest a more complex phase diagram for freestanding silicene or for silicene on a substrate than the simple buckled phase. We report for the first time a novel two-dimensional silicon and germanium allotropes, with a structure similar of that of MoS2 layer. After investigating a large range of lattice constants by first-principles calculations with OpenMX code, we show that this structure is the ground state for freestanding two-dimensional silicon and germanium layers instead of the usually considered low buckled silicene and germanene.

  7. First-principles LDA+U calculations and luminescence study of YNbO4

    Science.gov (United States)

    Leng Lim, Thong; Nazarov, Mihail; Yoon, Tiem Leong; Low, Lay Chen; Fauzi, M. N. Ahmad

    2014-09-01

    Yttrium niobate (YNb{{O}_{4}}) phosphor is studied experimentally and through first-principles calculations, in which the structural and electronic properties of YNb{{O}_{4}} are investigated using the local-density approximation LDA+U method. The absorption and luminescence experiments that were conducted on the host lattice show the band gap to be \\approx 4.1 eV. The LDA+U calculations allow us to obtain a band gap of 4.28 eV. The density of states obtained from the calculation shows that O 2p states contribute to the valence band. The lower conduction band is mainly composed of Nb 4d states, while the upper conduction bands involve contribution mainly from Y 4d states. The partial DOS of each atom in the niobate system is then compared to the ultraviolet (UV) and vacuum ultraviolet (VUV) spectra from A photoluminescence excitation (PLE) experiment to explain the nature of the bands observed.

  8. Comparative Study of Multiplet Structures of Mn4+ in K2SiF6, K2GeF6, and K2TiF6 Based on First-Principles Configuration-Interaction Calculations

    Science.gov (United States)

    Novita, Mega; Ogasawara, Kazuyoshi

    2012-02-01

    We performed first-principles configuration-interaction calculations of multiplet energies for Mn4+ in K2SiF6, K2GeF6, and K2TiF6 crystals. The results indicate that corrections based on a single-electron calculation are effective for the prediction of 4A2 → 4T2 and 4A2 → 4T1a transition energies, while such corrections are not necessary for the prediction of the 4A2 → 2E transition energy. The cluster size dependence of the multiplet energies is small. However, the 4A2 → 2E transition energy is slightly improved by using larger clusters including K ions. The theoretical multiplet energies are improved further by considering the lattice relaxation effect. As a result, the characteristic multiplet energy shifts depending on the host crystal are well reproduced without using any empirical parameters. Although K2GeF6 and K2TiF6 have lower symmetry than K2SiF6, the results indicate that the variation of the multiplet energy is mainly determined by the Mn-F bond length.

  9. First principle study of structural, electronic and magnetic properties of silicon doped zigzag boron nitride nanoribbon

    Science.gov (United States)

    Bahadur, Amar; Verma, Mohan L.; Mishra, Madhukar

    2015-04-01

    Using first principle calculation, we investigate the structural, electronic and magnetic properties of silicon doped zigzag boron nitride nanoribbon (ZBNNR). Our results show that the shift in position of silicon doping with respect to the ribbon edge causes change in the structural geometry, electronic structure and magnetization of ZBNNR. The band gap of silicon doped ZBNNR is found to become narrower as compared to that of perfect ZBNNR. We find that band gap and magnetic moment of ZBNNR can be tuned by substitutional silicon doping position and doping concentration.

  10. First-principles study of the elastic constants and optical properties of uranium metal

    Institute of Scientific and Technical Information of China (English)

    Chen Qiu-Yun; Tan Shi-Yong; Lai Xin-Chun; Chen Jun

    2012-01-01

    We perform first-principles calculations of the lattice constants,elastic constants,and optical properties for alphaand gamma-uranium based on the ultra-soft pseudopotential method.Lattice constants and equilibrium atomic volume are consistent pretty well with the experimental results.Some difference exists between our calculated elastic constants and the experimental data.Based on the satisfactory ground state electronic structure calculations,the optical conductivity,dielectric function,refractive index,and extinction coefficients are also obtained.These calculated optical properties are compared with our results and other published experimental data.

  11. Enhanced optoelectronic property of ZnO under negative pressure condition: a first-principles study

    Science.gov (United States)

    Singh, Santosh; Nath Tripathi, Madhvendra

    2016-08-01

    In contrary to high pressure phases of ZnO, recent experimental evidence suggests that β-BeO type lattice modification of ZnO may be realised under negative pressure condition generated by lattice mismatch or by applying strain. The first-principles calculation based on density functional theory (DFT) is employed to investigate the negative pressure phase β-BeO, and the outcomes of the structural, electronic, and optical properties of this phase are compared with the ambient condition wurtzite B4 phase of ZnO. Our phase transition study shows that the B4 phase transforms into the β-BeO phase around negative pressure of -4 GPa and this new phase retains its structural stability even under more negative pressure. Further, the volume of the β-BeO phase increases resulting in a low-density phase with more anisotropic nature and distorted tetrahedral around Zn (or O) atoms along with (2 + 2) coordination as compared to B4 phase. The electronic structure of low-density β-BeO phase changes significantly, however, the band gaps of both the phases are almost same. The change in electronic structure of β-BeO phase turns into a significant blue shift in lower energy region of optical spectra. Moreover, the smaller effective mass values of charge carriers in β-BeO phase compared to B4 phase indicate high mobilities of charge carriers to attain enhanced conductivity. Further, the analysis of optical properties of β-BeO phase indicate the smaller values of reflectivity and absorption coefficients and consequently an enhanced transmittance value of 90% in visible region of optical spectra. The lower effective masses of charge carriers and enhancement in transmittance makes the low density negative pressure β-BeO phase suitable for achieving enhanced optoelectronic property of ZnO.

  12. A comparative first-principles study on electronic structures and mechanical properties of ternary intermetallic compounds Al8Cr4Y and Al8Cu4Y: Pressure and tension effects

    Science.gov (United States)

    Yang, Wenchao; Pang, Mingjun; Tan, Yong; Zhan, Yongzhong

    2016-11-01

    An investigation into the bulk properties, elastic properties and Debye temperature under pressure, and deformation mode under tension of Al8Cu4Y and Al8Cr4Y compounds was investigated by using first principles calculations based on density functional theory. The calculated lattice constants for the ternary compounds (Al8Cu4Y and Al8Cr4Y) are in good agreement with the experimental data. It can be seen from interatomic distances that the bonding between Al1 atom and Cr, Y, and Al2 atoms in Al8Cr4Y are stronger than Al8Cu4Y. The results of cohesive energy show that Al8Cr4Y should be easier to be formed and much stronger chemical bonds than Al8Cu4Y. The bulk modulus B, shear modulus G, Young's modulus E and Poisson's ratio ν can be obtained by using the Voigt-Reuss-Hill averaging scheme. From the results of elastic properties, Al8Cr4Y has the stronger mechanical behavior than Al8Cu4Y. Our calculations also show that pressure has a greater effect on mechanical behavior for both compounds. The ideal tensile strength are obtained by stress-strain relationships under [001](001) uniaxial tensile deformation, which are 15.4 and 23.4 GPa for Al8Cu4Y and Al8Cr4Y, respectively. The total and partial density of states and electron charge density under uniaxial tensile deformations for Al8Cu4Y and Al8Cr4Y compounds are also calculated and discussed in this work.

  13. First principles study of CuAlO2 doping with S

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    We study the electronic properties of CuAlO2 doped with S by the first principles calculations and find that the band gap of CuAlO2 is reduced after the doping.At the same time,the effective masses are also reduced and the density of states could cross the Fermi level.These results show that the conductivity of CuAlO2 could be enhanced by doping the impurities of S,which needs to be further studied.

  14. Prediction of new high pressure structural sequence in thorium carbide: A first principles study

    Energy Technology Data Exchange (ETDEWEB)

    Sahoo, B. D., E-mail: bdsahoo@barc.gov.in; Joshi, K. D.; Gupta, Satish C. [Applied Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India)

    2015-05-14

    In the present work, we report the detailed electronic band structure calculations on thorium monocarbide. The comparison of enthalpies, derived for various phases using evolutionary structure search method in conjunction with first principles total energy calculations at several hydrostatic compressions, yielded a high pressure structural sequence of NaCl type (B1) → Pnma → Cmcm → CsCl type (B2) at hydrostatic pressures of ∼19 GPa, 36 GPa, and 200 GPa, respectively. However, the two high pressure experimental studies by Gerward et al. [J. Appl. Crystallogr. 19, 308 (1986); J. Less-Common Met. 161, L11 (1990)] one up to 36 GPa and other up to 50 GPa, on substoichiometric thorium carbide samples with carbon deficiency of ∼20%, do not report any structural transition. The discrepancy between theory and experiment could be due to the non-stoichiometry of thorium carbide samples used in the experiment. Further, in order to substantiate the results of our static lattice calculations, we have determined the phonon dispersion relations for these structures from lattice dynamic calculations. The theoretically calculated phonon spectrum reveal that the B1 phase fails dynamically at ∼33.8 GPa whereas the Pnma phase appears as dynamically stable structure around the B1 to Pnma transition pressure. Similarly, the Cmcm structure also displays dynamic stability in the regime of its structural stability. The B2 phase becomes dynamically stable much below the Cmcm to B2 transition pressure. Additionally, we have derived various thermophysical properties such as zero pressure equilibrium volume, bulk modulus, its pressure derivative, Debye temperature, thermal expansion coefficient and Gruneisen parameter at 300 K and compared these with available experimental data. Further, the behavior of zero pressure bulk modulus, heat capacity and Helmholtz free energy has been examined as a function temperature and compared with the experimental data of Danan [J

  15. Prediction of new high pressure structural sequence in thorium carbide: A first principles study

    Science.gov (United States)

    Sahoo, B. D.; Joshi, K. D.; Gupta, Satish C.

    2015-05-01

    In the present work, we report the detailed electronic band structure calculations on thorium monocarbide. The comparison of enthalpies, derived for various phases using evolutionary structure search method in conjunction with first principles total energy calculations at several hydrostatic compressions, yielded a high pressure structural sequence of NaCl type (B1) → Pnma → Cmcm → CsCl type (B2) at hydrostatic pressures of ˜19 GPa, 36 GPa, and 200 GPa, respectively. However, the two high pressure experimental studies by Gerward et al. [J. Appl. Crystallogr. 19, 308 (1986); J. Less-Common Met. 161, L11 (1990)] one up to 36 GPa and other up to 50 GPa, on substoichiometric thorium carbide samples with carbon deficiency of ˜20%, do not report any structural transition. The discrepancy between theory and experiment could be due to the non-stoichiometry of thorium carbide samples used in the experiment. Further, in order to substantiate the results of our static lattice calculations, we have determined the phonon dispersion relations for these structures from lattice dynamic calculations. The theoretically calculated phonon spectrum reveal that the B1 phase fails dynamically at ˜33.8 GPa whereas the Pnma phase appears as dynamically stable structure around the B1 to Pnma transition pressure. Similarly, the Cmcm structure also displays dynamic stability in the regime of its structural stability. The B2 phase becomes dynamically stable much below the Cmcm to B2 transition pressure. Additionally, we have derived various thermophysical properties such as zero pressure equilibrium volume, bulk modulus, its pressure derivative, Debye temperature, thermal expansion coefficient and Gruneisen parameter at 300 K and compared these with available experimental data. Further, the behavior of zero pressure bulk modulus, heat capacity and Helmholtz free energy has been examined as a function temperature and compared with the experimental data of Danan [J. Nucl. Mater. 57, 280

  16. First-principles approach to heat and mass transfer effects in model catalyst studies

    OpenAIRE

    Matera, S.; Reuter, K.

    2009-01-01

    We assess heat and mass transfer limitations in in situ studies of model catalysts with a first-principles based multiscale modeling approach that integrates a detailed description of the surface reaction chemistry and the macro-scale flow structures. Using the CO oxidation at RuO2(110) as a prototypical example we demonstrate that factors like a suppressed heat conduction at the backside of the thin single-crystal, and the build-up of a product boundary layer above the flat-faced surface pla...

  17. Stability and electronic structure of InN nanotubes from first-principles study

    Institute of Scientific and Technical Information of China (English)

    Chen Li-Juan

    2006-01-01

    The stability and electronic structure of hypothetical InN nanotubes were studied by first-principles density functional theory.It was found that the strain energies of InN nanotubes are smaller than those of carbon nanotubes of the same radius.Single-wall zigzag InN nanotubes were found to be semiconductors with a direct band gap while the armchair counterparts have an indirect band gap.The band gaps of nanotubes decrease with increasing diameter,similar to the case of carbon nanotubes.

  18. Substitutional Co dopant on the GaAs(110) surface: A first principles study

    Science.gov (United States)

    Fang, Zhou; Yi, Zhijun

    2016-12-01

    Using the first principles ground state method, the electronic properties of single Co dopant replacing one Ga atom on the GaAs(110) surface are studied. Our calculated local density of states (LDOS) at Co site presents several distinct peaks above the valence band maximum (VBM), and this agrees with recent experiments. Moreover, the calculated STM images at bias voltages of 2 eV and -2 eV also agree with experiments. We discussed the origin of Co impurity induced distinct peaks, which can be characterized with the hybridization between Co d orbitals and p-like orbitals of surface As and Ga atoms.

  19. Interactions of gas molecules with monolayer MoSe2: A first principle study

    Science.gov (United States)

    Sharma, Munish; Jamdagni, Pooja; Kumar, Ashok; Ahluwalia, P. K.

    2016-05-01

    We present a first principle study of interaction of toxic gas molecules (NO, NO2 and SO2) with monolayer MoSe2. The predicted order of sensitivity of gas molecule is NO2 > SO2 > NO. Adsorbed molecules strongly influence the electronic behaviour of monolayer MoSe2 by inducing impurity levels in the vicinity of Fermi energy. NO and SO2 is found to induce p-type doping effect while semiconductor to metallic transitions occur on NO2 adsorption. Our findings may guide the experimentalist for fabricating sensor devices based on MoSe2 monolayer.

  20. First Principle Study of Ferromagnetism in Cr-Doped In2O3

    Institute of Scientific and Technical Information of China (English)

    XIE Zhi; CHENG Wen-Dan; WU Dong-Sheng; HUANG Shu-Ping; HU Jian-Ming; ZHANG Hao; HU Hui

    2008-01-01

    We present a first principle study of Cr-doped In2O3 system using density func- tional theory. The obtained results show that the Cr ion prefers the cation site of the center of trigonally distorted octahedron and converges to high spin-polarized configuration in the ground state. The hybridization between d-states and the donor states is strong, and the spin-split donor impurity-band model is found to be the most favorable mechanism for the ferromagnetism in this system. The good ferromagnetic property of high Curie temperature is discussed in view of the electronic structure analyses.

  1. First-principles study of the dipole layer formation at metal-organic interfaces

    OpenAIRE

    2009-01-01

    We study the dipole layer formed at metal-organic interfaces by means of first-principles calculations. Interface dipoles are monitored by calculating the work function change of Au, Ag, Al, Mg and Ca surfaces upon adsorption of a monolayer of PTCDA (3,4,9,10-perylene-tetra-carboxylic-di-anhydride), perylene or benzene molecules. Adsorption of PTCDA leads to pinning of the work function for a range of metal substrates. It gives interface dipoles that compensate for the difference in the clean...

  2. Arsenene as a promising candidate for NO and NO2 sensor: A first-principles study

    Science.gov (United States)

    Liu, Can; Liu, Chun-Sheng; Yan, Xiaohong

    2017-03-01

    Based on first-principles calculations, we have studied the adsorption of CO, CO2, N2, NH3, NO and NO2 molecules on the pristine arsenene monolayer. These gas molecules are held by an interaction that is intermediate between the physisorbed and chemisorbed states. Furthermore, the adsorption of NO and NO2 can produce a noticeable modifications of the density of states near the Fermi level. Interestingly, only the adsorption of NO and NO2 can lead to a magnetic moment of 1 μB. Therefore, our results can provide a theoretical basis for the potential applications of arsenene monolayer in gas sensing with electrical and magnetic methods.

  3. First-principles study of hydrogen-enhanced phosphorus diffusion in silicon

    Energy Technology Data Exchange (ETDEWEB)

    The Anh, Le, E-mail: letheanh@jaist.ac.jp; Lam, Pham Tien; Manoharan, Muruganathan; Matsumura, Hideki; Otsuka, Nobuo; Hieu Chi, Dam [School of Materials Science, Japan Advanced Institute of Science and Technology, Asahidai 1-1, Nomishi, Ishikawa 923-1292 (Japan); Tien Cuong, Nguyen [Faculty of Physics, VNU University of Science, 334 Nguyen Trai, Thanh Xuan, Hanoi (Viet Nam); Mizuta, Hiroshi [School of Materials Science, Japan Advanced Institute of Science and Technology, Asahidai 1-1, Nomishi, Ishikawa 923-1292 (Japan); Nanoelectronics and Nanotechnologies Research Group, Electronics and Computer Science, Faculty of Physical Sciences and Engineering, University of Southampton, Highfield, Southampton, Hampshire SO17 1BJ (United Kingdom)

    2016-01-28

    We present a first-principles study on the interstitial-mediated diffusion process of neutral phosphorus (P) atoms in a silicon crystal with the presence of mono-atomic hydrogen (H). By relaxing initial Si structures containing a P atom and an H atom, we derived four low-energy P-H-Si defect complexes whose formation energies are significantly lower than those of P-Si defect complexes. These four defect complexes are classified into two groups. In group A, an H atom is located near a Si atom, whereas in group B, an H atom is close to a P atom. We found that the H atom pairs with P or Si atom and changes the nature bonding between P and Si atoms from out-of-phase conjugation to in-phase conjugation. This fact results in the lower formation energies compare to the cases without H atom. For the migration of defect complexes, we have found that P-H-Si defect complexes can migrate with low barrier energies if an H atom sticks to either P or Si atom. Group B complexes can migrate from one lattice site to another with an H atom staying close to a P atom. Group A complexes cannot migrate from one lattice site to another without a transfer of an H atom from one Si atom to another Si atom. A change in the structure of defect complexes between groups A and B during the migration results in a transfer of an H atom between P and Si atoms. The results for diffusion of group B complexes show that the presence of mono-atomic H significantly reduces the activation energy of P diffusion in a Si crystal, which is considered as a summation of formation energy and migration barrier energy, leading to the enhancement of diffusion of P atoms at low temperatures, which has been suggested by recent experimental studies.

  4. First-principles study on hydrogen adsorption on nitrogen doped graphene

    Science.gov (United States)

    Muhammad, Rafique; Shuai, Yong; Tan, He-Ping

    2017-04-01

    In this paper we have investigated the adsorption of Hydrogen on Nitrogen doped graphene in detail by means of first-principles calculations. A comprehensive study is performed of the structural, electronic and optical properties of hydrogen atoms adsorbed on dopant atoms sites and on carbon atoms neighboring dopant atoms. The effect of doping has been investigated by varying the concentration of doping atoms from 3.125%(one atom of nitrogen in 32 host atoms) to 6.25% (two nitrogen atoms in 32 host atoms). Similarly the effect of adsorption has been investigated by varying the concentration of hydrogen atoms and also varying the adsorption sites. Band structure, partial density of states (PDOS) and optical properties of pure, nitrogen doped and hydrogen adsorbed graphene sheet were calculated using VASP (Vienna ab-initio Simulation Package). The calculated results for pure graphene sheet were then compared with nitrogen doped graphene and Hydrogen adsorbed graphene sheet. It is found that upon nitrogen doping the Dirac point in the graphene band structure shifts below the Fermi Energy level and energy gap appears at the high symmetric K-point. On the other hand, by adsorption of Hydrogen atom, there is further change in the band structure near the Fermi level and also the energy gap at the high symmetric K-point is increased. There is change in the dielectric function and refractive index of the graphene after H atoms adsorption on N-doped graphene. The overall absorption spectra is decreased in case of nitrogen doping and after adsorption process of Hydrogen atoms. However a significant red shift in absorption towards visible range of radiation is found to occur for hydrogen atoms adsorbed on nitrogen doped graphene sheet. The reflectivity peak of graphene increases in low energy region after H adsorption on N-doped graphene. The results can be used to tune the Fermi Energy level and to tailor the optical properties of graphene sheet in visible region.

  5. Electrochemical potentials of layered oxide and olivine phosphate with aluminum substitution: A first principles study

    Indian Academy of Sciences (India)

    Arun Kumar Varanasi; Phani Kanth Sanagavarapu; Arghya Bhowmik; Mridula Dixit Bharadwaj; Balasubramanian Narayana; Umesh V Waghmare; Dipti Deodhare; Alind Sharma

    2013-12-01

    First-principles prediction of enhancement in the electrochemical potential of LiCoO2 with aluminum substitution has been realized through earlier experiments. For safer and less expensive Li-ion batteries, it is desirable to have a similar enhancement for alternative cathode materials, LiFePO4 and LiCoPO4. Here, we present first-principles density functional theory based analysis of the effects of aluminum substitution on electrochemical potential of LiCoO2, LiFePO4 and LiCoPO4. While Al substitution for transition metal results in increase in electrochemical potential of LiCoO2, it leads to reduction in LiFePO4 and LiCoPO4. Through comparative topological analysis of charge density of these materials, we identify a ratio of Bader charges that correlates with electrochemical potential and determine the chemical origin of these contrasting effects: while electronic charge from lithium is transferred largely to oxygen in LiCoO2, it gets shared by the oxygen and Co/Fe in olivine phosphates due to strong covalency between O and Co/Fe. Our work shows that covalency of transition metal–oxygen bond plays a key role in determining battery potential.

  6. Structures and magnetic properties of Co-Zr-B magnets studied by first-principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Xin; Ke, Liqin; Nguyen, Manh Cuong; Wang, Cai-Zhuang, E-mail: wangcz@ameslab.gov; Ho, Kai-Ming, E-mail: kmh@ameslab.gov [Ames Laboratory, U.S. DOE and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011 (United States)

    2015-06-28

    The structures and magnetic properties of Co-Zr-B alloys near the composition of Co{sub 5}Zr with B at. % ≤6% were studied using adaptive genetic algorithm and first-principles calculations. The energy and magnetic moment contour maps as a function of chemical composition were constructed for the Co-Zr-B magnet alloys through extensive structure searches and calculations. We found that Co-Zr-B system exhibits the same structure motif as the “Co{sub 11}Zr{sub 2}” polymorphs, and such motif plays a key role in achieving strong magnetic anisotropy. Boron atoms were found to be able to substitute cobalt atoms or occupy the “interruption” sites. First-principles calculations showed that the magnetocrystalline anisotropy energies of the boron-doped alloys are close to that of the high-temperature rhombohedral Co{sub 5}Zr phase and larger than that of the low-temperature Co{sub 5.25}Zr phase. Our calculations provide useful guidelines for further experimental optimization of the magnetic performances of these alloys.

  7. A First Principle Comparative Study on Chemisorption of H2 on C60, C80, and Sc3N@C80 in Gas Phase and Chemisorption of H2 on Solid Phase C60

    Directory of Open Access Journals (Sweden)

    Hongtao Wang

    2014-01-01

    Full Text Available The chemisorptions of H2 on fullerenes C60 and C80, endofullerene Sc3C@C80 and solid C60 were comparatively studied. A chain reaction mechanism for dissociative adsorption of H2 on solid C60 is proposed under high pressure. The breaking of H–H bond is concerted with the formation of two C–H bonds on two adjacent C60 in solid phase. The adsorption process is facilitated by the application of high pressure. The initial H2 adsorption on two adjacent C60 gives a much lower barrier 1.36 eV in comparison with the barrier of adsorption on a single C60 (about 3.0 eV. As the stereo conjugate aromaticity of C60 is destructed by the initial adsorption, some active sites are created. Hence the successive adsorption becomes easier with much low barriers (0.6 eV. In addition, further adsorption can create new active sites for the next adsorption. Thus, a chain reaction path is formed with the initial adsorption dominating the whole adsorption process.

  8. First Principle Study of Uranium Nitrides UN and UN2 Using DFT and DFT + U

    Directory of Open Access Journals (Sweden)

    T. Zergoug

    2015-12-01

    Full Text Available First principle calculation based on density functional theory (DFT was used to evaluate some physical properties of Uranium Nitrides. Adsorption of oxygen O atom and O2 molecule on/in (001 surfaces of both Uranium monoNitride (UN and diNitride (UN2 was then studied and compared mutually. To treat the strong correlation effects caused by 5f Uranium valence electrons, Hubbard-U advanced (DFT + U approach was employed to correct the exchange correlation functional GGA and PBE which are based on generalized gradient approximation. The functional are developed for the Vienna Abinitio Simulation Package (VASP and were used with the projector-augmented wave (PAW pseudo potentials. The structural and elastic-mechanical UN and UN2 properties were calculated within DFT and DFT + U methods. Then, Potential Energy Surfaces (PES concepts which correspond to the interaction between O atom (respectively O2 molecule and (001 on-surfaces / sub-surfaces uranium nitrides for several positions were determined to identify favorable adsorption sites. Physical properties calculation results of UN or UN2 are in order of magnitude of other theoretical values and show an acceptable precision compared to experiments. Hubbard U value of the DFT + U formalism was optimized to achieve Antiferromagnetic (AFM UN configuration and was effective at U = 1.625 eV. Optimization of UN2 was accomplished to attain experimental cell parameter of 5.31 A° and was reached for U = 2.6 eV. According to our calculation results, O2 diffusion through UN(001 and UN2(001 clean surfaces have demonstrated dissociation of the molecule from a distance of approximately d = 1.5 Å. Favored on surface modes for O atom adsorption were found to be near the bridge site for UN(001 and UN2(001. The O incorporation through UN(001 surface was at the bridge site, nevertheless, for UN2, merging of O atom in the (001 surface bridge site was not allowed.

  9. A first-principles study of He, Xe, Kr and O incorporation in thorium carbide

    Science.gov (United States)

    Pérez Daroca, D.; Llois, A. M.; Mosca, H. O.

    2015-05-01

    Thorium-based materials are currently being investigated in relation with their potential utilization in Generation-IV reactors as nuclear fuels. Understanding the incorporation of fission products and oxygen is very important to predict the behavior of nuclear fuels. A first approach to this goal is the study of the incorporation energies and stability of these elements in the material. By means of first-principles calculations within the framework of density functional theory, we calculate the incorporation energies of He, Xe, Kr and O atoms in Th and C vacancy sites, in tetrahedral interstitials and in Schottky defects along the and directions. We also analyze atomic displacements, volume modifications and Bader charges. This kind of results for ThC, to the best authors' knowledge, have not been obtained previously, neither experimentally, nor theoretically. This should deal as a starting point towards the study of the complex behavior of fission products in irradiated ThC.

  10. Ferroelectric mechanism of croconic acid: A first-principles and Monte Carlo study

    Science.gov (United States)

    Cai, Yaxuan; Luo, Shijun; Zhu, Zhanwu; Gu, Haoshuang

    2013-07-01

    The ferroelectric mechanism of croconic acid in terms of the electronic structure and the molecular structure was studied by first principles using the density functional theory with the generalized gradient approximation. The spontaneous polarization (Ps) was simulated by the Berry phase method. It is found that the large polarization originates from charge transfer due to the strong "push-pull" effect of electron-releasing and -withdrawing groups along the hydrogen bond. According to the characteristics of polarization of croconic acid, we constructed a one-dimensional ferroelectric Hamiltonian model to describe the ferroelectric properties of croconic acid. Based on the Hamiltonian model, the thermal properties of the ferroelectricity of croconic acid were studied by Monte Carlo method. The simulated Curie temperature is 756 K, and the spontaneous polarization keeps well temperature range stability up to 400 K. These results are in good agreement with the experimental data.

  11. Electronic and optical properties of RESn3 (RE=Pr & Nd) intermetallics: A first principles study

    Science.gov (United States)

    Pagare, G.; Abraham, Jisha A.; Sanyal, S. P.

    2015-06-01

    A theoretical study of structural, electronic and optical properties of RESn3 (RE = Pr & Nd) intermetallics have been investigated systematically using first principles density functional theory. The calculations are carried out within the PBE-GGA and LSDA for the exchange correlation potential. The ground state properties such as lattice parameter (a0), bulk modulus (B) and its pressure derivative (B') are calculated and the calculated lattice parameters show well agreement with the experimental results. We first time predict elastic constants for these compounds. From energy dispersion curves, it is found that these compounds are metallic in nature. The linear optical response of these compounds are also studied and the higher value of static dielectric constant shows the possibility to use them as good dielectric materials.

  12. The first-principles study on the doping effect of Re in Ni3A1

    Institute of Scientific and Technical Information of China (English)

    Song Yu; Chongyu Wang; Tao Yu

    2008-01-01

    Using first-principles density function for molecules method (DMol) and discrete variational method (DVM) based on the density functional theory, we studied the doping effect of Re in Ni3Al. The structure relaxation and the alloying energy show that Re has a strong A1 site preference and leads to the local deformation, which is in agreement with the experimental results and other theoretical results. In addition, the charge density difference and the bond order show that Re can strongly enhance the interatomic interaction between the nearest neighbor atoms. From the density of states and the Pauli spectrum, we find that resonance states and localized states are induced by doping Re, and the doped Re atom forms the hybridized bond with the nearest neighbor atoms.

  13. First-Principles Study of Defects in CuGaO2

    Institute of Scientific and Technical Information of China (English)

    FANG Zhi-Jie; FANG Cheng; SHI Li-Jie; LIU Yong-Hui; HE Man-Chao

    2008-01-01

    @@ Using the first-principles methods, we study the electronic structure, intrinsic and extrinsic defects doping in transparent conducting oxides CuGaO2. Intrinsic defects, acceptor-type and donor-type extrinsic defects in their relevant charge state are considered. The calculation result show that copper vacancy and oxygen interstitial are the relevant defects in CuGaO2. In addition, copper vacancy is the most efficient acceptor. Substituting Be for Ga is the prominent acceptor, and substituting Ca for Cu is the prominent donors in CuGaO2. Our calculation results are expected to be a guide for preparing n-type and p-type materials in CuGaO2.

  14. Cobalt (hydro)oxide electrodes under electrochemical conditions: a first principle study

    Science.gov (United States)

    Chen, Jia; Selloni, Annabella

    2013-03-01

    There is currently much interest in photoelectrochemical water splitting as a promising pathway towards sustainable energy production. A major issue of such photoelectrochemical devices is the limited efficiency of the anode, where the oxygen evolution reaction (OER) takes place. Cobalt (hydro)oxides, particularly Co3O4 and Co(OH)2, have emerged as promising candidates for use as OER anode materials. Interestingly, recent in-situ Raman spectroscopy studies have shown that Co3O4 electrodes undergo progressive oxidation and transform into oxyhydroxide, CoO(OH), under electrochemical working conditions. (Journal of the American Chemical Society 133, 5587 (2011))Using first principle electronic structure calculations, we provide insight into these findings by presenting results on the structural, thermodynamic, and electronic properties of cobalt oxide, hydroxide and oxydroxide CoO(OH), and on their relative stabilities when in contact with water under external voltage.

  15. Formaldehyde molecule adsorbed on doped graphene: A first-principles study

    Science.gov (United States)

    Liu, Xu-Ying; Zhang, Jian-Min

    2014-02-01

    Adsorption of formaldehyde (H2CO) on B-, N-, Si-, Al-, Cr-, Mn-, and Au-doped graphene was theoretically studied using first-principles approach based on density functional theory in order to exploit their potential applications as H2CO gas sensors. The electronic and magnetic properties of the graphene-molecule adsorption adducts are strongly dependent on the dopants. H2CO molecule is adsorbed weakly on B- and N-doped graphene; in general, strong chemisorption is observed on Si-, Al-, Cr-, Mn-, and Au-doped graphene. The most stable adsorption geometries, adsorption energies, magnetic moments, charge transfers, and density of states of these systems are thoroughly discussed. This work reveals that the sensitivity of graphene-based chemical gas sensors for H2CO can be drastically improved by introducing appropriate dopant. Al and Mn are found to be the best choices among all the dopants.

  16. Formaldehyde molecule adsorbed on doped graphene: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Xu-Ying; Zhang, Jian-Min, E-mail: jianm_zhang@yahoo.com

    2014-02-28

    Adsorption of formaldehyde (H{sub 2}CO) on B-, N-, Si-, Al-, Cr-, Mn-, and Au-doped graphene was theoretically studied using first-principles approach based on density functional theory in order to exploit their potential applications as H{sub 2}CO gas sensors. The electronic and magnetic properties of the graphene-molecule adsorption adducts are strongly dependent on the dopants. H{sub 2}CO molecule is adsorbed weakly on B- and N-doped graphene; in general, strong chemisorption is observed on Si-, Al-, Cr-, Mn-, and Au-doped graphene. The most stable adsorption geometries, adsorption energies, magnetic moments, charge transfers, and density of states of these systems are thoroughly discussed. This work reveals that the sensitivity of graphene-based chemical gas sensors for H{sub 2}CO can be drastically improved by introducing appropriate dopant. Al and Mn are found to be the best choices among all the dopants.

  17. First-principles study of superconducting hydrogen sulfide at pressure up to 500 GPa.

    Science.gov (United States)

    Durajski, Artur P; Szczęśniak, Radosław

    2017-06-30

    We investigate the possibility of achieving the room-temperature superconductivity in hydrogen sulfide (H3S) through increasing external pressure, a path previously widely used to reach metallization and superconducting state in novel hydrogen-rich materials. The electronic properties and superconductivity of H3S in the pressure range of 250-500 GPa are determined by the first-principles calculations. The metallic character of a body-centered cubic Im[Formula: see text]m structure is found over the whole studied pressure. Moreover, the absence of imaginary frequency in phonon spectrum implies that this structure is dynamically stable. Furthermore, our calculations conducted within the framework of the Eliashberg formalism indicate that H3S in the range of the extremely high pressures is a conventional strong-coupling superconductor with a high superconducting critical temperature, however, the maximum critical temperature does not exceed the value of 203 K.

  18. First Principles Study of Electronic and Magnetic Properties of Co-Doped Armchair Graphene Nanoribbons

    Directory of Open Access Journals (Sweden)

    Biao Li

    2015-01-01

    Full Text Available Using the first principles calculations, we have studied the atomic and electronic structures of single Co atom incorporated with divacancy in armchair graphene nanoribbon (AGNR. Our calculated results show that the Co atom embedded in AGNR gives rise to significant impacts on the band structures and the FM spin configuration is the ground state. The presence of the Co doping could introduce magnetic properties. The calculated results revealed the arising of spin gapless semiconductor characteristics with doping near the edge in both ferromagnetic (FM and antiferromagnetic (AFM magnetic configurations, suggesting the robustness for potential application of spintronics. Moreover, the electronic structures of the Co-doped AGNRs are strongly dependent on the doping sites and the edge configurations.

  19. First-principles study of Dirac and Dirac-like cones in phononic and photonic crystals

    KAUST Repository

    Mei, Jun

    2012-07-24

    By using the k•p method, we propose a first-principles theory to study the linear dispersions in phononic and photonic crystals. The theory reveals that only those linear dispersions created by doubly degenerate states can be described by a reduced Hamiltonian that can be mapped into the Dirac Hamiltonian and possess a Berry phase of -π. Linear dispersions created by triply degenerate states cannot be mapped into the Dirac Hamiltonian and carry no Berry phase, and, therefore should be called Dirac-like cones. Our theory is capable of predicting accurately the linear slopes of Dirac and Dirac-like cones at various symmetry points in a Brillouin zone, independent of frequency and lattice structure. © 2012 American Physical Society.

  20. First-principles study on initial stage of oxidation on Si(110) surface

    Energy Technology Data Exchange (ETDEWEB)

    Nagasawa, Takahiro; Shiba, Seiji; Sueoka, Koji [Department of System Engineering, Okayama Prefectural University, 111 Kuboki, Soja, Okayama 719-1197 (Japan)

    2011-03-15

    There is a great deal of engineering interest in Si (110) wafers as the substrates of large scale integrations (LSIs) in the next generation. However, few studies on Si (110) surface have been reported in comparison with those on other low-index surfaces, still less the mechanism of surface oxidation. We analyzed the surface structure and the initial stage of oxidation on the Si (110)-(16 x 2) clean surface with first-principles calculation. The results of our calculations showed that first, the stable structure of the Si (110) clean surface was the adatom-tetramer-interstitial (ATI) reconstruction. Second, pairs of pentagon (PPs) were preferentially oxidized in the initial stage of the oxidation. Third, the oxidation growth should progress with the clustering of O atoms. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  1. Band structure and optical properties of amber studied by first principles

    Energy Technology Data Exchange (ETDEWEB)

    Rao, Zhi-Fan, E-mail: raozhifan@163.com [Analysis and Testing Center of Yunnan, Kunming University of Science and Technology, Kunming 650093 (China); Zhou, Rong-Feng [Analysis and Testing Center of Yunnan, Kunming University of Science and Technology, Kunming 650093 (China)

    2013-03-01

    The band structure and density of states of amber is studied by the first principles calculation based on density of functional theory. The complex structure of amber has 214 atoms and the band gap is 5.0 eV. The covalent bond is combined C/O atoms with H atoms. The O 2p orbital is the biggest effect near the Fermi level. The optical properties' results show that the reflectivity is low, and the refractive index is 1.65 in visible light range. The highest absorption coefficient peak is at 172 nm and another higher peak is at 136 nm. These convince that the amber would have a pretty sheen and that amber is a good and suitable crystal for jewelry and ornaments.

  2. First-principle study of energy band structure of armchair graphene nanoribbons

    Science.gov (United States)

    Ma, Fei; Guo, Zhankui; Xu, Kewei; Chu, Paul K.

    2012-07-01

    First-principle calculation is carried out to study the energy band structure of armchair graphene nanoribbons (AGNRs). Hydrogen passivation is found to be crucial to convert the indirect band gaps into direct ones as a result of enhanced interactions between electrons and nuclei at the edge boundaries, as evidenced from the shortened bond length as well as the increased differential charge density. Ribbon width usually leads to the oscillatory variation of band gaps due to quantum confinement no matter hydrogen passivated or not. Mechanical strain may change the crystal symmetry, reduce the overlapping integral of C-C atoms, and hence modify the band gap further, which depends on the specific ribbon width sensitively. In practical applications, those effects will be hybridized to determine the energy band structure and subsequently the electronic properties of graphene. The results can provide insights into the design of carbon-based devices.

  3. Kittel law in BiFeO₃ ultrathin films: a first-principles-based study.

    Science.gov (United States)

    Prosandeev, S; Lisenkov, S; Bellaiche, L

    2010-10-01

    A first-principles-based effective Hamiltonian is used to investigate the thickness dependency of the size of straight-walled domains in ultrathin films made of the multiferroic BiFeO₃ (BFO) material. It is found that the Kittel law is followed, as in ferroelectric or ferromagnetic films. However, an original real-space decomposition of the different energetic terms of this effective Hamiltonian allows the discovery that the microscopic origins of such a law in BFO films dramatically differ from those in ferroelectric or ferromagnetic films. In particular, interactions between tilting of oxygen octahedra around the domain walls and magnetoelectric couplings near the surface (and away from the domain walls) play an important role in the observance of the Kittel law in the studied BFO films.

  4. Lithium halide monolayers: Structural, electronic and optical properties by first principles study

    Science.gov (United States)

    Safari, Mandana; Maskaneh, Pegah; Moghadam, Atousa Dashti; Jalilian, Jaafar

    2016-09-01

    Using first principle study, we investigate the structural, electronic and optical properties of lithium halide monolayers (LiF, LiCl, LiBr). In contrast to graphene and other graphene-like structures that form hexagonal rings in plane, these compounds can form and stabilize in cubic shape interestingly. The type of band structure in these insulators is identified as indirect type and ionic nature of their bonds are illustrated as well. The optical properties demonstrate extremely transparent feature for them as a result of wide band gap in the visible range; also their electron transitions are indicated for achieving a better vision on the absorption mechanism in these kinds of monolayers.

  5. First-principles study on the ferrimagnetic half-metallic Mn2FeAs alloy

    Science.gov (United States)

    Qi, Santao; Zhang, Chuan-Hui; Chen, Bao; Shen, Jiang; Chen, Nanxian

    2015-05-01

    Mn-based full-Heusler alloys are kinds of promising candidates for new half-metallic materials. Basing on first principles, the electronic structures and magnetic properties of the Mn2FeAs full-Heusler alloy have been investigated in detail. The Hg2CuTi-type Mn2FeAs compound obeys the Slater-Pauling rule, while the anti-parallel alignment atomic magnetic moments of Mn locating at different sites indicate it a ferrimagnetic alloy. The calculated spin-down bands behave half-metallic character, exhibiting a direct gap of 0.46 eV with a 100% spin polarization at the Fermi level. More studies show the compound would maintain half-metallic nature in a large range of variational lattice constants. We expect that our calculated results may trigger Mn2FeAs applying in the future spintronics field.

  6. The structural, electronic and phonon behavior of CsPbI3: A first principles study

    Science.gov (United States)

    Bano, Amreen; Khare, Preeti; Parey, Vanshree; Shukla, Aarti; Gaur, N. K.

    2016-05-01

    Metal halide perovskites are optoelectronic materials that have attracted enormous attention as solar cells with power conversion efficiencies reaching 20%. The benefit of using hybrid compounds resides in their ability to combine the advantage of these two classes of compounds: the high mobility of inorganic materials and the ease of processing of organic materials. In spite of the growing attention of this new material, very little is known about the electronic and phonon properties of the inorganic part of this compounds. A theoretical study of structural, electronic and phonon properties of metal-halide cubic perovskite, CsPbI3 is presented, using first-principles calculations with planewave pseudopotential method as personified in PWSCF code. In this approach local density approximation (LDA) is used for exchange-correlation potential.

  7. First-principle Studies on Ferromagnetism of Fe-doped AlN Diluted Magnetic Semiconductors

    Directory of Open Access Journals (Sweden)

    Honglei WU

    2016-11-01

    Full Text Available We have studied the electronic structures and magnetic properties of Fe-doped AlN by first-principles calculations within density functional theory. The calculated results show that AlN crystals doped by double Fe atoms display ferromagnetic properties, and the total magnetic moment is 10.0 µB per 72-atom supercell (3 × 3 × 2. The calculated energy differences between the antiferromagnetic (AFM and ferromagnetic (FM phases are 207 meV, which means FM state is a stable state. It is also found that the 3d-states of Fe dopants and the 2p-states of N atoms bonding to Fe dopants are the main contributors to the density of states at the Fermi level.DOI: http://dx.doi.org/10.5755/j01.ms.22.4.10750

  8. First-principles studies of HF molecule adsorption on intrinsic graphene and Al-doped graphene

    Science.gov (United States)

    Sun, Yuanyuan; Chen, Li; Zhang, Feiwu; Li, Daoyong; Pan, Hongzhe; Ye, Jun

    2010-10-01

    In the search for a high-sensitivity sensor for HF gas, the adsorption of HF molecules on both intrinsic and Al-doped graphene sheets is studied by first-principles calculations. We find that the adsorption mechanisms of HF molecules are different for intrinsic graphene and Al-doped graphene. Al-doped graphene has higher adsorption energy and shorter connecting distance to the HF molecule than intrinsic graphene. The calculated net electron transfers, electronic density difference images and densities of states give evidence that the adsorption of HF molecules on Al-doped graphene is by chemisorption, while there is weak physisorption on intrinsic graphene. Therefore, Al-doped graphene can be expected to have applications as a novel sensor for the detection of HF gas. The HF molecules adsorbed on Al-doped graphene material can be reactivated by applying an external electric field of 0.013 a.u.

  9. First-Principles Study of Photochemical Activation of CO2 by Ti-based Oxides

    Science.gov (United States)

    He, Haiying; Zapol, Peter; Curtiss, Larry

    2013-03-01

    The photochemical conversion of CO2 and H2O into energy-bearing hydrocarbon fuels provides an attractive way of mitigating the green-house gas CO2 and utilizing solar energy as a sustainable energy source. However, due to the high reduction potential and chemical inertness of CO2 molecules, the conversion rate of CO2 is impractically low. The activation of CO2 is critical in facilitating further reactions. By carrying out first-principles calculations of reaction pathways from CO2 to CO2-anions on Ti-based oxides including zeolites in the presence of photoexcited electrons, we have studied the initial step of CO2 activation via 1e transfer. It is shown that the CO2 reactivity of these surfaces strongly depends on the crystal structure, surface orientation, and presence of defects. This opens a new dimension in surface structure modification to enhance the CO2 adsorption and reduction on semiconductor surfaces.

  10. First-Principles Study of Li Doping in a Double-Wall Carbon Nanotube

    Institute of Scientific and Technical Information of China (English)

    WEN Yan-Wei; LIU Hui-Jun; PAN Lu; TAN Xiao-Jian; SHI Jing

    2009-01-01

    By performing first-principles calculatio ns,we study Li doping in a double-wall carbon nanotube where a (5,0)tube is confined inside a (14,0) tube.There are three possible sites for Li doping and two of them are energetically favorable.The change of energy band structure is closely related to the doping sites and the charge transfer is investigated.Bader charge analysis indicates that Li prefers to donate its electron to the inner (5,0) tube.Moreover,the Li capacity of the system can reach LiC4.74 which makes it a promising candidate for Li-ion battery materials.

  11. Vacancy Ordering In Co3AlCx Alloys: A First Principles Study

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Chao [Los Alamos National Laboratory

    2008-01-01

    Ordering of structural vacancies in non-stoichiometric Co{sub 3}AlC{sub x} alloys has been studied using a combination of first-principles total energy calculations, a cluster expansion technique, and Monte-Carlo simulations. In the proximity of the experimental1y observed composition of x {approx} 0.59, our exhaustive ground state search yields two stable vacancy-ordered structures: a cubic Co{sub 3}AlC{sub 0.5} phase and a trigonal Co{sub 3}AlC{sub 0.667} phase. By performing finite-temperature Monte-Carlo simulations, the order-disorder transition temperatures of Co{sub 3}AlC{sub 0.5} and CO{sub 3}AlC{sub 0.667} are predicted to be {approx}1925K and {approx}1630K, respectively.

  12. Boron/nitrogen pairs Co-doping in metallic carbon nanotubes: a first-principle study

    Institute of Scientific and Technical Information of China (English)

    Ouyang Fang-Ping; Peng Sheng-Lin; Chen Ling-Na; Sun Shu-Yuan; Xu Hui

    2011-01-01

    By using the first-principles calculations, the electronic structure and quantum transport properties of metallic carbon nanotubes with B/N pairs co-doping have been investigated. It is shown that the total energies of metallic carbon nanotubes are sensitive to the doping sites of the B/N pairs. The energy gaps of the doped metallic carbon nanotubes decrease with decreasing the concentration of the B/N pair not only along the tube axis but also around the tube. Moreover, the I-V characteristics and transmissions of the doped tubes are studied. Our results reveal that the conducting ability of the doped tube decreases with increasing the concentrations of the B/N pairs due to symmetry breaking of the system. This fact opens a new way to modulate band structures of metallic carbon nanotubes by doping B/N pair with suitable concentration and the novel characteristics are potentially useful in future applications.

  13. First principles study of crystal Si-doped Ge2Sb2Te5

    Science.gov (United States)

    Yan, Beibei; Yang, Fei; Chen, Tian; Wang, Minglei; Chang, Hong; Ke, Daoming; Dai, Yuehua

    2017-02-01

    Ge2Sb2Te5 (GST) and Si-doped GST with hexagonal structure were investigated by means of First-principles calcucations. We performed many kinds of doping types and studied the electronic properties of Si-doped GST with various Si concentrations. The theoretical calculations show that the lowest formation energy appeared when Si atoms substitute the Sb atoms (SiSb). With the increasing of Si concentrations from 10% to 30%, the impurity states arise around the Fermi level and the band gap of the SiSb structure broadens. Meanwhile, the doping supercell has the most favorable structure when the doping concentration keeps in 20%. The Si-doped GST exhibits p-type metallic characteristics more distinctly owing to the Fermi level moves toward the valence band. The Te p, d-orbitals electrons have greater impact on electronic properties than that of Te s-orbitals.

  14. First-principles study of roles of Cu and Cl in polycrystalline CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Ji-Hui; Park, Ji-Sang; Metzger, Wyatt [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Yin, Wan-Jian [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); College of Physics, Optoelectronics and Energy and Collaborative, Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215006 (China); Wei, Su-Huai, E-mail: suhuaiwei@csrc.ac.cn [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Beijing Computational Science Research Center, Beijing 100094 (China)

    2016-01-28

    Cu and Cl treatments are important processes to achieve high efficiency polycrystalline cadmium telluride (CdTe) solar cells, thus it will be beneficial to understand the roles they play in both bulk CdTe and CdTe grain boundaries (GBs). Using first-principles calculations, we systematically study Cu and Cl-related defects in bulk CdTe. We find that Cl has only a limited effect on improving p-type doping and too much Cl can induce deep traps in bulk CdTe, whereas Cu can enhance p-type doping of bulk CdTe. In the presence of GBs, we find that, in general, Cl and Cu will prefer to stay at GBs, especially for those with Te-Te wrong bonds, in agreement with experimental observations.

  15. Field emission of metal nanowires studied by first-principles methods

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Choong-Ki [Department of Physics, Ewha Womans University, Seoul 120-750 (Korea, Republic of); Lee, Bora [Department of Physics, Ewha Womans University, Seoul 120-750 (Korea, Republic of); Ihm, Jisoon [Department of Physics and Astronomy, Seoul National University, Seoul 151-742 (Korea, Republic of); Han, Seungwu [Department of Physics, Ewha Womans University, Seoul 120-750 (Korea, Republic of)

    2007-11-28

    We study the field-emission properties of an ultrathin silver nanowire using first-principles methods. The simulation and analysis of the field emission are carried out based on density-functional theory using a localized basis scheme. Through the explicit time evolution of wavefunctions, we obtain the emission currents and spatial distributions of emitted electrons from a silver nanowire. In contrast to carbon nanotubes, the localized states are not found. Instead, pronounced emission currents are observed for s-like extended states that are free of nodes in a plane normal to the field direction, and the total emission currents of a silver nanowire are found to be significantly larger than those of carbon nanotubes. A quantum-mechanical analysis is presented to explain the observed current enhancement. On the other hand, an ultrathin gold nanowire gives much smaller emission currents than the silver nanowire due to a larger work function.

  16. First-principles study of FeSe epitaxial films on SrTiO3

    Institute of Scientific and Technical Information of China (English)

    刘凯; 高淼; 卢仲毅; 向涛

    2015-01-01

    The discovery of high temperature superconductivity in FeSe films on SrTiO3 substrate has inspired great experimen-tal and theoretical interests. First-principles density functional theory calculations, which have played an important role in the study of bulk iron-based superconductors, also participate in the investigation of interfacial superconductivity. In this article, we review the calculation results on the electronic and magnetic structures of FeSe epitaxial films, emphasiz-ing on the interplay between different degrees of freedom, such as charge, spin, and lattice vibrations. Furthermore, the comparison between FeSe monolayer and bilayer films on SrTiO3 is discussed.

  17. First-principles study of lattice thermal conductivity of Td-WTe2

    Science.gov (United States)

    Liu, Gang; Sun, Hong Yi; Zhou, Jian; Li, Qing Fang; Wan, Xian-Gang

    2016-03-01

    The structural and thermal properties of bulk Td-WTe2 have been studied by using first-principles calculations based on the simple Klemens model and an iterative self-consistent method. Both methods show that lattice thermal conductivity is anisotropic, with the highest value in the (001) plane, and lowest one along the c-axis at 300 K. The calculated average thermal conductivity of WTe2 is in agreement with the experimental measurement. The size dependent thermal conductivity shows that nanostructuring of WTe2 can possibly further decrease the lattice thermal conductivity, which can improve the thermoelectric efficiency. Such extremely low thermal conductivity, even much lower than WSe2, makes WTe2 having many potential applications in thermal insulation and thermoelectric materials.

  18. First-Principles Study of Electronic Properties in PbS((1)OO) with Vacancy Defect

    Institute of Scientific and Technical Information of China (English)

    DING Zong-Ling; XING Huai-Zhong; XU Sheng-Lan; HUANG Yan; CHEN Xiao-Shuang

    2007-01-01

    Electronic properties of both Pb and S vacancy defects in PbS(100) have been studied using the first-principles density functional theory (DFT) calculations with the plane-wave pseudopotentials. It is found that the density of states (DOS) near the top of the valence band and the bottom of the conduction band is significantly modified by these defects. Our calculation indicates that in the case of S vacancy defects the Fermi energy shifts to the conduction band making it as an n-type PbS (donor). However, in the case of Pb vacancy, because of the appreciable change of the DOS, the system acts as a p-type PbS (accepter). In addition, the structural relaxation shows that the defect leads to outward relaxation of the nearest-neighbouring atoms and inward relaxation of the next-nearest neighbouring atoms.

  19. Hydrogen and fluorine co-decorated silicene: A first principles study of piezoelectric properties

    Energy Technology Data Exchange (ETDEWEB)

    Noor-A-Alam, Mohammad; Kim, Hye Jung; Shin, Young-Han, E-mail: hoponpop@ulsan.ac.kr [Department of Physics and EHSRC, University of Ulsan, Ulsan 680-749 (Korea, Republic of)

    2015-06-14

    A low-buckled silicene monolayer being centrosymmetric like graphene, in contrast to a piezoelectric hexagonal boron nitride (h-BN), is not intrinsically piezoelectric. However, based on first principles calculations, we show that chemical co-decoration of hydrogen (H) and fluorine (F) on opposite sides of silicene (i.e., one side is decorated with H, while the other one is with F) breaks the centrosymmetry. Redistributing the charge density due to the electronegativity difference between the atoms, non-centrosymmetric co-decoration induces an out-of-plane dipolar polarization and concomitant piezoelectricity into non-piezoelectric silicene monolayer. Our piezoelectric coefficients are comparable with other known two-dimensional piezoelectric materials (e.g., hydrofluorinated graphene/h-BN) and some bulk semiconductors, such as wurtzite GaN and wurtzite BN. Moreover, because of silicene's lower elastic constants compared to graphene or h-BN, piezoelectric strain constants are found significantly larger than those of hydrofluorinated graphene/h-BN. We also predict that a wide range of band gaps with an average of 2.52 eV can be opened in a low-buckled gapless semi-metallic silicene monolayer by co-decoration of H and F atoms on the surface.

  20. First Principles Studies of Perovskites for Intermediate Temperature Solid Oxide Fuel Cell Cathodes

    KAUST Repository

    Salawu, Omotayo Akande

    2017-05-15

    Fundamental advances in cathode materials are key to lowering the operating temperature of solid oxide fuel cells (SOFCs). Detailed understanding of the structural, electronic and defect formation characteristics are essential for rational design of cathode materials. In this thesis we employ first principles methods to study La(Mn/Co)O3 and LnBaCo2O5+δ (Ln = Pr, Gd; δ = 0.5, 1) as cathode for SOFCs. Specifically, factors affecting the O vacancy formation and migration are investigated. We demonstrate that for LaMnO3 the anisotropy effects often neglected at high operating temperatures become relevant when the temperature is lowered. We show that this fact has consequences for the material properties and can be further enhanced by strain and Sr doping. Tensile strain promotes both the O vacancy formation and migration in pristine and Sr doped LaMnO3, while Sr doping enhances the O vacancy formation but not the migration. The effect of A-site hole doping (Mg2+, Ca2+ or Ba2+) on the electronic and magnetic properties as well as the O vacancy formation and migration in LaCoO3 are studied. All three dopants are found to facilitate O vacancy formation. Substitution of La3+ with Ba2+/Mg2+ yields the lowest O vacancy formation energy for low/intermediate spin Co, implying that not only the structure, but also the spin state of Co is a key parameter. Only for low spin Co the ionic radius is correlated with the O migration barrier. Enhanced migration for intermediate spin Co is ascribed to the availability of additional space at the transition state. For LnBaCo2O5+δ we compare the O vacancy formation in GdBaCo2O5.5 (Pmmm symmetry) and GdBaCo2O6 (P4/mmm symmetry), and the influence of Sr doping. The O vacancy formation energy is demonstrated to be smaller in the already O deficient compound. This relation is maintained under Sr doping. It turns out that Sr doping can be utilized to significantly enhance the O vacancy formation in both compounds. The observed trends are

  1. Design of BAs-AlN monolayered honeycomb heterojunction structures: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Camacho-Mojica, Dulce C.; López-Urías, Florentino, E-mail: flo@ipicyt.edu.mx

    2016-04-15

    Graphical abstract: Single-layer honeycomb heterojunction structures based on alternated and coupled ribbons of BAs and AlN are investigated using first-principles density functional theory calculations. Optimized geometries, density of states, band-gaps, formation energies, and wave functions are studied for different ribbon widths joined along the zigzag and armchair edges. Optimized heterojunction geometries results revealed that BAs narrow ribbons exhibit a corrugation effect at the interface due to a lattice mismatch. From formation energy calculations, it was found that zigzag heterojunctions are more stable than the armchair heterojunctions. - Highlights: • We design new 2D-semiconductor heterojunction nanostructures. • Monolayers formed by alternated strips (heterojunctions) of aluminum-nitride and boron-arsenide, with graphene-like structure are explored by DFT method. • Due to the lattice mismatch, an effect of corrugation was observed in heterojunctions AlN and BAs. • Electronic band gaps are strongly dependent on width and chirality (zigzag or armchair) of the strips. • Formation energy calculations revealed that zigzag heterojunctions are more stable than the armchair heterojunctions. - Abstract: BAs and AlN are semiconductor materials with an indirect and direct gap respectively in the bulk phase. Recently, electronic calculations have demonstrated that a single-layer or few layers of BAs and AlN exhibit a graphite-like structure with interesting electronic properties. In this work, infinite sheets single-layer heterojunction structures based on alternated strips with honeycomb BAs and AlN layers are investigated using first-principles density functional theory calculations. Optimized geometries, density of states, band-gaps, formation energies, and wave functions are studied for different strip widths joined along zigzag and armchair edges. Results in optimized heterojunction geometries revealed that BAs narrow strips exhibit a corrugation

  2. Oxygen- and hydroxyl-edge termination of silicene nanoribbons studied by first-principles calculations

    Science.gov (United States)

    Li, Rui; Liu, Zhong-Li; Gu, Yanhong; Zhang, Weiying; Tan, Yonggang

    2016-05-01

    The geometrical structures and electronic properties of the armchair- and zigzag-edge silicene nanoribbons (SiNRs), terminated with oxygen and hydroxyl (ZSiNR-O, ZSiNR-OH, ASiNR-O, ASiNR-OH), have been investigated by using the first-principles method. It is found that the silicene edges are rippled upon the oxygen termination. On one edge of ZSiNR-O, the neighboring Si-O bonds move concordantly right (left) from the silicene plane, while on one edge of ASiNR-O, the neighboring Si-O bonds respectively move right and left to result in larger rippled amplitudes. Comparably, the influence of OH-termination on the silicene edge is small, inducing smaller rippled edges. The electronic structure calculations show that the px electrons of oxygen on the rippled edges of ZSiNR-O sp3 hybridize with the edge Si atoms, forming one more bands. The band gaps of the ASiNR-O and ASiNR-OH also obey the three-family behavior, due to the quantum confinement and the crucial effect of the edges. For ASiNR-OH, by taking account of the new atom chains formed by the hydrogen bonds of the neighboring OHs, the band gaps follow the same hierarchy of Δ3 p >Δ3 p - 1 >Δ3 p - 2 with those of ASiNR-Os.

  3. Piezoelectric properties of graphene oxide: A first-principles computational study

    Science.gov (United States)

    Chang, Zhenyue; Yan, Wenyi; Shang, Jin; Liu, Jefferson Zhe

    2014-07-01

    Some highly ordered compounds of graphene oxide (GO), e.g., the so-called clamped and unzipped GO, are shown to have piezoelectric responses via first-principles density functional calculations. By applying an electric field perpendicular to the GO basal plane, the largest value of in-plane strain and strain piezoelectric coefficient, d31 are found to be 0.12% and 0.24 pm/V, respectively, which are comparable with those of some advanced piezoelectric materials. An in-depth molecular structural analysis reveals that the deformation of the oxygen doping regions in the clamped GO dominates its overall strain output, whereas the deformation of the regions without oxygen dopant in the unzipped GO determines its overall piezoelectric strain. This understanding explains the observed dependence of d31 on oxygen doping rate, i.e., higher oxygen concentration giving rise to a larger d31 in the clamped GO whereas leading to a reduced d31 in the unzipped GO. As the thinnest two-dimensional piezoelectric materials, GO has a great potential for a wide range of micro/nano-electromechanical system (MEMS/NEMS) actuators and sensors.

  4. Thermodynamical and electronic properties of Bx Al1-x N alloys: A first principle study

    Science.gov (United States)

    Kumar, S.; Joshi, Suman; Joshi, B.; Auluck, S.

    2015-11-01

    A series of first principle calculations were carried out to investigate thermodynamical, electronic and optical properties of cubic Bx Al1-x N ordered alloys using supercell approach within density functional theory (DFT). Here we calculate the lattice constants using van der Waals density functional (vdW-DF) at several concentrations (x) of boron. We find that the vdW-DF prediction shows slightly better agreement with experiment in contrast to local density approximation (LDA)/generalized gradient approximation (GGA). The results show that the direct energy band gap (Γv-Γc) has strong nonlinear dependence on the concentration (x). At x=0.04 and 0.84, Bx Al1-x N has a phase transition from direct to an indirect band gap semiconductor. To describe the alloys' solubility, formation enthalpy were calculated and fitted to quadratic function to obtain interaction parameter. The calculated T-x phase diagram shows a broad miscibility gap with a high critical temperature equal to 3063 K. The calculated dielectric function is explained in terms of band structure and density of states and compared with the available experimental data, showing good agreement.

  5. First-principles study of thermal transport in nitrogenated holey graphene

    Science.gov (United States)

    Ouyang, Tao; Xiao, Huaping; Tang, Chao; Zhang, Xiaoliang; Hu, Ming; Zhong, Jianxin

    2017-01-01

    Nitrogenated holey graphene (NHG), a new two-dimensional graphene variant with a large fundamental direct band gap, has recently been successfully synthesized via a simple wet-chemical reaction. Motivated by its unique geometry and novel properties, we investigated the phonon transport properties of the material by combining first-principle calculations and the phonon Boltzmann transport equation. The lattice thermal conductivity of NHG at room temperature is predicted to be about 82.22 W mK-1, which is almost two orders of magnitude lower than that of graphene (about 3500 W mK-1). Deviating from the traditional understanding that thermal transport is usually largely contributed by the acoustic phonon modes for most suspended 2D materials, both out-of-plane flexural acoustic (ZA) and optical phonon modes make a more or less equal contribution, and their combination abnormally dominates the overall thermal transport in NHG. The major three-phonon process in NHG is further analyzed and the scattering between the acoustic and optical phonon modes like {{ZA}}/{{TA}}/{{LA}}+{{O}}≤ftrightarrow {{O}} is the main phonon process channel. Meanwhile, the mean free path distribution of different phonon modes is calculated for the purpose of the thermal management of NHG-based devices. Our results elucidate the unusual thermal transport properties of NHG as compared with the representative case of graphene, and underpin its potential application for use by the thermal management community.

  6. Hydrogen adsorption in HKUST-1: a combined inelastic neutron scattering and first-principles study

    Science.gov (United States)

    Brown, Craig M.; Liu, Yun; Yildirim, Taner; Peterson, Vanessa K.; Kepert, Cameron J.

    2009-05-01

    Hydrogen adsorption in high surface area nanoporous coordination polymers has attracted a great deal of interest in recent years due to the potential applications in energy storage. Here we present combined inelastic neutron scattering measurements and detailed first-principles calculations aimed at unraveling the nature of hydrogen adsorption in HKUST-1 (Cu3(1,3,5-benzenetricarboxylate)2), a metal-organic framework (MOF) with unsaturated metal centers. We reveal that, in this system, the major contribution to the overall binding comes from the classical Coulomb interaction which is not screened due to the open metal site; this explains the relatively high binding energies and short H2-metal distances observed in MOFs with exposed metal sites as compared to traditional ones. Despite the short distances, there is no indication of an elongation of the H-H bond for the bound H2 molecule at the metal site. We find that both the phonon and rotational energy levels of the hydrogen molecule are closely similar, making the interpretation of the inelastic neutron scattering data difficult. Finally, we show that the orientation of H2 has a surprisingly large effect on the binding potential, reducing the classical binding energy by almost 30%. The implication of these results for the development of MOF materials for better hydrogen storage is discussed.

  7. First-principles study on structural stability of 3d transition metal alloying magnesium hydride

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    A first-principles plane-wave pseudopotential method based on the density functional theory was used to investigate the energy and electronic structure of magnesium hydride (MgH2) alloyed by 3d transition metal elements. Through calculations of the negative heat formation of magnesium hydride alloyed by X (X denotes 3d transition metal) element, it is found that when a little X (not including Sc) dissolves into magnesium hydride, the structural stability of alloying systems decreases, which indicates that the dehydrogenation properties of MgH2 can be improved. After comparing the densities of states(DOS) and the charge distribution of MgH2 with or without X alloying, it is found that the improvement for the dehydrogenation properties of MgH2 alloyed by X attributes to the fact that the weakened bonding between magnesium and hydrogen is caused by the stronger interactions between X (not including Cu) and hydrogen. The calculation results of the improvement for the dehydrogenation properties of MgH2-X (X=Ti, V, Mn, Fe, Co,Ni, Cu) systems are in agreement with the experimental results. Hence, the dehydrogenation properties of MgH2 are expected to be improved by addition of Cr, Zn alloying elements.

  8. First principles DFT study of dye-sensitized CdS quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Jain, Kalpna; Singh, Kh. S. [Department of Physics, D. J. College, Baraut -250611, U.P. (India); Kishor, Shyam, E-mail: shyam387@gmail.com [Department of Chemistry, J. V. College, Baraut -250611, U.P. (India); Josefesson, Ida; Odelius, Michael [Fysikum, Albanova University Center, Stockholm University, S-106 91 Stockholm (Sweden); Ramaniah, Lavanya M. [High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai-400085 (India)

    2014-04-24

    Dye-sensitized quantum dots (QDs) are considered promising candidates for dye-sensitized solar cells. In order to maximize their efficiency, detailed theoretical studies are important. Here, we report a first principles density functional theory (DFT) investigation of experimentally realized dye - sensitized QD / ligand systems, viz., Cd{sub 16}S{sub 16}, capped with acetate molecules and a coumarin dye. The hybrid B3LYP functional and a 6−311+G(d,p)/LANL2dz basis set are used to study the geometric, energetic and electronic properties of these clusters. There is significant structural rearrangement in all the clusters studied - on the surface for the bare QD, and in the positions of the acetate / dye ligands for the ligated QDs. The density of states (DOS) of the bare QD shows states in the band gap, which disappear on surface passivation with the acetate molecules. Interestingly, in the dye-sensitised QD, the HOMO is found to be localized mainly on the dye molecule, while the LUMO is on the QD, as required for photo-induced electron injection from the dye to the QD.

  9. First-principles study of cesium adsorption to weathered micaceous clay minerals

    Science.gov (United States)

    Okumura, Masahiko; Nakamura, Hiroki; Machida, Masahiko

    2014-05-01

    , H. Nakamura, and M. Machida, Mechanism of Strong Affinity of Clay Minerals to Radioactive Cesium : First-Principles Calculation Study for Adsorption of Cesium at Frayed Edge Sites in Muscovite, Journal of the Physical Society of Japan 82, 033802 (2013).

  10. Strain Modulated Electronic Properties of Ge Nanowires - A First Principles Study

    CERN Document Server

    Logan, Paul

    2010-01-01

    We used density-functional theory based first principles simulations to study the effects of uniaxial strain and quantum confinement on the electronic properties of germanium nanowires along the [110] direction, such as the energy gap and the effective masses of the electron and hole. The diameters of the nanowires being studied are up to 50 {\\AA}. As shown in our calculations, the Ge [110] nanowires possess a direct band gap, in contrast to the nature of an indirect band gap in bulk. We discovered that the band gap and the effective masses of charge carries can be modulated by applying uniaxial strain to the nanowires. These strain modulations are size-dependent. For a smaller wire (~ 12 {\\AA}), the band gap is almost a linear function of strain; compressive strain increases the gap while tensile strain reduces the gap. For a larger wire (20 {\\AA} - 50 {\\AA}), the variation of the band gap with respect to strain shows nearly parabolic behavior: compressive strain beyond -1% also reduces the gap. In addition,...

  11. First Principles Study of Si/Ge Core-Shell nanowires under external uniaxial strain

    CERN Document Server

    Peng, Xihong; Logan, Paul

    2010-01-01

    Density-functional theory based first principles calculations are performed to study the effects of external uniaxial strain on the electronic states of Si/Ge core-shell nanowires along the [110] direction with the diameter of the wire up to 5 nm. As shown in the calculations, the [110] Si/Ge core-shell nanowires without external strain possess a direct band gap, in contrast to the nature of an indirect band gap in bulk Si and Ge. The band structure of the core-shell nanowires can be significantly modulated by an external strain. With a sufficient amount of tensile uniaxial strain, the band gap of the Si/Ge core-shell nanowires experiences a transition from direct to indirect. In addition, our studies showed that the effective masses of charge carriers can be also tuned by the external uniaxial strain. The effective mass of the hole increases dramatically with a tensile strain, while strain shows a minimal effect on tuning the effective mass of the electron. Finally, the relationship between the strain effect...

  12. NMR characterization of hydrocarbon adsorption on calcite surfaces: A first principles study

    Energy Technology Data Exchange (ETDEWEB)

    Bevilaqua, Rochele C. A.; Miranda, Caetano R. [Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, UFABC, Santo André, SP (Brazil); Rigo, Vagner A. [Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, UFABC, Santo André, SP (Brazil); Universidade Tecnológica Federal do Paraná, UTFPR, Cornélio Procópio, PR (Brazil); Veríssimo-Alves, Marcos [Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, UFABC, Santo André, SP (Brazil); Departamento de Física, ICEx, Universidade Federal Fluminense, UFF, Volta Redonda, RJ (Brazil)

    2014-11-28

    The electronic and coordination environment of minerals surfaces, as calcite, are very difficult to characterize experimentally. This is mainly due to the fact that there are relatively few spectroscopic techniques able to detect Ca{sup 2+}. Since calcite is a major constituent of sedimentary rocks in oil reservoir, a more detailed characterization of the interaction between hydrocarbon molecules and mineral surfaces is highly desirable. Here we perform a first principles study on the adsorption of hydrocarbon molecules on calcite surface (CaCO{sub 3} (101{sup ¯}4)). The simulations were based on Density Functional Theory with Solid State Nuclear Magnetic Resonance (SS-NMR) calculations. The Gauge-Including Projector Augmented Wave method was used to compute mainly SS-NMR parameters for {sup 43}Ca, {sup 13}C, and {sup 17}O in calcite surface. It was possible to assign the peaks in the theoretical NMR spectra for all structures studied. Besides showing different chemical shifts for atoms located on different environments (bulk and surface) for calcite, the results also display changes on the chemical shift, mainly for Ca sites, when the hydrocarbon molecules are present. Even though the interaction of the benzene molecule with the calcite surface is weak, there is a clearly distinguishable displacement of the signal of the Ca sites over which the hydrocarbon molecule is located. A similar effect is also observed for hexane adsorption. Through NMR spectroscopy, we show that aromatic and alkane hydrocarbon molecules adsorbed on carbonate surfaces can be differentiated.

  13. First-principles study of elastic mechanical responses to applied deformation of metal-organic frameworks

    Science.gov (United States)

    Banlusan, Kiettipong; Strachan, Alejandro

    2017-05-01

    We use density functional theory to compute the elastic constant tensors of two families of metal-organic frameworks (MOFs) to establish relationships between their structures and mechanical properties. The Zn family consist of Zn4O centers each coordinated by six organic linkers along the ⟨100⟩ directions; we studied three linkers of increasing lengths: 1,4-benzenedicarboxylate (BDC), 4,4'-biphenyl-dicarboxylate (BPDC), and 4,4''-terphenyl-dicarboxylate. This relatively weak connectivity leads to high anisotropy; in fact, Zn-MOFs exhibit extremely low shear modulus and are near a mechanical instability. In contrast, Zr family studied consists of Zr6O4(OH)4 centers each linked by fumarate, BDC, and BPDC ligands along the twelve ⟨110⟩ directions. The higher structural connectivity results in stiffer frameworks with lower anisotropy. The smallest Zr-MOF exhibits nearly isotropic elasticity with a Zener ratio of 1.06. The stiffest and most compliant directions of both families are directly related to the orientation of the organic linkers. Temperature has a significant effect on elastic moduli; for example, we observed reduction of average Young's modulus and shear modulus by about 30% from 0 K to 300 K in Zn-BPDC even when it exhibits large negative thermal expansion. We find the effect of temperature to be directionally dependent, leading to an increase in anisotropy upon increasing temperature. The predicted effects of temperature and anisotropy help reconcile a longstanding discrepancy between experiments and first principles calculations.

  14. A first-principles study of He, Xe, Kr and O incorporation in thorium carbide

    Energy Technology Data Exchange (ETDEWEB)

    Pérez Daroca, D., E-mail: pdaroca@tandar.cnea.gov.ar [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650 San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, 1033 Buenos Aires (Argentina); Llois, A.M. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650 San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, 1033 Buenos Aires (Argentina); Mosca, H.O. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650 San Martín, Buenos Aires (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM-CNEA, Av. General Paz 1499, 1650 San Martín, Buenos Aires (Argentina)

    2015-05-15

    Thorium-based materials are currently being investigated in relation with their potential utilization in Generation-IV reactors as nuclear fuels. Understanding the incorporation of fission products and oxygen is very important to predict the behavior of nuclear fuels. A first approach to this goal is the study of the incorporation energies and stability of these elements in the material. By means of first-principles calculations within the framework of density functional theory, we calculate the incorporation energies of He, Xe, Kr and O atoms in Th and C vacancy sites, in tetrahedral interstitials and in Schottky defects along the 〈1 1 1〉 and 〈1 0 0〉 directions. We also analyze atomic displacements, volume modifications and Bader charges. This kind of results for ThC, to the best authors’ knowledge, have not been obtained previously, neither experimentally, nor theoretically. This should deal as a starting point towards the study of the complex behavior of fission products in irradiated ThC.

  15. First Principles Study of HCN Adsorption on Graphene Doped with 5d Transition Metal

    Science.gov (United States)

    Dong, Hai-Kuan; Wang, Yong-Ping; Shi, Li Bin

    2016-11-01

    Hydrogen cyanide (HCN) adsorption on graphene doped with 5d transition metal (TM) is investigated by the first principles based on density functional theory. It is observed that Hg atom cannot be doped into graphene due to saturated valence electron configurations of 5d106s2. Three kinds of HCN adsorption configurations are investigated, in which H, C and N in HCN are close to the adsorption site, respectively. The most stable adsorption configuration is obtained by total energy optimization. HCN adsorption can be studied by adsorption energy and electron density difference. HCN can only be physisorbed on Ir, Pt and Au-doped graphenes, while chemisorption is observed for Lu, Hf, Ta, W, Re and Os-doped graphenes. The band structure is calculated by B3LYP and Generalized gradient approximation (GGA) functionals. It is observed from B3LYP method that the conductivity of Lu, Hf, Re and Os-doped graphenes does not obviously change before and after HCN adsorption. Ta and W-doped graphenes change from semiconductor to metal after adsorption of HCN molecule. The results indicate that Ta and W-doped graphenes may be a promising sensor for detecting HCN. This study provides a useful basis for understanding of a wide variety of physical properties on graphene.

  16. Graphene substrate-mediated catalytic performance enhancement of Ru nanoparticles: A first-principles study

    KAUST Repository

    Liu, Xin

    2012-01-01

    The structural, energetic and magnetic properties of Ru nanoparticles deposited on pristine and defective graphene have been thoroughly studied by first-principles based calculations. The calculated binding energy of a Ru 13 nanoparticle on a single vacancy graphene is as high as -7.41 eV, owing to the hybridization between the dsp states of the Ru particles with the sp 2 dangling bonds at the defect sites. Doping the defective graphene with boron would further increase the binding energy to -7.52 eV. The strong interaction results in the averaged d-band center of the deposited Ru nanoparticle being upshifted toward the Fermi level from -1.41 eV to -1.10 eV. Further study reveals that the performance of the nanocomposites against hydrogen, oxygen and carbon monoxide adsorption is correlated to the shift of the d-band center of the nanoparticle. Thus, Ru nanoparticles deposited on defective graphene are expected to exhibit both high stability against sintering and superior catalytic performance in hydrogenation, oxygen reduction reaction and hydrogen evolution reaction. © 2012 The Royal Society of Chemistry.

  17. First-principles study of thermodynamical and mechanical stabilities of thin copper film on tantalum

    Science.gov (United States)

    Hashibon, Adham; Elsässer, Christian; Mishin, Yuri; Gumbsch, Peter

    2007-12-01

    The adhesion, stability, and wetting behavior at interfaces between thin Cu films and clean Ta (110) substrates are investigated by first-principles calculations using density functional theory (DFT) in the local-density approximation. Interfaces between pseudomorphic body-centered-tetragonal thin films of Cu, strained face-centered-cubic thin films of Cu, and a single pseudomorphic monolayer of Cu on body-centered-cubic Ta (110) surfaces are studied. Various high-symmetry interface configurations are considered for each case. The mechanical stability of the interfaces is studied by the ideal work of separation, while the thermodynamic stability is investigated by Gibbs’ excess interface energy. All three interfaces are found to be thermodynamically unstable. An energy-weighting scheme extends the use of the DFT calculations to the case of an incoherent misfitting interface. The incoherent monolayer of Cu on Ta is thereby found to be thermodynamically stable. For coverages by more than a monolayer, the Cu atoms are expected to form three-dimensional islands on top of the Cu monolayer. With respect to interface separation, the monolayer is found to be bound more strongly to the Ta substrate than the thin film. Hence, failure is expected to occur not at the Cu/Ta interface but inside the Cu.

  18. Alloying InAs and InP nanowires for optoelectronic applications: A first principles study

    Energy Technology Data Exchange (ETDEWEB)

    Toniolo, Giuliano R.; Anversa, Jonas [Departamento de Fisica, Universidade Federal de Santa Maria, 97105-900, Santa Maria, RS (Brazil); Santos, Cláudia L. dos [Área de Ciências Tecnológicas, Centro Universitário Franciscano, 97010-032, Santa Maria, RS (Brazil); Piquini, Paulo, E-mail: paulo.piquini@ufsm.br [Departamento de Fisica, Universidade Federal de Santa Maria, 97105-900, Santa Maria, RS (Brazil)

    2014-08-01

    The capability of nanowires to relieve the stress introduced by lattice mismatching through radial relaxation opens the possibility to search for devices for optoelectronic applications. However, there are difficulties to fabricate, and therefore to explore the properties of nanowires with narrow diameters. Here we apply first principles calculations to study the electronic and optical properties of narrow InAs{sub 1−x}P{sub x} nanowires. Our results show that the absorption threshold can be pushed to near-ultraviolet region, and suggests that arrays of these nanowires with different diameters and compositions could be used as devices acting from the mid-infrared to the near-ultraviolet region. - Highlights: • The optical properties of InAsP alloy nanowires were studied using DFT calculations. • The variation of band edges and band offsets with composition were determined. • The dependence of the optical absorption with alloy composition was settled. • The onset for optical absorption is suggested to be pushed to the UV region.

  19. Topological properties of phosphorene-like monolayer group V semiconductor compounds: a first-principles study

    CERN Document Server

    Yu, Weiyang; Niu, Chun-Yao; Li, Chong; Cho, Jun-Hyung; Jia, Yu

    2015-01-01

    To broaden the scope of layered group V semiconductors, we propose a class of phosphorenelike monolayer group V semiconductor compounds, such as PN, AsP, SbP and BiP with black-phosphorus-like alpha-phase and blue-phosphorus-like beta-phase, respectively. Using first-principles density functional theory calculations, we study yet unrealized structural phases of these compounds. We find the black-phosphorus-like alpha-phase to be almost equally stable as the blue-phosphorus-like beta-phase. alpha-phase compounds display a direct band gap, while beta-phase compounds display an indirect band gap. Both alpha-phase and beta-phase monolayers depends sensitively on the in-layer strain, as is studied with alpha- and beta- AsP and BiP. Further more, We find that alpha-BiP presents an intriguing topological state when gained a compress from -8% to -10%, offering an unprecedented tunability in structural and electronic properties of BiP compound.

  20. First-principles and classical molecular dynamics study of threshold displacement energy in beryllium

    Science.gov (United States)

    Vladimirov, P. V.; Borodin, V. A.

    2017-02-01

    Beryllium selected as a neutron multiplier material for the tritium breeding blanket of fusion reactor should withstand high doses of fast neutron irradiation. The damage produced by irradiation is usually evaluated assuming that the number of atomic displacements to the threshold displacement energy, Ed, which is considered as an intrinsic material parameter. In this work the value of Ed for hcp beryllium is estimated simultaneously from classical and first-principles molecular dynamics simulations. Quite similar quantitative pictures of defect production are observed in both simulation types, though the predicted displacement threshold values seem to be approximately two times higher in the first-principles approach. We expect that, after more detailed first-principles investigations, this approach can be used for scaling the damage prediction predictions by classical molecular dynamics, opening a way for more consistent calculations of displacement damage in materials.

  1. Hydrogen influence on generalized stacking fault of zirconium basal plane: First-principles calculation study

    CERN Document Server

    Songjun, Hou; Zhi, Zeng

    2015-01-01

    The infuence of hydrogen on the generalized stacking fault (GSF) energy of the basal plane along the and directions in the hcp Zr were investigated by using the first-principles calculation method. The modification of the GSF energy were studied with respect to the different distances of H atoms away from the slip plane and hydrogen content there. The calculation results have shown that the GSF energy along the direction drastically reduces when H atoms locate nearby the slip plane. But H atoms slightly decrease the GSF barrier for the slipping case. Meanwhile, with the increase of hydrogen density around the slip plane, the GSF energies along both the shift directions further reduced. The physical origin of the reduction of GSF energy due to the existence of hydrogen atoms in Zr was analyzed based on the Bader charge method. It is interpreted by the Coulomb repulsion of the Zr atoms besides of the slip plane due to the charge transfer from Zr to H atoms.

  2. First-Principles Studies of Photoinduced Charge Transfer in Noncovalently Functionalized Carbon Nanotubes

    CERN Document Server

    Chu, Iek-Heng; Cheng, Hai-Ping

    2013-01-01

    We have studied the energetics, electronic structure, optical excitation, and electron relaxation of dinitromethane molecules (CH$_{2}$N$_{2}$O$_{4}$) adsorbed on semiconducting carbon nanotubes (CNTs) of chiral index (n,0) (n=7, 10, 13, 16, 19). Using first-principles density functional theory (DFT) with generalized gradient approximations and van der Waals corrections, we have calculated adsorption energies of dinitropentylpyrene, in which the dinitromethane is linked to the pyrene via an aliphatic chain, on a CNT. A 75.26 kJ/mol binding energy has been found, which explains why such aliphatic chain-pyrene units can be and have been used in experiments to bind functional molecules to CNTs. The calculated electronic structures show that the dinitromethane introduces a localized state inside the band gap of CNT systems of n=10, 13, 16 and 19; such a state can trap an electron when the CNT is photoexcited. We have therefore investigated the dynamics of intra-band relaxations using the reduced density matrix fo...

  3. First principles study of magneto-optical properties of Fe-doped ZnO

    Science.gov (United States)

    Shaoqiang, Guo; Qingyu, Hou; Zhenchao, Xu; Chunwang, Zhao

    2016-12-01

    Studies on optical band gaps and absorption spectra of Fe-doped ZnO have conflicting conclusions, such as contradictory redshifted and blueshifted spectra. To solve this contradiction, we constructed models of un-doped and Fe-doped ZnO using first-principles theory and optimized the geometry of the three models. Electronic structures and absorption spectra were also calculated using the GGA+U method. Higher doping content of Fe resulted in larger volume of doped system, and higher total energy resulted in lower stability. Higher formation energy also led to more difficult doping. Meanwhile, the band gaps broadened and the absorption spectra exhibited an evident blue shift. The calculations were in good agreement with the experimental results. Given the unipolar structure of ZnO, four possible magnetic coupling configurations for Zn14Fe2O16 were calculated to investigate the magnetic properties. Results suggest that Fe doping can improve ferromagnetism in the ZnO system and that ferromagnetic stabilization was mediated by p-d exchange interaction between Fe-3d and O-2p orbitals. Therefore, the doped system is expected to obtain high stability and high Curie temperature of diluted magnetic semiconductor material, which are useful as theoretical bases for the design and preparation of the Fe-doped ZnO system's magneto-optical properties.

  4. First-principles study of oxygen adsorption and diffusion on the UN(001) surface

    Science.gov (United States)

    Nie, J. L.; Ao, L.; Zu, X. T.; Huang, H.; Liu, K. Z.

    2015-12-01

    First-principles calculations have been performed to study the interaction of oxygen with UN(001) surface. The molecule oxygen was found to dissociate spontaneously on all considered adsorption sites on the surface. Atomic oxygen (O) preferred to adsorb on a hollow site or the top of uranium ions, which were energetically degenerate. Adsorption on top of nitrogen (N) ion was found to be unstable which may be attributed to the repulsion of negatively charged O with the N anions. In comparison with those on α-U(001)surface at the same coverage, the adsorption of O on UN(001) surface was found to be less stable, being about 0.7 eV higher in adsorption energy. The diffusion barrier for O on the surface was found to be ∼0.5 eV, similar to those of α-U(001)surface. The penetration of O into the substrate was difficult with a high barrier of 2.86 eV. Analysis on the density of states (DOS) has shown that the adsorbed oxygen has strong chemical interaction with surface ions, characterized by the hybridization of O 2p states with N 2p and U 6d, U 5f states.

  5. First-principles Study on Adsorption of Au Atom on Hydroxylated SiO2 Surfaee

    Institute of Scientific and Technical Information of China (English)

    WAN Miao; HE Kaihua; CHEN QiH; HONG Hanlie

    2011-01-01

    Adsorption of single gold (Au) atom at three kinds of sites (hollow,bridge and top) on the hydroxylated β-cristobalite SiO2 (111) surface was studied using the first-principles calculations with general gradient approximation (GGA).The results of adsorption energies and density of electronic states (DOS)suggest that the hollow and bridge sites have the basically equal capability of binding Au,while the ability of the Top site is weaker.Two new energy levels emerge after the adsorption at all sites; in DOS of the Hollow configuration,one locates at -0.15 eV,composed of Au 5d and O 2p electronic states,another just crosses through the Fermi level,consisting of Au 6s,H 1s and O 2p.In addition,Mulliken population analyses indicate that electron transfer takes place between the Au atom and the surface H and O atoms in the Hollow and Bridge configurations,which can be used to interpret the adsorption of Au onto the positions.However,neither H nor O chemically bonds with Au atom.

  6. First-principles study on Al4Sr as the heterogeneous nucleus of Mg2Si

    Science.gov (United States)

    Xia, Zhi; Li, Ke

    2016-12-01

    The interfacial structure, electronic structure, work of adhesion and interfacial energy of the Al4Sr(100)/Mg2Si(100) interface have been studied with first-principles calculations to clarify the heterogeneous nucleation potential of the Al4Sr particle for a primary Mg2Si phase. Eight models of the Al4Sr(100)/Mg2Si(100) interface with OT and HCP stacking were adopted for the interfacial model geometries. The results show that the Al-Mg terminations of HCP and Al-Si terminations of OT stacking, with lower interfacial spacing and higher interfacial adhesion, are the most favorable structures after relaxation. Al-Mg- and Al-Si-terminated interfaces, with a lower interfacial distance, form chemical bonds more easily. Metallic bonds are formed near the Al-Mg-terminated interface, while the Al-Si-terminated interface exhibits predominantly covalent bond characteristics. Moreover, the calculated interfacial energies of both terminations are negative in conditions involving excess Mg atoms. The interfacial energies of Al-Si are lower than those of Al-Mg termination, indicating that the Al-Si-terminated interface is more stable. From thermodynamic analysis, we discover that the Al4Sr particle can be an effective heterogeneous nucleation substrate for Mg2Si in a Mg-Al-Si alloy melt.

  7. First-principles studies on the charge density wave in uranium

    Science.gov (United States)

    Qiu, Ruizhi; Lu, Haiyan; Ao, Bingyun; Tang, Tao; Chen, Piheng

    2016-06-01

    The charge density wave (CDW) state of α-U (called {α1} -U) was studied through a first-principles total-energy minimization using the conjugate gradient algorithm. The optimized crystal structure of {α1} -U was found to have the space group Pbnm, which was proposed in the earlier Landau-type theory and is isostructural with the α-Np structure. In particular, the changes in the lattice parameters of Pbnm-U with respect to α-U are consistent with the experimental observations. In addition, the energetic stability of Pbnm-U with respect to α-U was confirmed by enthalpy calculations, and the value of the critical pressure in the pressure-induced quantum transition from Pbnm-U to α-U is in good agreement with the experimental result. Moreover, the phonon calculation verified the dynamical instability of α-U and the stability of Pbnm-U. Finally, the calculated electronic structures exhibit features of the CDW state.

  8. Stability and Electronic Properties of Hydrogenated MoS2 Monolayer: A First-Principles Study.

    Science.gov (United States)

    Zhang, Weibin; Zhang, Zhijun; Yang, Woochul

    2015-10-01

    First-principles total energy studies are used to investigate the stability of hydrogenated MoS2 monolayer (MoS2-Hx) (x = 1-8), which is a compound with different numbers of H atoms adsorbed on the MoS2 surface. Energetically, the S-top side of the MoS2 is found to be the most favorable for H-adsorption. H2S and graphene are well-known to be stable, and MoS2-Hx is predicted to be even more stable because its binding energy is lower than that of H2S and its formation energy and adsorption energy are lower than those of graphene. The analysis of the electronic density distribution and the orbital hybrid also shows that MoS2-Hx forms stable structures. In addition, the influence of the number of the adsorbed H-atoms in the MoS2-Hx on the electronic structure of the compound is also investigated. The MoS2-Hx band structure exhibits a dispersion and the MoS2-Hx band gap gradually decreases from 1.72 eV to 0 eV as the number of adsorbed H atoms increases. The corresponding work function increases as a result of the strengthening of the dipole moment formed between the H atoms that are adsorbed and the hydrogenated MoS2.

  9. Half-metallicity in hole-doped nitrogenated honey graphene: A first-principles study

    Science.gov (United States)

    Zhu, Jingzhong; Zhao, Yinchang; Zeng, Shuming; Ni, Jun

    2017-03-01

    We have investigated the structural, electronic and magnetic properties of hole-doped nitrogenated honey graphene by first-principles calculations. Remarkably, there exists a stable half-metallic ferromagnetism phase with the average spin magnetic moment per carrier of near 1.0 μB in this monolayer system as the carrier density increases from 0 to 1.5 ×1014 cm-2. With further increase of carrier density, the half-metal state vanishes, while the magnetic state remains until the carrier density reaches 4.5 ×1014 cm-2. Our analysis reveals that the predicted itinerant magnetism arises from an exchange splitting of the electronic states at the top of the valence band, where the density of states shows a van Hove singularity. In addition, we have also studied the electron-doped nitrogenated honey graphene, and find the magnetic features are similar to those of the hole-doped system. As synthesis of monolayer nitrogenated honey graphene was reported, half-metallicity of nitrogenated honey graphene are feasible.

  10. First-Principles Study on Magnetic Properties of V-Doped ZnO Nanotubes

    Institute of Scientific and Technical Information of China (English)

    ZHANG Fu-Chun; ZHANG Zhi-Yong; ZHANG Wei-Hu; YAN Jun-Feng; YUN Jiang-Ni

    2009-01-01

    Electronic and magnetic properties of V-doped ZnO nanotubes in which one of Zn2+ ions is substituted by V2+ ions are studied by the first-principles calculations of plane wave ultra-soft pseudo-potential technology based on the spin-density function theory. The computational results reveal that spontaneous magnetization in V-doped (9,0) ZnO nanotubes can be induced without p-type or n-type doping treatment, and the ferromagnetism is isotropic and independent of the chirality and diameter of the nanotubes. It is found that V-doped ZnO nanotubes have large magnetic moments and are ferromagnetic half-metal materials. Moreover, the ferromagnetic coupling among V atoms is generated by O 2p electron spins and V 3d electron spins localized at the exchanging interactions between magnetic transitional metal (TM) impurities. The appearance of ferromagnetism in V-doped ZnO nanotubes gives some reference to fabrication of a transparent ferromagnet which may have a great impact on industrial applications in magneto-optical devices.

  11. Structural, electronic and magnetic properties of Fe2-based full Heusler alloys: A first principle study

    Science.gov (United States)

    Dahmane, F.; Mogulkoc, Y.; Doumi, B.; Tadjer, A.; Khenata, R.; Bin Omran, S.; Rai, D. P.; Murtaza, G.; Varshney, Dinesh

    2016-06-01

    Using the first-principles density functional calculations, the structural, electronic and magnetic properties of the Fe2XAl (X=Cr, Mn, Ni) compounds in both the Hg2CuTi and Cu2MnAl-type structures were studied by the full-potential linearized augmented plane waves (FP-LAPW) method. The exchange and correlation potential is treated by the generalized-gradient approximation (GGA) where the results show that the Cu2MnAl-type structure is energetically more stable than the Hg2CuTi-type structure for the Fe2CrAl and Fe2MnAl compounds at the equilibrium volume. The full Heusler compounds Fe2XAl (X=Cr, Mn) are half-metallic in the Cu2MnAl-type structure. Fe2NiAl has a metallic character in both CuHg2Ti and AlCu2Mn-type structures. The total magnetic moments of the Fe2CrAl and Fe2MnAl compounds are 1.0 and 2.0 μB, respectively, which are in agreement with the Slater-Pauling rule Mtot=Ztot- 24.

  12. First-Principles Study of Structural, Magnetic, Electronic and Elastic Properties of PuC2

    Science.gov (United States)

    Yang, Rong; Tang, Bin; Gao, Tao; Ao, Bing-Yun

    2016-10-01

    We perform first-principles calculations of crystal structure, magnetism, electronic structure, chemical bonding and elastic properties for PuC2 using the standard local spin-density approximation (LSDA)+U scheme. The use of the Hubbard term to describe the 5f electrons of plutonium is discussed according to the lattice parameters, magnetism and densities of states. Our calculated lattice constants and magnetism are in good agreement with the experimental data or other theoretical calculations. It is shown that the total densities of states at the Fermi energy level mainly come from the contribution of narrow f band. The Pu-C bonds of PuC2 have a mixture of covalent character and ionic character, while covalent character is stronger than ionic character. The C1-C2 bonding has strong covalent character because of sp2 hybridization between C atoms. Lastly, the elastic properties of PuC2 are studied. We hope that our results can provide a useful reference for further theoretical and experimental research on PuC2. Supported by the National Natural Science Foundation of China under Grant Nos. 21371160, 21401173, and the Science Challenge Program of China

  13. Energetic Study of Helium Cluster Nucleation and Growth in 14YWT through First Principles

    Directory of Open Access Journals (Sweden)

    Yingye Gan

    2016-01-01

    Full Text Available First principles calculations have been performed to energetically investigate the helium cluster nucleation, formation and growth behavior in the nano-structured ferritic alloy 14YWT. The helium displays strong affinity to the oxygen:vacancy (O:Vac pair. By investigating various local environments of the vacancy, we find that the energy cost for He cluster growth increases with the appearance of solutes in the reference unit. He atom tends to join the He cluster in the directions away from the solute atoms. Meanwhile, the He cluster tends to expand in the directions away from the solute atoms. A growth criterion is proposed based on the elastic instability strain of the perfect iron lattice in order to determine the maximum number of He atoms at the vacancy site. We find that up to seven He atoms can be trapped at a single vacancy. However, it is reduced to five if the vacancy is pre-occupied by an oxygen atom. Furthermore, the solute atoms within nanoclusters, such as Ti and Y, will greatly limit the growth of the He cluster. A migration energy barrier study is performed to discuss the reduced mobility of the He atom/He cluster in 14YWT.

  14. First-principles study of hydrogen adsorption on Mo(1 1 0)

    Science.gov (United States)

    Zhou, Y. G.; Zu, X. T.; Nie, J. L.; Xiao, H. Y.

    2008-07-01

    First-principles calculations based on density functional theory-generalized gradient approximation method have been performed for hydrogen (H) adsorption on Mo(1 1 0) surface. For various coverages, the hollow (hol) site was found to be the most stable binding site. The adsorption energy of this site was slightly increased as the increasing of hydrogen coverage. Subsurface (sub) occupation at low and medium coverages was ruled out while it became to be stable at the coverage of 1 ML. This is also supported by the potential energy surface (PES) study for hydrogen diffusing from hol to sub site. It's interesting to find a surface reconstruction at the coverage of 1 ML, which is characterized by the lateral shift of the topmost layer for the sub adsorption. At higher coverage, the local density of states (LDOS) analysis showed that a new peak was clearly visible which was ascribed to a surface state induced by hydrogen adsorption. This surface state was mostly localized on the hydrogen atom and the first Mo layer, implying the hybridization of the hydrogen 1s states and the Mo metal states.

  15. Formation energies of intrinsic point defects in monoclinic VO2 studied by first-principles calculations

    Science.gov (United States)

    Cui, Yuanyuan; Liu, Bin; Chen, Lanli; Luo, Hongjie; Gao, Yanfeng

    2016-10-01

    VO2 is an attractive candidate for intelligent windows and thermal sensors. There are challenges for developing VO2-based devices, since the properties of monoclinic VO2 are very sensitive to its intrinsic point defects. In this work, the formation energies of the intrinsic point defects in monoclinic VO2 were studied through the first-principles calculations. Vacancies, interstitials, as well as antisites at various charge states were taken into consideration, and the finite-size supercell correction scheme was adopted as the charge correction scheme. Our calculation results show that the oxygen interstitial and oxygen vacancy are the most abundant intrinsic defects in the oxygen rich and oxygen deficient condition, respectively, indicating a consistency with the experimental results. The calculation results suggest that the oxygen interstitial or oxygen vacancy is correlated with the charge localization, which can introduce holes or electrons as free carriers and subsequently narrow the band gap of monoclinic VO2. These calculations and interpretations concerning the intrinsic point defects would be helpful for developing VO2-based devices through defect modifications.

  16. Electronic Structure of Cu(tmdt2 Studied with First-Principles Calculations

    Directory of Open Access Journals (Sweden)

    Kiyoyuki Terakura

    2012-08-01

    Full Text Available We have studied the electronic structure of Cu(tmdt2, a material related to single-component molecular conductors, by first-principles calculations. The total energy calculations for several different magnetic configurations show that there is strong antiferromagnetic (AFM exchange coupling along the crystal a-axis. The electronic structures are analyzed in terms of the molecular orbitals near the Fermi level of isolated Cu(tmdt2 molecule. This analysis reveals that the system is characterized by the half-filled pdσ(− band whose intermolecular hopping integrals have strong one-dimensionality along the crystal a-axis. As the exchange splitting of the band is larger than the band width, the basic mechanism of the AFM exchange coupling is the superexchange. It will also be shown that two more ligand orbitals which are fairly insensitive to magnetism are located near the Fermi level. Because of the presence of these orbitals, the present calculation predicts that Cu(tmdt2 is metallic even in its AFM state, being inconsistent with the available experiment. Some comments will be made on the difference between Cu(tmdt2 and Cu(dmdt2.

  17. Water confined in nanotubes and between graphene sheets: A first principle study

    Energy Technology Data Exchange (ETDEWEB)

    Cicero, G; Grossman, J C; Schwegler, E; Gygi, F; Galli, G

    2008-10-17

    Water confined at the nanoscale has been the focus of numerous experimental and theoretical investigations in recent years, y yet there is no consensus on such basic properties et as diffusion and the nature of hydrogen bonding (HB) under confinement. Unraveling these properties is important to understand fluid flow and transport at the nanoscale, and to shed light on the solvation of biomolecules. Here we report on a first principle, computational study focusing on water confined between prototypical non polar substrate, i.e. , single wall carbon nanotubes and graphene sheets, 1 to 2.5 nm apart. The results of our molecular dynamics simulations show the presence of a thin, interfacial liquid layer ({approx} 5 Angstroms) whose microscopic structure and thickness are independent of the distance between confining layers. The prop properties of the hydrogen bonded network are very similar to those of the bulk outside the interfacial region, even in the case of strong confinement , confinement. Our findings indicate that the perturbation induced by the presence of confining media is extremely local in liquid water, and we propose that many of the effects attributed to novel phases under confinement are determined by subtle electronic structure rearrangements occurring at the interface with the confining medium.

  18. First-principles study of the ternary semiconductor alloys (Ga,Al)(As,Sb)

    Energy Technology Data Exchange (ETDEWEB)

    El Haj Hassan, F., E-mail: hassan.f@ul.edu.l [Universite Libanaise, Faculte des sciences (I), Laboratoire de Physique de Materiaux, Elhadath, Beirut (Lebanon); Condensed Matter Section, The Abdus Salam International Centre for Theoretical Physics (ICTP), Strada Costiera 11, 34014 Trieste (Italy); Breidi, A. [Universite Libanaise, Faculte des sciences (I), Laboratoire de Physique de Materiaux, Elhadath, Beirut (Lebanon); Laboratoire de Physique des Milieux Denses, Universite Paul Verlaine-Metz, 1 Bd. Arago, 57078 Metz (France); Ghemid, S.; Amrani, B.; Meradji, H. [Laboratoire LPR, Departement de Physique, Faculte des Sciences, Universite de Annaba, Mascara 29000 (Algeria); Pages, O. [Laboratoire de Physique des Milieux Denses, Universite Paul Verlaine-Metz, 1 Bd. Arago, 57078 Metz (France)

    2010-06-04

    First-principles calculations are performed to study the structural, electronic, optical and thermodynamic properties of technologically important Al{sub x}Ga{sub 1-x}As, Al{sub x}Ga{sub 1-x}Sb, GaAs{sub x}Sb{sub 1-x} and AlAs{sub x}Sb{sub 1-x} ternary alloys using the full potential-linearized augmented plane wave plus local orbitals method within the density functional theory. We use both Wu-Cohen and Engel-Vosko generalized gradient approximations of the exchange-correlation energy that are based on the optimization of total energy and corresponding potential, respectively. Our investigation on the effect of composition on lattice constant, bulk modulus, ionicity, band gap, effective mass and refractive index for ternary alloys shows almost non-linear dependence on the composition. The bowing of the fundamental gap versus composition predicted by our calculations is in good agreement with available experiment data. The different roles of structural and chemical effects on the gap bowing and its variation with composition are identified and discussed. It is found that charge-exchange effect overwhelms the other contributions to the gap bowing. Besides, a regular-solution model is used to investigate the thermodynamic stability of the alloys which mainly indicates a phase miscibility gap. In addition, the quasi-harmonic Debye model is applied to determine the thermal properties at room temperature.

  19. Electronic and magnetic properties of nonmetal atoms doped blue phosphorene: First-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Huiling; Yang, Hui [Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), Department of Physics, Jilin University, Changchun 130012 (China); Wang, Hongxia [College of Mathematics, Physics and Information Science, Zhejiang Ocean University, Zhoushan 316000 (China); Du, Xiaobo [Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), Department of Physics, Jilin University, Changchun 130012 (China); Yan, Yu, E-mail: yanyu@jlu.edu.cn [Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), Department of Physics, Jilin University, Changchun 130012 (China)

    2016-06-15

    Using first-principles calculations, we study the geometrical structure, electronic structure and magnetic properties of substitutionally doped blue phosphorene with a series of nonmetallic atoms, including F, Cl, B, N, C, Si and O. The calculated formation energies and molecular dynamics simulations indicate that F, Cl, B, N, C, Si and O doped blue phosphorene are stable. Moreover, the substitutional doping of F, Cl, B and N cannot induce the magnetism in blue phosphorene due to the saturation or pairing of the valence electron of dopant and its neighboring P atoms. In contrast, ground states of C, Si and O doped blue phosphorene are spin-polarized and the magnetic moments induced by a doping atom are all 1.0 μ{sub B}, which is attributed to the appearance of an unpaired valence electron of C and Si and the formation of a nonbonding 3p electron of a neighboring P atom around O. Furthermore, the magnetic coupling between the moments induced by two C, Si and O are found to be long-range anti-ferromagnetic and the origin of the coupling can be attributed to the p–p hybridization interaction involving polarized electrons. - Highlights: • F, Cl, B, N, C, Si and O doped blue phosphorene are stable. • Substitutional doping of C, Si and O can produce the magnetism in blue phosphorene. • Magnetic coupling between two C, Si and O is long-range anti-ferromagnetic.

  20. Adsorption of CO molecules on doped graphene: A first-principles study

    Directory of Open Access Journals (Sweden)

    Weidong Wang

    2016-02-01

    Full Text Available As a typical kinds of toxic gases, CO plays an important role in environmental monitoring, control of chemical processes, space missions, agricultural and medical applications. Graphene is considered a potential candidate of gases sensor, so the adsorption of CO molecules on various graphene, including pristine graphene, Nitrogen-doped graphene (N-doped graphene and Aluminum-doped graphene (Al-doped graphene, are studied by using first-principles calculations. The optimal configurations, adsorption energies, charge transfer, and electronic properties including band structures, density of states and differential charge density are obtained. The adsorption energies of CO molecules on pristine graphene and N-doped graphene are −0.01 eV, and −0.03 eV, respectively. In comparison, the adsorption energy of CO on Al-doped graphene is much larger, −2.69 eV. Our results also show that there occurs a large amount of charge transfer between CO molecules and graphene sheet after the adsorption, which suggests Al-doped graphene is more sensitive to the adsorption of CO than pristine graphene and N-doped graphene. Therefore, the sensitivity of gases on graphene can be drastically improved by introducing the suitable dopants.

  1. Selectively doping barlowite for quantum spin liquid: A first-principles study

    Science.gov (United States)

    Liu, Zheng; Zou, Xiaolong; Mei, Jia-Wei; Liu, Feng

    2015-12-01

    Barlowite Cu4(OH) 6FBr is a newly found mineral containing Cu2 + kagome planes. Despite similarities in many aspects to herbertsmithite Cu3Zn (OH) 6Cl2 , the well-known quantum spin liquid (QSL) candidate, intrinsic barlowite turns out not to be a QSL, possibly due to the presence of Cu2 + ions in between kagome planes that induce interkagome magnetic interaction [Phys. Rev. Lett. 113, 227203 (2014), 10.1103/PhysRevLett.113.227203]. Using first-principles calculation, we systematically study the feasibility of selective substitution of the interkagome Cu ions with isovalent nonmagnetic ions as a function of ion concentration up to the stoichiometric limit. Unlike previous speculation of using larger dopants, such as Cd2 + and Ca2 +, we identify the most ideal stoichiometric doping elements to be Mg and Zn in forming Cu3Mg (OH) 6FBr and Cu3Zn (OH) 6FBr with the highest site selectivity and smallest lattice distortion. The equilibirium antisite disorder in Mg/Zn-doped barlowite is estimated to be one order of magnitude lower than that in herbertsmithite. The single-electron band structure and orbital component analysis show that the proposed selective doping effectively mitigates the difference between barlowite and herbertsmithite.

  2. Formaldehyde molecule adsorption on the doped monolayer MoS2: A first-principles study

    Science.gov (United States)

    Ma, Dongwei; Ju, Weiwei; Li, Tingxian; Yang, Gui; He, Chaozheng; Ma, Benyuan; Tang, Yanan; Lu, Zhansheng; Yang, Zongxian

    2016-05-01

    Based on first-principles calculations, formaldehyde (H2CO) adsorption on the pristine monolayer MoS2 and that doped with Cl, P, or Si was theoretically studied to explore the potential of the MoS2 sheets as H2CO gas sensors. It is found that under Mo-rich conditions it is viable for Cl to be filled into the S vacancies acting as n-type dopant and for P and Si acting as p-type dopants. The results on the H2CO adsorption on the pristine and the Cl-doped monolayer MoS2 indicate that both are insensitive to H2CO. In contrast, H2CO exhibits strong adsorption on the P or Si-doped monolayer MoS2. And there are large electron transfer from the P or Si-doped monolayer MoS2 to the H2CO and obvious change in the electronic densities of states of both systems induced by the H2CO adsorption. These suggest that P and Si can be appropriate dopants filled into MoS2 sheets for detecting H2CO molecule.

  3. Adsorption of CO molecules on doped graphene: A first-principles study

    Science.gov (United States)

    Wang, Weidong; Zhang, Yuxiang; Shen, Cuili; Chai, Yang

    2016-02-01

    As a typical kinds of toxic gases, CO plays an important role in environmental monitoring, control of chemical processes, space missions, agricultural and medical applications. Graphene is considered a potential candidate of gases sensor, so the adsorption of CO molecules on various graphene, including pristine graphene, Nitrogen-doped graphene (N-doped graphene) and Aluminum-doped graphene (Al-doped graphene), are studied by using first-principles calculations. The optimal configurations, adsorption energies, charge transfer, and electronic properties including band structures, density of states and differential charge density are obtained. The adsorption energies of CO molecules on pristine graphene and N-doped graphene are -0.01 eV, and -0.03 eV, respectively. In comparison, the adsorption energy of CO on Al-doped graphene is much larger, -2.69 eV. Our results also show that there occurs a large amount of charge transfer between CO molecules and graphene sheet after the adsorption, which suggests Al-doped graphene is more sensitive to the adsorption of CO than pristine graphene and N-doped graphene. Therefore, the sensitivity of gases on graphene can be drastically improved by introducing the suitable dopants.

  4. First-principles study of nanotubes within the tetragonal, hexagonal and dodecagonal cycle structures

    Science.gov (United States)

    BabaeiPour, M.; Safari, E. Keshavarz; Shokri, A. A.

    2017-02-01

    A systematic study has been done on the structural and electronic properties of carbon, boron nitride and aluminum nitride nanotubes with structure consisting of periodically distributed tetragonal (T ≡A2X2), hexagonal (H ≡A3X3) and dodecagonal (D ≡A6X6) (AX=C2, BN, AlN) cycles. The method has been performed using first-principles calculations based on density functional theory (DFT). The optimized lattice parameters, density of state (DOS) curves and band structure of THD-NTs are obtained for (3, 0) and (0, 2) types. Our calculation results indicate that carbon nanotubes of these types (THD-CNTs) behave as a metallic, but the boron nitride nanotubes (THD-BNNTs) (with a band gap of around 4 eV) as well as aluminum nitride nanotubes (THD-AlNNTs) (with a band gap of around 2.6 eV) behave as an semiconductor. The inequality in number of atoms in different directions is affected on structures and diameters of nanotubes and their walls curvature.

  5. First principle DFT study of electric field effects on the characteristics of bilayer graphene

    Energy Technology Data Exchange (ETDEWEB)

    Sabzyan, Hassan; Sadeghpour, Narges [Isfahan Univ. (Iran, Islamic Republic of). Dept. of Chemistry

    2017-04-01

    First principle density functional theory methods, local density and Perdew-Burke-Ernzerhof generalized gradient approximations with Goedecker pseudopotential (LDA-G and PBE-G), are used to study the electric field effects on the binding energy and atomic charges of bilayer graphene (BLG) at the Γ point of the Brillouin zone based on two types of unit cells (α and β) containing n{sub C}=8-32 carbon atoms. Results show that application of electric fields of 4-24 V/nm strengths reduces the binding energies and induces charge transfer between the two layers. The transferred charge increases almost linearly with the strength of the electric field for all sizes of the two types of unit cells. Furthermore, the charge transfer calculated with the α-type unit cells is more sensitive to the electric field strength. The calculated field-dependent contour plots of the differential charge densities of the two layers show details of charge density redistribution under the influence of the electric field.

  6. First-principle studies on the electronic structure of Fe3O4(110) surface

    Institute of Scientific and Technical Information of China (English)

    LI Yan-li; YAO Kai-lun; LIU Zu-li

    2007-01-01

    The first-principle was employed to study the six possible models for the Fe3O4(110) surface, namely the AB-terminated surface (AB model), the AB-terminated with Fen vacancy (AB-FeA vac model), the AB-terminated with FeB vacancy (AB-FeB vac model), the B-terminated surface (B model), the B-terminated surface with FeB vacancy (B-FeB vac model) and the B-terminated surface with O vacancy (B-O vac model). The stability, the electronic structure and the magnetic properties of the six surface models were also calculated. The results predict that the B-O vac model is more stable than other types of surface models. The half-metallic property remain in the AB and B models, while the other four surface models exhibit metallic properties. At the same time, the AB, AB-FeAvac, AB-FeB vac, B and the B-FeB vac models have ferrimagnetic properties, while the B-O vac model has antiferromagnetic property.

  7. Analytical study of Yang-Mills theory in the infrared from first principles

    CERN Document Server

    Siringo, Fabio

    2015-01-01

    Pure Yang-Mills SU(N) theory is studied in the Landau gauge and four dimensional space. While leaving the original Lagrangian unmodified, a double perturbative expansion is devised, based on a massive free-particle propagator. In dimensional regularization, all diverging mass terms cancel exactly in the double expansion, without the need to include mass counterterms that would spoil the symmetry of the Lagrangian. No free parameters are included that were not in the original theory, yielding a fully analytical approach from first principles. The expansion is safe in the infrared and is equivalent to the standard perturbation theory in the UV. At one-loop, explicit analytical expressions are given for the propagators and the running coupling and are found in excellent agreement with the data of lattice simulations. A universal scaling property is predicted for the inverse propagators and shown to be satisfied by the lattice data. Higher loops are found to be negligible in the infrared below 300 MeV where the c...

  8. Lattice-matched heterojunctions between topological and normal insulators: A first-principles study

    Science.gov (United States)

    Lee, Hyungjun; Yazyev, Oleg V.

    2017-02-01

    Gapless boundary modes at the interface between topologically distinct regions are one of the most salient manifestations of topology in physics. Metallic boundary states of time-reversal-invariant topological insulators (TIs), a realization of topological order in condensed matter, have been of much interest not only due to such a fundamental nature, but also due to their practical significance. These boundary states are immune to backscattering and localization owing to their topological origin, thereby opening up the possibility to tailor them for potential uses in spintronics and quantum computing. The heterojunction between a TI and a normal insulator (NI) is a representative playground for exploring such a topologically protected metallic boundary state and expected to constitute a building block for future electronic and spintronic solid-state devices based on TIs. Here, we report a first-principles study of two experimentally realized lattice-matched heterojunctions between TIs and NIs, Bi2Se3 (0001)/InP(111) and Bi2Te3 (0001)/BaF2(111). We evaluate the band offsets at these interfaces from many-body perturbation theory within the G W approximation as well as density-functional theory. Furthermore, we investigate the topological interface states, demonstrating that at these lattice-matched heterointerfaces, they are strictly localized and their helical spin textures are as well preserved as those at the vacuum-facing surfaces. These results taken together may help in designing devices relying on spin-helical metallic boundary states of TIs.

  9. First Principle DFT Study of Electric Field Effects on the Characteristics of Bilayer Graphene

    Science.gov (United States)

    Sabzyan, Hassan; Sadeghpour, Narges

    2017-01-01

    First principle density functional theory methods, local density and Perdew-Burke-Ernzerhof generalized gradient approximations with Goedecker pseudopotential (LDA-G & PBE-G), are used to study the electric field effects on the binding energy and atomic charges of bilayer graphene (BLG) at the Γ point of the Brillouin zone based on two types of unit cells (α and β) containing nC=8-32 carbon atoms. Results show that application of electric fields of 4-24 V/nm strengths reduces the binding energies and induces charge transfer between the two layers. The transferred charge increases almost linearly with the strength of the electric field for all sizes of the two types of unit cells. Furthermore, the charge transfer calculated with the α-type unit cells is more sensitive to the electric field strength. The calculated field-dependent contour plots of the differential charge densities of the two layers show details of charge density redistribution under the influence of the electric field.

  10. Energetic Study of Helium Cluster Nucleation and Growth in 14YWT through First Principles

    Energy Technology Data Exchange (ETDEWEB)

    Gan, Yingye [Clemson University; Zhao, Huijuan [Clemson University; Hoelzer, David T [ORNL; Yun, Di [Argonne National Laboratory (ANL); Yun, Di [Shanghai Jiao Tong University, China

    2016-01-01

    First principles calculations have been performed to energetically investigate the helium cluster nucleation, formation and growth behavior in the nano-structured ferritic alloy 14YWT. The helium displays strong affinity to the oxygen:vacancy (O:Vac) pair. By investigating various local environments of the vacancy, we find that the energy cost for He cluster growth increases with the appearance of solutes in the reference unit. He atom tends to join the He cluster in the directions away from the solute atoms. Meanwhile, the He cluster tends to expand in the directions away from the solute atoms. A growth criterion is proposed based on the elastic instability strain of the perfect iron lattice in order to determine the maximum number of He atoms at the vacancy site. We find that up to seven He atoms can be trapped at a single vacancy. However, it is reduced to five if the vacancy is pre-occupied by an oxygen atom. Furthermore, the solute atoms within nanoclusters, such as Ti and Y, will greatly limit the growth of the He cluster. A migration energy barrier study is performed to discuss the reduced mobility of the He atom/He cluster in 14YWT.

  11. Electronic and mechanical properties of Zr{sub 2}TiAl: A first principles study

    Energy Technology Data Exchange (ETDEWEB)

    Reddy, P. V. Sreenivasa, E-mail: kanchana@iith.ac.in; Kanchana, V., E-mail: kanchana@iith.ac.in [Department of Physics, Indian Institute of Technology Hyderabad, Ordnance Factory Estate, Yeddumailaram-502205, Andhra Pradesh (India)

    2014-04-24

    First principles study of electronic and mechanical properties of ternary phase Zr{sub 2}TiAl intermetallic compound has been carried out by using full potential linear augmented plane wave (FP-LAPW) method. Our calculated lattice parameter is in good agreement with the experiment. We find the magnetic phase of the compound to be stable with a magnetic moment of 1.95 μ{sub B}. The major contribution to the total magnetic moment arises mainly from the Ti atom with the local magnetic moment of 1.22 μ{sub B}. From the density of states plots we find the Ti-d and Zr-d to dominate at the Fermi level (E{sub F}) with enhanced crystal field splitting and exchange splitting found in Ti. The mechanical stability of the compound is confirmed from the calculated elastic constants, and we find the compound to be ductile in nature from the calculated Pugh’s ratio and Cauchy’s pressure.

  12. Elastic and vibrational properties of monoclinic HfO2 from first-principles study

    Science.gov (United States)

    Wu, Rui; Zhou, Bo; Li, Qian; Jiang, ZhenYi; Wang, WenBo; Ma, WenYan; Zhang, XiaoDong

    2012-03-01

    The elastic and vibrational properties of crystalline monoclinic HfO2 have been investigated using density functional perturbation theory. Using the Voigt and Reuss theory, we estimate the bulk, shear and Young's modulus for polycrystalline HfO2, which agree very well with the available experimental and theoretical data. Additionally, we present a systematic analysis of the elastic properties of HfO2 polymorphs and find the trends in the elastic parameters for the HfO2 structures are consistent with those for the ZrO2 structures. The choice of exchange-correlation functional has an important effect on the results of elastic and vibrational properties. The utilization of Hartwigzen-Goedecker-Hutter type functional is a great improvement on calculation of the zone-centre phonon frequencies, and shows the root-mean-square absolute deviation of 7 cm-1 with experiments. A rigorous assignment of all the Raman modes is achieved by combining symmetry analysis with the first-principles calculations, which helps us to identify the main peak and some other features of Raman spectra. Furthermore, the Raman spectrum of HfO2 powder has been simulated for the first time, providing a theoretical benchmark for the interpretation of the unresolved problems in experimental studies.

  13. First-principles study of hole polaron formation and migration in SrI2

    Science.gov (United States)

    Zhou, Fei; Sadigh, Babak; Aberg, Daniel

    2015-03-01

    We investigate the formation of self-trapped holes (STH) in the high performance scintillator material SrI2 using a recently developed first principles method, polaron self-interaction correction (pSIC). pSIC removes the significant spurious self-interaction of localized polaron states. It is capable of accurately reproduce the configurational energy landscape of polaronic states from optimized hybrid functionals at the computational cost of the local density approximation. We searched for and identified all symmetrically distinct STH states localized on neighboring I-I dimers, i.e. Vk centers, and found non-trivial relation between the STH formation energies and dimer separation. All possible polaron hopping paths of the type IAIB -->IBIC are investigated systematically with pSIC and the elastic band method, and paths with low migration barrier energy of about 0.2 eV were identified, suggesting high mobility in SrI2. We expect that the present approach can be applied to study polaron formation and migration in other materials. Support from the National Nuclear Security Administration Office of Nonproliferation Research and Development (NA-22) is acknowledged. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore N We acknowledge funding from the NA-22 agency.

  14. Temperature-dependent ideal strength and stacking fault energy of fcc Ni: a first-principles study of shear deformation.

    Science.gov (United States)

    Shang, S L; Wang, W Y; Wang, Y; Du, Y; Zhang, J X; Patel, A D; Liu, Z K

    2012-04-18

    Variations of energy, stress, and magnetic moment of fcc Ni as a response to shear deformation and the associated ideal shear strength (τ(IS)), intrinsic (γ(SF)) and unstable (γ(US)) stacking fault energies have been studied in terms of first-principles calculations under both the alias and affine shear regimes within the {111} slip plane along the and directions. It is found that (i) the intrinsic stacking fault energy γ(SF) is nearly independent of the shear deformation regimes used, albeit a slightly smaller value is predicted by pure shear (with relaxation) compared to the one from simple shear (without relaxation); (ii) the minimum ideal shear strength τ(IS) is obtained by pure alias shear of {111}; and (iii) the dissociation of the 1/2[110] dislocation into two partial Shockley dislocations (1/6[211] + 1/6[121]) is observed under pure alias shear of {111}. Based on the quasiharmonic approach from first-principles phonon calculations, the predicted γ(SF) has been extended to finite temperatures. In particular, using a proposed quasistatic approach on the basis of the predicted volume versus temperature relation, the temperature dependence of τ(IS) is also obtained. Both the γ(SF) and the τ(IS) of fcc Ni decrease with increasing temperature. The computed ideal shear strengths as well as the intrinsic and unstable stacking fault energies are in favorable accord with experiments and other predictions in the literature.

  15. Origin of current-induced forces in an atomic gold wire: A first-principles study

    DEFF Research Database (Denmark)

    Brandbyge, Mads; Stokbro, Kurt; Taylor, Jeremy Philip;

    2003-01-01

    We address the microscopic origin of the current-induced forces by analyzing results of first principles density functional calculations of atomic gold wires connected to two gold electrodes with different electrochemical potentials. We find that current induced forces are closely related...

  16. Hopping matrix elements from first-principles studies of overlapping fragments : Double exchange parameters in manganites

    NARCIS (Netherlands)

    Stoyanova, A.; Sousa, C.; De Graaf, C.; Broer, R.

    2006-01-01

    We recently developed a scheme for first-principles calculations of hopping matrix elements between localized states in extended systems. We apply the scheme to the determination of double exchange (DE) parameters in lightly hole-doped LaMnO(3) and electron-doped CaMnO(3). DE is one of the important

  17. Formaldehyde adsorption and decomposition on rutile (110): A first-principles study

    Science.gov (United States)

    Liu, Liming; Zhao, Jin

    2016-10-01

    We investigated the adsorption and decomposition of formaldehyde (HCHO) molecule on stoichiometric rutile TiO2(110) surface using first principles-calculations. By comparing the adsorption energy of one bidentate and two monodentate configurations, we found the bidentate configuration is the most stable one because of an additional C-O bond formation. The monodentate configuration can change into the bidentate configuration by overcoming a small barrier less than 0.1 eV. Then, we investigated the decomposition of HCHO which involves two deprotonation processes starting from different adsorption structures. The energy barrier of the first deprotonation is 1.3 eV and 1.1 eV for bidentate and monodentate configurations. After the first deprotonation, an adsorbed formate HCOO specie is formed. The second deprotonation needs 1.74 eV and 1.64 eV for bidentate and monodentate configurations, respectively. After that, an adsorbed CO2 is formed. It can desorb from the surface after overcoming a small barrier of 0.12 eV. In principle, it is also possible to obtain a CO molecule from the surface. Yet a large energy barrier higher than 1.74 eV needs to be overcome. By analyzing the energy level alignment of molecular orbitals with TiO2 energy band edges, we discussed the photocatalytic activity of the reactants and intermediates during the decomposition process. Our results give a clear description of the adsorption structure and thermal decomposition process of HCHO on rutile TiO2(110) surface. The discussion of photocatalytic reactivity based on energy level alignment provides valuable insights to understand the combined photocatalytic and thermally catalytic reactions.

  18. First-principles study of crystalline and amorphous AlMgB{sub 14}-based materials

    Energy Technology Data Exchange (ETDEWEB)

    Ivashchenko, V. I.; Shevchenko, V. I., E-mail: shev@materials.kiev.ua [Institute of Problems of Material Science, National Academy of Science of Ukraine, Krzhyzhanosky Str. 3, 03142 Kyiv (Ukraine); Turchi, P. E. A. [Lawrence Livermore National Laboratory (L-352), P.O. Box 808, Livermore, California 94551 (United States); Veprek, S. [Department of Chemistry, Technical University Munich, Lichtenbergstrasse 4, D-85747 Garching (Germany); Leszczynski, Jerzy [Department of Chemistry and Biochemistry, Interdisciplinary Center for Nanotoxicity, Jackson State University, Jackson, Mississippi 39217 (United States); Gorb, Leonid [Department of Chemistry and Biochemistry, Interdisciplinary Center for Nanotoxicity, Jackson State University, Jackson, Mississippi 39217 (United States); Badger Technical Services, LLC, Vicksburg, Mississippi 39180 (United States); Hill, Frances [U.S. Army ERDC, Vicksburg, Mississippi 39180 (United States)

    2016-05-28

    We report first-principles investigations of crystalline and amorphous boron and M1{sub x}M2{sub y}X{sub z}B{sub 14−z} (M1, M2 = Al, Mg, Li, Na, Y; X = Ti, C, Si) phases (so-called “BAM” materials). Phase stability is analyzed in terms of formation energy and dynamical stability. The atomic configurations as well as the electronic and phonon density states of these phases are compared. Amorphous boron consists of distorted icosahedra, icosahedron fragments, and dioctahedra, connected by an amorphous network. The presence of metal atoms in amorphous BAM materials precludes the formation of icosahedra. For all the amorphous structures considered here, the Fermi level is located in the mobility gap independent of the number of valence electrons. The intra-icosahedral vibrations are localized in the range of 800 cm{sup −1}, whereas the inter-icosahedral vibrations appear at higher wavenumbers. The amorphization leads to an enhancement of the vibrations in the range of 1100–1250 cm{sup −1}. The mechanical properties of BAM materials are investigated at equilibrium and under shear and tensile strain. The anisotropy of the ideal shear and tensile strengths is explained in terms of a layered structure of the B{sub 12} units. The strength of amorphous BAM materials is lower than that of the crystalline counterparts because of the partial fragmentation of the boron icosahedra in amorphous structures. The strength enhancement found experimentally for amorphous boron-based films is very likely related to an increase in film density, and the presence of oxygen impurities. For crystalline BAM materials, the icosahedra are preserved during elongation upon tension as well as upon shear in the (010)[100] slip system.

  19. First-principles study of lattice dynamics, structural phase transition, and thermodynamic properties of barium titanate

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Huai-Yong; Zhao, Ying-Qin; Lu, Qing [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics; Zeng, Zhao-Yi [Chongqing Normal Univ. (China). College of Physics and Electronic Engineering; Chinese Academy of Engineering Physics, Mianyang (China). National Key Laboratory for Shock Wave and Detonation Physics Research; Cheng, Yan [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics; Sichuan Univ., Chengdu (China). Key Laboratory of High Energy Density Physics and Technology of Ministry of Education

    2016-11-01

    Lattice dynamics, structural phase transition, and the thermodynamic properties of barium titanate (BaTiO{sub 3}) are investigated by using first-principles calculations within the density functional theory (DFT). It is found that the GGA-WC exchange-correlation functional can produce better results. The imaginary frequencies that indicate structural instability are observed for the cubic, tetragonal, and orthorhombic phases of BaTiO{sub 3} and no imaginary frequencies emerge in the rhombohedral phase. By examining the partial phonon density of states (PDOSs), we find that the main contribution to the imaginary frequencies is the distortions of the perovskite cage (Ti-O). On the basis of the site-symmetry consideration and group theory, we give the comparative phonon symmetry analysis in four phases, which is useful to analyze the role of different atomic displacements in the vibrational modes of different symmetry. The calculated optical phonon frequencies at Γ point for the four phases are in good agreement with other theoretical and experimental data. The pressure-induced phase transition of BaTiO{sub 3} among four phases and the thermodynamic properties of BaTiO{sub 3} in rhombohedral phase have been investigated within the quasi-harmonic approximation (QHA). The sequence of the pressure-induced phase transition is rhombohedral → orthorhombic → tetragonal → cubic, and the corresponding transition pressure is 5.17, 5.92, 6.65 GPa, respectively. At zero pressure, the thermal expansion coefficient α{sub V}, heat capacity C{sub V}, Grueneisen parameter γ, and bulk modulus B of the rhombohedral phase BaTiO{sub 3} are estimated from 0 K to 200 K.

  20. First Principles Study on the Interaction Mechanisms of Water Molecules on TiO₂ Nanotubes.

    Science.gov (United States)

    Dai, Jianhong; Song, Yan

    2016-12-16

    The adsorption properties of water molecules on TiO₂ nanotubes (TiO₂NT) and the interaction mechanisms between water molecules are studied by first principles calculations. The adsorption preferences of water molecules in molecular or dissociated states on clean and H-terminated TiO₂NT are evaluated. Adsorption of OH clusters on (0, 6) and (9, 0) TiO₂ nanotubes are first studied. The smallest adsorption energies are -1.163 eV and -1.383 eV, respectively, by examining five different adsorption sites on each type of tube. Eight and six adsorption sites were considered for OH adsorbtion on the H terminated (0, 6) and (9, 0) nanotubes. Water molecules are reformed with the smallest adsorption energy of -4.796 eV on the former and of -5.013 eV on the latter nanotube, respectively. For the adsorption of a single water molecule on TiO₂NT, the molecular state shows the strongest adsorption preference with an adsorption energy of -0.660 eV. The adsorption of multiple (two and three) water molecules on TiO₂NT is also studied. The calculated results show that the interactions between water molecules greatly affect their adsorption properties. Competition occurs between the molecular and dissociated states. The electronic structures are calculated to clarify the interaction mechanisms between water molecules and TiO₂NT. The bonding interactions between H from water and oxygen from TiO₂NT may be the reason for the dissociation of water on TiO₂NT.

  1. Comparison of Electronic and Optical Properties of GaN Monolayer and Bulk Structure: a First Principle Study

    Science.gov (United States)

    Imran, Muhammad; Hussain, Fayyaz; Rashid, Muhammad; Ullah, Hafeez; Sattar, Atif; Iqbal, Faisal; Ahmad, Ejaz

    2016-03-01

    The semiconducting two-dimensional (2D) architectures materials have potential applications in electronics and optics. The design and search of new 2D materials have attracted extensive attention recently. In this study, first principle calculation has been done on 2D gallium nitride (GaN) monolayer with respect to its formation and binding energies. The electronic and optical properties are also investigated. It is found that the single isolated GaN sheet is forming mainly ionic GaN bonds despite a slightly weaker GaN interaction as compared with its bulk counterpart. The dielectric constant value of 2D GaN is smaller as compared to 3D GaN due to less effective electronic screening effect in the layer, which is accompanied by lesser optical adsorption range and suggested to be a promising candidate in electronic and optoelectronic devices.

  2. On the transparent conducting oxide Al doped ZnO: First Principles and Boltzmann equations study

    Energy Technology Data Exchange (ETDEWEB)

    Slassi, A. [Institute of Nanomaterials and Nanotechnology, MAScIR, Rabat (Morocco); LMPHE (URAC 12), Faculté des Sciences, Université Mohammed V-Agdal, Rabat (Morocco); Naji, S. [LMPHE (URAC 12), Faculté des Sciences, Université Mohammed V-Agdal, Rabat (Morocco); Department of Physics, Faculty of Science, Ibb University, Ibb (Yemen); Benyoussef, A. [Institute of Nanomaterials and Nanotechnology, MAScIR, Rabat (Morocco); LMPHE (URAC 12), Faculté des Sciences, Université Mohammed V-Agdal, Rabat (Morocco); Hamedoun, M., E-mail: hamedoun@hotmail.com [Institute of Nanomaterials and Nanotechnology, MAScIR, Rabat (Morocco); El Kenz, A. [LMPHE (URAC 12), Faculté des Sciences, Université Mohammed V-Agdal, Rabat (Morocco)

    2014-08-25

    Highlights: • The incorporation of Al in ZnO increases the optical band edge absorption. • Incorporated Al creates shallow donor states of Al-3s around Fermi level. • Transmittance decreases in the visible and IR regions, while it increases in the UV region. • Electrical conductivity increases and reaches almost the saturation for high concentration of Al. - Abstract: We report, in this work, a theoretical study on the electronic, optical and electrical properties of pure and Al doped ZnO with different concentrations. In fact, we investigate these properties using both First Principles calculations within TB-mBJ approximation and Boltzmann equations under the constant relaxation time approximation for charge carriers. It is found out that, the calculated lattice parameters and the optical band gap of pure ZnO are close to the experimental values and in a good agreement with the other theoretical studies. It is also observed that, the incorporations of Al in ZnO increase the optical band edge absorption which leads to a blue shift and no deep impurities levels are induced in the band gap as well. More precisely, these incorporations create shallow donor states around Fermi level in the conduction band minimum from mainly Al-3s orbital. Beside this, it is found that, the transmittance is decreased in the visible and IR regions, while it is significantly improved in UV region. Finally, our calculations show that the electrical conductivity is enhanced as a result of Al doping and it reaches almost the saturation for high concentration of Al. These features make Al doped ZnO a transparent conducting electrode for optoelectronic device applications.

  3. First-principles study of boron speciation in calcite and aragonite

    Science.gov (United States)

    Balan, Etienne; Pietrucci, Fabio; Gervais, Christel; Blanchard, Marc; Schott, Jacques; Gaillardet, Jérome

    2016-11-01

    Despite the importance of boron as a proxy of past ocean pH, the crystal-chemical factors controlling its incorporation in the structure of calcium carbonates are still poorly understood. This is partly linked to an imperfect knowledge of the coordination, protonation state and local environment of boron species in these minerals. In the present study, we use first-principles quantum mechanical tools to model selected trigonal and tetragonal boron species in calcite and aragonite. The stable geometry of the models is obtained from standard energy minimization schemes or using a more advanced metadynamics exploration of their configurational space. The computation of 11B NMR chemical shifts and quadrupolar coupling parameters enables a straightforward comparison of the models to existing experimental NMR data. The results show that B in calcium carbonates does occur as structural species substituted for CO32- anions. The B speciation depends on the polymorph considered. In calcite, structural boron is present as partially deprotonated trigonal BO2(OH)2- species coexisting with a fraction of substituted B(OH)4- groups. In aragonite, the B(OH)4- substitution for CO32- anions is dominant. Different species, including entrapped B(OH)3 molecules and substituted BO33- groups also occur in biogenic samples. The diversity of B speciation reflects a diversity of B incorporation mechanisms and sheds light on previous studies confronting B isotopic composition determination with NMR observations. The mechanisms of boron incorporation in calcium carbonates are probably more complex than usually assumed in the literature using boron isotopes as a proxy of paleo-atmospheric CO2 reconstructions. Although not invalidating the empirical paleo-pH proxy, these results call for a better understanding of the fundamental mechanisms of boron incorporation in carbonates.

  4. First Principles Study on NaxLi1-xFePO4 As Cathode Material for Rechargeable Lithium Batteries

    Science.gov (United States)

    Ouyang, Chu-Ying; Wang, De-Yu; Shi, Si-Qi; Wang, Zhao-Xiang; Li, Hong; Huang, Xue-Jie; Chen, Li-Quan

    2006-01-01

    The electronic structure and ionic dynamic properties of pure and Na doped (Li site) LiFePO4 have been investigated by first-principles calculations. The band gap of the Na doped material is much narrow than that of the undoped one, indicating of better electronic conductive properties. First-principles based molecular dynamic simulations have been performed to examine the migration energy barriers for the Li ion diffusion. The results shown that the energy barriers for Li diffusion decreased a little along the one-dimensional diffusion pathway, indicating that the ionic conductive property is also improved, as compared with the high valance doping (such as Cr) cases.

  5. First principles study of magneto-optical properties of Fe-doped ZnO

    Energy Technology Data Exchange (ETDEWEB)

    Shaoqiang, Guo [College of Science, Inner Mongolia University of Technology, Hohhot 010051 (China); Qingyu, Hou, E-mail: by0501119@126.com [College of Science, Inner Mongolia University of Technology, Hohhot 010051 (China); Zhenchao, Xu [College of Science, Inner Mongolia University of Technology, Hohhot 010051 (China); Chunwang, Zhao [College of Science, Inner Mongolia University of Technology, Hohhot 010051 (China); College of Arts and Sciences, Shanghai Maritime University, Shanghai 201306 (China)

    2016-12-15

    Studies on optical band gaps and absorption spectra of Fe-doped ZnO have conflicting conclusions, such as contradictory redshifted and blueshifted spectra. To solve this contradiction, we constructed models of un-doped and Fe-doped ZnO using first-principles theory and optimized the geometry of the three models. Electronic structures and absorption spectra were also calculated using the GGA+U method. Higher doping content of Fe resulted in larger volume of doped system, and higher total energy resulted in lower stability. Higher formation energy also led to more difficult doping. Meanwhile, the band gaps broadened and the absorption spectra exhibited an evident blue shift. The calculations were in good agreement with the experimental results. Given the unipolar structure of ZnO, four possible magnetic coupling configurations for Zn{sub 14}Fe{sub 2}O{sub 16} were calculated to investigate the magnetic properties. Results suggest that Fe doping can improve ferromagnetism in the ZnO system and that ferromagnetic stabilization was mediated by p–d exchange interaction between Fe-3d and O-2p orbitals. Therefore, the doped system is expected to obtain high stability and high Curie temperature of diluted magnetic semiconductor material, which are useful as theoretical bases for the design and preparation of the Fe-doped ZnO system’s magneto-optical properties. - Highlights: • A biomonitoring tool for the freshwater zone of template estuaries. • Water quality characterization related to nutrients and organic matter enrichment. • The percentage of a group of 24 tolerant species were capable of detecting the impairment of the water quality. • Characterization of morpho-functional traits of the selected tolerant species.

  6. First-principles study of Ni-Al intermetallic compounds under various temperature and pressure

    Science.gov (United States)

    Wen, Zhiqin; Zhao, Yuhong; Hou, Hua; Tian, Jinzhong; Han, Peide

    2017-03-01

    The pressure dependence behaviors of structural and mechanical properties as well as the effect of temperature on thermodynamic properties of Ni-Al ordered intermetallic compounds (i. e. Ni3Al, Ni5Al3, NiAl, Ni2Al3 and NiAl3) are investigated in details by implementing first-principles calculations. The calculated lattice parameters, bulk modulus and its pressure derivative are well in agreement with available experimental and theoretical values at zero pressure. All the compounds are mechanically stable with pressure going up to 50 GPa, and the volume change resistance of nickel aluminum alloys can be improved by increasing pressure and Ni concentration. The shear deformation resistance, elastic stiffness and microhardness of nickel aluminum alloys can be strengthened by increasing the content of Ni5Al3 and Ni2Al3, and pressure can also enhance these properties of Ni5Al3, NiAl and Ni2Al3. The ductility of Ni3Al, Ni5Al3 and NiAl can be improved by increasing pressure, while brittle nature turns into ductile nature in 20-30 GPa and 10-20 GPa for Ni2Al3 and NiAl3, respectively. Furthermore, the elastic anisotropy of Ni3Al, Ni5Al3, Ni2Al3 and NiAl3 enhances with pressure, while NiAl shows few change with pressure increasing. In addition, Ni3Al is the most sensitive to pressure change among considered compounds. Finally, the Debye temperature, linear thermal expansion coefficient and heat capacity of these compounds are calculated using the quasi-harmonic Debye model in pressure ranging from 0 to 50 GPa and temperature ranging from 0 to 1200 K to elucidate the relationships between thermodynamic parameters and temperature under various pressure. The results are helpful insights into the study of nickel aluminum alloys.

  7. First-principles study of He trapping in η-Fe2C

    Science.gov (United States)

    He, Bing-Ling; Wang, Jin-Long; Tian, Zhi-Xue; Jiang, Li-Juan; Song, Wei; Wang, Bin

    2016-11-01

    The distribution of He in η-Fe2C has been studied by first-principles calculations. The formation energies of interstitial He and substitutional He (replacing Fe) are 3.76 eV and 3.49 eV, respectively, which are remarkably smaller than those in bcc Fe, indicating that He is more soluble in η-Fe2C than in bcc Fe. The binding potencies of both a substitutional-interstitial He pair (1.28 eV) and a substitutional-substitutional He pair (0.76 eV) are significantly weaker than those in bcc Fe. The binding energy between the two He atoms in an interstitial-interstitial He pair (0.31 eV) is the same as that in bcc Fe, but the diffusion barrier of interstitial He (0.35 eV) is much larger than that in bcc Fe, suggesting that it is more difficult for the interstitial He atom to agglomerate in η-Fe2C than in bcc Fe. Thus, self-trapping of He in η-Fe2C is less powerful than that in bcc Fe. As a consequence, small and dense η-Fe2C particles in ferritic steels might serve as scattered trapping centers for He, slow down He bubble growth at the initial stage, and make the steel more swelling resistant. Project supported by the Research Key Project of Science and Technology of Education Bureau of Henan Province, China (Grant Nos. 14A140030, 15A140032, 15B150010, and 15A430037) and the Innovation Talents Program of Science and Technology of Institution of Higher Education of Henan Province, China (Grant No. 14HASTIT044).

  8. Understanding CO2 capture mechanisms in aqueous hydrazine via combined NMR and first-principles studies.

    Science.gov (United States)

    Lee, Byeongno; Stowe, Haley M; Lee, Kyu Hyung; Hur, Nam Hwi; Hwang, Son-Jong; Paek, Eunsu; Hwang, Gyeong S

    2017-09-13

    Aqueous amines are currently the most promising solution for large-scale CO2 capture from industrial sources. However, molecular design and optimization of amine-based solvents have proceeded slowly due to a lack of understanding of the underlying reaction mechanisms. Unique and unexpected reaction mechanisms involved in CO2 absorption into aqueous hydrazine are identified using (1)H, (13)C, and (15)N NMR spectroscopy combined with first-principles quantum-mechanical simulations. We find production of both hydrazine mono-carbamate (NH2-NH-COO(-)) and hydrazine di-carbamate ((-)OOC-NH-NH-COO(-)), with the latter becoming more populated with increasing CO2 loading. Exchange NMR spectroscopy also demonstrates that the reaction products are in dynamic equilibrium under ambient conditions due to CO2 exchange between mono-carbamate and di-carbamate as well as fast proton transfer between un-protonated free hydrazine and mono-carbamate. The exchange rate rises steeply at high CO2 loadings, enhancing CO2 release, which appears to be a unique property of hydrazine in aqueous solution. The underlying mechanisms of these processes are further evaluated using quantum mechanical calculations. We also analyze and discuss reversible precipitation of carbamate and conversion of bicarbonate to carbamates. The comprehensive mechanistic study provides useful guidance for optimal design of amine-based solvents and processes to reduce the cost of carbon capture. Moreover, this work demonstrates the value of a combined experimental and computational approach for exploring the complex reaction dynamics of CO2 in aqueous amines.

  9. Identifying Mechanisms Behind the Tullio Phenomenon: a Computational Study Based on First Principles.

    Science.gov (United States)

    Grieser, Bernhard J; Kleiser, Leonhard; Obrist, Dominik

    2016-04-01

    Patients with superior canal dehiscence (SCD) suffer from events of dizziness and vertigo in response to sound, also known as Tullio phenomenon (TP). The present work seeks to explain the fluid-dynamical mechanisms behind TP. In accordance with the so-called third window theory, we developed a computational model for the vestibular signal pathway between stapes and SCD. It is based on first principles and accounts for fluid-structure interactions arising between endolymph, perilymph, and membranous labyrinth. The simulation results reveal a wave propagation phenomenon in the membranous canal, leading to two flow phenomena within the endolymph which are in close interaction. First, the periodic deformation of the membranous labyrinth causes oscillating endolymph flow which forces the cupula to oscillate in phase with the sound stimulus. Second, these primary oscillations of the endolymph induce a steady flow component by a phenomenon known as steady streaming. We find that this steady flow of the endolymph is typically in ampullofugal direction. This flow leads to a quasi-steady deflection of the cupula which increases until the driving forces of the steady streaming are balanced by the elastic reaction forces of the cupula, such that the cupula attains a constant deflection amplitude which lasts as long as the sound stimulus. Both response types have been observed in the literature. In a sensitivity study, we obtain an analytical fit which very well matches our simulation results in a relevant parameter range. Finally, we correlate the corresponding eye response (vestibulo-ocular reflex) with the fluid dynamics by a simplified model of lumped system constants. The results reveal a "sweet spot" for TP within the audible sound spectrum. We find that the underlying mechanisms which lead to TP originate primarily from Reynolds stresses in the fluid, which are weaker at lower sound frequencies.

  10. First-principles study of hydrogen incorporation mechanism in Mg2SiO4

    Science.gov (United States)

    Yamamoto, T.

    2012-12-01

    Most of the geoscientists believe that olivine-based minerals form the major constituent in the upper mantle, which extends to a depth of 660km. The Earth's upper mantle consists mainly of following three phases, alpha-, beta- and gamma-Mg2SiO4. Pressure induced phase transitions occur at about 10 GPa and 15 GPa under low temperature condition from alpha- to beta-Mg2SiO4, and from beta- to gamma-Mg2SiO4, respectively. The existence of beta-Mg2SiO4 gives rise to the discontinuity in seismic velocities at a depth of 410 km. It is widely accepted that the atmosphere and the oceans of the Earth are formed by degassing of the Earth's mantle. Most of the water and/or hydrogen may have been lost or it may still be stored in the Earth's mantle. If considerable amounts of hydrogen are present in the Earth's mantle, such hydrogen plays a key role in the geodynamics of the Earth's interior, because it affects the melting temperature and the transport properties of minerals as well as their elastic properties. Earlier high-pressure experiments suggested that main components of the transition zone of the Earth's mantle, wadsleyite and ringwoodite, can store significant amount of hydrogen [1-4]. More recently, it was reported that the lower mantle minerals, consisting of Mg-perovskite, magnesiowüstite and Ca-perovskite [5], can potentially store considerable amounts of hydrogen. However the effects of hydrogen solution on their physical properties and substitution mechanism of hydrogen in mantle minerals have not yet been fully understood. In the present study, the first-principles Density Functional Theory (DFT) calculations have been performed to investigate the influence of hydrogen incorporations on the compressional mechanism of the major components of upper mantle minerals in the Earth, i.e., forsterite (alpha-Mg2SiO4), wadsleyite (beta-Mg2SiO4) and ringwoodite (gamma-Mg2SiO4), and the mechanism of hydrogen incorporation in these minerals. Observed equilibrium volumes of

  11. Dehydrogenation characteristics of MgnH2n (n = 1-32) nanoclusters: A first-principles DFT study

    Science.gov (United States)

    Banerjee, P.; Chandrakumar, K. R. S.; Das, G. P.

    2015-06-01

    Ground state structures and dehydrogenation characteristics of MgnH2n (n = 1-32) nanoclusters have been investigated using first principles DFT approach. Dehydrogenation temperature gets reduced compared to the bulk rutile phase of MgH2, indicating its favorable usage for hydrogen storage.

  12. Hydrogen bond dynamics and vibrational spectral diffusion in aqueous solution of acetone: A first principles molecular dynamics study

    Indian Academy of Sciences (India)

    Bhabani S Mallik; Amalendu Chandra

    2012-01-01

    We present an ab initio molecular dynamics study of vibrational spectral diffusion and hydrogen bond dynamics in aqueous solution of acetone at room temperature. It is found that the frequencies of OD bonds in the acetone hydration shell have a higher stretch frequency than those in the bulk water. Also, on average, the frequencies of hydration shell OD modes are found to increase with increase in the acetone-water hydrogen bond distance. The vibrational spectral diffusion of the hydration shell water molecules reveals three time scales: A short-time relaxation (∼80 fs) corresponding to the dynamics of intact acetone-water hydrogen bonds, a slower relaxation (∼1.3 ps) corresponding to the lifetime of acetone-water hydrogen bonds and another longer time constant (∼12 ps) corresponding to the escape dynamics of water from the solute hydration shell. The present first principles results are compared with those of available experiments and classical simulations.

  13. Interaction of tetraethoxysilane with OH-terminated SiO2 (0 0 1) surface: A first principles study

    Science.gov (United States)

    Deng, Xiaodi; Song, Yixu; Li, Jinchun; Pu, Yikang

    2014-06-01

    First principles calculates have been performed to investigate the surface reaction mechanism of tetraethoxysilane (TEOS) with fully hydroxylated SiO2(0 0 1) substrate. In semiconductor industry, this is the key step to understand and control the SiO2 film growth in chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes. During the calculation, we proposed a model which breaks the surface dissociative chemisorption into two steps and we calculated the activation barriers and thermochemical energies for each step. Our calculation result for step one shows that the first half reaction is thermodynamically favorable. For the second half reaction, we systematically studied the two potential reaction pathways. The comparing result indicates that the pathway which is more energetically favorable will lead to formation of crystalline SiO2 films while the other will lead to formation of disordered SiO2 films.

  14. First-principles study of the local structure and crystal field of Yb2+ in sodium and potassium halides

    Institute of Scientific and Technical Information of China (English)

    Wen Jun; Duan Chang-Kui; Yin Min; Yu.V.Orlovskii; Xia Shang-Da; Zhang Yong-Fan

    2012-01-01

    The local coordination structures around the doping Yb2+ ions in sodium and potassium halides were calculated by using the first-principles supercell model.Both the cases with and without the charge compensation vacancy in the local environment of the doping Yb2+ were calculated to study the effect of the doping on the local coordination structures of Yb2+.Using the calculated local structures,we obtained the crystal-field parameters for the Yb2+ ions doped in sodium and potassium halides by a method based on the combination of the quantum-chemical calculations and the effective Hamiltonian method.The calculated crystal-field parameters were analyzed and compared with the fitted results.

  15. First-principles study of structural stability and elastic property of pre-perovskite PbTiO3

    Institute of Scientific and Technical Information of China (English)

    Liu Yong; Ni Li-Hong; Ren Zhao-Hui; Xu Gang; Li Xiang; Song Chen-Lu; Han Gao-Rong

    2012-01-01

    The structural stability and the elastic properties of a novel structure of lead titanate,which is named preperovskite PbTiO3 (PP-PTO) and is constructed with TiO6 octahedral columns arranged in a one-dimensional manner,are investigated by using first-principles calculations.PP-PTO is energetically unstable compared with conventional perovskite phases,however it is mechanically stable. The equilibrium transition pressures for changing from preperovskite to cubic and tetragonal phases are -0.5 GPa and -1.4 GPa,respectively,with first-order characteristics.Further,the differences in elastic properties between pre-perovskite and conventional perovskite phases are discussed for the covalent bonding network,which shows a highly anisotropic character in PP-PTO.This study provides a crucial insight into the structural stabilities of PP-PTO and conventional perovskite.

  16. Al embedded MgO barrier MTJ: A first principle study for application in fast and compact STT-MRAMs

    Science.gov (United States)

    Yadav, Manoj Kumar; Gupta, Santosh Kumar; Rai, Sanjeev; Pandey, Avinash C.

    2017-03-01

    The first principle comparative study of a novel single Al sheet embedded MgO and pure MgO barrier having Fe electrodes magnetic tunnel junction has been presented. Al embedded MgO is reported to provide enhanced spin polarised tunnelling current due to increase of spin-polarized density of states at Fermi energy in the barrier region. This novel MTJ provides a current density and resistance area (RA) product of 94.497 ×107 A / cm2 and 0.105  Ω - μm2 respectively. With such a low RA product; it allows higher deriving current due to which switching time of magnetization reversal reduces without inducing barrier related breakdowns in non-volatile magnetic random access memories. The low RA product and high current density of the proposed MTJ may have possible applications in integration with existing MOS circuits.

  17. a First-Principles Theoretical Study of Microstructural Deformations of Solids

    Science.gov (United States)

    Juan, Yumin

    1995-01-01

    The development of density functional theory (DFT) and advances in computational capabilities have made it possible to obtain reliable information on the energetics of structural transformations in solids. However, limitations do exist due to the use of the local density approximations (LDA) to the exchange-correlation functionals. Recently, there have been efforts to try to go beyond LDA by including gradient corrections, which are referred to as the generalized gradient approximation (GGA). To obtain an accurate assessment of these GGA functionals, we investigated in detail the applicability of two recently proposed functionals. The effects on the atomic charge distribution were studied. We also examined different approaches to construct pseudopotentials self-consistently in the context of gradient-corrected functionals. We concluded that although GGA functional produce improved results in some cases, in general LDA remains a reliable choice for the energetic calculations in solids. We considered a range of phenomena related to structural transformations of a prototypical covalent solid, namely silicon. We first studied the energetics for the high-pressure plastic flow of silicon by performing DFT total energy calculations for structural transformations which might correspond to mass flow. To explore the phase space efficiently, the magic strain concept was used. Entropy effects were taken into account with the use of Vineyard's transition state theory. An upper bound for the energy barrier was obtained from our study and has been found to be lower than the melting point of silicon, suggesting that such transformations may be possible under indentation. As a second application, we have obtained accurate generalized stacking fault (GSF) energy surfaces for both the (111) and (100) planes of silicon with first-principles calculations. The importance of this GSF energy surface is that it can be used to identify the value of the unstable stacking fault energy gamma

  18. A first-principles study of hydrogen interaction and saturation on ScAl{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Samolia, Madhu [Department of Chemistry, Indian Institute of Technology Ropar, Rupnagar 140001 (India); Dhilip Kumar, T.J., E-mail: dhilip@iitrpr.ac.in [Department of Chemistry, Indian Institute of Technology Ropar, Rupnagar 140001 (India)

    2013-03-05

    Graphical abstract: Electrostatic potential superimposed on electron density of H{sub 2}, Al{sub 4} and ScAI{sub 3}. Highlights: ► A first principles calculation on hydrogen interaction and saturation on stable ScAl{sub 3} cluster is performed. ► Sc atom has higher negative charge electron density over Al atom in ScAl{sub 3} from natural bond orbital charge analysis. ► H{sub 2} undergoes dissociative chemisorption on the Sc atop site resulting in Sc–H–AI bridge bond. ► H{sub 2} saturation on Sc site results initially in chemisorption and then physisorption with the maximum loading of 6 molecules resulting in stable ScAl{sub 3}H{sub 12} structure. -- Abstract: Complex metal hydrides are promising hydrogen storage material for mobile applications. The presence of scandium catalysts in complex metal hydrides is found to improve significantly the kinetics of H{sub 2} adsorption and desorption. The exact role of these additives is not completely understood. NMR studies suggests the presence of distorted ScAl{sub 3} phase which is attributed to the enhancement of reversible uptake and release rates of H{sub 2}. In this study, we have investigated the hydrogen interaction and saturation on stable ScAl{sub 3} cluster at various sites using the density functional theory by employing unrestricted B3LYP/6-311++G(d,p) and the GGA-PW91/DNP methods. From natural bond orbital charge analysis and electrostatic potential superimposed on electron density plots, ScAl{sub 3} is found to be more polarized and Sc atom in ScAl{sub 3} cluster has higher negative charge and electron density over Al atoms. H{sub 2} undergoes dissociative chemisorption on the Sc atop site in ScAl{sub 3} resulting in Sc–H–Al bridge structure. The hydrogen saturation is studied by sequential H{sub 2} adsorption on ScAl{sub 3} cluster. In the Sc site, the first H{sub 2} molecule undergoes dissociative chemisorption and further addition results in H{sub 2} physisorption with the maximum loading

  19. Magnetic, elastic and optical properties of zinc peroxide (ZnO{sub 2}): First principles study

    Energy Technology Data Exchange (ETDEWEB)

    Thapa, Ranjit, E-mail: ranjit.t@res.srmuniv.ac.in [SRM Research Institute, SRM University, Kattankulathur 603 203, Tamil Nadu (India); Ghosh, Saurabh, E-mail: sg827@cornell.edu [School of Applied and Engineering Physics, Cornell University, Ithaca, NY (United States); Sinthika, S.; Mathan Kumar, E. [SRM Research Institute, SRM University, Kattankulathur 603 203, Tamil Nadu (India); Park, Noejung [Interdisciplinary School of Green Energy, Ulsan National Institute of Science and Technology, Ulsan 689-798 (Korea, Republic of)

    2015-01-25

    Highlights: • XO{sub 2}{sup 2−} materials have on-site coulomb repulsion for p-electron of oxygen atoms. • The metal vacancy converts XO{sub 2} (peroxide based materials) as “d{sup 0} magnet”. • Mechanical stability and hardness of pure, Zn and O-vacant ZnO{sub 2}. • Zn vacancies tune the optical properties of ZnO{sub 2}, indicates applications in wide area. - Abstract: Using first principles method we elaborately discuss the magnetic, elastic and optical properties of pure, Zn and O vacant ZnO{sub 2}. It is found that the electronic structure and band gap of ZnO{sub 2} is not sensitive to the active on-site Coulomb interaction term U{sub d}, but found to be depending on the term U{sub p}. The role of orbitals subject to the correlation is thus completely opposite for the case of ZnO{sub 2} in respect of ZnO. Interestingly, the Zn vacancy converts ZnO{sub 2} as “d{sup 0} magnet”. Indeed, our analysis show that, Zn vacancy transmuted O{sub 2}{sup 2−} state into O{sub 2}{sup δ+2−} state, indicating the partially filled π{sup ∗} states are the governing reason for the d{sup 0} magnetism. Both HSE06 and PBE0 functional confirm the same. The similar phenomena has been observed for other peroxide materials XO{sub 2} (X = Mg, Ca, Sr, Ba) studied here. Our results suggest that this class of materials can be studied further to exploit its potential in spintronic devices. Further the elastic properties have been estimated for pure ZnO{sub 2} at different pressures and for Zn and O vacant ZnO{sub 2} to know the stability of the system. Zn vacancy in ZnO{sub 2} also tunes optical properties, indicating its potential application in other areas.

  20. Study on the electronic structure and the optical performance of YB6 by the first-principles calculations

    Directory of Open Access Journals (Sweden)

    Lihua Xiao

    2011-06-01

    Full Text Available The electronic structure and the optical performance of YB6 were investigated by first-principles calculations within the framework of density functional theory. It was found that the calculated results are in agreement with the relevant experimental data. Our theoretical studies showed that YB6 is a promising solar radiation shielding material for windows.

  1. 5,6-dihydroxyindole-2-carboxylic acid (DHICA): a First Principles Density-Functional Study

    CERN Document Server

    Powell, B J

    2016-01-01

    We report first principles density functional calculations for 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and several reduced forms. DHICA and 5,6-dihydroxyindole (DHI) are believed to be the basic building blocks of the eumelanins. Our results show that carboxylation has a significant effect on the physical properties of the molecules. In particular, the relative stabilities and the HOMO-LUMO gaps (calculated with the $\\Delta$SCF method) of the various redox forms are strongly affected. We predict that, in contrast to DHI, the density of unpaired electrons, and hence the ESR signal, in DHICA is negligibly small.

  2. Effect of curvature on structures and vibrations of zigzag carbon nanotubes: A first-principles study

    Indian Academy of Sciences (India)

    Mousumi Upadhyay Kahaly; Umesh V Waghmare

    2008-06-01

    First-principles pseudopotential-based density functional theory calculations of atomic and electronic structures, full phonon dispersions and thermal properties of zigzag single wall carbon nanotubes (SWCNTs) are presented. By determining the correlation between vibrational modes of a graphene sheet and of the nanotube, we understand how rolling of the sheet results in mixing between modes and changes in vibrational spectrum of graphene. We find that the radial breathing mode softens with decreasing curvature. We estimate thermal expansion coefficient of nanotubes within a quasiharmonic approximation and identify the modes that dominate thermal expansion of some of these SWCNTs both at low and high temperatures.

  3. First-principle study on the electronic structure of stressed CrSi2

    Institute of Scientific and Technical Information of China (English)

    ZHOU ShiYun; XIE Quan; YAN WanJun; CHEN Qian

    2009-01-01

    The electronic structure of stressed CrSi2 was calculated using the first-principle methods based on plane-wave pseudo-potential theory. The calculated results showed that, under the uniaxial compres-sion, the energy level of CrSi2 shifted toward high energy and its energy gap became wider with the increasing uniaxial stress, while the gap became narrower under the negative uniaxial stress. When the negative uniaxial stress was up to -18.5 Gpa, CrSi2 was converted into a direct-gap semiconductor with the band gap of 0.32 eV.

  4. First-principle study on the electronic structure of stressed CrSi2

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The electronic structure of stressed CrSi2 was calculated using the first-principle methods based on plane-wave pseudo-potential theory. The calculated results showed that, under the uniaxial compression, the energy level of CrSi2 shifted toward high energy and its energy gap became wider with the increasing uniaxial stress, while the gap became narrower under the negative uniaxial stress. When the negative uniaxial stress was up to -18.5 GPa, CrSi2 was converted into a direct-gap semiconductor with the band gap of 0.32 eV.

  5. First principles study of structural, electronic and mechanical properties of alkali nitride-KN

    Energy Technology Data Exchange (ETDEWEB)

    Murugan, A.; Rajeswarapalanichamy, R., E-mail: rrpalanichamy@gmail.com; Santhosh, M. [Department of Physics, N.M.S.S.V.N college, Madurai, Tamilnadu-625019 (India); Iyakutti, K. [Department of Physics and Nanotechnology, SRM University, Chennai, Tamilnadu-603203 (India)

    2015-06-24

    The structural, electronic and elastic properties of alkali- metal nitride (KN) is investigated by the first principles calculations based on density functional theory as implemented in Vienna ab-initio simulation package. At ambient pressure KN is stable in the ferromagnetic state with NaCl structure. The calculated lattice parameters are in good agreement with the available results. The electronic structure reveals that the KN is half metallic ferromagnet at normal pressure. A pressure-induced structural phase transition from NaCl to ZB phase is observed in KN. Half metallicity and ferromagnetism is maintained at all pressures.

  6. Structural phase transition and elastic properties of hafnium dihydride: A first principles study

    Energy Technology Data Exchange (ETDEWEB)

    Santhosh, M., E-mail: rrpalanichamy@gmail.com; Rajeswarapalanichamy, R., E-mail: rrpalanichamy@gmail.com; Sudhapriyanga, G.; Murugan, A.; Chinthia, A. Jemmy [Department of Physics, N.M.S.S.V.N College, Madurai, Tamil Nadu-625019 (India); Kanagaprabha, S. [Department of Physics, Kamaraj College, Tuticorin, Tamil Nadu-628003 (India); Iyakutti, K. [Department of Physics and Nanotechnology, SRM University, Chennai, Tamil Nadu-603203 (India)

    2014-04-24

    The structural and elastic properties of Hafnium dihydride (HfH{sub 2}) are investigated by first principles calculation based on density functional theory using Vienna ab-initio simulation package (VASP). The calculated lattice parameters are in good agreement with the available results. A pressure induced structural phase transition from CaF{sub 2} to FeS{sub 2} phase is observed in HfH{sub 2} at 10.75 GPa. The calculated elastic constants indicate that this hydride is mechanically stable at ambient condition.

  7. Half metallic ferromagnetism in alkali metal nitrides MN (M = Rb, Cs): A first principles study

    Energy Technology Data Exchange (ETDEWEB)

    Murugan, A., E-mail: rrpalanichamy@gmail.com; Rajeswarapalanichamy, R., E-mail: rrpalanichamy@gmail.com; Santhosh, M., E-mail: rrpalanichamy@gmail.com; Sudhapriyanga, G., E-mail: rrpalanichamy@gmail.com [Department of Physics, N.M.S.S.V.N College, Madurai, Tamilnadu-625019 (India); Kanagaprabha, S. [Department of Physics, Kamaraj College, Tuticorin, Tamil Nadu-628003 (India)

    2014-04-24

    The structural, electronic and elastic properties of two alkali metal nitrides (MN: M= Rb, Cs) are investigated by the first principles calculations based on density functional theory using the Vienna ab-initio simulation package. At ambient pressure the two nitrides are stable in ferromagnetic state with CsCl structure. The calculated lattice parameters are in good agreement with the available results. The electronic structure reveals that these materials are half metallic in nature. A pressure-induced structural phase transition from CsCl to ZB phase is observed in RbN and CsN.

  8. Molecular adsorption study of nicotine and caffeine on single-walled carbon nanotubes from first principles

    Science.gov (United States)

    Lee, Hyung-June; Kim, Gunn; Kwon, Young-Kyun

    2013-08-01

    Using first-principles calculations, we investigate the electronic structures and binding properties of nicotine and caffeine adsorbed on single-walled carbon nanotubes to determine whether CNTs are appropriate for filtering or sensing nicotine and caffeine molecules. We find that caffeine adsorbs more strongly than nicotine. The different binding characteristics are discussed by analyzing the modification of the electronic structure of the molecule-adsorbed CNTs. We also calculate the quantum conductance of the CNTs in the presence of nicotine or caffeine adsorbates and demonstrate that the influence of caffeine is stronger than nicotine on the conductance of the host CNT.

  9. First-principles study on bottom-up fabrication process of atomically precise graphene nanoribbons

    Science.gov (United States)

    Kaneko, Tomoaki; Tajima, Nobuo; Ohno, Takahisa

    2016-06-01

    We investigate the energetics of a polyanthracene formation in the bottom-up fabrication of atomically precise graphene nanoribbons on Au(111) using first-principles calculations based on the density functional theory. We show that the structure of precursor molecules plays a decisive role in the C-C coupling reaction. The reaction energy of the dimerization of anthracene dimers is a larger negative value than that of the dimerization of anthracene monomers, suggesting that the precursor molecule used in experiments has a favorable structure for graphene nanoribbon fabrication.

  10. First-principle study of Mg adsorption on Si(111) surfaces

    Institute of Scientific and Technical Information of China (English)

    Ying Min-Ju; Zhang Ping; Du Xiao-Long

    2009-01-01

    We have carried out first-principle calculations of Mg adsorption on Si(111) surfaces. Different adsorption sites and coverage effects have been considered. We found that the threefold hollow adsorption is energy-favoured in each coverage considered, while for the clean Si(111) surface of metallic feature, we found that 0.25 and 0.5 ML Mg adsorption leads to a semiconducting surface. The results for the electronic behaviour suggest a polarized covalent bonding between the Mg adatom and Si(111) surface.

  11. First-Principles Study on Electronic Structures and Optical Properties of Doped Ag Crystal

    Institute of Scientific and Technical Information of China (English)

    CAO Can; CHEN Ling-Na; JIA Shu-Ting; ZHANG Dan; XU Hui

    2012-01-01

    By using the first-principles calculation based on density functional theory,we investigate the electronic structures and optical properties of Cl-doped Ag crystal. The results show that the electronic structure of Cl-doped Ag crystal depends on the doped concentration and the site of impurity defect.Interestingly,the calculated adsorption spectra of Cl-doped Ag crystal show isotropy or anisotropy coincide with the symmetry of Ag crystal. These features are discussed to provide guidance to experimental efforts for Ag-based nanoeletronic devices.

  12. First-principles study of hydrogen storage on Li12F12 nano-cage

    Science.gov (United States)

    Zhang, Yafei; Cheng, Xinlu

    2017-03-01

    We use the first-principles calculation based on density functional theory (DFT) to investigate the hydrogen storage on Li12F12 nano-cage. Our result indicates the largest hydrogen gravimetric density is 7.14 wt% and this is higher than the 2017 target from the US department of energy (DOE). Meanwhile, the average adsorption energy is -0.161 eV/H2, which is desirable for absorbing and desorbing H2 molecules at near ambient conditions. These findings will have important implications on designing hydrogen storage materials in the future.

  13. First-principles study of water adsorption on α-SiO2 [110] surface

    Directory of Open Access Journals (Sweden)

    Venu Mankad

    2016-08-01

    Full Text Available We have investigated the structural and electronic properties of water molecule adsorbed silicon dioxide (α-SiO2 [110] surface and analyzed the influence of water molecule on its energetics, structure and elctronic propertes using density functional theory based first principles calculations. The inhomogeneous topology of the α-SiO2 clean surface promotes a total charge density displacement on the adsorbed water molecule and giving rise to electron-rich as well as hole-rich region. The electronic charge transfer from a α-SiO2 to the water molecule occurs upon the formation of a partially occupied level laying above conduction band level.

  14. First-principles calculations, experimental study, and thermodynamic modeling of the Al-Co-Cr system.

    Directory of Open Access Journals (Sweden)

    Xuan L Liu

    Full Text Available The phase relations and thermodynamic properties of the condensed Al-Co-Cr ternary alloy system are investigated using first-principles calculations based on density functional theory (DFT and phase-equilibria experiments that led to X-ray diffraction (XRD and electron probe micro-analysis (EPMA measurements. A thermodynamic description is developed by means of the calculations of phase diagrams (CALPHAD method using experimental and computational data from the present work and the literature. Emphasis is placed on modeling the bcc-A2, B2, fcc-γ, and tetragonal-σ phases in the temperature range of 1173 to 1623 K. Liquid, bcc-A2 and fcc-γ phases are modeled using substitutional solution descriptions. First-principles special quasirandom structures (SQS calculations predict a large bcc-A2 (disordered/B2 (ordered miscibility gap, in agreement with experiments. A partitioning model is then used for the A2/B2 phase to effectively describe the order-disorder transitions. The critically assessed thermodynamic description describes all phase equilibria data well. A2/B2 transitions are also shown to agree well with previous experimental findings.

  15. Insight into the Dzyaloshinskii-Moriya interaction through first-principles study of chiral magnetic structures

    Science.gov (United States)

    Sandratskii, L. M.

    2017-07-01

    The purpose of the paper is to gain deeper insight into microscopic formation of the Dzyaloshinskii-Moriya interaction (DMI). The paper aims at the development of the physical picture able to address apparently contradicting conclusions of recent studies concerning the location of the DMI energy in the real and reciprocal spaces as well as the relation between values of the atomic moments and the DMI strength. The main tools of our study are the first-principles calculations of the energies of the spiral magnetic states with opposite chiralities. We suggest a method of the calculation of the spiral structures with account for the spin-orbit coupling (SOC). It is based on the application of the generalized Bloch theorem and generalized Bloch functions and allows to reduce the consideration of arbitrary incommensurate spiral to small chemical unit cell. The method neglects the anisotropy in the plane orthogonal to the rotation axis of the spirals that does not influence importantly the DMI energy. For comparison, the supercell calculation with full account for the SOC is performed. The concrete calculations are performed for the Co/Pt bilayer. We consider the distribution of the DMI energy in both real and reciprocal spaces and the dependence of the DMI on the number of electrons. The results of the calculations reveal a number of energy compensations in the formation of the DMI. Thus, the partial atomic contributions as functions of the spiral wave vector q are nonmonotonic and have strongly varying slopes. However, in the total DMI energy these atom-related features compensate each other, resulting in a smooth q dependence. The reason for the peculiar form of the partial DMI contributions is a q -dependent difference in the charge distribution between q and -q spirals. The strongly q -dependent relation between atomic contributions shows that the real-space distribution of the DMI energy obtained for a selected q value cannot be considered as a general

  16. First-principles study of the nickel–silicon binary compounds under pressure

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Yuhong, E-mail: zyh388@sina.com [College of Materials Science and Engineering, North University of China, Taiyuan 030051 (China); Hou, Hua [College of Materials Science and Engineering, North University of China, Taiyuan 030051 (China); Zhao, Yuhui [Department of Mechanical and Electronic Engineering, Hebei College of Industry and Technology, Shijiazhuang 050091 (China); Han, Peide [College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024 (China)

    2015-08-15

    Highlights: • The structural and elastic properties of Ni–Si system under pressure are firstly studied. • The lattice parameters of NiSi{sub 2} are the most sensitive to external pressure change. • Ni{sub 3}Si, Ni{sub 31}Si{sub 12}, Ni{sub 2}Si (δ) and Ni{sub 3}Si{sub 2} are mechanical stability with pressure up to 50 GPa. • The hardness of the four compounds can be improved by increasing pressure. • Electronic structures are analyzed to understand pressure effect on the seven compounds. - Abstract: The effects of high pressure on structural, stable, elastic, thermodynamic properties and electronic structures of Ni–Si binary compounds (i.e. β-Ni{sub 3}Si, γ-Ni{sub 31}Si{sub 12}, δ-Ni{sub 2}Si, θ-Ni{sub 2}Si, ε-Ni{sub 3}Si{sub 2}, ε-NiSi and α-NiSi{sub 2}) have been firstly studied by first-principles calculation based on density functional theory method within generalized gradient approximation. The calculated lattice parameters of the seven compounds at zero pressure and zero temperature agree well with the available experimental values and previous theoretical data. The values of V/V{sub 0} decrease with pressure going up to 50 GPa and the rate of change decrease gradually. The lattice parameters of NiSi{sub 2} are the most sensitive to external pressure change. Ni{sub 3}Si, Ni{sub 31}Si{sub 12}, Ni{sub 2}Si (δ) and Ni{sub 3}Si{sub 2} are mechanical stability by estimating stability criteria with pressure ranging from 0 to 50 GPa. But Ni{sub 2}Si (θ), NiSi and NiSi{sub 2} are not mechanically stable with pressure up to 10, 40 and 30 GPa, respectively. The calculated results of bulk modulus B, shear modulus G and Young’s modulus E illustrate pressure can improve the hardness of Ni{sub 3}Si, Ni{sub 31}Si{sub 12}, Ni{sub 2}Si (δ) and Ni{sub 3}Si{sub 2} compounds. In addition, ratio of shear modulus to bulk modulus G/B shows that all the considered compounds are ductile materials except NiSi. The Debye temperature Θ{sub D} of Ni{sub 3}Si

  17. Fuzzy clustering, genetic algorithms and neuro-fuzzy methods compared for hybrid fuzzy-first principles modeling

    NARCIS (Netherlands)

    van Lith, Pascal; van Lith, P.F.; Betlem, Bernardus H.L.; Roffel, B.

    2002-01-01

    Hybrid fuzzy-first principles models can be a good alternative if a complete physical model is difficult to derive. These hybrid models consist of a framework of dynamic mass and energy balances, supplemented by fuzzy submodels describing additional equations, such as mass transformation and

  18. Fuzzy Clustering, Genetic Algorithms and Neuro-Fuzzy Methods Compared for Hybrid Fuzzy-First Principles Modeling

    NARCIS (Netherlands)

    Lith, Pascal F. van; Betlem, Ben H.L.; Roffel, Brian

    2002-01-01

    Hybrid fuzzy-first principles models can be a good alternative if a complete physical model is difficult to derive. These hybrid models consist of a framework of dynamic mass and energy balances, supplemented by fuzzy submodels describing additional equations, such as mass transformation and

  19. Fuzzy Clustering, Genetic Algorithms and Neuro-Fuzzy Methods Compared for Hybrid Fuzzy-First Principles Modeling

    NARCIS (Netherlands)

    Lith, Pascal F. van; Betlem, Ben H.L.; Roffel, Brian

    2002-01-01

    Hybrid fuzzy-first principles models can be a good alternative if a complete physical model is difficult to derive. These hybrid models consist of a framework of dynamic mass and energy balances, supplemented by fuzzy submodels describing additional equations, such as mass transformation and transfe

  20. Fuzzy Clustering, Genetic Algorithms and Neuro-Fuzzy Methods Compared for Hybrid Fuzzy-First Principles Modeling

    NARCIS (Netherlands)

    Lith, Pascal F. van; Betlem, Ben H.L.; Roffel, Brian

    2002-01-01

    Hybrid fuzzy-first principles models can be a good alternative if a complete physical model is difficult to derive. These hybrid models consist of a framework of dynamic mass and energy balances, supplemented by fuzzy submodels describing additional equations, such as mass transformation and transfe

  1. Charge Carrier Trapping at Surface Defects of Perovskite Solar Cell Absorbers: A First-Principles Study.

    Science.gov (United States)

    Uratani, Hiroki; Yamashita, Koichi

    2017-02-16

    The trapping of charge carriers at defects on surfaces or grain boundaries is detrimental for the performance of perovskite solar cells (PSCs). For example, it is the main limiting factor for carrier lifetime. Moreover, it causes hysteresis in the current-voltage curves, which is considered to be a serious issue for PSCs' operation. In this work, types of surface defects responsible for carrier trapping are clarified by a comprehensive first-principles investigation into surface defects of tetragonal CH3NH3PbI3 (MAPbI3). Considering defect formation energetics, it is proposed that a Pb-rich condition is preferred to an I-rich one; however, a moderate condition might possibly be the best choice. Our result paves the way for improving the performance of PSCs through a rational strategy of suppressing carrier trapping at surface defects.

  2. First principles study on the structural, electronic, and elastic properties of Na-As systems

    Science.gov (United States)

    Ozisik, H. B.; Colakoglu, K.; Deligoz, E.; Ozisik, H.

    2011-10-01

    We have performed the first principles calculation by using the plane-wave pseudopotential approach with the generalized gradient approximation for investigating the structural, electronic, and elastic properties Na-As systems (NaAs in NaP, LiAs and AuCu-type structures, NaAs 2 in MgCu 2-type structure, Na 3As in Na 3As, Cu 3P and Li 3Bi-type structures, and Na 5As 4 in A 5B 4-type structure). The lattice parameters, cohesive energy, formation energy, bulk modulus, and the first derivative of bulk modulus (to fit to Murnaghan's equation of state) of the related structures are calculated. The second-order elastic constants and the other related quantities such as Young's modulus, shear modulus, Poisson's ratio, sound velocities, and Debye temperature are also estimated.

  3. First-principles study on the elastic properties of Cu2GeSe3

    Science.gov (United States)

    Shao, Hezhu; Tan, Xiaojian; Jiang, Jun; Jiang, Haochuan

    2016-01-01

    The elastic properties of Cu2GeSe3, including bulk modulus, shear modulus, Young's modulus, Possion's ratio, and their anisotropic properties, have been investigated by using first-principles calculations. The calculated lattice parameters are in good agreement with previous calculations and experimental measurements. The result of bulk modulus by fitting the Birch-Murnaghan 3rd-order equation of state is well consistent with that calculated from the elastic constants. The ductile nature of Cu2GeSe3 is characterized according to Pugh's rule. The Debye temperature calculated from fitting heat capacity data is consistent with that obtained from sound velocity. Additionally, the elastic anisotropy is depicted in detail by plotting the directional dependence of the bulk and Young's moduli.

  4. Pressure-induced phase transition for ScVO{sub 4}: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Sheng, Shu-Fang, E-mail: shengshf@gmail.com [School of Physical Science and Information Engineering, Liaocheng University, Liaocheng 252059 (China); Shandong Provincial Key Laboratory of Optical Communication Science and Technology, Liaocheng 252059 (China)

    2013-10-01

    We theoretically investigated the structural stability and electronic properties of ScVO{sub 4} by the first-principles pseudopotential method. The tetragonal zircon-type and scheelite-type structures, LaTaO{sub 4}-type structure of ScVO{sub 4} have been considered. The calculations indicate that the LaTaO{sub 4}-type phase is not stable in the pressure 0–100 GPa, and the structural phase transformation from zircon to scheelite-type structure occurs at 5.4 GPa. The band structure shows that zircon-type structure at zero pressure and scheelite-type structure at transition pressure have direct gaps of 2.58 eV and 2.35 eV, respectively. The detailed volume changes during the phase transition were analyzed.

  5. The Interface between Gd and Monolayer MoS2: A First-Principles Study

    KAUST Repository

    Zhang, Xuejing

    2014-12-08

    We analyze the electronic structure of interfaces between two-, four- and six-layer Gd(0001) and monolayer MoS2 by first-principles calculations. Strong chemical bonds shift the Fermi energy of MoS2 upwards into the conduction band. At the surface and interface the Gd f states shift to lower energy and new surface/interface Gd d states appear at the Fermi energy, which are strongly hybridized with the Mo 4d states and thus lead to a high spin-polarization (ferromagnetically ordered Mo magnetic moments of 0.15 μB). Gd therefore is an interesting candidate for spin injection into monolayer MoS2.

  6. A novel anion interstitial defect structure in zinc-blende materials: A first-principles study

    Science.gov (United States)

    Yin, Yuan; Chen, Guangde; Ye, Honggang; Duan, Xiangyang; Zhu, Youzhang; Wu, Yelong

    2016-05-01

    The low-formation energy structure of anion interstitial defect in zinc-blende materials is usually identified as the tetrahedron central structure where the anion interstitial atom is surrounded by four countercation atoms. A line-type anion interstitial defect structure AD_il , however, is found to be lower in energy than the tetrahedron central anion interstitial defect structure by first-principles calculations. By analyzing the structural and electronical characters of this line-type defect in relative compounds of zinc-blende materials, we attribute this to the electronegativity shift trends and the bond forming, which lead to the hybridization types varying from sp 3 to sp-like and ending at sp.

  7. Structural, electronic and mechanical properties of rare earth nitride-ErN: A first principles study

    Energy Technology Data Exchange (ETDEWEB)

    Murugan, A.; Rajeswarapalanichamy, R., E-mail: rajeswarapalanichamy@gmail.com; Santhosh, M.; Priyanga, G. Sudha [Department of physics, N.M.S.S.V.N college, Madurai, Tamilnadu-625019 (India); Kanagaprabha, S. [Department of Physics, Kamaraj College, Tuticorin, Tamil Nadu 628 003 (India); Iyakutti, K. [Department of Physics and Nanotechnology, SRM University, Chennai, Tamilnadu-603203 (India)

    2015-06-24

    The structural, electronic and mechanical properties of rare earth nitride ErN is investigated by the first principles calculations based on density functional theory using the Vienna ab-initio simulation package. At ambient pressure ErN is stable in the ferromagnetic state with NaCl structure. The calculated lattice parameters are in good agreement with the available results. The electronic structure reveals that ErN is half metallic at normal pressure. A pressure-induced structural phase transition from NaCl (B1) to CsCl (B2) phase is observed in ErN. Ferromagnetic to non magnetic phase transition is predicted in ErN at high pressure.

  8. First-principles study of the noble metal-doped BN layer

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Yungang; Yang, Ping; Sun, Xin; Wang, Zhiguo; Zu, Xiaotao T.; Gao, Fei

    2011-04-18

    Intriguing electronic and magnetic properties of BN layer with noble metal (Pd, Pt, Ag and Au) doping are obtained by first-principles calculations. Adsorbed Pd (or Pt) reduces the band gap of BN sheet owing to the induction of impurity states. The unpaired electrons in the Ag (or Au)-adsorbed and the Pd (or Pt)-substituted BN layers are polarized, and thus exhibit a magnetic moment of 1.0 µB, leading to these BN configurations to be magnetic semiconductors. The half-metallic feature of the Ag-substituted BN layer, along with the delocalization of spin states, renders this configuration an excellent spin filter material. Thus, these findings offer a unique opportunity for developing BN-based nanoscale devices.

  9. First-principles molecular dynamics study of proton transfer mechanism in bovine cytochrome c oxidase

    Energy Technology Data Exchange (ETDEWEB)

    Kamiya, Katsumasa [Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577 (Japan); Boero, Mauro [Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577 (Japan); Tateno, Masaru [Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577 (Japan); Shiraishi, Kenji [CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan); Oshiyama, Atsushi [Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577 (Japan)

    2007-09-12

    Density functional based first-principles molecular dynamics calculations, performed on a model system extracted from the bovine cytochrome c oxidase, have been performed in an attempt to inspect the proton transfer mechanism across a peptide group. Our model system includes the specific Tyr440-Ser441 peptide group involved in a novel proton transfer path and shows that the Y440-S441 enol peptide group [-C(OH) = N-], which is a structural isomer of a keto form [-CO-NH-], is the product of the deprotonation of an imidic acid [-C(OH)-NH-] occurring in the vicinity of the deprotonated aspartic acid residue. For the subsequent enol-to-keto tautomerization, a direct H{sup +} transfer path in the Y440-S441 peptide group has been identified, in which the transition state takes a distorted four-membered ring structure.

  10. First-Principles Studies on Properties of Boron-Related Impurities in c-BN

    Institute of Scientific and Technical Information of China (English)

    TIAN Fu-Bo; WANG Xiao-Li; MA Yan-Ming; CUI Tian; LIU Bing-Bing; ZOU Guang-Tian

    2009-01-01

    We investigate,by first-principles calculations,the pressure dependence of formation enthalpies and defective geometry and bulk modulus of boron-related impurities (VB,CB,NB,and OB ) with different charged states in cubic boron nitride (c-BN) using a supercell approach.It is found that the nitrogen atoms surrounding the defect relax inward in the case of CB,while the nitrogen atoms relax outward in the other cases.These boron-related impurities become much more stable and have larger concentration with increasing pressure.The impurity C+B1 is found to have the lowest formation enthalpy,make the material exhibit semiconductor characters and have the bulk modulus higher than ideal c-BN and than those in the cases of other impurities.Our results suggest that the hardness of c-BN may be strengthened when a carbon atom substitutes at a B site.

  11. Tailoring graphene magnetism by zigzag triangular holes: A first-principles thermodynamics study

    Directory of Open Access Journals (Sweden)

    Muhammad Ejaz Khan

    2016-03-01

    Full Text Available We discuss the thermodynamic stability and magnetic property of zigzag triangular holes (ZTHs in graphene based on the results of first-principles density functional theory calculations. We find that ZTHs with hydrogen-passivated edges in mixed sp2/sp3 configurations (z211 could be readily available at experimental thermodynamic conditions, but ZTHs with 100% sp2 hydrogen-passivation (z1 could be limitedly available at high temperature and ultra-high vacuum conditions. Graphene magnetization near the ZTHs strongly depends on the type and the size of the triangles. While metallic z1 ZTHs exhibit characteristic edge magnetism due to the same-sublattice engineering, semiconducting z211 ZTHs do show characteristic corner magnetism when the size is small <2 nm. Our findings could be useful for experimentally tailoring metal-free carbon magnetism by simply fabricating triangular holes in graphene.

  12. Detection of nucleic acids by graphene-based devices: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Hua [School of Physics and Electronics, Central South University, Changsha 410083 (China); School of Physics and Electronic Science, Changsha University of Science and Technology, Changsha 410114 (China); Xu, Hui, E-mail: xuhui@csu.edu.cn, E-mail: ouyangfp06@tsinghua.org.cn; Ni, Xiang; Lin Peng, Sheng; Liu, Qi; Ping OuYang, Fang, E-mail: xuhui@csu.edu.cn, E-mail: ouyangfp06@tsinghua.org.cn [School of Physics and Electronics, Central South University, Changsha 410083 (China)

    2014-04-07

    Based on first-principles quantum transport calculations, we design a graphene-based biosensor device, which is composed of graphene nanoribbons electrodes and a biomolecule. It is found that when different nucleobases or poly nucleobase chains are located in the nanogap, the device presents completely different transport properties, showing different current informations. And the change of currents from 2 to 5 orders of magnitude for four different nucleobases suggests a great ability of discrimination by utilizing such a device. The physical mechanism of this phenomenon originates from their different chemical composition and structure. Moreover, we also explore the coupling effect of several neighboring bases and the size effect of the nanogap on transport properties. Our results show the possibility of rapid sequencing DNA by measuring such a transverse-current of the device, and provide a new idea for sequencing DNA.

  13. First principles molecular dynamics study of nitrogen vacancy complexes in boronitrene.

    Science.gov (United States)

    Ukpong, A M; Chetty, N

    2012-07-04

    We present the results of first principles molecular dynamics simulations of nitrogen vacancy complexes in monolayer hexagonal boron nitride. The threshold for local structure reconstruction is found to be sensitive to the presence of a substitutional carbon impurity. We show that activated nitrogen dynamics triggers the annihilation of defects in the layer through formation of Stone-Wales-type structures. The lowest energy state of nitrogen vacancy complexes is negatively charged and spin polarized. Using the divacancy complex, we show that their formation induces spontaneous magnetic moments, which is tunable by electron or hole injection. The Fermi level s-resonant defect state is identified as a unique signature of the ground state of the divacancy complex. Due to their ability to enhance structural cohesion, only the divacancy and the nitrogen vacancy carbon-antisite complexes are able to suppress the Fermi level resonant defect state to open a gap between the conduction and valence bands.

  14. First-principles study of Li ion diffusion in LiFePO4

    Science.gov (United States)

    Ouyang, Chuying; Shi, Siqi; Wang, Zhaoxiang; Huang, Xuejie; Chen, Liquan

    2004-03-01

    The diffusion mechanism of Li ions in the olivine LiFePO4 is investigated from first-principles calculations. The energy barriers for possible spatial hopping pathways are calculated with the adiabatic trajectory method. The calculations show that the energy barriers running along the c axis are about 0.6, 1.2, and 1.5 eV for LiFePO4, FePO4, and Li0.5FePO4, respectively. However, the other migration pathways have much higher energy barriers resulting in very low probability of Li-ion migration. This means that the diffusion in LiFePO4 is one dimensional. The one-dimensional diffusion behavior has also been shown with full ab initio molecular dynamics simulation, through which the diffusion behavior is directly observed.

  15. First principles study on the ferroelectricity of the perovskite ABO3 ferroelectrics

    Institute of Scientific and Technical Information of China (English)

    王渊旭; 钟维烈; 王春雷; 张沛霖; 苏绚涛

    2002-01-01

    In order to understand well the different ferroelectric behaviour of quantum paraelectrics and ferroelectrics andthe origin of the ferroelectricity of the solid solution KTa0.5Nb0.5O3(KTN), we calculated the electronic structure ofCaTiO3, BaTiO3 and KTN by first principles calculation. From total energy analysis, it is shown that, with increasingcell volume, the crystals (CaTiO3, SrTiO3) will have a ferroelectric instability. For BaTiO3, the ferroelectricity willdisappear as the cell volume is decreased. From the density of states analysis, it is shown that the hybridization betweenB d and O p is very important for the ferroelectric stability of ABO3 perovskite ferroelectrics. This is consistent withthe analysis of band structure.

  16. Optical property of amorphous semiconductor mercury cadmium telluride from first-principles study

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The structural and optical properties of amorphous semiconductor mercury cadmium telluride (a-MCT) are obtained by the first principles calculations. The total pair distribution functions and the density of states show that the a-MCT has the semiconductor characteristic. The calculated results of dielectric function show that E2 peak of the imaginary of dielectric function for the crystal mercury cadmium telluride abruptly disappears in the amorphous case due to the long-range disorders. And the imaginary of dielectric function of a-MCT shows a large broad peak, which is in agreement with the available results of other amorphous semiconductors. From the linear extrapolation of the curve ωε 2(ω)1/2 versus ω, it can be obtained that the optical energy gap of amorphous semiconductor Hg0.5Cd0.5Te is 0.51±0.05 eV.

  17. First principles study on the hydrophilic and conductive graphene doped with Al atoms.

    Science.gov (United States)

    Jiang, Q G; Ao, Z M; Jiang, Q

    2013-07-14

    The effect of the Al dopant on the dissociative adsorption of a H2O molecule on graphene is investigated using first principles calculations. It is found that doping Al into graphene can facilitate the dissociative adsorption of H2O molecules. The dissociative energy barrier is reduced from 3.609 eV on pristine graphene to 0.456 eV on Al-doped graphene and the reaction releases an energy of 0.413 eV, which indicates a smooth dissociative adsorption on Al-doped graphene at room temperature. In addition, the dissociative adsorption of H2O molecules can convert the Al-doped graphene from hydrophobic to hydrophilic while obtaining conductive graphene with doping concentration higher than 5.56%. This hydrophilic and conductive graphene has potential applications in supercapacitors and biomaterial supports.

  18. First principle study of the electronic structure of hafnium-doped anatase TiO2

    Institute of Scientific and Technical Information of China (English)

    Li Lezhong; Yang Weiqing; DingYingchun; Zhu Xinghua

    2012-01-01

    Crystal structures and electronic structures of hafnium doping anatase TiO2 were calculated by first principles with the plane-wave ultrasoft pseudopotential method based on the density functional theory within the generalized gradient approximation.The calculated results show that the lattice parameters a and c of Hf-doped anatase TiO2 are larger than those of intrinsic TiO2 under the same calculated condition.The calculated band structure and density of states show that the conduction band width of Hf-doped TiO2 is broadened which results in the band gap of Hf-doped being smaller than the band gap of TiO2.

  19. Rational design of Nb-based alloys for hydrogen separation: A first principles study

    Directory of Open Access Journals (Sweden)

    Byungki Ryu

    2013-02-01

    Full Text Available We have investigated the effect of alloying metal elements on hydrogen solubility and mechanical integrity of Nb-based alloys, Nb15M1 (where M = Ca–Zn, Ge, using first principles-based calculations. In general, the chemical interaction between the interstitial H and metal is weakened as the alloying element is changed from an early to a late transition metal, leading to lower H solubility and higher resistance to H embrittlement. This effect becomes more pronounced when a smaller alloying element is used due to stronger elastic interaction between interstitial H and metal atoms. These finding may provide scientific basis for rational design of Nb-based hydrogen separation membranes with tailored H solubility to effectively suppress H embrittlement while maintaining excellent hydrogen permeation rate.

  20. First-principles study of metallic carbon nanotubes with boron/nitrogen co-doping

    Institute of Scientific and Technical Information of China (English)

    Chen Ling-Na; Ma Song-Shan; OuYang Fang-Ping; Xiao Jin; Xu Hui

    2011-01-01

    Using the first-principles calculations, we investigate the electronic band structure and the quantum transport properties of metallic carbon nanotubes (MCNTs) with B/N pair co-doping. The results about formation energy show that the B/N pair co-doping configuration is a most stable structure. We find that the electronic structure and the transport properties are very sensitive to the doping concentration of the B/N pairs in MCNTs, where the energy gaps increase with doping concentration increasing both along the tube axis and around the tube, because the mirror symmetry of MCNT is broken by doping B/N pairs. In addition, we discuss conductance dips of the transmission spectrum of doped MCNTs. These unconventional doping effects could be used to design novel nanoelectronic devices.

  1. First-principles Study on Neutral Nitrogen Impurities in Zinc Oxide

    Institute of Scientific and Technical Information of China (English)

    Ping Li; Sheng-hua Deng; Yi-bao Li; Li Zhang; Guo-hong Liu; Jing Huang

    2012-01-01

    The atomic geometries,electronic structures,and formation energies of neutral nitrogen impurities in ZnO have been investigated by first-principles calculations.The nitrogen impurities are always deep acceptors,thus having no contributions to p-type conductivity.Among all the neutral nitrogen impurities,nitrogen substituting on an oxygen site has the lowest formation energy and the shallowest acceptor level,while nitrogen substituting on a zinc site has the second-lowest formation energy in oxygen-rich conditions.Nitrogen interstitials are unstable at the tetrahedral site and spontaneously relax into a kick-out configuration.Though nitrogen may occupy the octahedral site,the concentrations will be low for the high formation energy.The charge density distributions in various doping cases are discussed,and self-consistent results are obtained.

  2. Electronic properties of graphene nanoribbon doped by boron/nitrogen pair: a first-principles study

    Institute of Scientific and Technical Information of China (English)

    Xiao Jin; Yang Zhi-Xiong; Xie Wei-Tao; Xiao Li-Xin; Xu Hui; OuYang Fang-Ping

    2012-01-01

    By using the first-principles calculations,the electronic properties of graphene nanoribbon (GNR) doped by boron/nitrogen (B/N) bonded pair are investigated. It is found that B/N bonded pair tends to be doped at the edges of GNR and B/N pair doping in GNR is easier to carry out than single B doping and unbonded B/N co-doping in GNR.The electronic structure of GNR doped by B/N pair is very sensitive to doping site besides the ribbon width and chirality. Moreover,B/N pair doping can selectively adjust the energy gap of armchair GNR and can induce the semimetal-semiconductor transmission for zigzag GNR.This fact may lead to a possible method for energy band engineering of GNRs and benefit the design of graphene electronic device.

  3. Pressure-induced phase transition of AgClO4: A first-principles study

    Science.gov (United States)

    Cui, Shouxin; Huang, Lin; Li, Quanyi; Hu, Haiquan; Feng, Wenxia

    2013-07-01

    The high-pressure structural stability of AgClO4 is investigated by using first-principles calculations based on density functional theory (DFT). Our results demonstrate that the pressure-induced phase transformation of AgClO4 is the tetragonal structure (I4¯2m) to the orthorhombic barite-type structure (Pnma) at 3.5 GPa, and then to monoclinic structure (P21/m) at 54 GPa. The calculated electronic band structures indicate that tetragonal AgClO4 has indirect gap of 2.67 eV, barite-type and monoclinic structures at transition pressure have direct gap of 3.11 eV and 4.05 eV, respectively. The electron density difference indicates that there exist ionic interaction between these atoms. Based on the value of B/G ratio, tetragonal structure of AgClO4 is predicted to be ductile.

  4. Experimental and first-principles study of ferromagnetism in Mn-doped zinc stannate nanowires

    KAUST Repository

    Deng, Rui

    2013-07-17

    Room temperature ferromagnetism was observed in Mn-doped zinc stannate (ZTO:Mn) nanowires, which were prepared by chemical vapor transport. Structural and magnetic properties and Mn chemical states of ZTO:Mn nanowires were investigated by X-ray diffraction, superconducting quantum interference device (SQUID) magnetometry and X-ray photoelectron spectroscopy. Manganese predominantly existed as Mn2+ and substituted for Zn (Mn Zn) in ZTO:Mn. This conclusion was supported by first-principles calculations. MnZn in ZTO:Mn had a lower formation energy than that of Mn substituted for Sn (MnSn). The nearest neighbor MnZn in ZTO stabilized ferromagnetic coupling. This observation supported the experimental results. © 2013 AIP Publishing LLC.

  5. Polytypism in ZnS, ZnSe, and ZnTe: First-principles study

    KAUST Repository

    Boutaiba, F.

    2014-06-23

    We report results of first-principles calculations based on the projector augmented wave (PAW) method to explore the structural, thermodynamic, and electronic properties of cubic (3C) and hexagonal (6H, 4H, and 2H) polytypes of II-VI compounds: ZnS, ZnSe, and ZnTe. We find that the different bond stacking in II-VI polytypes remarkably influences the resulting physical properties. Furthermore, the degree of hexagonality is found to be useful to understand both the ground-state properties and the electronic structure of these compounds. The resulting lattice parameters, energetic stability, and characteristic band energies are in good agreement with available experimental data. Trends with hexagonality of the polytype are investigated.

  6. First Principles Study of Electronic Structure and Magnetic Properties of TMH (TM = Cr, Mn, Fe, Co

    Directory of Open Access Journals (Sweden)

    S. Kanagaprabha

    2013-01-01

    Full Text Available First principles calculations are performed using a tight-binding linear muffin-tin orbital (TB-LMTO method with local density approximation (LDA and atomic sphere approximation (ASA to understand the electronic properties of transition metal hydrides (TMH (TM = Cr, Mn, Fe, Co. The structural property, electronic structure, and magnetic properties are investigated. A pressure induced structural phase transition from cubic to hexagonal phase is predicted at the pressures of 50 GPa for CrH and 23 GPa for CoH. Also, magnetic phase transition is observed in FeH and CoH at the pressures of 10 GPa and 180 GPa, respectively.

  7. First principles study on defectives BN nanotubes for water splitting and hydrogen storage

    Science.gov (United States)

    Bevilacqua, Andressa C.; Rupp, Caroline J.; Baierle, Rogério J.

    2016-06-01

    First principles calculations within the spin polarized density functional approximation have been addressed to investigate the energetic stability, electronic and optical properties of defective BN nanotubes. Our results show that the presence of carbon impurities interacting with vacancies gives rise to defective electronic levels inside the nanotube band gap. By calculating the absorbance index, we have obtained a strong inter-band optical absorption in the visible region (around 2.1 eV) showing that defective BN nanotubes could be an efficient catalytic semiconductor material to be used within solar energy for water splitting. In addition, we observe that the adsorption energy for one and two H2 molecules on the defective surface is in the desired window for the system to be useful as a hydrogen storage medium.

  8. First Principles Study on NaxLi1-x FePO4 As Cathode Material for Rechargeable Lithium Batteries

    Institute of Scientific and Technical Information of China (English)

    OUYANG Chu-Ying; WANG De-Yu; SHI Si-Qi; WANG Zhao-Xiang; LI Hong; HUANG Xue-Jie; CHEN Li-Quan

    2006-01-01

    The electronic structure and ionic dynamic properties of pure and Na doped (Li site) LiFePO4 have been investigated by first-principles calculations.The band gap of the Na doped material is much narrow than that of the undoped one,indicating of better electronic conductive properties.First-principles based molecular dynamic simulations have been performed to examine the migration energy barriers for the Li ion diffusion.The results shown that the energy barriers for Li diffusion decreased a little along the one-dimensional diffusion pathway,indicating that the ionic conductive property is also improved.as compared with the high valance doping (such as Cr) cases.

  9. Infrared radiative properties of alumina up to the melting point: A first-principles study

    Science.gov (United States)

    Yang, J. Y.; Xu, M.; Liu, L. H.

    2016-11-01

    The high thermal emission of alumina dominates the radiative heat transfer of rocket exhaust plume. Yet numerous experimental measurements on radiative properties of alumina at high temperatures vary considerably from each other and cannot provide physical insight into the underlying mechanism. In this work, the ab initio molecular dynamics (AIMD) method and ab initio parameterized Drude model are combined to predict the radiative properties of alumina for temperatures up to 2327 K (the melting point) in the spectral range 1-12 μm. Contributed by different microscopic processes, the optical absorption of alumina in the spectral range 1-4 and 4-12 μm is described by two distinct methods. In the spectral range 4-12 μm, the multi-phonon process mainly contributes to optical absorption and can be simulated by the AIMD method based on the linear response theory. While in the spectral range 1-4 μm, the optical absorption is mainly caused by intrinsic carriers and can be effectively described by the ab initio parameterized Drude model. The first-principles calculations can successfully predict the infrared radiative properties of alumina at high temperatures and well reproduce the literature experiments. Moreover, the theoretical simulations verify that alumina can retain its semiconducting character even in the liquid phase and there emerges sharp increase in the near-infrared optical absorption of alumina upon melting.

  10. Structural, electronic, and elastic properties of K-As compounds: a first principles study.

    Science.gov (United States)

    Ozisik, Havva Bogaz; Colakoglu, Kemal; Deligoz, Engin; Ozisik, Haci

    2012-07-01

    First-principle calculations are performed to investigate the structural, elastic and electronic properties of K-As compounds (KAs in NaP, LiAs and AuCu-type structures, KAs(2) in MgCu(2)-type structure, K(3)As in Na(3)As, Cu(3)P and Li(3)Bi-type structures, and K(5)As(4) in A(5)B(4)-type structure). The lattice parameters, cohesive energy, formation energy, bulk modulus, and the first derivative of bulk modulus (to fit to the Murnaghan's equation of state) of the considered structures are calculated and reasonable agreement is obtained, and the phase transition pressure is also predicted. The repeated calculations on the electronic band structures and the related partial density of states are also given. The calculated second-order elastic constants based on the stress-strain method and the other related quantities such as Young's modulus, shear modulus, Poisson's ratio, sound velocities, Debye temperature, and shear anisotropy factors for considered structures are presented, and trends are discussed.

  11. First-principles study of the electronic and optical properties of ZnO nanowires

    Institute of Scientific and Technical Information of China (English)

    Zhang Fu-Chun; Zhang Zhi-Yong; Zhang Wei-Hu; Yan Jun-Feng; Yong Jiang-Ni

    2009-01-01

    The geometric, energetic, electronic structures and optical properties of ZnO nanowires (NWs) with hexagonal cross sections are investigated by using the first-principles calculation of plane wave ultra-soft pseudo-potential technology based on the density functional theory (DFT). The calculated results reveal that the initial Zn-O double layers merge into single layers after structural relaxations, the band gap and binding energies decrease with the increase of the ZnO nanowire size. Those properties show great dimension and size dependence. It is also found that the dielectric functions of ZnO NWs have different peaks with respect to light polarization, and the peaks of ZnO NWs exhibit a significant blueshift in comparison with those of bulk ZnO. Our results gives some reference to the thorough understanding of optical properties of ZnO, and also enables more precise monitoring and controlling during the growth of ZnO materials to be possible.

  12. First-principles study of amorphous Ga4Sb6Te3 phase-change alloys

    Science.gov (United States)

    Bouzid, Assil; Gabardi, Silvia; Massobrio, Carlo; Boero, Mauro; Bernasconi, Marco

    2015-05-01

    First-principles molecular dynamics simulations within the density functional theory framework were performed to generate amorphous models of the Ga4Sb6Te3 phase change alloy by quenching from the melt. We find that Ga-Sb and Ga-Te are the most abundant bonds with only a minor amount of Sb-Te bonds participating to the alloy network. Ga and four-coordinated Sb atoms present a tetrahedral-like geometry, whereas three-coordinated Sb atoms are in a pyramidal configuration. The tetrahedral-like geometries are similar to those of the crystalline phase of the two binary compounds GaTe and GaSb. A sizable fraction of Sb-Sb bonds is also present, indicating a partial nanoscale segregation of Sb. Despite the fact that the composition Ga4Sb6Te3 lies on the pseudobinary Ga Sb -Sb2Te3 tie line, the amorphous network can be seen as a mixture of the two binary compounds GaTe and GaSb with intertwined elemental Sb.

  13. Pressure and strain effects of hexagonal rare-earth manganites: a first-principles study.

    Science.gov (United States)

    Tan, Hengxin; Xu, Changsong; Li, Menglei; Wang, Shanying; Gu, Bing-Lin; Duan, Wenhui

    2016-03-31

    We have investigated the structural, electrical and magnetic properties as well as the phonon modes of hexagonal rare-earth manganites (RMnO3, R  =  Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu) under chemical pressure, hydrostatic pressure and epitaxial strain by first-principles calculations. The magnetic ground state of RMnO3 is found to have Γ4 magnetic configuration and to be stable under all considered external conditions. In contrast, the K3 phonon mode, which is the primary order parameter and responsible for the 'improper ferroelectricity', is greatly influenced by pressure and epitaxial strain. Consequently, the electric polarization is enhanced by 56.7% when the chemical pressure increases from R  =  Pr to R  =  Lu. The hydrostatic pressure can also improve the polarization to a certain degree, e.g. by 14.7% from 0 GPa to 40 GPa in LuMnO3. Finally, the dependence of polarization on the epitaxial strain is also given, revealing that the compressive strain could promote the ferroelectricity while tensile strain will suppress it.

  14. Study of the theoretical tensile strength of Fe by a first-principles computational tensile test

    Institute of Scientific and Technical Information of China (English)

    Liu Yue-Lin; Zhang Ying; Hong Rong-Jie; Lu Guang-Hong

    2009-01-01

    This paper employs a first-principles total-energy method to investigate the theoretical tensile strengths of bcc and fcc Fe systemically. It indicates that the theoretical tensile strengths are shown to be 12.4, 32.7, 27.5 Gpa for bcc Fe, and 48.1, 34.6, 51.2 Gpa for fcc Fe in the [001], [110] and [111] directions, respectively. For bec Fe, the [001] direction is shown to be the weakest direction due to the occurrence of a phase transition from ferromagnetic bcc Fe to high spin ferromagnetic fcc Fe. For fcc Fe, the [110] direction is the weakest direction duc to the formation of an instable saddle-point 'bct structure' in the tensile process. Furthermore, it demonstrates that a magnetic instability will occur under a tensile strain of 14%, characterized by the transition of ferromagnetic bcc Fe to paramagnetic fcc Fe. The results provide a good reference to understand the intrinsic mechanical properties of Fe as a potential structural material in the nuclear fusion Tokamak.

  15. Potential thermoelectric material open framework Si24 from a first-principles study

    Science.gov (United States)

    Ouyang, Tao; Zhang, Pei; Xiao, Huaping; Tang, Chao; Li, Jin; He, Chaoyu; Zhong, Jianxin

    2017-10-01

    Open framework Si24 is a new synthesis cage-like silicon allotrope with a quasi-direct bandgap and predicted to exhibit outstanding adsorption efficiency, foreshowing the potential applications in the photovoltaic community. In this paper, the thermoelectric property of such new Si structures is investigated by combining first-principles calculation and semiclassical Boltzmann transport theory. The calculations show that the Si24 possesses a superb Seebeck coefficient, and obviously anisotropic electronic conductivity. Owing to more energy extremums existing in the conduction band region, the power factor of Si24 in the n-type doping is always better than that in p-type samples. Anisotropic phonon transport property is observed as well in Si24 with average lattice thermal conductivity of 45.35 W m‑1 K‑1 at room temperature. Based on the electron relaxation time estimated from the experiment, the thermoelectric figure of merit of Si24 is found to be as high as 0.69 (n-type doping at 700 K) and 0.51 (p-type doping at 700 K) along the xx crystal direction, which is about two orders of magnitude larger than that of diamond Si (d-Si). The findings presented in this work shed light on the thermoelectric performance of Si24 and qualify that such new Si allotrope is a promising platform for achieving the recombination of photovoltaic and thermoelectric technologies together.

  16. First-principles study on magnetism of Ru monolayer under an external electric field

    Science.gov (United States)

    Kitaoka, Yukie; Imamura, Hiroshi

    Electric field control of magnetic properties such as magnetic moment and magnetic anisotropy has been attracted. For the 4 d TM films, on the other hand, it was recently reported that the ferromagnetism Pd thin-film is induced by application of an external electric field otherwise Pd thin-film shows paramagnetic. However, little attention has been paid to the magnetism of other 4 d TMs. Here, we investigate the magnetism of the free-standing Ru monolayer and that on MgO(001) substrate under an external electric field by using first-principles FLAPW method. We found that the free-standing Ru monolayer is ferromagnet with magnetic moment of 1.50 ¥muB /atom. The MA energy is 3.45 meV/atom, indicating perpendicular MA, at zero electric field (E=0) and increases up to 3.84 meV/atom by application of E=1 (V/¥AA). The Ru monolayer on MgO(001) substrate is also ferromagnet with magnetic moment of 0.89 ¥muB /atom. The MA energy is 1.49 meV/atom, indicating perpendicular MA, at E=0 and decreases to 1.33 meV/atom by application of E=1 (V/¥AA).

  17. Enhanced superconductivity in the high pressure phase of SnAs studied from first principles

    Science.gov (United States)

    Sreenivasa Reddy, P. V.; Kanchana, V.; Millichamp, T. E.; Vaitheeswaran, G.; Dugdale, S. B.

    2017-01-01

    First principles calculations are performed using density functional theory and density functional perturbation theory for SnAs. Total energy calculations show the first order phase transition from an NaCl structure to a CsCl one at around 37 GPa, which is also confirmed from enthalpy calculations and agrees well with experimental work. Calculations of the phonon structure and hence the electron-phonon coupling, λep, and superconducting transition temperature, Tc, across the phase diagram are performed. These calculations give an ambient pressure Tc, in the NaCl structure, of 3.08 K, in good agreement with experiment whilst at the transition pressure, in the CsCl structure, a drastically increased value of Tc = 12.2 K is found. Calculations also show a dramatic increase in the electronic density of states at this pressure. The lowest energy acoustic phonon branch in each structure also demonstrates some softening effects. Electronic structure calculations of the Fermi surface in both phases are presented for the first time as well as further calculations of the generalised susceptibility with the inclusion of matrix elements. These calculations indicate that the softening is not derived from Fermi surface nesting and it is concluded to be due to a wavevector-dependent enhancement of the electron-phonon coupling.

  18. First-principles study on anatase TiO2 codoped with nitrogen and praseodymium

    Science.gov (United States)

    Gao, Pan; Wu, Jing; Liu, Qing-Ju; Zhou, Wen-Fang

    2010-08-01

    The crystal structures, electronic structures and optical properties of nitrogen or/and praseodymium doped anatase TiO2 were calculated by first principles with the plane-wave ultrasoft pseudopotential method based on density functional theory. Highly efficient visible-light-induced nitrogen or/and praseodymium doped anatase TiO2 nanocrystal photocatalyst were synthesized by a microwave chemical method. The calculated results show that the photocatalytic activity of TiO2 can be enhanced by N doping or Pr doping, and can be further enhanced by N+Pr codoping. The band gap change of the codoping TiO2 is more obvious than that of the single ion doping, which results in the red shift of the optical absorption edges. The results are of great significance for the understanding and further development of visible-light response high activity modified TiO2 photocatalyst. The photocatalytic activity of the samples for methyl blue degradation was investigated under the irradiation of fluorescent light. The experimental results show that the codoping TiO2 photocatalytic activity is obviously higher than that of the single ion doping. The experimental results accord with the calculated results.

  19. Effect of metal doping on structural characteristics of amorphous carbon system: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Li, Xiaowei; Zhang, Dong [Key Laboratory of Marine Materials and Related Technologies, Key Laboratory of Marine Materials and Protective Technologies of Zhejiang Province, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China); Lee, Kwang-Ryeol, E-mail: krlee@kist.re.kr [Computational Science Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Wang, Aiying, E-mail: aywang@nimte.ac.cn [Key Laboratory of Marine Materials and Related Technologies, Key Laboratory of Marine Materials and Protective Technologies of Zhejiang Province, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China)

    2016-05-31

    First-principles calculation was performed to investigate the effect of metal doping on the structural characteristics of amorphous carbon system, and the 3d transition metals (TM) were particularly selected as representative case. Results showed that the total energy in TM–C systems caused by distorting the bond angles was reduced distinctly for comparison with that in C–C system. Further electronic structure revealed that as the 3d electrons of doped TM increased, the bond characteristic of highest occupied molecular orbital changed from bonding (Sc, Ti) to nonbonding (V, Cr, Mn, Fe) and finally to antibonding (Co, Ni, Cu) between the TM and C atoms. Meanwhile, the TM–C bond presented a mixture of the covalent and ionic characters. The decrease of strength and directionality of TM–C bonds resulted in the total energy change upon bond angle distortion, which demonstrated that the bond characteristics played an important role in reducing residual stress of TM-doped amorphous carbon systems. - Highlights: • The bond characteristics as 3d electrons changed from bonding, nonbonding to antibonding. • The TM–C bond was a mixture of covalent and ionic characters. • Reduced strength and directionality of TM–C bond led to small distortion energy change. • The weak TM–C bond accounted for the reduced compressive stress caused by TM.

  20. First-principles studies of the vibrational properties of amorphous carbon nitrides

    Institute of Scientific and Technical Information of China (English)

    Niu Li; Wang Xuan-Zhang; Zhu Jia-Qi; Gao Wei

    2013-01-01

    Raman spectra of amorphous carbon nitride films (a-C:N) resemble those of typical amorphous carbon (a-C),and no specific features in the spectra are shown due to N doping.The present work provides a correlation between the microstructure and vibrational properties of a-C:N films from first principles.The six periodic model structures of 64 atoms with various mass densities and nitrogen contents are generated by the liquid-quench method using Car-Parinello molecular dynamics.By using Raman coupling tensors calculated with the finite electric field method,Raman spectra are obtained.The calculated results show that the vibrations of C=N could directly contribute to the Raman spectrum.The similarity of the Raman line shapes of N-doped and N-free amorphous carbons is due to the overlapping of C=N and C=C vibration bands.In addition,the origin of characteristic Raman peaks is also given.

  1. Electronic Structures of S-Doped Capped C-SWNT from First Principles Study.

    Science.gov (United States)

    Wang, L; Zhang, Yz; Zhang, Yf; Chen, Xs; Lu, W

    2010-04-14

    The semiconducting single-walled carbon nanotube (C-SWNT) has been synthesized by S-doping, and they have extensive potential application in electronic devices. We investigated the electronic structures of S-doped capped (5, 5) C-SWNT with different doping position using first principles calculations. It is found that the electronic structures influence strongly on the workfunction without and with external electric field. It is considered that the extended wave functions at the sidewall of the tube favor for the emission properties. With the S-doping into the C-SWNT, the HOMO and LUMO charges distribution is mainly more localized at the sidewall of the tube and the presence of the unsaturated dangling bond, which are believed to enhance workfunction. When external electric field is applied, the coupled states with mixture of localized and extended states are presented at the cap, which provide the lower workfunction. In addition, the wave functions close to the cap have flowed to the cap as coupled states and to the sidewall of the tube mainly as extended states, which results in the larger workfunction. It is concluded that the S-doped C-SWNT is not incentive to be applied in field emitter fabrication. The results are also helpful to understand and interpret the application in other electronic devices.

  2. Electronic Structures of S-Doped Capped C-SWNT from First Principles Study

    Directory of Open Access Journals (Sweden)

    Chen XS

    2010-01-01

    Full Text Available Abstract The semiconducting single-walled carbon nanotube (C-SWNT has been synthesized by S-doping, and they have extensive potential application in electronic devices. We investigated the electronic structures of S-doped capped (5, 5 C-SWNT with different doping position using first principles calculations. It is found that the electronic structures influence strongly on the workfunction without and with external electric field. It is considered that the extended wave functions at the sidewall of the tube favor for the emission properties. With the S-doping into the C-SWNT, the HOMO and LUMO charges distribution is mainly more localized at the sidewall of the tube and the presence of the unsaturated dangling bond, which are believed to enhance workfunction. When external electric field is applied, the coupled states with mixture of localized and extended states are presented at the cap, which provide the lower workfunction. In addition, the wave functions close to the cap have flowed to the cap as coupled states and to the sidewall of the tube mainly as extended states, which results in the larger workfunction. It is concluded that the S-doped C-SWNT is not incentive to be applied in field emitter fabrication. The results are also helpful to understand and interpret the application in other electronic devices.

  3. Doping effects on the electronic properties of armchair phosphorene nanoribbons: A first-principles study

    Science.gov (United States)

    Zhou, Wenzhe; Zou, Hui; Xiong, Xiang; Zhou, Yu; Liu, Rutie; Ouyang, Fangping

    2017-10-01

    On the basis of first-principles density functional theory, the different electronic structures of marginal or central doped armchair phosphorene nanoribbons with various species were calculated. It was found that the bonds between the foreign atoms and the adjacent P atoms are energetically more stable for central doping. The electronic properties of the doped ribbons are strongly related to the valence electron number of foreign atoms. B-, N-, F-, Al-doped (type Ⅰ) armchair phosphorene nanoribbons remain nonmagnetic semiconductors. The bandgap of the central doped nanoribbons is larger than that of the marginal doped nanoribbons. C, O, Si, S doping (type Ⅱ) at the edge introduce about 1 μB delocalized magnetic moment, while significantly decreasing for central doping, which is associated with electron transferring from foreign atoms to neighboring P atoms. The magnetism introduced by type Ⅱ dopants is provided by multiple orbits between the foreign atoms and the adjacent P atoms and delocalized on the edge for marginal doping. These results prove that the presence and the location of isolated electrons are both important factors for modulation of magnetic properties of armchair phosphorene nanoribbons through substitutional doping.

  4. First-principles study of the electronic, optical properties and lattice dynamics of tantalum oxynitride.

    Science.gov (United States)

    Li, Pan; Fan, Weiliu; Li, Yanlu; Sun, Honggang; Cheng, Xiufeng; Zhao, Xian; Jiang, Minhua

    2010-08-01

    First-principles calculations of the electronic, optical properties and lattice dynamics of tantalum oxynitride are performed with the density functional theory plane-wave pseudopotential method. The analysis of the electronic structure shows a covalent nature in Ta-N bonds and Ta-O bonds. The hybridization of anion 2p and Ta 5d states results in enhanced dispersion of the valence band, raising the top of the valence band and leading to the visible-light response in TaON. It has a high dielectric constant, and the anisotropy is displayed obviously in the lower energy region. Our calculation indicated that TaON has excellent dielectric properties along [010] direction. Various optical properties, including the reflectivity, absorption coefficient, refractive index, and the energy-loss spectrum are derived from the complex dielectric function. We also present phonon dispersion relation, zone-center optical mode frequency, density of phonon states, and some thermodynamic properties. The experimental IR modes (B(u) at 808 cm(-1) and A(u) at 863 cm(-1)) are reproduced well and assigned to a combination of stretching and bending vibrations for the Ta-N bond and Ta-O bond. The thermodynamic properties of TaON, such as heat capacity and Debye temperature, which were important parameters for the measurement of crystal physical properties, were first given for reference. Our investigations provide useful information for the potential application of this material.

  5. Topological ferroelectricity in layered perovskite LaTaO4: A first principles study

    Science.gov (United States)

    Liu, Xiao Qiang; Li, Gui Jing; Chen, Xiang Ming

    2016-12-01

    The ferroelectricity in layered perovskite LaTaO4 is investigated by first-principles calculations. The rather large polarization (about 36 μC/cm2) along -c direction is obtained by the Berry phase approach. Ferroelectric phase can be induced by freezing a soft B1u mode from the prototype phase, and this mode involves the rotations of oxygen octahedron and the displacement of La3+ cations. The topological ferroelectricity is adopted based on the previous work to distinguish from the typical proper ferroelectrics, such as BaTiO3. The 0 K stable monoclinic phase can be regarded as an antiferroelectric phase since the polarization of the neighboring layer will be canceled each other. However, the ferroelectric phase is metastable because of the unexpected small barrier between paraelectric and monoclinic phase and narrow energy gap between ferroelectric and monoclinic phase, and this result can explain the previous experimental results. From the present work, the topological ferroelectricity in layered perovskite LaTaO4 is confirmed, and the rather high polarization makes the present compound as a promising candidate for the lead-free ferroelectric application.

  6. Stability of Mg-incorporated InN surfaces: first-principles study

    Science.gov (United States)

    Akiyama, T.; Nakamura, K.; Ito, T.; Song, J.-H.; Freeman, A. J.

    2009-03-01

    InN films are attractive materials for electronic and optelectronic applications. The growth of InN eptitaxial films with n-type and p-type conductivity has traditionally been performed along the polar directionootnotetextR.E. Jones et al., Phys. Rev. Lett, 96, 125505 (2006), which may result in large polarization fields along the growth direction, reducing the radiative efficiency of quantum-well light emitters. To overcome this drawback, the growth along nonpolar orientation such as (1010) and (1120) planes and its p-type doping have been recently carried out. We have addressed this issue by performing first-principles pseudopotential calculations for Mg-incorporated InN surfaces in various orientations, including (1010) and (1120) as well as (0001) and (0001) surfacesootnotetextJ.-H. Song et al., Phys. Rev. Lett. 101, 106803 (2008). The calculated surface energies demonstrate that qualitative trends in the stability of Mg-incorporated surfaces agree with those on GaN surfaces ootnotetextJ.E. Northrup, Appl. Phys. Lett. 86, 122108 (2005), although several surface reconstructions different from those on GaN surfaces are obtained. The effects of growth conditions on p-type doping are also discussed.

  7. First-principles study on electron transport through BN-dimer embedded zigzag carbon nanotubes

    Science.gov (United States)

    Egami, Yoshiyuki; Akera, Hiroshi

    2017-04-01

    First-principles calculations are performed for electron transmission through a metallic zigzag carbon nanotube with substitutional BN dimers parallel to the nanotube axis. The transmission coefficient is calculated in the energy range (around the charge neutrality point) in which there exist two degenerate subbands for each spin. Wave functions in the circumferential direction of one of the degenerate subbands can be chosen so as to have nodes at the position of a carbon dimer parallel to the nanotube axis. It is shown that the transmission probability of an incident wave with such wave-function nodes depends crucially on positions of BN dimers relative to the nodes. By placing each of dimers at one of the nodes, the transmission probability is substantially enhanced and is well described by the Born approximation in spite of spatially extended scattering potential due to ionized B and N. This suggests that the arrangement in the circumferential direction of various impurities influences transport through metallic zigzag carbon nanotubes.

  8. First-principles study of structural, elastic, and thermodynamic properties of ZrHf alloy

    Institute of Scientific and Technical Information of China (English)

    韦昭; 翟东; 邵晓红; 鲁勇; 张平

    2015-01-01

    Structural parameters, elastic constants, and thermodynamic properties of ordered and disordered solid solutions of ZrHf alloys are investigated through first-principles calculations based on density-functional theory (DFT). The special quasi-random structure (SQS) method is used to model the disordered phase as a single unit cell, and two lamella structures are generated to model the ordered alloys. Small strains are applied to the unit cells to measure the elastic behavior and mechanical stability of ZrHf alloys and to obtain the independent elastic constants by the stress–strain relationship. Phonon dispersions and phonon density of states are presented to verify the thermodynamic stability of the considered phases. Our results show that both the ordered and disordered phases of ZrHf alloys are structurally stable. Based on the obtained phonon frequencies, thermodynamic properties, including Gibbs free energy, entropy, and heat capacity, are predicted within the quasi-harmonic approximation. It is verified that there are no obvious differences in energy between ordered and disordered phases over a wide temperature range.

  9. Covalent nitrophenyl diazonium functionalized silicene for spintronics: a first-principles study.

    Science.gov (United States)

    Dai, Jun; Zeng, Xiao Cheng

    2015-07-21

    We predict some novel electronic and magnetic properties of a functionalized silicene sheet by nitrophenyl diazonium (NPD) using first-principles calculations in the framework of density functional theory with dispersion corrections. Our calculations at the HSE06 level show that for the three coverage ratios of NPD considered in this work (i.e., NPD : Si = 1 : 8, 1 : 18 and 1 : 32), spin-polarized electronic structures can be always realized with NPD adsorption although the bandgap decreases upon reducing the NPD coverage ratio. The quasi-localized pz electrons of Si are identified to be responsible for the ferrimagnetism in these two-dimensional systems. Remarkably, the system with the NPD : Si = 1 : 8 ratio is predicted to be a bipolar magnetic semiconductor. As such, half-metallicity can be realized by applying a gate voltage with reversible spin polarization, making NPD-1/8 a potential candidate for future spintronic applications. This work offers a new tailor-made functionalization approach to realize magnetic semiconducting silicene.

  10. Palladium nanoparticles/defective graphene composites as oxygen reduction electrocatalysts: A first-principles study

    KAUST Repository

    Liu, Xin

    2012-02-02

    The impact of graphene substrate-Pd nanoparticle interaction on the O, OH, and OOH adsorption that is directly related to the electrocatalytic performance of these composites in oxygen reduction reaction (ORR) has been investigated by first-principles-based calculations. The calculated binding energy of a Pd 13 nanoparticle on a single vacancy graphene is as high as -6.10 eV, owing to the hybridization between the dsp states of the Pd particles with the sp 2 dangling bonds at the defect sites. The strong interaction results in the averaged d-band center of the deposited Pd nanoparticles shifted away from the Fermi level from -1.02 to -1.45 eV. Doping the single vacancy graphene with B or N will further tune the average d-band center and also the activity of the composite toward O, OH, and OOH adsorption. The adsorption energies of O, OH, and OOH are reduced from -4.78, -4.38, and -1.56 eV on the freestanding Pd 13 nanoparticle to -4.57, -2.66, and -1.39 eV on Pd 13/single vacancy graphene composites, showing that the defective graphene substrate will not only stabilize the Pd nanoparticles but also reduce the adsorption energies of the O-containing species to the Pd particle, and so as the poisoning of the ORR active sites. © 2011 American Chemical Society.

  11. Strain field of the monovacancy in silicene: First-principles study

    Directory of Open Access Journals (Sweden)

    Rui Li

    2016-05-01

    Full Text Available The in-plane strain fields of single-vacancy silicene with different monovacancy (MV concentrations, as well as the corresponding electronic band structures, are investigated by using the first-principle calculations. Firstly the self-healing MV is found to be the most stable ground structure in silicene, which is different from the other 2D hexagonal honeycomb materials, e.g. graphene, h-BN. In the isolated MV center, the bonds along the pentagons are compressed, creating a compress field, and those close to the distorted hexagons are stretched, creating a stretch field. As the MV concentration increasing, the interacted compress field tends to corrugate the defected silicene, while the interacted stretch field impacts little on the low-buckled structure. Especially, the corrugation presents in those supercells with small MV concentration, just as the (4, 5, (4, 6, (4, 7, (4, 8 supercells. The corrugations approach zero at both low and high MV concentrations, and the (4, 6 supercell with a MV concentration of about 0.021, has a peak value of 3.23Å. The electronic calculations show that the linear dispersion at Γ point in pristine silicene is broken by the lower lattice symmetry of the self-healing MV reconstruction, which translates it into metal as well.

  12. Strain field of the monovacancy in silicene: First-principles study

    Science.gov (United States)

    Li, Rui; Liu, Zhongli; Ma, Wenqiang; Tan, Yonggang

    2016-05-01

    The in-plane strain fields of single-vacancy silicene with different monovacancy (MV) concentrations, as well as the corresponding electronic band structures, are investigated by using the first-principle calculations. Firstly the self-healing MV is found to be the most stable ground structure in silicene, which is different from the other 2D hexagonal honeycomb materials, e.g. graphene, h-BN. In the isolated MV center, the bonds along the pentagons are compressed, creating a compress field, and those close to the distorted hexagons are stretched, creating a stretch field. As the MV concentration increasing, the interacted compress field tends to corrugate the defected silicene, while the interacted stretch field impacts little on the low-buckled structure. Especially, the corrugation presents in those supercells with small MV concentration, just as the (4, 5), (4, 6), (4, 7), (4, 8) supercells. The corrugations approach zero at both low and high MV concentrations, and the (4, 6) supercell with a MV concentration of about 0.021, has a peak value of 3.23Å. The electronic calculations show that the linear dispersion at Γ point in pristine silicene is broken by the lower lattice symmetry of the self-healing MV reconstruction, which translates it into metal as well.

  13. Vacancy trapping mechanism for multiple hydrogen and helium in beryllium: a first-principles study.

    Science.gov (United States)

    Zhang, Pengbo; Zhao, Jijun; Wen, Bin

    2012-03-01

    The microscopic mechanism for H and He trapping by vacancy defects and bubble formation in a Be host lattice is investigated using first-principles calculations. A single He atom prefers to occupy a vacancy centre while H does not. He can segregate towards the vacancy from the interstitial site much more easily than H. Both H and He exhibit lower diffusion barriers from a remote interstitial to a vacancy with regard to their diffusion barriers inside a perfect Be solid. Up to five H or 12 He atoms can be accommodated into the monovacancy space, and the Be-He interaction is much weaker than Be-H. The physical origin for aggregation of multiple H or He atoms in a vacancy is further discussed. The strong tendency of H and He trapping at vacancies provides an explanation for why H and He bubbles were experimentally observed at vacancy defects in materials. We therefore argue that vacancies provide a primary nucleation site for bubbles of H and He gases inside Be materials.

  14. First-principles study of the elastic and thermodynamic properties of thorium hydrides at high pressure

    Science.gov (United States)

    Xiao-Lin, Zhang; Yuan-Yuan, Wu; Xiao-Hong, Shao; Yong, Lu; Ping, Zhang

    2016-05-01

    The high pressure behaviors of Th4H15 and ThH2 are investigated by using the first-principles calculations based on the density functional theory (DFT). From the energy-volume relations, the bct phase of ThH2 is more stable than the fcc phase at ambient conditions. At high pressure, the bct ThH2 and bcc Th4H15 phases are more brittle than they are at ambient pressure from the calculated elastic constants and the Poisson ratio. The thermodynamic stability of the bct phase ThH2 is determined from the calculated phonon dispersion. In the pressure domain of interest, the phonon dispersions of bcc Th4H15 and bct ThH2 are positive, indicating the dynamical stability of these two phases, while the fcc ThH2 is unstable. The thermodynamic properties including the lattice vibration energy, entropy, and specific heat are predicted for these stable phases. The vibrational free energy decreases with the increase of the temperature, and the entropy and the heat capacity are proportional to the temperature and inversely proportional to the pressure. As the pressure increases, the resistance to the external pressure is strengthened for Th4H15 and ThH2. Project supported by the Long-Term Subsidy Mechanism from the Ministry of Finance and the Ministry of Education of China.

  15. First-principles study of the stability and diffusion properties of hydrogen in zirconium carbide

    Science.gov (United States)

    Yang, Xiao-Yong; Lu, Yong; Zhang, Ping

    2016-10-01

    The stability and diffusion properties of interstitial hydrogen atom in bulk ZrC have been investigated by first-principles calculations. In energy, hydrogen atoms prefer to occupy the carbon substitutional site (C-SS) with a negative formation energy, consistent with the experimental observations. In the C-SS, the hydrogen atom obtains 0.702 electrons from its 1 NN Zr atoms, tending to achieve the most stable 1s2 electronic state. Two hydrogen atoms in the same tetrahedral interstitial site are able to form a pairing cluster along the direction with the Hsbnd H pair equilibrium distance of 1.30 Å, nearly twice the length of H2 bond, suggesting a relatively weak interaction between the Hsbnd H pair. The diffusion energy barriers of hydrogen in pure and vacancy pre-existing ZrC matrix are calculated. It is found that the presence of native vacancies will capture the hydrogen atoms due to the large energy barrier to jump out the vacancy. Furthermore, the temperature-dependent diffusion coefficients of interstitial hydrogen, deuterium, and tritium in ZrC are predicted using the transition state theory.

  16. First principles study of inert-gas (helium, neon, and argon) interactions with hydrogen in tungsten

    Science.gov (United States)

    Kong, Xiang-Shan; Hou, Jie; Li, Xiang-Yan; Wu, Xuebang; Liu, C. S.; Chen, Jun-Ling; Luo, G.-N.

    2017-04-01

    We have systematically evaluated binding energies of hydrogen with inert-gas (helium, neon, and argon) defects, including interstitial clusters and vacancy-inert-gas complexes, and their stable configurations using first-principles calculations. Our calculations show that these inert-gas defects have large positive binding energies with hydrogen, 0.4-1.1 eV, 0.7-1.0 eV, and 0.6-0.8 eV for helium, neon, and argon, respectively. This indicates that these inert-gas defects can act as traps for hydrogen in tungsten, and impede or interrupt the diffusion of hydrogen in tungsten, which supports the discussion on the influence of inert-gas on hydrogen retention in recent experimental literature. The interaction between these inert-gas defects and hydrogen can be understood by the attractive interaction due to the distortion of the lattice structure induced by inert-gas defects, the intrinsic repulsive interaction between inert-gas atoms and hydrogen, and the hydrogen-hydrogen repelling in tungsten lattice.

  17. Phase stability and electronic structure of UMo2Al20: A first-principles study

    Science.gov (United States)

    Liu, Peng-Chuang; Xian, Ya-Jiang; Wang, Xin; Zhang, Yu-Ting; Zhang, Peng-Cheng

    2017-09-01

    In this paper, the phase stability of UMo2Al20 was explored using cluster formula in combination with first-principles calculations. Cluster formula analysis uncovered that the compound was composed of two principal clusters, i.e. [Mo-Al12] and [U-Al16]. The electronic interactions between U, Mo and Al atoms in this compound were discussed using elastic property, Bader charges and energy-resolved local bonding analysis, as well as the electronic interactions between Mo and Al atoms in [Mo-Al12] cluster and between U and Al atoms in [U-Al16] cluster. It revealed that UMo2Al20 satisfied the mechanical stability criterion for cubic system, and exhibited near ionic bonding character with weak bonding directionality. The calculations within both standard DFT and HSE frameworks demonstrated that U and Al atoms acted as an electron donor while Mo atoms acted as electron acceptor. The intrinsic stability of UMo2Al20 mainly stemmed from the bonding states of Mo-Al bonds and Al-Al bonds in [Mo-Al12] cluster. These calculations provide a further insight on the CeCr2Al20-type ternary compounds.

  18. Improving SO{sub 2} gas sensing properties of graphene by introducing dopant and defect: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Xu-Ying [College of Physics and Information Technology, Shaanxi Normal University, Xian 710062, Shaanxi (China); Zhang, Jian-Min, E-mail: jianm_zhang@yahoo.com [College of Physics and Information Technology, Shaanxi Normal University, Xian 710062, Shaanxi (China); Xu, Ke-Wei [College of Physics and Mechanical and Electronic Engineering, Xian University of Arts and Science, Xian 710065, Shaanxi (China); Ji, Vincent [ICMMO/LEMHE, Université Paris-Sud 11, 91405 Orsay Cedex (France)

    2014-09-15

    Highlights: • SO{sub 2} molecule is weakly adsorbed on the IG and SW-G. • SO{sub 2} molecule shows strong interactions with the AlG and SW-AlG. • SW-AlG adsorption system gives a slightly large adsorption energy compared with AlG adsorption system. • SW-AlG is more sensitive for SO{sub 2} molecule than AlG. - Abstract: Adsorption of sulfur dioxide (SO{sub 2}) on intrinsic and modified graphene, including Stone–Wales (SW) defect, Al doping and a combination of these two, was theoretically studied using first-principles approach based on density functional theory (DFT). The most stable adsorption geometry, adsorption energy, magnetic moment, charge transfer and density of states of these systems are thoroughly discussed. It was found that SO{sub 2} molecule is weakly adsorbed on the intrinsic and SW defected graphenes and their electronic properties were slightly changed. The Al-doped graphene and the defect–dopant combination show high reactivity toward SO{sub 2}. Compared with Al-doped adsorption system, the adsorption energy for Al-doped SW defect adsorption system can be enhanced by the introduction of a SW defect. This work reveals that the sensitivity of graphene-based chemical gas sensors for SO{sub 2} can be drastically improved by introducing dopant and defect, and the Al-doped SW graphene is more suitable for SO{sub 2} gas detection.

  19. Vibrational Signatures in the THz Spectrum of 1,3-DNB: A First-Principles and Experimental Study

    OpenAIRE

    Ahmed, Towfiq; Azad, Abul K.; Chellappa, Raja; Higginbotham-Duque, Amanda; Dattelbaum, Dana M.; Zhu, Jian-Xin; Moore, David; Matthias J. Graf

    2016-01-01

    Understanding the fundamental processes of light-matter interaction is important for detection of explosives and other energetic materials, which are active in the infrared and terahertz (THz) region. We report a comprehensive study on electronic and vibrational lattice properties of structurally similar 1,3-dinitrobenzene (1,3- DNB) crystals through first-principles electronic structure calculations and THz spectroscopy measurements on polycrystalline samples. Starting from reported x-ray cr...

  20. Arsenene as a promising candidate for NO and NO{sub 2} sensor: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Can [School of Electronic Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210023 (China); Key Laboratory of Radio Frequency and Micro-Nano Electronics of Jiangsu Province, Nanjing 210023, Jiangsu (China); Liu, Chun-Sheng, E-mail: csliu@njupt.edu.cn [School of Electronic Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210023 (China); Key Laboratory of Radio Frequency and Micro-Nano Electronics of Jiangsu Province, Nanjing 210023, Jiangsu (China); Yan, Xiaohong [School of Electronic Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210023 (China); Key Laboratory of Radio Frequency and Micro-Nano Electronics of Jiangsu Province, Nanjing 210023, Jiangsu (China); College of Science, Nanjing University of Aeronautics and Astronautics, Nanjing 211106 (China)

    2017-03-26

    Based on first-principles calculations, we have studied the adsorption of CO, CO{sub 2}, N{sub 2}, NH{sub 3}, NO and NO{sub 2} molecules on the pristine arsenene monolayer. These gas molecules are held by an interaction that is intermediate between the physisorbed and chemisorbed states. Furthermore, the adsorption of NO and NO{sub 2} can produce a noticeable modifications of the density of states near the Fermi level. Interestingly, only the adsorption of NO and NO{sub 2} can lead to a magnetic moment of 1 μB. Therefore, our results can provide a theoretical basis for the potential applications of arsenene monolayer in gas sensing with electrical and magnetic methods. - Highlights: • A new type of two-dimensional single element semiconductor. • Investigated by first-principles calculations. • Easy desorption and good reversibility. • Gas sensing with electrical and magnetic methods.

  1. A first principle study on the interaction between acetylcholinesterase and acetylcholine, and also rivastigmine in alzheimer's disease case

    Science.gov (United States)

    Khoirunisa, V.; Rusydi, F.; Kasai, H.; Gandaryus, A. G.; Dipojono, H. K.

    2016-08-01

    The catalytic activity of acetylcholinesterase enzyme (AChE) relates to the symptom progress in Alzheimer's disease. Interaction of AChE with rivastigmine (from the medicine) can reduce its catalytic activity toward acetylcholine to decelerate the progression of Alzheimer's disease. This research attempts to study the interaction between AChE and rivastigmine, and also acetylcholine (without the presence of rivastigmine) using density functional theory by simplifying the reaction occurs in the active site, which is assumed to be C2H5OH, C3N2H3(Ch3), and CH3COO-. The results suggest that AChE interacts easier with acetylcholine than with rivastigmine, which implies that the medicine does not effectively reduce the catalytic activity of AChE. At this stage, no experimental data is available to be compared with the calculation results. Nonetheless, this study has shown a good prospect to understand the AChE-substrate interaction using a first-principles calculation.

  2. First-principles study of phase equilibria in Cu-Pt-Rh disordered alloys.

    Science.gov (United States)

    Yuge, Koretaka

    2009-10-14

    Phase stability of Cu-Pt-Rh ternary disordered alloys is examined by a combination of cluster expansion techniques and Monte Carlo statistical simulation based on first-principles calculation. The sign of pseudo-binary ECIs indicates that neighboring Cu and Pt strongly prefer unlike-atom pairs, Pt and Rh weakly prefer unlike-atom pairs, and Cu and Rh atoms prefer like-atom pairs, indicating that the ternary alloy retains the ordering tendency of the constituent binary alloys. The formation energy of a random alloy at T = 1200 K exhibits a negative sign for a wide range of Pt-rich compositions, while at Pt-poor compositions of x≤0.25, the formation energy has a positive value. Calculated affinities for the random alloy show the variety of energetically favored bonds for the alloy: Cu-Pt bonds in both first-and second-nearest neighbor (1-NN and 2-NN) are energetically preferred for all the composition range, the Pt-Rh bond in 1-NN is preferred at Pt-rich compositions, the Pt-Rh in 2-NN and Rh-Cu in 1-NN bonds are unfavored for all compositions, and the Rh-Cu bond in 2-NN is unfavored for Pt-poor compositions. We elucidate that the ordering tendency of 1-NN and 2-NN Cu-Pt, 2-NN Pt-Rh and 1-NN Cu-Rh atoms in constituent binary alloys is retained for the whole composition range of Cu-Pt-Rh ternary alloys, while that of 1-NN Pt-Rh and 2-NN Cu-Rh atoms significantly depends on composition.

  3. First-principles study and electronic structures of Mn-doped ultrathin ZnO nanofilms

    Institute of Scientific and Technical Information of China (English)

    E. Salmani; A. Benyoussef; H. Ez-Zahraouy; E. H. Saidi; O. Mounkachi

    2012-01-01

    The first-principles density functional calculation is used to investigate the electronic structures and magnetic properties of Mn-doped and N-co-doped ZnO nanofilms.The band structure calculation shows that the band gaps of ZnO films with 2,4,and 6 layers are larger than the band gap of the bulk with wurtzite structure and decrease with the increase of film thickness.However,the four-layer ZnO nanofilms exhibit ferromagnetic phases for Mn concentrations less than 24% and 12% for Mn-doping performed in the whole layers and two layers of the film respectively,while they exhibit spin glass phases for higher Mn concentrations.It is also found,on the one hand,that the spin glass phase turns into the ferromagnetic one,with the substitution of nitrogen atoms for oxygen atoms,for nitrogen concentrations higher than 16% and 5% for Mn-doping performed in the whole layers and two layers of the film respectively.On the other hand,the spin-glass state is more stable for ZnO bulk containing 5% of Mn impurities,while the ferromagnetic phase is stable by introducing the p-type carriers into the bulk system.Moreover,it is shown that using the effective field theory for ferromagnetic system,the Curie temperature is close to the room temperature for the undamped Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction.

  4. First-principles study of high-conductance DNA sequencing with carbon nanotube electrodes

    KAUST Repository

    Chen, X.

    2012-03-26

    Rapid and cost-effective DNA sequencing at the single nucleotide level might be achieved by measuring a transverse electronic current as single-stranded DNA is pulled through a nanometer-sized pore. In order to enhance the electronic coupling between the nucleotides and the electrodes and hence the current signals, we employ a pair of single-walled close-ended (6,6) carbon nanotubes (CNTs) as electrodes. We then investigate the electron transport properties of nucleotides sandwiched between such electrodes by using first-principles quantum transport theory. In particular, we consider the extreme case where the separation between the electrodes is the smallest possible that still allows the DNA translocation. The benzene-like ring at the end cap of the CNT can strongly couple with the nucleobases and therefore it can both reduce conformational fluctuations and significantly improve the conductance. As such, when the electrodes are closely spaced, the nucleobases can pass through only with their base plane parallel to the plane of CNT end caps. The optimal molecular configurations, at which the nucleotides strongly couple to the CNTs, and which yield the largest transmission, are first identified. These correspond approximately to the lowest energy configurations. Then the electronic structures and the electron transport of these optimal configurations are analyzed. The typical tunneling currents are of the order of 50 nA for voltages up to 1 V. At higher bias, where resonant transport through the molecular states is possible, the current is of the order of several μA. Below 1 V, the currents associated to the different nucleotides are consistently distinguishable, with adenine having the largest current, guanine the second largest, cytosine the third and, finally, thymine the smallest. We further calculate the transmission coefficient profiles as the nucleotides are dragged along the DNA translocation path and investigate the effects of configurational variations

  5. Compression-induced transformation of aldehydes into polyethers: a first-principles molecular dynamics study.

    Science.gov (United States)

    Mosey, Nicholas J

    2010-04-07

    First-principles molecular dynamics simulations are used to investigate the behavior of bulk acetaldehyde (MeCHO) under conditions of increasing pressure. The results demonstrate that increasing pressure causes the aldehydes to polymerize, yielding polyethers through a process involving the rapid formation of C-O bonds between multiple neighboring MeCHO molecules. Attempts to induce polyether formation at different densities through the application of geometric constraints show that polymerization occurs only once a critical density of approximately 1.7 g/cm(3) has been reached. The results of simulations performed at several different temperatures are also consistent with a process that is induced by reaching a critical density. The origins of this effect are rationalized in terms of the structural requirements for the formation of C-O bonds between multiple MeCHO molecules in rapid succession. Specifically, the collective formation of C-O bonds requires the typical distance between the sp(2) carbon atoms and oxygen atoms in neighboring MeCHO molecules to reach a value of approximately 2.5 A. Radial distribution functions calculated at different densities show that this structural requirement is reached when the density is near the observed threshold. The observed reaction may be useful in the context of lubrication, with polyethers being effective lubricants and the extreme conditions experienced in sliding contacts providing the ability to reach the high densities needed to induce the reaction. In this context, the calculations indicate that polyether formation is associated with significant energy dissipation, while energy dissipation is minimal once the polyethers are formed. Furthermore, the polyethers are stable with respect to multiple compression/decompression cycles and pressures of at least 60 GPa.

  6. Structure and mechanical properties of tantalum mononitride under high pressure: A first-principles study.

    Science.gov (United States)

    Chang, Jing; Zhao, Guo-Ping; Zhou, Xiao-Lin; Liu, Ke; Lu, Lai-Yu

    2012-10-15

    The structure and mechanical properties of tantalum mononitride (TaN) are investigated at high pressure from first-principles using the plane wave pseudopotential method within the local density approximation. Three stable phases were considered, i.e., two hexagonal phases (ε and θ) and a cubic δ phase. The obtained equilibrium structure parameters and ground state mechanical properties are in excellent agreement with the experimental and other theoretical results. A full elastic tensor and crystal anisotropy of the ultra-incompressible TaN in three stable phases are determined in the wide pressure range. Results indicated that the elastic properties of TaN in three phases are strongly pressure dependent. And the hexagonal θ-TaN is the most ultraincompressible among the consider phases, which suggests that the θ phase of TaN is a potential candidate structure to be one of the ultraincompressible and hard materials. By the elastic stability criteria, it is predicted that θ-TaN is not stable above 53.9 GPa. In addition, the calculated B/G ratio indicated that the ε and δ phases possess brittle nature in the range of pressure from 0 to 100 GPa. While θ phase is brittleness at low pressure (below 8.2 GPa) and is strongly prone to ductility at high pressure (above 8.2 GPa). The calculated elastic anisotropic factors for three phases of TaN suggest that they are elastically highly anisotropic and strongly dependent on the propagation direction.

  7. 3 Transition metal decorated B–C–N composite nanostructures for efficient hydrogen storage: A first-principles study

    Indian Academy of Sciences (India)

    S Bhattacharya; C Majumder; G P Das

    2009-06-01

    Ti decorated BC_4N nanotube has been studied using first-principles density functional approach, to explore the storage of molecular hydrogen. It combines the advantages of carbon nanotube, together with the thermal stability of BN nanotube. The local structural unit of BN3 and NB3 linked with B–N bonds are responsible for the extra stability of BC_4N nanotube as compared with CNT. While the host carbon nanotube is metallic, the substitutional doping of B and N with a large enough concentration (33%) turns it to semiconducting. Endohedral decoration, although energetically favourable, encounters a rather high barrier height of ∼4 eV, as obtained from our nudge elastic band calculation of the minimum energy path. Exohedral Ti@BC4N can bind up to four H2 molecules. For full Ti coverage, the system can absorb up to 5.6 wt% of hydrogen. Ab initio molecular dynamics simulation reveals that at 500 K hydrogen gets released in molecular form. We believe that this novel composite nanotube, functionalized by Ti atoms from outside, serves as a promising system for hydrogen storage.

  8. First-Principles Study of Fe-Doped ZnO Nanowires

    Institute of Scientific and Technical Information of China (English)

    张富春; 张威虎; 董军堂; 张志勇

    2011-01-01

    Using Srst-principles theory, we predict magnetic, electronic and optical properties in Fe-doped ZnO nanowires. The results show that ferromagnetic (FM) coupling of configuration V is the most stable, and the strong hybridization effect between FeZd and O2p states is found near the Fermi level, and it is obvious that the ferromagnetic system is electron-spin polarization of 100% and half-metallic. Given antiferromagnetic (AFM) coupling, the system generates small spin polarization near the Fermi level, indicating metalh'city. The magnetic moments mainly arise from FeZd orbitals. In addition, the results of optical properties show that the Fe-doped ZnO nanowires have apparent absorption peaks in the ultraviolet band and that there is a small red shift and a strong blue shift in the near and far ultraviolet band, indicating that Fe-doped ZnO nanowires are a type of magneto-optical materials with great promise.%Using first-principles theory,we predict magnetic,electronic and optical properties in Fe-doped ZnO nanowires.The results show that ferromagnetic(FM)coupling of configuration V is the most stable,and the strong hybridization effect between Fe3d and O2p states is found near the Fermi level,and it is obvious that the ferromagnetic system is electron-spin polarization of 100% and half-metallic.Given antiferromagnetic(AFM)coupling,the system generates small spin polarization near the Fermi level,indicating metallicity.The magnetic moments mainly arise from Fe3d orbitals.In addition,the results of optical properties show that the Fe-doped ZnO nanowires have apparent absorption peaks in the ultraviolet band and that there is a small red shift and a strong blue shift in the near and far ultraviolet band,indicating that Fe-doped ZnO nanowires are a type of magneto-optical materials with great promise.

  9. First-principles studies on graphene-supported transition metal clusters.

    Science.gov (United States)

    Sahoo, Sanjubala; Gruner, Markus E; Khanna, Shiv N; Entel, Peter

    2014-08-21

    Theoretical studies on the structure, stability, and magnetic properties of icosahedral TM13 (TM = Fe, Co, Ni) clusters, deposited on pristine (defect free) and defective graphene sheet as well as graphene flakes, have been carried out within a gradient corrected density functional framework. The defects considered in our study include a carbon vacancy for the graphene sheet and a five-membered and a seven-membered ring structures for graphene flakes (finite graphene chunks). It is observed that the presence of defect in the substrate has a profound influence on the electronic structure and magnetic properties of graphene-transition metal complexes, thereby increasing the binding strength of the TM cluster on to the graphene substrate. Among TM13 clusters, Co13 is absorbed relatively more strongly on pristine and defective graphene as compared to Fe13 and Ni13 clusters. The adsorbed clusters show reduced magnetic moment compared to the free clusters.

  10. Optical properties of orthovanadates, and periodates studied from first principles theory

    Energy Technology Data Exchange (ETDEWEB)

    Shwetha, G. [Department of Physics, Indian Institute of Technology Hyderabad, Ordnance Factory Estate, Yeddumailaram 502 205, Telangana (India); Kanchana, V., E-mail: kanchana@iith.ac.in [Department of Physics, Indian Institute of Technology Hyderabad, Ordnance Factory Estate, Yeddumailaram 502 205, Telangana (India); Vaitheeswaran, G. [Advanced Center of Research in High Energy Materials (ACRHEM), University of Hyderabad, Prof. C. R. Rao Road, Gachibowli, Hyderabad 500 046, Telangana (India)

    2015-08-01

    Detailed ab-initio studies on electronic structure and optical properties have been carried out for orthovanadates, and periodate compounds, ScVO{sub 4}, YVO{sub 4}, LuVO{sub 4}, and NaIO{sub 4}, KIO{sub 4}, RbIO{sub 4}, CsIO{sub 4} based on the Full potential linearized augmented plane wave method within the frame work of Density Functional Theory using Tran and Blaha modified Becke–Johnson potential (TB-mBJ). We have compared the optical properties of orthovanadates with periodates, and also with its high pressure phase. The main difference observed in moving from orthovanadates to periodates is the increase in band gap, and bands turn out to be less dispersive. By considering all these facts, we predict orthovanadates to be better scintillators than periodates, which is well explained from the band structure, and optical properties calculations. In addition, we also compared the optical properties of orthovanadates at ambient, and high pressure and we observed a decrease in the band gap of orthovanadates, increase in valence band width at high pressure when compared to ambient phase. Tuning the band gap, which is an important criteria for scintillators, can be observed in orthovanadates by decreasing the cation size, and also by moving to the high pressure scheelite phase. High pressure phase of orthovanadates might be more favourable as the zircon to scheelite transition is irreversible, and the transition pressure is also less around 8 GPa. - Graphical abstract: Display Omitted - Highlights: • Orthovanadates, periodates are insulators. • Band gap decreases with decrease in the cation size, and also moving to high pressure phase. • Orthovanadates are better host scintillators than periodates. • Orthovanadates can be better used as host scintillators in the high pressure phase.

  11. First-principles study of the rotational transitions of H2 physisorbed over benzene

    Science.gov (United States)

    Hamel, Sébastien; Côté, Michel

    2004-12-01

    In the ongoing search for promising compounds for hydrogen storage, novel porous metal-organic frameworks (MOFs) have been discovered recently [M. Eddadoudi, J. Kim, N. L. Rosi, D. Vodak, J. Wachter, M. O'Keeffe, and O. M. Yaghi, Science 295, 469 (2002); N. L. Rosi, J. Eckert, M. Eddadoudi, D. Vodak, J. Kim, M. O'Keeffe, and O. M. Yaghi, Science 300, 1127 (2003)]. Binding sites in these MOFs were deduced from inelastic neutron scattering (INS) spectroscopy of the rotational transitions of the adsorbed molecular hydrogen. In light of this discovery, it is important to have a fundamental understanding of hydrogen adsorption at different sites in this class of MOF materials. As a first step, here we study the case of H2 adsorbed on benzene as a model of the organic linkers in the microporous crystal. We access the density functional theory results by comparing with correlated ab initio methods, e.g., second-order Møller-Plesset and coupled cluster with noniterative triple excitations. Different approximations for the exchange-correlation potentials were accessed for a set of relevant properties (binding energy, energetically favored configuration, and distance between the adsorbents and adsorbates). In particular, theoretical rotational spectra of the adsorbed H2 were obtained that could be compared to the experimental INS spectra.

  12. First-Principles Study of Structure Property Relationships of Monolayer (Hydroxy)Oxide-Metal Bifunctional Electrocatalysts

    DEFF Research Database (Denmark)

    Zeng, Zhenhua; Kubal, Joseph; Greeley, Jeffrey Philip

    2015-01-01

    In the present study, on the basis of detailed density functional theory (DFT) calculations, and using Ni hydroxy(oxide) films on Pt(111) and Au(111) electrodes as model systems, we describe a detailed structural and electrocatalytic analysis of hydrogen evolution (HER) at three-phase boundaries...... of information that is inaccessible by purely experimental means, and these structures, in turn, strongly suggest that a bifunctional reaction mechanism for alkaline HER will be operative at the interface between the films, the metal substrates, and the surrounding aqueous medium. This bifunctionality produces...... important changes in the calculated barriers of key elementary reaction steps, including water activation and dissociation, as compared to traditional monofunctional Pt surfaces. The successful identification of the structures of thin metal films and three-phase boundary catalysts is not only an important...

  13. First-principle study on bonding mechanism of ZnO by LDA+U method

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, G.C. [Key Laboratory of Low Dimensional Materials and Application Technology (Xiangtan University), Ministry of Education, Institute of Modern Physics, Xiangtan University, Xiangtan 411105 (China); Sun, L.Z. [Key Laboratory of Low Dimensional Materials and Application Technology (Xiangtan University), Ministry of Education, Institute of Modern Physics, Xiangtan University, Xiangtan 411105 (China) and National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science, 200083 Shanghai (China)]. E-mail: lzsun@xtu.edu.cn; Zhong, X.L. [Key Laboratory of Low Dimensional Materials and Application Technology (Xiangtan University), Ministry of Education, Institute of Modern Physics, Xiangtan University, Xiangtan 411105 (China); Chen Xiaoshuang [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science, 200083 Shanghai (China)]. E-mail: xschen@mail.sitp.ac.cn; Wei Lu [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science, 200083 Shanghai (China); Wang, J.B. [Key Laboratory of Low Dimensional Materials and Application Technology (Xiangtan University), Ministry of Education, Institute of Modern Physics, Xiangtan University, Xiangtan 411105 (China)]. E-mail: jbwang@xtu.edu.cn

    2007-08-13

    The electronic structure and the bonding mechanism of ZnO have been studied by using the Full-Potential Linear Augmented Plane Wave (FP-LAPW) method within the density-functional theory (DFT) based on LDA+U exchange correlation potential. The valence and the bonding charge density are calculated and compared with those derived from LDA and GGA to describe the bonding mechanism. The charge transfer along with the bonding process is analyzed by using the theory of Atoms in Molecules (AIM). The bonding, the topological characteristics and the p-d coupling effects on the bonding mechanism of ZnO are shown quantitatively with the critical points (CPs) along the bonding trajectory and the charge in the atomic basins. Meanwhile, the bonding characteristics for wurtzite, zinc blende and rocksalt phase of ZnO are discussed systematically in the present paper.

  14. A first-principles high-pressure study of Hf2PX (X=B, C, N)

    Science.gov (United States)

    Li, Hui; Luo, Zhili; Liu, Zhe; Sun, Guodong; Wang, Zhenjun

    2017-06-01

    New members of MAX family Hf2PX (X=B, C, N) were studied by first-principles calculations under pressure range of 0-100 GPa. Their structural, elastic and electronic properties were reported. The results show that they are energetically stable at zero pressure and mechanically stable under pressure range from 0 to 100 GPa. It reveals that Hf2PB>Hf2PC>Hf2PN for the structural parameters of a and V, and Hf2PBpressure environments.

  15. Formation and Physical Properties of h-BN Atomic Layers: A First-Principles Density-Functional Study

    Directory of Open Access Journals (Sweden)

    Yoshitaka Fujimoto

    2017-01-01

    Full Text Available Hexagonal boron nitride (h-BN atomic layers have attracted much attention as a potential device material for future nanoelectronics, optoelectronics, and spintronics applications. This review aims to describe the recent works of the first-principles density-functional study on h-BN layers. We show physical properties induced by introduction of various kinds of defects in h-BN layers. We further discuss the relationship among the defect size, the strain, and the magnetic as well as the electronic properties.

  16. A first-principles study on Al-doped ZnO growth polarity on sapphire (0001) surface

    Science.gov (United States)

    Yang, Ping; Gao, Qian; Hu, Zhen-Peng; Zhang, Li-Xin

    2016-06-01

    Based on the first-principles method, the polarity inversion mechanism of Al-doped ZnO grown on sapphire (0001) substrate was investigated. This study revealed that the Al dopant tends to float on the surface of the buffer layer and leads to form ZnO nucleation islands of Zn-polarity without changing in-plane orientation. Finally, these islands evolve to wall-like nanostructure with Zn-termination. The results can explain the reason of the polarity inversion phenomenon in the experiment and supply more information for controlling the ZnO growth polarity.

  17. Electro-optic response of metal halide $\\rm{C_{s}PbI_{3}}$: A first-principles study

    Indian Academy of Sciences (India)

    AMREEN BANO; PREETI KHARE; N K GAUR

    2017-08-01

    A theoretical study of electronic and optical properties of metal-halide cubic perovskite, $\\rm{C_{s}PbI_{3}}$, is presented, using first-principles calculations with plane-wave pseudopotential method as implemented in the PWSCF code. In this approach, local density approximation (LDA) is used for exchange-correlation potential. A strong ionic bonding is observed between Cs and I orbitals and a weak covalent bonding is found between Pb-I and Cs-Pb orbitals. The optical properties of this compound are interesting and it has many applications in optoelectronic devices.

  18. Strong n-type molecule as low bias negative differential resistance device predicted by first-principles study

    Science.gov (United States)

    Min, Y.; Zhong, C. G.; Dong, Z. C.; Zhao, Z. Y.; Zhou, P. X.; Yao, K. L.

    2016-10-01

    A first-principles study of the transport properties of two thiolated pentacenes sandwiching ethyl is performed. The thiolated pentacene molecule shows strong n-type characteristics when contact Ag lead because of low work function about metal Ag. A strong negative differential resistance (NDR) effect with large peak-to-valley ratio of 758% is present under low bias. Our investigations indicate that strong n- or p-type molecules can be used as low bias molecular NDR devices and that the molecular NDR effect based on molecular-level leaving not on molecular-level crossing has no hysteresis.

  19. Electro-optic response of metal halide CsPbI_3: A first-principles study

    Science.gov (United States)

    Bano, Amreen; Khare, Preeti; Gaur, N. K.

    2017-08-01

    A theoretical study of electronic and optical properties of metal-halide cubic perovskite, CsPbI_3, is presented, using first-principles calculations with plane-wave pseudopotential method as implemented in the PWSCF code. In this approach, local density approximation (LDA) is used for exchange-correlation potential. A strong ionic bonding is observed between Cs and I orbitals and a weak covalent bonding is found between Pb-I and Cs-Pb orbitals. The optical properties of this compound are interesting and it has many applications in optoelectronic devices.

  20. First-principles study of the effects of Si doping on geometric and electronic structure of closed carbon nanotube

    Institute of Scientific and Technical Information of China (English)

    ZHOU Junzhe; WANG Chongyu

    2005-01-01

    The effects of Si doping on geometric and electronic structure of closed carbon nanotube (CNT) are studied by, a first-principles method, DMol. It is found that the local density of states at the Fermi level (EF) increases due to the Si-doping and the non-occupied states above the EF go down toward the lower energy range under an external electronic field. In addition, due to the doping of Si, a sub-tip on the CNT cap is formed, which consisted of the Si atom and its neighbor C atoms. From these results it is concluded that Si-doping is beneficial to the CNT field emission properties.

  1. First-principles study of the contractive reconstruction of gold and silver monolayers on gold, silver and aluminum

    Energy Technology Data Exchange (ETDEWEB)

    Takeuchi, Noboru.

    1990-11-16

    Using first-principles calculations in conjunction with modeling techniques, the author has investigated the structures of Au and Ag monolayers on a number of metal surfaces. Au(100) has a c(26 {times} 68) surface unit cell and the reconstruction has been interpreted as the top layer transforming to a contracted hexagonal-close-packed layer, superimposed on the square lattice of the underlying substrate atoms. Similar reconstructions have been observed on the 5d fcc metals Ir and Pt, but not in the 4d Rh, Pd, and Ag. The author studied the energetics of a monolayer of Au and Ag using first-principles calculations. The author found that it is energetically favorable for both Au and Ag to transform from a square to hexagonal arrangement and to contract to a higher surface density, but Au gains substantially more energy than Ag. This is true both for a monolayer in isolation as well as on top of a jellium surface. The author also calculated the mismatch energy (energy loss when the top layer loses registry with the substrate) for Au and Ag, and found that Ag has a slightly higher mismatch energy. The first-principles results thus offer a strong indication that Au(100) can reconstruct but Ag will not. The reconstruction is further studied with a 2 dimensional Frenkel-Kontorowa model, with parameters extracted from the total energy calculations. The author found that it is indeed energetically favorable for the top layer of Au(100), but not for Ag, to transform to a hexagonal-close-packed structure and contract. 85 refs., 34 figs., 8 tabs.

  2. First-principles study of atomic and electronic structures of kaolinite in soft rock

    Institute of Scientific and Technical Information of China (English)

    He Man-Chao; Zhao Jian; Fang Zhi-Jie

    2012-01-01

    Kaolinite is a kind of clay mineral which often causes large deformations in soft-rock tunnel engineering and thus causes safety issues.To deal with these engineering safety issues,the physical/chemical properties of the kaolinite should be studied from basic viewpoints.By using the density-functional theory,in this paper,the atomic and the electronic structures of the kaolinite are studied within the local-density approximation (LDA).It is found that the kaolinite has a large indirect band gap with the conduction band minimum (CBM) and the valence band maximum (VBM) being at the T and the B points,respeetively.The chemical bonding between the cation and the oxygen anion in kaolinite is mainly ionic,accompanied by a minor covalent component.It is pointed that the VBM and the CBM of kaolinite consist of oxygen 2p and cation s states,respectively.The bond lengths between different cations and anions,as well as of the different OH groups,are also compared.

  3. A treatise on first-principles studies of ZnO as diluted magnetic semiconductor

    Energy Technology Data Exchange (ETDEWEB)

    Nayak, Sanjeev Kumar

    2012-04-24

    The scope of the present thesis is to study the properties of ZnO doped with transition metal elements by the density functional theory (DFT).cc In this thesis, there is extensive study of the electronic structure of ZnO beyond the generalized gradient approximation (GGA) as exchange-correlation functional (E{sub xc}), which is well known to be associated with some drawback in predicting the semiconducting properties. One of the methods adopted for improvement is by adding extra correlation-energy to GGA (GGA+U) in line with the Hubbard model. We find that with adding U on Zn d-orbitals, the band gap improves with simultaneous shift of the Zn d-bands to lower energies. The band gap nevertheless is still far below the experimental value. Another approach to correct for the E{sub xc} is by the treatment of screened hybrid-functionals proposed by Heyd-Scuseria-Ernzerhof (HSE), where the contribution to the exchange energy is through the blend of some percentage of screened Hartree-Fock exchange and rest from the GGA exchange. The correlation energy is derived from GGA. This method also has limitations in describing the electronic structure of ZnO. A simple proposition of mixing the GGA+U and the hybrid-functional treatment may be a solution, which has been investigated in this work. The band structure of ZnO has been compared for various level of theory for E{sub xc}, namely, LDA, GGA, GGA+U, and HSE functionals with different screening lengths ({omega}). A proposal for HSE+U functionals has been been put forward and supported. Using some of the treatments for E{sub xc} as stated above, the magnetic properties of TM(Cr, Mn, Fe, Co, and Ni) doped ZnO are studied. Firstly, the electronic structure calculations for TM doped ZnO are done with the Korringa-Kohn-Rostoker (KKR) method with the LDA and using the coherent potential approximation (CPA). The exchange integrals are then calculated using the Liechtenstein's formalism, which are then used in the Monte Carlo

  4. First-principles study of {sup 75}As NQR in arsenic-chalcogenide compounds

    Energy Technology Data Exchange (ETDEWEB)

    Edwards, Arthur H [Air Force Research Laboratory, AFRL/RVSE, Kirtland AFB, NM 87117-5776 (United States); Taylor, P C [Department of Physics, Colorado School of Mines, Golden, CO 80401 (United States); Campbell, Kristy A [Department of Electrical and Computer Engineering, Boise State University, Boise, ID 83725 (United States); Pineda, Andrew C [Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, NM 87131-0001 (United States)

    2011-02-09

    We present a theoretical study of the nuclear quadrupole interaction, {nu}{sub Q}, of {sup 75}As in crystalline and amorphous materials containing sulfur and selenium, and compare them with experiment. We studied a combination of hydrogen-terminated molecular clusters and periodic cells at various levels of quantum chemical theory. The results show clearly that the standard density functional theory (DFT) approximations, LDA and GGA, underestimate the nuclear quadrupole (NQR) interaction systematically, while Hartree-Fock theory overestimates it to an even greater degree. However, various levels of configuration interaction and the B3LYP hybrid exchange-correlation functional, which includes some exact exchange, give very good quantitative agreement for As bonded only to the chalcogen species. As-As bonds require highly converged basis sets. We have performed a systematic study of the effect of local distortions around an arsenic atom on {nu}{sub Q} and {eta}. Using a simple, semiclassical model, we have combined our total energy results with our NQR calculations to predict {nu}{sub Q} lineshapes for bond angle and bond length distortions. Our predictions for lineshape, including first and second moments, are in excellent agreement with the results of Su et al for a-As{sub 2}S{sub 3}, a-As{sub 2}Se{sub 3} and a-AsSe. We offer new insight into the distortions that led to this inhomogeneous broadening. Our results show clearly that, for trivalent arsenic atoms with zero or one arsenic nearest neighbor, symmetric bond stretching is the predominant contributor to the {nu}{sub Q} linewidth. However, in the presence of two arsenic nearest neighbors, distortions of the As-As-As apex angle dominates and, in fact, leads to a much larger second moment, in agreement with experiment.

  5. First-principles study of (75)As NQR in arsenic-chalcogenide compounds.

    Science.gov (United States)

    Edwards, Arthur H; Taylor, P C; Campbell, Kristy A; Pineda, Andrew C

    2011-02-09

    We present a theoretical study of the nuclear quadrupole interaction, ν(Q), of (75)As in crystalline and amorphous materials containing sulfur and selenium, and compare them with experiment. We studied a combination of hydrogen-terminated molecular clusters and periodic cells at various levels of quantum chemical theory. The results show clearly that the standard density functional theory (DFT) approximations, LDA and GGA, underestimate the nuclear quadrupole (NQR) interaction systematically, while Hartree-Fock theory overestimates it to an even greater degree. However, various levels of configuration interaction and the B3LYP hybrid exchange-correlation functional, which includes some exact exchange, give very good quantitative agreement for As bonded only to the chalcogen species. As-As bonds require highly converged basis sets. We have performed a systematic study of the effect of local distortions around an arsenic atom on ν(Q) and η. Using a simple, semiclassical model, we have combined our total energy results with our NQR calculations to predict ν(Q) lineshapes for bond angle and bond length distortions. Our predictions for lineshape, including first and second moments, are in excellent agreement with the results of Su et al for a-As(2)S(3), a-As(2)Se(3) and a-AsSe. We offer new insight into the distortions that led to this inhomogeneous broadening. Our results show clearly that, for trivalent arsenic atoms with zero or one arsenic nearest neighbor, symmetric bond stretching is the predominant contributor to the ν(Q) linewidth. However, in the presence of two arsenic nearest neighbors, distortions of the As-As-As apex angle dominates and, in fact, leads to a much larger second moment, in agreement with experiment.

  6. A first principles study of phase stability, bonding, electronic and lattice dynamical properties of beryllium chalcogenides at high pressure

    Energy Technology Data Exchange (ETDEWEB)

    Dabhi, Shweta [Department of Physics, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar 364001 (India); Mankad, Venu [Central Institute of Plastic Engineering and Technology, Ahmedabad (India); Jha, Prafulla K., E-mail: prafullaj@yahoo.com [Department of Physics, Faculty of Science, The M.S. University of Baroda, Vadodara 390002 (India)

    2014-12-25

    Highlights: • First principles calculations are performed for BeS, BeSe and BeTe in B3, B8 and B1 phases. • They are indirect wide band gap semiconductors stable in B3 phase at ambient condition. • Phonon calculations at ambient and high pressure are reported. • The NiAs phase is dynamically stable at high pressure. - Abstract: The present paper reports a detailed and systematic theoretical study of structural, mechanical, electronic, vibrational and thermodynamical properties of three beryllium chalcogenides BeS, BeSe and BeTe in zinc blende, NiAs and rock salt phases by performing ab initio calculations based on density-functional theory. The calculated value of lattice constants and bulk modulus are compared with the available experimental and other theoretical data and found to agree reasonably well. These compounds are indirect wide band gap semiconductors with a partially ionic contribution in all considered three phases. The zinc blende phase of these chalcogenides is found stable at ambient condition and phase transition from zinc blende to NiAs structure is found to occur. The bulk modulus, its pressure derivative, anisotropic factor, Poission’s ratio, Young’s modulus for these are also calculated and discussed. The phonon dispersion curves of these beryllium chalcogenides in zinc blende phase depict their dynamical stability in this phase at ambient condition. We have also estimated the temperature variation of specific heat at constant volume, entropy and Debye temperature for these compounds in zinc blende phase. The variation of lattice-specific heat with temperature obeys the classical Dulong–Petit’s law at high temperature, while at low-temperature it obeys the Debye’s T{sup 3} law.

  7. A first-principles study of the thermodynamic and electronic properties of Mg and MgH2 nanowires.

    Science.gov (United States)

    Wu, Xinxing; Zhang, Ruiqi; Yang, Jinlong

    2016-07-28

    In this article, we studied the thermodynamic and electronic properties of Mg and MgH2 nanowires with different diameters, and elucidated why MgH2 nanowires are good hydrogen storage materials through first-principles calculations. Previous experiments have shown that the orientation relationship between Mg and MgH2 nanowires is the Mg[0001] direction parallel to the MgH2[110] direction. In our calculations, Mg nanowires oriented along the [0001] direction and MgH2 nanowires oriented along the [110] direction were built from bulk Mg and MgH2 crystals, respectively. We found that as the diameters of Mg and MgH2 nanowires decrease, Mg and MgH2 nanowires become more unstable, and the hydrogen desorption energies and temperatures of MgH2 nanowires decrease. That is, the thinner the MgH2 nanowires get, the more dramatically hydrogen desorption temperatures (Td) will decrease. Meanwhile, we also found that when the diameters of MgH2 nanowires are larger than 1.94 nm, the Td almost maintain the same value at about 440 K, only about 40 K lower than that of bulk MgH2 crystal; if the diameters are less than 1.94 nm, the Td reduce very quickly. In particular, compared with bulk MgH2 crystal, the Td of the thinnest MgH2 nanowire with a diameter of 0.63 nm can be reduced by 164 K. In addition, the electronic structure calculations showed that Mg nanowires are metals, while MgH2 nanowires are semiconductors. In particular, our results showed that the electronic structures of MgH2 nanowires are influenced by the surface effect and quantum size effect. That is to say, the band gaps of MgH2 nanowires are controlled by surface electronic states and the size of MgH2 nanowires.

  8. Extended homologous series of Sn-O layered systems: A first-principles study

    Science.gov (United States)

    Govaerts, Kirsten; Partoens, Bart; Lamoen, Dirk

    2016-10-01

    Apart from the most studied tin-oxide compounds, SnO and SnO2, intermediate states have been claimed to exist for more than a hundred years. In addition to the known homologous series (Seko et al., 2008 [27]), we here predict the existence of several new compounds with an O concentration between 50% (SnO) and 67% (SnO2). All these intermediate compounds are constructed from removing one or more (101) oxygen layers of SnO2. Since the van der Waals (vdW) interaction is known to be important for the Sn-Sn interlayer distances, we use a vdW-corrected functional, and compare these results with results obtained with PBE and hybrid functionals. We present the electronic properties of the intermediate structures and we observe a decrease of the band gap when (i) the O concentration increases and (ii) more SnO-like units are present for a given concentration. The contribution of the different atoms to the valence and conduction band is also investigated.

  9. First principles study of structural and electronic properties of different phases of boron nitride

    Energy Technology Data Exchange (ETDEWEB)

    Ahmed, Rashid [Centre for High Energy Physics, University of the Punjab, Lahore 54590 (Pakistan)], E-mail: rasofi@hotmail.com; Fazal-e-Aleem [Centre for High Energy Physics, University of the Punjab, Lahore 54590 (Pakistan); Hashemifar, S. Javad; Akbarzadeh, Hadi [Department of Physics, Isfahan University of Technology, 84156 Isfahan (Iran, Islamic Republic of)

    2007-11-15

    A theoretical study of structural and electronic properties of the four phases of BN (zincblende, wurtzite, hexagonal and rhombohedral) is presented. The calculations are done by full potential (linear) augmented plane wave plus local orbitals (APW+lo) method based on the density functional theory (DFT) as employed in WIEN2k code. Using the local density approximation (LDA) and generalized gradient approximation (GGA-PBE) for the exchange correlation energy functional, we have calculated lattice parameters, bulk modulus, its pressure derivative and cohesive energy. In order to calculate electronic band structure, another form of the generalized gradient approximation proposed by Engel and Vosko (GGA-EV) has been employed along with LDA and GGA-PBE. It is found that all the three approximations exhibit similar band structure qualitatively. However, GGA-EV gives energy band gap values closer to the measured data. Our results for structural and electronic properties are compared with the experimental and other theoretical results wherever these are available.

  10. First-principles study of point defects in CePO4 monazite

    Science.gov (United States)

    Yi, Yong; Zhao, Xiaofeng; Teng, Yuancheng; Bi, Beng; Wang, Lili; Wu, Lang; Zhang, Kuibao

    2016-12-01

    CePO4 monazite is an important radiation-resistant material that may act as a potential minor actinides waste form. Here, we present the results of the calculations for the basic radiation defect modellings in CePO4 crystals, along with the examination of their defect formation energies and effect of the defect concentrations. This study focused on building a fully-relaxed CePO4 model with the step iterative optimization from the DFT-GGA calculations using the VASP and CASTEP databases. The results show that the Frenkel defect configuration resulting from the center interstitials has a lower energy when compared to two adjacent orthophosphate centers (the saddle point position). High formation energies were found for all the types of intrinsic Frenkel and vacancy defects. The formation energies conform to the following trend (given in the decreasing order of energy): Ce Frenkel (12.41 eV) > O Frenkel (11.02 eV) > Ce vacancy (9.09 eV) > O vacancy (6.69 eV). We observed almost no effect from the defect concentrations on the defect formation energies.

  11. Doping LiMnPO4 with Cobalt and Nickel: A First Principle Study

    Directory of Open Access Journals (Sweden)

    Mauro Francesco Sgroi

    2017-04-01

    Full Text Available A density functional theory (DFT study has been carried out on transition metal phosphates with olivine structure and formula LiMPO4 (M = Fe, Mn, Co, Ni to assess their potential as cathode materials in rechargeable Li-ion batteries based on their chemical and structural stability and high theoretical capacity. The investigation focuses on LiMnPO4, which could offer an improved cell potential (4.1 V with respect to the reference LiFePO4 compound, but it is characterized by poor lithium intercalation/de-intercalation kinetics. Substitution of cations like Co and Ni in the olivine structure of LiMnPO4 was recently reported in an attempt to improve the electrochemical performances. Here the electronic structure and lithium intercalation potential of Ni- and Co-doped LiMnPO4 were calculated in the framework of the Hubbard U density functional theory (DFT+U method for highly correlated materials. Moreover, the diffusion process of lithium in the host structures was simulated, and the activation barriers in the doped and pristine structures were compared. Our calculation predicted that doping increases Li insertion potential while activation barriers for Li diffusion remain similar to the pristine material. Moreover, Ni and Co doping induces the formation of impurity states near the Fermi level and significantly reduces the band gap of LiMnPO4.

  12. Greatly enhanced adsorption of platinum on periodic graphene nanobuds: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Ashrafian, S.; Jahanshahi, M. [Nanoscale Simulation Group, Nanotechnology Research Institute, School of Chemical Engineering, Babol University of Technology, Babol (Iran, Islamic Republic of); Ganji, M. Darvish, E-mail: ganji_md@yahoo.com [Young Researchers and Elite club, Central Tehran Branch, Islamic Azad University, Tehran (Iran, Islamic Republic of); Agheb, R. [Faculty of Mechanical Engineering, Khaje Nasir Toosi University of Technology, P.O. Box 16315-1355, Tehran (Iran, Islamic Republic of)

    2015-10-01

    graphene complex. The very desirable Pt binding energy obtained accompanied by high specific surface area (because of fastened C{sub 60} molecules) and relatively weaker O{sub 2} binding energy of PGNBs compared with the pristine graphene lead to experimentally apprehend these novel hybrid nanostructured materials as a superior media for Pt adsorption. Our study recommends possible avenues for intensification the stability and electro-catalytic activity of platinum atoms on PGNB surfaces through hybrid engineering.

  13. Structure and dynamics of the water films confined between edges of pyrophyllite: A first principle study

    Science.gov (United States)

    Churakov, Sergey V.

    2007-03-01

    Edge sites of clay minerals play a key role for pH dependent sorption of ions from solutions of electrolytes. Pyrophyllite, Al 2[Si 4O 10](OH) 2, is an important structural prototype for a variety of 2:1 dioctahedral phyllosilicates but in contrast to the other clays has no permanent structural charge. The structure of thin water films confined between most common edges of 1Tc pyrophyllite: (0 1 0), (1 1 0) and (1 0 0), was analyzed by means of ab initio molecular dynamic simulations. The system setup allowed for a full flexibility of the interfaces and a proton exchange between the edges of pyrophyllite and water molecules in solution. The structure of hydrated surfaces is compared with the recent predictions of static geometry optimizations for edge-vacuum interfaces. All surfaces studied reveal a strong hydrophilic character of edge similar to the hydrated silica surface and the facets of simple layered hydroxides. Spontaneous proton transfer between different surface sites were observed in molecular dynamics simulations of the (0 1 0) interface. The proton bound to the tbnd Si sbnd OH site was found to exchange with the tbnd Al sbnd OH group by the mechanism tbnd Si sbnd OH +tbnd Al sbnd OH ↔tbnd Si sbnd O+tbnd Al sbnd OH 2+. The direction of the proton transfer agrees with the scale of relative proton affinities for surface sites obtained from the static calculations. Alternatively, the proton attached to the tbnd Al sbnd OH 2 site exchanges with the tbnd Al sbnd OH group. In both reactions, the protons are transferred through the chains of hydrogen bonds formed between water molecules in the solution and the surface sites. The observed mechanisms might be one of the basic schemes for the surface proton diffusion in compacted clays. Kinetics of the proton transfer at edge sites is limited by the rate of rearrangements of the water molecules near interface.

  14. Comparative study of A-site order in the lead-free bismuth titanates M{sub 1/2}Bi{sub 1/2}TiO{sub 3} (M=Li, Na, K, Rb, Cs, Ag, Tl) from first-principles

    Energy Technology Data Exchange (ETDEWEB)

    Gröting, Melanie, E-mail: groeting@mm.tu-darmstadt.de; Albe, Karsten, E-mail: albe@mm.tu-darmstadt.de

    2014-05-01

    We investigate the possibility of enhancing chemical order in the relaxor ferroelectric Na{sub 1/2}Bi{sub 1/2}TiO{sub 3} upon substitution of Na{sup +} by other monovalent cations M{sup +} using total energy calculations based on density functional theory. All chemically available monovalent cations M{sup +}, which are Li, Na, Ag, K, Tl, Rb and Cs, are considered and an analysis of the structurally relaxed structures in terms of symmetry-adapted distortion modes is given in order to quantify the chemically induced structural distortions. We demonstrate that the replacement of Na{sup +} by other monovalent cations can hardly alter the tendency of chemical order with respect to Na{sub 1/2}Bi{sub 1/2}TiO{sub 3}. Only Tl{sub 1/2}Bi{sub 1/2}TiO{sub 3} and Ag{sub 1/2}Bi{sub 1/2}TiO{sub 3} show enhanced tendency for chemical ordering. Both heavy metals behave similar to the light alkali metals in terms of structural relaxations and relative stabilities of the ordered configurations. Although a comparison of the Goldschmidt factors of components (M TiO{sub 3}){sup −} reveals for Tl a value above the upper stability limit for perovskites, the additional lone-pair effect of Tl{sup +} stabilizes the ordered structure. - Graphical abstract: Amplitudes of chemically induced distortion modes in different ordered perovskites M{sub 1/2}Bi{sub 1/2}TiO{sub 3} and visualisation of atomic displacements associated with distortion mode X{sup +}{sub 1} in the 001-ordered compounds Li{sub 1/2}Bi{sub 1/2}TiO{sub 3} and Cs{sub 1/2}Bi{sub 1/2}TiO{sub 3}. Due to a substantial size mismatch between bismuth (green) and caesium (dark blue), incorporation of the latter leads to enhanced displacements of oxygen atoms (red) and suppresses displacements of titanium (silver) as compared to lithium (light blue) or other smaller monovalent cations. - Highlights: • Lead-free A-site mixed bismuth titanates M{sub 1/2}Bi{sub 1/2}TiO{sub 3} are studied by first-principles calculations. • Investigation

  15. First-Principles Study of the Local Magnetic Moment on a N-Doped Cu2O(111)Surface

    Institute of Scientific and Technical Information of China (English)

    王治

    2011-01-01

    First-principles calculations based on density functional theory within the generalized gradient approximation are used to study on magnetism in N-doped Cu2O.It is interesting that nitrogen does not induce magnetism in bulk Cu2O,while shows a total magnetism moment of 1.0μB at the Cu2O(111)surface,which is mainly localized on the doped N atoms.The local magnetic moment at the N-doped Cu2O(111)surface can be explained in terms of the surface state.%First-principles calculations based on density functional theory within the generalized gradient approximation are used to study on magnetism in N-doped C112O. It is interesting that nitrogen does not induce magnetism in bulk Cu2O, while shows a total magnetism moment of 1.0μB at the C112O (111) surface, which is mainly localized on the doped JV atoms. The local magnetic moment at the N-doped Cu2O (111) surface can be explained in terms of the surface state.

  16. Al-Doped ZnO Monolayer as a Promising Transparent Electrode Material: A First-Principles Study

    Directory of Open Access Journals (Sweden)

    Mingyang Wu

    2017-03-01

    Full Text Available Al-doped ZnO has attracted much attention as a transparent electrode. The graphene-like ZnO monolayer as a two-dimensional nanostructure material shows exceptional properties compared to bulk ZnO. Here, through first-principle calculations, we found that the transparency in the visible light region of Al-doped ZnO monolayer is significantly enhanced compared to the bulk counterpart. In particular, the 12.5 at% Al-doped ZnO monolayer exhibits the highest visible transmittance of above 99%. Further, the electrical conductivity of the ZnO monolayer is enhanced as a result of Al doping, which also occurred in the bulk system. Our results suggest that Al-doped ZnO monolayer is a promising transparent conducting electrode for nanoscale optoelectronic device applications.

  17. Al-Doped ZnO Monolayer as a Promising Transparent Electrode Material: A First-Principles Study.

    Science.gov (United States)

    Wu, Mingyang; Sun, Dan; Tan, Changlong; Tian, Xiaohua; Huang, Yuewu

    2017-03-29

    Al-doped ZnO has attracted much attention as a transparent electrode. The graphene-like ZnO monolayer as a two-dimensional nanostructure material shows exceptional properties compared to bulk ZnO. Here, through first-principle calculations, we found that the transparency in the visible light region of Al-doped ZnO monolayer is significantly enhanced compared to the bulk counterpart. In particular, the 12.5 at% Al-doped ZnO monolayer exhibits the highest visible transmittance of above 99%. Further, the electrical conductivity of the ZnO monolayer is enhanced as a result of Al doping, which also occurred in the bulk system. Our results suggest that Al-doped ZnO monolayer is a promising transparent conducting electrode for nanoscale optoelectronic device applications.

  18. First-principles study of structural and electronic properties of different phases of GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Arabi, H. [Faculty of Science, Department of Physics, University of Birjand, Birjand (Iran, Islamic Republic of)]. E-mail: harabi@birjand.ac.ir; Pourghazi, A. [Faculty of Science, Department of Physics, University of Isfahan, Isfahan (Iran, Islamic Republic of); Ahmadian, F. [Faculty of Science, Department of Physics, University of Birjand, Birjand (Iran, Islamic Republic of); Nourbakhsh, Z. [Faculty of Science, Department of Physics, University of Isfahan, Isfahan (Iran, Islamic Republic of)

    2006-03-01

    We present a theoretical investigation of structural and electronic properties of the four known structural phases of GaAs (zinc-blende, sc16, cinnabar and Cmcm). We used the full potential linearized augmented plane wave method, within local density approximation, and also within generalized gradient approximation for the exchange correlation potential. The lattice constants, bulk modulus and its pressure derivative are calculated for each of the four phases. The data obtained for the transition pressures between different phases are presented. Band structures and densities of states of the four phases are also given. The results are compared with previous calculations and with experimental results.

  19. Surface structure and hole localization in bismuth vanadate: A first principles study

    Science.gov (United States)

    Kweon, Kyoung E.; Hwang, Gyeong S.

    2013-09-01

    The monoclinic and tetragonal phases of bismuth vanadate (BiVO4) have been found to exhibit significantly different photocatalytic activities for water splitting. To assess a possible surface effect on the phase-dependent behavior, we calculate and compare the geometries and electronic structures of the monoclinic and tetragonal BiVO4 (001) surfaces using hybrid density functional theory. The relaxed atomic configurations of these two surfaces are found to be nearly identical, while an excess hole shows a relatively stronger tendency to localize at the surface than the bulk in both phases. Possible factors for the phase-dependent photocatalytic activity of BiVO4 are discussed.

  20. First principles study on the molecular structure and vibrational spectra of ketoprofen

    Science.gov (United States)

    Liu, Lekun; Gao, Hongwei

    2012-11-01

    The aim of this work was to compare the performance of different DFT methods at different basis sets in predicting geometry and vibration spectrum of ketoprofen. The molecular geometry and vibrational frequencies of ketoprofen have been calculated using five different density function theory (DFT) methods, including LSDA, B3LYP, mPW1PW91, B3PW91 and HCTH, with various basis sets, including 6-311G, 6-311+G, 6-311++G, 6-311+G (d, p) and 6-311++G (2d, 2p). The results indicate that mPW1PW91/6-311++G (2d, 2p) level is clearly superior to all the remaining density functional methods in predicting the bond lengths and bond angles of ketoprofen. Mean absolute deviations between the calculated harmonic and observed fundamental vibration frequencies for each method shows that LSDA/6-311G method is the best to predict vibrational spectra of ketoprofen comparing other DFT methods.

  1. Surface structure and hole localization in bismuth vanadate: A first principles study

    Energy Technology Data Exchange (ETDEWEB)

    Kweon, Kyoung E.; Hwang, Gyeong S. [Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712 (United States)

    2013-09-23

    The monoclinic and tetragonal phases of bismuth vanadate (BiVO{sub 4}) have been found to exhibit significantly different photocatalytic activities for water splitting. To assess a possible surface effect on the phase-dependent behavior, we calculate and compare the geometries and electronic structures of the monoclinic and tetragonal BiVO{sub 4} (001) surfaces using hybrid density functional theory. The relaxed atomic configurations of these two surfaces are found to be nearly identical, while an excess hole shows a relatively stronger tendency to localize at the surface than the bulk in both phases. Possible factors for the phase-dependent photocatalytic activity of BiVO{sub 4} are discussed.

  2. First-Principle Study on the Interaction between Fe and Trivacancy in Graphene

    Directory of Open Access Journals (Sweden)

    Xielong Hu

    2016-01-01

    Full Text Available Ab initio calculations using density functional theory (DFT have been performed in order to explore structure and energy gap opening of graphene with bridged-trivacancy and single adsorbed with Fe atom. Compared to the previous reconstructed trivacancy adsorbed with Fe atom with the energy gap of 0.10 eV, one interesting structure for the Fe-doped bridged-trivacancy complex has been identified, with one Fe atom above the graphene plane, and possesses energy gap with the value of 0.32 eV in the bridged circumstance. The band gap can be explained by the decrease of the free electrons. These results provide insights to engineer graphene’s properties through defect addition and manipulation for industrial semiconductor applications such as the photocatalytic technology and graphene based electronics.

  3. The abnormal lattice contraction of plutonium hydrides studied by first-principles calculations

    Institute of Scientific and Technical Information of China (English)

    Ao Bing-Yun; Shi Peng; Guo Yong; Gao Tao

    2013-01-01

    Pu can be loaded with H forming complicated continuous solid solutions and compounds,and causing remarkable electronic and structural changes.Full potential linearized augmented plane wave methods combined with Hubbard parameter U and the spin-orbit effects are employed to investigate the electronic and structural properties of stoichiometric and non-stoichiometric face-centered cubic Pu hydrides (PuHx,x =2,2.25,2.5,2.75,3).The decreasing trend with increasing x of the calculated lattice parameters is in reasonable agreement with the experimental findings.A comparative analysis of the electronic-structure results for a series of PuHx compositions reveals that the lattice contraction results from the associated effects of the enhanced chemical bonding and the size effects involving the interstitial atoms.We find that the size effects are the driving force for the abnormal lattice contraction.

  4. Insight into CH4 dissociation on NiCu catalyst: A first-principles study

    Science.gov (United States)

    Liu, Hongyan; Zhang, Riguang; Yan, Ruixia; Li, Jingrui; Wang, Baojun; Xie, Kechang

    2012-08-01

    A density-functional theory method has been conducted to investigate the dissociation of CH4 on NiCu (1 1 1) surface. Two models: uniform surface slab model (Model A) and Cu-rich surface slab model (Model B) have been constructed to represent the NiCu (1 1 1) surface, in which the ratio of Ni/Cu is unit. The obtained results on the two models have been compared with those obtained on pure Ni (1 1 1) and Cu (1 1 1). It is found that the adsorption of CHx(x = 1-3) on Model B are weaker than on Model A. The rate-determining steps of CH4 dissociation on Model A and B both are the dissociation of CH, and the corresponding activation barriers are 1.37 and 1.63 eV, respectively. Obviously, it is approximately equal on Model A to that on pure Ni (1 1 1) [H. Liu, R. Zhang, R. Yan, B. Wang, K. Xie, Applied Surface Science 257 (2011) 8955], while it is lower by 0.58 eV on Model B compared to that on pure Cu (1 1 1). Therefore, the Cu-rich surface has better carbon-resistance ability than the uniform one. Those results well explain the experimental facts that NiCu/SiO2 has excellent catalytic performance and long-term stability [H.-W. Chen, C.-Y. Wang, C.-H. Yu, L.-T. Tseng, P.-H. Liao, Catalysis Today 97 (2004) 173], however, there is serious carbon deposition on NiCu/MgO-Al2O3 in CO2 reforming of methane [J. Zhang, H. Wang, A. K. Dalai, Journal of Catalysis 249 (2007) 300].

  5. Electronic structures and vibrational properties of coronene on Ru(0001): first-principles study

    Institute of Scientific and Technical Information of China (English)

    Zhang Yu-Yang; Du Shi-Xuan; Gao Hong-Jun

    2012-01-01

    We calculate the configurations,electronic structures,vibrational properties at the coronene/Ru(0001) interface,and adsorption of a single Pt atom on coronene/Ru(0001) based on density functional theory calculations.The geometric structures and electronic structures of the coronene on Ru(0001) are compared with those of the graphene/Ru(0001).The results show that the coronene/Ru(0001) can be a simplified model system used to describe the interaction between graphene and ruthenium.Further calculations of the vibrational properties of coronene molecule adsorbed on Ru(0001)suggest that the phonon properties of differently corrugated regions of graphene on Ru(0001) are different.This model system is also used to investigate the selective adsorption of Pt atoms on graphene/Ru(0001).The configurations of Pt on coronene/Ru(0001) with the lowest binding energy give clues to explain the experimental observation that a Pt cluster selectively adsorbs on the second highest regions of graphene/Ru(0001).This work provides a simple model for understanding the adsorption properties and vibrational properties of graphene on Ru(0001) substrate.

  6. Interplay between chemical and magnetic order in CoRh nanoparticles: A first principles theoretical study

    Energy Technology Data Exchange (ETDEWEB)

    Diaz Sanchez, Luis Enrique; Pastor, Gustavo [Institut fuer Theoretische Physik, Universitaet Kassel, Heinrich Plett Str. 40, 34132 Kassel (Germany); Dorantes Davila, Jesus [Instituto de Fisica, Universidad Autonoma de San Luis Potosi, Alvaro Obregon 64, 78000 San Luis Potosi (Mexico)

    2011-07-01

    The ground-state magnetic properties of Co{sub x}Rh{sub 1-x} nanoparticles having sizes N=43, 273 and 531 atoms, and Co concentrations x=0, 0.25, 0.5, and 0.75 are investigated in the framework of density functional theory. The role of chemical order on the magnetic behavior is quantified by considering different fully-segregated face-centered cubic atomic arrangements showing both spherical and planar CoRh interfaces: core-shell and left-right subclusters. The ground-state magnetization for each cluster is determined by using a fixed-moment method. Electron correlation effects are discussed by comparing the results of LSDA and GGA exchange-correlation functionals. All considered CoRh clusters are found to be magnetic with an average spin moment that is larger than in macroscopic alloys with similar concentrations. The effect of embedding pure Co(Rh) clusters with Rh(Co) outer shells is analyzed.

  7. Revealing a room temperature ferromagnetism in cadmium oxide nanoparticles: An experimental and first-principles study

    KAUST Repository

    Bououdina, Mohamed

    2015-03-26

    We obtain a single cadmium oxide phase from powder synthesized by a thermal decomposition method of cadmium acetate dehydrate. The yielded powder is annealed in air, vacuum, and H2 gas in order to create point defects. Magnetization-field curves reveal the appearance of diamagnetic behavior with a ferromagnetic component for all the powders. Powder annealing under vacuum and H2 atmosphere leads to a saturation magnetization 1.15 memu g-1 and 1.2 memu g-1 respectively with an increase by 45% and 16% compared to the one annealed in air. We show that annealing in vacuum produces mainly oxygen vacancies while annealing in H2 gas creates mainly Cd vacancy leading to room temperature ferromagnetic (RTFM) component together with known diamagnetic properties. Ab initio calculations performed on the CdO nanoparticles show that the magnetism is governed by polarized hybrid states of the Cd d and O p orbitals together with the vacancy. © The Royal Society of Chemistry 2015.

  8. Vibrational and dielectric properties of magnesium aluminate spinel: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Zeng, Qingfeng, E-mail: qfzeng@nwpu.edu.cn [National Key Laboratory of Thermostructure Composite Materials, Northwestern Polytechnical University, Xi' an, Shaanxi 710072 (China); Zhang, Litong [National Key Laboratory of Thermostructure Composite Materials, Northwestern Polytechnical University, Xi' an, Shaanxi 710072 (China); Zhang, Xian; Chen, Qichao [School of Technical Physics, Xidian University, Xi' an, Shaanxi 710071 (China); Feng, Zhiqiang [School of Mechanics and Engineering, Southwest Jiaotong University, Chengdu, Sichuan 611756 (China); Laboratoire de Mecanique et d' Energetique, Universite d' Evry, Evry 91020 (France); Cai, Yongqing [Department of Physics, National University of Singapore, Singapore 117542 (Singapore); Cheng, Laifei; Weng, Zuohai [National Key Laboratory of Thermostructure Composite Materials, Northwestern Polytechnical University, Xi' an, Shaanxi 710072 (China)

    2011-09-19

    The vibrational and dielectric properties of MgAl{sub 2}O{sub 4} are investigated within the framework of density functional perturbation theory. Results of phonon frequencies at the Brillouin zone center, static dielectric constant, and electronic dielectric constant are reported. In comparison with experimental results, we find that the generalized gradient approximation potential results in more accurate phonon frequencies than local density approximation potential does. Dielectric, refractive index, extinction coefficient and infrared reflectance spectra of MgAl{sub 2}O{sub 4} are given, and the figures suggest that MgAl{sub 2}O{sub 4} presents good transmission properties in the spectrum range above 1000 cm{sup -1} and below 300 cm{sup -1}. -- Highlights: → MgAl{sub 2}O{sub 4} has an electronic dielectric constant smaller than the lattice component. → GGA potential results in more accurate phonon frequencies compared to LDA potential. → Weak reflection peaks at 321 cm{sup -1} and 596 cm{sup -1} result in narrow LO-TO bands. → Infrared spectrum suggests good transmission above 1000 cm{sup -1} and below 300 cm{sup -1}.

  9. Electronic structures of long periodic stacking order structures in Mg: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Wang, William Yi, E-mail: yuw129@psu.edu [Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802 (United States); State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Shang, Shun Li; Wang, Yi [Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802 (United States); Darling, Kristopher A. [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Kecskes, Laszlo J. [U.S. Army Research Laboratory, Weapons and Materials Research Directorate, RDRL-WMM-B, Aberdeen Proving Ground, MD 21005 (United States); Mathaudhu, Suveen N. [Materials Science Division, U.S. Army Research Office, Research Triangle Park, NC 27709 (United States); Hui, Xi Dong [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Liu, Zi-Kui, E-mail: dr.liu@psu.edu [Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802 (United States)

    2014-02-15

    Graphical abstract: -- Highlight: • Formation energies of the LPSOs (γ{sub LPSO}) can be scaled with respect to the formation energy of I2. • γ{sub LPSO} depends on the number of fault layers. • Electron structures of the 10H, 14H, 18R and 24R originate from those of I2. • Electron structure and formation energy of the 6H are between those of I1 and I2. -- Abstract: Long period stacking order (LPSO) structures, such as 6H, 10H, 14H, 18R and 24R, play significant roles in enhancing the mechanical properties of Mg alloys and have been largely investigated separately. In the present work, through detailed investigations of deformation electron density, we show that the electron structures of 10H, 14H, 18R and 24R LPSO structures in Mg originate from those of deformation stacking faults in Mg, and their formation energies can be scaled with respect to formation energy and the number of layers of deformation stacking faults, while the electron structure and formation energy of the 6H LPSO structure are between those of deformation and growth stacking faults. The simulated images of high resolution transmission electron microscopy compare well with experimental observed ones. The understanding of LPSO structures in Mg enables future quantitative investigations of effects of alloying elements on properties of LPSO structures and Mg alloys.

  10. First-principles study of defect behavior in irradiated uranium monocarbide

    Science.gov (United States)

    Ducher, R.; Dubourg, R.; Barrachin, M.; Pasturel, A.

    2011-03-01

    Ab initio electron theory based on the projector-augmented-wave method in the generalized gradient approximation of the density functional theory is used for calculating formation and migration energies of point defects in uranium monocarbide (UC). The use of the Hubbard term to describe the 5f electrons of uranium is discussed on the basis of the density of states and cohesive energies. A formalism allowing the “raw” calculated energies to be normalized is proposed to take into account the compositional dependence of defective crystals. Such formation energies are then used to determine the population of predominant defects as a function of nonstoichiometry. We identify the most stable defects as uranium antisites and carbon vacancies for UC1-x, and dimers C2 for UC1+x. The most stable thermal defects are obtained, in turn, by formation of complex defects associating dimer C2 and carbon vacancies whereas carbon Frenkel pairs and Schottky defects require larger formation energies. The migration energies are also calculated for different mechanisms, using as diffusion vectors both thermal vacancy sources and preexisting constitutional defects in the case of off-stoichiometric alloys. We compare the calculated diffusion paths with available experimental data proposed by Matzke [J. Less-Common Met.JCOMAH0022-508810.1016/0022-5088(86)90573-4 121, 537 (1986)].

  11. Enhanced Li capacity in functionalized graphene: A first principle study with van der Waals correction

    Science.gov (United States)

    Chouhan, Rajiv K.; Raghani, Pushpa

    2015-09-01

    We have investigated the adsorption of Li on graphene oxide using density functional theory. We show a novel and simple approach to achieve a positive lithiation potential on epoxy and hydroxyl functionalized graphene, compared to the negative lithiation potential that has been found on prestine graphene. We included the van der Waals correction into the calculation so as to get a better picture of weak interactions. A positive lithiation potential suggests a favorable adsorption of Li on graphene oxide sheets that can lead to an increase in the specific capacity, which in turn can be used as an anode material in Li-batteries. We find a high specific capacity of ˜860 mAhg-1 by functionalizing the graphene sheet. This capacity is higher than the previously reported capacities that were achieved on graphene with high concentration of Stone-Wales (75%) and divacancy (16%) defects. Creating such high density of defects can make the entire system energetically unstable, whereas graphene oxide is a naturally occurring substance.

  12. First-principles study of superabundant vacancy formation in metal hydrides.

    Science.gov (United States)

    Zhang, Changjun; Alavi, Ali

    2005-07-13

    Recent experiments have established the generality of superabundant vacancies (SAV) formation in metal hydrides. Aiming to elucidate this intriguing phenomenon and to clarify previous interpretations, we employ density-functional theory to investigate atomic mechanisms of SAV formation in fcc hydrides of Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au. We have found that upon H insertion, vacancy formation energies reduce substantially. This is consistent with experimental suggestions. We demonstrate that the entropy effect, which has been proposed to explain SAV formation, is not the main cause. Instead, it is the drastic change of electronic structure induced by the H in the SAV hydrides, which is to a large extent responsible. Interesting trends in systems investigated are also found: ideal hydrides of 5d metals and noble metals are unstable compared to the corresponding pure metals, but the SAV hydrides are more stable than the corresponding ideal hydrides, whereas opposite results exist in the cases of Ni, Rh, and Pd. These trends of stabilities of the SAV hydrides are discussed in detail and a general understanding for SAV formation is provided. Finally, we propose an alternative reaction pathway to generate a SAV hydride from a metal alloy.

  13. A first-principles study of co-doping in lanthanum bromide

    Science.gov (United States)

    Aberg, Daniel; Sadigh, Babak; Schleife, Andre; Erhart, Paul

    2015-03-01

    It was recently shown that the energy resolution of Ce-doped LaBr3 scintillator radiation detectors can be crucially improved by co-doping with Sr, Ca, or Ba. Here we outline a mechanism for this enhancement on the basis of electronic structure calculations. We show that Sr dopants create and bind to Br vacancies, resulting in stable neutral complexes. The association with Sr causes the deep vacancy level to move toward the conduction band edge. This is essential for reducing the effective carrier density available for Auger quenching during thermalization of hot carriers. Subsequent de-trapping of electrons from the complexes can activate Ce dopants that have previously captured a hole leading to luminescence. This mechanism implies an overall reduction of Auger quenching of free carriers, which is expected to improve the linearity of the photon light yield with respect to the energy of incident electron or photon. Optical properties of the Ce-Sr-vacancy triple complex are discussed and compared to experiment. Prepared by LLNL under Contract DE-AC52-07NA27344. Support from the National Nuclear Security Administration Office of Nonproliferation Research and Development (NA-22) is acknowledged.

  14. Structural and electronic properties of Y2CrS4 from first-principles study

    Science.gov (United States)

    Wang, B.-T.; Yin, W.; Li, W.-D.; Wang, F.

    2011-04-01

    We systematically study the structural, electronic, and magnetic properties of chromium sulfide Y2CrS4 by using density-functional theory. We find that antiferromagnetic order is more energetically favorable than ferromagnetic state and near the Fermi level the main occupation is from Cr 3 d states.

  15. First-principles studies of phase stability and the structural and dynamical properties of metal hydrides

    Energy Technology Data Exchange (ETDEWEB)

    Chou, M.Y.

    1992-04-01

    This report discusses the following topics: calculation of the Structural Properties of Yttrium; dynamical and pairing properties of {alpha}-YH{chi}; electronic and structural properties of YH{sub 2} and YH{sub 3}; phase diagram of hydrogen on Ru(000); peierls distortion in hexagonal YH{sub 3}; and study of hydrogen in niobium and palladium.

  16. First-Principles Study of Thermoelectric Properties of Covalent Organic Frameworks

    Science.gov (United States)

    Chumakov, Yurii; Aksakal, Fatma; Dimoglo, Anatholy; Ata, Ali; Palomares-Sánchez, Salvador A.

    2016-07-01

    Covalent organic frameworks (COFs) are new emerging functional porous materials. Strong covalent bonds result in molecular building blocks that can be arranged in layered two-dimensional (2D) or three-dimensional (3D) periodic networks. However, to the best of our knowledge, there have been no reports on experimental and theoretical studies of thermoelectrical properties of COFs to date. Therefore, density functional theory (DFT) and the Boltzmann transport equation have been applied in this work to calculate the semiclassical transport coefficients for phthalocyanine (Pc)-based NiPc, NiPc-benzothiadiazole (BTDA), and Pc COFs. Owing to the well-ordered stacking of the phthalocyanine units and linkers in these compounds, charge-carrier transport is facilitated in the stacking direction. In all studied compounds, the highly directional character of π-orbitals provides band-structure engineering and produces a type of low-dimensional hole transport along the stacking direction. All studied compounds are indirect semiconductors. The low-dimensional transport of holes and the localized states in both valence and conduction bands prevent the electron-hole compensation effect in the Seebeck coefficients, correlating with the large Seebeck coefficients of the studied compounds. Insertion of the electron-deficient building block benzothiadiazole in the NiPc-BTDA COF leads to positive Seebeck coefficients along the a-, b-, and c-directions. The relaxation time was estimated in our investigations from DFT band-structure calculations and the experimentally defined mobility, leading to determination of the electrical conductivity and electronic contribution to the thermal conductivity, as well as figure of merit ( ZT) estimation. Ni atom provided greater electrical conductivity along the c-direction in comparison with metal-free Pc COF, and NiPc COF showed the highest thermoelectric performance among the studied COFs.

  17. A first-principles study of CO hydrogenation into methane on molybdenum carbides catalysts

    Science.gov (United States)

    Qi, Ke-Zhen; Wang, Gui-Chang; Zheng, Wen-Jun

    2013-08-01

    The reaction mechanisms for the CO hydrogenation to produce CH4 on both fcc-Mo2C (100) and hcp-Mo2C (101) surfaces are investigated using density functional theory calculations with the periodic slab model. Through systematic calculations for the mechanisms of the CO hydrogenation on the two surfaces, we found that the reaction mechanisms are the same on both fcc and hcp Mo2C catalysts, that is, CO → HCO → H2CO → H2COH → CH2 → CH3 → CH4. The activation energy of the rate-determining step (CH3 + H → CH4) on fcc-Mo2C (100) (0.84 eV) is lower than that on hcp-Mo2C (101) (1.20 eV), and that is why catalytic activity of fcc-Mo2C is higher than hcp-Mo2C for CO hydrogenation. Our calculated results are consistent with the experimental observations. The activity difference of these two surfaces mainly comes from the co-adsorption energy difference between initial state (IS) and transition state (TS), that is, the co-adsorption energy difference between IS and TS is - 0.04 eV on fcc Mo2C (100), while it is as high as 0.68 eV on hcp Mo2C (101), and thus leading to the lower activation barrier for the reaction of CH3 + H → CH4 on fcc-Mo2C (100) compared to that of hcp-Mo2C (101).

  18. Structural, electronic, mechanical, and dynamical properties of graphene oxides: A first principles study

    Science.gov (United States)

    Dabhi, Shweta D.; Gupta, Sanjay D.; Jha, Prafulla K.

    2014-05-01

    We report the results of a theoretical study on the structural, electronic, mechanical, and vibrational properties of some graphene oxide models (GDO, a-GMO, z-GMO, ep-GMO and mix-GMO) at ambient pressure. The calculations are based on the ab-initio plane-wave pseudo potential density functional theory, within the generalized gradient approximations for the exchange and correlation functional. The calculated values of lattice parameters, bulk modulus, and its first order pressure derivative are in good agreement with other reports. A linear response approach to the density functional theory is used to derive the phonon frequencies. We discuss the contribution of the phonons in the dynamical stability of graphene oxides and detailed analysis of zone centre phonon modes in all the above mentioned models. Our study demonstrates a wide range of energy gap available in the considered models of graphene oxide and hence the possibility of their use in nanodevices.

  19. First-principles study of the stability of fission products in uranium monocarbide

    Science.gov (United States)

    Bévillon, Émile; Ducher, Roland; Barrachin, Marc; Dubourg, Roland

    2012-07-01

    The incorporation and stability of fission products in uranium monocarbide are studied by means of Density Functional Theory using the generalized gradient approximation and projector-augmented waves method. The computations are performed considering incorporation sites of UC, such as the U, C and interstitial sites, and Schottky defects. The computed incorporation energies are discussed on the basis of the atomic size of the fission products, their chemical environment and the electronic structure. These energies show that all the studied fission products would preferentially occupy the U site. However, incorporation energies do not provide any further information on the fission product location in the case of unavailability of the sites which is why the concept of solution energies is also used. The solution energies obtained confirm that all the fission products are expected to be more stable on a U site of a single uranium vacancy or within a non-bound Schottky defect in equilibrium conditions.

  20. First-principles study of the stability of fission products in uranium monocarbide

    Energy Technology Data Exchange (ETDEWEB)

    Bevillon, Emile, E-mail: emile.bevillon@yahoo.fr [IRSN, SEMIC, DPAM, LETR, Centre de Cadarache, 13115 Saint Paul Lez Durance (France); Ducher, Roland; Barrachin, Marc; Dubourg, Roland [IRSN, SEMIC, DPAM, LETR, Centre de Cadarache, 13115 Saint Paul Lez Durance (France)

    2012-07-15

    The incorporation and stability of fission products in uranium monocarbide are studied by means of Density Functional Theory using the generalized gradient approximation and projector-augmented waves method. The computations are performed considering incorporation sites of UC, such as the U, C and interstitial sites, and Schottky defects. The computed incorporation energies are discussed on the basis of the atomic size of the fission products, their chemical environment and the electronic structure. These energies show that all the studied fission products would preferentially occupy the U site. However, incorporation energies do not provide any further information on the fission product location in the case of unavailability of the sites which is why the concept of solution energies is also used. The solution energies obtained confirm that all the fission products are expected to be more stable on a U site of a single uranium vacancy or within a non-bound Schottky defect in equilibrium conditions.

  1. Structural, electronic, mechanical, and dynamical properties of graphene oxides: A first principles study

    Energy Technology Data Exchange (ETDEWEB)

    Dabhi, Shweta D. [Department of Physics, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar 364001 (India); Gupta, Sanjay D. [V. B. Institute of Science, Department of Physics, C. U. Shah University, Wadhwan City - 363030, Surendranagar (India); Jha, Prafulla K., E-mail: prafullaj@yahoo.com [Department of Physics, Faculty of Science, The Maharaja Sayajirao University of Baroda, Vadodara-390002 (India)

    2014-05-28

    We report the results of a theoretical study on the structural, electronic, mechanical, and vibrational properties of some graphene oxide models (GDO, a-GMO, z-GMO, ep-GMO and mix-GMO) at ambient pressure. The calculations are based on the ab-initio plane-wave pseudo potential density functional theory, within the generalized gradient approximations for the exchange and correlation functional. The calculated values of lattice parameters, bulk modulus, and its first order pressure derivative are in good agreement with other reports. A linear response approach to the density functional theory is used to derive the phonon frequencies. We discuss the contribution of the phonons in the dynamical stability of graphene oxides and detailed analysis of zone centre phonon modes in all the above mentioned models. Our study demonstrates a wide range of energy gap available in the considered models of graphene oxide and hence the possibility of their use in nanodevices.

  2. Transmission Electron Microscopy of Single Wall Carbon Nanotube/Polymer Nanocomposites: A First-Principles Study

    Science.gov (United States)

    Sola, Francisco; Xia, Zhenhai; Lebrion-Colon, Marisabel; Meador, Michael A.

    2012-01-01

    The physics of HRTEM image formation and electron diffraction of SWCNT in a polymer matrix were investigated theoretically on the basis of the multislice method, and the optics of a FEG Super TWIN Philips CM 200 TEM operated at 80 kV. The effect of nanocomposite thickness on both image contrast and typical electron diffraction reflections of nanofillers were explored. The implications of the results on the experimental applicability to study dispersion, chirality and diameter of nanofillers are discussed.

  3. First-principles study of two-dimensional van der Waals heterojunctions

    OpenAIRE

    Hu, Wei; Yang, Jinlong

    2015-01-01

    Research on graphene and other two-dimensional (2D) materials, such as silicene, germanene, phosphorene, hexagonal boron nitride (h-BN), graphitic carbon nitride (g-C3N4), graphitic zinc oxide (g-ZnO) and molybdenum disulphide (MoS2), has recently received considerable interest owing to their outstanding properties and wide applications. Looking beyond this field, combining the electronic structures of 2D materials in ultrathin van der Waals heterojunctions has also emerged to widely study th...

  4. First-principles study of fully relaxed vacancies in GaAs

    OpenAIRE

    Laasonen, K; Nieminen, Risto M.; Puska, Martti J.

    1992-01-01

    The structural and electronic properties of vacancies in GaAs have been studied using ab initio molecular dynamics. The atomic structures of vacancies in different charge states have been optimized by using a simulated-annealing procedure. The neighbor-atom relaxations are modest for neutral, singly negative, and doubly negative Ga vacancies as well as for the neutral As vacancy. In the case of singly and doubly negative As vacancies, very strong inward relaxations are found. These inward rel...

  5. First-principles studies of chromium line-ordered alloys in a molybdenum disulfide monolayer

    Science.gov (United States)

    Andriambelaza, N. F.; Mapasha, R. E.; Chetty, N.

    2017-08-01

    Density functional theory calculations have been performed to study the thermodynamic stability, structural and electronic properties of various chromium (Cr) line-ordered alloy configurations in a molybdenum disulfide (MoS2) hexagonal monolayer for band gap engineering. Only the molybdenum (Mo) sites were substituted at each concentration in this study. For comparison purposes, different Cr line-ordered alloy and random alloy configurations were studied and the most thermodynamically stable ones at each concentration were identified. The configurations formed by the nearest neighbor pair of Cr atoms are energetically most favorable. The line-ordered alloys are constantly lower in formation energy than the random alloys at each concentration. An increase in Cr concentration reduces the lattice constant of the MoS2 system following the Vegard’s law. From density of states analysis, we found that the MoS2 band gap is tunable by both the Cr line-ordered alloys and random alloys with the same magnitudes. The reduction of the band gap is mainly due to the hybridization of the Cr 3d and Mo 4d orbitals at the vicinity of the band edges. The band gap engineering and magnitudes (1.65 eV to 0.86 eV) suggest that the Cr alloys in a MoS2 monolayer are good candidates for nanotechnology devices.

  6. First-principles study of the structural stability and electronic structures of TaN

    Energy Technology Data Exchange (ETDEWEB)

    Cao, C.L.; Yuan, G. [School of Information and Engineering, Ocean University of China, QingDao 266100 (China); Hou, Z.F. [Department of Physics, Fudan University, Shanghai 200433 (China)

    2008-08-15

    Using the plane-wave pseudopotential method within the generalized gradient approximation, we have studied the structural stability and electronic structures for several TaN phases. Our results show CoSn is the calculated ground-state structure of TaN among the five crystallographic structures that have been studied. The order of energetic stability of phase structures of TaN from low to high is: CsClstudied has a metallic nature. The calculated bulk modulus indicates that TaN in the WC structure may be a less compressible material. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. First-principles studies of the electronic and optical properties of 6H-SiC

    Energy Technology Data Exchange (ETDEWEB)

    Xie Changkun; Xu Pengshou; Xu Faqiang; Pan Haibin; Li Yonghua

    2003-08-01

    We study the electronic and optical properties of hexagonal 6H-SiC crystal, using ab initio full potential augmented plane wave method. The density of states (DOS) and band structure are presented based on local density function theory. From the electronic structure calculation, the imaginary part of the dielectric function has been obtained directly using the joint DOS and the optical matrix elements. With band gap correction, the real part of dielectric function can be derived from the imaginary part by the Kramers-Kronig relationship. The reflectivity for normal incidence is also calculated. The resulting spectrum is in good agreement with available experimental data in a wide energy range.

  8. Hydrogen spillover on DV (555-777) graphene – vanadium cluster system: First principles study

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, E. Mathan, E-mail: ranjit.t@res.srmuniv.ac.in, E-mail: mathanranjitha@gmail.com; Thapa, Ranjit, E-mail: ranjit.t@res.srmuniv.ac.in, E-mail: mathanranjitha@gmail.com [SRM Research Institute, SRM University, Kattankulathur, Tamil Nadu - 603203 (India); P, Sabarikirishwaran [Department of Physics and Nanotechnology, SRM University, Kattankulathur, Tamil Nadu - 603203 (India)

    2015-06-24

    Using dispersion corrected density functional theory (DFT+D), the interaction of Vanadium adatom and cluster with divacancy (555-777) defective graphene sheet has been studied elaborately. We explore the prospect of hydrogen storage on V{sub 4} cluster adsorbed divacancy graphene system. It has been observed that V{sub 4} cluster (acting as a catalyst) can dissociate the H{sub 2} molecule into H atoms with very low barrier energy. We introduce the spillover of the atomic hydrogen throughout the surface via external mediator gallane (GaH{sub 3}) to form a hydrogenated system.

  9. Tuning the chemical activity through PtAu nanoalloying: a first principles study

    KAUST Repository

    Mokkath, Junais Habeeb

    2013-06-21

    The electronic structure and adsorption properties of 1.5 nm sized Pt, Au, and PtAu nanoclusters are studied by density functional theory. We explain the recent experimental finding that 20% Au content in PtAu nanoparticles is optimal to induce a dramatically different catalytic behavior. Our results show that the d-band center together with the density of states at the Fermi energy can be used as an indicator of the chemical activity of PtAu nanoclusters. The most favorable adsorption sites on the cluster surfaces as a function of the Pt/Au ratio are identified using atomic H as a probe.

  10. A first principle study of the pressure dependent elastic properties of monazite LaPO4

    Science.gov (United States)

    Ali, Kawsar; Arya, A.; Ghosh, P. S.; Dey, G. K.

    2016-05-01

    DFT based ab-initio simulations have been performed to study the effect of pressure on the elastic properties of monazite LaPO4 which is a promising host material for immobilization of high level nuclear waste. The phase is found to be stable up to 30 GPa. The calculated polycrystalline bulk, shear and Young moduli show an increasing trend as a function of pressure. The ductility and anisotropy in shear modulus of the material have been found to increase with pressure; whilethe bulk modulus anisotropy decreases with pressure.

  11. First Principles Study on Electronic Structures of Mn2+:CdMoO4 Crystals

    Institute of Scientific and Technical Information of China (English)

    WANG Xi-En; LIU Ting-Yu; ZHANG Qi-Ren; ZHANG Hai-Yan; SONG Min; GUO Xiao-Feng; YIN Ji-Gang

    2008-01-01

    @@ Electronic structures of the Mn2+:CdMoO4 crystal are studied within the framework of the fully relativistic self-consistent Dirac-Slater theory,using a numerically discrete variation (DV-Xα)method.The calculated results indicate that the 3d states of Mn have donor energy level in the forbidden band of CdMoO4 crystal.The transition energy of O 2p→Mn 3d is 3.12 eV under excitation corresponding electronic transition being O2-+Mn2+ hvex=3.12 eV→ O-+Mn+hvem→O2+Mn2+.

  12. Electrostatic-field-enhanced photoexfoliation of bilayer benzene: A first-principles study

    Science.gov (United States)

    Uchida, Kazuki; Silaeva, Elena P.; Watanabe, Kazuyuki

    2016-06-01

    Photoexfoliation of bilayer benzene in an external electrostatic (dc) field is studied using time-dependent density functional theory combined with molecular dynamics. We find that the dc-field-induced force on the upper benzene in addition to the repulsive interaction between the positively charged benzene molecules induced by the laser field leads to fast athermal exfoliation. Thus, we conclude that the dc field enhances the photoexfoliation due to dc-field emission in addition to laser-assisted photoemission. The athermal exfoliation process is shown to depend crucially on the charge state of benzene molecules rather than on the excitation energy supplied by the laser.

  13. First Principles Study of Double Photoionization of H2 UsingExterior Complex Scaling

    Energy Technology Data Exchange (ETDEWEB)

    Rescigno, Thomas N.; Vanroose, Wim; Horner, Daniel A.; Martin,Fernando; McCurdy, C. William

    2006-07-21

    Exterior complex scaling provides a practical path forfirst-principles studies of atomic and molecular ionizationproblemssince it avoids explicit enforcement of asymptotic boundary conditionsfor 3-body Coulomb breakup. We have used the method of exterior complexscaling, implemented with both the discrete variable representation andB-splines, to obtain the first-order wave function for molecular hydrogencorresponding to a single photon having been absorbed by a correlatedinitial state. These wave functions are used to construct convergedtriple differential cross sections for double photoionization of alignedH2 molecules.

  14. Optical absorption of the blue fluorescent protein: a first-principles study.

    Science.gov (United States)

    Lopez, Xabier; Marques, Miguel A L; Castro, Alberto; Rubio, Angel

    2005-09-07

    An extensive study of the optical absorption spectra of the blue fluorescent protein (BFP) is presented. We investigate different protonation states of the chromophore (neutral, anionic, and cationic) and analyze the role of the protein environment and of thermal fluctuations. The role of the environment is 2-fold: (i) it induces structural modifications of the gas-phase chromophore, the most important being the torsion of the imida rings; and (ii) it makes a local-field modification of the external electromagnetic field. It turns out that the torsion of the imida rings shifts significantly the gas-phase spectra to lower energies, whereas the consistent inclusion of the closest residues field produces only minor modifications on the spectra. From all of the configurations studied, the neutral cis-HSD and the anionic HSA seem to be the most likely candidates to explain the experimental spectrum. Furthermore, the present results clearly rule out the presence of the cationic protonation state (HSP) of the chromophore. However, a better description of the measured experimental absorption data may be obtained when the temperature fluctuations of the floppy torsional motion of the two imida rings are included. Our results, together with previous work on the green fluorescent protein, demonstrate the power of combining time-dependent density functional calculations and optical absorption measurements to discern the relevant chemical information on the nature and state of chromopeptides.

  15. Mechanical and electronic coupling in few-layer graphene and hBN wrinkles: a first-principles study

    Science.gov (United States)

    Guo, Yufeng; Qiu, Jiapeng; Guo, Wanlin

    2016-12-01

    Wrinkle engineering is an important pathway to develop novel functional devices of two-dimensional materials. By combining first-principles calculations and continuum mechanics modelling, we have investigated the wrinkling of few-layer graphene and hexagonal boron nitride (hBN) and provide a way to estimate their bending stiffness. For few-layer wrinkles under the same strain, the magnitude of structural deformation of each constituent layer gradually decreases from bottom to top layers, while interlayer interaction increases with increasing layer number. Comparing with monolayer wrinkles, the electronic properties of few-layer wrinkles are more sensitive to bending deformation as mechanical and electronic coupling induce charge redistribution at the wrinkles, making few-layer graphene and hBN wrinkles suitable for electromechanical system application.

  16. Kaolinite: Defect defined material properties – A soft X-ray and first principles study of the band gap

    Energy Technology Data Exchange (ETDEWEB)

    Pietzsch, A., E-mail: annette.pietzsch@helmholtz-berlin.de [Institute for Methods and Instrumentation in Synchrotron Radiation Research G-ISRR, Helmholtz-Zentrum für Materialien und Energie GmbH, Albert-Einstein-Str. 15, 12489 Berlin (Germany); Nisar, J. [Pakistan Atomic Energy Commission (PAEC), P.O. Box 2151, Islamabad (Pakistan); Jämstorp, E. [Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Gråsjö, J. [Department of Pharmacy, Uppsala University, Box 580, 75123 Uppsala (Sweden); Århammar, C. [Coromant R& D, S-126 80 Stockholm (Sweden); Ahuja, R.; Rubensson, J.-E. [Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala (Sweden)

    2015-07-15

    Highlights: • The respective electronic structure of synthetic and natural kaolinite is compared. • The size of the band gap and thus many important material properties are defined by defect states in the band gap. • The oxygen-based defect states are identified and analyzed. • The band gap of kaolinite decreases significantly due to the forming of defects. - Abstract: By combining X-ray absorption spectroscopy and first principles calculations we have determined the electronic structure of synthetic and natural kaolinite as a model system for engineered and natural clay materials. We have analyzed defect states in the band gap and find that both natural and synthetic kaolinite contain defects where oxygen replaces hydrogen in one of the Al (0 0 1)-hydroxyl groups of the kaolinite clay sheets. The band gap of both synthetic and natural kaolinite is found to decrease by about 3.2 eV as this defect is formed.

  17. Cr doped topological insulator Bi2Se3 under external electric field: A first-principle study

    Science.gov (United States)

    Lian, Ruqian; Zhang, Jian-Min; Yang, Yanmin; Xu, Guigui; Zhong, Kehua; Huang, Zhigao

    2017-06-01

    In this paper, we investigated the magnetic topological insulator (MTI) Cr-doped Bi2Se3 film using first principles calculations based on the density functional theory (DFT). The band structure of Cr doped 3QL-Bi2Se3 film was calculated comparing with pure Bi2Se3 film. Our results demonstrate that the doping of Cr atom changes the degenerate surface state of pure Bi2Se3, inducing the ferromagnetism. Under the external electric field, the band gap of pure Bi2Se3 films is determined by the charge transfer and the effect of spin-orbital coupling (SOC). For the MTI, the electric field will redistribute the electrons and enhance the magnetism. Our results will further promote the development of the electronic and spintronic applications of topological insulator.

  18. Sensitizers in inelastic electron tunneling spectroscopy: a first-principles study of functional aromatics on Cu(111)

    Science.gov (United States)

    Burema, S. R.; Bocquet, M.-L.

    2012-08-01

    Low sensitivity is a key problem in inelastic electron tunneling spectroscopy (IETS) with the scanning tunneling microscope. Using first-principles simulations, we predict different means to tune the IETS sensitivity of symmetrical functional aromatics on a Cu(111) surface. We show how the IET-spectra of phenyl-NO2 compounds can be greatly enhanced as compared to pristine phenyl. More precisely, the NO2 substituent qualifies as a sensitizer of low-frequency wagging modes, but also as a quencher of high-frequency stretching modes. At variance, the CO2 substituent is found to suppress the whole IET-activity. The head-up (non-anchoring) and head-down (anchoring) configurations of the functional group lead to minor changes in the signals, nevertheless allowing access to discriminate configurational features. It is shown how to disentangle the electronic and steric effects of the substituent in the STM junction.

  19. First-principles study of interphase Ni3Sn in Sn-Ni alloy for anode of lithium ion battery

    Institute of Scientific and Technical Information of China (English)

    Hou Xian-Hua; Hu She-Jun; Li Wei-Shan; Ru Qiang; Yu Hong-Wen; Huang Zhao-Wen

    2008-01-01

    This paper investigates the mechanism of Li insertion into interphase NiaSn in Ni-Sn alloy for the anode of lithium ion battery by means of the first-principles plane-wave pseudopotential.Compared with other phases,it is found that the Ni3Sn has larger relative expansion ratio and lower electrochemical potential,with its specific plateaus voltage around 0.3 eV when lithium atoms are filled in all octahedral interstitial sites.and the relative expansion ratio increasing dramatically when the lithiated phase transits from octahedral interstitial sites to tetrahedral interstitial sites.So this phase is a devastating phase for whole alloy electrode materials.

  20. First-principles study of the transport behavior of zigzag graphene nanoribbons tailored by strain

    Directory of Open Access Journals (Sweden)

    Jinying Wang

    2012-03-01

    Full Text Available The charge transport properties of zigzag graphene nanoribbons (ZGNRs under uniaxial and shear strains are theoretically studied. Although all strained ZGNRs have similar metallic band structures, they show four types of transport behavior under bias voltages that depend on the type of strain and the mirror symmetry of the ZGNR. Under an applied uniaxial strain, the current of symmetric ZGNRs is consistently small, while for asymmetric ZGNRs it is large. In contrast, the current increases with increasing shear strain for symmetric ZGNRs while it decreases for asymmetric ZGNRs. The current properties merge when the shear strain exceeds a critical value, and the two systems then show similar behavior. Our results suggest that strained ZGNRs with an appropriate applied shear are ideal conducting wires.

  1. Atomic, electronic, and magnetic properties of bimetallic ZrCo clusters: A first-principles study

    Science.gov (United States)

    Chattaraj, D.; Bhattacharya, Saswata; Dash, Smruti; Majumder, C.

    2016-09-01

    Here, we report the atomic, electronic, and magnetic structures of small ZrmCon (m + n = 2, 4, 6, and 8) alloy clusters based on spin-polarized density functional theory under the plane wave based pseudo-potential approach. The ground state geometry and other low-lying stable isomers of each cluster have been identified using the cascade genetic algorithm scheme. On the basis of the relative energy, it is found that Zr2Co2 (for tetramer), Zr3Co3 (for hexamer), and Zr4Co4 (for octamer) are the most stable isomers than others. In order to underscore the hydrogen storage capacity of these small clusters, the hydrogen adsorption on the stable ZrmCon (m + n = 2, 4, 6, and 8) clusters has also been studied. The electronic structures of ZrmCon clusters with and without adsorbed hydrogen are described in terms of density of states spectra and charge density contours.

  2. First-principles study of the magnetism of Ni-doped MoS2 monolayer

    Science.gov (United States)

    Luo, Min; Hao Shen, Yu; Hao Chu, Jun

    2016-09-01

    The magnetic properties of Ni-doped monolayer MoS2 are investigated using the density function theory. The results show that two Ni-doped systems of the nearest-neighbor configuration are ferromagnetic. The p-d hybridization between the Ni dopant and its neighboring S atoms results in the splitting of energy levels near the Fermi energy. These results suggest the p-d hybridization mechanism for the magnetism of the Ni-doped MoS2 monolayer. The magnetic moment disappears with increasing Ni-Ni distance. Our studies predict the nearest two-Ni-doped MoS2 monolayers to be candidates for thin dilute magnetic semiconductors. Moreover, the formation energy calculations indicate that it would be easier to incorporate Ni atoms into a S-rich MoS2 monolayer in the experiment.

  3. First-principle study on optical properties of N-La-codoped anatase TiO

    Institute of Scientific and Technical Information of China (English)

    Wang Qing; Liang Ji-Feng; Zhang Ren-Hui; Li Qiang; Dai Jian-Feng

    2013-01-01

    The electronic structures,deformation charge density,dipole moment,and optical properties of N-La-codoped anatase titanium dioxide (TiO2) are studied using the plane-wave ultrasoft pseudopotential method based on the density functional theory (DFT).The optical properties of two-ion-doped TiO2 are analyzed via electronic structures,deformation charge density,and dipole moment.For the model of N-La-doped TiO2,a smaller atom fraction of N and La atoms induces better optical properties.The absorption edges of two doped TiO2 models redshift to the visible-light region.

  4. First Principles Molecular Dynamics Study of Catalysis for Polyolefins: the Ziegler-Natta Heterogeneous System.

    Directory of Open Access Journals (Sweden)

    Michele Parrinello

    2002-04-01

    Full Text Available Abstract: We review part of our recent ab initio molecular dynamics study on the Ti-based Ziegler-Natta supported heterogeneous catalysis of α-olefins. The results for the insertion of ethylene in the metal-carbon bond are discussed as a fundamental textbook example of polymerization processes. Comparison with the few experimental data available has shown that simulation can reproduce activation barriers and the overall energetics of the reaction with sufficient accuracy. This puts these quantum dynamical simulations in a new perspective as a virtual laboratory where the microscopic picture of the catalysis, which represents an important issue that still escapes experimental probes, can be observed and understood. These results are then discussed in comparison with a V-based catalyst in order to figure out analogies and differences with respect to the industrially more successful Tibased systems.

  5. First-principles study of CO adsorption on ZnO surfaces

    CERN Document Server

    Meyer, B

    2003-01-01

    Using density-functional theory we have calculated the equilibrium geometries and binding energies of a CO monolayer adsorbed on the nonpolar (1010) and the polar (0001)-Zn and (0001)-O surfaces of ZnO. Different adsorption sites and CO orientations were considered, and for the polar surfaces the influence of a hydrogen coverage upon CO adsorption was studied. For the clean surfaces we find that CO exclusively binds to Zn ions with a binding energy of 0.24 and 0.37 eV for the nonpolar (1010) and the polar (0001)-Zn surface, respectively. A purely repulsive interaction of CO with surface oxygen ions is obtained. On the other hand, if the polar surfaces are hydrogen saturated, we predict a weak chemisorption of CO to the OH-terminated (0001) surface with a binding energy of 0.20 eV but no CO adsorption for the ZnH-terminated (0001) face. (letter to the editor)

  6. Relaxations and bonding mechanism of arsenic in-situ impurities in MCT: first-principles study

    Institute of Scientific and Technical Information of China (English)

    SUN Li-zhong; ZHONG Xiang-li; WANG Jin-bin; CHEN Xiao-shuang; LU Wei

    2006-01-01

    The structural and electronic properties of the arsenic in-situ impurity in Hg1-xCdxTe(MCT) were studied by combining the full-potential linear augmented plane wave (FP-LAPW) and plane-wave pseudopotential methods base on the density functional theory. Structural relaxations, local charge density, densities of states are computed to investigate the effects of the impurity on the electronic structure. The bonding characteristics between the impurity and the host atoms are discussed by analysis of the valence charge density and the bonding charge density. The amphoteric behavior of arsenic impurity in MCT has been shown. The defect levels introduced by the in-situ arsenic impurities are determined by the single-particle electron energy calculations, which are in good agreement with the experimental results.

  7. Chemisorption of NO on Pt-decorated graphene as modified nanostructure media: A first principles study

    Science.gov (United States)

    Rad, Ali Shokuhi; Abedini, Ehsan

    2016-01-01

    We used density functional theory calculations (DFT) to search the potential of pristine as well as Pt-decorated graphene sheets as adsorbent/gas sensors for NO by considering the electronic properties of NO on these two surfaces. We found much higher adsorption energy, higher charge transfer, lower connecting distance, and higher orbital hybridizing of NO gas molecule on Pt-decorated graphene than pristine graphene. We used orbital analysis including density of states as well as frontier molecular orbital study for NO-surface systems because of more understanding of the kind of interaction. Our results reveal physisorption of NO on pristine graphene with adsorption energy of -24 kJ mol-1while in contrast much higher adsorption energy of -199 kJ mol-1 is achieved upon adsorption of NO on Pt-decorated graphene which is in the range of chemisorption.

  8. First-principles study of anharmonic phonon effects in tetrahedral semiconductors via an external electric field

    Science.gov (United States)

    Dabiri, Zohreh; Kazempour, Ali; Sadeghzadeh, Mohammad Ali

    2016-11-01

    The strength of phonon anharmonicity is investigated in the framework of the Density Functional Perturbation Theory via an applied constant electric field. In contrast to routine approaches, we have employed the electric field as an effective probe to quest after the quasi-harmonic and anharmonic effects. Two typical tetrahedral semiconductors (diamond and silicon) have been selected to test the efficiency of this approach. In this scheme the applied field is responsible for establishing the perturbation and also inducing the anharmonicity in systems. The induced polarization is a result of changing the electronic density while ions are located at their ground state coordinates or at a specified strain. Employing this method, physical quantities of the semiconductors are calculated in presence of the electron-phonon interaction directly and, phonon-phonon interaction, indirectly. The present approach, which is in good agreement with previous theoretical and experimental studies, can be introduced as a benchmark to simply investigate the anharmonicity and pertinent consequences in materials.

  9. First-principles study on thermodynamic properties and phase transitions in TiS(2).

    Science.gov (United States)

    Yu, Yonggang G; Ross, Nancy L

    2011-02-01

    Structural and vibrational properties of TiS(2) with the CdI(2) structure have been studied to high pressures from density functional calculations with the local density approximation (LDA). The calculated axial compressibility of the CdI(2)-type phase agrees well with experimental data and is typical of layered transition-metal dichalcogenides. The obtained phonon dispersions show a good correspondence with available experiments. A phonon anomaly is revealed at 0 GPa, but is much reduced at 20 GPa. The thermodynamic properties of this phase were also calculated at high pressures and high temperatures using the quasi-harmonic approximation. Our LDA study on the pressure-induced phase transition sequence predicts that the CdI(2)-type TiS(2), the phase stable at ambient conditions, should transform to the cotunnite phase at 15.1 GPa, then to a tetragonal phase (I4/mmm) at 45.0 GPa. The tetragonal phase remains stable to at least 500 GPa. The existence of the tetragonal phase at high pressures is consistent with our previous findings in NiS(2) (Yu and Ross 2010 J. Phys.: Condens. Matter 22 235401). The cotunnite phase, although only stable in a narrow pressure range between 15.1 and 45.0 GPa, displays the formation of a compact S network between 100 and 200 GPa, which is evidenced by a kink in the variation of unit cell lengths with pressure. The electron density analysis in cotunnite shows that valence electrons are delocalized from Ti atoms and concentrated near the S network.

  10. Magnetism, structure and chemical order in small CoPd clusters: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Mokkath, Junais Habeeb, E-mail: Junais.Mokkath@kaust.edu.sa

    2014-01-15

    The structural, electronic and magnetic properties of small Co{sub m}Pd{sub n}(N=m+n=8,m=0−N) nanoalloy clusters are studied in the framework of a generalized-gradient approximation to density-functional theory. The optimized cluster structures have a clear tendency to maximize the number of nearest-neighbor CoCo pairs. The magnetic order is found to be ferromagnetic-like (FM) for all the ground-state structures. Antiferromagnetic-like spin arrangements were found in some low-lying isomers. The average magnetic moment per atom μ{sup ¯}{sub N} increases approximately linearly with Co content. A remarkable enhancement of the local Co moments is observed as a result of Pd doping. This is a consequence of the increase in the number of Co d holes, due to CoPd charge transfer, combined with the reduced local coordination. The influence of spin–orbit interactions on the cluster properties is also discussed. - Highlights: • This work analyses the structural and magnetic properties of CoPd nanoclusters. • The magnetic order is found to be ferromagnetic-like for all the ground-state structures. • The average magnetic moment per atom increases approximately linearly with Co content. • The influence of spin–orbit interactions on the cluster properties is discussed.

  11. Structure determination of ultra dense magnesium borohydride: A first-principles study

    Science.gov (United States)

    Fan, Jing; Duan, Defang; Jin, Xilian; Bao, Kuo; Liu, Bingbing; Cui, Tian

    2013-06-01

    Magnesium borohydride (Mg(BH4)2) is one of the potential hydrogen storage materials. Recently, two experiments [Y. Filinchuk, B. Richter, T. R. Jensen, V. Dmitriev, D. Chernyshov, and H. Hagemann, Angew. Chem., Int. Ed. 50, 11162 (2011);, 10.1002/anie.201100675 L. George, V. Drozd, and S. K. Saxena, J. Phys. Chem. C 113, 486 (2009), 10.1021/jp807842t] found that α-Mg(BH4)2 can irreversibly be transformed to an ultra dense δ-Mg(BH4)2 under high pressure. Its volumetric hydrogen content at ambient pressure (147 g/cm3) exceeds twice of DOE's (U.S. Department of Energy) target (70 g/cm3) and that of α-Mg(BH4)2 (117 g/cm3) by 20%. In this study, the experimentally proposed P42nm structure of δ-phase has been found to be dynamically unstable. A new Fddd structure has been reported as a good candidate of δ-phase instead. Its enthalpy from 0 to 12 GPa is much lower than P42nm structure and the simulated X-ray diffraction spectrum is in satisfied agreement with previous experiments. In addition, the previously proposed P-3m1 structure, which is denser than Fddd, is found to be a candidate of ɛ-phase due to the agreement of Raman shifts.

  12. First-principles study of the structure of water layers on flat and stepped Pb electrodes.

    Science.gov (United States)

    Lin, Xiaohang; Evers, Ferdinand; Groß, Axel

    2016-01-01

    On the basis of perodic density functional theory (DFT) calculations, we have addressed the geometric structures and electronic properties of water layers on flat and stepped Pb surfaces. In contrast to late d-band metals, on Pb(111) the energy minimum structure does not correspond to an ice-like hexagonal arrangement at a coverage of 2/3, but rather to a distorted structure at a coverage of 1 due to the larger lattice constant of Pb. At stepped Pb surfaces, the water layers are pinned at the step edge and form a complex network consisting of rectangles, pentagons and hexagons. The thermal stability of the water layers has been studied by using ab initio molecular dynamics simulations (AIMD) at a temperature of 140 K. Whereas the water layer on Pb(111) is already unstable at this temperature, the water layers on Pb(100), Pb(311), Pb(511) and Pb(711) exhibit a higher stability because of stronger water-water interactions. The vibrational spectra of the water layers at the stepped surfaces show a characteristic splitting into three modes in the O-H stretch region.

  13. First-principles study on the electronic, elastic and thermodynamic properties of three novel germanium nitrides

    Science.gov (United States)

    Yuping, Cang; Xiaoling, Yao; Dong, Chen; Fan, Yang; Huiming, Yang

    2016-07-01

    The ultrasoft pseudo-potential plane wave method combined with the quasi-harmonic approach have been used to study the electronic, elastic and thermodynamic properties of the tetragonal, monoclinic and orthorhombic Ge3N4. The negative formation enthalpies, the satisfactory of Born's criteria and the linear variations of elastic constants with pressure indicate that the three polymorphs can retain their stabilities in the pressure range of 0-25 GPa. The three Ge3N4 are brittle solids at 0 GPa, while they behave in ductile manners in the pressure range of 5-25 GPa. t- and o-Ge3N4 are hard materials but anisotropic. m-Ge3N4 has the largest ductility among the three phases. The results reveal that m-Ge3N4 belongs to an indirect band gap semiconductor, while t- and o-Ge3N4 have direct band gaps. For the thermal properties, several interesting features can be observed above 300 K. o-Ge3N4 exhibits the largest heat capacity, while m-Ge3N4 shows the highest Debye temperature. The results predicted in this work can provide reference data for future experiments. Project supported by the National Natural Science Foundation of China (Nos. 61475132, 11475143, 61501392, 11304141) and the National Training Programs of Innovation and Entrepreneurship for Undergraduates (No. 201510477001).

  14. The first-principle study on the stability of trans-HCOH in various solvents

    Science.gov (United States)

    Nur Fadilla, Rizka; Dwi Aisyah, Nufida; Dipojono, Hermawan K.; Rusydi, Febdian

    2017-05-01

    We attempt to study about the solvent effects of the stability of trans-HCOH molecules using the density-functional theory. Experimentally, trans-HCOH rearranges to H2CO with half-life of two hours [1] which we theoretically proved that it occurs through quantum tunneling. [2] In this work, we calculate the rearrangement rate of the molecules in various solvents. The solvents are selected based on their dielectric constant values, from lower to higher ones; they are benzene, dichloroethane, benzaldehyde, acetone, methanol, ethanediol, dimethylsulfoxide, formic acid, water, and formamide. We use polarizable continuum to model the solvents (PCM). We begin from determining the reaction path from trans-HCOH to H2CO and its corresponding energy barrier using intrinsic reaction coordinate calculation with PCM. Then, we use Wentzel-Kramers-Brillouin (WKB) approximation to calculate the rearrangement rates. The calculation results showed a general trend in which there were arrangement rate was decreasing inversely proportional to dielectric constant value.

  15. Structure determination of ultra dense magnesium borohydride: a first-principles study.

    Science.gov (United States)

    Fan, Jing; Duan, Defang; Jin, Xilian; Bao, Kuo; Liu, Bingbing; Cui, Tian

    2013-06-07

    Magnesium borohydride (Mg(BH4)2) is one of the potential hydrogen storage materials. Recently, two experiments [Y. Filinchuk, B. Richter, T. R. Jensen, V. Dmitriev, D. Chernyshov, and H. Hagemann, Angew. Chem., Int. Ed. 50, 11162 (2011); L. George, V. Drozd, and S. K. Saxena, J. Phys. Chem. C 113, 486 (2009)] found that α-Mg(BH4)2 can irreversibly be transformed to an ultra dense δ-Mg(BH4)2 under high pressure. Its volumetric hydrogen content at ambient pressure (147 g/cm(3)) exceeds twice of DOE's (U.S. Department of Energy) target (70 g/cm(3)) and that of α-Mg(BH4)2 (117 g/cm(3)) by 20%. In this study, the experimentally proposed P4(2)nm structure of δ-phase has been found to be dynamically unstable. A new Fddd structure has been reported as a good candidate of δ-phase instead. Its enthalpy from 0 to 12 GPa is much lower than P4(2)nm structure and the simulated X-ray diffraction spectrum is in satisfied agreement with previous experiments. In addition, the previously proposed P-3m1 structure, which is denser than Fddd, is found to be a candidate of ε-phase due to the agreement of Raman shifts.

  16. Ferromagnetism in Gd doped ZnO nanowires: A first principles study

    KAUST Repository

    Aravindh, S. Assa

    2014-12-19

    In several experimental studies, room temperature ferromagnetism in Gd-doped ZnO nanostructures has been achieved. However, the mechanism and the origin of the ferromagnetism remain controversial. We investigate the structural, magnetic, and electronic properties of Zn 48O48 nanowires doped with Gd, using density functional theory. Our findings indicate that substitutionally incorporated Gd atoms prefer occupying the surface Zn sites. Moreover, the formation energy increases with the distance between Gd atoms, signifying that no Gd-Gd segregation occurs in the nanowires within the concentration limit of ≤2%. Gd induces ferromagnetism in ZnO nanowires with magnetic coupling energy up to 21 meV in the neutral state, which increases with additional electron and O vacancy, revealing the role of carriers in magnetic exchange. The potential for achieving room temperature ferromagnetism and high TC in ZnO:Gd nanowires is evident from the large ferromagnetic coupling energy (200 meV) obtained with the O vacancy. Density of states shows that Fermi level overlaps with Gd f states with the introduction of O vacancy, indicating the possibility of s-f coupling. These results will assist in understanding experimental findings in Gd-doped ZnO nanowires.

  17. Magnetism, structure and chemical order in small CoPd clusters: A first-principles study

    KAUST Repository

    Mokkath, Junais Habeeb

    2014-01-01

    The structural, electronic and magnetic properties of small ComPdn (N=m+n=8,m=0-N) nanoalloy clusters are studied in the framework of a generalized-gradient approximation to density-functional theory. The optimized cluster structures have a clear tendency to maximize the number of nearest-neighbor CoCo pairs. The magnetic order is found to be ferromagnetic-like (FM) for all the ground-state structures. Antiferromagnetic-like spin arrangements were found in some low-lying isomers. The average magnetic moment per atom μ̄N increases approximately linearly with Co content. A remarkable enhancement of the local Co moments is observed as a result of Pd doping. This is a consequence of the increase in the number of Co d holes, due to CoPd charge transfer, combined with the reduced local coordination. The influence of spin-orbit interactions on the cluster properties is also discussed. © 2013 Elsevier B.V.

  18. Radicalization and Radical Catalysis of Biomass Sugars: Insights from First-principles Studies

    Science.gov (United States)

    Yang, Gang; Zhu, Chang; Zou, Xianli; Zhou, Lijun

    2016-07-01

    Ab initio and density functional calculations are conducted to investigate the radicalization processes and radical catalysis of biomass sugars. Structural alterations due to radicalization generally focus on the radicalized sites, and radicalization affects H-bonds in D-fructofuranose more than in D-glucopyranose, potentially with outcome of new H-bonds. Performances of different functionals and basis sets are evaluated for all radicalization processes, and enthalpy changes and Gibbs free energies for these processes are presented with high accuracy, which can be referenced for subsequent experimental and theoretical studies. It shows that radicalization can be utilized for direct transformation of biomass sugars, and for each sugar, C rather than O sites are always preferred for radicalization, thus suggesting the possibility to activate C-H bonds of biomass sugars. Radical catalysis is further combined with Brønsted acids, and it clearly states that functionalization fundamentally regulates the catalytic effects of biomass sugars. In presence of explicit water molecules, functionalization significantly affects the activation barriers and reaction energies of protonation rather than dehydration steps. Tertiary butyl and phenyl groups with large steric hindrances or hydroxyl and amino groups resulting in high stabilities for protonation products drive the protonation steps to occur facilely at ambient conditions.

  19. First principle studies of electronic and magnetic properties of Lanthanide-Gold (RAu) binary intermetallics

    Science.gov (United States)

    Ahmad, Sardar; Ahmad, Rashid; Jalali-Asadabadi, S.; Ali, Zahid; Ahmad, Iftikhar

    2017-01-01

    In this article we explore the electronic and magnetic properties of RAu intermetallics (R=Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) for the first time. These properties are calculated by using GGA, GGA+U and hybrid density functional theory (HF) approaches. Our calculations show that HF provides superior results, consistent to the experimentally reported data. The chemical bonding between rare-earth and gold atoms within these compounds are explained on the basis of spin dependent electronic clouds in different planes, which shows predominantly ionic and metallic nature between Au and R atoms. The Cohesive energies of RAu compounds show direct relation with the melting points. Spin-dependent electronic band structure demonstrates that all these compounds are metallic in nature. The magnetic studies show that HoAu and LuAu are stable in non-magnetic structure, PrAu is stable in ferromagnetic phase and CeAu, NdAu, SmAu, GdAu, TbAu, DyAu, ErAu, TmAu, YbAu are anti-ferromagnetic materials.

  20. First-principles study on the magnetism of different dimensional Ru systems

    Institute of Scientific and Technical Information of China (English)

    Zhu Qiu-Xiang; Pang Hua; Li Fa-Shen

    2009-01-01

    The magnetism, the magnetocrystalline anisotropy and the optical properties of the monolayer and atomic chain of 4d transition-metal Ru are investigated by using the full-potential linearized-augmented-plane-wave method in a generalized gradient approximation. The magnetic moments are 1.039 μB/atom and 1.130 μB/atom for the monolayer and atomic chain, respectively. Both systems have large magnetocrystalline anisotropy energy (MAE). The magnetic easy axis is normal to the monolayer and perpendicular to the chain axis in the atomic chain. The optical properties of the two low-dimensional Ru systems are investigated by calculating the complex optical conductivity tensor. Both systems exhibit anisotropy in photoconductivity, especially for the atomic chain. The physical origins of MAE and photoconductivity are studied based on electronic structures. It is found that the changes in crystal field caused by different symmetry-breaking mechanisms in the two low-dimensional Ru systems result in MAE through spin-orbit coupling, while the anisotropy in photoconductivity mainly comes from the crystallographic anisotropy.

  1. First-principles study of Cl-terminated silicon nanoribbons electronic properties

    Science.gov (United States)

    Djabri, I.; Derradji, NE; Belghit, R.

    2016-10-01

    Based on density functional pseudopotential calculations, the electronic properties of Cl- -terminated silicene nanoribbons (SiNRs) -with either zigzag edge (ZSiNRs) or armchair edge (ASiNRs)- are studied. The results show that all the Cl-terminated ZSiNRs present a zero gaps except for the 2-, 3- and 4-ZSiNRs, which have narrow band gaps. We also found degenerate flat edge-state bands at Fermi level (EF),which give rise to a very large density of states (DOS). The Cl-terminated ASiNRs are semiconductors regardless of their widths and the band gaps exhibit oscillatory behavior allowing the classification into three distinct families as 3k, (3k + 1) and (3k + 2), where k is a positive integer. Furthermore, the band gaps are the largest for the 3k group, moderate for (3k+1) and the smallest for members of the (3k + 2). Because of the ρ—ϕ mixing effect, the total density of states (DOS) and projected density of states (PDOS) of Cl-terminated ASiNR show that the Cl atoms affect the width between the top of the valance band or the bottom of the conduction band. The charge density distributions show that there is covalent bonding between all sorts of Si-Si bonds, with ionic bonding between the edge Cl atom and the nearest Si atom. This results from the electro-negativity of Si atoms being smaller than that of Cl atoms.

  2. The photocatalytic properties of ultrathin bismuth oxychloride nanosheets: a first principles study.

    Science.gov (United States)

    Jing, Tao; Dai, Ying; Ma, Xiangchao; Wei, Wei; Huang, Baibiao

    2016-03-14

    Two-dimensional (2D) nanosheet structures have obvious advantages with respect to their bulk counterparts in photocatalytic reaction due to their extraordinary electronic and optical properties. So do the 2D BiOCl nanosheets with significant improvement of photocatalytic activity in the degradation of dyes shown by recent studies. In the present work, the surface energies, electronic structure and photocatalytic properties of ultrathin BiOCl nanosheets are examined by means of density functional theory to investigate the origin of their high photocatalytic performance. The results show that the Cl atom terminated BiOCl(001) surface possesses lower surface energy than others and is very likely to be introduced in the ultrathin nanosheet. Moreover, our proposed model accounts well for the origin of band edge upshift of the ultrathin BiOCl nanosheets with respect to BiOCl nanoplates observed in experiments. In addition, the presence of Bi vacancies on the surfaces of nanosheets can enhance the built-in electric field and further promote the separation of photo-generated carriers, which is extremely advantageous for the photocatalytic process. Our results provide a new insight into the high photocatalytic performance of BiOCl(001) nanosheets.

  3. First-principles study of low Miller index Ni3S2 surfaces in hydrotreating conditions.

    Science.gov (United States)

    Aray, Yosslen; Vega, David; Rodriguez, Jesus; Vidal, Alba B; Grillo, Maria Elena; Coll, Santiago

    2009-03-12

    Density functional theory (DFT) calculations combined with surface thermodynamic arguments and the Gibbs-Curie-Wulff equilibrium morphology formalism have been employed to explore the effect of the reaction conditions, temperature (T), and gas-phase partial pressures (PH2 and PH2S) on the stability of nickel sulfide (Ni3S2) surfaces. Furthermore, the strength and nature of chemical bonds for selected Ni3S2 surface cuts were investigated with the quantum theory of atoms in molecules methodology. A particular analysis of the electrostatic potential within this theoretical framework is performed to study the potential activity of nickel sulfide nanoparticles as hydrodesulfurization (HDS) catalysts. The calculated thermodynamic surface stabilities and the resulting equilibrium morphology model suggest that unsupported Ni3S2 nanoparticles mainly expose (111) and (111) type surface faces in HDS conditions. Analysis of the electrostatic potential mapped onto a selected electron density isocontour (0.001 au) on those expose surface reveals a poor potential reactivity toward electron-donating reagents (i.e., low Lewis acidity). Consequently, a very low attraction between coordinatively unsaturated active sites (Lewis sites) exposed at the catalytic particles and the S atoms coming from reagent polluting molecules does inactive these kinds of particles for HDS.

  4. First-Principles Study of Contact Resistance between Graphene and Metal Electrodes

    Science.gov (United States)

    Kaneko, Tomoaki; Ohno, Takahisa

    2013-03-01

    Graphene attracts much interest for post-silicon electronics material due to its outstanding electronic transport properties such as considerably high mobility at room temperature. For the application of electronics devices, contacting of metal electrodes is necessary and decreasing of contact resistance between graphene and the metal electrodes is regarded as one of a key issue. In this study, we investigate the contact resistance using DFT+NEGF method. We consider the Ni and Cu electrode within LDA and TM-type norm-conserving pseudo-potential. We employed PHASE code to determine the interface structures. Then, we constructed two terminal device structures in which current flows from metals to graphene. The electron transport properties were calculated using ASCOT code. For Ni electrode, the dependence of the electrode size qualitatively agrees well with that obtained by the experiments. But our results suggest that contact resistance can be reduced considerably. This research was supported by the grant for `Strategic Programs for Innovative Research' Field No. 4: Industrial Innovations from the MEXT's `Development and Use of Advanced, High-Performance, General-Purpose Supercomputers Project,' and carried out in p

  5. Field evaporation of ZnO: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Xia, Yu, E-mail: yuxia@dal.ca; Karahka, Markus; Kreuzer, H. J. [Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia B3H 3J5 (Canada)

    2015-07-14

    With recent advances in atom probe tomography of insulators and semiconductors, there is a need to understand high electrostatic field effects in these materials as well as the details of field evaporation. We use density functional theory to study field effects in ZnO clusters calculating the potential energy curves, the local field distribution, the polarizability, and the dielectric constant as a function of field strength. We confirm that, as in MgO, the HOMO-LUMO gap of a ZnO cluster closes at the evaporation field strength signaling field-induced metallization of the insulator. Following the structural changes in the cluster at the evaporation field strength, we can identify the field evaporated species, in particular, we show that the most abundant ion, Zn{sup 2+}, is NOT post-ionized but leaves the surface as 2+ largely confirming the experimental observations. Our results also help to explain problems related to stoichiometry in the mass spectra measured in atom probe tomography.

  6. A first principles study of the electronic structure, elastic and thermal properties of UB2

    Science.gov (United States)

    Jossou, Ericmoore; Malakkal, Linu; Szpunar, Barbara; Oladimeji, Dotun; Szpunar, Jerzy A.

    2017-07-01

    Uranium diboride (UB2) has been widely deployed for refractory use and is a proposed material for Accident Tolerant Fuel (ATF) due to its high thermal conductivity. However, the applicability of UB2 towards high temperature usage in a nuclear reactor requires the need to investigate the thermomechanical properties, and recent studies have failed in highlighting applicable properties. In this work, we present an in-depth theoretical outlook of the structural and thermophysical properties of UB2, including but not limited to elastic, electronic and thermal transport properties. These calculations were performed within the framework of Density Functional Theory (DFT) + U approach, using Quantum ESPRESSO (QE) code considering the addition of Coulomb correlations on the uranium atom. The phonon spectra and elastic constant analysis show the dynamic and mechanical stability of UB2 structure respectively. The electronic structure of UB2 was investigated using full potential linear augmented plane waves plus local orbitals method (FP-LAPW+lo) as implemented in WIEN2k code. The absence of a band gap in the total and partial density of states confirms the metallic nature while the valence electron density plot reveals the presence of covalent bond between adjacent B-B atoms. We predicted the lattice thermal conductivity (kL) by solving Boltzmann Transport Equation (BTE) using ShengBTE. The second order harmonic and third-order anharmonic interatomic force constants required as input to ShengBTE was calculated using the Density-functional perturbation theory (DFPT). However, we predicted the electronic thermal conductivity (kel) using Wiedemann-Franz law as implemented in Boltztrap code. We also show that the sound velocity along 'a' and 'c' axes exhibit high anisotropy, which accounts for the anisotropic thermal conductivity of UB2.

  7. First principles study on the magnetocrystalline anisotropy of Fe-Ga magnetostrictive alloys

    Institute of Scientific and Technical Information of China (English)

    Zheng Lei; Jiang Cheng-Bao; Shang Jia-Xiang; XU Hui-Bin

    2009-01-01

    This paper investigates the electronic structure and magnetocrystalline anisotropy of Fe-Ga magnetostrictive material by means of the full potential-linearized augmented plane-wave method within the generalized gradient approximation.The 3d-orbit splitting of Fe atoms in D03,B2-like and L12 crystalline structures of Fe-Ga is calculated with consideration of the crystal field as well as the spin-orbit coupling effect.Because of the frozen orbital angular momenta of the 3d-orbit for Fe atoms in Fe-Ga magnetostrictive alloys and the spin-orbit coupling,the distribution of the electron cloud is not isotropic,which leads to the anisotropy of exchange interaction between the different atoms.A method on estimating the magnetocrystalline anisotropy of Fe-Ga alloys by means of calculating orbit-projected density of states for Fe atoms is performed.The anisotropic distribution of the electron cloud of Fe atoms in these three crystalline structures of Fe-Ga is studied based on the above method showing the highest magnetic anisotropy for B2-like structure.This qualitative method comes closer to physical reality with a vivid physical view,which can evaluate the anisotropy of electron cloud for 3d transition atoms directly.The calculated results are in good agreement with both the previous theoretical computation and the tested value on the magnetic anisotropy constant,which con firms that the electron cloud anisotropy of Fe atoms could well characterize the magnetocrystalline anisotropy of Fe-Ga magnetostrictive material.

  8. Coordination mode of nitrate in uranyl(VI) complexes: a first-principles molecular dynamics study.

    Science.gov (United States)

    Bühl, Michael; Diss, Romain; Wipff, Georges

    2007-06-25

    According to Car-Parrinello molecular dynamics simulations for [UO(2)(NO(3))(3)](-), [UO(2)(NO(3))(4)](2-), and [UO(2)(OH(2))(4-)(NO(3))](+) complexes in the gas phase and in aqueous solution, the nitrate coordination mode to uranyl depends on the interplay between ligand-metal attractions, interligand repulsions, and solvation. In the trinitrate, the eta(2)-coordination is clearly favored in water and in the gas phase, leading to a coordination number (CN) of 6. According to pointwise thermodynamic integration involving constrained molecular dynamics simulations, a change in free energy of +6 kcal/mol is predicted for eta(2)- to eta(1)-transition of one of the three nitrate ligands in the gas phase. In the gas phase, the mononitrate-hydrate complex also prefers a eta(2)-binding mode but with a CN of 5, one H(2)O molecule being in the second shell. This contrasts with the aqueous solution where the nitrate binds in a eta(1)-fashion and uranyl coordinates to four H2O ligands. A driving force of ca. -3 kcal/mol is predicted for the eta(2)- to eta(1)- transition in water. This structural preference is interpreted in terms of steric arguments and differential solvation of terminal vs uranyl-coordinated O atoms of the nitrate ligands. The [UO(2)(NO(3))(4)](2-) complex with two eta(2)- and two eta(1)- coordinated nitrates, observed in the solid state, is stable for 1-2 ps in the gas phase and in solution. In the studied series, the modulation of uranyl-ligand distances upon immersion of the complex in water is found to depend on the nature of the ligand and the composition of the complex.

  9. Mechanism and kinetics for ammonium dinitramide (ADN) sublimation: a first-principles study.

    Science.gov (United States)

    Zhu, R S; Chen, Hui-Lung; Lin, M C

    2012-11-08

    The mechanism for sublimation of NH(4)N(NO(2))(2) (ADN) has been investigated quantum-mechanically with generalized gradient approximation plane-wave density functional theory calculations; the solid surface is represented by a slab model and the periodic boundary conditions are applied. The calculated lattice constants for the bulk ADN, which were found to consist of NH(4)(+)[ON(O)NNO(2)](-) units, instead of NH(4)(+)[N(NO(2))(2)](-), agree quite well with experimental values. Results show that three steps are involved in the sublimation/decomposition of ADN. The first step is the relaxation of the surface layer with 1.6 kcal/mol energy per NH(4)ON(O)NNO(2) unit; the second step is the sublimation of the surface layer to form a molecular [NH(3)]-[HON(O)NNO(2)] complex with a 29.4 kcal/mol sublimation energy, consistent with the experimental observation of Korobeinichev et al. (10) The last step is the dissociation of the [H(3)N]-[HON(O)NNO(2)] complex to give NH(3) and HON(O)NNO(2) with the dissociation energy of 13.9 kcal/mol. Direct formation of NO(2) (g) from solid ADN costs a much higher energy, 58.3 kcal/mol. Our calculated total sublimation enthalpy for ADN(s) → NH(3)(g) + HON(O)NNO(2)) (g), 44.9 kcal/mol via three steps, is in good agreement with the value, 42.1 kcal/mol predicted for the one-step sublimation process in this work and the value 44.0 kcal/mol computed by Politzer et al. (11) using experimental thermochemical data. The sublimation rate constant for the rate-controlling step 2 can be represented as k(sub) = 2.18 × 10(12) exp (-30.5 kcal/mol/RT) s(-1), which agrees well with available experimental data within the temperature range studied. The high pressure limit decomposition rate constant for the molecular complex H(3)N···HON(O)NNO(2) can be expressed by k(dec) = 3.18 × 10(13) exp (-15.09 kcal/mol/RT) s(-1). In addition, water molecules were found to increase the sublimation enthalpy of ADN, contrary to that found in the ammonium

  10. Electronic and optical properties of RESn{sub 3} (RE=Pr & Nd) intermetallics: A first principles study

    Energy Technology Data Exchange (ETDEWEB)

    Pagare, G., E-mail: gita-pagare@yahoo.co.in [Department of Physics, Government M. L. B. Girls P. G. Autonomous College, Bhopal-462002 (India); Abraham, Jisha A. [Department of Physics, Government M. L. B. Girls P. G. Autonomous College, Bhopal-462002 (India); Department of Physics, National Defence Academy, Pune-411023 (India); Sanyal, S. P. [Department of Physics, Barkatullah University, Bhopal-462026 (India)

    2015-06-24

    A theoretical study of structural, electronic and optical properties of RESn{sub 3} (RE = Pr & Nd) intermetallics have been investigated systematically using first principles density functional theory. The calculations are carried out within the PBE-GGA and LSDA for the exchange correlation potential. The ground state properties such as lattice parameter (a{sub 0}), bulk modulus (B) and its pressure derivative (B′) are calculated and the calculated lattice parameters show well agreement with the experimental results. We first time predict elastic constants for these compounds. From energy dispersion curves, it is found that these compounds are metallic in nature. The linear optical response of these compounds are also studied and the higher value of static dielectric constant shows the possibility to use them as good dielectric materials.

  11. First principles study of the alloying effect on chemical bonding characteristics of helium in La-Ni-M tritides

    Energy Technology Data Exchange (ETDEWEB)

    Hu, C.H. [Institute of Metal Research, Chinese Academy of Science, 72 Wenhua Road, Shenyang 110016 (China); Zhang, R.J. [Institute of Metal Research, Chinese Academy of Science, 72 Wenhua Road, Shenyang 110016 (China); Shi, L.Q. [Applied Ion Bean Physics Laboratory, Fudan University, Shanghai 200433 (China); Chen, D.M. [Institute of Metal Research, Chinese Academy of Science, 72 Wenhua Road, Shenyang 110016 (China); Wang, Y.M. [Institute of Metal Research, Chinese Academy of Science, 72 Wenhua Road, Shenyang 110016 (China)]. E-mail: ymwang@imr.ac.cn; Yang, K. [Institute of Metal Research, Chinese Academy of Science, 72 Wenhua Road, Shenyang 110016 (China)

    2005-11-15

    The alloying effect on the electronic structure of La-Ni-M tritides is investigated using the first principles discrete variational X{alpha}(DV-X{alpha}) method. The calculated results show that the covalent interaction between atoms will play a much more important role in studying the alloying effect on chemical bonding characteristics in La-Ni-M tritides than ionic interaction. It is also found that in La-Ni-M tritides helium forms stronger covalent bonds with the weaker hydride forming elements than La. By analyzing the relation between the binding energy difference and bond order, our study indicates that after some alloying elements substituting for Ni locating in 3g site in tritides, the helium retention capability becomes stronger, changes as the following sequence: Al > Cr > Mn > Fe > Co > Ni, and is also very distinct for Cu although the chemical bonding between Cu atom and Ni atom is degraded drastically.

  12. First-principles study of helium, carbon, and nitrogen in austenite, dilute austenitic iron alloys, and nickel

    Science.gov (United States)

    Hepburn, D. J.; Ferguson, D.; Gardner, S.; Ackland, G. J.

    2013-07-01

    An extensive set of first-principles density functional theory calculations have been performed to study the behavior of He, C, and N solutes in austenite, dilute Fe-Cr-Ni austenitic alloys, and Ni in order to investigate their influence on the microstructural evolution of austenitic steel alloys under irradiation. The results show that austenite behaves much like other face-centered cubic metals and like Ni in particular. Strong similarities were also observed between austenite and ferrite. We find that interstitial He is most stable in the tetrahedral site and migrates with a low barrier energy of between 0.1 and 0.2 eV. It binds strongly into clusters as well as overcoordinated lattice defects and forms highly stable He-vacancy (VmHen) clusters. Interstitial He clusters of sufficient size were shown to be unstable to self-interstitial emission and VHen cluster formation. The binding of additional He and V to existing VmHen clusters increases with cluster size, leading to unbounded growth and He bubble formation. Clusters with n/m around 1.3 were found to be most stable with a dissociation energy of 2.8 eV for He and V release. Substitutional He migrates via the dissociative mechanism in a thermal vacancy population but can migrate via the vacancy mechanism in irradiated environments as a stable V2He complex. Both C and N are most stable octahedrally and exhibit migration energies in the range from 1.3 to 1.6 eV. Interactions between pairs of these solutes are either repulsive or negligible. A vacancy can stably bind up to two C or N atoms with binding energies per solute atom up to 0.4 eV for C and up to 0.6 eV for N. Calculations in Ni, however, show that this may not result in vacancy trapping as VC and VN complexes can migrate cooperatively with barrier energies comparable to the isolated vacancy. This should also lead to enhanced C and N mobility in irradiated materials and may result in solute segregation to defect sinks. Binding to larger vacancy clusters

  13. First principles study on the charge density and the bulk modulus of the transition metals and their carbides and nitrides

    Institute of Scientific and Technical Information of China (English)

    Li Cheng-Bin; Li Ming-Kai; Yin Dong; Liu Fu-Qing; Fan Xiang-Jun

    2005-01-01

    A first principles study of the electronic properties and bulk modulus (B0) of the fcc and bcc transition metals,transition metal carbides and nitrides is presented. The calculations were performed by plane-wave pseudopotential method in the framework of the density functional theory with local density approximation. The density of states and the valence charge densities of these solids are plotted. The results show that B0 does not vary monotonically when the number of the valence d electrons increases. B0 reaches a maximum and then decreases for each of the four sorts of solids. It is related to the occupation of the bonding and anti-bonding states in the solid. The value of the valence charge density at the midpoint between the two nearest metal atoms tends to be proportional to B0.

  14. A first-principles study of electronic properties of H and F-terminated zigzag BNC nanoribbons

    Energy Technology Data Exchange (ETDEWEB)

    Alaal, Naresh [IITB-Monash Research Academy, Old CSE Building 2 nd Floor, IIT Bombay, Powai, Mumbai 400076, India. (India); Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India. (India); Department of Materials Engineering, Monash University, Clayton, Victoria -3800, Australia. (Australia); Medhekar, Nikhil [Department of Materials Engineering, Monash University, Clayton, Victoria -3800, Australia. (Australia); Shukla, Alok, E-mail: shukla@phy.iitb.ac.in [Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India. (India)

    2016-05-06

    Nanoribbons are quasi one-dimensional structures which have interesting electronic properties on the basis of their edge geometries, and width. We studied the electronic properties of hydrogen and fluorine-terminated zigzag BNC nanoribbons (BNCNRs) using a first-principles based density functional theory approach. We considered BNCNRs that were composed of an equal number of C-C and B-N dimers; one of the edges ends with an N atom and opposite edge ends with a C atom. These two edge atoms are passivated by H or F atoms. Our results suggest that hydrogen-terminated BNCNRs (H-BNCNRs) and flourine-terminated BNCNRs (F-BNCNRs) have different electronic properties. H-BNCNRs exhibit intrinsic half-metallic behavior while F-BNCNRs are indirect band gap semiconductors. Chemical functionalization of BNCNRs with H and F atoms show that BNCNRs have a diverse range of electronic properties.

  15. The structural, electronic and phonon behavior of CsPbI{sub 3}: A first principles study

    Energy Technology Data Exchange (ETDEWEB)

    Bano, Amreen, E-mail: banoamreen.7@gmail.com; Khare, Preeti; Parey, Vanshree; Shukla, Aarti; Gaur, N. K. [Department of Physics, Barkatullah University, Bhopal-462026 (India)

    2016-05-06

    Metal halide perovskites are optoelectronic materials that have attracted enormous attention as solar cells with power conversion efficiencies reaching 20%. The benefit of using hybrid compounds resides in their ability to combine the advantage of these two classes of compounds: the high mobility of inorganic materials and the ease of processing of organic materials. In spite of the growing attention of this new material, very little is known about the electronic and phonon properties of the inorganic part of this compounds. A theoretical study of structural, electronic and phonon properties of metal-halide cubic perovskite, CsPbI{sub 3} is presented, using first-principles calculations with planewave pseudopotential method as personified in PWSCF code. In this approach local density approximation (LDA) is used for exchange-correlation potential.

  16. First-Principles Study of the Role of Cu in Improving the Coercivity of Nd-Fe-B Permanent Magnets

    Science.gov (United States)

    Tatetsu, Y.; Tsuneyuki, S.; Gohda, Y.

    2016-12-01

    We study the magnetic and electronic properties of Cu-doped Nd2 Fe14 B /NdOx systems with first-principles calculations in order to understand the roles of Cu in improving the coercivity of Nd-Fe-B permanent magnets. By analyzing the formation energies of several model systems, we find that Cu prefers to be at the interface. We conclude that the Cu addition to Nd-Fe-B magnets is a practical way of not only increasing the anisotropy of Nd atoms at the interface but also of lessening the magnetic coupling between the Nd and Fe atoms. Particularly, substituting Fe at the interface of the main phase with Cu works effectively in terms of improving the magnetic anisotropy in Nd atoms. This may explain the coercivity improvements reported recently.

  17. First principles DFT study of weak C-H…O bonds in crystalline amino acids under pressure-alanine

    Science.gov (United States)

    Ramaniah, Lavanya M.; Kamal, C.; Sikka, S. K.

    2013-02-01

    Many crystalline solids containing C-H…O hydrogen bonds display blue shifting of the C-H stretching frequency under pressure. No agreed explanation is available for this. Here, we use first principles density functional theory, to determine the hydrogen atom positions to understand the cause of this blue shift. No neutron diffraction is feasible due to flux limitations for this purpose. As a first case, we have taken up the study of the amino acid, alanine. We find that the C_H_…O bond in it no longer remain isolated under compression as is case at ambient pressure. The hydrogen atom in the bond has now repulsive contacts with other atoms. This results in contraction of the C-H bond length and consequently to blue shifting as is found experimentally.

  18. Half-metallic ferromagnetism in C-doped zinc-blende ZnO:A first-principles study

    Institute of Scientific and Technical Information of China (English)

    Dan Xu; Yao Kai-Lun; Gao Guo-Ying; Ma Guo-Qiang

    2013-01-01

    We perform a first-principles study of electronic structure and magnetism of C-doped zinc-blende ZnO using the full-potential linearized augmented plane wave method.Results show that C-doped zinc-blende ZnO exhibits half-metallic ferromagnetism with a stable ferromagnetic ground state.The calculated magnetic moment of the 32-atom supercell containing one C dopant is 2.00 μB,and the C dopant contributes most.The calculated low formation energy suggests that C-doped zinc-blende ZnO is energetically stable.The hole-mediated double exchange mechanism can be used to explain the ferromagnetism in C-doped zinc-blende ZnO.

  19. First principles study of polarization-strain coupling in SrBi2Ta2O9

    Directory of Open Access Journals (Sweden)

    Qiong Yang

    2013-05-01

    Full Text Available Paraelectric and ferroelectric phase structures of SrBi2Ta2O9 were calculated using first-principles density functional theory. Berry phase method is used to study the spontaneous polarization in ferroelectric SrBi2Ta2O9. The spontaneous polarizations of SrBi2Ta2O9 experimental and relaxed structures were calculated to be 34.1 μC/cm2 and 21.0 μC/cm2, respectively, along the crystallographic a-axis. It is found that the spontaneous polarization can be improved by both of ab- and bc-biaxial tensile strains. And the polarization value shows a sizable enhancement by 45% when applying 2.4% ab-biaxial tensile strain. The strain effects on spontaneous polarization are explained in terms of the atomic off-centre displacements.

  20. On the electrostatic control achieved in transistors based on multilayered MoS2: A first-principles study

    Science.gov (United States)

    Lu, Anh Khoa Augustin; Pourtois, Geoffrey; Luisier, Mathieu; Radu, Iuliana P.; Houssa, Michel

    2017-01-01

    In this work, the electrostatic control in metal-oxide-semiconductor field-effect transistors based on MoS2 is studied, with respect to the number of MoS2 layers in the channel and to the equivalent oxide thickness of the gate dielectric, using first-principles calculations combined with a quantum transport formalism. Our simulations show that a compromise exists between the drive current and the electrostatic control on the channel. When increasing the number of MoS2 layers, a degradation of the device performances in terms of subthreshold swing and OFF currents arises due to the screening of the MoS2 layers constituting the transistor channel.

  1. First-principles Study on Infrared Absorptions of Transition Metal-doped ZnO with Oxygen Vacancy

    Institute of Scientific and Technical Information of China (English)

    Yinhua YAO; Quanxi CAO

    2013-01-01

    Using first-principle theory,the infrared absorptions of transition metal (Mn,Fe,Co,Ni)-doped ZnO were investigated.The results indicate that the absorptions of Mn-and Co-incorporated ZnO without oxygen vacancy are reduced,while those of Fe-and Ni-doped ZnO are raised.This is consistent with the previous experimental results.The effects of oxygen vacancy on the absorptions of the doped systems were predicted.When a neutral oxygen vacancy is introduced,all doping elements decrease the absorptions.On the contrary,the absorptions of the doped systems are enhanced if the vacancies are charged.Degraded absorptions can be obtained by increasing the permeability.However,the appearance of anti-bonding states may cause enhanced absorptions.In the current study,Mn-doped ZnO is the most suitable for use as low infrared absorption materials.

  2. Electronic and magnetic properties of dopant atoms in SnSe monolayer: a first-principles study

    CERN Document Server

    Wang, Qingxia; Fu, Xiaonan; Qiao, Chong; Xia, Congxin; Jia, Yu

    2015-01-01

    SnSe monolayer with orthorhombic Pnma GeS structure is an important two-dimensional (2D) indirect band gap material at room temperature. Based on first-principles density functional theory calculations, we present systematic studies on the electronic and magnetic properties of X (X = Ga, In, As, Sb) atoms doped SnSe monolayer. The calculated electronic structures show that Ga-doped system maintains semiconducting property while In-doped SnSe monolayer is half-metal. The As- and Sb- doped SnSe systems present the characteristics of n-type semiconductor. Moreover, all considered substitutional doping cases induce magnetic ground states with the magnetic moment of 1{\\mu}B. In addition, the calculated formation energies also show that four types of doped systems are thermodynamic stable. These results provide a new route for the potential applications of doped SnSe monolayer in 2D photoelectronic and magnetic semiconductor devices.

  3. First-principles Study of the Au surfactant on the growth of Zn vacancies in ZnO nanostructures

    Institute of Scientific and Technical Information of China (English)

    刘亚明

    2007-01-01

    Influence of Au surfactant on the growth of Zn atom vacancies in ZnO nanostructures has been investigated by using first-principles slab calculations based on density functional theory.The adsorption of Au atoms on the Zn -terminated(0001)polar surface with a(2×2)sudace unit cell is studied by using a standard supercell model.It is found that (1)the binding energies of Au atoms on (0001)-Zn increase and the most stable position of the Au atom is invariable;(2)on the (0001)surface,the preferred sites for Zn atom vacancy are on the first layer of Zn atoms;(3)Under the Au surfactant,the Zn atom vacancies become more difficult to form.

  4. Modulations of interlayer exchange coupling through ultrathin MgO-based magnetic tunnel junctions: First-principles study

    Science.gov (United States)

    Wang, Shizhuo; Xia, Ke; Min, Tai; Ke, Youqi

    2017-07-01

    Ultrathin MgO-based magnetic tunnel junction (MTJ) features high electron/heat current density, presenting important applications in spintronics. Here, we report a first-principles study of the interlayer exchange coupling (IEC) through ultrathin MgO-based MTJs. We investigate the effects of different modulations on the IEC, including temperature, different interfacial disorders, and the type and thickness of the ferromagnetic (FM) materials. It is found that the interfacial disorders, such as oxygen vacancies, boron and carbon impurities, can significantly influence the magnitude and sign of the IEC. The presence of interfacial disorders enhances the anti-FM coupling contribution and reduces the FM coupling contribution to the total IEC, and can thus change the total IEC from FM to Anti-FM in the ultrathin MTJ. We also find that FM materials have important effects on IEC: the IEC with CoFe alloy exhibits much weaker dependence on the interfacial disorders and temperature than that with the Fe. Our first-principles results provide a good explanation for the serious inconsistency between previous experimental measurements. Moreover, by studying the junction structure Vacuum/FM1/MgO/FM2 (FM1, FM2=Fe, CoFe), we find that the ultrathin FM1 layers can dramatically enhance the FM IEC and the IEC enhancement significantly depends on the combination of FM1-FM2. We show that the enhanced FM IEC with ultrathin FM1 can be sustained with a considerable amount of surface roughness in FM1 and interfacial disorder.

  5. First-principles study of structrural and corrected band properties of wurtzite Zn1-xCdxO and Zn1-xMgxO systems

    Institute of Scientific and Technical Information of China (English)

    Wang Zhi-Jun; Li Shou-Chun; Wang Lian-Yuan; Liu Zhen

    2009-01-01

    A first-principles method based on density functional theory (DFT), a generalized gradient approximation (GGA),and a projector-augmented wave (PAW) are used to study the structuai and band properties of wurtzite Zn1-xCdxO and Zn1-xMgxO (0 ≤x ≤1) ternary alloys. By taking into account all of the possible structures, the band gaps of Zn1-xCdxO and Zn1-xMgxO alloys are corrected and compared with experimental data.

  6. First principles modeling of the metal-electrolyte interface: A novel approach to the study of the electrochemical interface

    Energy Technology Data Exchange (ETDEWEB)

    Fernandez-Serra, Maria Victoria [Stony Brook Univ., NY (United States)

    2016-09-12

    The research objective of this proposal is the computational modeling of the metal-electrolyte interface purely from first principles. The accurate calculation of the electrostatic potential at electrically biased metal-electrolyte interfaces is a current challenge for periodic “ab-initio” simulations. It is also an essential requisite for predicting the correspondence between the macroscopic voltage and the microscopic interfacial charge distribution in electrochemical fuel cells. This interfacial charge distribution is the result of the chemical bonding between solute and metal atoms, and therefore cannot be accurately calculated with the use of semi-empirical classical force fields. The project aims to study in detail the structure and dynamics of aqueous electrolytes at metallic interfaces taking into account the effect of the electrode potential. Another side of the project is to produce an accurate method to simulate the water/metal interface. While both experimental and theoretical surface scientists have made a lot of progress on the understanding and characterization of both atomistic structures and reactions at the solid/vacuum interface, the theoretical description of electrochemical interfaces is still lacking behind. A reason for this is that a complete and accurate first principles description of both the liquid and the metal interfaces is still computationally too expensive and complex, since their characteristics are governed by the explicit atomic and electronic structure built at the interface as a response to environmental conditions. This project will characterize in detail how different theoretical levels of modeling describer the metal/water interface. In particular the role of van der Waals interactions will be carefully analyzed and prescriptions to perform accurate simulations will be produced.

  7. First-Principles Study of Structural,Magnetic,Electronic and Elastic Properties of PuC2简

    National Research Council Canada - National Science Library

    杨荣 唐斌 高涛 敖冰云

    2016-01-01

    We perform first-principles calculations of crystal structure,magnetism,electronic structure,chemical bonding and elastic properties for PuC2 using the standard local spin-density approximation(LSDA)+U...

  8. Experimental and first-principles study of the electronic transport properties of strained Bi2Te3 thin films on a flexible substrate

    Science.gov (United States)

    Inamoto, Takuya; Takashiri, Masayuki

    2016-09-01

    On the basis of an experimental and first-principles study, strain effects on the thermoelectric properties of bismuth telluride (Bi2Te3) thin films were investigated. Bi2Te3 thin films were deposited on flexible polyimide substrates using a radio frequency magnetron sputtering method at a substrate temperature of 200 °C. Prior to deposition, various compressive and tensile bending strains were applied to the films by changing the bending radii of the flexible substrates. The structural and thermoelectric properties of the completed samples were analyzed. It was found that the lattice parameters of all samples exhibited smaller values compared to that of standard data for Bi2Te3 (JCPDS 15-0863) because the substrates might have shrunk during the film deposition, indicated by the fact that all the samples presented various compressive lattice strains. A theoretical analysis was performed using the first-principles study based on density functional theory. We calculated the electronic band structures for Bi2Te3 with the different lattice strains and predicted the thermoelectric properties based on the semi-classical Boltzmann transport equation in the rigid band approximation. The lowest conduction band edge in the Bi2Te3 band structure narrowed as the compressive lattice strain increased, indicating that the effective mass became smaller. Finally, the experimentally measured thermoelectric properties were compared with those obtained by the calculation. It was found that the calculated results were in good agreement with the experimental results.

  9. First-Principles Study of Hydrogen Impact on the Formation and Migration of Helium Interstitial Defects in hcp Titanium

    Institute of Scientific and Technical Information of China (English)

    LU Yong-Fang; SHI Li-Qun; DING Wei; LONG Xing-Gui

    2012-01-01

    We present a first-principles study of the effects of hydrogen on helium behavior in hcp titanium.The calculation indicates that the dissolved H atoms in hcp Ti change the formation energy of the interstitial He atom,but they do not change the energetically favorable occupying site of the He atom,i.e.,the tetrahedral site is more favorable than the octahedral site.The impacts of H on the formation of interstitial He defects are directly related to the atomic environment around H atoms and their positions relative to interstitial He atoms as well.For He diffusion,a tetrahedral interstitial He atom can more easily migrate along the indirect tetrahedron-octahedron-tetrahedron path than the direct path of tetrahedron-tetrahedron.When a H atom exists in the first neighbor octahedral site from the He,the activation energy for He atom diffusion is 0.46eV,which is higher than that of the He atom diffusion in perfect crystal,0.41 eV.Increasing the number of H atoms to two,He diffusion needs much higher activation energy.This suggests that the H atoms around interstitial He may impede the migration of interstitial He atom in hcp Ti.%We present a first-principles study of the effects of hydrogen on helium behavior in hep titanium. The calculation indicates that the dissolved H atoms in hcp Ti change the formation energy of the interstitial He atom, but they do not change the energetically favorable occupying site of the He atom, I.e., the tetrahedral site is more favorable than the octahedral site. The impacts of H on the formation of interstitial He defects are directly related to the atomic environment around H atoms and their positions relative to interstitial He atoms as well. For He diffusion, a tetrahedral interstitial He atom can more easily migrate along the indirect tetrahedron-octahedron-tetrahedron path than the direct path of tetrahedron-tetrahedron. When a H atom exists in the first neighbor octahedral site from the He, the activation energy for He atom diffusion

  10. On structural and lattice dynamic stability of LaF{sub 3} under high pressure: A first principle study

    Energy Technology Data Exchange (ETDEWEB)

    Sahoo, B. D., E-mail: bdsahoo@barc.gov.in; Joshi, K. D.; Gupta, Satish C. [Applied Physics Division, Bhabha Atomic Research Centre, Mumbai-400085 (India)

    2015-06-24

    Structural and lattice dynamical stability of the LaF3 has been analyzed as a function of hydrostatic compression through first principle electronic band structure calculations. The comparison of enthalpies of various plausible structures calculated at various pressures suggests a phase transition from ambient condition tysonite structure (space group P-3c1) to a primitive orthorhombic structure (space group Pmmn) at a pressure of ∼19.5 GPa, in line with the experimental value of 16 GPa. Further, it is predicted that this phase will remain stable up to 100 GPa (the maximum pressure up to which calculations have been performed in the present work). The theoretically determined equation of state displays a good agreement with experimental data. Various physical quantities such as zero pressure equilibrium volume, bulk modulus, and pressure derivative of bulk modulus have been derived from the theoretically determined equation of state and compared with the available experimental data. Our lattice dynamic calculations correctly demonstrate that at zero pressure the tysonite structure is lattice dynamically stable whereas the Pmmn structure is unstable lattice dynamically. Further, at transition pressure the theoretically calculated phonon spectra clearly show that the Pmmn phase emerges as lattice dynamically stable phase whereas the tysonite structure becomes unstable dynamically, supporting our static lattice calculations.

  11. On structural and lattice dynamic stability of LaF3 under high pressure: A first principle study

    Science.gov (United States)

    Sahoo, B. D.; Joshi, K. D.; Gupta, Satish C.

    2015-06-01

    Structural and lattice dynamical stability of the LaF3 has been analyzed as a function of hydrostatic compression through first principle electronic band structure calculations. The comparison of enthalpies of various plausible structures calculated at various pressures suggests a phase transition from ambient condition tysonite structure (space group P-3c1) to a primitive orthorhombic structure (space group Pmmn) at a pressure of ˜19.5 GPa, in line with the experimental value of 16 GPa. Further, it is predicted that this phase will remain stable up to 100 GPa (the maximum pressure up to which calculations have been performed in the present work). The theoretically determined equation of state displays a good agreement with experimental data. Various physical quantities such as zero pressure equilibrium volume, bulk modulus, and pressure derivative of bulk modulus have been derived from the theoretically determined equation of state and compared with the available experimental data. Our lattice dynamic calculations correctly demonstrate that at zero pressure the tysonite structure is lattice dynamically stable whereas the Pmmn structure is unstable lattice dynamically. Further, at transition pressure the theoretically calculated phonon spectra clearly show that the Pmmn phase emerges as lattice dynamically stable phase whereas the tysonite structure becomes unstable dynamically, supporting our static lattice calculations.

  12. Hybrid phosphorene/graphene nanocomposite as an anode material for Na-ion batteries: a first-principles study

    Science.gov (United States)

    Wang, Linxia; Jiang, Zhiqiang; Li, Wei; Gu, Xiao; Huang, Li

    2017-04-01

    The potential application of the hybrid phosphorene/graphene (P/G) composites as an anode material in Na-ion batteries (NIBs) has been explored based on first-principles calculations. The calculated elastic constants reveal that the P/G has an ultrahigh stiffness, which can effectively suppress the undesirable structural deformation during the sodiation and desodiation cycles. Na atoms can strongly bind with the phosphorene single-layer (SP), double-layer (DP), and their composites with graphene (SP/G, DP/G, G/DP/G), and can even cause a sliding between the layers when the DP/G accommodate more Na atoms. The migration of Na in P/G is anisotropic with the minimum energy path along the zigzag channel. The low diffusion barriers of only about several tens of meV ensure the high mobility of Na within the layers, and thus lead to rapid charge/discharge capacity of P/G. The electronic structures show that the hybrid P/G becomes metallic with the Na incorporation, which contributes to the good electric conductivity in P/G. We further demonstrate that the average open circuit voltage (OCV) of DP/G is 0.53 V, which is comparable to other anode materials. These results suggest that P/G composites hold great potential to be a good anode material in NIBs.

  13. Exploring long-wave infrared transmitting materials with AxBy form: First-principles gene-like studies

    Science.gov (United States)

    Du, Jia-Ren; Chen, Nian-Ke; Li, Xian-Bin; Xie, Sheng-Yi; Tian, Wei Quan; Wang, Xian-Yin; Tu, Hai-Ling; Sun, Hong-Bo

    2016-02-01

    Long-wave infrared (8-12 μm) transmitting materials play critical roles in space science and electronic science. However, the paradox between their mechanical strength and infrared transmitting performance seriously prohibits their applications in harsh external environment. From the experimental view, searching a good window material compatible with both properties is a vast trail-and-error engineering project, which is not readily achieved efficiently. In this work, we propose a very simple and efficient method to explore potential infrared window materials with suitable mechanical property by first-principles gene-like searching. Two hundred and fifty-three potential materials are evaluated to find their bulk modulus (for mechanical performance) and phonon vibrational frequency (for optical performance). Seven new potential candidates are selected, namely TiSe, TiS, MgS, CdF2, HgF2, CdO, and SrO. Especially, the performances of TiS and CdF2 can be comparable to that of the most popular commercial ZnS at high temperature. Finally, we propose possible ranges of infrared transmission for halogen, chalcogen and nitrogen compounds respectively to guide further exploration. The present strategy to explore IR window materials can significantly speed up the new development progress. The same idea can be used for other material rapid searching towards special functions and applications.

  14. Exploring the catalytic activity of pristine T6[100] surface for oxygen reduction reaction: A first-principles study

    Science.gov (United States)

    Banerjee, Paramita; Chakrabarty, Soubhik; Thapa, Ranjit; Das, G. P.

    2017-10-01

    The electrocatalytic activity of T6[100] surface containing both sp3 (C1) and sp2 (C2) hybridized carbon atoms is explored using first-principles density functional theory based approach. The top layered C1 atom of the surface is found to be more active towards the oxygen reduction reaction (ORR), as compared to that of C2 atom. This is attributed to the presence of dangling σ bond in the corresponding C1 atom, leading to the high electron density near the Ferrmi level. Whereas, the π electron in the top layered C2 atom forms a weak out of plane network. As estimated from free energy profile, the overpotential is much lower when C1 is considered as the active site and the final step i.e desorption of final OH- ion is found to be the potential determining step. We have also reported the effect of Si dopant on the catalytic activity of T6[100] surface and explained the origin of high overpotential value in this case. Thus in this report, we propose a new metal-free catalyst i.e T6[100] surface, having both sp2 (maintains the high metallicity needed to reduce ohmic loss) and sp3 (helps in capturing the upcoming molecules) hybridized carbon atoms, as a potential candidate for ORR.

  15. The electronic structures and ferromagnetism of Fe-doped GaSb: The first-principle calculation study

    Science.gov (United States)

    Lin, Xue-ling; Niu, Cao-ping; Pan, Feng-chun; Chen, Huan-ming; Wang, Xu-ming

    2017-09-01

    The electronic structures and the magnetic properties of Fe doped GaSb have been investigated by the first-principles calculation based on the framework of the generalized gradient approximation (GGA) and GGA+U schemes. The calculated results indicated that Fe atoms tend to form the anti-ferromagnetic (AFM) coupling with the nearest-neighbor positions preferentially. Compared with the anti-ferromagnetic coupling, the ferromagnetic interactions occurred at the second nearest-neighbor and third nearest-neighbor sites have a bigger superiority energetically. The effect of strong electron correlation at Fe-d orbit taking on the magnetic properties predicted by GGA+U approach demonstrated that the ferromagnetic (FM) coupling between the Fe ions is even stronger in consideration of the strong electron correlation effect. The ferromagnetism in Fe doped GaSb system predicted by our investigation implied that the doping of Fe into GaSb can be as a vital routine for manufacturing the FM semiconductors with higher Curie temperature.

  16. First-principle study of quantum confinement effect on small sized silicon quantum dots using density-functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Anas, M. M.; Othman, A. P.; Gopir, G. [School of Applied Physics, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600, Bangi, Selangor (Malaysia)

    2014-09-03

    Density functional theory (DFT), as a first-principle approach has successfully been implemented to study nanoscale material. Here, DFT by numerical basis-set was used to study the quantum confinement effect as well as electronic properties of silicon quantum dots (Si-QDs) in ground state condition. Selection of quantum dot models were studied intensively before choosing the right structure for simulation. Next, the computational result were used to examine and deduce the electronic properties and its density of state (DOS) for 14 spherical Si-QDs ranging in size up to ∼ 2 nm in diameter. The energy gap was also deduced from the HOMO-LUMO results. The atomistic model of each silicon QDs was constructed by repeating its crystal unit cell of face-centered cubic (FCC) structure, and reconstructed until the spherical shape obtained. The core structure shows tetrahedral (T{sub d}) symmetry structure. It was found that the model need to be passivated, and hence it was noticed that the confinement effect was more pronounced. The model was optimized using Quasi-Newton method for each size of Si-QDs to get relaxed structure before it was simulated. In this model the exchange-correlation potential (V{sub xc}) of the electrons was treated by Local Density Approximation (LDA) functional and Perdew-Zunger (PZ) functional.

  17. First-principles study of the magnetic stability and the exchange couplings of LaMn2O5

    Science.gov (United States)

    El Hallani, F.; Naji, S.; Ez-Zahraouy, H.; Benyoussef, A.

    2013-10-01

    Using first principles calculations, the electronic and magnetic properties of the multiferroic LaMn2O5 have been studied. In particular, we have studied the magnetic stability of this material not only in ab-plane but also along c direction. Beside this, the exchange couplings between manganese ions have been calculated using Heisenberg model by including only the nearest neighbour interactions. It is shown that the stable magnetic order of LaMn2O5 is of antiferromagnetic type, which is in good agreement with the experiments. In order to show the effect of the temperature on the properties of our compound we have carried out this study using two crystal structures: the higher symmetric one (space group Pbam) that reported experimentally at T(98.8 k) and the lower symmetric one (space group Pmc21) that obtained from the relaxation, in our calculations, at T = 0 K starting from the stable magnetic order.This structure deformation at T = 0 can be related to the exchange coupling striction. The density of states show an insulating behavior in the antiferromagnetic state of LaMn2O5 at Fermi level and there is a small band gap, confirming the experimental fact that LaMn2O5 is an insulator. We have found that the nature of the mechanism of these magnetic exchange coupling is an indirect super-exchange.

  18. First-principles studies of phase stability and the structural and dynamical properties of hydrogen-metal systems. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Chou, M.Y.

    1993-05-01

    First-principles calculations were carried for the hydrogen-yttrium system using the pseudopotential method within the local density functional approximation (LDA). We have studied the nature of hydrogen pairing in the solid solution phase ({alpha}-YH{sub x}.) and identified the connection with electronic structure. The vibrational spectra, diffusion barrier, and migration path were also investigated. We have also studied the binding characteristics for different interstitial sites and the (420)-plane ordering of octahedral hydrogen in {beta}YH{sub 2+x} within the lattice gas model. Temperature-composition phase diagram was calculated by cluster variational method with the multibody interactions extracted from total energies of related ordered structures. Moreover, the discovery of Peierls distortions in YH{sub 3} explained the unusual hydrogen displacements found in neutron diffraction and the possibility of an excitonic insulating ground state was speculated. Several new improvements in the calculational techniques also been developed: Separable nonlocal pseudopotentials, scheme to calculate the full phonon spectrum, and distance dependent tight-binding parameters. The Ru(0001)-H system was also studied.

  19. First-principle study on bulk and (1 1 1) surface of MP (M = K and Rb) in rocksalt structure

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Qiang; Li, Lei; Xie, Huan-Huan; Lei, Gang; Deng, Jian-Bo; Hu, Xian-Ru, E-mail: huxianru@lzu.edu.cn

    2015-08-01

    The electronic and magnetic properties of bulk and (1 1 1) surfaces for MP (M = K and Rb) in rocksalt structure have been investigated by employing first-principle calculations. The results reveal that the compounds are half-metallic ferromagnets at the equilibrium lattice constants with large half-metallic band gaps of 0.46 and 0.74 eV. The (1 1 1) surfaces of KP and RbP keep their bulk half-metallic property. We study the stabilities of the bulk compounds and their (1 1 1) surfaces as well. The results show that those bulk compounds are more stable in the rocksalt structure than in the tetragonal structure. In addition, the K- and Rb-terminated surfaces are more stable than their P-terminated surfaces. - Highlights: • The half metallic properties of rocksalt-type KP and RbP are studied. • The Slater-Pauling behaviours, energy levels and fat-bands of them are discussed. • The properties to KP's and RBP's (1 1 1) surfaces have been investigated. • The stabilities of bulk compounds and surfaces are studied.

  20. Study of Cs adsorption on (100) surface of [001]-oriented GaN nanowires: A first principle research

    Science.gov (United States)

    Xia, Sihao; Liu, Lei; Kong, Yike; Wang, Honggang; Wang, Meishan

    2016-11-01

    Based on first-principle study, the adsorption mechanism of Cs on (100) crystal plane of GaN nanowire surface with coverage of 1/12 monolayer is explored. It is discovered that the most stable adsorption site is BN because of its lowest adsorption energy. The work function of GaN nanowire surface is reduced by 1.69 eV and will be further reduced with increasing Cs adsorption, which promotes the development of negative electron affinity (NEA) state of the materials. Furthermore, Cs adatom will make a great influence on the surface atomic structure, oppositely, little influence on the center atomic structure. There appears a dipole moment valued -6.93 Debye on the nanowire surface contributed to the formation the heterojunction on the surface, which is beneficial to the photoelectrons liberation. After Cs adsorption, the valence band and conduction band both move to lower energy side. The surface states mainly result from the hybridization of Cs 5s state with Ga 4p state and N 2p state. This study can help us to further experiment on the Cs adsorption processing on GaN nanowire and improve the photoemission performance of GaN nanowire devices.

  1. First-principles studies of the Gilbert damping and exchange interactions for half-metallic Heuslers alloys

    Science.gov (United States)

    Chico, Jonathan; Keshavarz, Samara; Kvashnin, Yaroslav; Pereiro, Manuel; Di Marco, Igor; Etz, Corina; Eriksson, Olle; Bergman, Anders; Bergqvist, Lars

    2016-06-01

    Heusler alloys have been intensively studied due to the wide variety of properties that they exhibit. One of these properties is of particular interest for technological applications, i.e., the fact that some Heusler alloys are half-metallic. In the following, a systematic study of the magnetic properties of three different Heusler families Co2Mn Z ,Co2FeZ , and Mn2V Z with Z=(Al,Si,Ga,Ge) is performed. A key aspect is the determination of the Gilbert damping from first-principles calculations, with special focus on the role played by different approximations, the effect that substitutional disorder and temperature effects. Heisenberg exchange interactions and critical temperature for the alloys are also calculated as well as magnon dispersion relations for representative systems, the ferromagnetic Co2Fe Si and the ferrimagnetic Mn2V Al . Correlation effects beyond standard density-functional theory are treated using both the local spin density approximation including the Hubbard U and the local spin density approximation plus dynamical mean field theory approximation, which allows one to determine if dynamical self-energy corrections can remedy some of the inconsistencies which were previously reported for these alloys.

  2. Effects of IIIB transition metals on optoelectronic and magnetic properties of HoMnO3:A first principles study

    Institute of Scientific and Technical Information of China (English)

    H. A. Rahnamaye Aliabad; Battal G. Yalcin

    2015-01-01

    The optoelectronic and magnetic properties of pure HoMnO3 and Ho0.67T0.33MnO3 (T =La, Y) alloys in hexagonal phase are theoretically investigated by using the first-principles calculations. The investigations are performed by means of the density functional theory through using the spin polarized generalized gradient approximation plus the Hubbard potential (SPGGA+U , Ueff=3 eV). The studied material HoMnO3 exhibits two indirect band gaps:1.58 eV for the spin-up state and 0.72 eV for the spin-down state along the S–G direction within the SPGGA+U approximation. It is found that the band gap of pure HoMnO3 for the spin-up state increases with increasing La and Y dopants. The results show that all of the studied materials have semi-metallic behaviors for the spin-up state and semiconducting character for the spin-down state. The substitutions of La and Y for Ho in HoMnO3 cause the static dielectric constant (ε0) to increase in the x direction but to decrease in the z direction. The calculated optical conductivity spectrum of HoMnO3 in a low energy range is in good agreement with the recent experimental data.

  3. Influences of Stone-Wales defects on the structure, stability and electronic properties of antimonene: A first principle study

    Science.gov (United States)

    Hu, Yonghong; Wu, Yunyi; Zhang, Shengli

    2016-12-01

    Defects are inevitably present in materials, and their existence strongly affects the fundamental physical properties of 2D materials. Here, we performed first-principles calculations to study the structural and electronic properties of antimonene with Stone-Wales defects, highlighting the differences in the structure and electronic properties. Our calculations show that the presence of a SW defect in antimonene changes the geometrical symmetry. And the band gap decreases in electronic band structure with the decrease of the SW defect concentration. The formation energy and cohesive energy of a SW defect in antimonene are studied, showing the possibility of its existence and its good stability, respectively. The difference charge density near the SW defect is explored, by which the structural deformations of antimonene are explained. At last, we calculated the STM images for the SW defective antimonene to provide more information and characters for possible experimental observation. These results may provide meaningful references to the development and design of novel nanodevices based on new 2D materials.

  4. Energetics and magnetism of Co-doped GaN(0001) surfaces: A first-principles study

    CERN Document Server

    Qin, Zhenzhen; Chen, Guangzhao Qin Lanli

    2014-01-01

    A comprehensive first-principles study of the energetics, electronic and magnetic properties of Co-doped GaN(0001) thin films are presented and the effect of surface structure on the magnetic coupling between Co atoms is demonstrated. It is found that Co atoms prefer to substitute the surface Ga sites in different growth conditions. In particular, a CoN/GaN interface structure with Co atoms replacing the first Ga layer is preferred under N-rich and moderately Ga-rich conditions, while CoGa$_x$/GaN interface is found to be energetically stable under extremely Ga-rich conditions. It's worth noting that the AFM coupling between Co atoms is favorable in clean GaN(0001) surface, but the existence of FM would be expected to occur as Co concentration increased in Ga-bilayer GaN(0001) surface. Our study provides the theoretical understanding for experimental research on Co-doped GaN films and might promise the Co:GaN system potential applications in spin injection devices.

  5. Alloying Effects on the Phase Stability and Mechanical Properties of Doped Cu-Sn IMCs: A First-Principle Study

    Science.gov (United States)

    Zhang, Yong; Yuan, Ding-Wang; Chen, Jiang-Hua; Zeng, Guang; Fan, Tou-Wen; Liu, Zi-Ran; Wu, Cui-Lan; Liu, Ling-Hong

    2016-08-01

    Cu-Sn phases are important intermetallic compounds formed at the interface between solder and substrate in the soldering process. They exist in several crystal structures ( η', η, η 1 and η 2, etc.). The solid-state phase transformation that occurs among Cu-Sn intermetallic compounds is a crucial issue for industry applications, because the associated volume change inevitably leads to microstructural instability. Generally, four alloying elements, i.e., Ni, Au, Zn, and indium (In), are used as alloying elements to stabilize the high temperature hexagonal η-phase. However, the physical mechanism of this stabilization effect, especially on the high temperature η 1 and η 2 phases, is still unclear. In the present study, first-principle calculations were performed to study the stability and mechanical properties of Cu5Sn4 ( η 1 and η 2) and Cu6Sn5 ( η') when doped with Ni, Au, Zn, and indium alloying elements. It is shown that their phase stability and mechanical properties could be enhanced by these elements in some circumstances. Ni-doping can significantly enhance both the stability and the mechanical properties of the three phases, whereas Zn-doping exhibits a significant effect on that of the η 2 phase.

  6. Adsorption properties of fission gases Xe and Kr on pristine and doped graphene: A first principle DFT study

    Science.gov (United States)

    Vazhappilly, Tijo; Ghanty, Tapan K.; Jagatap, B. N.

    2017-07-01

    Graphene has excellent adsorption properties due to large surface area and has been used in applications related to gas sorption and separation. The separation of radioactive noble gases using graphene is an interesting area of research relevant to nuclear waste management. Radioactive noble gases Xe and Kr are present in the off-gas streams from nuclear fission reactors and spent nuclear fuel reprocessing plants. The entrapment of these volatile fission gases is important in the context of nuclear safety. The separation of Xe from Kr is extremely difficult, and energy intensive cryogenic distillation is generally employed. Physisorption based separation techniques using porous materials is a cost effective alternative to expensive cryogenic distillation. Thus, adsorption of noble gases on graphene is relevant for fundamental understanding of physisorption process. The properties of graphene can be tuned by doping and incorporation of defects. In this regard, we study the binding affinity of Xe and Kr in pristine and doped graphene sheets. We employ first principle calculations using density functional theory, corrected for dispersion interactions. The structural parameters obtained from the current study show excellent agreement with the available theoretical and experimental observations on similar systems. Noble gas adsorption energies on pristine graphene match very well with the available literature. Our results show that the binding energy of fission gases Xe and Kr on graphene can be considerably improved through doping the lattice with a heteroatom.

  7. First-principles local density approximation (LDA)+ U and generalized gradient approximation (GGA) + U studies of plutonium oxides

    Institute of Scientific and Technical Information of China (English)

    Sun Bo; Zhang Ping

    2008-01-01

    The electronic structures and properties of PuO2 and Pu2O3 have been studied according to the first principles by using the all-electron projector-augmented-wave (PAW) method. The local density approximation (LDA)+U and the generalized gradient approximation (GGA)+U formalisms have been used to account for the strong on-site Coulomb repulsion among the localized Pu 5f electrons. We discuss how the properties of PuO2 and Pu2O3 are affected by choosing the values of U and exchange-correlation potential. Also, the oxidation reaction of Pu2O3, leading to the formation of PuO2, and its dependence on U and exchange-correlation potential have been studied. Our results show that by choosing an appropriate U it is possible to consistently describe structural, electronic, and thermodynamic properties of PuO2 and Pu2O3, which enable the modelling of the redox process involving Pu-based materials.

  8. The role of point defects in PbS, PbSe and PbTe: a first principles study.

    Science.gov (United States)

    Li, Wun-Fan; Fang, Chang-Ming; Dijkstra, Marjolein; van Huis, Marijn A

    2015-09-09

    Intrinsic defects are of central importance to many physical and chemical processes taking place in compound nanomaterials, such as photoluminescence, accommodation of off-stoichiometry and cation exchange. Here, the role of intrinsic defects in the above mentioned processes inside rock salt (RS) lead chalcogenide systems PbS, PbSe and PbTe (PbX) was studied systematically using first principles density functional theory. Vacancy, interstitial, Schottky and Frenkel defects were considered. Rock salt PbO was included for comparison. The studied physical properties include defect formation energy, local geometry relaxation, Bader charge analysis, and electronic structure. The defect formation energies show that monovacancy defects and Schottky defects are favoured over interstitial and Frenkel defects. Schottky dimers, where the cation vacancy and anion vacancy are adjacent to each other, have the lowest defect formation energies at 1.27 eV, 1.29 eV and 1.21 eV for PbS, PbSe and PbTe, respectively. Our results predict that a Pb monovacancy gives rise to a shallow acceptor state, while an X vacancy generates a deep donor state, and Schottky defects create donor-acceptor pairs inside the band gap. The surprisingly low formation energy of Schottky dimers suggests that they may play an important role in cation exchange processes, in contrast to the current notion that only single point defects migrate during cation exchange.

  9. First principles study of electronic structure dependent optical properties of oxychalcogenides BiOCu Ch ( Ch = S, Se, Te)

    Science.gov (United States)

    Ul Islam, A. K. M. Farid; Helal, M. A.; Liton, M. N. H.; Kamruzzaman, M.; Islam, H. M. Tariqul

    2017-04-01

    The optical properties of BiOCu Ch and their dependency on the electronic structures are investigated using first principles study. Modified Perdew-Burke-Ernzerhof generalized gradient approximation functional for solids are used to optimize lattice parameters. These optimized lattice parameters are used to calculate the electronic energy band, density of state and optical properties. It is observed that the optical constants are dependent on the energy band gap and also on the contribution of Copper and Chalcogen atoms in the formation of electronic band structure. The obtained results reveal that the optical constants are dominated by the inter-band transitions. In the case of higher incident photon energy these materials behave like metal, where optical constants are dominated by the free carriers. The obtained optical band gaps 0.60, 0.56 and 0.55 eV for BiOCuS, BiOCuSe and BiOCuTe, respectively are consistent with available theoretical results. We also calculate the carrier concentration, electrical conductivity, effective mass of the carrier and their temperature dependency using semi-classical BoltzTraP package. Among these three materials BiOCuTe shows higher electrical conductivity. Analyzing their optical properties, we conclude that these materials are useful in the optoelectronic devices such as coating materials, high frequency reflector, infrared radiation detector and emitter and also important to design quantum devices.

  10. First-principles study of the Pd–Si system and Pd(001)/SiC(001) hetero-structure

    Energy Technology Data Exchange (ETDEWEB)

    Turchi, P.E.A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Ivashchenko, V.I. [National Academy of Sciences of Ukraine (NASU), Kiev (Ukraine)

    2014-11-01

    First-principles molecular dynamics simulations of the Pd(001)/3C–SiC(001) nano-layered structure were carried out at different temperatures ranging from 300 to 2100 K. Various PdSi (Pnma, Fm3m, P6m2, Pm3m), Pd2Si (P6⁻2m, P63/mmc, P3m1, P3⁻1m) and Pd3Si (Pnma, P6322, Pm3m, I4/mmm) structures under pressure were studied to identify the structure of the Pd/Si and Pd/C interfaces in the Pd/SiC systems at high temperatures. It was found that a large atomic mixing at the Pd/Si interface occurred at 1500–1800 K, whereas the Pd/C interface remained sharp even at the highest temperature of 2100 K. At the Pd/C interface, voids and a graphite-like clustering were detected. Palladium and silicon atoms interact at the Pd/Si interface to mostly form C22-Pd2Si and D011-Pd3Si fragments, in agreement with experiment.

  11. Strain-induced insulator-metal transition in ferroelectric BaTiO3 (001) surface: First-principles study

    Science.gov (United States)

    Lin, Yang; Chang-An, Wang; Cong, Liu; Ming-Hui, Qin; Xu-Bing, Lu; Xing-Sen, Gao; Min, Zeng; Jun-Ming, Liu

    2016-07-01

    The electronic properties of TiO2-terminated BaTiO3 (001) surface subjected to biaxial strain have been studied using first-principles calculations based on density functional theory. The Ti ions are always inward shifted either at compressive or tension strains, while the inward shift of the Ba ions occurs only for high compressive strain, implying an enhanced electric dipole moment in the case of high compressive strain. In particular, an insulator-metal transition is predicted at a compressive biaxial strain of 0.0475. These changes present a very interesting possibility for engineering the electronic properties of ferroelectric BaTiO3 (001) surface. Project supported by the National Natural Science Foundation of China (Grant Nos. 1574091, 51272078, and 51431006), the Natural Science Foundation of Guangdong Province of China (Grant No. 2015A030313375), the Science and Technology Planning Project of Guangdong Province of China (Grant No. 2015B090927006), and the Program for International Innovation Cooperation Platform of Guangzhou City, China (Grant No. 2014J4500016).

  12. First-principles studies of electronic, optical, and mechanical properties of γ-Bi2Sn2O7

    Science.gov (United States)

    Chao-Hao, Hu; Xue-Hui, Yin; Dian-Hui, Wang; Yan, Zhong; Huai-Ying, Zhou; Guang-Hui, Rao

    2016-06-01

    The detailed theoretical studies of electronic, optical, and mechanical properties of γ-Bi2Sn2O7 are carried out by using first-principle density functional theory calculations. Our calculated results indicate that γ-Bi2Sn2O7 is the p-type semiconductor with an indirect band gap of about 2.72 eV. The flat electronic bands close to the valence band maximum are mainly composed of Bi-6s and O-2p states and play a key role in determining the electrical properties of γ-Bi2Sn2O7. The calculated complex dielectric function and macroscopic optical constants including refractive index, extinction coefficient, absorption coefficients, reflectivity, and electron energy-loss function show that γ-Bi2Sn2O7 is an excellent light absorbing material. The analysis on mechanical properties shows that γ-Bi2Sn2O7 is mechanically stable and highly isotropic. Project supported by the National Basic Research Program of China (Grant No. 2014CB643703), the National Natural Science Foundation of China (Grant Nos. 11164005, 11464008, and 51401060), the Natural Science Foundation of Guangxi Zhuang Autonomous Region, China (Grant Nos. 2014GXNSFGA118001 and 2012GXNSFGA060002), and the Fund from Guangxi Provincial Key Laboratory of Information Materials of Guangxi Zhuang Autonomous Region, China (Grant Nos. 1210908-215-Z and 131022-Z).

  13. First-principles study on the elastic properties of B‧ and Q phase in Al-Mg-Si (-Cu) alloys

    Science.gov (United States)

    Pan, Rong-Kai; Ma, Li; Bian, Nan; Wang, Ming-Hui; Li, Peng-Bo; Tang, Bi-Yu; Peng, Li-Ming; Ding, Wen-Jiang

    2013-01-01

    First-principles calculations within the density functional theory have been carried out to study the structural, elastic and electronic properties of B‧ and Q phases in Al-Mg-Si (-Cu) alloys. The obtained lattice constant a is reduced while c is increased with the addition of Cu into B‧ phase Al3Mg9Si7. The lower formation enthalpy of Q phase Al3Cu2Mg9Si7 shows that the structural stability is improved after the addition of Cu into the B‧ phase. The calculated elastic constants Cij with the exception of C13 for Q phase are larger than for B‧ phase. In addition, the derived bulk, shear, Young's modulus and Debye temperature except Poisson's ratio are also significantly increased with Cu addition, indicating that Q phase has a favorable improvement of hardness. The elastic anisotropies of the two phases are discussed in detail using several criteria, showing that the anisotropy degree of B‧ phase is larger than of Q phase. The electronic structures show that the two phases possess a mixed bonding character of covalent and ionic, and Cu-Si bonding is beneficial in stabilizing the Q phase due to the hybridization of Cu 3d and Si 3p orbits.

  14. First-principles study on structural and electronic properties of copper nanowire encapsulated into GaN nanotube

    Science.gov (United States)

    Ma, Liang-Cai; Zhang, Yan; Zhang, Jian-Min; Xu, Ke-Wei

    2011-09-01

    We present a systemic study of the structural and electronic properties of Cu n nanowires ( n=5, 9 and 13) encapsulated in armchair (8,8) gallium nitride nanotubes (GaNNTs) using the first-principles calculations. We find that the formation processes of these systems are all exothermic. The initial shapes are preserved without any visible changes for the Cu 5@(8,8) and Cu 9@(8,8) combined systems, but a quadratic-like cross-section shape is formed for the outer nanotube of the Cu 13@(8,8) combined system due to the stronger attraction between nanowire and nanotube. The electrons of Ga and N atoms in outer GaN sheath affect the electron conductance of the encapsulated metallic nanowire in the Cu 13@(8,8) combined system. But in the Cu 5@(8,8) and Cu 9@(8,8) combined systems, the conduction electrons are distributed only on the copper atoms, so charge transport will occur only in the inner copper nanowire, which is effectively insulated by the outer GaN nanotube. Considering the maximal metal filling ratio in nanotube, we know that the Cu 9@(8,8) combined system is top-priority in the ultra-large-scale integration (ULSI) circuits and micro-electromechanical systems (MEMS) devices that demand steady transport of electrons.

  15. Structural and electronic properties of copper nanowire encapsulated into BeO nanotube: First-principles study

    Science.gov (United States)

    Ma, Liang-Cai; Zhang, Jian-Min; Xu, Ke-Wei

    2012-02-01

    We present a systematic study on the structural and electronic properties of close-packed Cu nanowires encapsulated in a series of zigzag ( n,0) BeONTs using first-principles calculations. The initial shapes (cylindrical CuNWs and BeONTs) are preserved without any visible changes for the Cu m@( n,0) ( m=6 or 8, 8≤ n≤14) combined systems. The most stable combined systems are Cu 6@(10,0) and Cu 8@(11,0) with an optimal tube-wire distance of about 2.8 Å and a simple superposition of the band structures of their components near the Fermi level. A quantum conductance of 3G 0 is obtained for both Cu 6 and Cu 8 nanowires in either free-standing state or filled into BeONTs. The electron transport will occur only through the inner CuNW and the inert outer BeONT serves well as insulating cable sheath. So the Cu 6@(10,0) and Cu 8@(11,0) combined systems is top-priority in the ULSI circuits and MEMS devices that demand steady transport of electrons.

  16. Structural and electronic properties of copper nanowire encapsulated into BeO nanotube: First-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Ma Liangcai [College of Physics and Information Technology, Shaanxi Normal University, Xian 710062, Shaanxi (China); School of Physics and Electrical Information Engineering, Ningxia University, Yinchuan 750021, Ningxia (China); Zhang Jianmin, E-mail: jianm_zhang@yahoo.com [College of Physics and Information Technology, Shaanxi Normal University, Xian 710062, Shaanxi (China); Xu Kewei [Department of Physics, Xian University of Arts and Science, Xian 710065, Shaanxi (China)

    2012-02-15

    We present a systematic study on the structural and electronic properties of close-packed Cu nanowires encapsulated in a series of zigzag (n,0) BeONTs using first-principles calculations. The initial shapes (cylindrical CuNWs and BeONTs) are preserved without any visible changes for the Cu{sub m}-(n,0) (m=6 or 8, 8{<=}n{<=}14) combined systems. The most stable combined systems are Cu{sub 6}-(10,0) and Cu{sub 8}-(11,0) with an optimal tube-wire distance of about 2.8 Angstrom-Sign and a simple superposition of the band structures of their components near the Fermi level. A quantum conductance of 3G{sub 0} is obtained for both Cu{sub 6} and Cu{sub 8} nanowires in either free-standing state or filled into BeONTs. The electron transport will occur only through the inner CuNW and the inert outer BeONT serves well as insulating cable sheath. So the Cu{sub 6}-(10,0) and Cu{sub 8}-(11,0) combined systems is top-priority in the ULSI circuits and MEMS devices that demand steady transport of electrons.

  17. First principle study of the surface reactivity of layered lithium oxides LiMO2 (M = Ni, Mn, Co)

    Science.gov (United States)

    Vallverdu, Germain; Minvielle, Marie; Andreu, Nathalie; Gonbeau, Danielle; Baraille, Isabelle

    2016-07-01

    LiNixMnyCo1 - x - yO2 compounds (NMC) are layered oxides widely used in commercial lithium-ion batteries at the positive electrode. Nevertheless surface reactivity of this material is still not well known. As a first step, based on first principle calculations, this study deals with the electronic properties and the surface reactivity of LiMO2 (M = Co, Ni, Mn) compounds, considering the behavior of each transition metal separately in the same R 3 ̅ mα-NaFeO2-type structure, the one of LiCoO2 and NMC. For each compound, after a brief description of the bare slab electronic properties, we explored the acido-basic and redox properties of the (110) and (104) surfaces by considering the adsorption of a gaseous probe. The chemisorption of SO2 produces both sulfite or sulfate species associated respectively to an acido-basic or a reduction process. These processes are localized on the transition metals of the first two layers of the surface. Although sulfate species are globally favored, a different behavior is obtained depending on both the surface and the transition metal considered. We conclude with a simple scheme which describes the reduction processes on the both surfaces in terms of formal oxidation degrees of transition metals.

  18. First-principles study of thermal expansion and thermomechanics of single-layer black and blue phosphorus

    Science.gov (United States)

    Sun, Hongyi; Liu, Gang; Li, Qingfang; Wan, X. G.

    2016-05-01

    The linear thermal expansion coefficients (LTEC) and thermomechanics of single-layer black and blue phosphorus are systematically studied using first-principles based on quasiharmonic approximation. We find the thermal expansion of black phosphorus is very anisotropic. The LTEC along zigzag direction has a turning from negative to positive at around 138 K, while the LTEC along armchair direction is positive (except below 8 K) and about 2.5 times larger than that along zigzag direction at 300 K. For blue phosphorus, the LTEC is negative in the temperature range from 0 to 350 K. In addition, we find that the Young's modulus and Poisson's ratio of black phosphorus along zigzag direction are 4 to 5 times larger than those along armchair direction within considered temperature range, showing a remarkable anisotropic in-plane thermomechanics property. The mechanisms of these peculiar thermal properties are also explored. This work provides a theoretical understanding of the thermal expansion and thermomechanics of this single layer phosphorus family, which will be useful in nanodevices.

  19. First principles study of effects of vacancies on electronic, magnetic and optical properties of InN nanosheet

    Science.gov (United States)

    Farzan, M.; Elahi, S. M.; Abolhassani, M. R.; Salehi, H.

    2017-05-01

    Based on the first principle study within the generalized gradient approximation (GGA) in the density functional theory (DFT) implemented in Wien2k code, the effects of vacancies on electronic, magnetic and optical properties of InN nanosheet were investigated. We found that the vacancies in InN nanosheet induce spin polarized states in the band gap, and VN-defect, VIn-defect and VIn&N-defect induce local magnetic moments of (-0.01)μB , 3.0μB and 2.0μB , respectively. Also, we calculated the dielectric function, refraction index, extinction index, reflectivity, absorption coefficient, optical conductivity and energy loss function of the perfect InN nanosheet and VN-defect, VIn-defect and VIn&N-defect of InN nanosheet for both polarization directions of light, i.e. E||x (electric field parallel to nanosheet) and E||z (electric field perpendicular to nanosheet). Our results show that InN nanosheet is a semiconductor which is dependent on the type of vacancies and that the optical properties of perfect and defective InN nanosheets are anisotropic for both polarization states.

  20. First principles study of electronic structure dependent optical properties of oxychalcogenides BiOCuCh (Ch = S, Se, Te)

    Science.gov (United States)

    Ul Islam, A. K. M. Farid; Helal, M. A.; Liton, M. N. H.; Kamruzzaman, M.; Islam, H. M. Tariqul

    2016-11-01

    The optical properties of BiOCuCh and their dependency on the electronic structures are investigated using first principles study. Modified Perdew-Burke-Ernzerhof generalized gradient approximation functional for solids are used to optimize lattice parameters. These optimized lattice parameters are used to calculate the electronic energy band, density of state and optical properties. It is observed that the optical constants are dependent on the energy band gap and also on the contribution of Copper and Chalcogen atoms in the formation of electronic band structure. The obtained results reveal that the optical constants are dominated by the inter-band transitions. In the case of higher incident photon energy these materials behave like metal, where optical constants are dominated by the free carriers. The obtained optical band gaps 0.60, 0.56 and 0.55 eV for BiOCuS, BiOCuSe and BiOCuTe, respectively are consistent with available theoretical results. We also calculate the carrier concentration, electrical conductivity, effective mass of the carrier and their temperature dependency using semi-classical BoltzTraP package. Among these three materials BiOCuTe shows higher electrical conductivity. Analyzing their optical properties, we conclude that these materials are useful in the optoelectronic devices such as coating materials, high frequency reflector, infrared radiation detector and emitter and also important to design quantum devices.

  1. First-Principles Thermodynamics Study of Spinel MgAl 2 O 4 Surface Stability

    Energy Technology Data Exchange (ETDEWEB)

    Cai, Qiuxia; Wang, Jian-guo; Wang, Yong; Mei, Donghai

    2016-09-01

    The surface stability of all possible terminations for three low-index (111, 110, 100) structures of the spinel MgAl2O4 has been studied using first-principles based thermodynamic approach. The surface Gibbs free energy results indicate that the 100_AlO2 termination is the most stable surface structure under ultra-high vacuum at T=1100 K regardless of Al-poor or Al-rich environment. With increasing oxygen pressure, the 111_O2(Al) termination becomes the most stable surface in the Al-rich environment. The oxygen vacancy formation is thermodynamically favorable over the 100_AlO2, 111_O2(Al) and the (111) structure with Mg/O connected terminations. On the basis of surface Gibbs free energies for both perfect and defective surface terminations, the 100_AlO2 and 111_O2(Al) are the most dominant surfaces in Al-rich environment under atmospheric condition. This is also consistent with our previously reported experimental observation. This work was supported by a Laboratory Directed Research and Development (LDRD) project of the Pacific Northwest National Laboratory (PNNL). The computing time was granted by the National Energy Research Scientific Computing Center (NERSC). Part of computing time was also granted by a scientific theme user proposal in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL), which is a U.S. Department of Energy national scientific user facility located at PNNL in Richland, Washington.

  2. First-principles studies of magnetoelectric coupling in hexagonal LuFeO3 under applied electric fields

    Science.gov (United States)

    Zhang, Yubo; Wang, Hongwei; Dhuvad, Pratikkumar; Xu, Xiaoshan; Stengel, Massimiliano; Wu, Xifan

    The recently stabilized hexagonal LuFeO3 thin-film provides an opportunity in realizing the magnetoelectric coupling in multiferroic materials, in which the weak ferromagnetism due to Dzyaloshinskii-Moriya interaction was found to be closely associated with the trimerization (K3) mode. Here, we performed first-principles calculations in hexagonal LuFeO3 and studied the variations of weak ferromagnetic moment under applied electric fields. It is found that the weak ferromagnetism is a property that can be directly tuned by the external electric fields. As an improper ferroelectric material, such a magnetoelectric coupling is realized by the strong interaction between the trimerization mode and ferroelectric mode. Under the electric field poling, ferroelectric mode will respond. A change in ferroelectric distortion will in turn affect the amplitude of trimerization mode, and therefore, the weak ferromagnetism. Interestingly, the magnetoelectric coupling in LuFeO3 shows a strong nonlinear behavior originating again from the coupling between the trimerization and ferroelectric modes due to its improper nature.

  3. First-principles study of Al2Sm intermetallic compound on structural, mechanical properties and electronic structure

    Science.gov (United States)

    Lin, Jingwu; Wang, Lei; Hu, Zhi; Li, Xiao; Yan, Hong

    2017-02-01

    The structural, thermodynamic, mechanical and electronic properties of cubic Al2Sm intermetallic compound are investigated by the first-principles method on the basis of density functional theory. In light of the strong on-site Coulomb repulsion between the highly localized 4f electrons of Sm atoms, the local spin density approximation approach paired with additional Hubbard terms is employed to achieve appropriate results. Moreover, to examine the reliability of this study, the experimental value of lattice parameter is procured from the analysis of the TEM image and diffraction pattern of Al2Sm phase in the AZ31 alloy to verify the authenticity of the results originated from the computational method. The value of cohesive energy reveals Al2Sm to be a stable in absolute zero Kelvin. According to the stability criteria, the subject of this work is mechanically stable. Afterward, elastic moduli are deduced by performing Voigt-Reuss-Hill approximation. Furthermore, elastic anisotropy and anisotropy of sound velocity are discussed. Finally, the calculation of electronic density of states is implemented to explore the underlying mechanism of structural stability.

  4. Borophene as an anode material for Ca, Mg, Na or Li ion storage: A first-principle study

    Science.gov (United States)

    Mortazavi, Bohayra; Dianat, Arezoo; Rahaman, Obaidur; Cuniberti, Gianaurelio; Rabczuk, Timon

    2016-10-01

    Borophene, the boron atom analogue to graphene, being atomic thick have been just recently experimentally fabricated. In this work, we employ first-principles density functional theory calculations to investigate the interaction of Ca, Mg, Na or Li atoms with single-layer and free-standing borophene. We first identified the most stable binding sites and their corresponding binding energies as well and then we gradually increased the ions concentration. Our calculations predict strong binding energies of around 4.03 eV, 2.09 eV, 2.92 eV and 3.28 eV between the borophene substrate and Ca, Mg, Na or Li ions, respectively. We found that the binding energy generally decreases by increasing the ions content. Using the Bader charge analysis, we evaluate the charge transfer between the adatoms and the borophene sheet. Our investigation proposes the borophene as a 2D material with a remarkably high capacity of around 800 mA h/g, 1960 mA h/g, 1380 mA h/g and 1720 mA h/g for Ca, Mg, Na or Li ions storage, respectively. This study can be useful for the possible application of borophene for the rechargeable ion batteries.

  5. Electronic structure and optical properties of prominent phases of $\\rm{TiO_2}$: First-principles study

    Indian Academy of Sciences (India)

    SANTOSH SINGH; MADHVENDRA NATH TRIPATHI

    2017-07-01

    First-principles study based on density functional theory $\\rm{(DFT)}$ of two prominent phases, the rutile and the anatase phases, of titanium dioxide $\\rm{(TiO_2)}$ are reported within the generalized gradient approximation $\\rm{(GGA)}$. Our calculated band structure shows that there is a significant presence of O-2p and Ti-3d hybridization in the valence bands. These bands are well separated from the conduction bands by a direct band gap value of 1.73 eV in the rutile phase and an indirect band gap value of 2.03 eV in the anatase phase, from $\\Gamma$ to $\\rm{X}$. Our calculations reproduced the peaks in the conduction and valence band, are in good agreement with experimental observations.Our structural optimization for the rutile and anatase phase led to lattice parameter values of 4.62 Å and 2.99 Å rutile and 3.80 Å and 9.55 Å for anatase for $a$ and $c$. The static dielectric values 7.0 and 5.1 for the rutile and anatase phases respectively are in excellent agreement with experimental results. Our calculation of optical properties reveals that maximum value of the transmittance in anatase phase of $\\rm{(TiO_2)}$ may be achieved by considering the anisotropic behaviour of the optical spectra in the optical region for transparent conducting application.

  6. Adsorption and decomposition of dimethyl methylphosphonate on pristine and mono-vacancy defected graphene: A first principles study

    Science.gov (United States)

    Majumder, Chiranjib

    2017-10-01

    Here we report the adsorption and decomposition behavior of dimethyl methyl-phosphonate (DMMP) on pristine and defected graphene using the first principles theory. The primary objective of this study is to highlight the importance of a vacancy defect on the adsorption mechanism of a molecule. In order to account for the weak forces involved between the molecule and graphene, we have used dispersion corrected total energy calculations along with generalized gradient approximation scheme for the exchange correlation energy. Among various possible configurations, the most stable geometry shows oxygen atom of the DMMP molecule favors to be close to the surface plane and bind with one of the unsaturated carbon atoms at the defect site. The molecule-substrate interaction energy is stronger for defected graphene than pristine graphene. The decomposition of the DMMP molecule at the vacancy site of the defected graphene has been investigated. For the dissociative adsorption, it is seen that the Csbnd H bond of the DMMP breaks and H atom is transferred to one of the low-coordinated C-atoms at the vicinity of the defect, forming new Csbnd H bond. In addition, the Csbnd C bond formation between graphene and DMMP occurs. Finally, the nature of bonding and electronic structure at the interface was interpreted through site projected electronic density of states analysis.

  7. Structural, electronic and magnetic properties of Fe{sub 2}-based full Heusler alloys: A first principle study

    Energy Technology Data Exchange (ETDEWEB)

    Dahmane, F., E-mail: fethallah05@gmail.com [Département de SM, Institue des sciences et des technologies, Centre universitaire de Tissemsilt, 38000, Tissemsilt (Algeria); Modelling and Simulation in Materials Science Laboratory, Physics Department, University of Sidi Bel-Abbes, 22000 Sidi Bel-Abbes (Algeria); Mogulkoc, Y. [Department of Engineering Physics, Ankara University, Ankara (Turkey); Doumi, B.; Tadjer, A. [Modelling and Simulation in Materials Science Laboratory, Physics Department, University of Sidi Bel-Abbes, 22000 Sidi Bel-Abbes (Algeria); Khenata, R. [Laboratoire de Physique Quantique de la Matière et de Modélisation Mathématique (LPQ3M), Université de Mascara, 29000 Mascara (Algeria); Bin Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O Box 2455, Riyadh 11451 (Saudi Arabia); Rai, D.P. [Department of Physics, Pachhunga University College, Aizawl-796001 (India); Murtaza, G. [Materials Modeling Lab, Department of Physics, Islamia College University, Peshawar (Pakistan); Varshney, Dinesh [Materials Science Laboratory, School of Physics, Vigyan Bhavan, Devi Ahilya University, Khandwa Road Campus, Indore 452001 (India)

    2016-06-01

    Using the first-principles density functional calculations, the structural, electronic and magnetic properties of the Fe{sub 2}XAl (X=Cr, Mn, Ni) compounds in both the Hg{sub 2}CuTi and Cu{sub 2}MnAl-type structures were studied by the full-potential linearized augmented plane waves (FP-LAPW) method. The exchange and correlation potential is treated by the generalized-gradient approximation (GGA) where the results show that the Cu{sub 2}MnAl-type structure is energetically more stable than the Hg{sub 2}CuTi-type structure for the Fe{sub 2}CrAl and Fe{sub 2}MnAl compounds at the equilibrium volume. The full Heusler compounds Fe{sub 2}XAl (X=Cr, Mn) are half-metallic in the Cu{sub 2}MnAl-type structure. Fe{sub 2}NiAl has a metallic character in both CuHg{sub 2}Ti and AlCu{sub 2}Mn-type structures. The total magnetic moments of the Fe{sub 2}CrAl and Fe{sub 2}MnAl compounds are 1.0 and 2.0 μ{sub B}, respectively, which are in agreement with the Slater–Pauling rule M{sub tot}=Z{sub tot}− 24.

  8. Structural, electronic, and vibrational properties of high-density amorphous silicon: a first-principles molecular-dynamics study.

    Science.gov (United States)

    Morishita, Tetsuya

    2009-05-21

    We report a first-principles study of the structural, electronic, and dynamical properties of high-density amorphous (HDA) silicon, which was found to be formed by pressurizing low-density amorphous (LDA) silicon (a normal amorphous Si) [T. Morishita, Phys. Rev. Lett. 93, 055503 (2004); P. F. McMillan, M. Wilson, D. Daisenberger, and D. Machon, Nature Mater. 4, 680 (2005)]. Striking structural differences between HDA and LDA are revealed. The LDA structure holds a tetrahedral network, while the HDA structure contains a highly distorted tetrahedral network. The fifth neighboring atom in HDA tends to be located at an interstitial position of a distorted tetrahedron composed of the first four neighboring atoms. Consequently, the coordination number of HDA is calculated to be approximately 5 unlike that of LDA. The electronic density of state (EDOS) shows that HDA is metallic, which is consistent with a recent experimental measurement of the electronic resistance of HDA Si. We find from local EDOS that highly distorted tetrahedral configurations enhance the metallic nature of HDA. The vibrational density of state (VDOS) also reflects the structural differences between HDA and LDA. Some of the characteristic vibrational modes of LDA are dematerialized in HDA, indicating the degradation of covalent bonds. The overall profile of the VDOS for HDA is found to be an intermediate between that for LDA and liquid Si under pressure (high-density liquid Si).

  9. First-principles model potentials for lattice-dynamical studies: general methodology and example of application to ferroic perovskite oxides.

    Science.gov (United States)

    Wojdeł, Jacek C; Hermet, Patrick; Ljungberg, Mathias P; Ghosez, Philippe; Íñiguez, Jorge

    2013-07-31

    We present a scheme to construct model potentials, with parameters computed from first principles, for large-scale lattice-dynamical simulations of materials. We mimic the traditional solid-state approach to the investigation of vibrational spectra, i.e., we start from a suitably chosen reference configuration of the compound and describe its energy as a function of arbitrary atomic distortions by means of a Taylor series. Such a form of the potential-energy surface is general, trivial to formulate for any material, and physically transparent. Further, such models involve clear-cut approximations, their precision can be improved in a systematic fashion, and their simplicity allows for convenient and practical strategies to compute/fit the potential parameters. We illustrate our scheme with two challenging cases in which the model potential is strongly anharmonic, namely, the ferroic perovskite oxides PbTiO3 and SrTiO3. Studying these compounds allows us to better describe the connection between the so-called effective-Hamiltonian method and ours (which may be seen as an extension of the former), and to show the physical insight and predictive power provided by our approach-e.g., we present new results regarding the factors controlling phase-transition temperatures, novel phase transitions under elastic constraints, an improved treatment of thermal expansion, etc.

  10. First-principles study of intercalation of alkali ions in FeSe for solid-state batteries

    Science.gov (United States)

    Jiang, Zhiqiang; Gu, Xiao; Wang, Linxia; Huang, Li

    2016-08-01

    Electrochemical properties of alkali ions (Li+, Na+, and K+) intercalating into FeSe have been studied based on first-principles calculations within density functional theory. The intercalation sites of lithium ions are found to be different from sodium and potassium ions due to the small ionic radius of lithium. Calculations of minimum energy path on the diffusions of Li+, Na+, and K+ in FeSe show that the activation energies for those alkali ions increase with their ionic radii. Lithium ions have a rather smaller diffusion barrier of about 0.20 eV, which leads to a bigger diffusion coefficient of about 6.3 ×10-6cm2 /s . We also show that FeSe has a flat discharging stage at about 1.0 V with lithium ions. These results indicate that XFe2Se2 (X = Li, Na, K) may be potential electrochemical active materials, especially for solid-state electrolyte and supercapacitors.

  11. First principles study of Al-doped graphene as nanostructure adsorbent for NO2 and N2O: DFT calculations

    Science.gov (United States)

    Rad, Ali Shokuhi

    2015-12-01

    We studied the first principles adsorption phenomena of nitrogen dioxide (NO2) and nitrous oxide (N2O) molecules on the surface of pristine graphene and Al-doped graphene using density functional theory (DFT) calculations. The adsorption energies have been calculated for different possible configurations of the molecules on the surface of pristine and Al-doped graphene. Our calculations reveal that the Al-doped graphene has significant adsorption energy, elevated net charge transferring values and smaller bond distances to gases than that of pristine graphene because of the chemical interaction of the mentioned molecules. Furthermore, the calculated density of states (DOS) show the existing of noteworthy orbital hybridization between NO2 as well as N2O and Al-doped graphene during adsorption process which is proving to strong interaction while there is no evidence for hybridization between the those molecules and the pristine graphene. Our calculated adsorption energies for the most stable states for NO2 and N2O was -62.2 kJ mol-1 (-48.5 kJ mol-1 BSSE corrected energy) and -33.9 kJ mol-1 (-22.7 kJ mol-1 corrected energy), which are correspond to chemisorption process. These results point to the suitability of Al-doped graphene as a powerful sensor for practical applications.

  12. First principles study of structural, electronic, elastic and thermal properties of YX (X = Cd, In, Au, Hg and Tl) intermetallics

    Science.gov (United States)

    Chouhan, Sunil Singh; Pagare, Gitanjali; Rajagopalan, M.; Sanyal, S. P.

    2012-08-01

    The structural, electronic, elastic and thermal properties of YX (X = Cd, In, Au, Hg and Tl) intermetallic compounds crystallizing in B2-type structure have been studied using first principles density functional theory within generalized gradient approximation (GGA) for the exchange correlation potential. Amongst all the YX compounds, YIn is stable in distorted tetragonal (P4/mmm) CuAu-type structure at ambient pressure with very small energy difference of 0.00681 Ry. but it undergoes to CsCl-type (B2 phase) structure at 23.3 GPa. Rest of the compounds are stable in B2 structure at ambient condition. The values of elastic moduli as a function of pressure are also reported. The ductility of these compounds has been analyzed using the Pugh rule. Our calculated results indicate that YTl is the most ductile amongst all the B2-YX compounds. YAu is the hardest and less compressible compound due to the largest bulk modulus. The elastic properties such as Young's modulus (E), Poisson's ratio (σ) and anisotropic ratio (A) are also predicted. The anisotropic factor is found to be unity for YHg which shows that this compound is isotropic.

  13. First-principles study of the adsorption properties of atoms and molecules on UN2 (001) surface

    Science.gov (United States)

    Xu, Mengjuan; Liu, Guangdong; Ao, Bingyun; Chen, Piheng; Hu, Wangyu; Deng, Huiqiu

    2017-09-01

    Uranium nitrides are one kind of accident-tolerant fuels and have been paid more attention recently. With the first-principles Density-Functional Theory (DFT) calculations, the adsorptions properties of some typical atoms, molecules and radical (including O, H, H2, O2, H2O and OH) adsorbed on the UN2 (001) surface have been studied in the present work. The preferred sites and stable configurations for those adsorbates on the UN2 (001) surface have been obtained. It's found that O or H atom prefers to be adsorbed at the bridge site; O2 adsorption will dissociate into two O atoms and occupy the nearest neighbor bridge sites; the interaction between H2 molecule and the UN2 (001) surface is very weak; OH prefers to occupy the bridge site with its O-H bond vertical to the surface; the surface adsorption of H2O is non-dissociated and adsorption energies are dependent on the initial structures and adsorption modes.

  14. Electronic structure and optical properties of prominent phases of TiO2: First-principles study

    Science.gov (United States)

    Singh, Santosh; Tripathi, Madhvendra Nath

    2017-07-01

    First-principles study based on density functional theory (DFT) of two prominent phases, the rutile and the anatase phases, of titanium dioxide (TiO_2) are reported within the generalized gradient approximation (GGA). Our calculated band structure shows that there is a significant presence of O-2p and Ti-3d hybridization in the valence bands. These bands are well separated from the conduction bands by a direct band gap value of 1.73 eV in the rutile phase and an indirect band gap value of 2.03 eV in the anatase phase, from Γ to X. Our calculations reproduced the peaks in the conduction and valence band, are in good agreement with experimental observations. Our structural optimization for the rutile and anatase phase led to lattice parameter values of 4.62 Å and 2.99 Å rutile and 3.80 Å and 9.55 Å for anatase for a and c. The static dielectric values 7.0 and 5.1 for the rutile and anatase phases respectively are in excellent agreement with experimental results. Our calculation of optical properties reveals that maximum value of the transmittance in anatase phase of TiO_2 may be achieved by considering the anisotropic behaviour of the optical spectra in the optical region for transparent conducting application.

  15. Co-doping as a tool for tuning the optical properties of singlewalled carbon nanotubes: A first principles study

    Science.gov (United States)

    Sharma, Deepa; Jaggi, Neena

    2017-07-01

    This paper presents a first principles study on the effect of co-doping on various optical spectra of a zigzag single-walled carbon nanotube (SWCNT). Optical spectra of a pristine SWCNT, SWCNT co-doped with Aluminum (Al) & Phosphorus (P) and another one co-doped with Al, P and Nitrogen (N) have been calculated using density functional theory (DFT).The theory has been implemented using the Cambridge sequential total energy package (CASTEP) code available as a userfriendly module with the software 'Material Studio'. Polarized and unpolarized light as well as light through polycrystalline media have been considered. The dependence of various spectra on the status of incident light presents a clear evidence of anisotropicity in the optical properties. Analysis of the simulated spectra involves calculation and comparison of different optical properties like dielectric function, reflectivity, refractive index, conductivity and loss function for the pristine and co-doped SWCNTs. Noticeable variations are observed in the optical properties on simultaneously doping the SWCNT with Al and P and then further introducing N atom into the structure so that it can be concluded that co-doping (simultaneous doping with different combinations of dopants) can be evolved as a novel and effective tool for tailoring the optical properties of SWCNTs as per the requirements while designing an optical device. It will prove to be highly significant for effective designing of SWCNT based sensitive optical devices for a variety of technological applications.

  16. First-principles study of a double-cation alkali metal borohydride LiK(BH{sub 4}){sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Xiao Xiaobing; Yu Weiyang; Tang Biyu [Key Laboratory of Low Dimensional Materials and Application Technology of the Ministry of Education, Department of Physics, Xiangtan University, Hunan Province, 411105 (China)], E-mail: tangbiyu@gxu.edu.cn

    2008-11-05

    Metal borohydrides have been attracting great interest as potential candidates for use as advanced hydrogen storage materials because of their high gravimetric hydrogen densities. In the present study, first-principles calculations have been performed for the newly reported dual-cation alkali metal borohydride LiK(BH{sub 4}){sub 2}, using density functional theory (DFT) within the generalized gradient approximation and the projected augmented wave method. LiK(BH{sub 4}){sub 2} is found to have an orthorhombic structure in the space group Pnma (No 62) with nearly ideal tetrahedral shape. It is an insulating material having a DFT-calculated wide band gap of 6.08 eV. Analysis of the electronic structure shows an ionic interaction between metal cations and (BH{sub 4}){sup -} and the covalent B-H interaction within the (BH{sub 4}){sup -} tetrahedron. The enthalpy of the formation reaction from primary elements is calculated and found to be -449.8 kJ mol{sup -1}. The decomposition temperature (T{sub dec}) of LiK(BH{sub 4}){sub 2} lies between those of LiBH{sub 4} and KBH{sub 4}, which suggests that the hydrogen decomposition temperature of metal borohydrides can be precisely adjusted by the appropriate combination of cations.

  17. First-principles LDA+U study of magnetism in CuxIn1-xN

    Science.gov (United States)

    González-García, Alvaro; López-Pérez, William; González-Hernández, Rafael

    2013-03-01

    We have carried out First-principles spin-polarized calculations in order to study the electronic structure and magnetism in Cu-doped InN using the LDA+U and LDA formalisms within density functional theory (DFT) with a plane-wave ultrasoft pseudopotential scheme. We found a stable ferromagnetic state in Cu0.0625In0.9375N with a total magnetization of 1.98μB per supercell, indicating Cu orders ferromagnetically in InN. The results indicate that the ferromagnetic ground state originates from the hybridized Cu(3d)-N(2p)-In(5p)-N(2p) chain formed through p-d coupling. Formation energy and ground state calculations have been performed for ferromagnetic and antiferromagnetic states of CuxIn1-xN (x=0,0625 and 0,125) by LDA+U and LDA formalisms. A weak ferromagnetic behavior for CuxIn1-xN (x=0,125) was found. The results predicted an AFM ground state for cases where the Cu atoms are closer. For longer Cu-Cu distances a stable FM ground state was found. This ferromagnetic behavior in CuxIn1-xN (x=0,125) could be tuned with In or N vacancies.

  18. Exploring adsorption and desorption characteristics of molecular hydrogen on neutral and charged Mg nanoclusters: A first principles study

    Science.gov (United States)

    Banerjee, Paramita; Chandrakumar, K. R. S.; Das, G. P.

    2016-05-01

    To surmount the limitations of bulk MgH2 for the purpose of hydrogen storage, we report here, a detailed first principles density functional theory (DFT) based study on the structure and stability of neutral (Mgm) and positively charged (Mgm+) Mg nanoclusters of different sizes (m = 2, 4, 8 and 12) and their interaction with molecular hydrogen (H2). Our results demonstrate that H2 is weakly bound to the Mg nanoclusters through van der Waals interactions. Incorporation of Grimme's dispersion correction (D3) in the DFT based exchange-correlation functionals leads to improved accuracy of H2 interaction energy (IE) values that fall within an energy window (between physisorption and chemisorption) desirable for hydrogen storage. Energy decomposition analysis reveals the significance of polarization energy for these Mg-H2 binding. Ab-initio molecular dynamics simulation shows that complete dehydrogenation from these Mg nanoclusters occur at ∼100 °C which is a significant improvement over bulk MgH2 (∼300 °C).

  19. Anisotropic electronic band structure of intrinsic Si(110) studied by angle-resolved photoemission spectroscopy and first-principles calculations

    Science.gov (United States)

    Matsushita, Stephane Yu; Takayama, Akari; Kawamoto, Erina; Hu, Chunping; Hagiwara, Satoshi; Watanabe, Kazuyuki; Takahashi, Takashi; Suto, Shozo

    2017-09-01

    We have studied the electronic band structure of the hydrogen-terminated Si(110)-(1 ×1 ) [H:Si(110)-(1 ×1 )] surface using angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations in the framework of density functional theory with local density approximation (LDA). The bulk-truncated H:Si(110)-(1 ×1 ) surface is a good template to investigate the electronic band structure of the intrinsic Si(110). In the ARPES spectra, seven bulk states and one surface state due to the H-H interaction are observed clearly. The four bulk states consisting of Si 3 px y orbitals exhibit anisotropic band dispersions along the high symmetric direction of Γ ¯-X ¯ and Γ ¯-X¯' directions, where one state shows one-dimensional character. The calculated band structures show a good agreement with the experimental results except the surface state. We discuss the exact nature of electronic band structures and the applicability of LDA. We have estimated the anisotropic effective masses of electrons and holes of Si(110) for device application.

  20. First-principles study of structural, electronic, vibrational, dielectric and elastic properties of tetragonal Ba₂YTaO₆

    Energy Technology Data Exchange (ETDEWEB)

    Ganeshraj, C.; Santhosh, P. N., E-mail: santhosh@physics.iitm.ac.in [Low Temperature Physics Laboratory, Department of Physics, Indian Institute of Technology Madras, Chennai 600 036, Tamil Nadu (India)

    2014-10-14

    We report first-principles study of structural, electronic, vibrational, dielectric, and elastic properties of Ba₂YTaO₆, a pinning material in high temperature superconductors (HTS), by using density functional theory. By using different exchange-correlation potentials, the accuracy of the calculated lattice constants of Ba₂YTaO₆ has been achieved with GGA-RPBE, since many important physical quantities crucially depend on change in volume. We have calculated the electronic band structure dispersion, total and partial density of states to study the band gap origin and found that Ba₂YTaO₆ is an insulator with a direct band gap of 3.50 eV. From Mulliken population and charge density studies, we conclude that Ba₂YTaO₆ have a mixed ionic-covalent character. Moreover, the vibrational properties, born effective charges, and the dielectric permittivity tensor have been calculated using linear response method. Vibrational spectrum determined through our calculations agrees well with the observed Raman spectrum, and allows assignment of symmetry labels to modes. We perform a detailed analysis of the contribution of the various infrared-active modes to the static dielectric constant to explain its anisotropy, while electronic dielectric tensor of Ba₂YTaO₆ is nearly isotropic, and found that static dielectric constant is in good agreement with experimental value. The six independent elastic constants were calculated and found that tetragonal Ba₂YTaO₆ is mechanically stable. Other elastic properties, including bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and elastic anisotropy ratios are also investigated and found that Poisson's ratio and Young's modulus of Ba₂YTaO₆ are similar to that of other pinning materials in HTS.

  1. First-principles study of structural, electronic, vibrational, dielectric and elastic properties of tetragonal Ba2YTaO6

    Science.gov (United States)

    Ganeshraj, C.; Santhosh, P. N.

    2014-10-01

    We report first-principles study of structural, electronic, vibrational, dielectric, and elastic properties of Ba2YTaO6, a pinning material in high temperature superconductors (HTS), by using density functional theory. By using different exchange-correlation potentials, the accuracy of the calculated lattice constants of Ba2YTaO6 has been achieved with GGA-RPBE, since many important physical quantities crucially depend on change in volume. We have calculated the electronic band structure dispersion, total and partial density of states to study the band gap origin and found that Ba2YTaO6 is an insulator with a direct band gap of 3.50 eV. From Mulliken population and charge density studies, we conclude that Ba2YTaO6 have a mixed ionic-covalent character. Moreover, the vibrational properties, born effective charges, and the dielectric permittivity tensor have been calculated using linear response method. Vibrational spectrum determined through our calculations agrees well with the observed Raman spectrum, and allows assignment of symmetry labels to modes. We perform a detailed analysis of the contribution of the various infrared-active modes to the static dielectric constant to explain its anisotropy, while electronic dielectric tensor of Ba2YTaO6 is nearly isotropic, and found that static dielectric constant is in good agreement with experimental value. The six independent elastic constants were calculated and found that tetragonal Ba2YTaO6 is mechanically stable. Other elastic properties, including bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and elastic anisotropy ratios are also investigated and found that Poisson's ratio and Young's modulus of Ba2YTaO6 are similar to that of other pinning materials in HTS.

  2. Study of Cs adsorption on (100) surface of [001]-oriented GaN nanowires: A first principle research

    Energy Technology Data Exchange (ETDEWEB)

    Xia, Sihao [Department of Optoelectronic Technology, School of Electronic and Optical Engineering, Nanjing University of Science and Technology Nanjing, 210094 (China); Liu, Lei, E-mail: liu1133_cn@sina.com.cn [Department of Optoelectronic Technology, School of Electronic and Optical Engineering, Nanjing University of Science and Technology Nanjing, 210094 (China); Kong, Yike [Department of Optoelectronic Technology, School of Electronic and Optical Engineering, Nanjing University of Science and Technology Nanjing, 210094 (China); Wang, Honggang; Wang, Meishan [School of Information and Electrical Engineering, Ludong University, Yantai 264025 (China)

    2016-11-30

    Highlights: • B{sub N} is the most stable adsorption site. • Work function is reduced after Cs adsorption. • Surface atomic structures are reconstructed. • Surface states near fermi level is contributed to the hybridization of Cs 5s state with Ga 4p and N 2p state. • NEA surface is demonstrated after Cs adsorption on GaN nanowire surface. - Abstract: Based on first-principle study, the adsorption mechanism of Cs on (100) crystal plane of GaN nanowire surface with coverage of 1/12 monolayer is explored. It is discovered that the most stable adsorption site is B{sub N} because of its lowest adsorption energy. The work function of GaN nanowire surface is reduced by 1.69 eV and will be further reduced with increasing Cs adsorption, which promotes the development of negative electron affinity (NEA) state of the materials. Furthermore, Cs adatom will make a great influence on the surface atomic structure, oppositely, little influence on the center atomic structure. There appears a dipole moment valued −6.93 Debye on the nanowire surface contributed to the formation the heterojunction on the surface, which is beneficial to the photoelectrons liberation. After Cs adsorption, the valence band and conduction band both move to lower energy side. The surface states mainly result from the hybridization of Cs 5s state with Ga 4p state and N 2p state. This study can help us to further experiment on the Cs adsorption processing on GaN nanowire and improve the photoemission performance of GaN nanowire devices.

  3. First-principles study on the ferrimagnetic half-metallic Mn{sub 2}FeAs alloy

    Energy Technology Data Exchange (ETDEWEB)

    Qi, Santao [Institute for Applied Physics, University of Science and Technology Beijing, Beijing 100083 (China); Zhang, Chuan-Hui, E-mail: zhangch@ustb.edu.cn [National Center for Materials Service Safety, University of Science and Technology Beijing, Beijing 100083 (China); Chen, Bao; Shen, Jiang [Institute for Applied Physics, University of Science and Technology Beijing, Beijing 100083 (China); Chen, Nanxian [Institute for Applied Physics, University of Science and Technology Beijing, Beijing 100083 (China); Department of Physics, Tsinghua University, Beijing 100084 (China)

    2015-05-15

    Mn-based full-Heusler alloys are kinds of promising candidates for new half-metallic materials. Basing on first principles, the electronic structures and magnetic properties of the Mn{sub 2}FeAs full-Heusler alloy have been investigated in detail. The Hg{sub 2}CuTi-type Mn{sub 2}FeAs compound obeys the Slater-Pauling rule, while the anti-parallel alignment atomic magnetic moments of Mn locating at different sites indicate it a ferrimagnetic alloy. The calculated spin-down bands behave half-metallic character, exhibiting a direct gap of 0.46 eV with a 100% spin polarization at the Fermi level. More studies show the compound would maintain half-metallic nature in a large range of variational lattice constants. We expect that our calculated results may trigger Mn{sub 2}FeAs applying in the future spintronics field. - Graphical abstract: The d orbitals of Mn and Fe atoms split into multi-degenerated levels which create new bonding and nonbonding states. These exchange splitting shift the Fermi level to origin band gap.▪ - Highlights: • The electronic structure and magnetic properties of Mn{sub 2}FeAs full-Heusler alloy were studied. • A total magnetic moment of 3μ{sub B} was obtained for Mn{sub 2}FeAs alloy, following the SP rule M{sub t}=Z{sub t}−24. • The origin of ferrimagnetism and half-metallic character in Mn{sub 2}FeAs were discussed.

  4. First principles study on half-metallic properties of Heusler compounds Ti2VZ (Z=Al, Ga, and In)

    Science.gov (United States)

    Galehgirian, S.; Ahmadian, F.

    2015-01-01

    First principles calculations using the self-consistent full-potential linearized augmented plane wave (FPLAPW) method in the framework of density functional theory (DFT) were performed to study the electronic structures and magnetic properties of new full-Heusler compounds Ti2VZ (Z=Al, Ga, and In). Electronic structure calculations showed that Ti2VZ (Z=Al, Ga, and In) compounds in AlCu2Mn-type are conventional ferrimagnets. The Ti2VAl, Ti2VGa, and Ti2VIn compounds in the CuHg2Ti-type structure have half-metallic characteristics with a respective majority band gap of 0.52, 0.51, and 0.59 eV at the equilibrium lattice parameter. The origin of half-metallicity in these compounds was also discussed. The total magnetic moments of Ti2VZ (Z=Al, Ga, and In) compounds in the CuHg2Ti-type structures were 2 μB per formula unit which were in agreement with Slater-Pauling rule (Mtot=18-Ztot). The Ti2VAl, Ti2VGa, and Ti2VIn compounds in the CuHg2Ti-type structure respectively showed half-metallic characteristics at lattice constants ranges of 6.12-7.17 Å, 5.99-7.12 Å, and 6.31-7.06 Å, indicating the lattice distortion did not affect the half-metallic properties of these compounds which makes them interesting materials in the spintronics field.

  5. Review on first-principles study of defect properties of CdTe as a solar cell absorber

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Ji-Hui; Yin, Wan-Jian; Park, Ji-Sang; Ma, Jie; Wei, Su-Huai

    2016-07-15

    CdTe is one of the leading materials for high-efficiency, low-cost, and thin-film solar cells. In this work, we review the recent first-principles study of defect properties of CdTe and present that: (1) When only intrinsic defects are present, p-type doping in CdTe is weak and the hole density is low due to the relatively deep acceptor levels of Cd vacancy. (2) When only intrinsic defects present, the dominant non-radiative recombination center in p-type CdTe is Te-2+/Cd, which limits the carrier lifetime to be around 200 ns. (3) Extrinsic p-type doping in CdTe by replacing Te with group V elements generally will be limited by the formation of AX centers. This could be overcome through a non-equilibrium cooling process and the hole density can achieve 10^17 cm-3. However, the long-term stability will be a challenging issue. (4) Extrinsic p-type doping by replacing Cd with alkaline group I elements is limited by alkaline interstitials and a non-equilibrium cooling process can efficiently enhance the hole density to the order of 10^17 cm-3. (5) Cu and Cl treatments are discussed. In bulk CdTe, Cu can enhance p-type doping, but Cl is found to be unsuitable for this. Both Cu and Cl show segregation at grain boundaries, especially at those with Te-Te wrong bonds. (6) External impurities are usually incorporated by diffusion. Therefore, the diffusion processes in CdTe are investigated. We find that cation interstitial (Nai, Cui) diffusion follows relatively simple diffusion paths, but anion diffusion (Cli, Pi) follows more complicated paths due to the degenerated defect wavefunctions.

  6. Thermal decomposition of trimethylgallium Ga(CH3)3: a shock-tube study and first-principles calculations.

    Science.gov (United States)

    Fikri, Mustapha; Makeich, Alexander; Rollmann, Georg; Schulz, Christof; Entel, Peter

    2008-07-17

    The thermal decomposition of Ga(CH3)3 has been studied both experimentally in shock-heated gases and theoretically within an ab-initio framework. Experiments for pressures ranging from 0.3 to 4 bar were performed in a shock tube equipped with atomic resonance absorption spectroscopy (ARAS) for Ga atoms at 403.3 nm. Time-resolved measurements of Ga atom concentrations were conducted behind incident waves as well as behind reflected shock waves at temperatures between 1210 and 1630 K. The temporal variation in Ga-atom concentration was described by a reaction mechanism involving the successive abstraction of methyl radicals from Ga(CH3)3 (R1), Ga(CH3)2 (R2), and GaCH3 (R3), respectively, where the last reaction is the rate-limiting step leading to Ga-atom formation. The rate constant of this reaction (R3) was deduced from a simulation of the measured Ga-atom concentration profiles using thermochemical data from ab-initio calculations for the reactions R1 and R2 as input. The Rice-Ramsperger-Kassel-Marcus (RRKM) method including variational transition state theory was applied for reaction R3 assuming a loose transition state. Structural parameters and vibrational frequencies of the reactant and transition state required for the RRKM calculations were obtained from first-principles simulations. The energy barrier E3(0) of reaction R3, which is the most sensitive parameter in the calculation, was adjusted until the RRKM rate constant matched the experimental one and was found to be E(0) = 288 kJ/mol. This value is in a good agreement with the corresponding ab-initio value of 266 kJ/mol. The rate constant of reaction R3 was found to be k 3/(cm(3) mol(-1)s(-1)) = 2.34 x 10(11) exp[-23330(K/ T)].

  7. Markedly different adsorption behaviors of gas molecules on defective monolayer MoS2: a first-principles study.

    Science.gov (United States)

    Li, Hongxing; Huang, Min; Cao, Gengyu

    2016-06-01

    Sulfur vacancy (SV) is one of the most typical defects in two-dimensional monolayer MoS2, leading to reactive sites. We presented a systematic study of the adsorption behaviors of gas molecules, CO2, N2, H2O, CO, NH3, NO, O2, H2 and NO2, on monolayer MoS2 with single SV by first-principles calculations. It was found that CO2, N2 and H2O molecules physisorbed at the proximity of single SV. Our adsorption energy calculations and charge transfer analysis showed that the interactions between CO2, N2 and H2O molecules and defective MoS2 are stronger than the cases of CO2, N2 and H2O molecules adsorbed on pristine MoS2, respectively. The defective MoS2 based gas sensors may be more sensitive to CO2, N2 and H2O molecules than pristine MoS2 based ones. CO, NO, O2 and NH3 molecules were found to chemisorb at the S vacancy site and thus modify the electronic properties of defective monolayer MoS2. Magnetism was induced upon adsorption of NO molecules and the defective states induced by S vacancy can be completely removed upon adsorption of O2 molecules, which may provide some helpful information for designing new MoS2 based nanoelectronic devices in future. The H2 and NO2 molecules were found to dissociate at S vacancy. The dissociation of NO2 molecules resulted in O atoms located at the S vacancy site and NO molecules physisorbed on O-doped MoS2. The calculated results showed that NO2 molecules can help heal the S vacancy of the MoS2 monolayer.

  8. Review on first-principles study of defect properties of CdTe as a solar cell absorber

    Science.gov (United States)

    Yang, Ji-Hui; Yin, Wan-Jian; Park, Ji-Sang; Ma, Jie; Wei, Su-Huai

    2016-08-01

    CdTe is one of the leading materials for high-efficiency, low-cost, and thin-film solar cells. In this work, we review the recent first-principles study of defect properties of CdTe and present that: (1) When only intrinsic defects are present, p-type doping in CdTe is weak and the hole density is low due to the relatively deep acceptor levels of Cd vacancy. (2) When only intrinsic defects present, the dominant non-radiative recombination center in p-type CdTe is T{e}Cd2+, which limits the carrier lifetime to be around 200 ns. (3) Extrinsic p-type doping in CdTe by replacing Te with group V elements generally will be limited by the formation of AX centers. This could be overcome through a non-equilibrium cooling process and the hole density can achieve {10}17 {{{cm}}}-3. However, the long-term stability will be a challenging issue. (4) Extrinsic p-type doping by replacing Cd with alkaline group I elements is limited by alkaline interstitials and a non-equilibrium cooling process can efficiently enhance the hole density to the order of {10}17 {{{cm}}}-3. (5) Cu and Cl treatments are discussed. In bulk CdTe, Cu can enhance p-type doping, but Cl is found to be unsuitable for this. Both Cu and Cl show segregation at grain boundaries, especially at those with Te-Te wrong bonds. (6) External impurities are usually incorporated by diffusion. Therefore, the diffusion processes in CdTe are investigated. We find that cation interstitial (Nai, Cui) diffusion follows relatively simple diffusion paths, but anion diffusion (Cli, Pi) follows more complicated paths due to the degenerated defect wavefunctions.

  9. Nature of proton dynamics in a polymer electrolyte membrane, nafion: a first-principles molecular dynamics study.

    Science.gov (United States)

    Choe, Yoong-Kee; Tsuchida, Eiji; Ikeshoji, Tamio; Yamakawa, Shunsuke; Hyodo, Shi-Aki

    2009-05-28

    First-principles molecular dynamics simulations have been carried out to investigate the nature of proton dynamics in Nafion, a representative polymer electrolyte membrane (PEM) widely used in PEM fuel cells. From the trajectories of the simulations, diffusion coefficients for the protonic defects were calculated to be 0.3 x 10(-5) cm(2) s(-1) and 7.1 x 10(-5) cm(2) s(-1) for lambda = 4.25 and 12.75, respectively, where lambda denotes hydration levels inside Nafion defined as a number of water molecules per sulfonic group. Our simulations show that proton hopping probability does not depend much on the water content inside Nafion. This finding indicates that the classical vehicular (or en masse) diffusion model, which has been employed to account for the slow diffusion process of protons in low water-content Nafion, is an oversimplification and does not correctly describe proton dynamics. Furthermore, it is found that difference in the value of the proton diffusion coefficient with respect to water content inside Nafion is related to the different character of proton hopping occurring in the water hydrogen bond network. When the water content is low, the proton hopping occurs in a manner that does not contribute constructively to proton mobility, while when the water content is high, it occurs in a manner which is beneficial to overall proton mobility. Such a different nature of proton hoppings arises mainly from the difference in the connectivity of water hydrogen bond network. Our results broadly support earlier simulation studies and provide the molecular level origin of properties arising from the proton dynamics in Nafion.

  10. Structural and mechanical properties of Al―Mg―B films: Experimental study and first-principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Ivashchenko, V.I.; Scrynskyy, P.L. [Frantsevych Institute for Problems of Material Science, NAS of Ukraine, 3, Krzhyzhanovsky Str., 03142 Kyiv (Ukraine); Dub, S.N. [Bakul Institute for Superhard Materials, NAS of Ukraine, 2, Avtozavodska Str., 04074 Kyiv (Ukraine); Butenko, O.O.; Kozak, A.O.; Sinelnichenko, O.K. [Frantsevych Institute for Problems of Material Science, NAS of Ukraine, 3, Krzhyzhanovsky Str., 03142 Kyiv (Ukraine)

    2016-01-29

    The Al―Mg―B films were deposited on silicon substrates by direct current magnetron sputtering from the AlMgB{sub 14} target at low discharge power and at substrate temperature ranging from 100 to 500 °C. The deposited films have been annealed at 1000 °C in vacuum, and characterized by X-ray diffraction, atomic force microscopy, Fourier transform infra-red spectroscopy, nano- and micro-indentation, and scratch testing. The films exhibit lower hardness than the bulk AlMgB{sub 14} material, which is due to their amorphous structure in which the strong intra-icosahedron B―B bonds are almost lacking and the weaker B―O bonds are predominant. After the annealing, a reduction of a number of B―O bonds and a formation of crystallites in the films lead to an increase in the nanohardness and elastic modulus. The as-deposited films exhibit a low coefficient of friction of 0.08–0.12. First-principles studies show that the icosahedra in amorphous AlMgB{sub 14}-based materials are not fully developed, which is the reason of their lower mechanical performance. - Highlights: • Al―Mg―B films were deposited at different substrate temperatures. • The as-deposited films were amorphous, whereas the annealed ones were nanostructured. • Mechanical properties were analyzed as functions of substrate and annealing temperatures. • Ab-initio MD simulations of AlMgB{sub 14}-based materials were carried out. • Both experimental and theoretical investigations enabled one to explain film properties.

  11. Engineering the work function of armchair graphene nanoribbons using strain and functional species: a first principles study.

    Science.gov (United States)

    Peng, Xihong; Tang, Fu; Copple, Andrew

    2012-02-22

    First principles density functional theory calculations were performed to study the effects of strain, edge passivation, and surface functional species on the structural and electronic properties of armchair graphene nanoribbons (AGNRs), with a particular focus on the work function. The work function was found to increase with uniaxial tensile strain and decrease with compression. The variation of the work function under strain is primarily due to the shift of the Fermi energy with strain. In addition, the relationship between the work function variation and the core level shift with strain is discussed. Distinct trends of the core level shift under tensile and compressive strain were discovered. For AGNRs with the edge carbon atoms passivated by oxygen, the work function is higher than for nanoribbons with the edge passivated by hydrogen under a moderate strain. The difference between the work functions in these two edge passivations is enlarged (reduced) under a sufficient tensile (compressive) strain. This has been correlated to a direct-indirect bandgap transition for tensile strains of about 4% and to a structural transformation for large compressive strains at about - 12%. Furthermore, the effect of the surface species decoration, such as H, F, or OH with different covering density, was investigated. It was found that the work function varies with the type and coverage of surface functional species. Decoration with F and OH increases the work function while H decreases it. The surface functional species were decorated on either one side or both sides of AGNRs. The difference in the work functions between one-sided and two-sided decorations was found to be relatively small, which may suggest an introduced surface dipole plays a minor role.

  12. Tunable electronic structures of germanium monochalcogenide nanosheets via light non-metallic atom functionalization: a first-principles study.

    Science.gov (United States)

    Ding, Yi; Wang, Yanli

    2016-08-17

    Germanium monochalcogenides, i.e. GeS and GeSe sheets, are isoelectronic analogues of phosphorene, which have been synthesized in recent experiments (P. Ramasamy et al., J. Mater. Chem. C, 2016, 4, 479). Utilizing first-principles calculations, we have investigated their tunable electronic and magnetic properties via light non-metallic atom (B, C, N, O, Si, P, S) functionalization. We find that on these GeS and GeSe sheets O and S adatoms prefer to locate at the top site above the Ge atom, while the other ones like to occupy the anion site, which push the original S/Se atom to the hollow site instead. O and S adatoms slightly affect the semiconducting behaviour of the doped systems, while B, C, N, Si, P ones will drastically modify their band structures and induce versatile spintronic properties. Through the supercell calculations, B and C adatoms are found to induce a bipolar semiconducting behaviour in the decorated systems, while the N/P adatom will cause a spin-gapless-semiconducting/nearly-half-metallic feature in them. The B/C/N/Si/P-substituted GeS/GeSe sheet can be formed by removing the hollow-site S/Se atom from the adatom-decorated structures, which exhibit an opposite semiconducting/metallic behaviour to their phosphorene counterparts. A general odd-even rule is proposed for this phenomenon, which shows that an odd (even) number of valence electron difference between the substitution and host atoms would cause a metallic (semiconducting) feature in the substituted systems. Our study demonstrates that atom functionalization is an efficient way to tailor the properties of GeS and GeSe nanosheets, which have adaptable electronic properties for potential applications in nanoelectronics and spintronics.

  13. Electronic structure and magnetism of Ge(Sn)TMXTe1-X (TM = V, Cr, Mn): A first principles study

    Science.gov (United States)

    Liu, Yong; Bose, S. K.; Kudrnovský, J.

    2016-12-01

    This work presents the results of first principles calculations of the electronic and magnetic properties of the compound SnTe and GeTe in zinc blende (ZB) and rock salt (RS) structures, doped with 3d transition metal V, Cr, and Mn. The present study, initiated from the viewpoint of potential application in spintronics, is motivated by our earlier work involving these two compounds, where the doping was limited to the Sn and Ge sublattices. In view of some discrepancies between our calculated results and the available experimental data, in this work we have examined the effect of the Te-sublattice doping. The case of Mn-doping, where the previous results of calculations seemed to differ most from the experimentally available data, is examined further by looking at the effect of Mn atoms partially occupying interstitial sites as well. From the standpoint of potential application in spintronics, we look for half-metallic (HM) states and tabulate their properties in both rock salt and zinc blende structures. ZB structure is found to be more conducive to HM state in general. Among the binary compounds we identify several HM candidates: VGe, VSn, MnGe, MnSn and MnTe at their equilibrium volumes and all in ZB structure. Estimates of the Curie temperature for the ferromagnetic compounds including the half-metals are presented. It is shown that despite the ferromagnetic (FM) nature of the Mn-Mn interaction for the Te-doped case, a simultaneous doping of both Ge(Sn)- and Te-sublattice with Mn atoms would leave the material predominantly antiferromagnetic (AFM).

  14. First-principles study of twin grain boundaries in epitaxial BaSi2 on Si(111)

    Science.gov (United States)

    Baba, Masakazu; Kohyama, Masanori; Suemasu, Takashi

    2016-08-01

    Epitaxial films of BaSi2 on Si(111) for solar cell applications possess three epitaxial variants and exhibit a minority carrier diffusion length (ca. 9.4 μm) much larger than the domain size (ca. 0.2 μm); thus, the domain boundaries (DBs) between the variants do not act as carrier recombination centers. In this work, transmission electron microscopy (TEM) was used to observe the atomic arrangements around the DBs in BaSi2 epitaxial films on Si(111), and the most stable atomic configuration was determined by first-principles calculations based on density functional theory to provide possible interface models. Bright-field TEM along the a-axis of BaSi2 revealed that each DB was a twin boundary between two different epitaxial variants, and that Ba(II) atoms form hexagons containing central Ba(I) atoms in both the bulk and DB regions. Four possible interface models containing Ba(I)-atom interface layers were constructed, each consistent with TEM observations and distinguished by the relationship between the Si tetrahedron arrays in the two domains adjacent across the interface. This study assessed the structural relaxation of initial interface models constructed from surface slabs terminated by Ba(I) atoms or from zigzag surface slabs terminated by Si tetrahedra and Ba(II) atoms. In these models, the interactions or relative positions between Si tetrahedra appear to dominate the relaxation behavior and DB energies. One of the four interface models whose relationship between first-neighboring Si tetrahedra across the interface was the same as that in the bulk was particularly stable, with a DB energy of 95 mJ/m2. There were no significant differences in the partial densities of states and band gaps between the bulk and DB regions, and it was therefore concluded that such DBs do not affect the minority carrier properties of BaSi2.

  15. First principles study for the key electronic, optical and nonlinear optical properties of novel donor-acceptor chalcones.

    Science.gov (United States)

    Muhammad, Shabbir; Al-Sehemi, Abdullah G; Su, Zhongmin; Xu, Hongliang; Irfan, Ahmad; Chaudhry, Aijaz Rasool

    2017-03-01

    Using first-principle methods, several key electronic, optical and nonlinear optical properties are calculated for two recently synthesized chalcone derivatives i.e. (2E)-3-(4-methylphenyl)-1-(3-nitrophenyl)prop-2-en-1-one (comp.1) and (2E)-3-[4-(dimethylamino)phenyl]-1-(3-nitrophenyl)prop-2-en-1-one (comp.2). The calculation of dipole moment, polarizability , anisotropy of polarizability as well as second hyperpolarizability (usually considered as a signature for two photon absorption phenomenon) are performed using density functional theory methods at PBE0/6-311G** level of theory. The linear average polarizability for comp.1 and comp.2 are found to be 32.15×10(-24) and 38.76×10(-24)esu, respectively. Similarly, the second hyperpolarizability amplitudes of comp.1 and comp.2 are found to be reasonably larger mounting to 79.31×10(-36) and 181.36×10(-36)esu, respectively. The importance of donor end is determined by comparing p-methylphenyl group of comp.1 with that of N,N-dimethylaniline group of comp.2 that results a remarkable increase in its amplitude, which is ∼2 times larger as compared with that of comp.1 owing to the stronger donor-acceptor configuration of comp.2. Interestingly, a comparison of average static third-order nonlinear polarizabilities shows that amplitudes of comp.1 and comp.2 are ∼13 times and ∼29 times larger than that of para-nitroaniline (a typical standard push-pull NLO-phore) at the same PBE0/6-311G** level of theory, which indicates a real time NLO application of our titled compounds. Time dependent density functional theory (TD-DFT) calculations along with frontier molecular orbitals, density of states (DOS), second hyperpolarizability density analysis and molecular electrostatic potential (MEP) diagrams are used to trace the origin of electro-optical as well as structure property relationships. Copyright © 2016 Elsevier Inc. All rights reserved.

  16. First-principles study of electronic structures and stability of body-centered cubic Ti-Mo alloys by special quasirandom structures.

    Science.gov (United States)

    Sahara, Ryoji; Emura, Satoshi; Ii, Seiichiro; Ueda, Shigenori; Tsuchiya, Koichi

    2014-06-01

    The electronic structures and structural properties of body-centered cubic Ti-Mo alloys were studied by first-principles calculations. The special quasirandom structures (SQS) model was adopted to emulate the solid solution state of the alloys. The valence band electronic structures of Ti-Mo and Ti-Mo-Fe alloys were measured by hard x-ray photoelectron spectroscopy. The structural parameters and valence band photoelectron spectra were calculated using first-principles calculations. The results obtained with the SQS models showed better agreement with the experimental results than those obtained using the conventional ordered structure models. This indicates that the SQS model is effective for predicting the various properties of solid solution alloys by means of first-principles calculations.

  17. First-principles study of the optical properties of MgxTi1-xH2

    NARCIS (Netherlands)

    van Setten, Michiel J.; Er, Suleyman; Brocks, Geert; de Groot, Robert A.; de Wijs, Gilles A.

    Thin films of MgxTi1-x show an optical black state upon hydrogenation. We calculate the dielectric function and the optical properties of MgxTi1-xH2, x=0.5, 0.75, and 0.875 using first-principles density-functional theory. We argue that the black state is an intrinsic property of these compounds,

  18. A systematic first principle method to study magnetic properties of FeMo, CoMo and NiMo

    CERN Document Server

    Bhattacharjee, A K; Halder, A; Mookerjee, A; Touheed, M

    2003-01-01

    We use the first principle TB-LMTO (Tight-Binding Linear Muffin Tin Orbital) method combined with the ASM (Augmented Space Method) to take care of disorder beyond the mean field (CPA - Cohetent Potential Approximation) approximation. We analyze binary alloys between magnetic transition metals Fe, Co, Ni and non-magnetic Mo to find out the effect of disorder on electronic structure and consequently magnetic properties of the alloys.

  19. First-principles study of the optical properties of MgxTi1-xH2

    NARCIS (Netherlands)

    van Setten, Michiel J.; Er, Suleyman; Brocks, Geert; de Groot, Robert A.; de Wijs, Gilles A.

    2009-01-01

    Thin films of MgxTi1-x show an optical black state upon hydrogenation. We calculate the dielectric function and the optical properties of MgxTi1-xH2, x=0.5, 0.75, and 0.875 using first-principles density-functional theory. We argue that the black state is an intrinsic property of these compounds, un

  20. Elastic, electronic and magnetic properties of new oxide perovskite BaVO3: a first-principles study

    OpenAIRE

    Bannikov, V. V.

    2014-01-01

    The structural, elastic, magnetic properties, as well as electronic structure and chemical bonding picture of new oxide 3d1-perovskite BaVO3, recently synthesized, were systematically investigated involving the first-principles FLAPW-GGA calculations. The obtained results are discussed in comparison with available experimental data, as well as with those obtained before for isostructural and isoelectronic SrVO3 perovskite.

  1. Surface alloy formation of noble adatoms adsorbed on Si(111)-{radical}3x{radical}3-Pb surface: a first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Li Chong; Wang Fei; Sun, Q; Jia Yu, E-mail: jiayu@zzu.edu.cn [Center for Clean Energy and Quantum Structures, and School of Physics and Engineering, Zhengzhou University, Zhengzhou 450052 (China)

    2011-07-06

    The geometric structures, stability and electronic properties of initial stages of surface alloy formation for noble atoms adsorbed on Si(111)-{radical}3x{radical}3-Pb surfaces have been comparatively and extensively studied by using first-principles calculations within density functional theory. Our results revealed that an Au trimer rather than a tetramer adsorption induces a surface alloy by combining with Pb atoms in covalent bonds, exhibiting semiconducting characteristics due to the localization of surface states. The stability of the two-dimensional (2D) surface alloy obeys the Hume-Rothery rule. The electronic structures of the 2D surface alloy are sensitive to the number of Au adatoms and can be modulated by the quantity of Au adatoms. Unlike the Au atoms, our further calculations indicated that adsorption of Ag or Cu atoms on the surface cannot form a surface alloy with Pb atoms in the surface layer due to a weaker interaction or smaller radius.

  2. Structural stability of scandium on nonpolar GaN (112{sup ¯}0) and (101{sup ¯}0) surfaces: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    González-Hernández, Rafael, E-mail: rhernandezj@uninorte.edu.co [Grupo de Investigación en Física Aplicada, Departamento de Física, Universidad del Norte, Barranquilla (Colombia); Martínez, Gustavo; López-Perez, William [Grupo de Investigación en Física Aplicada, Departamento de Física, Universidad del Norte, Barranquilla (Colombia); Rodriguez, Jairo Arbey [Grupo de Estudio de Materiales, Departamento de Física, Universidad Nacional de Colombia, Bogotá (Colombia)

    2014-01-01

    First-principles calculations based on density-functional theory have been implemented to study the scandium (Sc) adsorption and incorporation on nonpolar GaN (112{sup ¯}0) and (101{sup ¯}0) surfaces. It is found that Sc adatom prefers to reside at bridge positions, between the hollow and top sites, on both GaN nonpolar surfaces. In addition, calculating the relative surface energy of several Sc configurations, we constructed a phase diagram showing the energetically most stable surfaces as a function of the Ga chemical potentials. Based on these results, we have found that incorporation of Sc adatoms in the Ga-substitutional site is energetically more favorable compared with the adsorption on the top layers. This effect leads to the formation of ScN interlayers on nonpolar GaN (112{sup ¯}0) and (101{sup ¯}0) surfaces, which reduces the dislocation densities between GaN and ScN.

  3. First-Principles Study of Tetragonal BaTiO3 Subjected to Uniaxial Tensile Stress along the c Axis

    Institute of Scientific and Technical Information of China (English)

    WANG Chun-Mei; DUAN Yi-Feng; CHEN Chang-Qing

    2009-01-01

    Tetragonal Ba TiO3 under uniaxial tensile stress along the c axis is investigated from first principles. The structural parameters and polarization show a little abrupt change near a critical stress σc of 4.57 GPa, which is related to the uniaxial tensile stress induced change of elastic constants. We also find that the ferroelectric lattice distortion increases with the increasing stress. Moreover, it is found that uniaxial tensile stress can enhance the piezoelectric strain coefficients, which reach their maximum values at the stress σc.

  4. First-principles study on molecular dissociation under metallization pressure in aromatic monomolecular crystals with iodine atoms

    CERN Document Server

    Tateyama, Y

    2002-01-01

    We have examined the metallization mechanism and possibility of molecular dissociation in iodanil (IA) and hexa-iodobenzene (HIB) under pressure by using first-principles calculations. We found that the metallization in IA is caused by the band overlap in the molecular phase and dissociation does not follow the metallization. In HIB, on the other hand, the band overlap mechanism is found to be less probable, which implies that a structural transformation will occur before the metallization. Both mechanisms are completely different from that for I sub 2 diatomic molecular crystal, and suggest essential roles of C sub 6 rings and O atoms.

  5. First-principles study of electronic structure, optical and phonon properties of α-ZrW2O8

    Science.gov (United States)

    Li, Jinping; Meng, Songhe; Qin, Liyuan; Lu, Hantao

    2016-12-01

    ZrW2O8 exhibits isotropic negative thermal expansions over its entire temperature range of stability, yet so far its physical properties and mechanism have not been fully addressed. In this article, the electronic structure, elastic, thermal, optical and phonon properties of α-ZrW2O8 are systematically investigated from first principles. The agreements between the generalized gradient approximation (GGA) calculation and experiments are found to be quite satisfactory. The calculation results can be useful in relevant material designs, e.g., when ZrW2O8 is employed to adjust the thermal expansion coefficient of ceramic matrix composites.

  6. Investigation of structural stability and elastic properties of Zrh and Zrh{sub 2}: A first principles study

    Energy Technology Data Exchange (ETDEWEB)

    Kanagaprabha, S. [Department of Physics, Kamaraj College, Tuticorin, Tamil nadu-628003 (India); Rajeswarapalanichamy, R., E-mail: rrpalanichamy@gmail.com; Sudhapriyanga, G., E-mail: rrpalanichamy@gmail.com; Murugan, A., E-mail: rrpalanichamy@gmail.com; Santhosh, M., E-mail: rrpalanichamy@gmail.com [Department of Physics, N.M.S.S.V.N College, Madurai, Tamilnadu-625019 (India); Iyakutti, K. [Department of Physics and Nanotechnology, SRM University, Chennai, Tamilnadu-603203 (India)

    2014-04-24

    The electronic, structural and mechanical properties of ZrH and ZrH{sub 2} are investigated by means of first principles calculation based on density functional theory as implemented in VASP code with generalized gradient approximation. The calculated ground state properties are in good agreement with previous experimental and other theoretical results. Among the six crystallographic structures considered for ZrH, ZB phase is found to be the most stable phase, whereas ZrH{sub 2} is energetically stable in tetragonal structure at ambient condition. A structural phase transition from ZB→NaCl at a pressure 10 GPa is predicted for ZrH.

  7. First-principles DFT+\\emph{U} study of structural and electronic properties of PbCrO$_{3}$

    OpenAIRE

    Wang, Bao-Tian; Yin, Wen; Li, Wei-Dong; Wang, Fangwei

    2010-01-01

    We have performed a systematic first-principles investigation to calculate the structural, electronic, and magnetic properties of PbCrO$_{3}$, CrPbO$_{3}$ as well as their equiproportional combination. The local density approximation (LDA)$+U$ and the generalized gradient approximation$+U$ theoretical formalisms have been used to account for the strong on-site Coulomb repulsion among the localized Cr 3d electrons. By choosing the Hubbard \\emph{U} parameter around 4 eV, ferromagnetic, and/or a...

  8. Spin-split bands of metallic hydrogenated ZnO ( 10 1 ¯ 0 surface: First-principles study

    Directory of Open Access Journals (Sweden)

    Moh. Adhib Ulil Absor

    2016-02-01

    Full Text Available For spintronics applications, generation of significant spin transport is required, which is achieved by applying a semiconductor surface exhibiting metallic spin-split surface-state bands. We show that metallic spin-split surface-state bands are achieved on hydrogenated ZnO ( 10 1 ¯ 0 surface by using first-principles density-functional theory calculations. We find that these metallic surface-state bands with dominant Zn-s and p orbitals exhibit Rashba spin splitting with a strong anisotropic character. This finding makes spintronics devices using oxide electronics surface materials possible.

  9. Emergence of intrinsic half-metallicity in MoS2 nano-crystals : A first principles study

    Science.gov (United States)

    Mandal, S. C.; Chatterjee, S.; Taraphder, A.

    2017-05-01

    Using first principles density functional theory we investigate the electronic structure of MoS2 nano-crystals of diameter 1nm. Our calculations suggest that MoS2 nano-crystals are inherently half-metallic, the half-metallicity being robust with respect to the constitution as well as the morphology of the surface and also with respect to the length of the nano-crystal. Thus, MoS2 nano-crystals, may turn out to be very important for application in spintronics based solid state devices.

  10. First-Principles Study of Orthorhombic Perovskites MgSiO3 up to 120GPa and Its Geophysical Implications

    Institute of Scientific and Technical Information of China (English)

    DENG Li-Wei; ZHAO Ji-Jun; JI Guang-Fu; GONG Zi-Zheng; WEI Dong-Qing

    2006-01-01

    @@ High-pressure behaviour of orthorhombic MgSiO3 perovskite crystal is simulated by using the density functional theory and plane-wave pseudopotentials approach up to 120GPa pressure at zero temperature. The lattice constants and mass density of the MgSiO3 crystal as functions of pressure are computed, and the corresponding bulk modulus and bulk velocity are evaluated. Our theoretical results agree well with the high-pressure experimental data. A thermodynamic method is introduced to correct the temperature effect on the 0-K first-principles results of bulk wave velocity, bulk modulus and mass density in lower mantle P/T range. Taking into account the temperature corrections, the corrected mass density, bulk modulus and bulk wave velocity of MgSiO3-perovskite are estimated from the first-principles results to be 2%, 4%, and 1% lower than the preliminary reference Earth model (PREM) profile, respectively, supporting the possibility of a pure perovskite lower mantle model.

  11. First-principles study on the lattice stability of elemental Co, Rh, and Ir in the ⅧB group

    Institute of Scientific and Technical Information of China (English)

    TAO Huijin; YIN Jian; YIN Zhimin; ZHANG Chuangfu; LI Jie; HUANG Boyun

    2009-01-01

    Lattice constants, total energies, and densities of state of transition metals Co, Rh, and Ir in the VIIIB group with different crystalline structures were calculated via generalized gradient approximation (GGA) of the total energy plane wave pseudopotentiai method in first-principles. The lattice stabilities of Rh and Ir are △Gbcc-hcp △Gfcc-hcp 0, agreeing well with those of the projector augmented wave method in first-principles and the CALPHAD method in spite of elemental Co. Analyses of the electronic smlctures to lattice stability show that crystalline Rh and Ir with fcc structures have the obvious characteristic of a stable phase, agreeing with the results of total energy calculations. Analyses of atomic populations show that the transition rate of electrons from the s state to the p or d state for hop, fcc, and bcc crystals of Co and Rh increases with the elemental period number to form a stronger cohesion, a higher cohesive energy, or a more stable lattice between atoms in heavier metals.

  12. Theoretical study of optical characteristics of multilayer coatings ZnO/CdS/CdTe using first-principles calculations

    Science.gov (United States)

    Derkaoui, Z.; Kebbab, Z.; Miloua, R.; Benramdane, N.

    2009-08-01

    A new method for predicting optical characteristics of multilayer coatings based on calculated material properties is presented. This method combines the use of the full potential linear-augmented plane wave method (FP-LAPW) within the framework of the Density Functional Theory (DFT) and the optical matrix approach for modeling the multilayer assembly. The simulation process is applied to thin films of the II-VI semiconductors compounds. The optical constants of each thin film are determined by using the first principle calculations. Each layer is represented by the square Abeles matrix, including all necessary data in the calculation of the optical characteristics (as transmittance, reflectance and absorbance). The simulation of multilayer optical response includes the effect of thickness, light polarization and incident angle. The obtained results are helpful in the design of the multilayer systems with required properties.

  13. First-Principles Study of Substitution of Cu and Au for Ni in Ni3Sn2

    Science.gov (United States)

    Tian, Yali; Wu, Ping; Lu, Zhengxiong

    2016-09-01

    The effects of substitution of Cu and Au for Ni on the mechanical, thermodynamic and electronic properties of two different Ni3Sn2 structures are investigated by first-principles calculations. Cu atom at Ni2 site and Au atom at Ni1 site of the η phase lead to the thermodynamic stable structure. For the λ phase, Au atom can only replace the Ni1 site. Substitution causes the decrease of the polycrystalline elastic modulus and the Debye temperature. The degree of anisotropy along Z axis decreases dramatically for η phase, but it increases along Y axis for λ phase after substitution. The Ni3Sn2-based intermetallics are all ductile; the η phase is more ductile than the λ phase. The electronic density of states manifest an energy gap appearing in η phase and the effective mass of the η phase is lower than λ phase.

  14. First-principles studies of di-arsenic interstitial and its implications for arsenic-interstitial diffusion in crystalline silicon

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Yonghyun [Microelectronics Research Center, University of Texas at Austin, Austin, TX 78758 (United States); Kirichenko, Taras A. [Freescale Semiconductor Inc., 3501 Ed Bluestein Blvd., Austin, TX 78721 (United States); Kong, Ning [Microelectronics Research Center, University of Texas at Austin, Austin, TX 78758 (United States); Larson, Larry [SEMATECH, 2706 Montopolis Drive., Austin, TX 78741 (United States); Banerjee, Sanjay K. [Microelectronics Research Center, University of Texas at Austin, Austin, TX 78758 (United States)], E-mail: banerjee@ece.utexas.edu

    2007-12-15

    We propose new structural configurations and novel diffusion mechanisms for neutral di-arsenic interstitial (As{sub 2}I{sub 2}) in silicon with a first-principle density functional theory simulation within the generalized gradient approximation. With an assumption of excess silicon interstitials and high arsenic concentrations, neutral As{sub 2}I{sub 2} is expected to be favorable and mobile with low-migration barrier. Moreover, because the diffusion barrier of arsenic interstitial pairs (AsI) is very low (< 0.2 eV) under the same conditions, As{sub 2}I{sub 2} can be easily formed and likely intermediate stage of larger arsenic interstitial clusters.

  15. First-principles study on the magnetic and electronic properties of Al or P doped armchair silicene nanoribbons

    Science.gov (United States)

    Zhang, Xiaojiao; Zhang, Dan; Xie, Fang; Zheng, Xialian; Wang, Haiyan; Long, Mengqiu

    2017-07-01

    Using the first-principles calculations, we investigate the geometric structure, electronic and magnetic properties of armchair silicene nanoribbons (ASiNRs) doped with aluminum (Al) or phosphorus (P) atoms. Total energy analysis shows that both Al and P atoms are preferentially doping at the edge site of ASiNRs. And the magnetism can be found in both Al and P doped systems. For Al doped ASiNRs, we find that the magnetic moment and band gap are dependent on the ribbon width. While for P doped ASiNRs, the magnetic moment always keeps 1μB and is independent of the ribbon width, meanwhile the band gap oscillates with a period of three with the ribbon width increasing. Our results present a new avenue for band engineering of SiNRs and benefit for the designing of silicone-based nano-spin-devices in nanoelectronics.

  16. First-principles study for vacancy-induced magnetism in nonmagnetic ferroelectric BaTiO3.

    Science.gov (United States)

    Cao, D; Cai, M Q; Zheng, Yue; Hu, W Y

    2009-12-14

    The possibilities of vacancy-induced magnetism in perovskite BaTiO(3) are investigated by first-principles calculations. Calculated results show that both titanium and oxygen vacancies could induce magnetism, but the barium vacancy did not induce magnetism. New and interesting magnetic properties of half-metallic magnetism are found in BaTiO(3) induced by the Ti-vacancy. Based on the density of states and the spin charge density distribution of BaTiO(3), we discuss the different origins of magnetism induced by the partial spin-polarized O 2p states around Ti vacancies and the partially filled d-states Ti around the oxygen vacancies. The discrepancy between the magnetic moments in the cubic phase and the tetragonal phase is due to anisotropic spin polarization induced by structure distortions. Our calculations would enable exploring magneto-electric coupling in nonmagnetic ferroelectric oxides.

  17. Ca- and Sc-based ternary AlB2-like crystals: a first-principles study

    Science.gov (United States)

    Tsetseris, Leonidas

    2017-02-01

    The aluminum diboride (AlB2) crystal structure comprises intercalated metal atoms between honeycomb sheets. In addition to metal diborides, which represent the most common family of AlB2-like structures, many more materials are known to crystallize in this geometry. Here we use first-principles calculations to probe the structural and electronic properties of several such systems. Specifically, we investigate the stability of various polymorphs of CaAuAs, CaAuP, CaCuP, ScAuGe, ScAuSi, Ca2AgSi3 and Ca2AuGe3 and find lattice parameters in excellent agreement with available experimental data. The analysis of densities of states and band structure diagrams show that all materials are metallic. However, the details of band dispersion vary significantly, from typical metals such as CaAuP, to almost semi-metallic behaviour in CaCuP.

  18. Diverse anisotropy of phonon transport in two-dimensional IV-VI compounds: A first-principles study

    CERN Document Server

    Qin, Guangzhao; Fang, Wu-Zhang; Zhang, Li-Chuan; Yue, Sheng-Ying; Yan, Qing-Bo; Hu, Ming; Su, Gang

    2016-01-01

    New class two-dimensional (2D) materials beyond graphene, including layered and non-layered, and their heterostructures, are currently attracting increasing interest due to their promising applications in nanoelectronics, optoelectronics and clean energy, where thermal transport property is one of the fundamental physical parameters. In this paper, we systematically investigated the phonon transport properties of 2D orthorhombic IV-VI compounds of $GeS$, $GeSe$, $SnS$ and $SnSe$ by solving the Boltzmann transport equation (BTE) based on first-principles calculations. Despite the similar puckered (hinge-like) structure along the armchair direction as phosphorene, the four monolayer compounds possess diverse anisotropic properties in many aspects, such as group velocity, Young's modulus and lattice thermal conductivity ($\\kappa$), etc. Especially, the $\\kappa$ along the zigzag and armchair directions of monolayer $GeS$ shows the strongest anisotropy while monolayer $SnS$ and $SnSe$ shows an almost isotropy in p...

  19. Structural stability and mechanical property of Ni(111)-graphene-Ni(111) layered composite: A first-principles study

    Science.gov (United States)

    Rong, Ximing; Chen, Jun; Li, Jing-Tian; Zhuang, Jun; Ning, Xi-Jing

    2015-12-01

    A first-principles calculation of the structural stability and mechanical property of Ni(111)-graphene-Ni(111) layered composite was presented. Three different structural models were considered, and the most stable interfacial structure had been determined with top-fcc structure in both sides of graphene. Stretching calculations demonstrate that the tensile stress of the composite can reach twice of that of pure Ni in the ranges of 0-0.2 strain. The Young’s modulus in triaxial directions are 384 (x), 362 (y), and 303 (z) GPa for the Ni(111)-graphene-Ni(111) structure, and 212 (x), 251 (y), and 273 (z) GPa for pure single-crystal Ni(111).

  20. Site occupancy of transition elements in C15 NbCr2 laves phase: A first-principles study

    Directory of Open Access Journals (Sweden)

    Long Q.

    2017-01-01

    Full Text Available Using first-principles calculations, site occupancy behaviors of transition elements in C15 NbCr2 Laves phase are systematically investigated. Elements Y, Sc, Zr, Hf, Cd, Ta, Ti and Ag prefer to occupy the Nb site, and elements Zn, Pt, Re, Tc, Ir, V, Os, Rh, Ru, Ni, Co, Mn, Fe and Cu favor to occupy the Cr site; whereas elements Mo, W, Pd and Au have weak site preference for Cr or Nb site. The present calculations agree well with the available experimental and previously calculated results. It was found that the site occupancy behavior of transition elements in NbCr2 is mainly affected by the radii of transition elements. The present calculations also propose the correlation between the site preference energy and radii of transition elements.