Guidez, Emilie B; Gordon, Mark S
2015-03-12
The modeling of dispersion interactions in density functional theory (DFT) is commonly performed using an energy correction that involves empirically fitted parameters for all atom pairs of the system investigated. In this study, the first-principles-derived dispersion energy from the effective fragment potential (EFP) method is implemented for the density functional theory (DFT-D(EFP)) and Hartree-Fock (HF-D(EFP)) energies. Overall, DFT-D(EFP) performs similarly to the semiempirical DFT-D corrections for the test cases investigated in this work. HF-D(EFP) tends to underestimate binding energies and overestimate intermolecular equilibrium distances, relative to coupled cluster theory, most likely due to incomplete accounting for electron correlation. Overall, this first-principles dispersion correction yields results that are in good agreement with coupled-cluster calculations at a low computational cost.
Density functional studies: First principles and semiempirical calculations of clusters and surfaces
International Nuclear Information System (INIS)
Sinnott, S.B.
1993-01-01
In the research presented here, various theoretical electronic structure techniques are utilized to analyze widely different systems from silicon clusters to transition metal solids and surfaces. For the silicon clusters, first principles density functional methods are used to investigate Si N for N = 2-8. The goal is to understand the different types of bonding that can occur in such small clusters where the coordination of the atoms differs substantially from that of the stable bulk tetrahedral bonding. Such uncoordinated structures can provide a good test of more approximate theories that can be used eventually to model silicon surfaces, of obvious technological importance. For the transition metal systems, non-self-consistent electronic structure methods are used to provide an understanding of the driving force for surface relaxations. An in-depth analysis of the results is presented and the physical basis of surface relaxation within the theory is discussed. In addition, the limitations inherent in calculations of metal surface relaxation are addressed. Finally, in an effort to increase understanding of approximate methods, a novel non-self-consistent density functional electronic structure method is developed that is ∼1000 times faster computationally than more sophisticated methods. This new method is tested for a variety of systems including diatomics, mixed clusters, surfaces and bulk lattices. The strengths and weaknesses of the new theory are discussed in detail, leading to greater understanding of non-self-consistent density functional theories as a whole
First principles density functional theory study of Pb doped α-MnO2 catalytic materials
Song, Zilin; Yan, Zhiguo; Yang, Xiaojun; Bai, Hang; Duan, Yuhua; Yang, Bin; Leng, Li
2018-03-01
The impact of Pb in the tunnels of manganese oxide octahedral molecular sieves on chemical state of Mn species and lattice oxygen were investigated utilizing density functional theory calculations. The results show that the Pb dopant in the tunnels of OMS-2 could reduce the average valence states of Mn. The lower energy required for bulk oxygen defects formation in Pb-OMS-2 validates the activation of lattice oxygen by inclusion of tunnel dopant. The inclusion of Pb promotes the catalytic oxidation activity of OMS-2 by reducing the energy required for the surface lattice oxygen migration during the Mars - van Krevelen oxidation process.
Sun, Jianwei; Remsing, Richard C; Zhang, Yubo; Sun, Zhaoru; Ruzsinszky, Adrienn; Peng, Haowei; Yang, Zenghui; Paul, Arpita; Waghmare, Umesh; Wu, Xifan; Klein, Michael L; Perdew, John P
2016-09-01
One atom or molecule binds to another through various types of bond, the strengths of which range from several meV to several eV. Although some computational methods can provide accurate descriptions of all bond types, those methods are not efficient enough for many studies (for example, large systems, ab initio molecular dynamics and high-throughput searches for functional materials). Here, we show that the recently developed non-empirical strongly constrained and appropriately normed (SCAN) meta-generalized gradient approximation (meta-GGA) within the density functional theory framework predicts accurate geometries and energies of diversely bonded molecules and materials (including covalent, metallic, ionic, hydrogen and van der Waals bonds). This represents a significant improvement at comparable efficiency over its predecessors, the GGAs that currently dominate materials computation. Often, SCAN matches or improves on the accuracy of a computationally expensive hybrid functional, at almost-GGA cost. SCAN is therefore expected to have a broad impact on chemistry and materials science.
Institute of Scientific and Technical Information of China (English)
GAO Xue; ZHANG Yue; SHANG Jia-Xiang
2011-01-01
We choose a Si/Ge interface as a research object to investigate the infiuence of interface disorder on thermal boundary conductance. In the calculations, the diffuse mismatch model is used to study thermal boundary conductance between two non-metallic materials, while the phonon dispersion relationship is calculated by the first-principles density functional perturbation theory. The results show that interface disorder limits thermal transport. The increase of atomic spacing at the interface results in weakly coupled interfaces and a decrease in the thermal boundary conductance. This approach shows a simplistic method to investigate the relationship between microstructure and thermal conductivity.%We choose a Si/Ge interface as a research object to investigate the influence of interface disorder on thermal boundary conductance.In the calculations,the diffuse mismatch model is used to study thermal boundary conductance between two non-metallic materials,while the phonon dispersion relationship is calculated by the first-principles density functional perturbation theory.The results show that interface disorder limits thermal transport.The increase of atomic spacing at the interface results in weakly coupled interfaces and a decrease in the thermal boundary conductance.This approach shows a simplistic method to investigate the relationship between microstructure and thermal conductivity.It is well known that interfaces can play a dominant role in the overall thermal transport characteristics of structures whose length scale is less than the phonon mean free path.When heat flows across an interface between two different materials,there exists a temperature jump at the interface.Thermal boundary conductance (TBC),which describes the efficiency of heat flow at material interfaces,plays an importance role in the transport of thermal energy in nanometerscale devices,semiconductor superlattices,thin film multilayers and nanocrystalline materials.[1
International Nuclear Information System (INIS)
Anas, M. M.; Othman, A. P.; Gopir, G.
2014-01-01
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 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 xc ) of the electrons was treated by Local Density Approximation (LDA) functional and Perdew-Zunger (PZ) functional
International Nuclear Information System (INIS)
Zunger, A.; Cohen, M.L.
1978-01-01
We present a method for obtaining first-principles nonlocal atomic pseudopotentials in the density-functional formalism by direct inversion of the pseudopotential eigenvalue problem, where the pseudo-wave-functions are represented as a unitary rotation of the exact all-electron wave functions. The usual pseudopotential nonuniqueness of the orbitals is fixed by imposing the physically appealing constraints of maximum similarity to the all-electron wave functions and minimum radial kinetic energy. These potentials are shown to yield very accurate energy eigenvalues, total energy differences, and wave-function moments over a wide range of excited atomic configurations. We have calculated the potentials for 68 transition and nontransition elements of rows 1--5 in the Periodic Table. Their characteristic features, such as classical turning points and minimum potential radii, faithfully reflect the chemical regularities of the Periodic Table. The nonempirical nature of these potentials permits both an analysis of their dominant features in terms of the underlying interelectronic potentials and the systematic improvement of their predictions through inclusion of appropriate correlation terms. As these potentials accurately reproduce both energy eigenvalues and wave functions and can be readily fit to analytic forms with known asymptotic behavior, they can be used directly for studies of many structural and electronic properties of solids
Nakayama, Masanobu; Kotobuki, Masashi; Munakata, Hirokazu; Nogami, Masayuki; Kanamura, Kiyoshi
2012-07-28
The research and development of rechargeable all-ceramic lithium batteries are vital to realize their considerable advantages over existing commercial lithium ion batteries in terms of size, energy density, and safety. A key part of such effort is the development of solid-state electrolyte materials with high Li(+) conductivity and good electrochemical stability; lithium-containing oxides with a garnet-type structure are known to satisfy the requirements to achieve both features. Using first-principles density functional theory (DFT), we investigated the electrochemical stability of garnet-type Li(x)La(3)M(2)O(12) (M = Ti, Zr, Nb, Ta, Sb, Bi; x = 5 or 7) materials against Li metal. We found that the electrochemical stability of such materials depends on their composition and structure. The electrochemical stability against Li metal was improved when a cation M was chosen with a low effective nuclear charge, that is, with a high screening constant for an unoccupied orbital. In fact, both our computational and experimental results show that Li(7)La(3)Zr(2)O(12) and Li(5)La(3)Ta(2)O(12) are inert to Li metal. In addition, the linkage of MO(6) octahedra in the crystal structure affects the electrochemical stability. For example, perovskite-type La(1/3)TaO(3) was found, both experimentally and computationally, to react with Li metal owing to the corner-sharing MO(6) octahedral network of La(1/3)TaO(3), even though it has the same constituent elements as garnet-type Li(5)La(3)Ta(2)O(12) (which is inert to Li metal and features isolated TaO(6) octahedra).
Hu, Hang; Reven, Linda; Rey, Alejandro
2013-10-17
The structure and mechanical properties of gold nanorods and their interactions with alkenthiolate self-assembled monolayers have been determined using a novel first-principle density functional theory simulation approach. The multifaceted, 1-dimensional, octagonal nanorod has alternate Au100 and Au110 surfaces. The structural optimization of the gold nanorods was performed with a mixed basis: the outermost layer of gold atoms used double-ζ plus polarization (DZP), the layer below used double-ζ (DZ), and the inner layers used single-ζ (SZ). The final structure compares favorably with simulations using DZP for all atoms. Phonon dispersion calculations and ab initio molecular dynamics (AIMD) were used to establish the dynamic and thermal stability of the system. From the AIMD simulations it was found that the nanorod system will undergo significant surface reconstruction at 300 K. In addition, when subjected to mechanical stress in the axial direction, the nanorod responds as an orthotropic material, with uniform expansion along the radial direction. The Young's moduli are 207 kbar in the axial direction and 631 kbar in the radial direction. The binding of alkanethiolates, ranging from methanethiol to pentanethiol, caused formation of surface point defects on the Au110 surfaces. On the Au100 surfaces, the defects occurred in the inner layer, creating a small surface island. These defects make positive and negative concavities on the gold nanorod surface, which helps the ligand to achieve a more stable state. The simulation results narrowed significant knowledge gaps on the alkanethiolate adsorption process and on their mutual interactions on gold nanorods. The mechanical characterization offers a new dimension to understand the physical chemistry of these complex nanoparticles.
International Nuclear Information System (INIS)
Mohanta, S.K.; Mishra, S.N.; Srivastava, S.K.
2014-01-01
We present first principles calculations of electronic structure and magnetic properties of dilute transition metal (3d, 4d and 5d) impurities in a Gd host. The calculations have been performed within the density functional theory using the full potential linearized augmented plane wave technique and the GGA+U method. The spin and orbital contributions to the magnetic moment and the hyperfine fields have been computed. We find large magnetic moments for 3d (Ti–Co), 4d (Nb–Ru) and 5d (Ta–Os) impurities with magnitudes significantly different from the values estimated from earlier mean field calculation [J. Magn. Magn. Mater. 320 (2008) e446–e449]. The exchange interaction between the impurity and host Gd moments is found to be positive for early 3d elements (Sc–V) while in all other cases an anti-ferromagnetic coupling is observed. The trends for the magnetic moment and hyperfine field of d-impurities in Gd show qualitative difference with respect to their behavior in Fe, Co and Ni. The calculated total hyperfine field, in most cases, shows excellent agreement with the experimental results. A detailed analysis of the Fermi contact hyperfine field has been made, revealing striking differences for impurities having less or more than half filled d-shell. The impurity induced perturbations in host moments and the change in the global magnetization of the unit cell have also been computed. The variation within each of the d-series is found to correlate with the d–d hybridization strength between the impurity and host atoms. - Highlights: • Detailed study of transition metal impurities in ferromagnetic Gd has been carried out. • The trends in impurity magnetic moment are qualitatively different from Fe, Co and Ni. • The variation within each of the d-series is found to correlate with the d–d hybridization strength between the impurity and host atoms. • Experimental trend in a hyperfine field has been reproduced successfully
Kuisma, Mikael; Sakko, Arto; Rossi, Tuomas P.; Larsen, Ask H.; Enkovaara, Jussi; Lehtovaara, Lauri; Rantala, Tapio T.
2015-01-01
We observe using ab initio methods that localized surface plasmon resonances in icosahedral silver nanoparticles enter the asymptotic region already between diameters of 1 and 2 nm, converging close to the classical quasistatic limit around 3.4 eV. We base the observation on time-dependent density-functional theory simulations of the icosahedral silver clusters Ag$_{55}$ (1.06 nm), Ag$_{147}$ (1.60 nm), Ag$_{309}$ (2.14 nm), and Ag$_{561}$ (2.68 nm). The simulation method combines the adiabat...
First-principle study of nanostructures of functionalized graphene
Indian Academy of Sciences (India)
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 ...
Fernando L. Dri; Louis G. Jr. Hector; Robert J. Moon; Pablo D. Zavattieri
2013-01-01
In spite of the significant potential of cellulose nanocrystals as functional nanoparticles for numerous applications, a fundamental understanding of the mechanical properties of defect-free, crystalline cellulose is still lacking. In this paper, the elasticity matrix for cellulose IÃ with hydrogen bonding network A was calculated using ab initio...
Directory of Open Access Journals (Sweden)
Ala Aldin M. H. M. Darghouth
2015-12-01
Full Text Available Ionization potentials (IPs and electron affinities (EAs are important quantities input into most models for calculating the open-circuit voltage (Voc of organic solar cells. We assess the semi-empirical density-functional tight-binding (DFTB method with the third-order self-consistent charge (SCC correction and the 3ob parameter set (the third-order DFTB (DFTB3 organic and biochemistry parameter set against experiments (for smaller molecules and against first-principles GW (Green’s function, G, times the screened potential, W calculations (for larger molecules of interest in organic electronics for the calculation of IPs and EAs. Since GW calculations are relatively new for molecules of this size, we have also taken care to validate these calculations against experiments. As expected, DFTB is found to behave very much like density-functional theory (DFT, but with some loss of accuracy in predicting IPs and EAs. For small molecules, the best results were found with ΔSCF (Δ self-consistent field SCC-DFTB calculations for first IPs (good to ± 0.649 eV. When considering several IPs of the same molecule, it is convenient to use the negative of the orbital energies (which we refer to as Koopmans’ theorem (KT IPs as an indication of trends. Linear regression analysis shows that KT SCC-DFTB IPs are nearly as accurate as ΔSCF SCC-DFTB eigenvalues (± 0.852 eV for first IPs, but ± 0.706 eV for all of the IPs considered here for small molecules. For larger molecules, SCC-DFTB was also the ideal choice with IP/EA errors of ± 0.489/0.740 eV from ΔSCF calculations and of ± 0.326/0.458 eV from (KT orbital energies. Interestingly, the linear least squares fit for the KT IPs of the larger molecules also proves to have good predictive value for the lower energy KT IPs of smaller molecules, with significant deviations appearing only for IPs of 15–20 eV or larger. We believe that this quantitative analysis of errors in SCC-DFTB IPs and EAs may be of
Kim, Sunghee; Kim, Ki Chul; Lee, Seung Woo; Jang, Seung Soon
2016-07-27
Understanding the thermodynamic stability and redox properties of oxygen functional groups on graphene is critical to systematically design stable graphene-based positive electrode materials with high potential for lithium-ion battery applications. In this work, we study the thermodynamic and redox properties of graphene functionalized with carbonyl and hydroxyl groups, and the evolution of these properties with the number, types and distribution of functional groups by employing the density functional theory method. It is found that the redox potential of the functionalized graphene is sensitive to the types, number, and distribution of oxygen functional groups. First, the carbonyl group induces higher redox potential than the hydroxyl group. Second, more carbonyl groups would result in higher redox potential. Lastly, the locally concentrated distribution of the carbonyl group is more beneficial to have higher redox potential compared to the uniformly dispersed distribution. In contrast, the distribution of the hydroxyl group does not affect the redox potential significantly. Thermodynamic investigation demonstrates that the incorporation of carbonyl groups at the edge of graphene is a promising strategy for designing thermodynamically stable positive electrode materials with high redox potentials.
Sun, Qiang; Selloni, Annabella; Myers, T. H.; Doolittle, W. Alan
2006-11-01
Density functional theory calculations of oxygen adsorption and incorporation at the polar GaN(0001) and GaN(0001¯) surfaces have been carried out to explain the experimentally observed reduced oxygen concentration in GaN samples grown by molecular beam epitaxy in the presence of high energy (˜10keV) electron beam irradiation [Myers , J. Vac. Sci. Technol. B 18, 2295 (2000)]. Using a model in which the effect of the irradiation is to excite electrons from the valence to the conduction band, we find that both the energy cost of incorporating oxygen impurities in deeper layers and the oxygen adatom diffusion barriers are significantly reduced in the presence of the excitation. The latter effect leads to a higher probability for two O adatoms to recombine and desorb, and thus to a reduced oxygen concentration in the irradiated samples, consistent with experimental observations.
Hashemi, Zohreh; Rafiezadeh, Shohreh; Hafizi, Roohollah; Hashemifar, S. Javad; Akbarzadeh, Hadi
2018-04-01
Evolutionary algorithm is combined with full-potential ab initio calculations to investigate conformational space of (MoS2)n and (MoSe2)n (n = 1-10) nanoclusters and to identify the lowest energy structural isomers of these systems. It is argued that within both BLYP and PBE functionals, these nanoclusters favor sandwiched planar configurations, similar to their ideal planar sheets. The second order difference in total energy (Δ2 E) of the lowest energy isomers is computed to estimate the abundance of the clusters at different sizes and to determine the magic sizes of (MoS2)n and (MoSe2)n nanoclusters. In order to investigate the electronic properties of nanoclusters, their energy gap is calculated by several methods, including hybrid functionals (B3LYP and PBE0), GW approach, and Δ scf method. At the end, the vibrational modes of the lowest lying isomers are calculated by using the force constants method and the IR active modes of the systems are identified. The vibrational spectra are used to calculate the Helmholtz free energy of the systems and then to investigate abundance of the nanoclusters at finite temperatures.
Exact results and open questions in first principle functional RG
International Nuclear Information System (INIS)
Le Doussal, Pierre
2010-01-01
Some aspects of the functional RG (FRG) approach to pinned elastic manifolds (of internal dimension d) at finite temperature T > 0 are reviewed and reexamined in this much expanded version of Le Doussal (2006) . The particle limit d = 0 provides a test for the theory: there the FRG is equivalent to the decaying Burgers equation, with viscosity ν ∼ T-both being formally irrelevant. An outstanding question in FRG, i.e. how temperature regularizes the otherwise singular flow of T = 0 FRG, maps to the viscous layer regularization of inertial range Burgers turbulence (i.e. to the construction of the inviscid limit). Analogy between Kolmogorov scaling and FRG cumulant scaling is discussed. First, multi-loop FRG corrections are examined and the direct loop expansion at T > 0 is shown to fail already in d = 0, a hierarchy of ERG equations being then required (introduced in Balents and Le Doussal (2005) ). Next we prove that the FRG function R(u) and higher cumulants defined from the field theory can be obtained for any d from moments of a renormalized potential defined in an sliding harmonic well. This allows to measure the fixed point function R(u) in numerics and experiments. In d = 0 the beta function (of the inviscid limit) is obtained from first principles to four loop. For Sinai model (uncorrelated Burgers initial velocities) the ERG hierarchy can be solved and the exact function R(u) is obtained. Connections to exact solutions for the statistics of shocks in Burgers and to ballistic aggregation are detailed. A relation is established between the size distribution of shocks and the one for droplets. A droplet solution to the ERG functional hierarchy is found for any d, and the form of R(u) in the thermal boundary layer is related to droplet probabilities. These being known for the d = 0 Sinai model the function R(u) is obtained there at any T. Consistency of the ε=4-d expansion in one and two loop FRG is studied from first principles, and connected to shock and
Keswani, Bhavna C.; Saraf, Deepashri; Patil, S. I.; Kshirsagar, Anjali; James, A. R.; Kolekar, Y. D.; Ramana, C. V.
2018-05-01
We report on the combined experimental and theoretical simulation results of lead-free ferroelectrics, Ba(1-x)CaxTiO3 (x = 0.0-0.3) and BaTi(1-y)ZryO3 (y = 0.0-0.2), synthesized by standard solid state reaction method. First principles density functional calculations are used to investigate the electronic structure, dynamical charges, and spontaneous polarization of these compounds. In addition, the structural, ferroelectric, piezoelectric, and dielectric properties are studied using extensive experiments. The X-ray diffraction and temperature dependent Raman spectroscopy studies indicate that the calcium (Ca) substituted compositions exhibit a single phase crystal structure, while zirconium (Zr) substituted compositions are biphasic. The scanning electron micrographs reveal the uniform and highly dense microstructure. The presence of polarization-electric field and strain-electric field hysteresis loops confirms the ferroelectric and piezoelectric nature of all the compositions. Our results demonstrate higher values for polarization, percentage strain, piezoelectric coefficients, and electrostrictive coefficient compared to those existing in the literature. For smaller substitutions of Ca and Zr in BaTiO3, a direct piezoelectric coefficient (d33) is enhanced, while the highest d33 value (˜300 pC/N) is observed for BaTi0.96Zr0.04O3 due to the biphasic ferroelectric behavior. Calculation of Born effective charges indicates that doping with Ca or Zr increases the dynamical charges on Ti as well as on O and decreases the dynamical charge on Ba. An increase in the dynamical charges on Ti and O is ascribed to the increase in covalency of Ti-O bond that reduces the polarizability of the crystal. A broader range of temperatures is demonstrated to realize the stable phase in the Ca substituted compounds. The results indicate enhancement in the temperature range of applicability of these compounds for device applications. The combined theoretical and experimental study is
First-principle study of nanostructures of functionalized graphene
Indian Academy of Sciences (India)
2014-06-04
Jun 4, 2014 ... gen, the impact of electronegativity on band gap, binding energy and bond length is visible. It is ... Recent theoretical research has also focussed on .... density of states (figure 3 in [25]) are in close agreement with our results.
first principles derivation of a stress function for axially symmetric
African Journals Online (AJOL)
HOD
governing partial differential equations of linear isotropic elasticity were reduced to the solution of the biharmonic ... The stress function was then applied to solve the axially symmetric ..... [1] Borg S.K.: Fundamentals of Engineering Elasticity,.
Corrosion Thermodynamics of Magnesium and Alloys from First Principles as a Function of Solvation
Limmer, Krista; Williams, Kristen; Andzelm, Jan
Thermodynamics of corrosion processes occurring on magnesium surfaces, such as hydrogen evolution and water dissociation, have been examined with density functional theory (DFT) to evaluate the effect of impurities and dilute alloying additions. The modeling of corrosion thermodynamics requires examination of species in a variety of chemical and electronic states in order to accurately represent the complex electrochemical corrosion process. In this study, DFT calculations for magnesium corrosion thermodynamics were performed with two DFT codes (VASP and DMol3), with multiple exchange-correlation functionals for chemical accuracy, as well as with various levels of implicit and explicit solvation for surfaces and solvated ions. The accuracy of the first principles calculations has been validated against Pourbaix diagrams constructed from solid, gas and solvated charged ion calculations. For aqueous corrosion, it is shown that a well parameterized implicit solvent is capable of accurately representing all but the first coordinating layer of explicit water for charged ions.
Towards Rational Design of Functional Fluoride and Oxyfluoride Materials from First Principles
Charles, Nenian
Complex transition metal compounds (TMCs) research has produced functional materials with a range of properties, including ferroelectricity, colossal magnetoresistance, nonlinear optical activity and high-temperature superconductivity. Conventional routes to tune properties in transition metal oxides, for example, have relied primarily on cation chemical substitution and interfacial effects in thin film heterostructures. In heteroanionic TMCs, exhibiting two chemically distinct anions coordinating the same or different cations, engineering of the anion sub-lattice for property control is a promising alternative approach. The presence of multiple anions provides additional design variables, such as anion order, that are absent in homoanionic counterparts. The more complex structural and chemical phase space of heteroanionic materials provides a unique opportunity to realize enhanced or unanticipated electronic, optical, and magnetic responses. Although there is growing interest in heteroanionic materials, and synthetic and characterization advances are occurring for these materials, the crystal-chemistry principles for realizing structural and property control are only slowing emerging. This dissertation employs anion engineering to investigate phenomena in transition metal fluorides and oxyfluorides compounds using first principles density functional theory calculations. Oxyfluorides are particularly intriguing owing their tendency to stabilize highly ordered anion sublattices as well as the potential to combine the advantageous properties of transition metal oxides and fluorides. This work 1) addresses the challenges of studying fluorides and oxyfluorides using first principles calculations; 2) evaluates the feasibility of using external stimuli, such as epitaxial strain and hydrostatic pressure, to control properties of fluorides and oxyfluorides; and 3) formulates a computational workflow based on multiple levels of theory and computation to elucidate structure
Nguyen, Ngoc Linh; Borghi, Giovanni; Ferretti, Andrea; Marzari, Nicola
The determination of spectral properties of the DNA and RNA nucleobases from first principles can provide theoretical interpretation for experimental data, but requires complex electronic-structure formulations that fall outside the domain of applicability of common approaches such as density-functional theory. In this work, we show that Koopmans-compliant functionals, constructed to enforce piecewise linearity in energy functionals with respect to fractional occupation-i.e., with respect to charged excitations-can predict not only frontier ionization potentials and electron affinities of the nucleobases with accuracy comparable or superior with that of many-body perturbation theory and high-accuracy quantum chemistry methods, but also the molecular photoemission spectra are shown to be in excellent agreement with experimental ultraviolet photoemsision spectroscopy data. The results highlight the role of Koopmans-compliant functionals as accurate and inexpensive quasiparticle approximations to the spectral potential, which transform DFT into a novel dynamical formalism where electronic properties, and not only total energies, can be correctly accounted for.
International Nuclear Information System (INIS)
Kakehashi, Yoshiro; Chandra, Sumal
2016-01-01
We have developed a first-principles local ansatz wavefunction approach with momentum-dependent variational parameters on the basis of the tight-binding LDA+U Hamiltonian. The theory goes beyond the first-principles Gutzwiller approach and quantitatively describes correlated electron systems. Using the theory, we find that the momentum distribution function (MDF) bands of paramagnetic bcc Fe along high-symmetry lines show a large deviation from the Fermi–Dirac function for the d electrons with e g symmetry and yield the momentum-dependent mass enhancement factors. The calculated average mass enhancement m*/m = 1.65 is consistent with low-temperature specific heat data as well as recent angle-resolved photoemission spectroscopy (ARPES) data. (author)
Kakehashi, Yoshiro; Chandra, Sumal
2016-04-01
We have developed a first-principles local ansatz wavefunction approach with momentum-dependent variational parameters on the basis of the tight-binding LDA+U Hamiltonian. The theory goes beyond the first-principles Gutzwiller approach and quantitatively describes correlated electron systems. Using the theory, we find that the momentum distribution function (MDF) bands of paramagnetic bcc Fe along high-symmetry lines show a large deviation from the Fermi-Dirac function for the d electrons with eg symmetry and yield the momentum-dependent mass enhancement factors. The calculated average mass enhancement m*/m = 1.65 is consistent with low-temperature specific heat data as well as recent angle-resolved photoemission spectroscopy (ARPES) data.
Directory of Open Access Journals (Sweden)
Soleyman Majidi
Full Text Available In this work, we investigated the electronic and structural properties of various defects including single Sn and C vacancies, double vacancy of the Sn and C atoms, anti-sites, position exchange and the Stone–Wales (SW defects in SnC nanosheets by using density-functional theory (DFT. We found that various vacancy defects in the SnC monolayer can change the electronic and structural properties. Our results show that the SnC is an indirect band gap compound, with the band gap of 2.10 eV. The system turns into metal for both structure of the single Sn and C vacancies. However, for the double vacancy contained Sn and C atoms, the structure remains semiconductor with the direct band gap of 0.37 eV at the G point. We also found that for anti-site defects, the structure remains semiconductor and for the exchange defect, the structure becomes indirect semiconductor with the K-G point and the band gap of 0.74 eV. Finally, the structure of SW defect remains semiconductor with the direct band gap at K point with band gap of 0.54 eV. Keywords: SnC nanosheets, Density-functional theory, First-principles calculations, Electronic density of states, Band gap
Hu, S. X.; Gao, R.; Ding, Y.; Collins, L. A.; Kress, J. D.
2017-04-01
Using density-functional theory-based molecular-dynamics simulations, we have investigated the equation of state for silicon in a wide range of plasma density and temperature conditions of ρ =0.001 -500 g /c m3 and T =2000 -108K . With these calculations, we have established a first-principles equation-of-state (FPEOS) table of silicon for high-energy-density (HED) plasma simulations. When compared with the widely used SESAME-EOS model (Table 3810), we find that the FPEOS-predicted Hugoniot is ˜20% softer; for off-Hugoniot plasma conditions, the pressure and internal energy in FPEOS are lower than those of SESAME EOS for temperatures above T ≈ 1-10 eV (depending on density), while the former becomes higher in the low-T regime. The pressure difference between FPEOS and SESAME 3810 can reach to ˜50%, especially in the warm-dense-matter regime. Implementing the FPEOS table of silicon into our hydrocodes, we have studied its effects on Si-target implosions. When compared with the one-dimensional radiation-hydrodynamics simulation using the SESAME 3810 EOS model, the FPEOS simulation showed that (1) the shock speed in silicon is ˜10% slower; (2) the peak density of an in-flight Si shell during implosion is ˜20% higher than the SESAME 3810 simulation; (3) the maximum density reached in the FPEOS simulation is ˜40% higher at the peak compression; and (4) the final areal density and neutron yield are, respectively, ˜30% and ˜70% higher predicted by FPEOS versus the traditional simulation using SESAME 3810. All of these features can be attributed to the larger compressibility of silicon predicted by FPEOS. These results indicate that an accurate EOS table, like the FPEOS presented here, could be essential for the precise design of targets for HED experiments.
International Nuclear Information System (INIS)
Yang, J.Y.; Liu, L.H.; Tan, J.Y.
2014-01-01
The study of temperature dependence of thermophysical parameter dielectric function is key to understanding thermal radiative transfer in high-temperature environments. Limited by self-radiation and thermal oxidation, however, it is difficult to directly measure the high-temperature dielectric function of solids with present experimental technologies. In this work, we implement two first-principles methods, the ab initio molecular dynamics (AIMD) and density functional perturbation theory (DFPT), to study the temperature dependence of dielectric function of germanium (Ge) in the UV–vis spectral range in order to provide data of high-temperature dielectric function for radiative transfer study in high-temperature environments. Both the two methods successfully predict the temperature dependence of dielectric function of Ge. Moreover, the good agreement between the calculated results of the AIMD approach and experimental data at 825 K enables us to predict the high-temperature dielectric function of Ge with the AIMD method in the UV–vis spectral range. - Highlights: • The temperature dependence of dielectric function of germanium (Ge) is investigated with two first-principles methods. • The temperature effect on dielectric function of Ge is discussed. • The high-temperature dielectric function of Ge is predicted
First principles calculations using density matrix divide-and-conquer within the SIESTA methodology
International Nuclear Information System (INIS)
Cankurtaran, B O; Gale, J D; Ford, M J
2008-01-01
The density matrix divide-and-conquer technique for the solution of Kohn-Sham density functional theory has been implemented within the framework of the SIESTA methodology. Implementation details are provided where the focus is on the scaling of the computation time and memory use, in both serial and parallel versions. We demonstrate the linear-scaling capabilities of the technique by providing ground state calculations of moderately large insulating, semiconducting and (near-) metallic systems. This linear-scaling technique has made it feasible to calculate the ground state properties of quantum systems consisting of tens of thousands of atoms with relatively modest computing resources. A comparison with the existing order-N functional minimization (Kim-Mauri-Galli) method is made between the insulating and semiconducting systems
International Nuclear Information System (INIS)
Peng Xihong; Tang Fu; Copple, Andrew
2012-01-01
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. (paper)
First-principles X-ray absorption dose calculation for time-dependent mass and optical density.
Berejnov, Viatcheslav; Rubinstein, Boris; Melo, Lis G A; Hitchcock, Adam P
2018-05-01
A dose integral of time-dependent X-ray absorption under conditions of variable photon energy and changing sample mass is derived from first principles starting with the Beer-Lambert (BL) absorption model. For a given photon energy the BL dose integral D(e, t) reduces to the product of an effective time integral T(t) and a dose rate R(e). Two approximations of the time-dependent optical density, i.e. exponential A(t) = c + aexp(-bt) for first-order kinetics and hyperbolic A(t) = c + a/(b + t) for second-order kinetics, were considered for BL dose evaluation. For both models three methods of evaluating the effective time integral are considered: analytical integration, approximation by a function, and calculation of the asymptotic behaviour at large times. Data for poly(methyl methacrylate) and perfluorosulfonic acid polymers measured by scanning transmission soft X-ray microscopy were used to test the BL dose calculation. It was found that a previous method to calculate time-dependent dose underestimates the dose in mass loss situations, depending on the applied exposure time. All these methods here show that the BL dose is proportional to the exposure time D(e, t) ≃ K(e)t.
International Nuclear Information System (INIS)
Umari, P; Pasquarello, Alfredo
2003-01-01
The HH and HV Raman spectra of vitreous silica are calculated from first principles for a model structure consisting of a disordered network of corner-sharing tetrahedra, for which the vibrational properties were obtained previously. We analyse the contribution of specific atomic motions to the Raman spectra and perform a detailed comparison with respect to the vibrational density of states. We find that the HV spectrum closely resembles the vibrational density of states. By comparison, the HH spectrum shows significant differences and arises almost exclusively from oxygen vibrations
Energy Technology Data Exchange (ETDEWEB)
Umari, P; Pasquarello, Alfredo [Institut de Theorie des Phenomenes Physiques (ITP), Ecole Polytechnique Federale de Lausanne (EPFL), CH-1015 Lausanne (Switzerland); Institut Romand de Recherche Numerique en Physique des Materiaux (IRRMA), CH-1015 Lausanne (Switzerland)
2003-04-30
The HH and HV Raman spectra of vitreous silica are calculated from first principles for a model structure consisting of a disordered network of corner-sharing tetrahedra, for which the vibrational properties were obtained previously. We analyse the contribution of specific atomic motions to the Raman spectra and perform a detailed comparison with respect to the vibrational density of states. We find that the HV spectrum closely resembles the vibrational density of states. By comparison, the HH spectrum shows significant differences and arises almost exclusively from oxygen vibrations.
First-principles electronic functionalization of silicene and germanene by adatom chemisorption
Energy Technology Data Exchange (ETDEWEB)
Broek, B. van den; Houssa, M.; Scalise, E. [Semiconductor Physics Laboratory, Department of Physics and Astronomy, University of Leuven, Celestijnenlaan 200 D, B-3001 Leuven (Belgium); Pourtois, G. [IMEC, 75 Kapeldreef, B-3001 Leuven (Belgium); Department of Chemistry, Plasmant Research Group, University of Antwerp, B-2610 Wilrijk-Antwerp (Belgium); Afanas‘ev, V.V.; Stesmans, A. [Semiconductor Physics Laboratory, Department of Physics and Astronomy, University of Leuven, Celestijnenlaan 200 D, B-3001 Leuven (Belgium)
2014-02-01
This study presents first-principles results on the electronic functionalization of silicene and germanene monolayers by means of chemisorption of adatom species H, Li, F, Sc, Ti, V. Three general adatom-monolayer configurations are considered, each having its distinct effect on the electronic structure, yielding metallic or semiconducting dispersions depending on the adatom species and configuration. The induced bandgap is a (in)direct Γ gap ranging from 0.2 to 2.3 eV for both silicene and germanene. In general the alternating configuration was found to be the most energetically stable. The boatlike and chairlike conformers are degenerate with the former having anisotropic effective carrier masses. The top configuration leads to the planar monolayer and predominately to a gapped dispersion. The hollow configuration with V adatoms retains the Dirac cone, but with strong orbital planar hybridization at the Fermi level. We also observe a planar surface state the Fermi level for the latter systems.
Sadasivam, Sridhar; Ye, Ning; Feser, Joseph P.; Charles, James; Miao, Kai; Kubis, Tillmann; Fisher, Timothy S.
2017-02-01
Heat transfer across metal-semiconductor interfaces involves multiple fundamental transport mechanisms such as elastic and inelastic phonon scattering, and electron-phonon coupling within the metal and across the interface. The relative contributions of these different transport mechanisms to the interface conductance remains unclear in the current literature. In this work, we use a combination of first-principles calculations under the density functional theory framework and heat transport simulations using the atomistic Green's function (AGF) method to quantitatively predict the contribution of the different scattering mechanisms to the thermal interface conductance of epitaxial CoSi2-Si interfaces. An important development in the present work is the direct computation of interfacial bonding from density functional perturbation theory (DFPT) and hence the avoidance of commonly used "mixing rules" to obtain the cross-interface force constants from bulk material force constants. Another important algorithmic development is the integration of the recursive Green's function (RGF) method with Büttiker probe scattering that enables computationally efficient simulations of inelastic phonon scattering and its contribution to the thermal interface conductance. First-principles calculations of electron-phonon coupling reveal that cross-interface energy transfer between metal electrons and atomic vibrations in the semiconductor is mediated by delocalized acoustic phonon modes that extend on both sides of the interface, and phonon modes that are localized inside the semiconductor region of the interface exhibit negligible coupling with electrons in the metal. We also provide a direct comparison between simulation predictions and experimental measurements of thermal interface conductance of epitaxial CoSi2-Si interfaces using the time-domain thermoreflectance technique. Importantly, the experimental results, performed across a wide temperature range, only agree well with
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).
International Nuclear Information System (INIS)
Shao, Xiji; Li, Detian; Cai, Jianqiu; Luo, Haijun; Dong, Changkun
2016-01-01
Graphical abstract: - Highlights: • Substitutional nitrogen atom doping in capped (5, 5) SWNT is investigated. • Serious defects appear from breaks of C−N bonds with N contents of above 23.3 at.%. • Work function drops after N doping and may reach 4.1 eV. - Abstract: The structural and electronic properties of the capped (5, 5) single-walled carbon nanotube (SWNT), including the structural stability, the work function, and the charge transfer performance, are investigated for the substitutional nitrogen atom doping under different concentrations by first-principles density functional theory. The geometrical structure keeps almost intact with single or two N atom doping, while C−N bonds may break up with serious defects for N concentrations of 23.3 at.% and above. The SWNT remains metallic and the work function drops after doping due to the upward shift of Fermi level, leading to the increase of the electrical conductivity. N doping enhances the oxygen reduction activity stronger than N adsorption because of higher charge transfers.
Surface structure and properties of functionalized nanodiamonds: a first-principles study
International Nuclear Information System (INIS)
Datta, Aditi; Kirca, Mesut; Fu Yao; To, Albert C
2011-01-01
The goal of this work is to gain fundamental understanding of the surface and internal structure of functionalized detonation nanodiamonds (NDs) using quantum mechanics based density functional theory (DFT) calculations. The unique structure of ND assists in the binding of different functional groups to its surface which in turn facilitates binding with drug molecules. The ability to comprehensively model the surface properties, as well as drug-ND interactions during functionalization, is a challenge and is the problem of our interest. First, the structure of NDs of technologically relevant size (∼5 nm) was optimized using classical mechanics based molecular mechanics simulations. Quantum mechanics based density functional theory (DFT) was then employed to analyse the properties of smaller relevant parts of the optimized cluster further to address the effect of functionalization on the stability of the cluster and reactivity at its surface. It is found that functionalization is preferred over reconstruction at the (100) surface and promotes graphitization in the (111) surface for NDs functionalized with the carbonyl oxygen (C = O) group. It is also seen that the edges of ND are the preferred sites for functionalization with the carboxyl group (-COOH) vis-a-vis the corners of ND.
Surface structure and properties of functionalized nanodiamonds: a first-principles study
Energy Technology Data Exchange (ETDEWEB)
Datta, Aditi; Kirca, Mesut; Fu Yao; To, Albert C, E-mail: albertto@pitt.edu [Department of Mechanical Engineering and Materials Science and Department of Civil and Environmental Engineering, University of Pittsburgh, Pittsburgh, PA 15261 (United States)
2011-02-11
The goal of this work is to gain fundamental understanding of the surface and internal structure of functionalized detonation nanodiamonds (NDs) using quantum mechanics based density functional theory (DFT) calculations. The unique structure of ND assists in the binding of different functional groups to its surface which in turn facilitates binding with drug molecules. The ability to comprehensively model the surface properties, as well as drug-ND interactions during functionalization, is a challenge and is the problem of our interest. First, the structure of NDs of technologically relevant size ({approx}5 nm) was optimized using classical mechanics based molecular mechanics simulations. Quantum mechanics based density functional theory (DFT) was then employed to analyse the properties of smaller relevant parts of the optimized cluster further to address the effect of functionalization on the stability of the cluster and reactivity at its surface. It is found that functionalization is preferred over reconstruction at the (100) surface and promotes graphitization in the (111) surface for NDs functionalized with the carbonyl oxygen (C = O) group. It is also seen that the edges of ND are the preferred sites for functionalization with the carboxyl group (-COOH) vis-a-vis the corners of ND.
Zheng, Bing; Yu, Hai-tao; Xie, Ying; Lian, Yong-fu
2014-11-26
First-principles density functional theory calculations were performed to study the effect of Li adsorption on the structural and electronic properties, particularly the work function, of boron α-sheet. The calculated binding energies indicated that boron α-sheet could be well stabilized by the adsorption of Li atoms. Furthermore, the work functions of Li-adsorbed boron α-sheets were observed to decrease drastically with increasing Li coverage. The work functions are lower than that of Mg and even, for some of them, lower than that of Ca, indicating a considerable potential application of Li-adsorbed boron α-sheets as field-emission and electrode materials. Based on the calculated geometric and electronic structures, we discuss in details some possible aspects affecting the work function. The Li coverage dependence of the work functions of Li-adsorbed boron α-sheets was further confirmed by electrostatic potential analyses. The relationship between the work function variation and the Fermi and vacuum energy level shifts was also discussed, and we observed that the variation of the work function is primarily associated with the shift of the Fermi energy level. It is the surface dipole formed by the interaction between adatoms and substrate that should be responsible for the observed variation of the work function, whereas the increasing negative charge and rumpling for boron α-sheet only play minor roles. Additionally, the effect of Li adatoms on the work function of boron α-sheet was confirmed to be much stronger than that of graphene or a graphene double layer.
Hunton, D.; Pilinski, M.; Crowley, G.; Azeem, I.; Fuller-Rowell, T. J.; Matsuo, T.; Fedrizzi, M.; Solomon, S. C.; Qian, L.; Thayer, J. P.; Codrescu, M.
2014-12-01
Much as aircraft are affected by the prevailing winds and weather conditions in which they fly, satellites are affected by variability in the density and motion of the near earth space environment. Drastic changes in the neutral density of the thermosphere, caused by geomagnetic storms or other phenomena, result in perturbations of satellite motions through drag on the satellite surfaces. This can lead to difficulties in locating important satellites, temporarily losing track of satellites, and errors when predicting collisions in space. As the population of satellites in Earth orbit grows, higher space-weather prediction accuracy is required for critical missions, such as accurate catalog maintenance, collision avoidance for manned and unmanned space flight, reentry prediction, satellite lifetime prediction, defining on-board fuel requirements, and satellite attitude dynamics. We describe ongoing work to build a comprehensive nowcast and forecast system for neutral density, winds, temperature, composition, and satellite drag. This modeling tool will be called the Atmospheric Density Assimilation Model (ADAM). It will be based on three state-of-the-art coupled models of the thermosphere-ionosphere running in real-time, using assimilative techniques to produce a thermospheric nowcast. It will also produce, in realtime, 72-hour predictions of the global thermosphere-ionosphere system using the nowcast as the initial condition. We will review the requirements for the ADAM system, the underlying full-physics models, the plethora of input options available to drive the models, a feasibility study showing the performance of first-principles models as it pertains to satellite-drag operational needs, and review challenges in designing an assimilative space-weather prediction model. The performance of the ensemble assimilative model is expected to exceed the performance of current empirical and assimilative density models.
First-Principles Studies of Functionalized Si(111) in Air and in Water
Li, Yan; Galli, Giulia
2011-03-01
We have investigated structural, electronic and vibrational properties of hydrogen and methyl-terminated Si(111) surfaces both in air and in contact with water, by combining density functional theory and many-body perturbation theory within the GW approximations. The computed surface dipole moments for both H-Si(111) and CH3-Si(111) surfaces were found to be consistent with measured electron affinities (EAs), and can be explain by simple electronegative trends. While GW self-energy corrections greatly improve the absolute values of EAs, the EA difference of the two surfaces remains overestimated by about 0.3 eV. The variations in CH3 frequencies, e.g. the umbrella mode and CH stretching mode, for the surface in air and water are also well reproduced by our calculations. The influence exerted by the adsorption of water molecules on the hydrophobic H-Si(111) and CH3-(111) surfaces, in particular, on the EAs and the surface vibrational frequencies will be discussed and compared with recent experiments. This work was funded by NSF under Grant No. CHE-0802907.
First principles calculations for liquids and solids using maximally localized Wannier functions
Swartz, Charles W., VI
The field of condensed matter computational physics has seen an explosion of applicability over the last 50+ years. Since the very first calculations with ENIAC and MANIAC the field has continued to pushed the boundaries of what is possible; from the first large-scale molecular dynamics simulation, to the implementation of Density Functional Theory and large scale Car-Parrinello molecular dynamics, to million-core turbulence calculations by Standford. These milestones represent not only technological advances but theoretical breakthroughs and algorithmic improvements as well. The work in this thesis was completed in the hopes of furthering such advancement, even by a small fraction. Here we will focus mainly on the calculation of electronic and structural properties of solids and liquids, where we shall implement a wide range of novel approaches that are both computational efficient and physically enlightening. To this end we routinely will work with maximally localized Wannier functions (MLWFs) which have recently seen a revival in mainstream scientific literature. MLWFs present us with interesting opportunity to calculate a localized orbital within the planewave formalism of atomistic simulations. Such a localization will prove to be invaluable in the construction of layer-based superlattice models, linear scaling hybrid functional schemes and model quasiparticle calculations. In the first application of MLWF we will look at modeling functional piezoelectricity in superlattices. Based on the locality principle of insulating superlattices, we apply the method of Wu et al to the piezoelectric strains of individual layers under iifixed displacement field. For a superlattice of arbitrary stacking sequence an accurate model is acquired for predicting piezoelectricity. By applying the model in the superlattices where ferroelectric and antiferrodistortive modes are in competition, functional piezoelectricity can be achieved. A strong nonlinear effect is observed and can
Directory of Open Access Journals (Sweden)
Shenoy Vivek
2011-01-01
Full Text Available Abstract The magnetic properties of metal-functionalized graphitic carbon nitride nanotubes were investigated based on first-principles calculations. The graphitic carbon nitride nanotube can be either ferromagnetic or antiferromagnetic by functionalizing with different metal atoms. The W- and Ti-functionalized nanotubes are ferromagnetic, which are attributed to carrier-mediated interactions because of the coupling between the spin-polarized d and p electrons and the formation of the impurity bands close to the band edges. However, Cr-, Mn-, Co-, and Ni-functionalized nanotubes are antiferromagnetic because of the anti-alignment of the magnetic moments between neighboring metal atoms. The functionalized nanotubes may be used in spintronics and hydrogen storage.
Jaiswal, Neeraj K.; Kumar, Amit; Patel, Chandrabhan
2018-05-01
Tailoring the electronic band gap of graphene nanoribbons (GNR) through edge functionalization and understanding the adsorption of guest adatoms on GNR is crucial for realization of upcoming organic devices. In the present work, we have investigated the structural stability and electronic property of bromine (Br) termination at the edges of zigzag GNR (ZGNR). The migration pathways of Br adatom on ZGNR have also been discussed along four different diffusion paths. It is revealed that Br termination induces metallicity in ZGNR and caused upward shifting of Fermi level. Further, the migration is predicted to take place preferable along the ribbon edges whereas across the ribbon width, migration is least probable to take place due to sufficiently higher migration barrier of ˜160 meV.
International Nuclear Information System (INIS)
Kumar, Mukesh; Persson, Clas
2013-01-01
Ternary delafossite compounds are potential materials for optoelectronic devices. Employing a first-principles method, we calculate the structural, electronic, and optical properties of the silver based compounds AgMO 2 (M=Al, Ga or In), which crystallize in delafossite structure. Our calculations show that these AgMO 2 oxides have indirect band gaps and the gap energies are in the region of 1.6–3.0 eV whereas, the lowest direct band gap energies are estimated in the range of 2.6–4.3 eV. Furthermore, we find that AgMO 2 compounds exhibit a strong anisotropy for the dielectric function and absorption spectra. The absorption onset for these compounds occurs well above the band gap energies. Overall, we show that the hybrid functional improves the lattice parameters and band gap energies and the calculated values are in good agreement with the experimental values
First-principles study of SnS electronic properties using LDA, PBE and HSE06 functionals
Ibragimova, R.; Ganchenkova, M.; Karazhanov, S.; Marstein, E. S.
2018-03-01
Recently, tin sulphide (SnS) has emerged as a promising alternative to conventional CIGS and CZTC for use in solar cells, possessing such properties as non-toxicity, low cost and production stability. SnS has a high theoretically predicted efficiency above 20%, but the experimentally achieved efficiency so far is as low as 4.36%. The reason for the low achieved efficiency is unclear. One of the powerful tools to get deeper insights about the nature of the problem is first-principles calculation approaches. That is why SnS has become an attractive subject for first-principles calculations recently. Previously calculated data, however, show a widespread of such fundamental value as the bandgap varying from 0.26 to 1.26 eV. In order to understand a reason for that, in this work, we concentrate on a systematic study of calculation parameters effects on the resulting electronic structure, with the particular attention paid to the influence of the exchange-correlation functional chosen for calculations. Several exchange-correlation functionals (LDA, PBE and HSE06) were considered. The systematic analysis has shown that the bandgap variation can result from a tensile/compressive hydrostatic pressure introduced by non-equilibrium lattice parameters used for the calculations. The study of the applicability of three functionals has shown that HSE06 gives the best match to both experimentally obtained bandgap and the XPS valence band spectra. LDA underestimates the bandgap but qualitatively reproduces experimentally measured valence DOS similar to that of HSE06 in contrast to PBE. PBE underestimates the bandgap and does not match to the measured XPS spectra.
DEFF Research Database (Denmark)
Palsgaard, Mattias Lau Nøhr; Crovetto, Andrea; Gunst, Tue
2016-01-01
In this paper we present a method to obtain the band offset of semiconductor heterointerfaces from Density Functional Theory together with the nonequilibrium Green's function method. Band alignment and detailed properties of the interface between Cu2ZnSnSe4 and CdS are extracted directly from first...... principles simulations. The interface is important for photovoltaics applications where in particular the band offsets are important for efficiency. The band bending pose a problem for accurate atomistic simulations of band offsets due to its long range. Here we investigate two different methods for dealing...... with band bending directly. One involves doping the materials to induce a shorter screening length. The other method is to apply a voltage bias across the interface to correct for the band bending. The calculated band offsets agree well with previous experimental and theoretical studies and, interestingly...
Kakehashi, Yoshiro; Chandra, Sumal
2017-03-01
The momentum distribution function (MDF) bands of iron-group transition metals from Sc to Cu have been investigated on the basis of the first-principles momentum dependent local ansatz wavefunction method. It is found that the MDF for d electrons show a strong momentum dependence and a large deviation from the Fermi-Dirac distribution function along high-symmetry lines of the first Brillouin zone, while the sp electrons behave as independent electrons. In particular, the deviation in bcc Fe (fcc Ni) is shown to be enhanced by the narrow eg (t2g) bands with flat dispersion in the vicinity of the Fermi level. Mass enhancement factors (MEF) calculated from the jump on the Fermi surface are also shown to be momentum dependent. Large mass enhancements of Mn and Fe are found to be caused by spin fluctuations due to d electrons, while that for Ni is mainly caused by charge fluctuations. Calculated MEF are consistent with electronic specific heat data as well as recent angle resolved photoemission spectroscopy data.
Wagle, Fabian; Steinle-Neumann, Gerd; de Koker, Nico
2018-03-01
We report results on electronic transport properties of liquid Fe-S alloys at conditions of planetary cores, computed using first-principle techniques in the Kubo-Greenwood formalism. We describe a combined effect of resistivity saturation due to temperature, compression, and chemistry by comparing the electron mean free path from the Drude response of optical conductivity to the mean interatomic distance. At high compression and high sulfur concentration the Ioffe-Regel condition is satisfied, and the temperature coefficient of resistivity changes sign from positive to negative. We show that this happens due to a decrease in the d density of states at the Fermi level in response to thermal broadening.
Energy Technology Data Exchange (ETDEWEB)
Berdiyorov, G.R., E-mail: gberdiyorov@qf.org.qa; Madjet, M.E., E-mail: mmadjet@qf.org.qa
2016-12-30
Highlights: • Effect of surface termination on the optoelectronic properties of TiC{sub 2} is studied. • Fluorinated, oxidized and hydroxylated surfaces are considered. • Partial charges are calculated. • Absorption of the system increases by surface passivation. • Electronic transport reduces considerably due to the termination. - Abstract: Using the first-principles density functional theory, we study the effect of surface functionalization on the structural and optoelectronic properties of recently proposed quasi-two-dimensional material TiC{sub 2} [T. Zhao, S. Zhang, Y. Guo, Q. Wang, Nanoscale 8 (2016) 233]. Hydrogenated, fluorinated, oxidized and hydroxylated surfaces are considered. Significant changes in the lattice parameters and partial charge distributions are found due to the surface termination. Direct contribution of the adatoms to the system density of states near the Fermi level is obtained, which has a major impact on the optoelectronic properties of the material. For example, surface termination results in larger absorption in the visible range of the spectrum. The electronic transport is also affected by the surface functionalization: the current in the system can be reduced by an order of magnitude. These findings indicate the importance of the effects of surface passivation on optoelectronic properties of this quasi-2D material.
Indian Academy of Sciences (India)
We have used density functional theory to obtain the binding curves for a variety of hypothetical periodic structures of Al, Si, Pb, Sn and Au. Upon examining the resulting database of results for equilibrium bond lengths and radial force constants (within a nearest-neighbour model), we find that both decrease smoothly as ...
Nery, Jean Paul; Allen, Philip B.; Antonius, Gabriel; Reining, Lucia; Miglio, Anna; Gonze, Xavier
2018-03-01
The electron-phonon interaction causes thermal and zero-point motion shifts of electron quasiparticle (QP) energies ɛk(T ) . Other consequences of interactions, visible in angle-resolved photoemission spectroscopy (ARPES) experiments, are broadening of QP peaks and appearance of sidebands, contained in the electron spectral function A (k ,ω ) =-ℑ m GR(k ,ω ) /π , where GR is the retarded Green's function. Electronic structure codes (e.g., using density-functional theory) are now available that compute the shifts and start to address broadening and sidebands. Here we consider MgO and LiF, and determine their nonadiabatic Migdal self-energy. The spectral function obtained from the Dyson equation makes errors in the weight and energy of the QP peak and the position and weight of the phonon-induced sidebands. Only one phonon satellite appears, with an unphysically large energy difference (larger than the highest phonon energy) with respect to the QP peak. By contrast, the spectral function from a cumulant treatment of the same self-energy is physically better, giving a quite accurate QP energy and several satellites approximately spaced by the LO phonon energy. In particular, the positions of the QP peak and first satellite agree closely with those found for the Fröhlich Hamiltonian by Mishchenko et al. [Phys. Rev. B 62, 6317 (2000), 10.1103/PhysRevB.62.6317] using diagrammatic Monte Carlo. We provide a detailed comparison between the first-principles MgO and LiF results and those of the Fröhlich Hamiltonian. Such an analysis applies widely to materials with infrared(IR)-active phonons.
Boron Fullerenes: A First-Principles Study
Directory of Open Access Journals (Sweden)
Gonzalez Szwacki Nevill
2007-01-01
Full Text Available AbstractA family of unusually stable boron cages was identified and examined using first-principles local-density functional method. The structure of the fullerenes is similar to that of the B12icosahedron and consists of six crossing double-rings. The energetically most stable fullerene is made up of 180 boron atoms. A connection between the fullerene family and its precursors, boron sheets, is made. We show that the most stable boron sheets are not necessarily precursors of very stable boron cages. Our finding is a step forward in the understanding of the structure of the recently produced boron nanotubes.
Energy Technology Data Exchange (ETDEWEB)
Wu Yurong [College of Electromechanical Engineering, Hunan University of Science and Technology, Xiantang 411201 (China); Hu Wangyu [Department of Applied Physics, Hunan University, Changsha 410082 (China)], E-mail: wangyuhu2001cn@yahoo.com.cn; Han Shaochang [Department of Applied Physics, Hunan University, Changsha 410082 (China)
2008-10-01
First-principles calculations have been used to study the elastic and electronic properties of ductility rare-earth alloy YM (M=Ag, Cu, Rh) systems. The ductility mechanism for these alloys is studied from microscopic aspect, via electronic density of states (DOS). The Fermi energy lies near a local minimum, and the hybridization is stronger than that of the common NiAl alloy, demonstrating that the ductility of these alloys is much better than that of NiAl alloy. Elastic modulus, namely, shear modulus C'=(C{sub 11}-C{sub 12})/2, bulk modulus B and C{sub 44} are calculated by volume-conserving orthorhombic, hydrostatic pressure and tri-axial shear strain, respectively. Moreover, lattice parameters, antiphase boundary (APB) energies and unstable stacking fault energies of these alloys are also studied. The APB energies are greater than the unstable stacking fault energies for these alloy systems, and this is a characteristic of the ductility rare-earth alloy. The APB energies of YRh are the highest ones in these three YM alloys, which make dislocation dissociation difficult. The DOS and APB energy results show that the ductility of YRh may be worst in these three YM systems.
International Nuclear Information System (INIS)
Wu Yurong; Hu Wangyu; Han Shaochang
2008-01-01
First-principles calculations have been used to study the elastic and electronic properties of ductility rare-earth alloy YM (M=Ag, Cu, Rh) systems. The ductility mechanism for these alloys is studied from microscopic aspect, via electronic density of states (DOS). The Fermi energy lies near a local minimum, and the hybridization is stronger than that of the common NiAl alloy, demonstrating that the ductility of these alloys is much better than that of NiAl alloy. Elastic modulus, namely, shear modulus C'=(C 11 -C 12 )/2, bulk modulus B and C 44 are calculated by volume-conserving orthorhombic, hydrostatic pressure and tri-axial shear strain, respectively. Moreover, lattice parameters, antiphase boundary (APB) energies and unstable stacking fault energies of these alloys are also studied. The APB energies are greater than the unstable stacking fault energies for these alloy systems, and this is a characteristic of the ductility rare-earth alloy. The APB energies of YRh are the highest ones in these three YM alloys, which make dislocation dissociation difficult. The DOS and APB energy results show that the ductility of YRh may be worst in these three YM systems
Energy Technology Data Exchange (ETDEWEB)
Faye, Omar, E-mail: omf071@mail.usask.ca [Department of Mechanical Engineering, College of Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, S7N 5A9 Saskatchewan (Canada); Department of Condensed Matter Physics, Cheikh Anta Diop University, Dakar (Senegal); Szpunar, Jerzy A; Szpunar, Barbara [Department of Mechanical Engineering, College of Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, S7N 5A9 Saskatchewan (Canada); Beye, Aboubaker Chedikh [Department of Condensed Matter Physics, Cheikh Anta Diop University, Dakar (Senegal)
2017-01-15
Highlights: • H{sub 2} adsorption in single and double-sided Pd-G(3x3) and the effect of NH radical on graphene were studied. • Strong interaction of Pd and graphene in double-sided Pd-G(3x3) than that in the single-sided Pd-G(3x3). • The storage capacity was 3.622 wt% with a binding energy of 0.658 eV/H2. • The increase of NH radicals on Pd-G(3x3) enhanced the binding of Pd atoms on the graphene sheet. • We predicted that 2NH-dopant at the opposite site of Pd atoms prevents the desorption of Pd atom from graphene sheet. - Abstract: We conducted a detailed theoretical investigation of the structural and electronic properties of single and double sided Pd-functionalized graphene and NH-doped Pd-functionalized graphene, which are shown to be efficient materials for hydrogen storage. Nitrene radical dopant was an effective addition required for enhancing the Pd binding on the graphene sheet as well as the storage of hydrogen. We found that up to eight H{sub 2} molecules could be adsorbed by double-sided Pd-functionalized graphene at 0 K with an average binding energy in the range 1.315–0.567 eVA gravimetric hydrogen density of 3.622 wt% was reached in the Pd-functionalized graphene on both sides. The binding mechanism of H{sub 2} molecules came not only the polarization mechanism between Pd and H atoms but also from the binding of the Pd atoms on the graphene sheet and the orbital hybridization. The most crucial part of our work is measuring the effect of nitrene radical on the H{sub 2} adsorption on Pd-functionalized graphene. Our calculations predicted that the addition of NH radicals on Pd-functionalized graphene enhance the binding of H{sub 2} molecules, which helps also to avoid the desorption of Pd(H{sub 2}){sub n} (n = 1–5) complexes from graphene sheet. Our results also predict Pd-functionalized NH-doped graphene is a potential hydrogen storage medium for on-board applications.
International Nuclear Information System (INIS)
Faye, Omar; Szpunar, Jerzy A; Szpunar, Barbara; Beye, Aboubaker Chedikh
2017-01-01
Highlights: • H_2 adsorption in single and double-sided Pd-G(3x3) and the effect of NH radical on graphene were studied. • Strong interaction of Pd and graphene in double-sided Pd-G(3x3) than that in the single-sided Pd-G(3x3). • The storage capacity was 3.622 wt% with a binding energy of 0.658 eV/H2. • The increase of NH radicals on Pd-G(3x3) enhanced the binding of Pd atoms on the graphene sheet. • We predicted that 2NH-dopant at the opposite site of Pd atoms prevents the desorption of Pd atom from graphene sheet. - Abstract: We conducted a detailed theoretical investigation of the structural and electronic properties of single and double sided Pd-functionalized graphene and NH-doped Pd-functionalized graphene, which are shown to be efficient materials for hydrogen storage. Nitrene radical dopant was an effective addition required for enhancing the Pd binding on the graphene sheet as well as the storage of hydrogen. We found that up to eight H_2 molecules could be adsorbed by double-sided Pd-functionalized graphene at 0 K with an average binding energy in the range 1.315–0.567 eVA gravimetric hydrogen density of 3.622 wt% was reached in the Pd-functionalized graphene on both sides. The binding mechanism of H_2 molecules came not only the polarization mechanism between Pd and H atoms but also from the binding of the Pd atoms on the graphene sheet and the orbital hybridization. The most crucial part of our work is measuring the effect of nitrene radical on the H_2 adsorption on Pd-functionalized graphene. Our calculations predicted that the addition of NH radicals on Pd-functionalized graphene enhance the binding of H_2 molecules, which helps also to avoid the desorption of Pd(H_2)_n (n = 1–5) complexes from graphene sheet. Our results also predict Pd-functionalized NH-doped graphene is a potential hydrogen storage medium for on-board applications.
Zhu, Jinguo; Wang, Yapeng; Tian, Ting; Zhang, Qianfan
2018-03-01
Polymeric adsorbents have been attracting increasing attention because of their favorable structrual properties and effectiveness of solving small molecules contaminants. However, due to the absence of deep insight into the adsorption mechanism of polymeric adsorbents, researches on new polymeric adsorbents can only be carried out by repeated experiments and tests, which is extremely inefficient. Therefore, investigating the adsorption process of polymeric adsorbents, especially the mechanism of adsorbing various air pollutant molecules by materials modelling and simulation, is of great significance. Here in this work, we systematically studied the adsorption mechanism by first-principles computation with van der Waals interaction. It demonstrates that the adsorption between them was pure physisorption originating from the hydrogen bond and intermolecular forces consisting of Keesom force, Debye force and London dispersion force. The proportions of these forces varied according to different adsorption systems. The adsorption effects were determined by the polymers’ dipole moment and polarizability. The adsorption performance of some polymers with special structures was also investigated to explore their possibility as potential adsorbents. The results of our simulation can provide some guidance for developing new polymeric adsorbents with better performance.
Czech Academy of Sciences Publication Activity Database
Ulrich, C. M.; Hashibon, A.; Svoboda, Jiří; Elsässer, C.; Helm, D.; Riedel, H.
2011-01-01
Roč. 59, č. 20 (2011), s. 7634-7644 ISSN 1359-6454 R&D Projects: GA ČR GAP204/10/1784 Institutional research plan: CEZ:AV0Z20410507 Keywords : Bonding * Diffusion * Intermetallic compounds Subject RIV: BJ - Thermodynamics Impact factor: 3.755, year: 2011
First principles calculation of two dimensional antimony and antimony arsenide
Energy Technology Data Exchange (ETDEWEB)
Pillai, Sharad Babu, E-mail: sbpillai001@gmail.com; Narayan, Som; Jha, Prafulla K. [Department. of Physics, Faculty of Science, The M. S. University of Baroda, Vadodara-390002 (India); Dabhi, Shweta D. [Department of Physics, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar-364001 (India)
2016-05-23
This work focuses on the strain dependence of the electronic properties of two dimensional antimony (Sb) material and its alloy with As (SbAs) using density functional theory based first principles calculations. Both systems show indirect bandgap semiconducting character which can be transformed into a direct bandgap material with the application of relatively small strain.
First-principles prediction of liquid/liquid interfacial tension
DEFF Research Database (Denmark)
Andersson, Martin Peter; Bennetzen, M.V.; Klamt, A.
2014-01-01
of groundwater aquifers contaminated by chlorinated solvents to drug delivery and a host of industrial processes. Here, we present a model for predicting interfacial tension from first principles using density functional theory calculations. Our model requires no experimental input and is applicable to liquid...
First-principles simulations of heat transport
Puligheddu, Marcello; Gygi, Francois; Galli, Giulia
2017-11-01
Advances in understanding heat transport in solids were recently reported by both experiment and theory. However an efficient and predictive quantum simulation framework to investigate thermal properties of solids, with the same complexity as classical simulations, has not yet been developed. Here we present a method to compute the thermal conductivity of solids by performing ab initio molecular dynamics at close to equilibrium conditions, which only requires calculations of first-principles trajectories and atomic forces, thus avoiding direct computation of heat currents and energy densities. In addition the method requires much shorter sequential simulation times than ordinary molecular dynamics techniques, making it applicable within density functional theory. We discuss results for a representative oxide, MgO, at different temperatures and for ordered and nanostructured morphologies, showing the performance of the method in different conditions.
First principles study of electronic, elastic and thermal properties of lutetium intermetallics
International Nuclear Information System (INIS)
Pagare, Gitanjali; Chouhan, Sunil Singh; Soni, Pooja; Sanyal, S.P.; Rajagopalan, M.
2011-01-01
In the present work, the electronic, elastic and thermal properties of lutetium intermetallics LuX have been studied theoretically by using first principles calculations based on density functional theory (DFT) with the generalized gradient approximation (GCA)
International Nuclear Information System (INIS)
Boos, H.E.; Shiroishi, M.; Takahashi, M.
2005-01-01
We show how correlation functions of the spin-1/2 Heisenberg chain without magnetic field in the anti-ferromagnetic ground state can be explicitly calculated using information contained in the quantum Knizhnik-Zamolodchikov equation [qKZ]. We find several fundamental relations which the inhomogeneous correlations should fulfill. On the other hand, it turns out that these relations can fix the form of the correlations uniquely. Actually, applying this idea, we have obtained all the correlation functions on five sites. Particularly by taking the homogeneous limit, we have got the analytic form of the fourth-neighbor pair correlator j z S j+4 z >
First-principles elasticity of monocarboaluminate hydrates
Moon, J.
2014-07-01
The elasticity of monocarboaluminate hydrates, 3CaO·Al2O3·CaCO3·xH2O (x = 11 or 8), has been investigated by first-principles calculations. Previous experimental study revealed that the fully hydrated monocarboaluminate (x = 11) exhibits exceptionally low compressibility compared to other reported calcium aluminate hydrates. This stiff hydration product can contribute to the strength of concrete made with Portland cements containing calcium carbonates. In this study, full elastic tensors and mechanical properties of the crystal structures with different water contents (x = 11 or 8) are computed by first-principles methods based on density functional theory. The results indicate that the compressibility of monocarboaluminate is highly dependent on the water content in the interlayer region. The structure also becomes more isotropic with the addition of water molecules in this region. Since the monocarboaluminate is a key hydration product of limestone added cement, elasticity of the crystal is important to understand its mechanical impact on concrete. Besides, it is put forth that this theoretical calculation will be useful in predicting the elastic properties of other complex cementitous materials and the influence of ion exchange on compressibility.
First-principles elasticity of monocarboaluminate hydrates
Moon, J.; Yoon, S.; Wentzcovitch, R. M.; Monteiro, P. J. M.
2014-01-01
The elasticity of monocarboaluminate hydrates, 3CaO·Al2O3·CaCO3·xH2O (x = 11 or 8), has been investigated by first-principles calculations. Previous experimental study revealed that the fully hydrated monocarboaluminate (x = 11) exhibits exceptionally low compressibility compared to other reported calcium aluminate hydrates. This stiff hydration product can contribute to the strength of concrete made with Portland cements containing calcium carbonates. In this study, full elastic tensors and mechanical properties of the crystal structures with different water contents (x = 11 or 8) are computed by first-principles methods based on density functional theory. The results indicate that the compressibility of monocarboaluminate is highly dependent on the water content in the interlayer region. The structure also becomes more isotropic with the addition of water molecules in this region. Since the monocarboaluminate is a key hydration product of limestone added cement, elasticity of the crystal is important to understand its mechanical impact on concrete. Besides, it is put forth that this theoretical calculation will be useful in predicting the elastic properties of other complex cementitous materials and the influence of ion exchange on compressibility.
International Nuclear Information System (INIS)
Palummo, M.; Reining, L.; Ballone, P.
1993-01-01
In this paper we outline the major features of the ''ab-initio'' simulation scheme of Car and Parrinello, focusing on the physical ideas and computational details at the basis of its efficiency and success. We briefly review the main applications of the method. We discuss the limitations of the standard scheme, as well as recent developments proposed in order to extend the reach of the method. Moreover, we consider more in detail two specific subjects. First, we describe a simple improvement (Gradient Corrections) on the basic approximation of the ''ab-initio'' simulation, i.e. the Local Density Approximation. These corrections can be easily and efficiently included in the Car-Parrinello code, bringing computed structural and cohesive properties significantly closer to their experimental values. Finally, we discuss the choice of the pseudopotential, with special attention to the possibilities and limitations of the last generation of soft pseudopotentials. (orig.)
International Nuclear Information System (INIS)
Freyss, M.
2015-01-01
This chapter gives an introduction to first-principles electronic structure calculations based on the density functional theory (DFT). Electronic structure calculations have a crucial importance in the multi-scale modelling scheme of materials: not only do they enable one to accurately determine physical and chemical properties of materials, they also provide data for the adjustment of parameters (or potentials) in higher-scale methods such as classical molecular dynamics, kinetic Monte Carlo, cluster dynamics, etc. Most of the properties of a solid depend on the behaviour of its electrons, and in order to model or predict them it is necessary to have an accurate method to compute the electronic structure. DFT is based on quantum theory and does not make use of any adjustable or empirical parameter: the only input data are the atomic number of the constituent atoms and some initial structural information. The complicated many-body problem of interacting electrons is replaced by an equivalent single electron problem, in which each electron is moving in an effective potential. DFT has been successfully applied to the determination of structural or dynamical properties (lattice structure, charge density, magnetisation, phonon spectra, etc.) of a wide variety of solids. Its efficiency was acknowledged by the attribution of the Nobel Prize in Chemistry in 1998 to one of its authors, Walter Kohn. A particular attention is given in this chapter to the ability of DFT to model the physical properties of nuclear materials such as actinide compounds. The specificities of the 5f electrons of actinides will be presented, i.e., their more or less high degree of localisation around the nuclei and correlations. The limitations of the DFT to treat the strong 5f correlations are one of the main issues for the DFT modelling of nuclear fuels. Various methods that exist to better treat strongly correlated materials will finally be presented. (author)
Guster, Bogdan; Canadell, Enric; Pruneda, Miguel; Ordejón, Pablo
2018-04-01
We present a density functional theory study of the electronic structure of single-layer TiSe2, and focus on the charge density wave (CDW) instability present on this 2D material. We explain the 2× 2 periodicity of the CDW from the phonon band structure of the undistorted crystal, which is unstable under one of the phonon modes at the M point. This can be understood in terms of a partial band gap opening at the Fermi level, which we describe on the basis of the symmetry of the involved crystal orbitals, leading to an energy gain upon the displacement of the atoms following the phonon mode in a 2 × 1 structure. Furthermore, the combination of the corresponding phonons for the three inequivalent M points of the Brillouin zone leads to the 2 × 2 distortion characteristic of the CDW state. This leads to a further opening of a full gap, which reduces the energy of the 2 × 2 structure compared to the 2 × 1 one of a single M point phonon, and makes the CDW structure the most stable one. We also analyze the effect of charge injection into the layer on the structural instability. We predict that the 2 × 2 structure only survives for a certain range of doping levels, both for electrons and for holes, as doping reduces the energy gain due to the gap opening. We predict the transition from the commensurate 2 × 2 distortion to an incommensurate one with increasing wavelength upon increasing the doping level, followed by the appearance of the undistorted 1 × 1 structure for larger carrier concentrations.
International Nuclear Information System (INIS)
Chen, Lanli; Wang, Xiaofang; Shi, Siqi; Cui, Yuanyuan; Luo, Hongjie; Gao, Yanfeng
2016-01-01
Graphical abstract: - Highlights: • After adsorption, there is a charge transfer from Ag to VO_2(1 0 0) surface, which thus increases the electron concentration in VO_2 thin film. • Ag adsorption on VO_2(1 0 0) surface process is an exothermic chemical process, and the adsorption system is stable. • The work function can be tuned by Ag adsorption on and incorporation into the VO_2(1 0 0) surface, which in turn regulates the phase transition temperature of VO_2. - Abstract: VO_2 is an attractive material for application to thermochromic optoelectronic devices such as smart windows, and Ag/VO_2 double-layered structure can effectively decrease the phase transition temperature (T_c) of VO_2 thin film, which is very important for practical application of VO_2. Previous works has shown that the decrease in phase transition temperature (T_c) seems to be relevant with the work function of VO_2 in Ag/VO_2 double-layered thin film, although the underlying mechanism of tuning its T_c by Ag incorporation and adsorption on the VO_2(1 0 0) surface has been rarely investigated. Our first-principles calculations reveal that the adsorption of Ag atoms on the VO_2(1 0 0) surface rather than incorporation of Ag exhibits a lower work function, which is ascribed to an integrated effect of charge transfer from Ag to VO_2(1 0 0) surface and enhanced surface dipole moment. The results suggest that the decrease in work function of VO_2 with Ag adsorption favors the reduction in T_c. The current findings are helpful to understand the fundamental mechanism for yielding high-efficiency VO_2-based optoelectronic devices.
Energy Technology Data Exchange (ETDEWEB)
Chen, Lanli; Wang, Xiaofang [School of Materials Science and Engineering, Shanghai University, Shanghai 200444 (China); Shi, Siqi, E-mail: sqshi@shu.edu.cn [School of Materials Science and Engineering, Shanghai University, Shanghai 200444 (China); Materials Genome Institute, Shanghai University, Shanghai 200444 (China); Cui, Yuanyuan [School of Materials Science and Engineering, Shanghai University, Shanghai 200444 (China); Luo, Hongjie [School of Materials Science and Engineering, Shanghai University, Shanghai 200444 (China); Materials Genome Institute, Shanghai University, Shanghai 200444 (China); Gao, Yanfeng, E-mail: yfgao@shu.edu.cn [School of Materials Science and Engineering, Shanghai University, Shanghai 200444 (China)
2016-03-30
Graphical abstract: - Highlights: • After adsorption, there is a charge transfer from Ag to VO{sub 2}(1 0 0) surface, which thus increases the electron concentration in VO{sub 2} thin film. • Ag adsorption on VO{sub 2}(1 0 0) surface process is an exothermic chemical process, and the adsorption system is stable. • The work function can be tuned by Ag adsorption on and incorporation into the VO{sub 2}(1 0 0) surface, which in turn regulates the phase transition temperature of VO{sub 2}. - Abstract: VO{sub 2} is an attractive material for application to thermochromic optoelectronic devices such as smart windows, and Ag/VO{sub 2} double-layered structure can effectively decrease the phase transition temperature (T{sub c}) of VO{sub 2} thin film, which is very important for practical application of VO{sub 2}. Previous works has shown that the decrease in phase transition temperature (T{sub c}) seems to be relevant with the work function of VO{sub 2} in Ag/VO{sub 2} double-layered thin film, although the underlying mechanism of tuning its T{sub c} by Ag incorporation and adsorption on the VO{sub 2}(1 0 0) surface has been rarely investigated. Our first-principles calculations reveal that the adsorption of Ag atoms on the VO{sub 2}(1 0 0) surface rather than incorporation of Ag exhibits a lower work function, which is ascribed to an integrated effect of charge transfer from Ag to VO{sub 2}(1 0 0) surface and enhanced surface dipole moment. The results suggest that the decrease in work function of VO{sub 2} with Ag adsorption favors the reduction in T{sub c}. The current findings are helpful to understand the fundamental mechanism for yielding high-efficiency VO{sub 2}-based optoelectronic devices.
Zhao, Hongxia; Yang, Yong; Shu, Xin; Wang, Yanwei; Ran, Qianping
2018-04-09
First-principle calculations, especially by the density functional theory (DFT) methods, are becoming a power technique to study molecular structure and properties of organic/inorganic interfaces. This review introduces some recent examples on the study of adsorption models of organic molecules or oligomers on mineral surfaces and interfacial properties obtained from first-principles calculations. The aim of this contribution is to inspire scientists to benefit from first-principle calculations and to apply the similar strategies when studying and tailoring interfacial properties at the atomistic scale, especially for those interested in the design and development of new molecules and new products. Copyright © 2017. Published by Elsevier B.V.
Song, Jian; Lou, Huan
2018-05-01
Investigations of the adsorptions of representative gases (NO2, NH3, H2S, SO2, CO, and HCHO) on different Ag-functionalized monolayer MoS2 surfaces were performed by first principles methods. The adsorption configurations, adsorption energies, electronic structure properties, and charge transfer were calculated, and the results show that the adsorption activities to gases of monolayer MoS2 are dramatically enhanced by the Ag-modification. The Ag-modified perfect MoS2 (Ag-P) and MoS2 with S-vacancy (Ag-Vs) substrates exhibit a more superior adsorption activity to NO2 than other gases, which is consistent with the experimental reports. The charge transfer processes of different molecules adsorbed on different surfaces exhibit various characteristics, with potential benefits to gas selectivity. For instance, the NO2 and SO2 obtain more electrons from both Ag-P and Ag-Vs substrates but the NH3 and H2S donate more electrons to materials than others. In addition, the CO and HCHO possess totally opposite charge transfer directs on both substrates, respectively. The BS and PDOS calculations show that semiconductor types of gas/Ag-MoS2 systems are more determined by the metal-functionalization of material, and the directs and numbers of charge transfer process between gases and adsorbents can cause the increase or decline of material resistance theoretically, which is helpful to gas detection and distinction. The further analysis indicates suitable co-operation between the gain-lost electron ability of gas and metallicity of featuring metal might adjust the resistivity of complex and contribute to new thought for metal-functionalization. Our works provide new valuable ideas and theoretical foundation for the potential improvement of MoS2-based gas sensor performances, such as sensitivity and selectivity.
Debnath, Bimal; Sarkar, Utpal; Debbarma, Manish; Bhattacharjee, Rahul; Chattopadhyaya, Surya
2018-02-01
First principle based theoretical initiative is taken to tune the optoelectronic properties of binary strontium chalcogenide semiconductors by doping magnesium atom(s) into their rock-salt unit cells at specific concentrations x = 0.0, 0.25, 0.50, 0.75 and 1.0 and such tuning is established by studying structural, electronic and optical properties of designed binary compounds and ternary alloys employing WC-GGA, B3LYP and mBJ exchange-correlation functionals. Band structure of each compound is constructed and respective band gaps under all the potential schemes are measured. The band gap bowing and its microscopic origin are calculated using quadratic fit and Zunger's approach, respectively. The atomic and orbital origins of electronic states in the band structure of any compound are explored from its density of states. The nature of chemical bonds between the constituent atoms in each compound is explored from the valence electron density contour plots. Optical properties of any specimen are explored from the computed spectra of its dielectric function, refractive index, extinction coefficient, normal incidence reflectivity, optical conductivity optical absorption and energy loss function. Several calculated results are compared with available experimental and earlier theoretical data.
First-principles study of complex material systems
He, Lixin
This thesis covers several topics concerning the study of complex materials systems by first-principles methods. It contains four chapters. A brief, introductory motivation of this work will be given in Chapter 1. In Chapter 2, I will give a short overview of the first-principles methods, including density-functional theory (DFT), planewave pseudopotential methods, and the Berry-phase theory of polarization in crystallines insulators. I then discuss in detail the locality and exponential decay properties of Wannier functions and of related quantities such as the density matrix, and their application in linear-scaling algorithms. In Chapter 3, I investigate the interaction of oxygen vacancies and 180° domain walls in tetragonal PbTiO3 using first-principles methods. Our calculations indicate that the oxygen vacancies have a lower formation energy in the domain wall than in the bulk, thereby confirming the tendency of these defects to migrate to, and pin, the domain walls. The pinning energies are reported for each of the three possible orientations of the original Ti--O--Ti bonds, and attempts to model the results with simple continuum models are discussed. CaCu3Ti4O12 (CCTO) has attracted a lot of attention recently because it was found to have an enormous dielectric response over a very wide temperature range. In Chapter 4, I study the electronic and lattice structure, and the lattice dynamical properties, of this system. Our first-principles calculations together with experimental results point towards an extrinsic mechanism as the origin of the unusual dielectric response.
First principles studies of multiferroic materials
International Nuclear Information System (INIS)
Picozzi, Silvia; Ederer, Claude
2009-01-01
Multiferroics, materials where spontaneous long-range magnetic and dipolar orders coexist, represent an attractive class of compounds, which combine rich and fascinating fundamental physics with a technologically appealing potential for applications in the general area of spintronics. Ab initio calculations have significantly contributed to recent progress in this area, by elucidating different mechanisms for multiferroicity and providing essential information on various compounds where these effects are manifestly at play. In particular, here we present examples of density-functional theory investigations for two main classes of materials: (a) multiferroics where ferroelectricity is driven by hybridization or purely structural effects, with BiFeO 3 as the prototype material, and (b) multiferroics where ferroelectricity is driven by correlation effects and is strongly linked to electronic degrees of freedom such as spin-, charge-, or orbital-ordering, with rare-earth manganites as prototypes. As for the first class of multiferroics, first principles calculations are shown to provide an accurate qualitative and quantitative description of the physics in BiFeO 3 , ranging from the prediction of large ferroelectric polarization and weak ferromagnetism, over the effect of epitaxial strain, to the identification of possible scenarios for coupling between ferroelectric and magnetic order. For the second class of multiferroics, ab initio calculations have shown that, in those cases where spin-ordering breaks inversion symmetry (e.g. in antiferromagnetic E-type HoMnO 3 ), the magnetically induced ferroelectric polarization can be as large as a few μC cm -2 . The examples presented point the way to several possible avenues for future research: on the technological side, first principles simulations can contribute to a rational materials design, aimed at identifying spintronic materials that exhibit ferromagnetism and ferroelectricity at or above room temperature. On the
Forecast of Piezoelectric Properties of Crystalline Materials from First Principles Calculation
International Nuclear Information System (INIS)
Zheng Yanqing; Shi Erwei; Chen Jianjun; Zhang Tao; Song Lixin
2006-01-01
In this paper, forecast of piezoelectric tensors are presented. Piezo crystals including quartz, quartz-like crystals, known and novel crystals of langasite-type structure are treated with density-functional perturb theory (DFPT) using plane-wave pseudopotentials method, within the local density approximation (LDA) to the exchange-correlation functional. Compared with experimental results, the ab initio calculation results have quantitative or semi-quantitative accuracy. It is shown that first principles calculation opens a door to the search and design of new piezoelectric material. Further application of first principles calculation to forecast the whole piezoelectric properties are also discussed
First Principles Simulation of a Ceramic/ Metal Interface with Misfit
International Nuclear Information System (INIS)
Benedek, R.; Alavi, A.; Seidman, D. N.; Yang, L. H.; Muller, D. A.; Woodward, C.
2000-01-01
The relaxed atomic structure of a model ceramic/metal interface, {222}MgO/Cu , is simulated, including lattice constant mismatch, using first principles local-density functional theory plane wave pseudopotential methods. The 399-atom computational unit cell contains 36 O and 49 Cu atoms per layer in accordance with the 7/6 ratio of MgO to Cu lattice constants. The atomic layers on both sides of the interface warp to optimize the local bonding. The interface adhesive energy is calculated. The interface electronic structure is found to vary appreciably with the local environment. (c) 2000 The American Physical Society
First-principles calculations of novel materials
Sun, Jifeng
Computational material simulation is becoming more and more important as a branch of material science. Depending on the scale of the systems, there are many simulation methods, i.e. first-principles calculation (or ab-initio), molecular dynamics, mesoscale methods and continuum methods. Among them, first-principles calculation, which involves density functional theory (DFT) and based on quantum mechanics, has become to be a reliable tool in condensed matter physics. DFT is a single-electron approximation in solving the many-body problems. Intrinsically speaking, both DFT and ab-initio belong to the first-principles calculation since the theoretical background of ab-initio is Hartree-Fock (HF) approximation and both are aimed at solving the Schrodinger equation of the many-body system using the self-consistent field (SCF) method and calculating the ground state properties. The difference is that DFT introduces parameters either from experiments or from other molecular dynamic (MD) calculations to approximate the expressions of the exchange-correlation terms. The exchange term is accurately calculated but the correlation term is neglected in HF. In this dissertation, DFT based first-principles calculations were performed for all the novel materials and interesting materials introduced. Specifically, the DFT theory together with the rationale behind related properties (e.g. electronic, optical, defect, thermoelectric, magnetic) are introduced in Chapter 2. Starting from Chapter 3 to Chapter 5, several representative materials were studied. In particular, a new semiconducting oxytelluride, Ba2TeO is studied in Chapter 3. Our calculations indicate a direct semiconducting character with a band gap value of 2.43 eV, which agrees well with the optical experiment (˜ 2.93 eV). Moreover, the optical and defects properties of Ba2TeO are also systematically investigated with a view to understanding its potential as an optoelectronic or transparent conducting material. We find
Laboratory Density Functionals
Giraud, B. G.
2007-01-01
We compare several definitions of the density of a self-bound system, such as a nucleus, in relation with its center-of-mass zero-point motion. A trivial deconvolution relates the internal density to the density defined in the laboratory frame. This result is useful for the practical definition of density functionals.
First Principles Calculations for X-ray Resonant Spectra and Elastic Properties
International Nuclear Information System (INIS)
Yongbin Lee
2006-01-01
In this thesis, we discuss applications of first principles methods to x-ray resonant spectra and elastic properties calculation. We start with brief reviews about theoretical background of first principles methods, such as density functional theory, local density approximation (LDA), LDA+U, and the linear augmented plane wave (LAPW) method to solve Kohn-Sham equations. After that we discuss x-ray resonant scattering (XRMS), x-ray magnetic circular dichroism (XMCD) and the branching problem in the heavy rare earths Ledges. In the last chapter we discuss the elastic properties of the second hardest material AlMgB 14
Sim, Eun Seob; Chung, Yong-Chae
2018-03-01
In this study, the influence of the non-uniform surface of F- and O-functionalized Ti2C on the anchoring behavior of lithium polysulfide (LiPS) is investigated using density functional theory. In order to consider the non-uniform surface, the substitutional, vacancy, and S-trapped sites of F- and O-functionalized Ti2C are designed. The anchoring behavior is investigated considering the adsorption energy of LiPS, reactivity between Li atoms and the substrate, and the reduction state of the S atoms. On the F-substitutional site of the O-functionalized surface, it is confirmed that the suppressing mechanism changes from the neutralization of S atoms to the anchoring of LiPS. However, too strong of an interaction between Ti atoms exposed at the vacancy site and S atoms induces trapping of the S atom at the vacancies of both F- and O-functionalized surfaces. As a result of the trapping of the S atom, the use of active material decreases. In addition, the S-trapped site originated from the vacancy site does not affect the suppressing mechanism. In conclusion, to optimize the Ti2C-based MXene as an anchoring material for Li-S batteries, the preparation process should be focused on eliminating the vacancy of functional groups.
Credibility is the first principle
International Nuclear Information System (INIS)
Beecher, William
2002-01-01
The first principle of an effective public affairs program on nuclear energy is credibility. If credibility is lacking, no matter how artful the message, it will not be persuasive. There has long been a problem in the United States. For years much of the industry followed the practice, when there was an event at a nuclear power plant that resulted in an unplanned release of radioactivity, to tell the public there was 'no release' if in fact the release was below the technical specifications of what the NRC mandates as being safe. The NRC is a safety regulator. It can tell nuclear power plant operators what to do, or not do, when it comes to safety, but doesn't have the right to tell them what to say to the public. The example of an emergency exercise and the NRC press release on that occasion showed the direction how companies could be influenced to behave in order to prevent such avoidably negative news coverage, i.e. attaining credibility when public anxiety is concerned
Primordial Black Holes from First Principles (Overview)
Lam, Casey; Bloomfield, Jolyon; Moss, Zander; Russell, Megan; Face, Stephen; Guth, Alan
2017-01-01
Given a power spectrum from inflation, our goal is to calculate, from first principles, the number density and mass spectrum of primordial black holes that form in the early universe. Previously, these have been calculated using the Press- Schechter formalism and some demonstrably dubious rules of thumb regarding predictions of black hole collapse. Instead, we use Monte Carlo integration methods to sample field configurations from a power spectrum combined with numerical relativity simulations to obtain a more accurate picture of primordial black hole formation. We demonstrate how this can be applied for both Gaussian perturbations and the more interesting (for primordial black holes) theory of hybrid inflation. One of the tools that we employ is a variant of the BBKS formalism for computing the statistics of density peaks in the early universe. We discuss the issue of overcounting due to subpeaks that can arise from this approach (the ``cloud-in-cloud'' problem). MIT UROP Office- Paul E. Gray (1954) Endowed Fund.
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...
First-principles study of the interaction and charge transfer between graphene and metals
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,
International Nuclear Information System (INIS)
Chui, S.T.; Kasowski, R.V.; Hsu, W.Y.
1989-01-01
We argue that because of the anisotropic nature of YBa 2 Cu 3 O/sub 7-//sub x/, one-dimensional-type charge- and spin-density fluctuations produce an effective attraction that overcomes the electron-electron Coulomb repulsion, but only at large distances. This effective attraction is further enhanced by band-structure effects such that a substantial superconducting transition temperature can be obtained. Without making any assumption of the symmetry of the gap function, we solve the Bardeen-Cooper-Schrieffer (BCS) superconducting gap equation for the six bands closest to the Fermi level. A highly anisotropic gap function with a maximum of about 0.11 eV is found. From the linearized gap equation, a transition temperature of about 0.035 eV is obtained. This is about one-quarter the maximum of the gap function, consistent with the experimental ratio of the transition temperature to the gap determined from tunneling, infrared, and nuclear quadrupole resonance measurements. The important participants to the superconducting pair come from electrons close to planar copper [Cu(2)] and chain oxygen [O(1) and O(4)] sites, consistent with recent quadrupole resonance measurements. Our calculation produces a coherence length of the order of 30 A in the xy direction, the same order of magnitude as the experimental result and considerably smaller than the conventional magnitude of ordinary BCS materials. Similar calculations for YBa 2 Cu 3 O/sub 6.5/ where periodic O vacancies are introduced along the one-dimensional Cu-O chains shows that the transition temperature is reduced by half
International Nuclear Information System (INIS)
Engel, J.
2007-01-01
The Hohenberg-Kohn theorem and Kohn-Sham procedure are extended to functionals of the localized intrinsic density of a self-bound system such as a nucleus. After defining the intrinsic-density functional, we modify the usual Kohn-Sham procedure slightly to evaluate the mean-field approximation to the functional, and carefully describe the construction of the leading corrections for a system of fermions in one dimension with a spin-degeneracy equal to the number of particles N. Despite the fact that the corrections are complicated and nonlocal, we are able to construct a local Skyrme-like intrinsic-density functional that, while different from the exact functional, shares with it a minimum value equal to the exact ground-state energy at the exact ground-state intrinsic density, to next-to-leading order in 1/N. We briefly discuss implications for real Skyrme functionals
First principles study of α and δ-Pu
International Nuclear Information System (INIS)
Chattaraj, Debabrata; Dash, Smruti
2017-01-01
The structural and electronic properties of α-and δ-Pu has been investigated using state of the art first principles method. All the calculations have been performed using a plane wave based pseudopotential method under the framework of spin polarized density functional theory. The effect of relativistic spin-orbit interactions on these properties has been investigated. The calculated lattice parameters are found to be within ±1% of the experimental data. The cohesive energy of α-and δ-Pu are calculated to be -3.125 and -3.126 eV/atom. The nature of chemical bonding present in those phases of Pu is depicted by calculated density of states spectra. (author)
International Nuclear Information System (INIS)
Kusakabe, K; Ikuno, Y k; Nagara, H; Harada, K
2009-01-01
Stable oxygen sites on a PdO film over a Pd(100) thin structure with a (√5x√5)R27 o surface unit cell are determined using the first-principles electronic structure calculations with the generalized gradient approximation. The adsorbed monatomic oxygen goes to a site bridging two twofold-coordinated Pd atoms or to a site bridging a twofold-coordinated Pd atom and a fourfold-coordinated Pd atom. Estimated reaction energies of CO oxidation by reduction of the oxidized PdO film and N 2 O reduction mediated by oxidation of the PdO film are both exothermic. Motion of the adsorbed oxygen atom between the two stable sites is evaluated using the nudged elastic band method, where an energy barrier for a translational motion of the adsorbed oxygen may become ∼0.45 eV, which is low enough to allow fluxionality of the surface oxygen at high temperatures. The oxygen fluxionality is allowed by the existence of twofold-coordinated Pd atoms on the PdO film, whose local structure has a similarity to that of Pd catalysts for the Suzuki-Miyaura cross-coupling. Although NO x (including NO 2 and NO) reduction is not always catalyzed by the PdO film only, we conclude that continual redox reactions may happen mediated by oxygen-adsorbed PdO films over a Pd surface structure, when the influx of NO x and CO continues, and when the reaction cycle is kept on a well-designed oxygen surface.
First-principles structures for the close-packed and the 7/2 motif of collagen
DEFF Research Database (Denmark)
Jalkanen, Karl J.; Olsen, Kasper; Knapp-Mohammady, Michaela
2012-01-01
The newly proposed close-packed motif for collagen and the more established 7/2 structure are investigated and compared. First-principles semi-empirical wave function theory and Kohn-Sham density functional theory are applied in the study of these relatively large and complex structures. The stru......The newly proposed close-packed motif for collagen and the more established 7/2 structure are investigated and compared. First-principles semi-empirical wave function theory and Kohn-Sham density functional theory are applied in the study of these relatively large and complex structures...
A first-principles approach to finite temperature elastic constants
Energy Technology Data Exchange (ETDEWEB)
Wang, Y; Wang, J J; Zhang, H; Manga, V R; Shang, S L; Chen, L-Q; Liu, Z-K [Department of Materials Science and Engineering, Pennsylvania State University, University Park, PA 16802 (United States)
2010-06-09
A first-principles approach to calculating the elastic stiffness coefficients at finite temperatures was proposed. It is based on the assumption that the temperature dependence of elastic stiffness coefficients mainly results from volume change as a function of temperature; it combines the first-principles calculations of elastic constants at 0 K and the first-principles phonon theory of thermal expansion. Its applications to elastic constants of Al, Cu, Ni, Mo, Ta, NiAl, and Ni{sub 3}Al from 0 K up to their respective melting points show excellent agreement between the predicted values and existing experimental measurements.
A first-principles approach to finite temperature elastic constants
International Nuclear Information System (INIS)
Wang, Y; Wang, J J; Zhang, H; Manga, V R; Shang, S L; Chen, L-Q; Liu, Z-K
2010-01-01
A first-principles approach to calculating the elastic stiffness coefficients at finite temperatures was proposed. It is based on the assumption that the temperature dependence of elastic stiffness coefficients mainly results from volume change as a function of temperature; it combines the first-principles calculations of elastic constants at 0 K and the first-principles phonon theory of thermal expansion. Its applications to elastic constants of Al, Cu, Ni, Mo, Ta, NiAl, and Ni 3 Al from 0 K up to their respective melting points show excellent agreement between the predicted values and existing experimental measurements.
density functional theory approach
Indian Academy of Sciences (India)
YOGESH ERANDE
2017-07-27
Jul 27, 2017 ... a key role in all optical switching devices, since their optical properties can be .... optimized in the gas phase using Density Functional Theory. (DFT).39 The ...... The Mediation of Electrostatic Effects by Sol- vents J. Am. Chem.
Semiclassical universe from first principles
International Nuclear Information System (INIS)
Ambjorn, J.; Jurkiewicz, J.; Loll, R.
2005-01-01
Causal dynamical triangulations in four dimensions provide a background-independent definition of the sum over space-time geometries in non-perturbative quantum gravity. We show that the macroscopic four-dimensional world which emerges in the Euclidean sector of this theory is a bounce which satisfies a semiclassical equation. After integrating out all degrees of freedom except for a global scale factor, we obtain the ground state wave function of the universe as a function of this scale factor
First-principles calculations of structural, electronic and optical properties of CdxZn1-xS alloys
Noor, Naveed Ahmed; Ikram, Nazma; Ali, Sana Zulfiqar; Nazir, Safdar; Alay-E-Abbas, Syed Muhammad; Shaukat, Ali
2010-01-01
Structural, electronic and optical properties of ternary alloy system CdxZn1-xS have been studied using first-principles approach based on density functional theory. Electronic structure, density of states and energy band gap values for CdxZn1-xS
International Nuclear Information System (INIS)
Das, M.P.
1984-07-01
The state of the art of the density functional formalism (DFT) is reviewed. The theory is quantum statistical in nature; its simplest version is the well-known Thomas-Fermi theory. The DFT is a powerful formalism in which one can treat the effect of interactions in inhomogeneous systems. After some introductory material, the DFT is outlined from the two basic theorems, and various generalizations of the theorems appropriate to several physical situations are pointed out. Next, various approximations to the density functionals are presented and some practical schemes, discussed; the approximations include an electron gas of almost constant density and an electron gas of slowly varying density. Then applications of DFT in various diverse areas of physics (atomic systems, plasmas, liquids, nuclear matter) are mentioned, and its strengths and weaknesses are pointed out. In conclusion, more recent developments of DFT are indicated
GPU based acceleration of first principles calculation
International Nuclear Information System (INIS)
Tomono, H; Tsumuraya, K; Aoki, M; Iitaka, T
2010-01-01
We present a Graphics Processing Unit (GPU) accelerated simulations of first principles electronic structure calculations. The FFT, which is the most time-consuming part, is about 10 times accelerated. As the result, the total computation time of a first principles calculation is reduced to 15 percent of that of the CPU.
Heating electrons with ion irradiation: A first-principles approach
International Nuclear Information System (INIS)
Pruneda, J.M.; Sanchez-Portal, D.; Arnau, A.; Juaristi, J.I.; Artacho, E.
2009-01-01
Using time-dependent density functional theory we calculate from first-principles the rate of energy transfer from a moving charged particle to the electrons in an insulating material. The behavior of the electronic stopping power in LiF (a wide band gap insulator) versus projectile velocity displays an effective threshold velocity of 8.2 Bohr/asec for the proton, consistent with recent experimental observations. The calculated proton/antiproton stopping power ratio is 2.4 at velocities slightly above the threshold (16.5 Bohr/asec) as compared to the experimental value of 2.1. The approximations introduced in this new non-perturbative methodology are discussed, and results on the velocity dependence of the stopping power, the locality of the energy transfer, and other characteristics of the host material are presented.
Electronic Stopping Power in LiF from First Principles
International Nuclear Information System (INIS)
Pruneda, J. M.; Sanchez-Portal, D.; Arnau, A.; Juaristi, J. I.; Artacho, Emilio
2007-01-01
Using time-dependent density-functional theory we calculate from first principles the rate of energy transfer from a moving proton or antiproton to the electrons of an insulating material, LiF. The behavior of the electronic stopping power versus projectile velocity displays an effective threshold velocity of ∼0.2 a.u. for the proton, consistent with recent experimental observations, and also for the antiproton. The calculated proton/antiproton stopping-power ratio is ∼2.4 at velocities slightly above the threshold (v∼0.4 a.u.), as compared to the experimental value of 2.1. The projectile energy loss mechanism is observed to be extremely local
Point defects in thorium nitride: 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 (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas (Argentina); Llois, A.M. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas (Argentina); Mosca, H.O. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM-CNEA (Argentina)
2016-11-15
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.
First-principles study of point defects in thorium carbide
International Nuclear Information System (INIS)
Pérez Daroca, D.; Jaroszewicz, S.; Llois, A.M.; Mosca, H.O.
2014-01-01
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
Point defects in thorium nitride: A first-principles study
International Nuclear Information System (INIS)
Pérez Daroca, D.; Llois, A.M.; Mosca, H.O.
2016-01-01
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.
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.
Quantal density functional theory
Sahni, Viraht
2016-01-01
This book deals with quantal density functional theory (QDFT) which is a time-dependent local effective potential theory of the electronic structure of matter. The treated time-independent QDFT constitutes a special case. In the 2nd edition, the theory is extended to include the presence of external magnetostatic fields. The theory is a description of matter based on the ‘quantal Newtonian’ first and second laws which is in terms of “classical” fields that pervade all space, and their quantal sources. The fields, which are explicitly defined, are separately representative of electron correlations due to the Pauli exclusion principle, Coulomb repulsion, correlation-kinetic, correlation-current-density, and correlation-magnetic effects. The book further describes Schrödinger theory from the new physical perspective of fields and quantal sources. It also describes traditional Hohenberg-Kohn-Sham DFT, and explains via QDFT the physics underlying the various energy functionals and functional derivatives o...
Thermodynamic properties of Mg2Si and Mg2Ge investigated by first principles method
International Nuclear Information System (INIS)
Wang, Hanfu; Jin, Hao; Chu, Weiguo; Guo, Yanjun
2010-01-01
The lattice dynamics and thermodynamic properties of Mg 2 Si and Mg 2 Ge are studied based on the first principles calculations. We obtain the phonon dispersion curves and phonon density of states spectra using the density functional perturbation theory with local density approximations. By employing the quasi-harmonic approximation, we calculate the temperature dependent Helmholtz free energy, bulk modulus, thermal expansion coefficient, specific heat, Debye temperature and overall Grueneisen coefficient. The results are in good agreement with available experimental data and previous theoretical studies. The thermal conductivities of both compounds are then estimated with the Slack's equation. By carefully choosing input parameters, especially the acoustic Debye temperature, we find that the calculated thermal conductivities agree fairly well with the experimental values above 80 K for both compounds. This demonstrates that the lattice thermal conductivity of simple cubic semiconductors may be estimated with satisfactory accuracy by combining the Slack's equation with the necessary thermodynamics parameters derived completely from the first principles calculations.
First-principles calculations of mobility
Krishnaswamy, Karthik
First-principles calculations can be a powerful predictive tool for studying, modeling and understanding the fundamental scattering mechanisms impacting carrier transport in materials. In the past, calculations have provided important qualitative insights, but numerical accuracy has been limited due to computational challenges. In this talk, we will discuss some of the challenges involved in calculating electron-phonon scattering and carrier mobility, and outline approaches to overcome them. Topics will include the limitations of models for electron-phonon interaction, the importance of grid sampling, and the use of Gaussian smearing to replace energy-conserving delta functions. Using prototypical examples of oxides that are of technological importance-SrTiO3, BaSnO3, Ga2O3, and WO3-we will demonstrate computational approaches to overcome these challenges and improve the accuracy. One approach that leads to a distinct improvement in the accuracy is the use of analytic functions for the band dispersion, which allows for an exact solution of the energy-conserving delta function. For select cases, we also discuss direct quantitative comparisons with experimental results. The computational approaches and methodologies discussed in the talk are general and applicable to other materials, and greatly improve the numerical accuracy of the calculated transport properties, such as carrier mobility, conductivity and Seebeck coefficient. This work was performed in collaboration with B. Himmetoglu, Y. Kang, W. Wang, A. Janotti and C. G. Van de Walle, and supported by the LEAST Center, the ONR EXEDE MURI, and NSF.
Electronic structure and ionicity of actinide oxides from first principles
DEFF Research Database (Denmark)
Petit, Leon; Svane, Axel; Szotek, Z.
2010-01-01
The ground-state electronic structures of the actinide oxides AO, A2O3, and AO2 (A=U, Np, Pu, Am, Cm, Bk, and Cf) are determined from first-principles calculations, using the self-interaction corrected local spin-density approximation. Emphasis is put on the degree of f-electron localization, whi...
First-principle optimal local pseudopotentials construction via optimized effective potential method
International Nuclear Information System (INIS)
Mi, Wenhui; Zhang, Shoutao; Wang, Yanchao; Ma, Yanming; Miao, Maosheng
2016-01-01
The local pseudopotential (LPP) is an important component of orbital-free density functional theory, a promising large-scale simulation method that can maintain information on a material’s electron state. The LPP is usually extracted from solid-state density functional theory calculations, thereby it is difficult to assess its transferability to cases involving very different chemical environments. Here, we reveal a fundamental relation between the first-principles norm-conserving pseudopotential (NCPP) and the LPP. On the basis of this relationship, we demonstrate that the LPP can be constructed optimally from the NCPP for a large number of elements using the optimized effective potential method. Specially, our method provides a unified scheme for constructing and assessing the LPP within the framework of first-principles pseudopotentials. Our practice reveals that the existence of a valid LPP with high transferability may strongly depend on the element.
First-principles calculation of the magnetic properties of paramagnetic fcc iron
International Nuclear Information System (INIS)
Johnson, D.D.; Gyorffy, B.L.; Pinski, F.J.; Staunton, J.; Stocks, G.M.
1985-01-01
Using the disordered local moment picture of itinerant magnetism, we present calculations of the temperature and volume dependence of the magnetic moment and spin-spin correlations for fcc Fe in the paramagnetic state. These calculations are based on the parameter-free, first principles approach of local spin density functional theory and the coherent potential approximation is used to treat the disorder associated with the random orientation of the local moments
Shugani, Mani; Aynyas, Mahendra; Sanyal, S. P.
2018-05-01
We present a structural, Electronic and Fermi surface properties of Aluminum Praseodymium (AlPr) using First-principles density functional calculation by using full potential linearized augmented plane wave (FP-LAPW) method within generalized gradient approximation (GGA). The ground state properties along with electronic and Fermi surface properties are studied. It is found that AlPr is metallic and the bonding between Al and Pr is covalent.
Anomalous doping effect in black phosphorene from first-principles calculations
Yu, Weiyang; Zhu, Zhili; Niu, Chun-Yao; Li, Chong; Cho, Jun-Hyung; Jia, Yu
2014-01-01
Using first-principles density functional theory calculations, we investigate the geometries, electronic structures, and thermodynamic stabilities of substitutionally doped phosphorene sheets with group III, IV, V, and VI elements. We find that the electronic properties of phosphorene are drastically modified by the number of valence electrons in dopant atoms. The dopants with even number of valence electrons enable the doped phosphorenes to have a metallic feature, while the dopants with odd...
Phases of Ca from first principles
International Nuclear Information System (INIS)
Qiu, S L; Marcus, P M
2009-01-01
Structures and properties of many of the phases of Ca under pressure are calculated from first principles by a systematic procedure that minimizes total energy E with respect to structure under the constraint of constant volume V. The minima of E are followed on successive sweeps of lattice parameters for 11 of 14 Bravais symmetries for one-atom-per-cell structures. The structures include the four orthorhombic phases. Also included are the hexagonal close-packed and cubic diamond phases with two atoms per primitive cell. No uniquely orthorhombic phases are found; all one-atom orthorhombic phases over a mega-bar pressure range are identical to higher-symmetry phases. The simple cubic phase is shown to be stable where it is the ground state. The number of distinct one-atom phases reduces to five plus the two two-atom phases. For each of these phases the Gibbs free energy at pressure p, G(p), is calculated for a non-vibrating lattice; the functions G(p) give the ground state at each p, the relative stabilities of all phases and the thermodynamic phase transition pressures for all phase transitions over a several-megabar range.
DEFF Research Database (Denmark)
Gunst, Tue; Brandbyge, Mads; Palsgaard, Mattias Lau Nøhr
2017-01-01
is in both methods calculated in a post-processing step to a self consistent DFT calculation. The first method is based on first order perturbation theory in the EPC self-energy within the Lowest Order Expansion (LOE) approximation. The method requires calculation of the first-principles EPC in the device......We present two different methods which both enable large-scale first-principles device simulations including electron-phonon coupling (EPC). The methods are based on Density Functional Theory and Nonequilibrium Greens Functions (DFT- NEGF) calculations of electron transport. The inelastic current...
ShunLi Shang; Louis G. Hector Jr.; Paul Saxe; Zi-Kui Liu; Robert J. Moon; Pablo D. Zavattieri
2014-01-01
Anisotropy and temperature dependence of structural, thermodynamic and elastic properties of crystalline cellulose Iβ were computed with first-principles density functional theory (DFT) and a semi-empirical correction for van der Waals interactions. Specifically, we report the computed temperature variation (up to 500...
Generalization of first-principles thermodynamic model: Application to hexagonal close-packed ε-Fe3N
DEFF Research Database (Denmark)
Bakkedal, Morten B.; Shang, Shu- Li; Liu, Zi-Kui
2016-01-01
A complete first-principles thermodynamic model was developed and applied to hexagonal close-packed structure ε-Fe3N. The electronic structure was calculated using density functional theory and the quasiharmonic phonon approximation to determine macroscopic thermodynamic properties at finite...
DEFF Research Database (Denmark)
Mattsson, T.R.; Wahnström, G.; Bengtsson, L.
1997-01-01
First-principles density-functional calculations of hydrogen adsorption on the Ni (001) surface have been performed in order to get a better understanding of adsorption and diffusion of hydrogen on metal surfaces. We find good agreement with experiments for the adsorption energy, binding distance...
International Nuclear Information System (INIS)
Szasz, L.; Berrios-Pagan, I.; McGinn, G.
1975-01-01
A new Density-Functional formula is constructed for atoms. The kinetic energy of the electron is divided into two parts: the kinetic self-energy and the orthogonalization energy. Calculations were made for the total energies of neutral atoms, positive ions and for the He isoelectronic series. For neutral atoms the results match the Hartree-Fock energies within 1% for atoms with N 36 the results generally match the HF energies within 0.1%. For positive ions the results are fair; for the molecular applications a simplified model is developed in which the kinetic energy consists of the Weizsaecker term plus the Fermi energy reduced by a continuous function. (orig.) [de
First-principle calculations of the structural, electronic ...
Indian Academy of Sciences (India)
First-principle calculations were performed to study the structural, electronic, thermodynamic and thermal properties of ... functional theory (DFT) combined with the quasi-harmonic .... is consistent with Vegard's law which assumes that the lat- tice constant varies .... reflects a charge-transfer effect which is due to the different.
Surface regulated arsenenes as Dirac materials: From density functional calculations
International Nuclear Information System (INIS)
Yuan, Junhui; Xie, Qingxing; Yu, Niannian; Wang, Jiafu
2017-01-01
Highlights: • The presence of Dirac cones in chemically decorated buckled arsenene AsX (X = CN, NC, NCO, NCS, and NCSe) has been revealed. • First-principles calculations show that all these chemically decorated arsenenes are kinetically stable in defending thermal fluctuations in room temperature. - Abstract: Using first principle calculations based on density functional theory (DFT), we have systematically investigated the structure stability and electronic properties of chemically decorated arsenenes, AsX (X = CN, NC, NCO, NCS and NCSe). Phonon dispersion and formation energy analysis reveal that all the five chemically decorated buckled arsenenes are energetically favorable and could be synthesized. Our study shows that wide-bandgap arsenene would turn into Dirac materials when functionalized by -X (X = CN, NC, NCO, NCS and NCSe) groups, rendering new promises in next generation high-performance electronic devices.
First principles molecular dynamics without self-consistent field optimization
International Nuclear Information System (INIS)
Souvatzis, Petros; Niklasson, Anders M. N.
2014-01-01
We present a first principles molecular dynamics approach that is based on time-reversible extended Lagrangian Born-Oppenheimer molecular dynamics [A. M. N. Niklasson, Phys. Rev. Lett. 100, 123004 (2008)] in the limit of vanishing self-consistent field optimization. The optimization-free dynamics keeps the computational cost to a minimum and typically provides molecular trajectories that closely follow the exact Born-Oppenheimer potential energy surface. Only one single diagonalization and Hamiltonian (or Fockian) construction are required in each integration time step. The proposed dynamics is derived for a general free-energy potential surface valid at finite electronic temperatures within hybrid density functional theory. Even in the event of irregular functional behavior that may cause a dynamical instability, the optimization-free limit represents a natural starting guess for force calculations that may require a more elaborate iterative electronic ground state optimization. Our optimization-free dynamics thus represents a flexible theoretical framework for a broad and general class of ab initio molecular dynamics simulations
Elastic properties of cubic perovskite BaRuO{sub 3} from first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Han Deming; Liu Xiaojuan; Lv Shuhui; Li Hongping [State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Meng Jian, E-mail: jmeng@ciac.jl.c [State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China)
2010-08-01
We present first-principles investigations on the structural and elastic properties of the cubic perovskite BaRuO{sub 3} using density-functional theory within both local density approximation (LDA) and generalized gradient approximation (GGA). Basic physical properties, such as lattice constant, shear modulus, elastic constants (C{sub ij}) are calculated. The calculated energy band structures show that the cubic perovskite BaRuO{sub 3} is metallic. We have also predicted the Young's modulus (Y), Poisson's ratio ({upsilon}), and Anisotropy factor (A).
First-principles investigation of mechanical properties of silicene, germanene and stanene
Mortazavi, Bohayra; Rahaman, Obaidur; Makaremi, Meysam; Dianat, Arezoo; Cuniberti, Gianaurelio; Rabczuk, Timon
2017-03-01
Two-dimensional allotropes of group-IV substrates including silicene, germanene and stanene have recently attracted considerable attention in nanodevice fabrication industry. These materials involving the buckled structure have been experimentally fabricated lately. In this study, first-principles density functional theory calculations were utilized to investigate the mechanical properties of single-layer and free-standing silicene, germanene and stanene. Uniaxial tensile and compressive simulations were carried out to probe and compare stress-strain properties; such as the Young's modulus, Poisson's ratio and ultimate strength. We evaluated the chirality effect on the mechanical response and bond structure of the 2D substrates. Our first-principles simulations suggest that in all studied samples application of uniaxial loading can alter the electronic nature of the buckled structures into the metallic character. Our investigation provides a general but also useful viewpoint with respect to the mechanical properties of silicene, germanene and stanene.
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.
Thermodynamics of the hexagonal close-packed iron-nitrogen system from first-principles
DEFF Research Database (Denmark)
Bakkedal, Morten Bjørn
to hexagonal systems and a numerically tractable extended equation of state is developed to describe thermody-namic equilibrium properties at finite temperature.The model is applied to ε-Fe3N specifically. Through the versatility of the model, equi-librium lattice parameters, the bulk modulus, and the thermal......First-principles thermodynamic models are developed for the hexagonal close-packed ε-Fe-N system. The system can be considered as a hexagonal close-packed host lattice of iron atoms and with the nitrogen atoms residing on a sublattice formed by the octahedral interstices. The iron host lattice...... is assumed fixed.The models are developed entirely from first-principles calculations based on fundamen-tal quantum mechanical calculation through the density functional theory approach with the atomic numbers and crystal structures as the only input parameters. A complete thermody-namic description should...
Analytic representation for first-principles pseudopotentials
International Nuclear Information System (INIS)
Lam, P.K.; Cohen, M.L.; Zunger, A.
1980-01-01
The first-principles pseudopotentials developed by Zunger and Cohen are fit with a simple analytic form chosen to model the main physical properties of the potentials. The fitting parameters for the first three rows of the Periodic Table are presented, and the quality of the fit is discussed. The parameters reflect chemical trends of the elements. We find that a minimum of three parameters is required to reproduce the regularities of the Periodic Table. Application of these analytic potentials is also discussed
First principles studies of complex oxide surfaces and interfaces
International Nuclear Information System (INIS)
Noguera, Claudine; Finocchi, Fabio; Goniakowski, Jacek
2004-01-01
Oxides enter our everyday life and exhibit an impressive variety of physical and chemical properties. The understanding of their behaviour, which is often determined by the electronic and atomic structures of their surfaces and interfaces, is a key question in many fields, such as geology, environmental chemistry, catalysis, thermal coatings, microelectronics, and bioengineering. In the last decade, first principles methods, mainly those based on the density functional theory, have been frequently applied to study complex oxide surfaces and interfaces, complementing the experimental observations. In this work, we discuss some of these contributions, with emphasis on several issues that are especially important when dealing with oxides: the local electronic structure at interfaces, and its connection with chemical reactivity; the charge redistribution and the bonding variations, in relation to screening properties; and the possibility of bridging the gap between model and real systems by taking into account the chemical environments and the effect of finite temperatures, and by performing simulations on systems of an adequate (large) size
Defect ordering in aliovalently doped cubic zirconia from first principles
International Nuclear Information System (INIS)
Bogicevic, A.; Wolverton, C.; Crosbie, G.M.; Stechel, E.B.
2001-01-01
Defect ordering in aliovalently doped cubic-stabilized zirconia is studied using gradient corrected density-functional calculations. Intra- and intersublattice ordering interactions are investigated for both cation (Zr and dopant ions) and anion (oxygen ions and vacancies) species. For yttria-stabilized zirconia, the crystal structure of the experimentally identified, ordered compound δ-Zr 3 Y 4 O 12 is established, and we predict metastable zirconia-rich ordered phases. Anion vacancies repel each other at short separations, but show an energetic tendency to align as third-nearest neighbors along directions. Calculations with divalent (Be, Mg, Ca, Sr, Ba) and trivalent (Y, Sc, B, Al, Ga, In) oxides show that anion vacancies prefer to be close to the smaller of the cations (Zr or dopant ion). When the dopant cation is close in size to Zr, the vacancies show no particular preference, and are thus less prone to be bound preferentially to any particular cation type when the vacancies traverse such oxides. This ordering tendency offers insight into the observed high conductivity of Y 2 O 3 - and Sc 2 O 3 -stabilized zirconia, as well as recent results using, e.g., lanthanide oxides. The calculations point to In 2 O 3 as a particularly promising stabilizer for high ionic conductivity. Thus we are able to directly link (thermodynamic) defect ordering to (kinetic) ionic conductivity in cubic-stabilized zirconia using first-principles atomistic calculations
beta-sheet preferences from first principles
DEFF Research Database (Denmark)
Rossmeisl, Jan; Bækgaard, Iben Sig Buur; Gregersen, Misha Marie
2003-01-01
The natural amino acids have different preferences of occurring in specific types of secondary protein structure. Simulations are performed on periodic model â-sheets of 14 different amino acids, at the level of density functional theory, employing the generalized gradient approximation. We find ...
A first-principle for the nervous system
Vadakkan, Kunjumon
2016-01-01
Higher brain functions such as perception and memory are first-person internal sensations whose mechanisms can have options to concurrently activate motor neurons for behavioral action. By setting up all the required constraints using available information from different levels, a theoretical examination from a first-person frame of reference led to the derivation of a first-principle of the structure-function units. These units operate in synchrony with the synaptically-connected neural circ...
Hierarchical Coupling of First-Principles Molecular Dynamics with Advanced Sampling Methods.
Sevgen, Emre; Giberti, Federico; Sidky, Hythem; Whitmer, Jonathan K; Galli, Giulia; Gygi, Francois; de Pablo, Juan J
2018-05-14
We present a seamless coupling of a suite of codes designed to perform advanced sampling simulations, with a first-principles molecular dynamics (MD) engine. As an illustrative example, we discuss results for the free energy and potential surfaces of the alanine dipeptide obtained using both local and hybrid density functionals (DFT), and we compare them with those of a widely used classical force field, Amber99sb. In our calculations, the efficiency of first-principles MD using hybrid functionals is augmented by hierarchical sampling, where hybrid free energy calculations are initiated using estimates obtained with local functionals. We find that the free energy surfaces obtained from classical and first-principles calculations differ. Compared to DFT results, the classical force field overestimates the internal energy contribution of high free energy states, and it underestimates the entropic contribution along the entire free energy profile. Using the string method, we illustrate how these differences lead to different transition pathways connecting the metastable minima of the alanine dipeptide. In larger peptides, those differences would lead to qualitatively different results for the equilibrium structure and conformation of these molecules.
First-principles study on the creation of holes in high Tc cuprates
International Nuclear Information System (INIS)
Ambrosch-Draxl, C.; Sherman, E.Ya.; Auer, H.; Thonhauser, T.
2004-01-01
We investigate the charge redistribution in high T c cuprates as a function of pressure, composition, and doping. To this extent we have performed first-principles calculations based on density functional theory for several representatives of the Hg based cuprates. In particular, we focus on the creation of holes in the copper-oxygen planes. Conclusions are drawn about the similarities and differences between the three parameters influencing the superconducting transition temperature. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Energy Technology Data Exchange (ETDEWEB)
Zhao, P., E-mail: ss_zhaop@ujn.edu.c [School of Science, University of Jinan, Jinan 250022 (China); Liu, D.S. [School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China); Department of Physics, Jining University, Qufu 273155 (China); Wang, P.J.; Zhang, Z. [School of Science, University of Jinan, Jinan 250022 (China); Fang, C.F.; Ji, G.M. [School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China)
2011-02-15
By applying non-equilibrium Green's function (NEGF) formalism combined with first-principles density functional theory (DFT), we have investigated the electronic transport properties of the anthraquinone-based molecular switch. The molecule that comprises the switch can be converted between the hydroquinone (HQ) and anthraquinone (AQ) forms via redox reactions. The transmission spectra of these two forms are remarkably distinctive. Our results show that the current through the HQ form is significantly larger than that through the AQ form, which suggests that this system has attractive potential application in future molecular switch technology.
International Nuclear Information System (INIS)
Zhao, P.; Liu, D.S.; Wang, P.J.; Zhang, Z.; Fang, C.F.; Ji, G.M.
2011-01-01
By applying non-equilibrium Green's function (NEGF) formalism combined with first-principles density functional theory (DFT), we have investigated the electronic transport properties of the anthraquinone-based molecular switch. The molecule that comprises the switch can be converted between the hydroquinone (HQ) and anthraquinone (AQ) forms via redox reactions. The transmission spectra of these two forms are remarkably distinctive. Our results show that the current through the HQ form is significantly larger than that through the AQ form, which suggests that this system has attractive potential application in future molecular switch technology.
First-principles study of the diffusion mechanisms of the self-interstitial in germanium
International Nuclear Information System (INIS)
Carvalho, A; Jones, R; Janke, C; Goss, J P; Briddon, P R; Oeberg, S
2008-01-01
The self-interstitial in germanium can assume multiple configurations depending on the temperature and charge state. Here, we employ a first-principles density functional method to investigate the diffusion mechanisms of this defect. The energy barriers associated with the transformation between different structures are determined by the climbing nudged elastic band method, as a function of the charge state. The relation between the thermodynamic properties of the self-interstitial and the temperature evolution of electron radiation damage in germanium are discussed
TOPICAL REVIEW: First principles studies of multiferroic materials
Picozzi, Silvia; Ederer, Claude
2009-07-01
Multiferroics, materials where spontaneous long-range magnetic and dipolar orders coexist, represent an attractive class of compounds, which combine rich and fascinating fundamental physics with a technologically appealing potential for applications in the general area of spintronics. Ab initio calculations have significantly contributed to recent progress in this area, by elucidating different mechanisms for multiferroicity and providing essential information on various compounds where these effects are manifestly at play. In particular, here we present examples of density-functional theory investigations for two main classes of materials: (a) multiferroics where ferroelectricity is driven by hybridization or purely structural effects, with BiFeO3 as the prototype material, and (b) multiferroics where ferroelectricity is driven by correlation effects and is strongly linked to electronic degrees of freedom such as spin-, charge-, or orbital-ordering, with rare-earth manganites as prototypes. As for the first class of multiferroics, first principles calculations are shown to provide an accurate qualitative and quantitative description of the physics in BiFeO3, ranging from the prediction of large ferroelectric polarization and weak ferromagnetism, over the effect of epitaxial strain, to the identification of possible scenarios for coupling between ferroelectric and magnetic order. For the second class of multiferroics, ab initio calculations have shown that, in those cases where spin-ordering breaks inversion symmetry (e.g. in antiferromagnetic E-type HoMnO3), the magnetically induced ferroelectric polarization can be as large as a few µC cm-2. The examples presented point the way to several possible avenues for future research: on the technological side, first principles simulations can contribute to a rational materials design, aimed at identifying spintronic materials that exhibit ferromagnetism and ferroelectricity at or above room temperature. On the
First principles study of AlBi
International Nuclear Information System (INIS)
Amrani, B.; Achour, H.; Louhibi, S.; Tebboune, A.; Sekkal, N.
2008-05-01
Using the first principles method of the full potential linear augmented plane waves (FPLAPW), the structural and the electronic properties of AlBi are investigated. It is found that this compound has a small and direct semiconducting gap at Γ. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of the volume, the bulk modulus, the variation of the thermal expansion α, as well as the Debye temperature θ D and the heat capacity C v are successfully obtained in the whole range from 0 to 30 GPa and temperature range from 0 to 1200 K. (author)
First-principles molecular dynamics for metals
International Nuclear Information System (INIS)
Fernando, G.W.; Qian, G.; Weinert, M.; Davenport, J.W.
1989-01-01
A Car-Parrinello-type first-principles molecular-dynamics approach capable of treating the partial occupancy of electronic states that occurs at the Fermi level in a metal is presented. The algorithms used to study metals are both simple and computationally efficient. We also discuss the connection between ordinary electronic-structure calculations and molecular-dynamics simulations as well as the role of Brillouin-zone sampling. This extension should be useful not only for metallic solids but also for solids that become metals in their liquid and/or amorphous phases
Density functionals from deep learning
McMahon, Jeffrey M.
2016-01-01
Density-functional theory is a formally exact description of a many-body quantum system in terms of its density; in practice, however, approximations to the universal density functional are required. In this work, a model based on deep learning is developed to approximate this functional. Deep learning allows computational models that are capable of naturally discovering intricate structure in large and/or high-dimensional data sets, with multiple levels of abstraction. As no assumptions are ...
Electrical properties of improper ferroelectrics from first principles
Stengel, Massimiliano; Fennie, Craig J.; Ghosez, Philippe
2012-09-01
We study the interplay of structural and polar distortions in hexagonal YMnO3 and short-period PbTiO3/SrTiO3 (PTO/STO) superlattices by means of first-principles calculations at constrained electric displacement field D. We find that in YMnO3 the tilts of the oxygen polyhedra produce a robustly polar ground state, which persists at any choice of the electrical boundary conditions. Conversely, in PTO/STO the antiferrodistortive instabilities alone do not break inversion symmetry, and open-circuit boundary conditions restore a nonpolar state. We suggest that this qualitative difference naturally provides a route to rationalizing the concept of “improper ferroelectricity” from the point of view of first-principles theory. We discuss the implications of our arguments for the design of novel multiferroic materials with enhanced functionalities and for the symmetry analysis of the phase transitions.
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.
International Nuclear Information System (INIS)
Zhou, Bi-Cheng; Shang, Shun-Li; Wang, Yi; Liu, Zi-Kui
2016-01-01
First-principles calculations based on density functional theory have been used to calculate the temperature-dependent dilute tracer diffusion coefficients for 47 substitutional alloying elements in hexagonal closed packed (hcp) Mg by combining transition state theory and an 8-frequency model. The minimum energy pathways and the saddle point configurations during solute migration are calculated with the climbing image nudged elastic band method. Vibrational properties are obtained using the quasi-harmonic Debye model with inputs from first-principles calculations. An improved generalized gradient approximation of PBEsol is used in the present first-principles calculations, which is able to well describe both vacancy formation energies and vibrational properties. It is found that the solute diffusion coefficients in hcp Mg are roughly inversely proportional to the bulk modulus of the dilute alloys, which reflects the solutes' bonding to Mg. Transition metal elements with d electrons show strong interactions with Mg and have large diffusion activation energies. Correlation effects are not negligible for solutes Ca, Na, Sr, Se, Te, and Y, in which the direct solute migration barriers are much smaller than the solvent (Mg) migration barriers. Calculated diffusion coefficients are in remarkable agreement with available experimental data in the literature.
Liquid Water from First Principles: Validation of Different Sampling Approaches
Energy Technology Data Exchange (ETDEWEB)
Mundy, C J; Kuo, W; Siepmann, J; McGrath, M J; Vondevondele, J; Sprik, M; Hutter, J; Parrinello, M; Mohamed, F; Krack, M; Chen, B; Klein, M
2004-05-20
A series of first principles molecular dynamics and Monte Carlo simulations were carried out for liquid water to assess the validity and reproducibility of different sampling approaches. These simulations include Car-Parrinello molecular dynamics simulations using the program CPMD with different values of the fictitious electron mass in the microcanonical and canonical ensembles, Born-Oppenheimer molecular dynamics using the programs CPMD and CP2K in the microcanonical ensemble, and Metropolis Monte Carlo using CP2K in the canonical ensemble. With the exception of one simulation for 128 water molecules, all other simulations were carried out for systems consisting of 64 molecules. It is found that the structural and thermodynamic properties of these simulations are in excellent agreement with each other as long as adiabatic sampling is maintained in the Car-Parrinello molecular dynamics simulations either by choosing a sufficiently small fictitious mass in the microcanonical ensemble or by Nos{acute e}-Hoover thermostats in the canonical ensemble. Using the Becke-Lee-Yang-Parr exchange and correlation energy functionals and norm-conserving Troullier-Martins or Goedecker-Teter-Hutter pseudopotentials, simulations at a fixed density of 1.0 g/cm{sup 3} and a temperature close to 315 K yield a height of the first peak in the oxygen-oxygen radial distribution function of about 3.0, a classical constant-volume heat capacity of about 70 J K{sup -1} mol{sup -1}, and a self-diffusion constant of about 0.1 Angstroms{sup 2}/ps.
Spectroscopy of organic semiconductors from first principles
Sharifzadeh, Sahar; Biller, Ariel; Kronik, Leeor; Neaton, Jeffery
2011-03-01
Advances in organic optoelectronic materials rely on an accurate understanding their spectroscopy, motivating the development of predictive theoretical methods that accurately describe the excited states of organic semiconductors. In this work, we use density functional theory and many-body perturbation theory (GW/BSE) to compute the electronic and optical properties of two well-studied organic semiconductors, pentacene and PTCDA. We carefully compare our calculations of the bulk density of states with available photoemission spectra, accounting for the role of finite temperature and surface effects in experiment, and examining the influence of our main approximations -- e.g. the GW starting point and the application of the generalized plasmon-pole model -- on the predicted electronic structure. Moreover, our predictions for the nature of the exciton and its binding energy are discussed and compared against optical absorption data. We acknowledge DOE, NSF, and BASF for financial support and NERSC for computational resources.
Stability, electronic and thermodynamic properties of aluminene from first-principles calculations
International Nuclear Information System (INIS)
Yuan, Junhui; Yu, Niannian; Xue, Kanhao; Miao, Xiangshui
2017-01-01
Highlights: • We have predicted two NEW stable phases of atomic layer aluminum, buckled and 8-Pmmn aluminene. • We have revealed the electronic structures and bonding characteristics of aluminene. • Thermodynamic properties of aluminene were investigated based on phonon properties. - Abstract: Using first-principles calculations based on density functional theory (DFT), we have investigated the structure stability and electronic properties of both buckled and 8-Pmmn phase aluminene. Phonon dispersion analysis reveals that the buckled and 8-Pmmn aluminene are dynamically stable. The band structure shows that both the buckled and 8-Pmmn aluminene exhibit metallic behavior. Finally, the thermodynamic properties are investigated based on phonon properties.
First principles calculation on the adsorption of water on lithium-montmorillonite (Li-MMT)
International Nuclear Information System (INIS)
Wungu, Triati Dewi Kencana; Agusta, Mohammad Kemal; Saputro, Adhitya Gandaryus; Kasai, Hideaki; Dipojono, Hermawan Kresno
2012-01-01
The interaction of water molecules and lithium-montmorillonite (Li-MMT) is theoretically investigated using density functional theory (DFT) based first principles calculation. The mechanism of water adsorption at two different water concentrations on Li-MMT as well as their structural and electronic properties are investigated. It is found that the adsorption stability in Li-MMT is higher in higher water concentration. It is also found that an adsorbed water molecule on Li-MMT causes the Li to protrude from the MMT surface, so it is expected that Li may be mobile on H 2 O/Li-MMT.
First principles calculation on the adsorption of water on lithium-montmorillonite (Li-MMT).
Wungu, Triati Dewi Kencana; Agusta, Mohammad Kemal; Saputro, Adhitya Gandaryus; Dipojono, Hermawan Kresno; Kasai, Hideaki
2012-11-28
The interaction of water molecules and lithium-montmorillonite (Li-MMT) is theoretically investigated using density functional theory (DFT) based first principles calculation. The mechanism of water adsorption at two different water concentrations on Li-MMT as well as their structural and electronic properties are investigated. It is found that the adsorption stability in Li-MMT is higher in higher water concentration. It is also found that an adsorbed water molecule on Li-MMT causes the Li to protrude from the MMT surface, so it is expected that Li may be mobile on H(2)O/Li-MMT.
Stability, electronic and thermodynamic properties of aluminene from first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Yuan, Junhui [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Yu, Niannian [School of Science, Wuhan University of Technology, Wuhan, Hubei 430070 (China); Xue, Kanhao, E-mail: xkh@hust.edu.cn [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Miao, Xiangshui [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China)
2017-07-01
Highlights: • We have predicted two NEW stable phases of atomic layer aluminum, buckled and 8-Pmmn aluminene. • We have revealed the electronic structures and bonding characteristics of aluminene. • Thermodynamic properties of aluminene were investigated based on phonon properties. - Abstract: Using first-principles calculations based on density functional theory (DFT), we have investigated the structure stability and electronic properties of both buckled and 8-Pmmn phase aluminene. Phonon dispersion analysis reveals that the buckled and 8-Pmmn aluminene are dynamically stable. The band structure shows that both the buckled and 8-Pmmn aluminene exhibit metallic behavior. Finally, the thermodynamic properties are investigated based on phonon properties.
First-Principles Vibrational Electron Energy Loss Spectroscopy of β -Guanine
Radtke, G.; Taverna, D.; Lazzeri, M.; Balan, E.
2017-07-01
A general approach to model vibrational electron energy loss spectra obtained using an electron beam positioned away from the specimen is presented. The energy-loss probability of the fast electron is evaluated using first-principles quantum mechanical calculations (density functional theory) of the dielectric response of the specimen. The validity of the method is assessed using recently measured anhydrous β -guanine, an important molecular solid used by animals to produce structural colors. The good agreement between theory and experiments lays the basis for a quantitative interpretation of this spectroscopy in complex systems.
First-principle calculation of refractive indices of BAlN and BGaN
Alqatari, Feras; Li, Kuang-Hui; Liu, Kaikai; Li, Xiaohang
2018-01-01
The refractive indices of BAlN and BGaN ternary alloys are being investigated using first-principle calculation. The hybrid density functional theory is applied to determine the refractive indices of different alloys. A peculiar bowing effect in the static refractive indices and crossovers of different refractive index curves are found. We speculate that the explanation to these phenomena lies in the interband transitions of electrons where each band bows at a different rate from the other. An average of these bowing effects may result in the bowing of refractive indices.
International Nuclear Information System (INIS)
Chandel, Surjeet Kumar; Kumar, Arun; Bharti, Ankush; Sharma, Raman
2015-01-01
Using first principles density functional theoretical calculations, the present paper reports a systematic study of phonon dispersion curves in pristine carbon (CNT) and silicon nanotubes (SiNT) having chirality (6,6) in the armchair configuration. Some of the phonon modes are found to have negative frequencies which leads to instability of the systems under study. The number of phonon branches has been found to be thrice as much as the number of atoms. The frequency of the higher optical bands varies from 1690 to 1957 cm −1 for CNT(6,6) while it is 596 to 658 cm −1 for SiNT
First principles study of CaTIO3 crystal in paraelectric and ferroelectric phases
International Nuclear Information System (INIS)
Hashemi, H.; Kompany, A.; Hosseini, M.
2005-01-01
Electronic properties of CaTiO 3 crystal in paraelectric and ferroelectric phases have been studied by first principles, using Hohenberg-kohn-sham density functional theory. In paraelectric phase the results show an indirect band gap of about at 2eV at Γ-R direction in the Brillouin zone and a strong hybridization between Ti-3d an O-2P orbital. In ferroelectric phase a direct band gap of about 1 eV is seen at ***Γ point. Up to our knowledge no data has been reported on the ferroelectric phase so far, therefore our results might be useful for the future works
Arif Khalil, R. M.; Ahmad, Javed; Rana, Anwar Manzoor; Bukhari, Syed Hamad; Tufiq Jamil, M.; Tehreem, Tuba; Nissar, Umair
2018-05-01
In this investigation, structural, dynamical and thermal properties of black and blue phosphorene (P) are presented through the first principles calculations based on the density functional theory (DFT). These DFT calculations depict that due to the approximately same values of ground state energy at zero Kelvin and Helmholtz free energy at room-temperature, it is expected that both structures can coexist at transition temperature. Lattice dynamics of both phases were investigated by using the finite displacement supercell approach. It is noticed on the basis of harmonic approximation thermodynamic calculations that the blue phase is thermodynamically more stable than the black phase above 155 K.
First-principles studies on the adsorption of molecular oxygen on Ba(110) surface
International Nuclear Information System (INIS)
Li, S.F.; Xue Xinlian; Li Pinglin; Li Xinjian; Jia Yu
2006-01-01
The adsorption of O 2 on Ba(110) surface is studied with first-principles calculations based on density functional theory. Our calculations predict that O 2 may prefer to dissociative adsorption on Ba(110) surface without obvious barrier. Also our results do not support the model of charge transfer from the surface to the molecule as a bond breaking mechanism. Instead, the increasing hybridization between O 2 orbitals and the d states of Ba(110) surface may play an important role in the dissociation adsorption
First-principles theory of inelastic currents in a scanning tunneling microscope
DEFF Research Database (Denmark)
Stokbro, Kurt; Hu, Ben Yu-Kuang; Thirstrup, C.
1998-01-01
A first-principles theory of inelastic tunneling between a model probe tip and an atom adsorbed on a surface is presented, extending the elastic tunneling theory of Tersoff and Hamann. The inelastic current is proportional to the change in the local density of states at the center of the tip due...... to the addition of the adsorbate. We use the theory to investigate the vibrational heating of an adsorbate below a scanning tunneling microscopy tip. We calculate the desorption rate of PI from Si(100)-H(2 X 1) as a function of the sample bias and tunnel current, and find excellent a,agreement with recent...
First principles calculations for interaction of tyrosine with (ZnO)3 cluster
Singh, Satvinder; Singh, Gurinder; Kaura, Aman; Tripathi, S. K.
2018-04-01
First Principles Calculations have been performed to study interactions of Phenol ring of Tyrosine (C6H5OH) with (ZnO)3 atomic cluster. All the calculations have been performed under the Density Functional Theory (DFT) framework. Structural and electronic properties of (ZnO)3/C6H5OH have been studied. Gaussian basis set approach has been adopted for the calculations. A ring type most stable (ZnO)3 atomic cluster has been modeled, analyzed and used for the calculations. The compatibility of the results with previous studies has been presented here.
First-principles calculations of a high-pressure synthesized compound PtC
International Nuclear Information System (INIS)
Li Linyan; Yu Wen; Jin Changqing
2005-01-01
The first-principles density-functional method is used to study the recently high-pressure synthesized compound PtC. It is confirmed by our calculations that platinum carbide has a zinc-blende ground-state phase at zero pressure and that the rock-salt structure is a high-pressure phase. The theoretical transition pressure from zinc-blende to rock-salt structure is determined to be 52 GPa. Furthermore, our calculation shows the possibility that the PtC experimentally synthesized under high pressure conditions might undergo a transition from rock-salt to zinc-blende structure after a pressure quench to ambient conditions
First-principle calculation of refractive indices of BAlN and BGaN
Alqatari, Feras
2018-03-27
The refractive indices of BAlN and BGaN ternary alloys are being investigated using first-principle calculation. The hybrid density functional theory is applied to determine the refractive indices of different alloys. A peculiar bowing effect in the static refractive indices and crossovers of different refractive index curves are found. We speculate that the explanation to these phenomena lies in the interband transitions of electrons where each band bows at a different rate from the other. An average of these bowing effects may result in the bowing of refractive indices.
Ammonia synthesis from first principles calculations
DEFF Research Database (Denmark)
Honkala, Johanna Karoliina; Hellman, Anders; Remediakis, Ioannis
2005-01-01
. When the size distribution of ruthenium particles measured by transmission electron microscopy was used as the [ink between the catalyst material and the theoretical treatment, the calculated rate was within a factor of 3 to 20 of the experimental rate. This offers hope for computer-based methods......The rate of ammonia synthesis over a nanoparticle ruthenium catalyst can be calculated directly on the basis of a quantum chemical treatment of the problem using density functional theory. We compared the results to measured rates over a ruthenium catalyst supported on magnesium aluminum spinet...
A method of orbital analysis for large-scale first-principles simulations
International Nuclear Information System (INIS)
Ohwaki, Tsukuru; Otani, Minoru; Ozaki, Taisuke
2014-01-01
An efficient method of calculating the natural bond orbitals (NBOs) based on a truncation of the entire density matrix of a whole system is presented for large-scale density functional theory calculations. The method recovers an orbital picture for O(N) electronic structure methods which directly evaluate the density matrix without using Kohn-Sham orbitals, thus enabling quantitative analysis of chemical reactions in large-scale systems in the language of localized Lewis-type chemical bonds. With the density matrix calculated by either an exact diagonalization or O(N) method, the computational cost is O(1) for the calculation of NBOs associated with a local region where a chemical reaction takes place. As an illustration of the method, we demonstrate how an electronic structure in a local region of interest can be analyzed by NBOs in a large-scale first-principles molecular dynamics simulation for a liquid electrolyte bulk model (propylene carbonate + LiBF 4 )
Glass polymorphism in amorphous germanium probed by first-principles computer simulations
Mancini, G.; Celino, M.; Iesari, F.; Di Cicco, A.
2016-01-01
The low-density (LDA) to high-density (HDA) transformation in amorphous Ge at high pressure is studied by first-principles molecular dynamics simulations in the framework of density functional theory. Previous experiments are accurately reproduced, including the presence of a well-defined LDA-HDA transition above 8 GPa. The LDA-HDA density increase is found to be about 14%. Pair and bond-angle distributions are obtained in the 0-16 GPa pressure range and allowed us a detailed analysis of the transition. The local fourfold coordination is transformed in an average HDA sixfold coordination associated with different local geometries as confirmed by coordination number analysis and shape of the bond-angle distributions.
Obtaining the electrostatic screening from first principles
International Nuclear Information System (INIS)
Shaviv, N.J.; Shaviv, G.
2003-01-01
We derive the electrostatic screening effect from first principles and show the basic properties of the screening process. We in particular show that under the conditions prevailing in the Sun the number of particles in the Debye sphere is of the order of unity. Consequently; fluctuations play a dominant role in the screening process. The fluctuations lead to an effective time dependent potential. Particles with low kinetic energy lose on the average energy to the plasma and vice versa with high energy particles. We derive general conditions on the screening energy and show under what conditions the Salpeter approximation is obtained. The connection between the screening and relaxation processes in the plasma is exposed
The density functional theory and the charged fluid molecular dynamics
International Nuclear Information System (INIS)
Hansen, J.P.; Zerah, G.
1993-01-01
Car and Parrinello had the idea of combining the density functional theory (Hohenberg, Kohn and Sham) to the 'molecular dynamics' numerical modelling method, in order to simulate metallic or co-valent solids and liquids from the first principles. The objective of this paper is to present a simplified version of this method ab initio, applicable to classical and quantal charged systems. The method is illustrated with recent results on charged colloidal suspensions and highly correlated electron-proton plasmas. 1 fig., 21 refs
Energy Technology Data Exchange (ETDEWEB)
McGrath, M; Siepmann, J I; Kuo, I W; Mundy, C J; VandeVondele, J; Hutter, J; Mohamed, F; Krack, M
2004-12-02
A series of first principles Monte Carlo simulations in the isobaric-isothermal ensemble were carried out for liquid water at ambient conditions (T = 298 K and p = 1 atm). The Becke-Lee-Yang-Parr (BLYP) exchange and correlation energy functionals and norm-conserving Goedecker-Teter-Hutter (GTH) pseudopotentials were employed with the CP2K simulation package to examine systems consisting of 64 water molecules. The fluctuations in the system volume encountered in simulations in the isobaric-isothermal ensemble requires a reconsideration of the suitability of the typical charge density cutoff and the regular grid generation method previously used for the computation of the electrostatic energy in first principles simulations in the microcanonical or canonical ensembles. In particular, it is noted that a much higher cutoff is needed and that the most computationally efficient method of creating grids can result in poor simulations. Analysis of the simulation trajectories using a very large charge density cutoff at 1200 Ry and four different grid generation methods point to a substantially underestimated liquid density of about 0.85 g/cm{sup 3} resulting in a somewhat understructured liquid (with a value of about 2.7 for the height of the first peak in the oxygen/oxygen radial distribution function) for BLYP-GTH water at ambient conditions.
Next generation extended Lagrangian first principles molecular dynamics.
Niklasson, Anders M N
2017-08-07
Extended Lagrangian Born-Oppenheimer molecular dynamics [A. M. N. Niklasson, Phys. Rev. Lett. 100, 123004 (2008)] is formulated for general Hohenberg-Kohn density-functional theory and compared with the extended Lagrangian framework of first principles molecular dynamics by Car and Parrinello [Phys. Rev. Lett. 55, 2471 (1985)]. It is shown how extended Lagrangian Born-Oppenheimer molecular dynamics overcomes several shortcomings of regular, direct Born-Oppenheimer molecular dynamics, while improving or maintaining important features of Car-Parrinello simulations. The accuracy of the electronic degrees of freedom in extended Lagrangian Born-Oppenheimer molecular dynamics, with respect to the exact Born-Oppenheimer solution, is of second-order in the size of the integration time step and of fourth order in the potential energy surface. Improved stability over recent formulations of extended Lagrangian Born-Oppenheimer molecular dynamics is achieved by generalizing the theory to finite temperature ensembles, using fractional occupation numbers in the calculation of the inner-product kernel of the extended harmonic oscillator that appears as a preconditioner in the electronic equations of motion. Material systems that normally exhibit slow self-consistent field convergence can be simulated using integration time steps of the same order as in direct Born-Oppenheimer molecular dynamics, but without the requirement of an iterative, non-linear electronic ground-state optimization prior to the force evaluations and without a systematic drift in the total energy. In combination with proposed low-rank and on the fly updates of the kernel, this formulation provides an efficient and general framework for quantum-based Born-Oppenheimer molecular dynamics simulations.
Kanagaprabha, S.; Rajeswarapalanichamy, R.; Sudhapriyanga, G.; Murugan, A.; Santhosh, M.; Iyakutti, K.
2015-06-01
The structural and mechanical properties of CrH and MnH are investigated using 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. A structural phase transition from NaCl to NiAs phase at a pressure of 76 GPa is predicted for both CrH and MnH.
SYNTHESIS, CHARACTERIZATION AND DENSITY FUNCTIONAL ...
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We synthesized a number of aniline derivatives containing acyl groups to compare their barriers of rotation around ... KEY WORDS: Monoacyl aniline, Synthesis, Density functional theory, Rotation barrier. INTRODUCTION. Developments in ...
First principle study of sodium decorated graphyne
Energy Technology Data Exchange (ETDEWEB)
Sarkar, Utpal, E-mail: utpalchemiitkgp@yahoo.com [Assam University, Silchar (India); Bhattacharya, Barnali [Assam University, Silchar (India); Seriani, Nicola [The Abdus Salam ICTP, Trieste (Italy)
2015-11-05
Highlights: • Presence of Na decreases the stability of the system. • Na-decorated graphyne compounds are metallic and might be used in electronics. • The sodium-adsorbed graphyne can be used as electrodes in Na-ion battery. - Abstract: We present first-principles calculations of the electronic properties of Na-decorated graphyne. This structure of the graphyne family is a direct band gap semiconductor with a band gap of 0.44 eV in absence of sodium, but Na-decorated graphyne compounds are metallic, and can then be employed as carbon-based conductors. Metallization is due to charge donation from sodium to carbon. Pristine graphyne is more stable than Na-decorated graphyne, therefore is seems probable that, if this material should be employed as electrode in Na-ion batteries, it would lead to the formation of metallic sodium rather than well dispersed sodium ions. On the other side, this property might be useful if graphyne is employed in water desalination. Finally, the abrupt change from a semiconducting to a metallic state in presence of a small amount of sodium might be exploited in electronics, e.g. for the production of smooth metal–semiconductor interfaces through spatially selective deposition of sodium.
THERMODYNAMIC MODELING AND FIRST-PRINCIPLES CALCULATIONS
Energy Technology Data Exchange (ETDEWEB)
Turchi, P; Abrikosov, I; Burton, B; Fries, S; Grimvall, G; Kaufman, L; Korzhavyi, P; Manga, R; Ohno, M; Pisch, A; Scott, A; Zhang, W
2005-12-15
The increased application of quantum mechanical-based methodologies to the study of alloy stability has required a re-assessment of the field. The focus is mainly on inorganic materials in the solid state. In a first part, after a brief overview of the so-called ab initio methods with their approximations, constraints, and limitations, recommendations are made for a good usage of first-principles codes with a set of qualifiers. Examples are given to illustrate the power and the limitations of ab initio codes. However, despite the ''success'' of these methodologies, thermodynamics of complex multi-component alloys, as used in engineering applications, requires a more versatile approach presently afforded within CALPHAD. Hence, in a second part, the links that presently exist between ab initio methodologies, experiments, and CALPHAD approach are examined with illustrations. Finally, the issues of dynamical instability and of the role of lattice vibrations that still constitute the subject of ample discussions within the CALPHAD community are revisited in the light of the current knowledge with a set of recommendations.
Safeguards First Principle Initiative (SFPI) Cost Model
International Nuclear Information System (INIS)
Price, Mary Alice
2010-01-01
The Nevada Test Site (NTS) began operating Material Control and Accountability (MC and A) under the Safeguards First Principle Initiative (SFPI), a risk-based and cost-effective program, in December 2006. The NTS SFPI Comprehensive Assessment of Safeguards Systems (COMPASS) Model is made up of specific elements (MC and A plan, graded safeguards, accounting systems, measurements, containment, surveillance, physical inventories, shipper/receiver differences, assessments/performance tests) and various sub-elements, which are each assigned effectiveness and contribution factors that when weighted and rated reflect the health of the MC and A program. The MC and A Cost Model, using an Excel workbook, calculates budget and/or actual costs using these same elements/sub-elements resulting in total costs and effectiveness costs per element/sub-element. These calculations allow management to identify how costs are distributed for each element/sub-element. The Cost Model, as part of the SFPI program review process, enables management to determine if spending is appropriate for each element/sub-element.
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...
Novel Natural Convection Heat Sink Design Concepts From First Principles
2016-06-01
CONVECTION HEAT SINK DESIGN CONCEPTS FROM FIRST PRINCIPLES by Derek E. Fletcher June 2016 Thesis Advisor: Garth Hobson Second Reader...COVERED Master’s Thesis 4. TITLE AND SUBTITLE NOVEL NATURAL CONVECTION HEAT SINK DESIGN CONCEPTS FROM FIRST PRINCIPLES 5. FUNDING NUMBERS 6...CONVECTION HEAT SINK DESIGN CONCEPTS FROM FIRST PRINCIPLES Derek E. Fletcher Lieutenant Commander, United States Navy B.S., Southwestern
JDFTx: Software for joint density-functional theory
Directory of Open Access Journals (Sweden)
Ravishankar Sundararaman
2017-01-01
Full Text Available Density-functional theory (DFT has revolutionized computational prediction of atomic-scale properties from first principles in physics, chemistry and materials science. Continuing development of new methods is necessary for accurate predictions of new classes of materials and properties, and for connecting to nano- and mesoscale properties using coarse-grained theories. JDFTx is a fully-featured open-source electronic DFT software designed specifically to facilitate rapid development of new theories, models and algorithms. Using an algebraic formulation as an abstraction layer, compact C++11 code automatically performs well on diverse hardware including GPUs (Graphics Processing Units. This code hosts the development of joint density-functional theory (JDFT that combines electronic DFT with classical DFT and continuum models of liquids for first-principles calculations of solvated and electrochemical systems. In addition, the modular nature of the code makes it easy to extend and interface with, facilitating the development of multi-scale toolkits that connect to ab initio calculations, e.g. photo-excited carrier dynamics combining electron and phonon calculations with electromagnetic simulations.
First-Principles Investigations on Europium Monoxide
Wang, Hao
2011-05-01
Europium monoxide is both an insulator and a Heisenberg ferromagnet (Tc=69 K). In the present thesis, the author has investigated the electronic structure of different types of EuO by density functional theory. The on-site Coulomb interaction of the localized Eu 4f and 5d electrons, which is wrongly treated in the standard generalized gradient approximation method, is found to be crucial to obtain the correct insulating ground state as observed in experiments. Our results show that the ferromagnetism is stable under pressure, both hydrostatic and uniaxial. For both types of pressure an insulator-metal transition is demonstrated. Moreover, the experimentally observed insulator-metal transition in oxygen deficient and gadolinium-doped EuO is reproduced in our calculations for impurity concentrations of 6.25% and 25%. Furthermore, a 10- layer EuO thin film is theoretically predicted to be an insulator with a narrow band gap of around 0.08 eV, while the Si/EuO interface shows metallic properties with the Si and O 2p as well as Eu 5d bands crossing the Fermi level.
Wave-function functionals for the density
International Nuclear Information System (INIS)
Slamet, Marlina; Pan Xiaoyin; Sahni, Viraht
2011-01-01
We extend the idea of the constrained-search variational method for the construction of wave-function functionals ψ[χ] of functions χ. The search is constrained to those functions χ such that ψ[χ] reproduces the density ρ(r) while simultaneously leading to an upper bound to the energy. The functionals are thereby normalized and automatically satisfy the electron-nucleus coalescence condition. The functionals ψ[χ] are also constructed to satisfy the electron-electron coalescence condition. The method is applied to the ground state of the helium atom to construct functionals ψ[χ] that reproduce the density as given by the Kinoshita correlated wave function. The expectation of single-particle operators W=Σ i r i n , n=-2,-1,1,2, W=Σ i δ(r i ) are exact, as must be the case. The expectations of the kinetic energy operator W=-(1/2)Σ i ∇ i 2 , the two-particle operators W=Σ n u n , n=-2,-1,1,2, where u=|r i -r j |, and the energy are accurate. We note that the construction of such functionals ψ[χ] is an application of the Levy-Lieb constrained-search definition of density functional theory. It is thereby possible to rigorously determine which functional ψ[χ] is closer to the true wave function.
Introduction to First-Principles Electronic Structure Methods: Application to Actinide Materials
International Nuclear Information System (INIS)
Klepeis, J E
2005-01-01
The purpose of this paper is to provide an introduction for non-experts to first-principles electronic structure methods that are widely used in the field of condensed-matter physics, including applications to actinide materials. The methods I describe are based on density functional theory (DFT) within the local density approximation (LDA) and the generalized gradient approximation (GGA). In addition to explaining the meaning of this terminology I also describe the underlying theory itself in some detail in order to enable a better understanding of the relative strengths and weaknesses of the methods. I briefly mention some particular numerical implementations of DFT, including the linear muffin-tin orbital (LMTO), linear augmented plane wave (LAPW), and pseudopotential methods, as well as general methodologies that go beyond DFT and specifically address some of the weaknesses of the theory. The last third of the paper is devoted to a few selected applications that illustrate the ideas discussed in the first two-thirds. In particular, I conclude by addressing the current controversy regarding magnetic DFT calculations for actinide materials. Throughout this paper particular emphasis is placed on providing the appropriate background to enable the non-expert to gain a better appreciation of the application of first-principles electronic structure methods to the study of actinide and other materials
First-principles investigation of strain effects on the energy gaps in silicon nanoclusters
International Nuclear Information System (INIS)
Peng, X-H; Alizadeh, A; Bhate, N; Varanasi, K K; Kumar, S K; Nayak, S K
2007-01-01
First-principles density functional calculations were performed to study strain effects on the energy gaps in silicon nanoclusters with diameter ranging from 0.6 to 2 nm. Hydrostatic and non-hydrostatic strains have been found to affect the energy gaps differently. For the same strain energy density, non-hydrostatic strain leads to a significantly larger change in the energy gap of silicon clusters compared to that of the hydrostatic strain case. In contrast, hydrostatic and non-hydrostatic strain effects on the energy gaps of bulk Si or larger size Si quantum dots are comparable. Non-hydrostatic strains break the tetrahedral bonding symmetry in silicon, resulting in significant variation in the energy gaps due to the splitting of the degenerate orbitals in the clusters. Our results suggest that the combination of energy gaps and strains permits the engineering of photoluminescence in silicon nanoclusters and offers the possibility of designing novel optical devices and chemical sensors
First-principles investigations of the physical properties of binary uranium silicide alloys
International Nuclear Information System (INIS)
Yang, Jin; Long, Jianping; Yang, Lijun; Li, Dongmei
2013-01-01
Graphical abstract: Total density of states for USi 2 . Display Omitted -- Abstract: The structural, elastic properties and the Debye temperature of binary Uranium Silicide (U-Si) alloys are investigated by using the first-principles plane-wave pseudopotential density function theory within the generalized gradient approximation (GGA). The ground states properties are found to agree with the available experimental data. The mechanical properties like shear modulus, Young’s modulus, Poisson’s ratio σ and ratio B/G are also calculated. Finally, The averaged sound velocity (v m ), the longitudinal sound velocity (v l ), transverse sound velocity (v t ) and the Debye temperature (θ D ) are obtained. However, the theoretical values are slightly different from few existed experiment data because the latter was obtained at room temperature while the former one at 0 K
Introduction to First-Principles Electronic Structure Methods: Application to Actinide Materials
International Nuclear Information System (INIS)
Klepeis, J E
2006-01-01
This paper provides an introduction for non-experts to first-principles electronic structure methods that are widely used in condensed-matter physics. Particular emphasis is placed on giving the appropriate background information needed to better appreciate the use of these methods to study actinide and other materials. Specifically, I describe the underlying theory sufficiently to enable an understanding of the relative strengths and weaknesses of the methods. I also explain the meaning of commonly used terminology, including density functional theory (DFT), local density approximation (LDA), and generalized gradient approximation (GGA), as well as linear muffin-tin orbital (LMTO), linear augmented plane wave (LAPW), and pseudopotential methods. I also briefly discuss methodologies that extend the basic theory to address specific limitations. Finally, I describe a few illustrative applications, including quantum molecular dynamics (QMD) simulations and studies of surfaces, impurities, and defects. I conclude by addressing the current controversy regarding magnetic calculations for actinide materials
First-principles method for electron-phonon coupling and electron mobility
DEFF Research Database (Denmark)
Gunst, Tue; Markussen, Troels; Stokbro, Kurt
2016-01-01
We present density functional theory calculations of the phonon-limited mobility in n-type monolayer graphene, silicene, and MoS2. The material properties, including the electron-phonon interaction, are calculated from first principles. We provide a detailed description of the normalized full......-band relaxation time approximation for the linearized Boltzmann transport equation (BTE) that includes inelastic scattering processes. The bulk electron-phonon coupling is evaluated by a supercell method. The method employed is fully numerical and does therefore not require a semianalytic treatment of part...... of the problem and, importantly, it keeps the anisotropy information stored in the coupling as well as the band structure. In addition, we perform calculations of the low-field mobility and its dependence on carrier density and temperature to obtain a better understanding of transport in graphene, silicene...
First-principles studies of PETN molecular crystal vibrational frequencies under high pressure
Perger, Warren; Zhao, Jijun
2005-07-01
The vibrational frequencies of the PETN molecular crystal were calculated using the first-principles CRYSTAL03 program which employs an all-electron LCAO approach and calculates analytic first derivatives of the total energy with respect to atomic displacements. Numerical second derivatives were used to enable calculation of the vibrational frequencies at ambient pressure and under various states of compression. Three different density functionals, B3LYP, PW91, and X3LYP were used to examine the effect of the exchange-correlation functional on the vibrational frequencies. The pressure-induced shift of the vibrational frequencies will be presented and compared with experiment. The average deviation with experimental results is shown to be on the order of 2-3%, depending on the functional used.
First-principles modeling of titanate/ruthenate superlattices
Junquera, Javier
2013-03-01
The possibility to create highly confined two-dimensional electron gases (2DEG) at oxide interfaces has generated much excitement during the last few years. The most widely studied system is the 2DEG formed at the LaO/TiO2 polar interface between LaAlO3 and SrTiO3, where the polar catastrophe at the interface has been invoked as the driving force. More recently, partial or complete delta doping of the Sr or Ti cations at a single layer of a SrTiO3 matrix has also been used to generate 2DEG. Following this recipe, we report first principles characterization of the structural and electronic properties of (SrTiO3)5/(SrRuO3)1 superlattices, where all the Ti of a given layer have been replaced by Ru. We show that the system exhibits a spin-polarized two-dimensional electron gas extremely confined to the 4 d orbitals of Ru in the SrRuO3 layer, a fact that is independent of the level of correlation included in the simulations. For hybrid functionals or LDA+U, every interface in the superlattice behaves as minority-spin half-metal ferromagnet, with a magnetic moment of μ = 2.0 μB/SrRuO3 unit. The shape of the electronic density of states, half metallicity and magnetism are explained in terms of a simplified tight-binding model, considering only the t2 g orbitals plus (i) the bi-dimensionality of the system, and (ii) strong electron correlations. Possible applications are discussed, from their eventual role in thermoelectric applications to the possible tuning of ferromagnetic properties of the 2DEG with the polarization of the dielectric. Work done in collaboration with P. García, M. Verissimo-Alves, D. I. Bilc, and Ph. Ghosez. Financial support provided by MICINN Grant FIS2009-12721-C04-02, and by the European Union Grant No. CP-FP 228989-2 ``OxIDes.'' The authors thankfully acknowledge the computer resources, technical expertise and assistance provided by the BSC/RES.
First-principles modeling of magnetic misfit interfaces
Grytsyuk, Sergiy; Schwingenschlö gl, Udo
2013-01-01
We investigate the structural and magnetic properties of interfaces with large lattice mismatch, choosing Pt/Co and Au/Co as prototypes. For our first-principles calculations, we reduce the lattice mismatch to 0.2% by constructing Moiré supercells. Our results show that the roughness and atomic density, and thus the magnetic properties, depend strongly on the substrate and thickness of the Co slab. An increasing thickness leads to the formation of a Co transition layer at the interface, especially for Pt/Co due to strong Pt-Co interaction. A Moiré supercell with a transition layer is found to reproduce the main experimental findings and thus turns out to be the appropriate model for simulating magnetic misfit interfaces.
First-principles modeling of magnetic misfit interfaces
Grytsiuk, Sergii
2013-08-16
We investigate the structural and magnetic properties of interfaces with large lattice mismatch, choosing Pt/Co and Au/Co as prototypes. For our first-principles calculations, we reduce the lattice mismatch to 0.2% by constructing Moiré supercells. Our results show that the roughness and atomic density, and thus the magnetic properties, depend strongly on the substrate and thickness of the Co slab. An increasing thickness leads to the formation of a Co transition layer at the interface, especially for Pt/Co due to strong Pt-Co interaction. A Moiré supercell with a transition layer is found to reproduce the main experimental findings and thus turns out to be the appropriate model for simulating magnetic misfit interfaces.
First-principles study of dielectric properties of cerium oxide
International Nuclear Information System (INIS)
Yamamoto, Takenori; Momida, Hiroyoshi; Hamada, Tomoyuki; Uda, Tsuyoshi; Ohno, Takahisa
2005-01-01
We have theoretically investigated the dielectric properties of fluorite CeO 2 as well as hexagonal and cubic Ce 2 O 3 by using first-principles pseudopotentials techniques within the local density approximation. Calculated electronic and lattice dielectric constants of CeO 2 are in good agreement with previous theoretical and experimental results. For Ce 2 O 3 , the hexagonal phase has a lattice dielectric constant comparable to that of CeO 2 , whereas the cubic phase has a much smaller one. We have concluded that the enhancement of the dielectric constant in CeO 2 epitaxially grown on Si is not due to its lattice expansion experimentally observed nor regular formation of oxygen vacancies in CeO 2
First principles molecular dynamics of metal/water interfaces under bias potential
Pedroza, Luana; Brandimarte, Pedro; Rocha, Alexandre; Fernandez-Serra, Marivi
2014-03-01
Understanding the interaction of the water-metal system at an atomic level is extremely important in electrocatalysts for fuel cells, photocatalysis among other systems. The question of the interface energetics involves a detailed study of the nature of the interactions between water-water and water-substrate. A first principles description of all components of the system is the most appropriate methodology in order to advance understanding of electrochemically processes. In this work we describe, using first principles molecular dynamics simulations, the dynamics of a combined surface(Au and Pd)/water system both in the presence and absence of an external bias potential applied to the electrodes, as one would come across in electrochemistry. This is accomplished using a combination of density functional theory (DFT) and non-equilibrium Green's functions methods (NEGF), thus accounting for the fact that one is dealing with an out-of-equilibrium open system, with and without van der Waals interactions. DOE Early Career Award No. DE-SC0003871.
Development of a Knowledge Base of Ti-Alloys From First-Principles and Thermodynamic Modeling
Marker, Cassie
An aging population with an active lifestyle requires the development of better load-bearing implants, which have high levels of biocompatibility and a low elastic modulus. Titanium alloys, in the body centered cubic phase, are great implant candidates, due to their mechanical properties and biocompatibility. The present work aims at investigating the thermodynamic and elastic properties of bcc Tialloys, using the integrated first-principles based on Density Functional Theory (DFT) and the CALculation of PHAse Diagrams (CALPHAD) method. The use of integrated first-principles calculations based on DFT and CALPHAD modeling has greatly reduced the need for trial and error metallurgy, which is ineffective and costly. The phase stability of Ti-alloys has been shown to greatly affect their elastic properties. Traditionally, CALPHAD modeling has been used to predict the equilibrium phase formation, but in the case of Ti-alloys, predicting the formation of two metastable phases o and alpha" is of great importance as these phases also drastically effect the elastic properties. To build a knowledge base of Ti-alloys, for biomedical load-bearing implants, the Ti-Mo-Nb-Sn-Ta-Zr system was studied because of the biocompatibility and the bcc stabilizing effects of some of the elements. With the focus on bcc Ti-rich alloys, a database of thermodynamic descriptions of each phase for the pure elements, binary and Ti-rich ternary alloys was developed in the present work. Previous thermodynamic descriptions for the pure elements were adopted from the widely used SGTE database for global compatibility. The previous binary and ternary models from the literature were evaluated for accuracy and new thermodynamic descriptions were developed when necessary. The models were evaluated using available experimental data, as well as the enthalpy of formation of the bcc phase obtained from first-principles calculations based on DFT. The thermodynamic descriptions were combined into a database
Band gap of β-PtO2 from first-principles
Directory of Open Access Journals (Sweden)
Yong Yang
2012-06-01
Full Text Available We studied the band gap of β-PtO2 using first-principles calculations based on density functional theory (DFT. The results are obtained within the framework of the generalized gradient approximation (GGA, GGA+U, GW, and the hybrid functional methods. For the different types of calculations, the calculated band gap increases from ∼0.46 eV to 1.80 eV. In particular, the band gap by GW (conventional and self-consistent calculation shows a tendency of converging to ∼1.25 ± 0.05 eV. The effect of on-site Coulomb interaction on the bonding characteristics is also analyzed.
All-phosphorus flexible devices with non-collinear electrodes: a first principles study.
Li, Junjun; Ruan, Lufeng; Wu, Zewen; Zhang, Guiling; Wang, Yin
2018-03-07
With the continuous expansion of the family of two-dimensional (2D) materials, flexible electronics based on 2D materials have quickly emerged. Theoretically, predicting the transport properties of the flexible devices made up of 2D materials using first principles is of great importance. Using density functional theory combined with the non-equilibrium Green's function formalism, we calculated the transport properties of all-phosphorus flexible devices with non-collinear electrodes, and the results predicted that the device with compressed metallic phosphorene electrodes sandwiching a P-type semiconducting phosphorene shows a better and robust conducting behavior against the bending of the semiconducting region when the angle between the two electrodes is less than 45°, which indicates that this system is very promising for flexible electronics. The calculation of a quantum transport system with non-collinear electrodes demonstrated in this work will provide more interesting information on mesoscopic material systems and related devices.
Differentiation from First Principles Using Spreadsheets
Lim, Kieran F.
2008-01-01
In the teaching of calculus, the algebraic derivation of the derivative (gradient function) enables the student to obtain an analytic "global" gradient function. However, to the best of this author's knowledge, all current technology-based approaches require the student to obtain the derivative (gradient) at a single point by…
Anisotropic elastic and thermal properties of titanium borides by first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Sun, Liang; Gao, Yimin [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049 (China); Xiao, Bing [Department of Physics and Quantum Theory Group, School of Science and Engineering, Tulane University, New Orleans, LA 70118 (United States); Li, Yefei, E-mail: yefeili@126.com [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049 (China); Wang, Guoliang [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049 (China)
2013-12-05
Highlights: •Elastic properties of titanium borides are calculated by first principles calculation. •Thermodynamical stability of titanium borides is analyzed. •Heat capacity and thermal expansion coefficient for titanium borides are calculated and compared. •Grüneisen parameters of titanium borides are calculated. -- Abstract: The anisotropic elastic and thermal expansions of the titanium borides (TiB{sub 2}, Ti{sub 3}B{sub 4}, TiB{sub P}nma and TiB{sub F}m3{sup ¯}m) are calculated from first-principles using density functional theory. All borides show different anisotropic elastic properties; the bulk, shear and Young’s moduli are consistent with those determined experimentally. The temperature dependence of thermal expansions is mainly caused by the restoration of thermal energy due to phonon excitations at low temperature. When the temperature is higher than 500 K, the volumetric coefficient is increased linearly by increasing temperature. Meanwhile, the heat capacities of titanium borides are obtained based on the knowledge of thermal expansion coefficient and the elasticity, the calculations are in good agreement with the experiments.
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.
Mechanical properties of layered oxysulfide CaZnOS from first principle calculations
Energy Technology Data Exchange (ETDEWEB)
Zhang, Zhi-Jun [Department of Physics, Dongguk University, Pildong-ro, Choong-gu, Seoul, 100-715 (Korea, Republic of); Feng, Ang [Key Laboratory of Transparent Opto-Functional Inorganic Materials of Chinese Academy of Sciences, Shanghai Institute of Ceramics, Shanghai, 200050 (China); Zhang, Shao-Lin; Zhang, Wei-Bin [Department of Physics, Dongguk University, Pildong-ro, Choong-gu, Seoul, 100-715 (Korea, Republic of); Yang, Woochul, E-mail: wyang@dongguk.edu [Department of Physics, Dongguk University, Pildong-ro, Choong-gu, Seoul, 100-715 (Korea, Republic of)
2016-06-15
Elastic and tensile properties of mixed-anion oxysulfide CaZnOS have been theoretically investigated by first principle method of density functional theory (DFT). Elastic constants were obtained by stress–strain relationships, and bulk structure parameters including bulk modulus, shear modulus, as well as Poisson's ratio were then calculated using Voigt-Reuses-Hill (VRH) approximation. The results of shear anisotropic factors, compressibility anisotropic factor and directional Young's modulus showed that CaZnOS is almost elastically isotropic in {001} planes and maintains elastic anisotropy in {100} or {010} planes. Chemical bond anisotropy shown by Mulliken atomic charges and bond overlap populations is responsible for the elastic anisotropy behavior aforementioned. Moreover, theoretical uniaxial and biaxial tensile results showed the crystal collapsed at strain more than 12%, except in the biaxial extension where CaZnOS collapsed at strain of 7%. - Highlights: • Elastic and theoretical tensile properties of CaZnOS have been investigated by first principle method. • CaZnOS is elastically isotropic in {001} planes and maintains elastic anisotropy in {100} or {010} planes. • Mulliken atomic charges and bond overlap populations are responsible for the elastic anisotropy behavior.
Temperature-dependent stability of stacking faults in Al, Cu and Ni: first-principles analysis.
Bhogra, Meha; Ramamurty, U; Waghmare, Umesh V
2014-09-24
We present comparative analysis of microscopic mechanisms relevant to plastic deformation of the face-centered cubic (FCC) metals Al, Cu, and Ni, through determination of the temperature-dependent free energies of intrinsic and unstable stacking faults along [1 1̄ 0] and [1 2̄ 1] on the (1 1 1) plane using first-principles density-functional-theory-based calculations. We show that vibrational contribution results in significant decrease in the free energy of barriers and intrinsic stacking faults (ISFs) of Al, Cu, and Ni with temperature, confirming an important role of thermal fluctuations in the stability of stacking faults (SFs) and deformation at elevated temperatures. In contrast to Al and Ni, the vibrational spectrum of the unstable stacking fault (USF[1 2̄ 1]) in Cu reveals structural instabilities, indicating that the energy barrier (γusf) along the (1 1 1)[1 2̄ 1] slip system in Cu, determined by typical first-principles calculations, is an overestimate, and its commonly used interpretation as the energy release rate needed for dislocation nucleation, as proposed by Rice (1992 J. Mech. Phys. Solids 40 239), should be taken with caution.
Density functional theory of nuclei
International Nuclear Information System (INIS)
Terasaki, Jun
2008-01-01
The density functional theory of nuclei has come to draw attention of scientists in the field of nuclear structure because the theory is expected to provide reliable numerical data in wide range on the nuclear chart. This article is organized to present an overview of the theory to the people engaged in the theory of other fields as well as those people in the nuclear physics experiments. At first, the outline of the density functional theory widely used in the electronic systems (condensed matter, atoms, and molecules) was described starting from the Kohn-Sham equation derived on the variational principle. Then the theory used in the field of nuclear physics was presented. Hartree-Fock and Hartree-Fock-Bogolyubov approximation by using Skyrme interaction was explained. Comparison of the results of calculations and experiments of binding energies and ground state mean square charge radii of some magic number nuclei were shown. The similarity and dissimilarity between the two streams were summarized. Finally the activities of the international project of Universal Nuclear Energy Density Functional (UNEDF) which was started recently lead by US scientist was reported. This project is programmed for five years. One of the applications of the project is the calculation of the neutron capture cross section of nuclei on the r-process, which is absolutely necessary for the nucleosynthesis research. (S. Funahashi)
Nuclear log interpretation by first principle
International Nuclear Information System (INIS)
Oelgaard, P.L.
1988-07-01
A weakness connected to the present interpretation of nuclear borehole logs is that the interdependence of the various logs and physical effects of importance for the tools are not always taken into account in a correct way. Therefore a new approach to the interpretation of nuclear borehole logs is considered. It is based on the logs obtained with the natural gamma, the neutron porosity, the gamma density, and the pulsed neutron tools. For each of these tools a model, taking into account the important physical effects, is established. These models are incorporated into a computer programme which from the tool signals calculates, by use of iteration, a consistent set of the corresponding formation properties. In the paper the models developed for the four tools and the interpretation programme are briefly described. An example of the use of the interpretation programme is given and compared with a conventional interpretation. (author)
Exploring the nucleon structure from first principles of QCD
Energy Technology Data Exchange (ETDEWEB)
Bietenholz, W. [Universidad Nacional Autonoma de Mexico (Mexico). Inst. de Ciencias Nucleares; Cundy, N.; Goeckeler, M. [Regensburg Univ. (DE). Inst. fuer Theoretische Physik] (and others)
2010-04-15
Quantum Chromodynamics (QCD) is generally assumed to be the fundamental theory underlying nuclear physics. In recent years there is progress towards investigating the nucleon structure from first principles of QCD. Although this structure is best revealed in Deep Inelastic Scattering, a consistent analysis has to be performed in a fully non-perturbative scheme. The only known method for this purpose are lattice simulations. We first sketch the ideas of Monte Carlo simulations in lattice gauge theory. Then we comment in particular on the issues of chiral symmetry and operator mixing. Finally we present our results for the Bjorken variable of a single quark, and for the second Nachtmann moment of the nucleon structure functions. (orig.)
First-Principles Lattice Dynamics Method for Strongly Anharmonic Crystals
Tadano, Terumasa; Tsuneyuki, Shinji
2018-04-01
We review our recent development of a first-principles lattice dynamics method that can treat anharmonic effects nonperturbatively. The method is based on the self-consistent phonon theory, and temperature-dependent phonon frequencies can be calculated efficiently by incorporating recent numerical techniques to estimate anharmonic force constants. The validity of our approach is demonstrated through applications to cubic strontium titanate, where overall good agreement with experimental data is obtained for phonon frequencies and lattice thermal conductivity. We also show the feasibility of highly accurate calculations based on a hybrid exchange-correlation functional within the present framework. Our method provides a new way of studying lattice dynamics in severely anharmonic materials where the standard harmonic approximation and the perturbative approach break down.
Exploring the nucleon structure from first principles of QCD
International Nuclear Information System (INIS)
Bietenholz, W.; Cundy, N.; Goeckeler, M.
2010-04-01
Quantum Chromodynamics (QCD) is generally assumed to be the fundamental theory underlying nuclear physics. In recent years there is progress towards investigating the nucleon structure from first principles of QCD. Although this structure is best revealed in Deep Inelastic Scattering, a consistent analysis has to be performed in a fully non-perturbative scheme. The only known method for this purpose are lattice simulations. We first sketch the ideas of Monte Carlo simulations in lattice gauge theory. Then we comment in particular on the issues of chiral symmetry and operator mixing. Finally we present our results for the Bjorken variable of a single quark, and for the second Nachtmann moment of the nucleon structure functions. (orig.)
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...
Density functional theory: Foundations reviewed
Energy Technology Data Exchange (ETDEWEB)
Kryachko, Eugene S., E-mail: eugene.kryachko@ulg.ac.be [Bogolyubov Institute for Theoretical Physics, Kiev, 03680 (Ukraine); Ludeña, Eduardo V., E-mail: popluabe@yahoo.es [Centro de Química, Instituto Venezolano de Investigaciones Científicas, IVIC, Apartado 21827, Caracas 1020-A (Venezuela, Bolivarian Republic of); Prometheus Program, Senescyt (Ecuador); Grupo Ecuatoriano para el Estudio Experimental y Teórico de Nanosistemas, GETNano, USFQ, N104-E, Quito (Ecuador); Escuela Politécnica Superior del Litoral, ESPOL, Guayaquil (Ecuador)
2014-11-10
Guided by the above motto (quotation), we review a broad range of issues lying at the foundations of Density Functional Theory, DFT, a theory which is currently omnipresent in our everyday computational study of atoms and molecules, solids and nano-materials, and which lies at the heart of modern many-body computational technologies. The key goal is to demonstrate that there are definitely the ways to improve DFT. We start by considering DFT in the larger context provided by reduced density matrix theory (RDMT) and natural orbital functional theory (NOFT), and examine the implications that N-representability conditions on the second-order reduced density matrix (2-RDM) have not only on RDMT and NOFT but, also, by extension, on the functionals of DFT. This examination is timely in view of the fact that necessary and sufficient N-representability conditions on the 2-RDM have recently been attained. In the second place, we review some problems appearing in the original formulation of the first Hohenberg–Kohn theorem which is still a subject of some controversy. In this vein we recall Lieb’s comment on this proof and the extension to this proof given by Pino et al. (2009), and in this context examine the conditions that must be met in order that the one-to-one correspondence between ground-state densities and external potentials remains valid for finite subspaces (namely, the subspaces where all Kohn–Sham solutions are obtained in practical applications). We also consider the issue of whether the Kohn–Sham equations can be derived from basic principles or whether they are postulated. We examine this problem in relation to ab initio DFT. The possibility of postulating arbitrary Kohn–Sham-type equations, where the effective potential is by definition some arbitrary mixture of local and non-local terms, is discussed. We also deal with the issue of whether there exists a universal functional, or whether one should advocate instead the construction of problem
First principles study of hydroxyapatite surface
Slepko, Alexander; Demkov, Alexander A.
2013-07-01
The biomineral hydroxyapatite (HA) [Ca10(PO4)6(OH)2] is the main mineral constituent of mammal bone. We report a theoretical investigation of the HA surface. We identify the low energy surface orientations and stoichiometry under a variety of chemical environments. The surface most stable in the physiologically relevant OH-rich environment is the OH-terminated (1000) surface. We calculate the work function of HA and relate it to the surface composition. For the lowest energy OH-terminated surface we find the work function of 5.1 eV, in close agreement with the experimentally reported range of 4.7 eV-5.1 eV [V. S. Bystrov, E. Paramonova, Y. Dekhtyar, A. Katashev, A. Karlov, N. Polyaka, A. V. Bystrova, A. Patmalnieks, and A. L. Kholkin, J. Phys.: Condens. Matter 23, 065302 (2011), 10.1088/0953-8984/23/6/065302].
Relic neutrino asymmetry evolution from first principles
International Nuclear Information System (INIS)
Bell, N.F.; Volkas, R.R.; Wong, Y.Y.Y.
1998-09-01
The exact Quantum Kinetic Equations for a two-flavour active-sterile neutrino system are used to provide a systematic derivation of approximate evolution equations for the relic neutrino asymmetry. An extension of the adiabatic approximation for matter-affected neutrino oscillations is developed which incorporates decoherence due to collisions. Exact and approximate expressions for the decoherence and repopulation functions are discussed. A first pass is made over the exact treatment of multi-flavour partially incoherent oscillations. (authors)
Designing Next Generation Rechargeable Battery Materials from First-Principles
Kim, Soo
Technology has advanced rapidly, especially in the twenty-first century, influencing our day-to-day life on unprecedented levels. Most such advances in technology are closely linked to, and often driven by, the discovery and design of new materials. It follows that the discovery of new materials can not only improve existing technologies but also lead to revolutionary ones. In particular, there is a growing need to develop new energy materials that are reliable, clean, and affordable for emerging applications such as portable electronics, electric vehicles, and power grid systems. Many researchers have been actively searching for more cost-effective and clean electrode materials for lithium-ion batteries (LIBs) during the last few decades. These new electrode materials are also required to achieve higher electrochemical performance, compared to the already commercialized electrodes. Unfortunately, discovering the next sustainable energy materials based on a traditional 'trial-and-error' method via experiment would be extremely slow and difficult. In the last two decades, computational compilations of battery material properties such as voltage, diffusivity, and phase stability against irreversible phase transformation(s) using first-principles density functional theory (DFT) calculations have helped researchers to understand the underlying mechanism in many oxide materials that are used as LIB electrodes. Here, we have examined the (001) and (111) surface structures of LiMn2O4 (LMO) spinel cathode materials using DFT calculations within the generalized gradient approximation (GGA) + U approach. Our theoretical results explain the observation of a wide spectrum of polyhedral shapes between (001)- and (111)-dominated LMO particles in experiments, which can be described by the narrow range of surface energies and their sensitivity to synthesis conditions. We further show that single-layer graphene coatings help suppress manganese dissolution in LMO by chemically
Jump rates for surface diffusion of large molecules from first principles
Energy Technology Data Exchange (ETDEWEB)
Shea, Patrick, E-mail: patrick.shea@dal.ca; Kreuzer, Hans Jürgen [Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia B3H 3J5 (Canada)
2015-04-21
We apply a recently developed stochastic model for the surface diffusion of large molecules to calculate jump rates for 9,10-dithioanthracene on a Cu(111) surface. The necessary input parameters for the stochastic model are calculated from first principles using density functional theory (DFT). We find that the inclusion of van der Waals corrections to the DFT energies is critical to obtain good agreement with experimental results for the adsorption geometry and energy barrier for diffusion. The predictions for jump rates in our model are in excellent agreement with measured values and show a marked improvement over transition state theory (TST). We find that the jump rate prefactor is reduced by an order of magnitude from the TST estimate due to frictional damping resulting from energy exchange with surface phonons, as well as a rotational mode of the diffusing molecule.
Gao, Qin; Yao, Sanxi; Widom, Michael
2015-03-01
Density functional theory (DFT) provides an accurate and first-principles description of solid structures and total energies. However, it is highly time-consuming to calculate structures with hundreds of atoms in the unit cell and almost not possible to calculate thousands of atoms. We apply and adapt machine learning algorithms, including compressive sensing, support vector regression and artificial neural networks to fit the DFT total energies of substitutionally disordered boron carbide. The nonparametric kernel method is also included in our models. Our fitted total energy model reproduces the DFT energies with prediction error of around 1 meV/atom. The assumptions of these machine learning models and applications of the fitted total energies will also be discussed. Financial support from McWilliams Fellowship and the ONR-MURI under the Grant No. N00014-11-1-0678 is gratefully acknowledged.
Energy band modulation of graphane by hydrogen-vacancy chains: A first-principles study
Directory of Open Access Journals (Sweden)
Bi-Ru Wu
2014-08-01
Full Text Available We investigated a variety of configurations of hydrogen-vacancy chains in graphane by first-principles density functional calculation. We found that graphane with two zigzag H-vacancy chains segregated by one or more H chain is generally a nonmagnetic conductor or has a negligible band gap. However, the same structure is turned into a semiconductor and generates a magnetic moment if either one or both of the vacancy chains are blocked by isolated H atoms. If H-vacancy chains are continuously distributed, the structure is similar to a zigzag graphene nanoribbon embedded in graphane. It was also found that the embedded zigzag graphene nanoribbon is antiferromagnetic, and isolated H atoms left in the 2-chain nanoribbon can tune the band gap and generate net magnetic moments. Similar effects are also obtained if bare carbon atoms are present outside the nanoribbon. These results are useful for designing graphene-based nanoelectronic circuits.
International Nuclear Information System (INIS)
Iwata, K.; Matsumiya, T.; Sawada, H.; Kawakami, K.
2003-01-01
The method is presented to predict the activity coefficients and the interaction parameters of the solute elements in infinite dilute Si solutions by the use of first-principles calculations based on density functional theory. In this method, the regular solution model is assumed. The calculated activity coefficients in solid Si are converted to those in molten Si by the use of the solid-liquid partition coefficients. Furthermore, the interaction parameters in solid Si solutions are calculated and compared with reported experimental values of those in liquid Si solutions. The results show that the calculated activity coefficients and interaction parameters of Al, Fe, Ti and Pb in Si solutions are in good agreement with the tendency of the experiments. However, the calculations have some quantitative discrepancy from the experiments. It is expected that consideration of the excess entropy would reduce this discrepancy
First-principles study on band structures and electrical transports of doped-SnTe
Directory of Open Access Journals (Sweden)
Xiao Dong
2016-06-01
Full Text Available Tin telluride is a thermoelectric material that enables the conversion of thermal energy to electricity. SnTe demonstrates a great potential for large-scale applications due to its lead-free nature and the similar crystal structure to PbTe. In this paper, the effect of dopants (i.e., Mg, Ca, Sr, Ba, Eu, Yb, Zn, Cd, Hg, and In on the band structures and electrical transport properties of SnTe was investigated based on the first-principles density functional theory including spin–orbit coupling. The results show that Zn and Cd have a dominant effect of band convergence, leading to power factor enhancement. Indium induces obvious resonant states, while Hg-doped SnTe exhibits a different behavior with defect states locating slightly above the Fermi level.
Near-infrared radiation absorption properties of covellite (CuS using first-principles calculations
Directory of Open Access Journals (Sweden)
Lihua Xiao
2016-08-01
Full Text Available First-principles density functional theory was used to investigate the electronic structure, optical properties and the origin of the near-infrared (NIR absorption of covellite (CuS. The calculated lattice constant and optical properties are found to be in reasonable agreement with experimental and theoretical findings. The electronic structure reveals that the valence and conduction bands of covellite are determined by the Cu 3d and S 3p states. By analyzing its optical properties, we can fully understand the potential of covellite (CuS as a NIR absorbing material. Our results show that covellite (CuS exhibits NIR absorption due to its metal-like plasma oscillation in the NIR range.
Effects of hydrogen on Mn-doped GaN: A first principles calculation
International Nuclear Information System (INIS)
Wu, M.S.; Xu, B.; Liu, G.; Lei, X.L.; Ouyang, C.Y.
2013-01-01
First-principles calculations based on spin density functional theory are performed to study the effects of H on the structural, electronic and magnetic properties of the Mn-doped GaN dilute magnetic semiconductors. Our results show that the interstitial H atom prefers to bond with N atom rather than Mn atom, which means that H favors to form the N–H complex rather than Mn–H complex in the Mn-doped GaN. After introducing one H atom in the system, the total magnetic moment of the Mn-doped GaN increases by 25%, from 4.0μ B to 5.0μ B . The physics mechanism of the increase of magnetic moment after hydrogenation in Mn-doped GaN is discussed
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.
Directory of Open Access Journals (Sweden)
Bidai K.
2017-06-01
Full Text Available First-principles density functional theory calculations have been performed to investigate the structural, elastic and thermodynamic properties of rubidium telluride in cubic anti-fluorite (anti-CaF2-type structure. The calculated ground-state properties of Rb2Te compound such as equilibrium lattice parameter and bulk moduli are investigated by generalized gradient approximation (GGA-PBE that are based on the optimization of total energy. The elastic constants, Young’s and shear modulus, Poisson ratio, have also been calculated. Our results are in reasonable agreement with the available theoretical and experimental data. The pressure dependence of elastic constant and thermodynamic quantities under high pressure are also calculated and discussed.
A first-principles study of the electronic structure of the sulvanite compounds
Energy Technology Data Exchange (ETDEWEB)
Osorio-Guillen, J.M., E-mail: jorge.osorio@fisica.udea.edu.co [Instituto de Fisica, Universidad de Antioquia, Medellin A.A. 1226 (Colombia); Espinosa-Garcia, W.F. [Instituto de Fisica, Universidad de Antioquia, Medellin A.A. 1226 (Colombia)
2012-03-15
We have investigated by means of first-principles total energy calculations the electronic structure of the sulvanite compounds: Cu{sub 3}VS{sub 4}, Cu{sub 3}NbS{sub 4} and Cu{sub 3}TaS{sub 4}; the later is a possible candidate as a p-type transparent conductor with potential applications in solar cells and electrochromic devices. The calculated electronic structure shows that these compounds are indirect band gap semiconductors, with the valence band maximum located at the R-point and the conduction band minimum located at the X-point. The character of the valence band maximum is dominated by Cu d-states and the character of the conduction band minimum is due to the d-states of the group five elements. From the calculated charge density and electron localisation function we can conclude that the sulvanite compounds are polar covalent semiconductors.
First-principles atomistic Wulff constructions for an equilibrium rutile TiO2 shape modeling
Jiang, Fengzhou; Yang, Lei; Zhou, Dali; He, Gang; Zhou, Jiabei; Wang, Fanhou; Chen, Zhi-Gang
2018-04-01
Identifying the exposed surfaces of rutile TiO2 crystal is crucial for its industry application and surface engineering. In this study, the shape of the rutile TiO2 was constructed by applying equilibrium thermodynamics of TiO2 crystals via first-principles density functional theory (DFT) and Wulff principles. From the DFT calculations, the surface energies of six low-index stoichiometric facets of TiO2 are determined after the calibrations of crystal structure. And then, combined surface energy calculations and Wulff principles, a geometric model of equilibrium rutile TiO2 is built up, which is coherent with the typical morphology of fully-developed equilibrium TiO2 crystal. This study provides fundamental theoretical guidance for the surface analysis and surface modification of the rutile TiO2-based materials from experimental research to industry manufacturing.
First-Principles Study of the Polar TiC/Ti Interface
Institute of Scientific and Technical Information of China (English)
Limin LIU; Shaoqing WANG; Hengqiang YE
2003-01-01
The interface structure, work of adhesion, and bonding character of the polar TiC/Ti interface have been examined by the first-principles density functional plane-wave pseudopotential calculations. Both Ti- and C-terminated interfaces including six different interface structures were calculated, which present quite different features. For the Ti-terminated interface, the interfacial Ti-Ti bond has a strong metallic and weak covalent character; while for the C-terminated interface, the interfacial bond is a strong polar covalent interaction between the Ti-3d and C-2p orbital.The work of adhesion of C-terminated interface is nearly 9 J/m2 stronger than that of the Ti-terminated. It is found that each termination has relatively large work of adhesion, which is consistent with other polar interfaces.
First Principles Modeling and Interpretation of Ionization-Triggered Charge Migration in Molecules
Bruner, Adam; Hernandez, Sam; Mauger, Francois; Abanador, Paul; Gaarde, Mette; Schafer, Ken; Lopata, Ken
Modeling attosecond coherent charge migration in molecules is important for understanding initial steps of photochemistry and light harvesting processes. Ionization triggered hole migration can be difficult to characterize and interpret as the dynamics can be convoluted with excited states. Here, we introduce a real-time time-dependent density functional theory (RT-TDDFT) approach for modeling such dynamics from first principles. To isolate the specific hole dynamics from excited states, Fourier transform analysis and orbital occupations are used to provide a spatial hole representation in the frequency domain. These techniques are applied to hole transfer across a thiophene dimer as well as core-hole triggered valence motion in nitrosobenzene. This work was supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award No. DE-SC0012462.
First-principles study of hydrogen diffusion in transition metal Rhodium
International Nuclear Information System (INIS)
Bao, Wulijibilige; Cui, Xin; Wang, Zhi-Ping
2015-01-01
In this study, the diffuse pattern and path of hydrogen in transition metal rhodium are investigated by the first-principles calculations. Density functional theory is used to calculate the system energies of hydrogen atom occupying different positions in rhodium crystal lattice. The results indicate that the most stable position of hydrogen atom in rhodium crystal lattice locates at the octahedral interstice, and the tetrahedral interstice is the second stable site. The activation barrier energy for the diffusion of atomic hydrogen in transition metal rhodium is quantified by determining the most favorable path, i.e., the minimum-energy pathway for diffusion, that is the indirect octahedral-tetrahedral-octahedral (O-T-O) pathway, and the activation energy is 0.8345eV
Anomalous doping effect in black phosphorene using first-principles calculations.
Yu, Weiyang; Zhu, Zhili; Niu, Chun-Yao; Li, Chong; Cho, Jun-Hyung; Jia, Yu
2015-07-07
Using first-principles density functional theory calculations, we investigate the geometries, electronic structures, and thermodynamic stabilities of substitutionally doped phosphorene sheets with group III, IV, V, and VI elements. We find that the electronic properties of phosphorene are drastically modified by the number of valence electrons in dopant atoms. The dopants with an even number of valence electrons enable the doped phosphorenes to have a metallic feature, while the dopants with an odd number of valence electrons retain a semiconducting feature. This even-odd oscillating behavior is attributed to the peculiar bonding characteristics of phosphorene and the strong hybridization of sp orbitals between dopants and phosphorene. Furthermore, the calculated formation energies of various substitutional dopants in phosphorene show that such doped systems can be thermodynamically stable. These results propose an intriguing route to tune the transport properties of electronic and photoelectronic devices based on phosphorene.
Hu, Xue-Rong; Zheng, Ji-Ming; Ren, Zhao-Yu
2018-04-01
Based on first-principles calculations within the framework of density functional theory, we study the electronic properties of phosphorene/graphene heterostructures. Band gaps with different sizes are observed in the heterostructure, and charges transfer from graphene to phosphorene, causing the Fermi level of the heterostructure to shift downward with respect to the Dirac point of graphene. Significantly, strong coupling between two layers is discovered in the band spectrum even though it has a van der Waals heterostructure. A tight-binding Hamiltonian model is used to reveal that the resonance of the Bloch states between the phosphorene and graphene layers in certain K points combines with the symmetry matching between band states, which explains the reason for the strong coupling in such heterostructures. This work may enhance the understanding of interlayer interaction and composition mechanisms in van der Waals heterostructures consisting of two-dimensional layered nanomaterials, and may indicate potential reference information for nanoelectronic and optoelectronic applications.
Optoelectronic and magnetic properties of Mn-doped indium tin oxide: A first-principles study
Nath Tripathi, Madhvendra; Saeed Bahramy, Mohammad; Shida, Kazuhito; Sahara, Ryoji; Mizuseki, Hiroshi; Kawazoe, Yoshiyuki
2012-10-01
The manganese doped indium tin oxide (ITO) has integrated magnetics, electronics, and optical properties for next generation multifunctional devices. Our first-principles density functional theory (DFT) calculations show that the manganese atom replaces b-site indium atom, located at the second coordination shell of the interstitial oxygen in ITO. It is also found that both anti-ferromagnetic and ferromagnetic behaviors are realizable. The calculated magnetic moment of 3.95μB/Mn as well as the high transmittance of ˜80% for a 150 nm thin film of Mn doped ITO is in good agreement with the experimental data. The inclusion of on-site Coulomb repulsion corrections via DFT + U methods turns out to improve the optical behavior of the system. The optical behaviors of this system reveal its suitability for the magneto-opto-electronic applications.
International Nuclear Information System (INIS)
Noh, Seunghyo; Kwak, Dohyun; Lee, Juseung; Kang, Joonhee; Han, Byungchan
2014-01-01
We utilized first-principles density-functional-theory (DFT) calculations to evaluate the thermodynamic feasibility of a pyroprocessing methodology for reducing the volume of high-level radioactive materials and recycling spent nuclear fuels. The thermodynamic properties of transuranium elements (Pu, Np and Cm) were obtained in electrochemical equilibrium with a LiCl-KCl molten salt as ionic phases and as adsorbates on a W(110) surface. To accomplish the goal, we rigorously calculated the double layer interface structures on an atomic resolution, on the thermodynamically most stable configurations on W(110) surfaces and the chemical activities of the transuranium elements for various coverages of those elements. Our results indicated that the electrodeposition process was very sensitive to the atomic level structures of Cl ions at the double-layer interface. Our studies are easily expandable to general electrochemical applications involving strong redox reactions of transition metals in non-aqueous solutions.
First-principles prediction of shape memory behavior and ferrimagnetism in Mn2NiSn
International Nuclear Information System (INIS)
Paul, Souvik; Ghosh, Subhradip
2011-01-01
Using first-principles density functional theory, we show that, in Mn 2 NiSn, an energy lowering phase transition from the cubic to tetragonal phase occurs which indicates a martensitic phase transition. This structural phase transition is nearly volume-conserving, implying that this alloy can exhibit shape memory behavior. The magnetic ground state is a ferrimagnetic one with antiparallel Mn spin moments. The calculated moments with different electronic structure methods in the cubic phase compare well with each other but differ from the experimental values by more than 1 μ B . The reason behind this discrepancy is explored by considering antisite disorder in our calculations, which indicates that the site ordering in this alloy can be quite complex.
Quantum Chemistry of Solids The LCAO First Principles Treatment of Crystals
Evarestov, Robert A
2007-01-01
Quantum Chemistry of Solids delivers a comprehensive account of the main features and possibilities of LCAO methods for the first principles calculations of electronic structure of periodic systems. The first part describes the basic theory underlying the LCAO methods applied to periodic systems and the use of wave-function-based (Hartree-Fock), density-based (DFT) and hybrid hamiltonians. The translation and site symmetry consideration is included to establish connection between k-space solid-state physics and real-space quantum chemistry methods in the framework of cyclic model of an infinite crystal. The inclusion of electron correlation effects for periodic systems is considered on the basis of localized crystalline orbitals. The possibilities of LCAO methods for chemical bonding analysis in periodic systems are discussed. The second part deals with the applications of LCAO methods for calculations of bulk crystal properties, including magnetic ordering and crystal structure optimization. The discussion o...
Wobbled electronic properties of lithium clusters: Deterministic approach through first principles
Kushwaha, Anoop Kumar; Nayak, Saroj Kumar
2018-03-01
The innate tendency to form dendritic growth promoted through cluster formation leading to the failure of a Li-ion battery system have drawn significant attention of the researchers towards the effective destabilization of the cluster growth through selective implementation of electrolytic media such as acetonitrile (MeCN). In the present work, using first principles density functional theory and continuum dielectric model, we have investigated the origin of oscillatory nature of binding energy per atom of Lin (n ≤ 8) under the influence of MeCN. In the gas phase, we found that static mean polarizability is strongly correlated with binding energy and shows oscillatory nature with cluster size due to the open shell of Lin cluster. However, in acetonitrile medium, the binding energy has been correlated with electrostatic Lin -MeCN interaction and it has been found that both of them possess wobbled behavior characterized by the cluster size.
First-principles calculations of the electronic and structural properties of GaSb
Energy Technology Data Exchange (ETDEWEB)
Castaño-González, E.-E. [Universidad del Norte, Grupo de Investigación en Física Aplicada, Departamento de Física (Colombia); Seña, N. [Universidad Nacional de Colombia-Colombia, Departamento de Física, Grupo de Materiales Nanoestructurados y sus Aplicaciones (Colombia); Mendoza-Estrada, V.; González-Hernández, R., E-mail: rhernandezj@uninorte.edu.co [Universidad del Norte, Grupo de Investigación en Física Aplicada, Departamento de Física (Colombia); Dussan, A. [Universidad Nacional de Colombia-Colombia, Departamento de Física, Grupo de Materiales Nanoestructurados y sus Aplicaciones (Colombia); Mesa, F., E-mail: fredy.mesa@urosario.edu.co [Universidad del Rosario, Grupo NanoTech, Facultad de Ciencias Naturales y Matemáticas (Colombia)
2016-10-15
In this paper, we carried out first-principles calculations in order to investigate the structural and electronic properties of the binary compound gallium antimonide (GaSb). This theoretical study was carried out using the Density Functional Theory within the plane-wave pseudopotential method. The effects of exchange and correlation (XC) were treated using the functional Local Density Approximation (LDA), generalized gradient approximation (GGA): Perdew–Burke–Ernzerhof (PBE), Perdew-Burke-Ernzerhof revised for solids (PBEsol), Perdew-Wang91 (PW91), revised Perdew–Burke–Ernzerhof (rPBE), Armiento–Mattson 2005 (AM05) and meta-generalized gradient approximation (meta-GGA): Tao–Perdew–Staroverov–Scuseria (TPSS) and revised Tao–Perdew–Staroverov–Scuseria (RTPSS) and modified Becke-Johnson (MBJ). We calculated the densities of state (DOS) and band structure with different XC potentials identified and compared them with the theoretical and experimental results reported in the literature. It was discovered that functional: LDA, PBEsol, AM05 and RTPSS provide the best results to calculate the lattice parameters (a) and bulk modulus (B{sub 0}); while for the cohesive energy (E{sub coh}), functional: AM05, RTPSS and PW91 are closer to the values obtained experimentally. The MBJ, Rtpss and AM05 values found for the band gap energy is slightly underestimated with those values reported experimentally.
First-Principles Thermodynamics of Energetic Materials
2012-01-01
thermal and zero-point energy ( ZPE ) effects on the crystalline environment [8]. By including vdW, thermal, and ZPE effects into DFT (DFT+vdW+T...by their relation to experiment (triangles) pure DFT over-predicts, while DFT+vdW under-predicts the EOSs. Only when temperature and ZPE effects...crystals with ZPE effects still included. To get a sense of how the vdW damping function might affect the calculation of the dynamical matrix, the
International Nuclear Information System (INIS)
Katagiri, Hideki; Shimoi, Yukihiro; Abe, Shuji
2004-01-01
Backbone structures of polydiacetylene are studied with first-principles electronic structure method using plane-waves within generalized gradient approximation (GGA) of density functional theory. In spin-restricted calculations a coarse k-point sampling gives a potential energy curve with two local minima corresponding to acetylene and butatriene structures. However, the potential barrier between the two structures rapidly decreases with increasing number of k-points, which results in destabilization of the butatriene structure. Spin polarization effects also destabilize the butatriene structure, inducing atom-centered spin-density-wave state. These potential energies were compared with those obtained by Hartree-Fock, density functional within local density approximation (LDA) and GGA, and hybrid density functional methods using a gaussian basis set. The comparison shows that the density functional methods within LDA and GGA favor the destabilization of the butatriene structure in contrast to the Hartree-Fock method
First principles calculations of interstitial and lamellar rhenium nitrides
Energy Technology Data Exchange (ETDEWEB)
Soto, G., E-mail: gerardo@cnyn.unam.mx [Universidad Nacional Autonoma de Mexico, Centro de Nanociencias y Nanotecnologia, Km 107 Carretera Tijuana-Ensenada, Ensenada Baja California (Mexico); Tiznado, H.; Reyes, A.; Cruz, W. de la [Universidad Nacional Autonoma de Mexico, Centro de Nanociencias y Nanotecnologia, Km 107 Carretera Tijuana-Ensenada, Ensenada Baja California (Mexico)
2012-02-15
Highlights: Black-Right-Pointing-Pointer The possible structures of rhenium nitride as a function of composition are analyzed. Black-Right-Pointing-Pointer The alloying energy is favorable for rhenium nitride in lamellar arrangements. Black-Right-Pointing-Pointer The structures produced by magnetron sputtering are metastable variations. Black-Right-Pointing-Pointer The structures produced by high-pressure high-temperature are stable configurations. Black-Right-Pointing-Pointer The lamellar structures are a new category of interstitial dissolutions. - Abstract: We report here a systematic first principles study of two classes of variable-composition rhenium nitride: i, interstitial rhenium nitride as a solid solution and ii, rhenium nitride in lamellar structures. The compounds in class i are cubic and hexagonal close-packed rhenium phases, with nitrogen in the octahedral and tetrahedral interstices of the metal, and they are formed without changes to the structure, except for slight distortions of the unit cells. In the compounds in class ii, by contrast, the nitrogen inclusion provokes stacking faults in the parent metal structure. These faults create trigonal-prismatic sites where the nitrogen residence is energetically favored. This second class of compounds produces lamellar structures, where the nitrogen lamellas are inserted among multiple rhenium layers. The Re{sub 3}N and Re{sub 2}N phases produced recently by high-temperature and high-pressure synthesis belong to this class. The ratio of the nitrogen layers to the rhenium layers is given by the composition. While the first principle calculations point to higher stability for the lamellar structures as opposed to the interstitial phases, the experimental evidence presented here demonstrates that the interstitial classes are synthesizable by plasma methods. We conclude that rhenium nitrides possess polymorphism and that the two-dimensional lamellar structures might represent an emerging class of materials
First principles calculations of interstitial and lamellar rhenium nitrides
International Nuclear Information System (INIS)
Soto, G.; Tiznado, H.; Reyes, A.; Cruz, W. de la
2012-01-01
Highlights: ► The possible structures of rhenium nitride as a function of composition are analyzed. ► The alloying energy is favorable for rhenium nitride in lamellar arrangements. ► The structures produced by magnetron sputtering are metastable variations. ► The structures produced by high-pressure high-temperature are stable configurations. ► The lamellar structures are a new category of interstitial dissolutions. - Abstract: We report here a systematic first principles study of two classes of variable-composition rhenium nitride: i, interstitial rhenium nitride as a solid solution and ii, rhenium nitride in lamellar structures. The compounds in class i are cubic and hexagonal close-packed rhenium phases, with nitrogen in the octahedral and tetrahedral interstices of the metal, and they are formed without changes to the structure, except for slight distortions of the unit cells. In the compounds in class ii, by contrast, the nitrogen inclusion provokes stacking faults in the parent metal structure. These faults create trigonal-prismatic sites where the nitrogen residence is energetically favored. This second class of compounds produces lamellar structures, where the nitrogen lamellas are inserted among multiple rhenium layers. The Re 3 N and Re 2 N phases produced recently by high-temperature and high-pressure synthesis belong to this class. The ratio of the nitrogen layers to the rhenium layers is given by the composition. While the first principle calculations point to higher stability for the lamellar structures as opposed to the interstitial phases, the experimental evidence presented here demonstrates that the interstitial classes are synthesizable by plasma methods. We conclude that rhenium nitrides possess polymorphism and that the two-dimensional lamellar structures might represent an emerging class of materials within binary nitride chemistry.
Density functional theory study of Al-doped hematite
International Nuclear Information System (INIS)
Rivera, Richard; Stashans, Arvids; Piedra, Lorena; Pinto, Henry P
2012-01-01
Using first-principles density functional theory calculations within the generalized gradient approximation (GGA) as well as the GGA+U approach, we study Al-doped α-Fe 2 O 3 crystals. Structural, electronic, magnetic and optical properties due to impurity incorporation have been investigated and discussed in detail. Atomic displacements and Bader charges on atoms have been computed, showing that Al dopant converts the chemical bonding in its neighbourhood into a more ionic one. This work enhances our knowledge about how a crystalline lattice reacts in the presence of an Al impurity. It was found that Al incorporation produces some local changes in the band structure of the material without the creation of local energy levels within the band gap. The results provide evidence for changes in the magnetic moments in the vicinity of a defect, which means that α-Fe 2 O 3 doped with aluminum might not act as an antiferromagnetic substance.
First-Principles Investigations of Defects in Minerals
Verma, Ashok K.
2011-07-01
The ideal crystal has an infinite 3-dimensional repetition of identical units which may be atoms or molecules. But real crystals are limited in size and they have disorder in stacking which as called defects. Basically three types of defects exist in solids: 1) point defects, 2) line defects, and 3) surface defects. Common point defects are vacant lattice sites, interstitial atoms and impurities and these are known to influence strongly many solid-state transport properties such as diffusion, electrical conduction, creep, etc. In thermal equilibrium point defects concentrations are determined by their formation enthalpies and their movement by their migration barriers. Line and surface defects are though absent from the ideal crystal in thermal equilibrium due to higher energy costs but they are invariably present in all real crystals. Line defects include edge-, screw- and mixed-dislocations and their presence is essential in explaining the mechanical strength and deformation of real crystals. Surface defects may arise at the boundary between two grains, or small crystals, within a larger crystal. A wide variety of grain boundaries can form in a polycrystal depending on factors such growth conditions and thermal treatment. In this talk we will present our first-principles density functional theory based defect studies of SiO2 polymorphs (stishovite, CaCl2-, α-PbO2-, and pyrite-type), Mg2SiO4 polymorphs (forsterite, wadsleyite and ringwoodite) and MgO [1-3]. Briefly, several native point defects including vacancies, interstitials, and their complexes were studied in silica polymorphs upto 200 GPa. Their values increase by a factor of 2 over the entire pressure range studied with large differences in some cases between different phases. The Schottky defects are energetically most favorable at zero pressure whereas O-Frenkel pairs become systematically more favorable at pressures higher than 20 GPa. The geometric and electronic structures of defects and migrating
Open-system Kohn-Sham density functional theory.
Zhou, Yongxi; Ernzerhof, Matthias
2012-03-07
A simple model for electron transport through molecules is provided by the source-sink potential (SSP) method [F. Goyer, M. Ernzerhof, and M. Zhuang, J. Chem. Phys. 126, 144104 (2007)]. In SSP, the boundary conditions of having an incoming and outgoing electron current are enforced through complex potentials that are added to the Hamiltonian. Depending on the sign of the imaginary part of the potentials, current density is generated or absorbed. In this way, a finite system can be used to model infinite molecular electronic devices. The SSP has originally been developed for the Hückel method and subsequently it has been extended [F. Goyer and M. Ernzerhof, J. Chem. Phys. 134, 174101 (2011)] to the Hubbard model. Here we present a step towards its generalization for first-principles electronic structure theory methods. In particular, drawing on our earlier work, we discuss a new generalized density functional theory for complex non-Hermitian Hamiltonians. This theory enables us to combine SSP and Kohn-Sham theory to obtain a method for the description of open systems that exchange current density with their environment. Similarly, the Hartree-Fock method is extended to the realm of non-Hermitian, SSP containing Hamiltonians. As a proof of principle, we present the first applications of complex-density functional theory (CODFT) as well as non-Hermitian Hartree-Fock theory to electron transport through molecules. © 2012 American Institute of Physics
Energy Technology Data Exchange (ETDEWEB)
Tayran, Ceren; Aydin, Sezgin [Department of Physics, Sciences Faculty, Gazi University, 06500, Ankara (Turkey)
2017-05-15
The structural, elastic, mechanical, and electronic properties of lithium aluminum tetraboride (LiAlB{sub 4}) under hydrostatic pressure have been investigated by using first-principles density functional theory calculations. The effects of pressure on the lattice parameters, volume, and bond lengths are studied. It is indicated from the calculated elastic constants that LiAlB{sub 4} compound is mechanically stable on 0-40 GPa pressure range. And, by means of these elastic constants set, some mechanical properties such as bulk, shear and Young's moduli, and then Poisson's ratio are determined as a function of pressure. Also, the ductile or brittle nature of LiAlB{sub 4} is examined. Additionally, using the first-principles data obtained from the geometry optimizations, the hardness of LiAlB{sub 4} is calculated, and its nature is investigated under pressure. Furthermore, in order to reveal the effects of pressure on the electronic and binding behavior of the compound, band structures, total and partial density of states, charge densities, Mulliken atomic charges, and bond overlap populations are searched as a function of pressure. To check the stability of the compound, phonon dispersion curves are calculated. And, the results are compared with the other convenient borides. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
International Nuclear Information System (INIS)
Kim, Yonghyun; Kirichenko, Taras A.; Kong, Ning; Larson, Larry; Banerjee, Sanjay K.
2007-01-01
We propose new structural configurations and novel diffusion mechanisms for neutral di-arsenic interstitial (As 2 I 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 2 I 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 ( 2 I 2 can be easily formed and likely intermediate stage of larger arsenic interstitial clusters
DEFF Research Database (Denmark)
Strange, Mikkel; Thygesen, Kristian Sommer
2011-01-01
-electron interactions are described by th=e many-body GW approximation. The conductance follows an exponential length dependence: Gn = Gc exp(-βn). The main difference from standard density functional theory (DFT) calculations is a significant reduction of the contact conductance, Gc, due to an improved alignment......The calculation of the electronic conductance of nanoscale junctions from first principles is a long-standing problem in the field of charge transport. Here we demonstrate excellent agreement with experiments for the transport properties of the gold/alkanediamine benchmark system when electron...
First-principles study for the enhanced sulfur tolerance of Ni(1 1 1) surface alloyed with Pb
Zhang, Yanxing; Yang, Zongxian
2018-04-01
The adsorption of H2S, HS, S, H and the dissociation of H2S on the Ni2Pb/Ni (1 1 1) are systematically studied using the first-principles method based on density functional theory. It is found that H2S dissociation barriers are greatly increased by alloying with Pb atoms in the Ni(1 1 1) surface, while the barrier for H2S formation is greatly reduced. In addition, the adsorption of sulfur atom is weakened a lot. The results indicate that alloying with Pb may be a good way to increase the sulfur tolerance of Ni based anode catalysts of solid oxide fuel cells.
Half-metallic ferromagnetism in Fe-doped Zn3P2 from first-principles calculations
International Nuclear Information System (INIS)
Jaiganesh, G.; Jaya, S. Mathi
2014-01-01
Using the first-principles calculations based on the density functional theory, we have studied the magnetism and electronic structure of Fe-doped Zinc Phosphide (Zn 3 P 2 ). Our results show that the half-metallic ground state and ferromagnetic stability for the small Fe concentrations considered in our study. The stability of the doped material has been studied by calculating the heat of formation and analyzing the minimum total energies in nonmagnetic and ferromagnetic phases. A large value of the magnetic moment is obtained from our calculations and our calculation suggests that the Fe-doped Zn 3 P 2 may be a useful material in semiconductor spintronics
Minimal nuclear energy density functional
Bulgac, Aurel; Forbes, Michael McNeil; Jin, Shi; Perez, Rodrigo Navarro; Schunck, Nicolas
2018-04-01
We present a minimal nuclear energy density functional (NEDF) called "SeaLL1" that has the smallest number of possible phenomenological parameters to date. SeaLL1 is defined by seven significant phenomenological parameters, each related to a specific nuclear property. It describes the nuclear masses of even-even nuclei with a mean energy error of 0.97 MeV and a standard deviation of 1.46 MeV , two-neutron and two-proton separation energies with rms errors of 0.69 MeV and 0.59 MeV respectively, and the charge radii of 345 even-even nuclei with a mean error ɛr=0.022 fm and a standard deviation σr=0.025 fm . SeaLL1 incorporates constraints on the equation of state (EoS) of pure neutron matter from quantum Monte Carlo calculations with chiral effective field theory two-body (NN ) interactions at the next-to-next-to-next-to leading order (N3LO) level and three-body (NNN ) interactions at the next-to-next-to leading order (N2LO) level. Two of the seven parameters are related to the saturation density and the energy per particle of the homogeneous symmetric nuclear matter, one is related to the nuclear surface tension, two are related to the symmetry energy and its density dependence, one is related to the strength of the spin-orbit interaction, and one is the coupling constant of the pairing interaction. We identify additional phenomenological parameters that have little effect on ground-state properties but can be used to fine-tune features such as the Thomas-Reiche-Kuhn sum rule, the excitation energy of the giant dipole and Gamow-Teller resonances, the static dipole electric polarizability, and the neutron skin thickness.
A method of orbital analysis for large-scale first-principles simulations
Energy Technology Data Exchange (ETDEWEB)
Ohwaki, Tsukuru [Advanced Materials Laboratory, Nissan Research Center, Nissan Motor Co., Ltd., 1 Natsushima-cho, Yokosuka, Kanagawa 237-8523 (Japan); Otani, Minoru [Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Ozaki, Taisuke [Research Center for Simulation Science (RCSS), Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292 (Japan)
2014-06-28
An efficient method of calculating the natural bond orbitals (NBOs) based on a truncation of the entire density matrix of a whole system is presented for large-scale density functional theory calculations. The method recovers an orbital picture for O(N) electronic structure methods which directly evaluate the density matrix without using Kohn-Sham orbitals, thus enabling quantitative analysis of chemical reactions in large-scale systems in the language of localized Lewis-type chemical bonds. With the density matrix calculated by either an exact diagonalization or O(N) method, the computational cost is O(1) for the calculation of NBOs associated with a local region where a chemical reaction takes place. As an illustration of the method, we demonstrate how an electronic structure in a local region of interest can be analyzed by NBOs in a large-scale first-principles molecular dynamics simulation for a liquid electrolyte bulk model (propylene carbonate + LiBF{sub 4})
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.
A first principles study of the mechanical, electronic, and vibrational properties of lead oxide
Zhuravlev, Yu. N.; Korabel'nikov, D. V.
2017-11-01
The first principles study of the crystal structure, chemical bonds, elastic and mechanical properties, electron energy band structure and density, and normal long-wave vibrations of nine phases of lead monoxide, dioxide, and tetraoxide has been performed under normal and external pressure within the framework of density functional theory (DFT) with the Perdew-Becke-Ernzerhof (PBE) gradient exchange-correlation functional and its hybrid version with a 25-% Hartree-Fock (HF) exchange contribution in the basis of localized atom orbitals. The behavior of physical parameters has been studied using the cold four- and threeparameter equations of state. The parameters of the crystal structures are in satisfactory agreement with experimental data, and elastic constants indicate their mechanical stability and anisotropy in the elastic properties. The elasticity, shear, and Young moduli, hardness, acoustic velocities, and Debye temperature of dioxide on the one hand and monoxide and tetraoxide on the other hand appreciably differ from each other. The difference between electron properties may be explained by the character of hybridization in the upper filled and lower empty energy bands as evident from the density of states. In monoxide, the indirect band gap width decreases with increasing pressure at a rate of 0.16 eV/GPa, and the direct band gap width increases at a rate of 0.13 eV/GPa. To identify crystalline phases, the frequencies and intensities of long-wave modes active in IR and Raman spectra have been calculated.
First-principles calculation on electronic properties of zinc oxide by zinc–air system
Directory of Open Access Journals (Sweden)
Ahmad Azmin Mohamad
2017-07-01
Full Text Available First-principles calculations are performed to study the electronic properties of zinc oxide (ZnO formed on an anode after discharging a Zn–air system. Prior to calculation, the ZnO is characterised by X-ray diffraction using Rietveld refinement. Diffracted patterns proved the formation of single phase ZnO, while Rietveld analysis shows that the ZnO has a hexagonal wurtzite structure with lattice parameters, a = 3.244 and c = 5.199 Å. Geometry optimisation of the hexagonal wurtzite structure of the ZnO is performed using various exchange–correlation energy functionals. The local density approximation functional method is used to explain the structure, electronic band structure and density of state properties of hexagonal ZnO. The calculated energy band gap was 0.75 eV while the density of states reveals that the O 2p (the top valence band and Zn 4s (the bottom conduction band states domination.
First-principle calculations of structural, electronic, optical, elastic ...
Indian Academy of Sciences (India)
S CHEDDADI
2017-11-28
Nov 28, 2017 ... First-principle calculations on the structural, electronic, optical, elastic and thermal properties of the chalcopyrite ... The Kohn–Sham equations were solved using the ... RMTKmax = 7 was used for all the investigated systems,.
First-principles data-driven discovery of transition metal oxides for artificial photosynthesis
Yan, Qimin
We develop a first-principles data-driven approach for rapid identification of transition metal oxide (TMO) light absorbers and photocatalysts for artificial photosynthesis using the Materials Project. Initially focusing on Cr, V, and Mn-based ternary TMOs in the database, we design a broadly-applicable multiple-layer screening workflow automating density functional theory (DFT) and hybrid functional calculations of bulk and surface electronic and magnetic structures. We further assess the electrochemical stability of TMOs in aqueous environments from computed Pourbaix diagrams. Several promising earth-abundant low band-gap TMO compounds with desirable band edge energies and electrochemical stability are identified by our computational efforts and then synergistically evaluated using high-throughput synthesis and photoelectrochemical screening techniques by our experimental collaborators at Caltech. Our joint theory-experiment effort has successfully identified new earth-abundant copper and manganese vanadate complex oxides that meet highly demanding requirements for photoanodes, substantially expanding the known space of such materials. By integrating theory and experiment, we validate our approach and develop important new insights into structure-property relationships for TMOs for oxygen evolution photocatalysts, paving the way for use of first-principles data-driven techniques in future applications. This work is supported by the Materials Project Predictive Modeling Center and the Joint Center for Artificial Photosynthesis through the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract No. DE-AC02-05CH11231. Computational resources also provided by the Department of Energy through the National Energy Supercomputing Center.
Equilibration and analysis of first-principles molecular dynamics simulations of water
Dawson, William; Gygi, François
2018-03-01
First-principles molecular dynamics (FPMD) simulations based on density functional theory are becoming increasingly popular for the description of liquids. In view of the high computational cost of these simulations, the choice of an appropriate equilibration protocol is critical. We assess two methods of estimation of equilibration times using a large dataset of first-principles molecular dynamics simulations of water. The Gelman-Rubin potential scale reduction factor [A. Gelman and D. B. Rubin, Stat. Sci. 7, 457 (1992)] and the marginal standard error rule heuristic proposed by White [Simulation 69, 323 (1997)] are evaluated on a set of 32 independent 64-molecule simulations of 58 ps each, amounting to a combined cumulative time of 1.85 ns. The availability of multiple independent simulations also allows for an estimation of the variance of averaged quantities, both within MD runs and between runs. We analyze atomic trajectories, focusing on correlations of the Kohn-Sham energy, pair correlation functions, number of hydrogen bonds, and diffusion coefficient. The observed variability across samples provides a measure of the uncertainty associated with these quantities, thus facilitating meaningful comparisons of different approximations used in the simulations. We find that the computed diffusion coefficient and average number of hydrogen bonds are affected by a significant uncertainty in spite of the large size of the dataset used. A comparison with classical simulations using the TIP4P/2005 model confirms that the variability of the diffusivity is also observed after long equilibration times. Complete atomic trajectories and simulation output files are available online for further analysis.
Half-metallic ferromagnetism in Fe, Co and Ni doped BaS: First principles calculations
Maurya, Savita; Sharma, Ramesh; Bhamu, K. C.
2018-04-01
The first principle investigation of structural, electronic, magnetic and optical properties of Ba1-xTMxS (x = 0.25) have been done using FPLAW method within the density functional theory (DFT) using generalized gradient approximation (GGA) for exchange correlation potential using two different functionals which are the PBE-sol and the modified Becke and Johnson local (spin) density approximation (mBJLDA). It was found that mBJLDA functional offer better account for the electronic structure of the Fe, Co and Ni-doped BaS. It was also observed that Fe/Co/Ni d, S p and Ba d states play a major role in determining the electronic properties of this alloy system. Investigation results shows that Ba0.75(Fe/Co/Ni)0.25S is ferromagnetic with magnetic moment of 3.72 µB, 2.73908 µB and 1.74324 µB at Fe, Co and Ni sites respectively. Complex dielectric constant ɛ(ω) and normal incidence reflectivity R(ω) are also been investigate for broad range of photon energies. These results are compared with the some reported existing experimental values.
First Principles Thermodynamics of Minerals at HP–HT Conditions: MgO as a Prototypical Material
Directory of Open Access Journals (Sweden)
Donato Belmonte
2017-09-01
Full Text Available Ab initio thermodynamic properties, equation of state and phase stability of periclase (MgO, B1-type structure have been investigated in a broad P–T range (0–160 GPa; 0–3000 K in order to set a model reference system for phase equilibria simulations under deep Earth conditions. Phonon dispersion calculations performed on large supercells using the finite displacement method and in the framework of quasi-harmonic approximation highlight the performance of the Becke three-parameter Lee-Yang-Parr (B3LYP hybrid density functional in predicting accurate thermodynamic functions (heat capacity, entropy, thermal expansivity, isothermal bulk modulus and phase reaction boundaries at high pressure and temperature. A first principles Mie–Grüneisen equation of state based on lattice vibrations directly provides a physically-consistent description of thermal pressure and P–V–T relations without any need to rely on empirical parameters or other phenomenological formalisms that could give spurious anomalies or uncontrolled extrapolations at HP–HT. The post-spinel phase transformation, Mg2SiO4 (ringwoodite = MgO (periclase + MgSiO3 (bridgmanite, is taken as a computational example to illustrate how first principles theory combined with the use of hybrid functionals is able to provide sound results on the Clapeyron slope, density change and P–T location of equilibrium mineral reactions relevant to mantle dynamics.
International Nuclear Information System (INIS)
Xie, Z.L.; Dy, K.S.; Wu, S.Y.
1997-01-01
A real-space scheme has been developed for a first-principles calculation of electronic structures and total energies of atomic clusters. The scheme is based on the combination of the tight-binding linear muffin-tin orbital (TBLMTO) method and the method of real-space Green close-quote s function. With this approach, the local electronic density of states can be conveniently determined from the real-space Green close-quote s function. Furthermore, the full electron density of a cluster can be directly calculated in real space. The scheme has been shown to be very efficient due to the incorporation of the method of real-space Green close-quote s function and Delley close-quote s method of evaluating multicenter integrals. copyright 1996 The American Physical Society
Oxygen vacancy effects in HfO2-based resistive switching memory: First principle study
Directory of Open Access Journals (Sweden)
Yuehua Dai
2016-08-01
Full Text Available The work investigated the shape and orientation of oxygen vacancy clusters in HfO2-base resistive random access memory (ReRAM by using the first-principle method based on the density functional theory. Firstly, the formation energy of different local Vo clusters was calculated in four established orientation systems. Then, the optimized orientation and charger conductor shape were identified by comparing the isosurface plots of partial charge density, formation energy, and the highest isosurface value of oxygen vacancy. The calculated results revealed that the [010] orientation was the optimal migration path of Vo, and the shape of system D4 was the best charge conductor in HfO2, which effectively influenced the SET voltage, formation voltage and the ON/OFF ratio of the device. Afterwards, the PDOS of Hf near Vo and total density of states of the system D4_010 were obtained, revealing the composition of charge conductor was oxygen vacancy instead of metal Hf. Furthermore, the migration barriers of the Vo hopping between neighboring unit cells were calculated along four different orientations. The motion was proved along [010] orientation. The optimal circulation path for Vo migration in the HfO2 super-cell was obtained.
Absorption of CO2 on Carbon-based Sensors: First-Principle Analysis
Tit, Nacir; Elezzi, Mohammed; Abdullah, Hasan; Bahlouli, Hocine; Yamani, Zain
We present first-principle investigation of the adsorption properties of CO and CO2 molecules on both graphene and carbon nano-tubes (CNTs) in presence of metal catalysis, mainly iron (Fe). The relaxations were carried out using the self-consistent-charge density-functional tight-binding (SCC-DFTB) code in neglect of heat effects. The results show the following: (1) Defected graphene is found to have high sensitivity and high selectivity towards chemisorption of CO molecules and weak physisorption with CO2 molecules. (2) In case of CNTs, the iron ``Fe'' catalyst plays an essential role in capturing CO2 molecules. The Fe ad-atoms on the surface of CNT introduce huge density of states at Fermi level, but the capture of CO2 molecules would reduce that density and consequently reduce conductivity and increase sensitivity. Concerning the selectivity, we have studied the sensitivity versus various gas molecules (such as: O2, N2, H2, H2O, and CO). Furthermore, to assess the effect of catalysis on sensitivity, we have studied the sensitivity of other metal catalysts (such as: Ni, Co, Ti, and Sc). We found that CNT-Fe is highly sensitive and selective towards detection of CO and CO2 molecules. CNT being conductive or semiconducting does not matter much on the adsorption properties.
Thermophysical properties of paramagnetic Fe from first principles
Ehteshami, Hossein; Korzhavyi, Pavel A.
2017-12-01
A computationally efficient, yet general, free-energy modeling scheme is developed based on first-principles calculations. Finite-temperature disorder associated with the fast (electronic and magnetic) degrees of freedom is directly included in the electronic structure calculations, whereas the vibrational free energy is evaluated by a proposed model that uses elastic constants to calculate average sound velocity of the quasiharmonic Debye model. The proposed scheme is tested by calculating the lattice parameter, heat capacity, and single-crystal elastic constants of α -, γ -, and δ -iron as functions of temperature in the range 1000-1800 K. The calculations accurately reproduce the well-established experimental data on thermal expansion and heat capacity of γ - and δ -iron. Electronic and magnetic excitations are shown to account for about 20% of the heat capacity for the two phases. Nonphonon contributions to thermal expansion are 12% and 10% for α - and δ -Fe and about 30% for γ -Fe. The elastic properties predicted by the model are in good agreement with those obtained in previous theoretical treatments of paramagnetic phases of iron, as well as with the bulk moduli derived from isothermal compressibility measurements [N. Tsujino et al., Earth Planet. Sci. Lett. 375, 244 (2013), 10.1016/j.epsl.2013.05.040]. Less agreement is found between theoretically calculated and experimentally derived single-crystal elastic constants of γ - and δ -iron.
The elastic and thermodynamic properties of ZrMo2 from first principles calculations
International Nuclear Information System (INIS)
Liu, Xian-Kun; Zhou, Wei; Zheng, Zhou; Peng, Shu-Ming
2014-01-01
Highlights: • Elastic and thermodynamic properties of ZrMo 2 under high temperature and pressure are calculated by first principles. • Mechanical stability is testified from elastic constants at zero pressure. • Phonon scattering of ZrMo 2 under different temperature are obtained. - Abstract: The elastic and thermodynamic properties of ZrMo 2 under high temperature and pressure are investigated by first-principles calculations based on pseudopotential plane-wave density functional theory (DFT) within the generalized gradient approximation (GGA) and quasi-harmonic Debye model. The calculated lattice parameters are in good agreement with the available experimental data. The calculated elastic constants of ZrMo 2 increase monotonically with increasing pressure, and the relationship between the elastic constants and pressure show that ZrMo 2 satisfies the mechanical stability criteria under applied pressure (0–65 GPa). The related mechanical properties such as bulk modulus (B), shear modulus (G), Young’s modulus (E), and Poisson’s ratio (v) are also studied for polycrystalline of ZrMo 2 . The calculated B/G value shows that ZrMo 2 behaves in a ductile manner, and higher pressure can significantly improve the ductility of ZrMo 2 . The pressure and temperature dependencies of the relative volume, the bulk modulus, the elastic constants, the heat capacity and the thermal expansion coefficient, as well as the Grüneisen parameters are obtained and discussed by the quasi-harmonic Debye model in the ranges of 0–1800 K and 0–65 GPa
The interaction of oxygen with TiC(001): Photoemission and first-principles studies
International Nuclear Information System (INIS)
Rodriguez, J.A.; Liu, P.; Dvorak, J.; Jirsak, T.; Gomes, J.; Takahashi, Y.; Nakamura, K.
2004-01-01
High-resolution photoemission and first-principles density-functional slab calculations were used to study the interaction of oxygen with a TiC(001) surface. Atomic oxygen is present on the TiC(001) substrate after small doses of O 2 at room temperature. A big positive shift (1.5-1.8 eV) was detected for the C 1s core level. These photoemission studies suggest the existence of strong O↔C interactions. A phenomenon corroborated by the results of first-principles calculations, which show a CTiTi hollow as the most stable site for the adsorption of O. Ti and C atoms are involved in the adsorption and dissociation of the O 2 molecule. In general, the bond between O and the TiC(001) surface contains a large degree of ionic character. The carbide→O charge transfer is substantial even at high coverages (>0.5 ML) of oxygen. At 500 K and large doses of O 2 , oxidation of the carbide surface occurs with the removal of C and formation of titanium oxides. There is an activation barrier for the exchange of Ti-C and Ti-O bonds which is overcome only by the formation of C-C or C-O bonds on the surface. The mechanism for the removal of a C atom as CO gas involves a minimum of two O adatoms, and three O adatoms are required for the formation of CO 2 gas. Due to the high stability of TiC, an O adatom alone cannot induce the generation of a C vacancy in a flat TiC(001) surface
Dai, Jiayu; Hou, Yong; Yuan, Jianmin
2010-06-18
Electron-ion interactions are central to numerous phenomena in the warm dense matter (WDM) regime and at higher temperature. The electron-ion collisions induced friction at high temperature is introduced in the procedure of ab initio molecular dynamics using the Langevin equation based on density functional theory. In this framework, as a test for Fe and H up to 1000 eV, the equation of state and the transition of electronic structures of the materials with very wide density and temperature can be described, which covers a full range of WDM up to high energy density physics. A unified first principles description from condensed matter to ideal ionized gas plasma is constructed.
Li, Pan; Zhang, Jianxin; Ma, Shiyu; Jin, Huixin; Zhang, Youjian; Zhang, Wenyang
2018-06-01
The structural, elastic, electronic properties and Debye temperature of Ni3Ta under different pressures are investigated using the first-principles method based on density functional theory. Our calculated equilibrium lattice parameters at 0 GPa well agree with the experimental and previous theoretical results. The calculated negative formation enthalpies and elastic constants both indicate that Ni3Ta is stable under different pressures. The bulk modulus B, shear modulus G, Young's modulus E and Poisson's ratio ν are calculated by the Voigt-Reuss-Hill method. The bigger ratio of B/G indicates Ni3Ta is ductile and the pressure can improve the ductility of Ni3Ta. In addition, the results of density of states and the charge density difference show that the stability of Ni3Ta is improved by the increasing pressure. The Debye temperature ΘD calculated from elastic modulus increases along with the pressure.
On possibility of superconductivity in SnSb: A first principle study
Energy Technology Data Exchange (ETDEWEB)
Dabhi, Shweta D. [Department of Physics, M. K. Bhavnagar University, Bhavnagar 364001 (India); Shrivastava, Deepika [Department of Physics, Barkatullah University, Bhopal 462026 (India); Jha, Prafulla K., E-mail: prafullaj@yahoo.com [Department of Physics, Faculty of Science, The M. S. University of Baroda, Vadodara 390002 (India); Sanyal, Sankar P. [Department of Physics, Barkatullah University, Bhopal 462026 (India)
2016-09-15
Highlights: • Superconducting property of SnSb is predicted by ab-initio calculations. • Electronic properties of SnSb in RS phase shows metallic behaviour similar to SnAs. • Phonon dispersion confirms the dynamical stability of SnSb in RS phase. • Superconducting transition temperature is 3.1 K, slightly lower than that of SnAs. • Calculated thermodynamic properties are also reported. - Abstract: The electronic, phonon structure and superconducting properties of tin antimonide (SnSb) in rock-salt (RS) structure are calculated using first-principles density functional theory. The electronic band structure and density of states show metallic behavior. The phonon frequencies are positive throughout the Brillouin zone in rock-salt structure indicating its stability in that phase. Superconductivity of SnSb in RS phase is discussed in detail by calculating phonon linewidths, Eliashberg spectral function, electron-phonon coupling constant and superconducting transition temperature. SnSb is found to have a slightly lower T{sub C} (3.1 K), as compared to SnAs.
The first-principles calculations for the elastic properties of Zr2Al under compression
International Nuclear Information System (INIS)
Yuan Xiaoli; Wei Dongqing; Chen Xiangrong; Zhang Qingming; Gong Zizheng
2011-01-01
Graphical abstract: The calculated elastic constants C ij as a function of pressure P. Display Omitted Research highlights: → It is found that the five independent elastic constants increase monotonically with pressure. C 11 and C 33 vary rapidly as pressure increases, C 13 and C 12 becomes moderate. However, C 44 increases comparatively slowly with pressure. Figure shows excellent satisfaction of the calculated elastic constants of Zr 2 Al to these equations and hence in our calculation, the Zr 2 Al is mechanically stable at pressure up to 100 GPa. - Abstract: The first-principles calculations were applied to investigate the structural, elastic constants of Zr 2 Al alloy with increasing pressure. These properties are based on the plane wave pseudopotential density functional theory (DFT) method within the generalized gradient approximation (GGA) for exchange and correlation. The result of the heat of formation of Zr 2 Al crystal investigated is in excellent consistent with results from other study. The anisotropy, the shear modulus, and Young's modulus for the ideal polycrystalline Zr 2 Al are also studied. It is found that (higher) pressure can significantly improve the ductility of Zr 2 Al. Moreover, the elastic constants of Zr 2 Al increase monotonically and the anisotropies decrease with the increasing pressure. Finally, it is observed that Zr d electrons are mainly contributed to the density of states at the Fermi level.
First-principles calculation of transport property in nano-devices under an external magnetic field
International Nuclear Information System (INIS)
Chen Jingzhe; Zhang Jin; Han Rushan
2008-01-01
The mesoscopic quantum interference phenomenon (QIP) can be observed and behaves as the oscillation of conductance in nano-devices when the external magnetic field changes. Excluding the factor of impurities or defects, specific QIP is determined by the sample geometry. We have improved a first-principles method based on the matrix Green's function and the density functional theory to simulate the transport behaviour of such systems under a magnetic field. We have studied two kinds of QIP: universal conductance fluctuation (UCF) and Aharonov–Bohm effect (A–B effect). We find that the amplitude of UCF is much smaller than the previous theoretical prediction. We have discussed the origin of difference and concluded that due to the failure of ergodic hypothesis, the ensemble statistics is not applicable, and the conductance fluctuation is determined by the flux-dependent density of states (DOSs). We have also studied the relation between the UCF and the structure of sample. For a specific structure, an atomic circle, the A–B effect is observed and the origin of the oscillation is also discussed
First-principles investigation of Fe-doped MgSiO3-ilmenite
International Nuclear Information System (INIS)
Stashans, Arvids; Rivera, Krupskaya; Pinto, Henry P.
2012-01-01
First principles density functional theory and generalised gradient approximation (GGA) have been exploited to investigate Fe-doped ilmenite-type MgSiO 3 mineral. Strong electron correlation effects not included in a density-functional formalism are described by a Hubbard-type on-site Coulomb repulsion (the DFT+U approach). Microstructure of equilibrium geometries, electronic band structures as well as magnetic properties are computed and discussed in detail. Hartree-Fock methodology is used as an extra tool to study optical properties of the same system. For equilibrium state of the doped mineral we find zigzag-type atomic rearrangements around the Fe impurity. The inclusion of correlation effects leads to an improved description of the electronic properties. In particular, it is discovered that Fe incorporation produces local energy levels within the band-gap of the material. Using ΔSCF method optical absorption energies are found to be equal to 2.2 and 2.6 eV leading to light absorption at longer wavelengths compared to the undoped MgSiO 3 . Our results provide evidence on the occurrence of local magnetic moment in the region surrounding iron dopant. According to the outcomes, the Fe⇒Mg reaction can be described as substitutionally labile with Fe 2+ complex being found in the high-spin state at low pressure MgSiO 3 -ilmenite conditions.
First-principles investigation of Fe-doped MgSiO{sub 3}-ilmenite
Energy Technology Data Exchange (ETDEWEB)
Stashans, Arvids, E-mail: arvids@utpl.edu.ec [Grupo de Fisicoquimica de Materiales, Universidad Tecnica Particular de Loja, Apartado 11-01-608, Loja (Ecuador); Rivera, Krupskaya [Grupo de Fisicoquimica de Materiales, Universidad Tecnica Particular de Loja, Apartado 11-01-608, Loja (Ecuador); Escuela de Geologia y Minas, Universidad Tecnica Particular de Loja, Apartado 11-01-608, Loja (Ecuador); Pinto, Henry P. [Interdisciplinary Center for Nanotoxicity, Department of Chemistry, Jackson State University, Jackson, Mississippi 39217-0510 (United States)
2012-06-15
First principles density functional theory and generalised gradient approximation (GGA) have been exploited to investigate Fe-doped ilmenite-type MgSiO{sub 3} mineral. Strong electron correlation effects not included in a density-functional formalism are described by a Hubbard-type on-site Coulomb repulsion (the DFT+U approach). Microstructure of equilibrium geometries, electronic band structures as well as magnetic properties are computed and discussed in detail. Hartree-Fock methodology is used as an extra tool to study optical properties of the same system. For equilibrium state of the doped mineral we find zigzag-type atomic rearrangements around the Fe impurity. The inclusion of correlation effects leads to an improved description of the electronic properties. In particular, it is discovered that Fe incorporation produces local energy levels within the band-gap of the material. Using {Delta}SCF method optical absorption energies are found to be equal to 2.2 and 2.6 eV leading to light absorption at longer wavelengths compared to the undoped MgSiO{sub 3}. Our results provide evidence on the occurrence of local magnetic moment in the region surrounding iron dopant. According to the outcomes, the Fe Rightwards-Double-Arrow Mg reaction can be described as substitutionally labile with Fe{sup 2+} complex being found in the high-spin state at low pressure MgSiO{sub 3}-ilmenite conditions.
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.
Alay-e-Abbas, S. M.; Shaukat, A.
2011-05-01
First-principles density functional theory calculations have been performed for structural, electronic and optical properties of three polymorphic forms of rubidium telluride. Our calculations show that the sequence of pressure induced phase transitions for Rb 2Te is Fm3¯m → Pnma → P6 3/mmc which is governed by the coordination numbers of the anions. From our calculated low transition pressure value for the Fm3¯m phase to the Pnma phase transition of Rb 2Te, the experimentally observed meta-stability of Fm3¯m phase at ambient conditions seems reasonable. The electronic band structure has been calculated for all the three phases and the change in the energy band gap is discussed for the transitioning phases. The energy band gaps obtained for the three phases of Rb 2Te decrease on going from the meta-stable phase to the high-pressure phases. Total and partial density of states for the polymorphs of Rb 2Te has been computed to elucidate the contribution of various atomic states on the electronic band structure. Furthermore, optical properties for all the polymorphic forms have been presented in form of the complex dielectric function.
Density functionals in the laboratory frame
International Nuclear Information System (INIS)
Giraud, B. G.
2008-01-01
We compare several definitions of the density of a self-bound system, such as a nucleus, in relation with its center-of-mass zero-point motion. A trivial deconvolution relates the internal density to the density defined in the laboratory frame. This result is useful for the practical definition of density functionals
Determination of structure and properties of molecular crystals from first principles.
Szalewicz, Krzysztof
2014-11-18
CONSPECTUS: Until recently, it had been impossible to predict structures of molecular crystals just from the knowledge of the chemical formula for the constituent molecule(s). A solution of this problem has been achieved using intermolecular force fields computed from first principles. These fields were developed by calculating interaction energies of molecular dimers and trimers using an ab initio method called symmetry-adapted perturbation theory (SAPT) based on density-functional theory (DFT) description of monomers [SAPT(DFT)]. For clusters containing up to a dozen or so atoms, interaction energies computed using SAPT(DFT) are comparable in accuracy to the results of the best wave function-based methods, whereas the former approach can be applied to systems an order of magnitude larger than the latter. In fact, for monomers with a couple dozen atoms, SAPT(DFT) is about equally time-consuming as the supermolecular DFT approach. To develop a force field, SAPT(DFT) calculations are performed for a large number of dimer and possibly also trimer configurations (grid points in intermolecular coordinates), and the interaction energies are then fitted by analytic functions. The resulting force fields can be used to determine crystal structures and properties by applying them in molecular packing, lattice energy minimization, and molecular dynamics calculations. In this way, some of the first successful determinations of crystal structures were achieved from first principles, with crystal densities and lattice parameters agreeing with experimental values to within about 1%. Crystal properties obtained using similar procedures but empirical force fields fitted to crystal data have typical errors of several percent due to low sensitivity of empirical fits to interactions beyond those of the nearest neighbors. The first-principles approach has additional advantages over the empirical approach for notional crystals and cocrystals since empirical force fields can only be
First principles calculation of material properties of group IV elements and III-V compounds
Malone, Brad Dean
first principles calculations of the quasiparticle and optical excitation spectra of recently predicted silicon and germanium polytypes in the body-centered-tetragonal (bct) structure. The quasiparticle spectra calculated within the GW approximation predict that both silicon and germanium in the bct structure are small band gap materials. The optical spectra are then evaluated by solving the Bethe-Salpeter equation taking into account. • We examine the low-pressure phases of Ge in Chapter 6 by performing first principles calculations of the electronic structure and lattice dynamics of the R8, BC8, ST12, and hexagonal diamond structures of Ge. To aid future experimental investigation, we include predictions of the Raman-active frequencies of these phases as well as present the full phonon dispersion throughout the zone. • In Chapter 7 we demonstrate how first principles calculations can be used to predict new structures. In a study aimed at finding new useful forms of silicon, we use an ab initio random structure searching (AIRSS) method to identify a new phase of silicon in the Ibamstructure. The Ibam phase is found to be semimetallic within density functional theory with a small band overlap, and it is expected that quasiparticle corrections using the GW approximation would yield a semiconducting state with a small band gap. • We present a first-principles study of boron and phosphorus substitutional defects in Si-XII in Chapter 8. Recent result from nanoindentation experiments reveal that the Si-XII phase is semiconducting and has the interesting property that it can be doped n- and p-type at room temperature without an annealing step. Using the hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE), we examine the formation energies of the B and P defects at the two distinct atomic sites in Si-XII to find on which site the substitutional defects are more easily accommodated. We also estimate the thermodynamic transition levels of each defect in its relevant
Caliskan, Serkan
2018-05-01
Using first principles study, through Density Functional Theory combined with Non Equilibrium Green's Function Formalism, electronic properties of endohedral N@C20 fullerene molecule joining Au electrodes (Au-N@C20) was addressed in the presence of spin property. The electronic transport behavior across the Au-N@C20 molecular junction was investigated by spin resolved transmission, density of states, molecular orbitals, differential conductance and current-voltage (I-V) characteristics. Spin asymmetric variation was clearly observed in the results due to single N atom encapsulated in the C20 fullerene cage, where the N atom played an essential role in the electronic behavior of Au-N@C20. This N@C20 based molecular bridge, exhibiting a spin dependent I-V variation, revealed a metallic behavior within the bias range from -1 V to 1 V. The induced magnetic moment, spin polarization and other relevant quantities associated with the spin resolved transport were elucidated.
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...
Reliability evaluation of thermophysical properties from first-principles calculations.
Palumbo, Mauro; Fries, Suzana G; Dal Corso, Andrea; Kürmann, Fritz; Hickel, Tilmann; Neugebauer, Jürg
2014-08-20
Thermophysical properties, such as heat capacity, bulk modulus and thermal expansion, are of great importance for many technological applications and are traditionally determined experimentally. With the rapid development of computational methods, however, first-principles computed temperature-dependent data are nowadays accessible. We evaluate various computational realizations of such data in comparison to the experimental scatter. The work is focussed on the impact of different first-principles codes (QUANTUM ESPRESSO and VASP), pseudopotentials (ultrasoft and projector augmented wave) as well as phonon determination methods (linear response and direct force constant method) on these properties. Based on the analysis of data for two pure elements, Cr and Ni, consequences for the reliability of temperature-dependent first-principles data in computational thermodynamics are discussed.
Density functional theory and parallel processing
International Nuclear Information System (INIS)
Ward, R.C.; Geist, G.A.; Butler, W.H.
1987-01-01
The authors demonstrate a method for obtaining the ground state energies and charge densities of a system of atoms described within density functional theory using simulated annealing on a parallel computer
Insights into the ammonia synthesis from first-principles
DEFF Research Database (Denmark)
Hellmann, A.; Honkala, Johanna Karoliina; Remediakis, Ioannis
2006-01-01
-properties, such as apparent activation energies and reaction orders, are calculated from the first-principles model. Our analysis shows that the reaction order of N-2 is unity under all considered conditions, whereas the reaction orders of H-2 and NH3 depend on reaction conditions. (c) 2006 Elsevier B.V. All rights reserved.......A new set of measurements is used to further test a recently published first-principles model for the ammonia (NH3) synthesis on an unpromoted Ru-based catalyst. A direct comparison shows an overall good agreement in NH3 productivity between the model and the experiment. In addition, macro...
Directory of Open Access Journals (Sweden)
Gulebaglan Sinem Erden
2015-01-01
Full Text Available We performed first-principles calculations to obtain the electronic, optical, elastic, lattice-dynamical and thermodynamic properties of RbH compound with rock salt structure. The ground-state properties, i.e., the lattice constant and the band gap were investigated using a plane wave pseudopotential method within density functional theory. The calculated lattice constant, bulk modulus, energy band gap and elastic constants are reported and compared with previous theoretical and experimental results. Our calculated results and the previous results which are obtained from literature are in a good agreement. Moreover, real and imaginary parts of complex dielectric function, reflectivity spectrum, absorption, extinction coefficient and loss function as a function of photon energy and refractive index with respect to photon wavelength were calculated. In addition, temperature dependent thermodynamic properties such as Helmholtz free energy, internal energy, entropy and specific heat have been studied.
A Density Functional Theory Study
Lim, XiaoZhi
2011-12-11
Complexes with pincer ligand moieties have garnered much attention in the past few decades. They have been shown to be highly active catalysts in several known transition metal-catalyzed organic reactions as well as some unprecedented organic transformations. At the same time, the use of computational organometallic chemistry to aid in the understanding of the mechanisms in organometallic catalysis for the development of improved catalysts is on the rise. While it was common in earlier studies to reduce computational cost by truncating donor group substituents on complexes such as tertbutyl or isopropyl groups to hydrogen or methyl groups, recent advancements in the processing capabilities of computer clusters and codes have streamlined the time required for calculations. As the full modeling of complexes become increasingly popular, a commonly overlooked aspect, especially in the case of complexes bearing isopropyl substituents, is the conformational analysis of complexes. Isopropyl groups generate a different conformer with each 120 ° rotation (rotamer), and it has been found that each rotamer typically resides in its own potential energy well in density functional theory studies. As a result, it can be challenging to select the most appropriate structure for a theoretical study, as the adjustment of isopropyl substituents from a higher-energy rotamer to the lowest-energy rotamer usually does not occur during structure optimization. In this report, the influence of the arrangement of isopropyl substituents in pincer complexes on calculated complex structure energies as well as a case study on the mechanism of the isomerization of an iPrPCP-Fe complex is covered. It was found that as many as 324 rotamers can be generated for a single complex, as in the case of an iPrPCP-Ni formato complex, with the energy difference between the global minimum and the highest local minimum being as large as 16.5 kcalmol-1. In the isomerization of a iPrPCP-Fe complex, it was found
Underscreening in ionic liquids: a first principles analysis
Rotenberg, Benjamin; Bernard, Olivier; Hansen, Jean-Pierre
2018-02-01
An attempt is made to understand the underscreening effect, observed in concentrated electrolyte solutions or melts, on the basis of simple, admittedly crude models involving charged (for the ions) and neutral (for the solvent molecules) hard spheres. The thermodynamic and structural properties of these ‘primitive’ and ‘semi-primitive’ models are calculated within mean spherical approximation, which provides the basic input required to determine the partial density response functions. The screening length λS , which is unambiguously defined in terms of the wave-number-dependent response functions, exhibits a cross-over from a low density, Debye-like regime, to a regime where λS increases with density beyond a critical density at which the Debye length λD becomes comparable to the ion diameter. In this high density regime the ratio λ_S/λD increases according to a power law, in qualitative agreement with experimental measurements, albeit at a much slower rate.
Atomistic properties of helium in hcp titanium: A first-principles study
International Nuclear Information System (INIS)
Wang Yongli; Liu, Shi; Rong Lijian; Wang Yuanming
2010-01-01
First-principles calculations based on density functional theory have been performed to investigate the behaviors of He in hcp-type Ti. The most favorable interstitial site for He is not an ordinary octahedral or tetrahedral site, but a novel interstitial site (called FC) with a formation energy as low as 2.67 eV, locating the center of the face shared by two adjacent octahedrons. The origin was further analyzed by composition of formation energy of interstitial He defects and charge density of defect-free hcp Ti. It has also been found that an interstitial He atom can easily migrate along direction with an activation energy of 0.34 eV and be trapped by another interstitial He atom with a high binding energy of 0.66 eV. In addition, the small He clusters with/without Ti vacancy have been compared in details and the formation energies of He n V clusters with a pre-existing Ti vacancy are even higher than those of He n clusters until n ≥ 3.
Structure and stacking faults in layered Mg-Zn-Y alloys: A first-principles study
International Nuclear Information System (INIS)
Datta, Aditi; Waghmare, U.V.; Ramamurty, U.
2008-01-01
We use first-principles density functional theory total energy calculations based on pseudo-potentials and plane-wave basis to assess stability of the periodic structures with different stacking sequences in Mg-Zn-Y alloys. For pure Mg, we find that the 6-layer (6l) structure with the ABACAB stacking is most stable after the lowest energy hcp (2l) structure with ABAB stacking. Addition of 2 at.% Y leads to stabilization of the structure to 6l sequence whereas the addition of 2 at.% Zn makes the 6l energetically comparable to that of the hcp. Stacking fault (SF) on the basal plane of 6l structure is higher in energy than that of the hcp 2l Mg, which further increases upon Y doping and decreases significantly with Zn doping. SF energy surface for the prismatic slip indicates activation of non-basal slip in alloys with a 6l structure. Charge density analysis shows that the 2l and 6l structures are electronically similar which might be a cause for better stability of 6l structure over a 4l sequence or other periodic structures. Thus, in an Mg-Zn-Y alloy, Y stabilizes the long periodicity, while its mechanical properties are further improved due to Zn doping
Electronic and Optical Properties of Two-Dimensional GaN from First-Principles.
Sanders, Nocona; Bayerl, Dylan; Shi, Guangsha; Mengle, Kelsey A; Kioupakis, Emmanouil
2017-12-13
Gallium nitride (GaN) is an important commercial semiconductor for solid-state lighting applications. Atomically thin GaN, a recently synthesized two-dimensional material, is of particular interest because the extreme quantum confinement enables additional control of its light-emitting properties. We performed first-principles calculations based on density functional and many-body perturbation theory to investigate the electronic, optical, and excitonic properties of monolayer and bilayer two-dimensional (2D) GaN as a function of strain. Our results demonstrate that light emission from monolayer 2D GaN is blueshifted into the deep ultraviolet range, which is promising for sterilization and water-purification applications. Light emission from bilayer 2D GaN occurs at a similar wavelength to its bulk counterpart due to the cancellation of the effect of quantum confinement on the optical gap by the quantum-confined Stark shift. Polarized light emission at room temperature is possible via uniaxial in-plane strain, which is desirable for energy-efficient display applications. We compare the electronic and optical properties of freestanding two-dimensional GaN to atomically thin GaN wells embedded within AlN barriers in order to understand how the functional properties are influenced by the presence of barriers. Our results provide microscopic understanding of the electronic and optical characteristics of GaN at the few-layer regime.
International Nuclear Information System (INIS)
Gao, Zhiyong; Chen, Baishu; Meng, Xianglong; Cai, Wei
2013-01-01
Highlights: •Site preference and phase stability of NiMnGaTi are studied by first-principles. •The Ti atoms prefer to occupy the Ga sites in the Ni 2 MnGa austenitic phase. •The phase stability becomes worse when Ga is replaced by Ti. •The phase stability is discussed based on the densities of states. -- Abstract: The effects of Ti content on martensitic transformation and phase stability of Ni 50 Mn 25 Ga 25−x Ti x shape memory alloys were investigated from first-principles calculations based on density functional theory. The formation energy results indicate that the added Ti preferentially occupies the Ga sites in Ni 2 MnGa alloy due to the lowest formation energy. The total energy difference between austenite and martensite increases with Ti alloying, being relevant to the experimentally reported changes in martensitic transformation temperature. The phase stability of Ni 50 Mn 25 Ga 25−x Ti x austenite decreases with increasing Ti content, which results from the reduced Ni 3d–Mn 3d hybridization when Ga is replaced by Ti
Thermopower switching by magnetic field: first-principles calculations
DEFF Research Database (Denmark)
Maslyuk, Volodymyr V.; Achilles, Steven; Sandratskii, Leonid
2013-01-01
We present first-principles studies of the thermopower of the organometallic V4Bz5 molecule attached between Co electrodes with noncollinear magnetization directions. Different regimes in the formation of the noncollinear magnetic state of the molecule lead to a remarkable nonmonotonous dependence...
First principles study of lithium insertion in bulk silicon
Wan, Wenhui; Zhang, Qianfan; Cui, Yi; Wang, Enge
2010-01-01
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
Towards first principles modeling of electrochemical electrode-electrolyte interfaces
DEFF Research Database (Denmark)
Nielsen, Malte; Björketun, Mårten; Hansen, Martin Hangaard
2015-01-01
We present a mini-perspective on the development of first principles modeling of electrochemical interfaces. We show that none of the existing methods deal with all the thermodynamic constraints that the electrochemical environment imposes on the structure of the interface. We present two...
First principles calculations of structural, electronic and thermal ...
Indian Academy of Sciences (India)
Home; Journals; Bulletin of Materials Science; Volume 37; Issue 5. First principles calculations of structural, electronic and thermal properties of lead chalcogenides PbS, PbSe and PbTe compounds. N Boukhris H Meradji S Amara Korba S Drablia S Ghemid F El Haj Hassan. Volume 37 Issue 5 August 2014 pp 1159-1166 ...
Molecular Electronics: Insight from First-Principles Transport Simulations
DEFF Research Database (Denmark)
Paulsson, Magnus; Frederiksen, Thomas; Brandbyge, Mads
2010-01-01
Conduction properties of nanoscale contacts can be studied using first-principles simulations. Such calculations give insight into details behind the conductance that is not readily available in experiments. For example, we may learn how the bonding conditions of a molecule to the electrodes affect...
First-principles approach to noncollinear magnetism: Towards spin dynamics
DEFF Research Database (Denmark)
Sharma, S.; Dewhurst, J.K.; Ambrosch-Draxl, C.
2007-01-01
A description of noncollinear magnetism in the framework of spin-density functional theory is presented for the exact exchange energy functional which depends explicitly on two-component spinor orbitals. The equations for the effective Kohn-Sham scalar potential and magnetic field are derived...
First-principles study on the effect of high In doping on the conductivity of ZnO
International Nuclear Information System (INIS)
Hou Qing-Yu; Li Ji-Jun; Ying Chun; Zhao Chun-Wang; Zhao Er-Jun; Zhang Yue
2013-01-01
Based on the density functional theory (DFT), using first-principles plane-wave ultrasoft pseudopotential method, the models of the unit cell of pure ZnO and two highly In-doped supercells of Zn 0.9375 In 0.0625 O and Zn 0.875 In 0.125 O are constructed, and the geometry optimizations of the three models are carried out. The total density of states (DOS) and the band structures (BS) are also calculated. The calculation results show that in the range of high doping concentration, when the doping concentration is hihger than a specific value, the conductivity decreases with the increase of the doping concentration of In in ZnO, which is in consistence with the change trend of the experimental results
Rakitin, M. S.; Mirzoev, A. A.; Mirzaev, D. A.
2018-04-01
Mobile hydrogen, when dissolving in metals, redistributes due to the density gradients and elastic stresses, and enables destruction processes or phase transformations in local volumes of a solvent metal. It is rather important in solid state physics to investigate these interactions. The first-principle calculations performed in terms of the density functional theory, are used for thermodynamic simulation of the elastic stress effect on the energy of hydrogen dissolution in α-Fe crystal lattice. The paper presents investigations of the total energy of Fe-H system depending on the lattice parameter. As a result, the relation is obtained between the hydrogen dissolution energy and stress. A good agreement is shown between the existing data and simulation results. The extended equation is suggested for the chemical potential of hydrogen atom in iron within the local stress field. Two parameters affecting the hydrogen distribution are compared, namely local stress and phase transformations.
Role of anion doping on electronic structure and magnetism of GdN by first principles calculations
Zhang, Xuejing; Mi, Wenbo; Guo, Zaibing; Cheng, Yingchun; Chen, Guifeng; Bai, Haili
2014-01-01
We have investigated the electronic structure and magnetism of anion doped GdN1-yXy (X = B, C, O, F, P, S and As) systems by first-principles calculations based on density functional theory. GdN 1-yXy systems doped by O, C, F, P, and S atoms are more stable than those doped by B and As atoms because of relatively high binding energies. The anion doping and the N defect states modify the density of states at the Fermi level, resulting in a decrease in spin polarization and a slight increase in the magnetic moment at the Gd and N sites. © 2014 The Royal Society of Chemistry.
First-principles study of direct and narrow band gap semiconducting β-CuGaO2
International Nuclear Information System (INIS)
Nguyen, Manh Cuong; Zhao, Xin; Wang, Cai-Zhuang; Ho, Kai-Ming
2015-01-01
Semiconducting oxides have attracted much attention due to their great stability in air or water and the abundance of oxygen. Recent success in synthesizing a metastable phase of CuGaO 2 with direct narrow band gap opens up new applications of semiconducting oxides as absorber layer for photovoltaics. Using first-principles density functional theory calculations, we investigate the thermodynamic and mechanical stabilities as well as the structural and electronic properties of the β-CuGaO 2 phase. Our calculations show that the β-CuGaO 2 structure is dynamically and mechanically stable. The energy band gap is confirmed to be direct at the Γ point of Brillouin zone. The optical absorption occurs right at the band gap edge and the density of states near the valance band maximum is large, inducing an intense absorption of light as observed in experiment. (paper)
Perger, Warren F.; Zhao, Jijun; Winey, J. M.; Gupta, Y. M.
2006-07-01
The vibrational frequencies of the PETN molecular crystal were calculated using the first-principles CRYSTAL03 program which employs an all-electron LCAO approach and calculates analytic first derivatives of the total energy with respect to atomic displacements. Numerical second derivatives were used to enable calculation of the vibrational frequencies at ambient pressure and under various states of compression. Three different density functionals, B3LYP, PW91, and X3LYP were used to examine the effect of the exchange-correlation functional on the vibrational frequencies. The average deviation with experimental results is shown to be on the order of 2-3%, depending on the functional used. The pressure-induced shift of the vibrational frequencies is presented.
Rectification of graphene self-switching diodes: First-principles study
Ghaziasadi, Hassan; Jamasb, Shahriar; Nayebi, Payman; Fouladian, Majid
2018-05-01
The first principles calculations based on self-consistent charge density functional tight-binding have performed to investigate the electrical properties and rectification behavior of the graphene self-switching diodes (GSSD). The devices contained two structures called CG-GSSD and DG-GSSD which have metallic or semiconductor gates depending on their side gates have a single or double hydrogen edge functionalized. We have relaxed the devices and calculated I-V curves, transmission spectrums and maximum rectification ratios. We found that the DG-MSM devices are more favorable and more stable. Also, the DG-MSM devices have better maximum rectification ratios and current. Moreover, by changing the side gates widths and behaviors from semiconductor to metal, the threshold voltages under forward bias changed from +1.2 V to +0.3 V. Also, the maximum currents are obtained from 1.12 μA to 10.50 μA. Finally, the MSM and SSS type of all devices have minimum and maximum values of voltage threshold and maximum rectification ratios, but the 769-DG devices don't obey this rule.
Toward a Monte Carlo program for simulating vapor-liquid phase equilibria from first principles
Energy Technology Data Exchange (ETDEWEB)
McGrath, M; Siepmann, J I; Kuo, I W; Mundy, C J; Vandevondele, J; Sprik, M; Hutter, J; Mohamed, F; Krack, M; Parrinello, M
2004-10-20
Efficient Monte Carlo algorithms are combined with the Quickstep energy routines of CP2K to develop a program that allows for Monte Carlo simulations in the canonical, isobaric-isothermal, and Gibbs ensembles using a first principles description of the physical system. Configurational-bias Monte Carlo techniques and pre-biasing using an inexpensive approximate potential are employed to increase the sampling efficiency and to reduce the frequency of expensive ab initio energy evaluations. The new Monte Carlo program has been validated through extensive comparison with molecular dynamics simulations using the programs CPMD and CP2K. Preliminary results for the vapor-liquid coexistence properties (T = 473 K) of water using the Becke-Lee-Yang-Parr exchange and correlation energy functionals, a triple-zeta valence basis set augmented with two sets of d-type or p-type polarization functions, and Goedecker-Teter-Hutter pseudopotentials are presented. The preliminary results indicate that this description of water leads to an underestimation of the saturated liquid density and heat of vaporization and, correspondingly, an overestimation of the saturated vapor pressure.
First-principles Hubbard U approach for small molecule binding in metal-organic frameworks
Energy Technology Data Exchange (ETDEWEB)
Mann, Gregory W., E-mail: gmann@berkeley.edu [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Mesosphere, Inc., San Francisco, California 94105 (United States); Lee, Kyuho, E-mail: kyuholee@lbl.gov [Department of Chemical and Biomolecular Engineering, University of California, Berkeley, California 94720 (United States); Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Synopsys, Inc., Mountain View, California 94043 (United States); Cococcioni, Matteo, E-mail: matteo.cococcioni@epfl.ch [Theory and Simulation of Materials (THEOS), École Polytechnique Fédérale de Lausanne, Lausanne (Switzerland); Smit, Berend, E-mail: Berend-Smit@berkeley.edu [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Department of Chemical and Biomolecular Engineering, University of California, Berkeley, California 94720 (United States); Laboratory of Molecular Simulation, Institut des Sciences et Ingénierie Chimiques, Valais Ecole Polytechnique Fédérale de Lausanne (EPFL), Rue de l’Industrie 17, CH-1951 Sion (Switzerland); Neaton, Jeffrey B., E-mail: jbneaton@lbl.gov [Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Physics, University of California, Berkeley, California 94720 (United States); Kavli Energy NanoSciences Institute at Berkeley, Berkeley, California 94720 (United States)
2016-05-07
We apply first-principles approaches with Hubbard U corrections for calculation of small molecule binding energetics to open-shell transition metal atoms in metal-organic frameworks (MOFs). Using density functional theory with van der Waals dispersion-corrected functionals, we determine Hubbard U values ab initio through an established linear response procedure for M-MOF-74, for a number of different metal centers (M = Ti, V, Cr, Mn, Fe, Co, Ni, and Cu). While our ab initio U values differ from those used in previous work, we show that they result in lattice parameters and electronic contributions to CO{sub 2}-MOF binding energies that lead to excellent agreement with experiments and previous results, yielding lattice parameters within 3%. In addition, U-dependent calculations for an example system, Co-MOF-74, suggest that the CO{sub 2} binding energy grows monotonically with the value of Hubbard U, with the binding energy shifting 4 kJ/mol (or 0.041 eV) over the range of U = 0-5.4 eV. These results provide insight into an approximate but computationally efficient means for calculation of small molecule binding energies to open-shell transition metal atoms in MOFs and suggest that the approach can be predictive with good accuracy, independent of the cations used and the availability of experimental data.
International Nuclear Information System (INIS)
Bondi, Robert J.; Desjarlais, Michael P.; Thompson, Aidan P.; Brennecka, Geoff L.; Marinella, Matthew J.
2013-01-01
We apply first-principles density-functional theory (DFT) calculations, ab-initio molecular dynamics, and the Kubo-Greenwood formula to predict electrical conductivity in Ta 2 O x (0 ≤ x ≤ 5) as a function of composition, phase, and temperature, where additional focus is given to various oxidation states of the O monovacancy (V O n ; n = 0,1+,2+). In the crystalline phase, our DFT calculations suggest that V O 0 prefers equatorial O sites, while V O 1+ and V O 2+ are energetically preferred in the O cap sites of TaO 7 polyhedra. Our calculations of DC conductivity at 300 K agree well with experimental measurements taken on Ta 2 O x thin films (0.18 ≤ x ≤ 4.72) and bulk Ta 2 O 5 powder-sintered pellets, although simulation accuracy can be improved for the most insulating, stoichiometric compositions. Our conductivity calculations and further interrogation of the O-deficient Ta 2 O 5 electronic structure provide further theoretical basis to substantiate V O 0 as a donor dopant in Ta 2 O 5 . Furthermore, this dopant-like behavior is specific to the neutral case and not observed in either the 1+ or 2+ oxidation states, which suggests that reduction and oxidation reactions may effectively act as donor activation and deactivation mechanisms, respectively, for V O n in Ta 2 O 5
The helium effect at grain boundaries in Fe-Cr alloys: A first-principles study
Energy Technology Data Exchange (ETDEWEB)
Zemła, M.R., E-mail: marcin.zemla@wimpw.edu.pl [Faculty of Materials Science and Engineering, Warsaw University of Technology, Wołoska 141, 02-507 Warsaw (Poland); Wróbel, J.S.; Wejrzanowski, T. [Faculty of Materials Science and Engineering, Warsaw University of Technology, Wołoska 141, 02-507 Warsaw (Poland); Nguyen-Manh, D. [CCFE, Culham Science Centre, Abingdon, Oxon OX14 3DB (United Kingdom); Kurzydłowski, K.J. [Faculty of Materials Science and Engineering, Warsaw University of Technology, Wołoska 141, 02-507 Warsaw (Poland)
2017-02-15
Helium is produced in the structural materials in nuclear power plants by nuclear transmutation following neutron irradiation. Since the solubility of helium in all metals is extremely low, helium tends to be trapped at defects such as vacancies, dislocations and grain boundaries, which cause material embrittlement. Density functional theory (DFT) calculations were performed in order to investigate the helium effect at grain boundaries (GBs) in iron-chromium alloys. Both cohesive energy and magnetic properties at symmetric Σ3(1 1 1) and Σ5(2 1 0) tilt Fe GBs are studied in the presence of Cr and He atoms. It is found that the presence of Cr atoms increases cohesive energy, at different He concentrations, and strongly influences magnetic properties at the GBs. The effect of the segregation energy of helium atom as a function of the different positions of Cr atoms located inside/outside a GB has been considered. Results of the present first-principles study enable one to clarify the role of Cr in understanding the helium effect in Fe-Cr-based alloys.
Bechtel, Jonathon S.; Van der Ven, Anton
2018-04-01
Halide substitution gives rise to a tunable band gap as a function of composition in halide perovskite materials. However, photoinduced phase segregation, observed at room temperature in mixed halide A Pb (IxBr1-x) 3 systems, limits open circuit voltages and decreases photovoltaic device efficiencies. We investigate equilibrium phase stability of orthorhombic P n m a γ -phase CsM (XxY1-x) 3 perovskites where M is Pb or Sn, and X and Y are Br, Cl, or I. Finite-temperature phase diagrams are constructed using a cluster expansion effective Hamiltonian parameterized from first-principles density-functional-theory calculations. Solid solution phases for CsM (IxBr1-x) 3 and CsM (BrxCl1-x) 3 are predicted to be stable well below room temperature while CsM (IxCl1-x) 3 systems have miscibility gaps that extend above 400 K. The height of the miscibility gap correlates with the difference in volume between end members. Also layered ground states are found on the convex hull at x =2 /3 for CsSnBr2Cl ,CsPbI2Br , and CsPbBrCl2. The impact of these ground states on the finite temperature phase diagram is discussed in the context of the experimentally observed photoinduced phase segregation.
First-Principles Study of Enhanced Magnetoelectric Effects at the Fe/MgO(001) Interface
Niranjan, M. K.; Jaswal, S. S.; Tsymbal, E. Y.; Duan, C.-G.
2010-03-01
The magnetoelectric effect allows affecting magnetic properties of materials by electric fields with potential for technological applications such as electrically controlled magnetic data storage. In this study we explore, using first-principles methods, the magnetoelectric effect at the Fe/MgO(001) interface^,1. By explicitly introducing an electric field in our density-functional calculations we demonstrate that the magnetic moment of Fe atoms at the interface changes linearly as a function of the applied electric field with the surface magnetoelectric coefficient being strongly enhanced as compared to that for the clean Fe(001) surface.^1 The effect originates from the increased screening charge associated with a large dielectric constant of MgO. The influence of electric field on relative occupancy of the Fe-3d orbitals leads to significant change in the surface magnetocrystalline anisotropy. These results are compared with the available experimental work.^2 Our results indicate that using high-k dielectrics at the interface with ferromagnetic metals may be very effective in controlling the magnetic properties by electric fields thereby leading to interesting device applications. ^1 C.-G. Duan et al., Phys. Rev. Lett. 101, 137201 (2008). ^2 T. Maruyama et al., Nat. Nanotech., 4, 158 (2009).
Band Offsets at the Interface between Crystalline and Amorphous Silicon from First Principles
Jarolimek, K.; Hazrati, E.; de Groot, R. A.; de Wijs, G. A.
2017-07-01
The band offsets between crystalline and hydrogenated amorphous silicon (a -Si ∶H ) are key parameters governing the charge transport in modern silicon heterojunction solar cells. They are an important input for macroscopic simulators that are used to further optimize the solar cell. Past experimental studies, using x-ray photoelectron spectroscopy (XPS) and capacitance-voltage measurements, have yielded conflicting results on the band offset. Here, we present a computational study on the band offsets. It is based on atomistic models and density-functional theory (DFT). The amorphous part of the interface is obtained by relatively long DFT first-principles molecular-dynamics runs at an elevated temperature on 30 statistically independent samples. In order to obtain a realistic conduction-band position the electronic structure of the interface is calculated with a hybrid functional. We find a slight asymmetry in the band offsets, where the offset in the valence band (0.29 eV) is larger than in the conduction band (0.17 eV). Our results are in agreement with the latest XPS measurements that report a valence-band offset of 0.3 eV [M. Liebhaber et al., Appl. Phys. Lett. 106, 031601 (2015), 10.1063/1.4906195].
Ma, Xia-Xia; Li, Ze-Sheng
2018-01-01
Oxygen molecule has a negative effect on perovskite solar cells, which has been investigated experimentally. However, detailed theoretical research is still rare. This study presents a microscopic view to reveal the interaction mechanism between O2 and perovskite based on the first-principles calculation. The results show that O2 is adsorbed on the (100) surface of MAPbI3 perovskite mainly by Van der Waals force. O2 adsorption makes the MAPbI3 surface generate a small number of positive charges, which leads to the increase of the work function of the MAPbI3 surface. This is in agreement with the experimental measurement. And increased work function of MAPbI3 surface is not beneficial to electron transfer from perovskite to electronic extraction layer (such as TiO2). Comparison of the density of states (DOS) of the clean (100) surface and the adsorbed system shows that an in-gap state belonging to O2 appears, which can explain the phenomenon observed from experiments that electron transfers from the surface of perovskite to O2 to form superoxide. The theoretical power conversion efficiency of the system with and without O2 adsorption is evaluated, and it turns out that the power conversion efficiency of the system with O2 adsorption is slightly lower than that of the system without O2 adsorption. This result indicates that avoiding the introduction of O2 molecules between perovskite and electronic extraction layer is beneficial to the perovskite solar cell.
First-principles Hubbard U approach for small molecule binding in metal-organic frameworks
International Nuclear Information System (INIS)
Mann, Gregory W.; Lee, Kyuho; Cococcioni, Matteo; Smit, Berend; Neaton, Jeffrey B.
2016-01-01
We apply first-principles approaches with Hubbard U corrections for calculation of small molecule binding energetics to open-shell transition metal atoms in metal-organic frameworks (MOFs). Using density functional theory with van der Waals dispersion-corrected functionals, we determine Hubbard U values ab initio through an established linear response procedure for M-MOF-74, for a number of different metal centers (M = Ti, V, Cr, Mn, Fe, Co, Ni, and Cu). While our ab initio U values differ from those used in previous work, we show that they result in lattice parameters and electronic contributions to CO 2 -MOF binding energies that lead to excellent agreement with experiments and previous results, yielding lattice parameters within 3%. In addition, U-dependent calculations for an example system, Co-MOF-74, suggest that the CO 2 binding energy grows monotonically with the value of Hubbard U, with the binding energy shifting 4 kJ/mol (or 0.041 eV) over the range of U = 0-5.4 eV. These results provide insight into an approximate but computationally efficient means for calculation of small molecule binding energies to open-shell transition metal atoms in MOFs and suggest that the approach can be predictive with good accuracy, independent of the cations used and the availability of experimental data.
Energy vs. density on paths toward more exact density functionals.
Kepp, Kasper P
2018-03-14
Recently, the progression toward more exact density functional theory has been questioned, implying a need for more formal ways to systematically measure progress, i.e. a "path". Here I use the Hohenberg-Kohn theorems and the definition of normality by Burke et al. to define a path toward exactness and "straying" from the "path" by separating errors in ρ and E[ρ]. A consistent path toward exactness involves minimizing both errors. Second, a suitably diverse test set of trial densities ρ' can be used to estimate the significance of errors in ρ without knowing the exact densities which are often inaccessible. To illustrate this, the systems previously studied by Medvedev et al., the first ionization energies of atoms with Z = 1 to 10, the ionization energy of water, and the bond dissociation energies of five diatomic molecules were investigated using CCSD(T)/aug-cc-pV5Z as benchmark at chemical accuracy. Four functionals of distinct designs was used: B3LYP, PBE, M06, and S-VWN. For atomic cations regardless of charge and compactness up to Z = 10, the energy effects of the different ρ are energy-wise insignificant. An interesting oscillating behavior in the density sensitivity is observed vs. Z, explained by orbital occupation effects. Finally, it is shown that even large "normal" problems such as the Co-C bond energy of cobalamins can use simpler (e.g. PBE) trial densities to drastically speed up computation by loss of a few kJ mol -1 in accuracy. The proposed method of using a test set of trial densities to estimate the sensitivity and significance of density errors of functionals may be useful for testing and designing new balanced functionals with more systematic improvement of densities and energies.
Energy Technology Data Exchange (ETDEWEB)
Hu, S. X., E-mail: shu@lle.rochester.edu; Goncharov, V. N.; McCrory, R. L.; Skupsky, S. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Collins, L. A.; Kress, J. D. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
2016-04-15
Using quantum molecular-dynamics (QMD) methods based on the density functional theory, we have performed first-principles investigations of the ionization and thermal conductivity of polystyrene (CH) over a wide range of plasma conditions (ρ = 0.5 to 100 g/cm{sup 3} and T = 15 625 to 500 000 K). The ionization data from orbital-free molecular-dynamics calculations have been fitted with a “Saha-type” model as a function of the CH plasma density and temperature, which gives an increasing ionization as the CH density increases even at low temperatures (T < 50 eV). The orbital-free molecular dynamics method is only used to gauge the average ionization behavior of CH under the average-atom model in conjunction with the pressure-matching mixing rule. The thermal conductivities (κ{sub QMD}) of CH, derived directly from the Kohn–Sham molecular-dynamics calculations, are then analytically fitted with a generalized Coulomb logarithm [(lnΛ){sub QMD}] over a wide range of plasma conditions. When compared with the traditional ionization and thermal conductivity models used in radiation–hydrodynamics codes for inertial confinement fusion simulations, the QMD results show a large difference in the low-temperature regime in which strong coupling and electron degeneracy play an essential role in determining plasma properties. Hydrodynamic simulations of cryogenic deuterium–tritium targets with CH ablators on OMEGA and the National Ignition Facility using the QMD-derived ionization and thermal conductivity of CH have predicted ∼20% variation in target performance in terms of hot-spot pressure and neutron yield (gain) with respect to traditional model simulations.
Density functional theory in quantum chemistry
Tsuneda, Takao
2014-01-01
This book examines density functional theory based on the foundation of quantum chemistry. Unconventional in approach, it reviews basic concepts, then describes the physical meanings of state-of-the-art exchange-correlation functionals and their corrections.
A Safari Through Density Functional Theory
Dreizler, Reiner M.; Lüdde, Cora S.
Density functional theory is widely used to treat quantum many body problems in many areas of physics and related fields. A brief survey of this method covering foundations, functionals and applications is presented here.
International Nuclear Information System (INIS)
Bennett, Joseph W.; Rabe, Karin M.
2012-01-01
In this concept paper, the development of strategies for the integration of first-principles methods with crystallographic database mining for the discovery and design of novel ferroelectric materials is discussed, drawing on the results and experience derived from exploratory investigations on three different systems: (1) the double perovskite Sr(Sb 1/2 Mn 1/2 )O 3 as a candidate semiconducting ferroelectric; (2) polar derivatives of schafarzikite MSb 2 O 4 ; and (3) ferroelectric semiconductors with formula M 2 P 2 (S,Se) 6 . A variety of avenues for further research and investigation are suggested, including automated structure type classification, low-symmetry improper ferroelectrics, and high-throughput first-principles searches for additional representatives of structural families with desirable functional properties. - Graphical abstract: Integration of first-principles methods with crystallographic database mining, for the discovery and design of novel ferroelectric materials, could potentially lead to new classes of multifunctional materials. Highlights: ► Integration of first-principles methods and database mining. ► Minor structural families with desirable functional properties. ► Survey of polar entries in the Inorganic Crystal Structural Database.
Density of states functions for photonic crystals
International Nuclear Information System (INIS)
McPhedran, R.C.; McOrist, J.; Sterke, C.M. de; Nicorovici, N.A.; Botten, L.C.; Asatryan, A.A.
2004-01-01
We discuss density of states functions for photonic crystals, in the context of the two-dimensional problem for arrays of cylinders of arbitrary cross section. We introduce the mutual density of states (MDOS), and show that this function can be used to calculate both the local density of states (LDOS), which gives position information for emission of radiation from photonic crystals, and the spectral density of states (SDOS), which gives angular information. We establish the connection between MDOS, LDOS, SDOS and the conventional density of states, which depends only on frequency. We relate all four functions to the band structure and propagating states within the crystal, and give numerical examples of the relation between band structure and density of states functions
A multiconfigurational hybrid density-functional theory
DEFF Research Database (Denmark)
Sharkas, Kamal; Savin, Andreas; Jensen, Hans Jørgen Aagaard
2012-01-01
We propose a multiconfigurational hybrid density-functional theory which rigorously combines a multiconfiguration self-consistent-field calculation with a density-functional approximation based on a linear decomposition of the electron-electron interaction. This gives a straightforward extension ...
Magnetic fields and density functional theory
Energy Technology Data Exchange (ETDEWEB)
Salsbury Jr., Freddie [Univ. of California, Berkeley, CA (United States)
1999-02-01
A major focus of this dissertation is the development of functionals for the magnetic susceptibility and the chemical shielding within the context of magnetic field density functional theory (BDFT). These functionals depend on the electron density in the absence of the field, which is unlike any other treatment of these responses. There have been several advances made within this theory. The first of which is the development of local density functionals for chemical shieldings and magnetic susceptibilities. There are the first such functionals ever proposed. These parameters have been studied by constructing functionals for the current density and then using the Biot-Savart equations to obtain the responses. In order to examine the advantages and disadvantages of the local functionals, they were tested numerically on some small molecules.
Magnetic fields and density functional theory
International Nuclear Information System (INIS)
Salsbury, Freddie Jr.
1999-01-01
A major focus of this dissertation is the development of functionals for the magnetic susceptibility and the chemical shielding within the context of magnetic field density functional theory (BDFT). These functionals depend on the electron density in the absence of the field, which is unlike any other treatment of these responses. There have been several advances made within this theory. The first of which is the development of local density functionals for chemical shieldings and magnetic susceptibilities. There are the first such functionals ever proposed. These parameters have been studied by constructing functionals for the current density and then using the Biot-Savart equations to obtain the responses. In order to examine the advantages and disadvantages of the local functionals, they were tested numerically on some small molecules
Directory of Open Access Journals (Sweden)
Shenyu Dai
2018-03-01
Full Text Available The structural, electrical and mid-infrared optical properties of wurtzite structured ZnSe nanowires with different Chromium impurity distribution are investigated using first-principles calculation based on density-functional theory (DFT. The formation energies have been calculated to study the relative stabilities of different Cr doping positions. It is shown that when the Cr doping position shifted from the center to the edge, the splitting energy between 5T2 and 5E levels of Cr d-orbitals is decreased and a redshift is observed in the calculated infrared absorption spectra. A probable reason for these effects of the impurity distribution is discussed. Keywords: First-principles, Nanowires, Impurity distribution, Cr-doped ZnSe
ONETEP: linear-scaling density-functional theory with plane-waves
International Nuclear Information System (INIS)
Haynes, P D; Mostof, A A; Skylaris, C-K; Payne, M C
2006-01-01
This paper provides a general overview of the methodology implemented in onetep (Order-N Electronic Total Energy Package), a parallel density-functional theory code for largescale first-principles quantum-mechanical calculations. The distinctive features of onetep are linear-scaling in both computational effort and resources, obtained by making well-controlled approximations which enable simulations to be performed with plane-wave accuracy. Titanium dioxide clusters of increasing size designed to mimic surfaces are studied to demonstrate the accuracy and scaling of onetep
Site specific interaction between ZnO nanoparticles and tyrosine: A density functional theory study
Singh, Satvinder; Singh, Janpreet; Singh, Baljinder; Singh, Gurinder; Kaura, Aman; Tripathi, S. K.
2018-05-01
First Principles Calculations have been performed on ZnO/Tyrosine atomic complex to study site specific interaction of Tyrosine and ZnO nanoparticles. Calculated results shows that -COOH group present in Tyrosine is energetically more favorable than -NH2 group. Interactions show ionic bonding between ZnO and Tyrosine. All the calculations have been performed under the Density Functional Theory (DFT) framework. Structural and electronic properties of (ZnO)3/Tyrosine complex have been studied. Gaussian basis set approach has been adopted for the calculations. A ring type most stable (ZnO)3 atomic cluster has been modeled, analyzed and used for the calculations.
Can the Tafel equation be derived from first principles?
International Nuclear Information System (INIS)
Gutman, E.M.
2005-01-01
A century ago, Tafel disapproved the attempts to derive the empirical equation named after him by thermodynamic methods. He noted that his observations referred to irreversible electrochemical reactions, where thermodynamics is inapplicable. This statement seems to remain valid until today. Indeed, it is impossible as yet to predict the kinetic parameters for chemical processes by determining rate constants and reaction orders from 'first principles', unless strictly specialized and, to a great extent, artificial models are developed. Nevertheless, in this paper an attempt to derive the kinetic law of mass action from 'first principles' is made in macroscopic formulation. It has turned out to be possible owing to the methods of thermodynamics of irreversible processes that were unknown in Tafel's time
First-Principle Study of the Optical Properties of Dilute-P GaN1-xPx Alloys.
Borovac, Damir; Tan, Chee-Keong; Tansu, Nelson
2018-04-16
An investigation on the optical properties of dilute-P GaN 1-x P x alloys by First-Principle Density Functional Theory (DFT) methods is presented, for phosphorus (P) content varying from 0% up to 12.5%. Findings on the imaginary and real part of the dielectric function are analyzed and the results are compared with previously reported theoretical works on GaN. The complex refractive index, normal-incidence reflectivity and birefringence are presented and a difference in the refractive index in the visible regime between GaN and GaNP alloys of ~0.3 can be engineered by adding minute amounts of phosphorus, indicating strong potential for refractive index tunability. The optical properties of the GaN 1-x P x alloys indicate their strong potential for implementation in various III-nitride-based photonic waveguide applications and Distributed Bragg Reflectors (DBR).
Lu, Dao-Bang; Song, Yu-Ling
2018-03-01
Based on density functional theory, we perform first-principles investigations to study the optical properties of the O-, F- and H-terminated SiC nanoribbons with armchair edges (ASiCNRs). By irradiating with an external electromagnetic field, we calculate the dielectric function, reflection spectra, energy loss coefficient and the real part of the conductance. It is demonstrated that the optical constants are sensitive to the low-energy range, different terminal atoms do not make much difference in the shape of the curves of the optical constants for the same-width ASiCNR, and the optical constants of wider nanoribbons usually have higher peaks than that of the narrower ones in low energy range. We hope that our study helps in experimental technology of fabricating high-quality SiC-based nanoscale photoelectric device.
Energy Technology Data Exchange (ETDEWEB)
Vladimirov, P.V. [Institute for Applied Materials – Applied Materials Physics, Karlsruhe Institute of Technology, P.O. Box 3640, 76021 Karlsruhe (Germany); Borodin, V.A., E-mail: Borodin_VA@nrcki.ru [National Research Center “Kurchatov Institute”, 123182 Moscow (Russian Federation); NRNU MEPhI, 115409 Moscow (Russian Federation)
2017-02-15
Highlights: • Beryllium is a functional material of future fusion reactors. • The threshold displacement energy by fast particles is studied. • Classical and first principles simulations are used. - Abstract: 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, E{sub d}, which is considered as an intrinsic material parameter. In this work the value of E{sub d} 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.
Infrared spectra of jennite and tobermorite from first-principles
Energy Technology Data Exchange (ETDEWEB)
Vidmer, Alexandre, E-mail: alexandre@vidmer.com; Sclauzero, Gabriele; Pasquarello, Alfredo
2014-06-01
The infrared absorption spectra of jennite, tobermorite 14 Å, anomalous tobermorite 11 Å, and normal tobermorite 11 Å are simulated within a density-functional-theory scheme. The atomic coordinates and the cell parameters are optimized resulting in structures which agree with previous studies. The vibrational frequencies and modes are obtained for each mineral. The vibrational density of states is analyzed through extensive projections on silicon tetrahedra, oxygen atoms, OH groups, and water molecules. The coupling with the electric field is achieved through the use of density functional perturbation theory, which yields Born effective charges and dielectric constants. The simulated absorption spectra reproduce well the experimental spectra, thereby allowing for a detailed interpretation of the spectral features in terms of the underlying vibrational modes. In the far-infrared part of the absorption spectra, the interplay between Ca and Si related vibrations leads to differences which are sensitive to the calcium/silicon ratio of the mineral.
Disordered crystals from first principles I: Quantifying the configuration space
Kühne, Thomas D.; Prodan, Emil
2018-04-01
This work represents the first chapter of a project on the foundations of first-principle calculations of the electron transport in crystals at finite temperatures. We are interested in the range of temperatures, where most electronic components operate, that is, room temperature and above. The aim is a predictive first-principle formalism that combines ab-initio molecular dynamics and a finite-temperature Kubo-formula for homogeneous thermodynamic phases. The input for this formula is the ergodic dynamical system (Ω , G , dP) defining the thermodynamic crystalline phase, where Ω is the configuration space for the atomic degrees of freedom, G is the space group acting on Ω and dP is the ergodic Gibbs measure relative to the G-action. The present work develops an algorithmic method for quantifying (Ω , G , dP) from first principles. Using the silicon crystal as a working example, we find the Gibbs measure to be extremely well characterized by a multivariate normal distribution, which can be quantified using a small number of parameters. The latter are computed at various temperatures and communicated in the form of a table. Using this table, one can generate large and accurate thermally-disordered atomic configurations to serve, for example, as input for subsequent simulations of the electronic degrees of freedom.
First-principles thermodynamic calculations of diffusion characteristics of impurities in γ-iron
International Nuclear Information System (INIS)
Tsuru, T.; Kaji, Y.
2013-01-01
Because solute impurities have an effect on embrittlement through segregation under irradiation, solute stability and the influence of irradiation on the diffusion characteristics of impurities become prominent due to several acceleration effects of high irradiance circumstances in irradiated materials. In this study, the diffusion characteristics of several impurities in non-magnetic fcc iron are investigated using first-principles density functional theory (DFT) calculations. In accordance with classical diffusion and transition state theories, we nonempirically evaluated the contribution to properties of the binding energy between vacancy and each impurity and the migration enthalpy. The migration energy was calculated using the nudged elastic band method with DFT. The vacancy formation energy, including the entropic contributions to free energies in γ-iron, was evaluated by considering vibrational phonon frequencies based on frozen phonons employing the harmonic approximation for the lattice dynamics. Consequently, we confirmed that the binding energy between large-radius impurities and vacancies is larger than that with an equivalent size of the solvent element, and that the migration enthalpies of these impurities are quite small compared with self diffusion. This finding may indicate that the electronic binding states at the saddle point have a large influence on the migration of impurities
Energy Technology Data Exchange (ETDEWEB)
Clima, Sergiu, E-mail: clima@imec.be; Chen, Yang Yin; Goux, Ludovic; Govoreanu, Bogdan; Degraeve, Robin; Fantini, Andrea; Jurczak, Malgorzata [imec, Kapeldreef 75, 3001 Leuven (Belgium); Chen, Chao Yang [imec, Kapeldreef 75, 3001 Leuven (Belgium); Katholieke Universiteit Leuven, 3001 Leuven (Belgium); Pourtois, Geoffrey [imec, Kapeldreef 75, 3001 Leuven (Belgium); PLASMANT, University of Antwerp, 2610 Antwerpen (Belgium)
2016-06-14
Resistive Random Access Memories are among the most promising candidates for the next generation of non-volatile memory. Transition metal oxides such as HfOx and TaOx attracted a lot of attention due to their CMOS compatibility. Furthermore, these materials do not require the inclusion of extrinsic conducting defects since their operation is based on intrinsic ones (oxygen vacancies). Using Density Functional Theory, we evaluated the thermodynamics of the defects formation and the kinetics of diffusion of the conducting species active in transition metal oxide RRAM materials. The gained insights based on the thermodynamics in the Top Electrode, Insulating Matrix and Bottom Electrode and at the interfaces are used to design a proper defect reservoir, which is needed for a low-energy reliable switching device. The defect reservoir has also a direct impact on the retention of the Low Resistance State due to the resulting thermodynamic driving forces. The kinetics of the diffusing conducting defects in the Insulating Matrix determine the switching dynamics and resistance retention. The interface at the Bottom Electrode has a significant impact on the low-current operation and long endurance of the memory cell. Our first-principles findings are confirmed by experimental measurements on fabricated RRAM devices.
Electric field effect of GaAs monolayer from first principles
Directory of Open Access Journals (Sweden)
Jiongyao Wu
2017-03-01
Full Text Available Using first-principle calculations, we investigate two-dimensional (2D honeycomb monolayer structures composed of group III-V binary elements. It is found that such compound like GaAs should have a buckled structure which is more stable than graphene-like flat structure. This results a polar system with out-of-plane dipoles arising from the non-planar structure. Here, we optimized GaAs monolayer structure, then calculated the electronic band structure and the change of buckling height under external electric field within density functional theory using generalized gradient approximation method. We found that the band gap would change proportionally with the electric field magnitude. When the spin-orbit coupling (SOC is considered, we revealed fine spin-splitting at different points in the reciprocal space. Furthermore, the valence and conduction bands spin-splitting energies due to SOC at the K point of buckled GaAs monolayers are found to be weakly dependent on the electric field strength. Finally electric field effects on the spin texture and second harmonic generation are discussed. The present work sheds light on the control of physical properties of GaAs monolayer by the applied electric field.
Nagura, Takuya; Kawachi, Shingo; Chokawa, Kenta; Shirakawa, Hiroki; Araidai, Masaaki; Kageshima, Hiroyuki; Endoh, Tetsuo; Shiraishi, Kenji
2018-04-01
It is expected that the off-state leakage current of MOSFETs can be reduced by employing vertical body channel MOSFETs (V-MOSFETs). However, in fabricating these devices, the structure of the Si pillars sometimes cannot be maintained during oxidation, since Si atoms sometimes disappear from the Si/oxide interface (Si missing). Thus, in this study, we used first-principles calculations based on the density functional theory, and investigated the Si emission behavior at the various interfaces on the basis of the Si emission model including its atomistic structure and dependence on Si crystal orientation. The results show that the order in which Si atoms are more likely to be emitted during thermal oxidation is (111) > (110) > (310) > (100). Moreover, the emission of Si atoms is enhanced as the compressive strain increases. Therefore, the emission of Si atoms occurs more easily in V-MOSFETs than in planar MOSFETs. To reduce Si missing in V-MOSFETs, oxidation processes that induce less strain, such as wet or pyrogenic oxidation, are necessary.
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.
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.
Adsorption of alkali and alkaline-earth metal atoms on stanene: A first-principles study
Energy Technology Data Exchange (ETDEWEB)
Kadioglu, Yelda; Ersan, Fatih [Department of Physics, Adnan Menderes University, 09100 Aydın (Turkey); Gökoğlu, Gökhan [Department of Physics, Karabük University, 78050 Karabük (Turkey); Aktürk, Olcay Üzengi [Department of Electrical & Electronics Engineering, Adnan Menderes University, 09100 Aydın (Turkey); Nanotechnology Application and Research Center, Adnan Menderes University, 09100 Aydın (Turkey); Aktürk, Ethem, E-mail: ethem.akturk@adu.edu.tr [Department of Physics, Adnan Menderes University, 09100 Aydın (Turkey); Nanotechnology Application and Research Center, Adnan Menderes University, 09100 Aydın (Turkey)
2016-09-01
This paper presents a study on the adsorption of alkali and alkaline-earth metal atoms on single-layer stanene with different levels of coverage using first-principles plane wave calculations within spin-polarized density functional theory. The most favorable adsorption site for alkali atoms (Li, Na, K) were found to be the hollow site similar to other group IV single-layers, but the case of alkaline-earths on stanene is different from silicene and germanene. Whereas Mg and Ca are bound to stanene at hollow site, the bridge site is found to be energetically favorable for Be adatom. All adsorbed atoms are positively charged due to the charge transfer from adatom to stanene single-layer. The semimetallic bare stanene become metallic except for Be adsorption. The Beryllium adsorption give rise to non-magnetic semiconducting ground state. Our results illustrate that stanene has a reactive and functionalizable surface similar to graphene or silicene. - Highlights: • Alkali and alkaline-earth metal atoms form stronger bonds with stanene compared to other group IV monolayers. • Semi-metallic stanene becomes nonmagnetic metal for Li, Na, K, Mg, and Ca atoms adsorption. • Semi-metallic stanene becomes nonmagnetic semiconductor with 94 meV band gap for Be atom adsorption.
International Nuclear Information System (INIS)
Clima, Sergiu; Chen, Yang Yin; Goux, Ludovic; Govoreanu, Bogdan; Degraeve, Robin; Fantini, Andrea; Jurczak, Malgorzata; Chen, Chao Yang; Pourtois, Geoffrey
2016-01-01
Resistive Random Access Memories are among the most promising candidates for the next generation of non-volatile memory. Transition metal oxides such as HfOx and TaOx attracted a lot of attention due to their CMOS compatibility. Furthermore, these materials do not require the inclusion of extrinsic conducting defects since their operation is based on intrinsic ones (oxygen vacancies). Using Density Functional Theory, we evaluated the thermodynamics of the defects formation and the kinetics of diffusion of the conducting species active in transition metal oxide RRAM materials. The gained insights based on the thermodynamics in the Top Electrode, Insulating Matrix and Bottom Electrode and at the interfaces are used to design a proper defect reservoir, which is needed for a low-energy reliable switching device. The defect reservoir has also a direct impact on the retention of the Low Resistance State due to the resulting thermodynamic driving forces. The kinetics of the diffusing conducting defects in the Insulating Matrix determine the switching dynamics and resistance retention. The interface at the Bottom Electrode has a significant impact on the low-current operation and long endurance of the memory cell. Our first-principles findings are confirmed by experimental measurements on fabricated RRAM devices.
First principles simulations of antiphase defects on the SP 90{sup 0} partial dislocation in silicon
Energy Technology Data Exchange (ETDEWEB)
Valladares, Alexander; Sutton, A P [Materials Modelling Laboratory, Department of Materials, University of Oxford, OX1 3PH (United Kingdom)
2006-04-19
We study the structure and energies of formation of antiphase defects on the single period (SP) 90{sup 0} partial dislocation in silicon using a first principles density functional method. We consider two types of antiphase defect, the type first proposed by Hirsch (1980 J. Microsc. 118 3) wholly inside the dislocation core, and another type that lies partly outside the core. Both types are stable and contain one atom which is threefold coordinated. Each of these atoms has a dangling hybrid which lies in a direction perpendicular to the dislocation line on the slip plane. We obtain values of 1.39 {+-} 0.03 eV and 1.41 {+-} 0.03 eV for the average formation energy of single antiphase defects of the inside and outside types, respectively. We have obtained, using a tight binding scheme, band structures corresponding to these two types of defect, and we find both of them to be associated with states in the gap and each dangling hybrid to contain one electron.
First principles simulations of antiphase defects on the SP 900 partial dislocation in silicon
International Nuclear Information System (INIS)
Valladares, Alexander; Sutton, A P
2006-01-01
We study the structure and energies of formation of antiphase defects on the single period (SP) 90 0 partial dislocation in silicon using a first principles density functional method. We consider two types of antiphase defect, the type first proposed by Hirsch (1980 J. Microsc. 118 3) wholly inside the dislocation core, and another type that lies partly outside the core. Both types are stable and contain one atom which is threefold coordinated. Each of these atoms has a dangling hybrid which lies in a direction perpendicular to the dislocation line on the slip plane. We obtain values of 1.39 ± 0.03 eV and 1.41 ± 0.03 eV for the average formation energy of single antiphase defects of the inside and outside types, respectively. We have obtained, using a tight binding scheme, band structures corresponding to these two types of defect, and we find both of them to be associated with states in the gap and each dangling hybrid to contain one electron
Photoexcitation and Photochemical Stability of Organic Photovoltaic Materials from First Principles
Sai, Na; Leung, Kevin
2013-03-01
The development of high efficiency organic photovoltaics (OPV) has recently become enabled by the synthesis of new conjugated polymers with low band gap that allow light absorption over a broader range of the spectrum. Stability of these new polymers, a key requirement for commercialization, has not yet received sufficient attention. Here, we report first-principles theoretical modeling of photo-induced degradation of OPV polymers carried out using ab-initio density functional theory (DFT). We report photooxidation routes and reaction products for reactive species including superoxide oxygen anions and hydroxyl groups interacting with the standard workhorse OPV polymer, poly(3-hexyl-thiophene) (P3HT). We discuss theoretical issues and challenges affecting the modeling such reactions in OPV polymers. We also discuss the application of theoretical methods to low-band-gap polymers, and in particular, the effect of the chemical substitution on the photoexcitation properties of these new polymers. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Deparment of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. This work is supported by the Energy Frontier Research Center funded by the U.S. DOE Office of Basic Energy Sciences under Award number DE-SC0001091.
Li, Yubo; Wang, Pengtao; Hua, Fei; Zhan, Shijie; Wang, Xiaozhi; Luo, Jikui; Yang, Hangsheng
2018-03-01
Electronic properties of cubic boron nitride (c-BN) doped with group IIA elements were systematically investigated using the first principle calculation based on density functional theory. The electronic bandgap of c-BN was found to be narrowed when the impurity atom substituted either the B (IIA→B) or the N (IIA→N) atom. For IIA→B, a shallow accept level degenerated into valence band (VB); while for IIA→N, a shallow donor level degenerated conduction band (CB). In the cases of IIBe→N and IIMg→N, deep donor levels were also induced. Moreover, a zigzag bandgap narrowing pattern was found, which is in consistent with the variation pattern of dopants' radius of electron occupied outer s-orbital. From the view of formation energy, the substitution of B atom under N-rich conditions and the substitution of N atom under B-rich conditions were energetically favored. Our simulation results suggested that Mg and Ca are good candidates for p-type dopants, and Ca is the best candidate for n-type dopant.
First principles crystal engineering of nonlinear optical materials. I. Prototypical case of urea
Masunov, Artëm E.; Tannu, Arman; Dyakov, Alexander A.; Matveeva, Anastasia D.; Freidzon, Alexandra Ya.; Odinokov, Alexey V.; Bagaturyants, Alexander A.
2017-06-01
The crystalline materials with nonlinear optical (NLO) properties are critically important for several technological applications, including nanophotonic and second harmonic generation devices. Urea is often considered to be a standard NLO material, due to the combination of non-centrosymmetric crystal packing and capacity for intramolecular charge transfer. Various approaches to crystal engineering of non-centrosymmetric molecular materials were reported in the literature. Here we propose using global lattice energy minimization to predict the crystal packing from the first principles. We developed a methodology that includes the following: (1) parameter derivation for polarizable force field AMOEBA; (2) local minimizations of crystal structures with these parameters, combined with the evolutionary algorithm for a global minimum search, implemented in program USPEX; (3) filtering out duplicate polymorphs produced; (4) reoptimization and final ranking based on density functional theory (DFT) with many-body dispersion (MBD) correction; and (5) prediction of the second-order susceptibility tensor by finite field approach. This methodology was applied to predict virtual urea polymorphs. After filtering based on packing similarity, only two distinct packing modes were predicted: one experimental and one hypothetical. DFT + MBD ranking established non-centrosymmetric crystal packing as the global minimum, in agreement with the experiment. Finite field approach was used to predict nonlinear susceptibility, and H-bonding was found to account for a 2.5-fold increase in molecular hyperpolarizability to the bulk value.
Anchoring platinum on graphene using metallic adatoms: a first principles investigation
International Nuclear Information System (INIS)
Sen, F G; Alpas, A T; Qi, Y
2012-01-01
First principles calculations based on spin-polarized density functional theory were used to identify metallic adatoms that would strengthen the Pt(111)/graphene interface (with a low work of separation of 0.009 J m -2 ), when the adatom was placed between the Pt(111) and the graphene. It was shown that the strength of the Pt-adatom bond, which had a metallic character, increased with the amount of charge transferred from the adatom to the Pt. The carbon-adatom bond, on the other hand, had a mixed ionic and covalent character and was weaker than the Pt-adatom bond for each of the 25 elements considered. Consequently, the total Pt(111)/graphene interface strength and, hence, the anchoring effect of the adatom were controlled by the carbon-adatom bond strength. Metals with unfilled d orbitals increased the Pt/graphene interface strength to above 0.5 J m -2 . The carbon-adatom bond strength was proportional to the ratio between the charge transferred from the adatom to the graphene (ΔZ C ) and the charge transferred to the Pt surface (ΔZ Pt ); i.e., the ΔZ C /ΔZ Pt ratio defined the ability of an adatom to anchor Pt to graphene. For Ir, Os, Ru, Rh and Re, ΔZ C /ΔZ Pt > 1.0, making these elements the most effective adatoms for anchoring Pt to graphene. (paper)
First-principles study of amorphous Ga4Sb6Te3 phase-change alloys
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.
A first-principles and experimental study of helium diffusion in periclase MgO
Song, Zhewen; Wu, Henry; Shu, Shipeng; Krawczynski, Mike; Van Orman, James; Cherniak, Daniele J.; Bruce Watson, E.; Mukhopadhyay, Sujoy; Morgan, Dane
2018-02-01
The distribution of He isotopes is used to trace heterogeneities in the Earth's mantle, and is particularly useful for constraining the length scale of heterogeneity due to the generally rapid diffusivity of helium. However, such an analysis is challenging because He diffusivities are largely unknown in lower mantle phases, which can influence the He profiles in regions that cycle through the lower mantle. With this motivation, we have used first-principles simulations based on density functional theory to study He diffusion in MgO, an important lower mantle phase. We first studied the case of interstitial helium diffusion in perfect MgO and found a migration barrier of 0.73 eV at zero pressure. Then we used the kinetic Monte Carlo method to study the case of substitutional He diffusion in MgO, where we assumed that He diffuses on the cation sublattice through cation vacancies. We also performed experiments on He diffusion at atmospheric pressure using ion implantation and nuclear reaction analysis in both as-received and Ga-doped samples. A comparison between the experimental and simulation results are shown. This work provides a foundation for further studies at high-pressure.
First principles calculation of thermodynamic properties of NaAlSi ternary
International Nuclear Information System (INIS)
Qin Jining; Lu Weijie; Zhang Di; Fan Tongxiang
2012-01-01
PbFCl-type NaAlSi ternary is a corrosion compound found in aluminum, which is used as a sealing material in sodium sulfur battery. To understand and control the corrosion process, it is important to predict its quantitative properties. In this study, a first-principles calculation has been carried out to calculate its equilibrium lattice parameters, bulk modulus and pressure derivative of bulk modulus by both all-electron full-potential linear augmented plane wave scheme and pseudopotential plane wave scheme within the generalized gradient approximation. The theoretical results show good agreement with the available experimental data. The thermodynamic properties, including the specific heat capacity and entropy with pressure up to 9 GPa, have been investigated for the first time by coupling of density functional perturbation theory and quasiharmonic approximation. The volume and linear thermal expansion coefficients were estimated and the results show that the linear thermal expansion on c-axis is nearly twice as large as that on a-axis within the calculated temperature.
Mechanical properties and chemical bonding of the Os–B system: A first-principles study
International Nuclear Information System (INIS)
Ji Zongwei; Hu Chaohao; Wang Dianhui; Zhong Yan; Yang Jiong; Zhang Wenqing; Zhou Huaiying
2012-01-01
The mechanical properties of Os–B compounds containing different boron contents have been investigated systemically by first-principles calculations. Two previously unreported crystal structures of Os 2 B 5 and OsB 3 , crystallizing in space groups R3m and P-6m2 respectively, are determined using the ab initio evolutionary structure prediction. The calculated elastic constants, bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, and hardness for Os–B compounds are in good agreement with the available experimental values. Our results show that the hardness of osmium borides increases with increasing boron content. Os 2 B 5 and OsB 3 , with hardnesses of 34.4 and 36.9 GPa respectively, can almost be considered as potential superhard materials. Further analyses on density of states, crystal orbital Hamilton population, and electron localization function demonstrate that the electronic structure of Os–B compounds is directly responsible for their particular mechanical properties. High hardness in Os 2 B 5 and OsB 3 is mainly attributed to the occurrence of strong B–B covalent bonds and the disappearance of some ductile Os–Os metallic bonds.
Clean Os(0001) electronic surface states: A first-principle fully relativistic investigation
Urru, Andrea; Dal Corso, Andrea
2018-05-01
We analyze the electronic structure of the Os(0001) surface by means of first-principle calculations based on Fully Relativistic (FR) Density Functional Theory (DFT) and a Projector Augmented-Wave (PAW) approach. We investigate surface states and resonances analyzing their spin-orbit induced energy splitting and their spin polarization. The results are compared with previously studied surfaces Ir(111), Pt(111), and Au(111). We do not find any surface state in the gap similar to the L-gap of the (111) fcc surfaces, but find Rashba split resonances that cross the Fermi level and, as in the recently studied Ir(111) surface, have a characteristic downward dispersion. Moreover, for some selected surface states we study the spin polarization with respect to k∥, the wave-vector parallel to the surface. In some cases, such as the Rashba split resonances, the spin polarization shows a smooth behavior with slow rotations, in others the rotation is faster, due to mixing and anti-crossing of the states.
Boron, nitrogen, and nickel impurities in GeC nanoribbons: A first-principles investigation
Energy Technology Data Exchange (ETDEWEB)
Xu, Zhuo; Li, Yangping, E-mail: liyp@nwpu.edu.cn; Liu, Zhengtang
2017-07-01
Highlights: • The impurities preferentially substitutes the Ge atom at the ribbon edge. • The impurities could result in a reduction of the band gap of 7-AGeCNR. • The impurities turns the metallic behavior of 4-ZGeCNR into semiconductor. • The impurities could change the magnetic moment of 4-ZGeCNR. • The impurities could introduce magnetic moments into the non-magnetic 7-AGeCNR. - Abstract: Using first-principles calculations based on the density functional theory we investigated the structural, electronic and magnetic properties of substitutional boron, nitrogen, and nickel impurities in germanium carbide (GeC) nanoribbons. Hydrogen terminated GeC ribbons with armchair and zigzag edges are considered here. We observed that all three impurities preferentially substitutes the Ge atom at the ribbon edge. In addition, the electronic band structures of the doped systems indicate that (i) the impurities could introduce impurity bands in the band gap and resulting in a reduction of the band gap of 7-AGeCNR, (ii) the metallic behavior of 4-ZGeCNR turns into semiconductor because of the incorporation of the impurities, (iii) the impurities could change the magnetic moment of 4-ZGeCNR and even introduce magnetic moment into the non-magnetic 7-AGeCNR.
Tang, Yu; Cheng, Feng; Li, Decong; Deng, Shuping; Chen, Zhong; Sun, Luqi; Liu, Wenting; Shen, Lanxian; Deng, Shukang
2018-06-01
SnSe is a promising thermoelectric material with a record high dimensionless figure of merit ZT at high temperature ∼923 K. However, the ZT values for low-Temperature Pnma phase SnSe are just 0.1-0.9. Here, we use First-principle combine with Boltzmann transport theory methods to study the effect of tensile and compressible strain on the thermoelectric transport properties. The power factor of SnSe with -4% strain have a large boost along b and c directions of 7.7 and 3.9 μW cm-1 K-2, respectively, which are 2.5 and 2 times as large as those pristine SnSe. The charge density distributions reveal that the overlap of wave function has significant change due to the changed bond lengths and bond angles under different strain, which lead to the change of band gap and band dispersion. Our work provides a new effective strategy to enhance the thermoelectric properties of materials.
Ji, Xiang; Wang, Yang; Zhang, Junqian
2018-06-01
The lithium diffusion in graphite anode, which is the most widely used commercial electrode material today, affects the charge/discharge performance of lithium-ion batteries. In this study, the anisotropic strain effects on lithium diffusion in graphite anodes are systematically investigated using first-principles calculations based on density functional theory (DFT) with van der Waals corrections. It is found that the effects of external applied strains along various directions of LixC6 (i.e., perpendicular or parallel to the basal planes of the graphite host) on lithium diffusivity are different. Along the direction perpendicular to the graphite planes, the tensile strain facilitates in-plane Li diffusion by reducing the energy barrier, and the compressive strain hinders in-plane Li diffusion by raising the energy barrier. In contrast, the in-plane biaxial tensile strain (parallel to the graphite planes) hinders in-plane Li diffusion, and the in-plane biaxial compressive strain facilitates in-plane Li diffusion. Furthermore, both in-plane and transverse shear strains slightly influence Li diffusion in graphite anodes. A discussion is presented to explain the anisotropic strain dependence of lithium diffusion. This research provides data for the continuum modelling of the electrodes in the lithium-ion batteries.
International Nuclear Information System (INIS)
Zhang Xiao-Lin; Wu Yuan-Yuan; Shao Xiao-Hong; Lu Yong; Zhang Ping
2016-01-01
The high pressure behaviors of Th 4 H 15 and ThH 2 are investigated by using the first-principles calculations based on the density functional theory (DFT). From the energy–volume relations, the bct phase of ThH 2 is more stable than the fcc phase at ambient conditions. At high pressure, the bct ThH 2 and bcc Th 4 H 15 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 ThH 2 is determined from the calculated phonon dispersion. In the pressure domain of interest, the phonon dispersions of bcc Th 4 H 15 and bct ThH 2 are positive, indicating the dynamical stability of these two phases, while the fcc ThH 2 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 Th 4 H 15 and ThH 2 . (paper)
Bondi, Robert J.; Fox, Brian P.; Marinella, Matthew J.
2017-06-01
We apply density-functional theory calculations to predict dopant modulation of electrical conductivity (σo) for seven dopants (C, Si, Ge, H, F, N, and B) sampled at 18 quantum molecular dynamics configurations of five independent insertion sites into two (high/low) baseline references of σo in amorphous Ta2O5, where each reference contains a single, neutral O vacancy center (VO0). From this statistical population (n = 1260), we analyze defect levels, physical structure, and valence charge distributions to characterize nanoscale modification of the atomistic structure in local dopant neighborhoods. C is the most effective dopant at lowering Ta2Ox σo, while also exhibiting an amphoteric doping behavior by either donating or accepting charge depending on the host oxide matrix. Both B and F robustly increase Ta2Ox σo, although F does so through elimination of Ta high charge outliers, while B insertion conversely creates high charge O outliers through favorable BO3 group formation, especially in the low σo reference. While N applications to dope and passivate oxides are prevalent, we found that N exacerbates the stochasticity of σo we sought to mitigate; sensitivity to the N insertion site and some propensity to form N-O bond chemistries appear responsible. We use direct first-principles predictions of σo to explore feasible Ta2O5 dopants to engineer improved oxides with lower variance and greater repeatability to advance the manufacturability of resistive memory technologies.
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.
Dielectric Screening Meets Optimally Tuned Density Functionals.
Kronik, Leeor; Kümmel, Stephan
2018-04-17
A short overview of recent attempts at merging two independently developed methods is presented. These are the optimal tuning of a range-separated hybrid (OT-RSH) functional, developed to provide an accurate first-principles description of the electronic structure and optical properties of gas-phase molecules, and the polarizable continuum model (PCM), developed to provide an approximate but computationally tractable description of a solvent in terms of an effective dielectric medium. After a brief overview of the OT-RSH approach, its combination with the PCM as a potentially accurate yet low-cost approach to the study of molecular assemblies and solids, particularly in the context of photocatalysis and photovoltaics, is discussed. First, solvated molecules are considered, with an emphasis on the challenge of balancing eigenvalue and total energy trends. Then, it is shown that the same merging of methods can also be used to study the electronic and optical properties of molecular solids, with a similar discussion of the pros and cons. Tuning of the effective scalar dielectric constant as one recent approach that mitigates some of the difficulties in merging the two approaches is considered. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Hydrogen storage on graphene: First-principle calculations
Boukhvalov, D.W.; Katsnelson, M.I.; Lichtenstein, A.I.
2007-01-01
Density functional calculations of electronic structure, total energy, structural distortions, and magnetism for hydrogenated single-layer, bilayer, and multi-layer graphene are performed. It is found that hydrogen-induced magnetism can survives only at very low concentrations of hydrogen
International Nuclear Information System (INIS)
Chen, Xin; Xu, Lei; Liu, Lin-Lin; Zhao, Lu-Si; Chen, Chun-Ping; Zhang, Yong; Wang, Xiao-Chun
2017-01-01
Highlights: • Formaldehyde molecule (H_2CO) is a common environmental pollutant with strong toxicity. • Total 36 different initial configurations of H_2CO molecule adsorbing onto three types of substrates have been investigated. • The Ti-doped graphene has the enough binding energy, significant changes in electronic structure, and reasonable short recovery time 10"−"3 s. • The Ti-doped graphene is a promising candidate for detecting formaldehyde gas. - Abstract: The adsorption of H_2CO molecule on pristine and transition metal (Ti and V) doped graphene samples were investigated via a first-principles approach based on density functional theory. The most stable adsorption geometry, energy and charge transfer of H_2CO molecule on pristine and doped graphene are discussed respectively. We have found that Ti and V dopant atoms can significantly enhance the interaction between H_2CO molecule and graphene. The calculated net electron transfers, electronic density difference images and densities of states give the evidence that the H_2CO molecules stay on Ti (or V) – doped graphene by chemisorption. After H_2CO adsorption, there are significant changes in electronic structure near the Fermi level, for both two systems of Ti and V doped graphene. This indicates distinct changes of electron transport properties. We have also found that H_2CO molecule has a larger absorption energy on V-doped graphene (1.939 eV) compared with Ti-doped graphene (1.120 eV). It is shown that the Ti-doped graphene has enough binding energy, adequate changes in electronic structure and reasonable short recovery time 10"−"3 s, making it a promising candidate for detecting formaldehyde gas.
First-principles calculation of adsorption of shale gas on CaCO3 (100) surfaces.
Luo, Qiang; Pan, Yikun; Guo, Ping; Wang, Zhouhua; Wei, Na; Sun, Pengfei; Liu, Yuxiao
2017-06-16
To demonstrate the adsorption strength of shale gas to calcium carbonate in shale matrix, the adsorption of shale gas on CaCO3 (100) surfaces was studied using the first-principles method, which is based on the density functional theory (DFT). The structures and electronic properties of CH4, C2H6, CO2 and N2 molecules were calculated by the generalized gradient approximation (GGA), for a coverage of 1 monolayer (ML). Under the same conditions, the density of states (DOS) of CaCO3 (100) surfaces before and after the adsorption of shale gas molecules at high-symmetry adsorption sites were compared. The results showed that the adsorption energies of CH4, C2H6, CO2 and N2 on CaCO3 (100) surfaces were between 0.2683 eV and -0.7388 eV. When a CH4 molecule was adsorbed at a hollow site and its 2 hydrogen atoms were parallel to the long diagonal (H3) on the CaCO3 (100) surface, it had the most stable adsorption, and the adsorption energy was only -0.4160 eV. The change of adsorption energy of CH4 was no more than 0.0535 eV. Compared with the DOS distribution of CH4 before adsorption, it shifted to the left overall after adsorption. At the same time, the partial density of states (PDOS) curves of CaCO3 (100) surfaces before and after adsorption basically overlapped. This work showed that the adsorption effect of shale gas on calcium carbonate is very weak, and the adsorption is physisorption at the molecular level.
Energy Technology Data Exchange (ETDEWEB)
Chen, Xin [Institute of Atomic and Molecular Physics, Jilin University, Changchun, 130012 (China); Institute of Theoretical Chemistry, Jilin University, Changchun 130012 (China); Xu, Lei [Institute of Atomic and Molecular Physics, Jilin University, Changchun, 130012 (China); College of Physics, Jilin University, Changchun, 130012 (China); Liu, Lin-Lin; Zhao, Lu-Si; Chen, Chun-Ping [Institute of Atomic and Molecular Physics, Jilin University, Changchun, 130012 (China); Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy (Jilin University), Changchun, 130012 (China); Zhang, Yong [Department of Electrical and Computer Engineering, The University of North Carolina at Charlotte, Charlotte, NC 28223-0001 (United States); Wang, Xiao-Chun, E-mail: wangxiaochun@jlu.edu.cn [Institute of Atomic and Molecular Physics, Jilin University, Changchun, 130012 (China); Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy (Jilin University), Changchun, 130012 (China)
2017-02-28
Highlights: • Formaldehyde molecule (H{sub 2}CO) is a common environmental pollutant with strong toxicity. • Total 36 different initial configurations of H{sub 2}CO molecule adsorbing onto three types of substrates have been investigated. • The Ti-doped graphene has the enough binding energy, significant changes in electronic structure, and reasonable short recovery time 10{sup −3} s. • The Ti-doped graphene is a promising candidate for detecting formaldehyde gas. - Abstract: The adsorption of H{sub 2}CO molecule on pristine and transition metal (Ti and V) doped graphene samples were investigated via a first-principles approach based on density functional theory. The most stable adsorption geometry, energy and charge transfer of H{sub 2}CO molecule on pristine and doped graphene are discussed respectively. We have found that Ti and V dopant atoms can significantly enhance the interaction between H{sub 2}CO molecule and graphene. The calculated net electron transfers, electronic density difference images and densities of states give the evidence that the H{sub 2}CO molecules stay on Ti (or V) – doped graphene by chemisorption. After H{sub 2}CO adsorption, there are significant changes in electronic structure near the Fermi level, for both two systems of Ti and V doped graphene. This indicates distinct changes of electron transport properties. We have also found that H{sub 2}CO molecule has a larger absorption energy on V-doped graphene (1.939 eV) compared with Ti-doped graphene (1.120 eV). It is shown that the Ti-doped graphene has enough binding energy, adequate changes in electronic structure and reasonable short recovery time 10{sup −3} s, making it a promising candidate for detecting formaldehyde gas.
Energy vs. density on paths toward exact density functionals
DEFF Research Database (Denmark)
Kepp, Kasper Planeta
2018-01-01
Recently, the progression toward more exact density functional theory has been questioned, implying a need for more formal ways to systematically measure progress, i.e. a “path”. Here I use the Hohenberg-Kohn theorems and the definition of normality by Burke et al. to define a path toward exactness...
Doping and defects in YBa2Cu3O7: Results from hybrid density functional theory
Schwingenschlö gl, Udo; Schuster, Cosima
2012-01-01
7 in two prototypical configurations: Ca doped (hole doping) and O deficient (electron doping). By means of first principles calculations for fully relaxed structures, we evaluate the orbital occupations. We find that the change of the charge density
Multicomponent density functional theory embedding formulation
Energy Technology Data Exchange (ETDEWEB)
Culpitt, Tanner; Brorsen, Kurt R.; Pak, Michael V.; Hammes-Schiffer, Sharon, E-mail: shs3@illinois.edu [Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Ave, Urbana, Illinois 61801 (United States)
2016-07-28
Multicomponent density functional theory (DFT) methods have been developed to treat two types of particles, such as electrons and nuclei, quantum mechanically at the same level. In the nuclear-electronic orbital (NEO) approach, all electrons and select nuclei, typically key protons, are treated quantum mechanically. For multicomponent DFT methods developed within the NEO framework, electron-proton correlation functionals based on explicitly correlated wavefunctions have been designed and used in conjunction with well-established electronic exchange-correlation functionals. Herein a general theory for multicomponent embedded DFT is developed to enable the accurate treatment of larger systems. In the general theory, the total electronic density is separated into two subsystem densities, denoted as regular and special, and different electron-proton correlation functionals are used for these two electronic densities. In the specific implementation, the special electron density is defined in terms of spatially localized Kohn-Sham electronic orbitals, and electron-proton correlation is included only for the special electron density. The electron-proton correlation functional depends on only the special electron density and the proton density, whereas the electronic exchange-correlation functional depends on the total electronic density. This scheme includes the essential electron-proton correlation, which is a relatively local effect, as well as the electronic exchange-correlation for the entire system. This multicomponent DFT-in-DFT embedding theory is applied to the HCN and FHF{sup −} molecules in conjunction with two different electron-proton correlation functionals and three different electronic exchange-correlation functionals. The results illustrate that this approach provides qualitatively accurate nuclear densities in a computationally tractable manner. The general theory is also easily extended to other types of partitioning schemes for multicomponent systems.
External field as the functional of inhomogeneous density and the density matrix functional approach
Bobrov, V.B.; Trigger, S.A.; Vlasov, Y.P.
2012-01-01
Based on the Hohenberg-Kohn lemma and the hypotheses of the density functional existence for the external-field potential, it is shown that the strict result of the density functional theory is the equation of the external-field potential as the density functional. This result leads to the
Progress towards an effective model for FeSe from high-accuracy first-principles quantum Monte Carlo
Busemeyer, Brian; Wagner, Lucas K.
While the origin of superconductivity in the iron-based materials is still controversial, the proximity of the superconductivity to magnetic order is suggestive that magnetism may be important. Our previous work has suggested that first-principles Diffusion Monte Carlo (FN-DMC) can capture magnetic properties of iron-based superconductors that density functional theory (DFT) misses, but which are consistent with experiment. We report on the progress of efforts to find simple effective models consistent with the FN-DMC description of the low-lying Hilbert space of the iron-based superconductor, FeSe. We utilize a procedure outlined by Changlani et al.[1], which both produces parameter values and indications of whether the model is a good description of the first-principles Hamiltonian. Using this procedure, we evaluate several models of the magnetic part of the Hilbert space found in the literature, as well as the Hubbard model, and a spin-fermion model. We discuss which interaction parameters are important for this material, and how the material-specific properties give rise to these interactions. U.S. Department of Energy, Office of Science, Office of Advanced Scientific Computing Research, Scientific Discovery through Advanced Computing (SciDAC) program under Award No. FG02-12ER46875, as well as the NSF Graduate Research Fellowship Program.
Pang, Yujia; Li, Wenliang; Zhang, Jingping
2017-09-15
A novel type of porous organic frameworks, based on Mg-porphyrin, with diamond-like topology, named POF-Mgs is computationally designed, and the gas uptakes of CO 2 , H 2 , N 2 , and H 2 O in POF-Mgs are investigated by Grand canonical Monte Carlo simulations based on first-principles derived force fields (FF). The FF, which describes the interactions between POF-Mgs and gases, are fitted by dispersion corrected double-hybrid density functional theory, B2PLYP-D3. The good agreement between the obtained FF and the first-principle energies data confirms the reliability of the FF. Furthermore our simulation shows the presence of a small amount of H 2 O (≤ 0.01 kPa) does not much affect the adsorption quantity of CO 2 , but the presence of higher partial pressure of H 2 O (≥ 0.1 kPa) results in the CO 2 adsorption decrease significantly. The good performance of POF-Mgs in the simulation inspires us to design novel porous materials experimentally for gas adsorption and purification. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.
International Nuclear Information System (INIS)
Liu, YangZhen; Jiang, YeHua; Zhou, Rong; Feng, Jing
2014-01-01
Highlights: • The stability and elastic constants of carbides are studied by first principles. • The rules of modulus of MC compounds are discussed by their group. • The hardness of carbides is estimated in this paper at the first time. -- Abstract: The first principles calculations based on density functional theory (DFT) were adopted to investigate the stability, elastic constants, chemical bonding, Debye temperature and hardness of MC (M = Ti, V, Zr, Nb, Hf and Ta) compounds. The cohesive energy and formation enthalpy of these carbides indicate that they are thermodynamically stable structures. The population analysis was used to discuss the chemical bonding of these carbides. The elastic constants and moduli of these compounds were calculated. The results show that the bulk moduli of the carbides of transition metals from the fourth group (TiC, ZrC, HfC) are lower than the fifth group (VC, NbC, TaC). However, the Young’s moduli of the carbides from fourth group are higher than the fifth group. The hardness of compounds was estimated using a semi empirical hardness theory
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.
Locality of correlation in density functional theory
Energy Technology Data Exchange (ETDEWEB)
Burke, Kieron [Department of Chemistry, University of California, Irvine, California 92697 (United States); Cancio, Antonio [Department of Physics and Astronomy, Ball State University, Muncie, Indiana 47306 (United States); Gould, Tim [Qld Micro- and Nanotechnology Centre, Griffith University, Nathan, Qld 4111 (Australia); Pittalis, Stefano [CNR-Istituto di Nanoscienze, Via Campi 213A, I-41125 Modena (Italy)
2016-08-07
The Hohenberg-Kohn density functional was long ago shown to reduce to the Thomas-Fermi (TF) approximation in the non-relativistic semiclassical (or large-Z) limit for all matter, i.e., the kinetic energy becomes local. Exchange also becomes local in this limit. Numerical data on the correlation energy of atoms support the conjecture that this is also true for correlation, but much less relevant to atoms. We illustrate how expansions around a large particle number are equivalent to local density approximations and their strong relevance to density functional approximations. Analyzing highly accurate atomic correlation energies, we show that E{sub C} → −A{sub C} ZlnZ + B{sub C}Z as Z → ∞, where Z is the atomic number, A{sub C} is known, and we estimate B{sub C} to be about 37 mhartree. The local density approximation yields A{sub C} exactly, but a very incorrect value for B{sub C}, showing that the local approximation is less relevant for the correlation alone. This limit is a benchmark for the non-empirical construction of density functional approximations. We conjecture that, beyond atoms, the leading correction to the local density approximation in the large-Z limit generally takes this form, but with B{sub C} a functional of the TF density for the system. The implications for the construction of approximate density functionals are discussed.
Density dependence of the nuclear energy-density functional
Papakonstantinou, Panagiota; Park, Tae-Sun; Lim, Yeunhwan; Hyun, Chang Ho
2018-01-01
Background: The explicit density dependence in the coupling coefficients entering the nonrelativistic nuclear energy-density functional (EDF) is understood to encode effects of three-nucleon forces and dynamical correlations. The necessity for the density-dependent coupling coefficients to assume the form of a preferably small fractional power of the density ρ is empirical and the power is often chosen arbitrarily. Consequently, precision-oriented parametrizations risk overfitting in the regime of saturation and extrapolations in dilute or dense matter may lose predictive power. Purpose: Beginning with the observation that the Fermi momentum kF, i.e., the cubic root of the density, is a key variable in the description of Fermi systems, we first wish to examine if a power hierarchy in a kF expansion can be inferred from the properties of homogeneous matter in a domain of densities, which is relevant for nuclear structure and neutron stars. For subsequent applications we want to determine a functional that is of good quality but not overtrained. Method: For the EDF, we fit systematically polynomial and other functions of ρ1 /3 to existing microscopic, variational calculations of the energy of symmetric and pure neutron matter (pseudodata) and analyze the behavior of the fits. We select a form and a set of parameters, which we found robust, and examine the parameters' naturalness and the quality of resulting extrapolations. Results: A statistical analysis confirms that low-order terms such as ρ1 /3 and ρ2 /3 are the most relevant ones in the nuclear EDF beyond lowest order. It also hints at a different power hierarchy for symmetric vs. pure neutron matter, supporting the need for more than one density-dependent term in nonrelativistic EDFs. The functional we propose easily accommodates known or adopted properties of nuclear matter near saturation. More importantly, upon extrapolation to dilute or asymmetric matter, it reproduces a range of existing microscopic
Excited-state density functional theory
International Nuclear Information System (INIS)
Harbola, Manoj K; Hemanadhan, M; Shamim, Md; Samal, P
2012-01-01
Starting with a brief introduction to excited-state density functional theory, we present our method of constructing modified local density approximated (MLDA) energy functionals for the excited states. We show that these functionals give accurate results for kinetic energy and exchange energy compared to the ground state LDA functionals. Further, with the inclusion of GGA correction, highly accurate total energies for excited states are obtained. We conclude with a brief discussion on the further direction of research that include the construction of correlation energy functional and exchange potential for excited states.
Sb2Te3 crystal a potential absorber material for broadband photodetector: A first-principles study
Directory of Open Access Journals (Sweden)
Abdullahi Lawal
Full Text Available Antimony telluride (Sb2Te3, a layered semiconductor material, is considered a promising absorbing material for a high-performance optoelectronic device within broadband wavelengths because of remarkable features like strong optical absorbance and the narrow direct band gap. In this work, based on the first-principles approach, we investigate in detail the structural, electronic and optical properties of the hexagonal Sb2Te3 compound. The structural and electronic properties were computed using the first-principles approach, treating exchange–correlation potential with generalized gradient approximation (GGA within density functional theory (DFT. Furthermore, for accurate prediction of the band gap, we go beyond DFT and calculated band structure using GW correction. The optical properties, namely, imaginary and real parts of complex dielectric function, absorption coefficient, refractive index, reflectivity, extinction coefficient, electron energy loss function and optical conductivity are performed by quasi-particle many-body perturbation theory (MBPT via Bethe-Salpeter equation (BSE. The computed structural parameters are in good agreement with available experimental data. The obtained quasi-particle (GW correction band structure show the semiconducting character of Sb2Te3 material with a direct band gap Eg of 0.221 eV, in agreement with previously reported value (Eg = 0.210 eV while the projected density of states indicates (PDOS that the p-orbital of Sb and Te atoms are responsible for material properties near the Fermi level. To our knowledge, our first reported calculations of optical properties, with the inclusion of electron-hole effects are consistent with available experimental measurements. Consistencies of our findings with experimental data validate the effectiveness of electron-hole interaction for theoretical investigation of optical properties. Keywords: DFT, Quasi-particle many-body perturbation theory, Bethe
Xenon Defects in Uranium Dioxide From First Principles and Interatomic Potentials
Thompson, Alexander
In this thesis, we examine the defect energetics and migration energies of xenon atoms in uranium dioxide (UO2) from first principles and interatomic potentials. We also parameterize new, accurate interatomic potentials for xenon and uranium dioxide. To achieve accurate energetics and provide a foundation for subsequent calculations, we address difficulties in finding consistent energetics within Hubbard U corrected density functional theory (DFT+U). We propose a method of slowly ramping the U parameter in order to guide the calculation into low energy orbital occupations. We find that this method is successful for a variety of materials. We then examine the defect energetics of several noble gas atoms in UO2 for several different defect sites. We show that the energy to incorporate large noble gas atoms into interstitial sites is so large that it is energetically favorable for a Schottky defect cluster to be created to relieve the strain. We find that, thermodynamically, xenon will rarely ever be in the interstitial site of UO2. To study larger defects associated with the migration of xenon in UO 2, we turn to interatomic potentials. We benchmark several previously published potentials against DFT+U defect energetics and migration barriers. Using a combination of molecular dynamics and nudged elastic band calculations, we find a new, low energy migration pathway for xenon in UO2. We create a new potential for xenon that yields accurate defect energetics. We fit this new potential with a method we call Iterative Potential Refinement that parameterizes potentials to first principles data via a genetic algorithm. The potential finds accurate energetics for defects with relatively low amounts of strain (xenon in defect clusters). It is important to find accurate energetics for these sorts of low-strain defects because they essentially represent small xenon bubbles. Finally, we parameterize a new UO2 potential that simultaneously yields accurate vibrational properties
Energy Technology Data Exchange (ETDEWEB)
Yamaguchi, Kizashi [Institute for Nano Science Design Center, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan and TOYOTA Physical and Chemical Research Institute, Nagakute, Aichi, 480-1192 (Japan); Nishihara, Satomichi; Saito, Toru; Yamanaka, Shusuke; Kitagawa, Yasutaka; Kawakami, Takashi; Yamada, Satoru; Isobe, Hiroshi; Okumura, Mitsutaka [Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan)
2015-01-22
First principle calculations of effective exchange integrals (J) in the Heisenberg model for diradical species were performed by both symmetry-adapted (SA) multi-reference (MR) and broken-symmetry (BS) single reference (SR) methods. Mukherjee-type (Mk) state specific (SS) MR coupled-cluster (CC) calculations by the use of natural orbital (NO) references of ROHF, UHF, UDFT and CASSCF solutions were carried out to elucidate J values for di- and poly-radical species. Spin-unrestricted Hartree Fock (UHF) based coupled-cluster (CC) computations were also performed to these species. Comparison between UHF-NO(UNO)-MkMRCC and BS UHF-CC computational results indicated that spin-contamination of UHF-CC solutions still remains at the SD level. In order to eliminate the spin contamination, approximate spin-projection (AP) scheme was applied for UCC, and the AP procedure indeed corrected the error to yield good agreement with MkMRCC in energy. The CC double with spin-unrestricted Brueckner's orbital (UBD) was furthermore employed for these species, showing that spin-contamination involved in UHF solutions is largely suppressed, and therefore AP scheme for UBCCD removed easily the rest of spin-contamination. We also performed spin-unrestricted pure- and hybrid-density functional theory (UDFT) calculations of diradical and polyradical species. Three different computational schemes for total spin angular momentums were examined for the AP correction of the hybrid (H) UDFT. HUDFT calculations followed by AP, HUDFT(AP), yielded the S-T gaps that were qualitatively in good agreement with those of MkMRCCSD, UHF-CC(AP) and UB-CC(AP). Thus a systematic comparison among MkMRCCSD, UCC(AP) UBD(AP) and UDFT(AP) was performed concerning with the first principle calculations of J values in di- and poly-radical species. It was found that BS (AP) methods reproduce MkMRCCSD results, indicating their applicability to large exchange coupled systems.
Relativistic density functional for nuclear structure
2016-01-01
This book aims to provide a detailed introduction to the state-of-the-art covariant density functional theory, which follows the Lorentz invariance from the very beginning and is able to describe nuclear many-body quantum systems microscopically and self-consistently. Covariant density functional theory was introduced in nuclear physics in the 1970s and has since been developed and used to describe the diversity of nuclear properties and phenomena with great success. In order to provide an advanced and updated textbook of covariant density functional theory for graduate students and nuclear physics researchers, this book summarizes the enormous amount of material that has accumulated in the field of covariant density functional theory over the last few decades as well as the latest developments in this area. Moreover, the book contains enough details for readers to follow the formalism and theoretical results, and provides exhaustive references to explore the research literature.
Synthesis, Crystal Structure, Density Function Theory, Molecular ...
African Journals Online (AJOL)
Tropical Journal of Pharmaceutical Research February 2016; 15 (2): 385-392 ... tested for its antimicrobial activities and computational studies including density function test (DFT) and docking ... agonists [4], selective dopamine D3 and D4 ...
A classical density functional investigation of nucleation
International Nuclear Information System (INIS)
Ghosh, Satinath; Ghosh, Swapan K.
2009-01-01
Study of nucleation and growth phenomena in condensation is of prime importance in various applications such as crystal growth, nanoparticle synthesis, pattern formation etc. The knowledge of nucleation barrier in condensation is necessary to control the nucleation kinetics, size of the nanoparticles etc. Classical nucleation theory (CNT) assumes the density of the drop as bulk density irrespective of the size of the drop and overestimates the nucleation barrier. Here we are interested in solving the problem analytically using density functional theory (DFT) with square gradient approximation along the lines of Cahn and Hilliard. Nucleation barrier and density profile obtained in this work are consistent with other works based on nonclassical theory. (author)
First principles calculation of L21+A2 coherent equilibria in the Fe-Al-Ti system
International Nuclear Information System (INIS)
Alonso, Paula R.; Gargano, Pablo H.; Ramirez-Caballero, Gustavo E.; Balbuena, Perla B.; Rubiolo, Gerardo H.
2009-01-01
By combining first-principles density functional total energy calculations and statistical mechanics the ground state and the phase equilibria at finite temperatures of the ternary system Fe-Al-Ti have been investigated. Total energy calculations have been performed by means of the Wien 2k code to establish the ground state energetic. A cluster expansion method was therewith used to describe solid solutions. At several chosen finite temperatures the cluster variation method in the irregular tetrahedron approximation was employed in order to calculate the iron rich ternary bcc equilibria. It is confirmed that there are two kinds of phase separations of the bcc phase, A2+L2 1 and B2+L2 1 .
Electronic structure and equation of state of Sm2Co17 from first-principles DFT+ U
Huang, Patrick; Butch, Nicholas P.; Jeffries, Jason R.; McCall, Scott K.
2013-03-01
Rare-earth intermetallics have important applications as permanent magnet materials, and the rational optimization of their properties would benefit greatly from guidance from ab initio modeling. However, these systems are particularly challenging for current electronic structure methods. Here, we present an ab initio study of the prototype material Sm2Co17 and related compounds, using density functional theory with a Hubbard correction for the Sm 4 f-electrons (DFT+ U method) and ultrasoft pseudopotentials. The Hubbard U parameter is derived from first principles [Cococcioni and de Gironcoli, PRB 71, 035105 (2005)], not fit to experiment. Our calculations are in good agreement with recent photoemission measurements at ambient pressure and the equation of state up to 40 GPa, thus supporting the validity of our DFT+ U model. Prepared by LLNL under Contract DE-AC52-07NA27344.
Fe magnetic moment formation and exchange interaction in Fe{sub 2}P: A first-principles study
Energy Technology Data Exchange (ETDEWEB)
Liu, X.B., E-mail: liuxubo@uta.edu [Department of Physics, University of Texas at Arlington, Arlington, TX 76019 (United States); Ping Liu, J.; Zhang, Qiming [Department of Physics, University of Texas at Arlington, Arlington, TX 76019 (United States); Altounian, Z. [Center for the Physics of Materials and Department of Physics, McGill University, 3600 University Street, Montreal, Quebec, H3A 2T8 (Canada)
2013-03-15
Electronic structure and magnetic properties of Fe{sub 2}P have been studied by a first-principles density functional theory calculation. The ground state is ferromagnetic and the calculated magnetic moments for Fe{sub 1} (3f) and Fe{sub 2} (3g) are 0.83 and 2.30μ{sub B}, respectively. The nearest neighbor inter-site magnetic exchange coupling parameter at the Fe{sub 1} layer (0.02 mRy) is much smaller than that at the Fe{sub 2} layer (1.29 mRy). The Fe moment at the 3f site is metastable and sensitive to the inter-site exchange interaction with its magnetic neighbors, which is responsible for the first order magnetic transition and large magneto-caloric effect around T{sub C}.
Directory of Open Access Journals (Sweden)
Fuda Guo
2016-01-01
Full Text Available The phase stability, mechanical, electronic, and thermodynamic properties of In-Zr compounds have been explored using the first-principles calculation based on density functional theory (DFT. The calculated formation enthalpies show that these compounds are all thermodynamically stable. Information on electronic structure indicates that they possess metallic characteristics and there is a common hybridization between In-p and Zr-d states near the Fermi level. Elastic properties have been taken into consideration. The calculated results on the ratio of the bulk to shear modulus (B/G validate that InZr3 has the strongest deformation resistance. The increase of indium content results in the breakout of a linear decrease of the bulk modulus and Young’s modulus. The calculated theoretical hardness of α-In3Zr is higher than the other In-Zr compounds.
Li-Decorated β12-Borophene as Potential Candidates for Hydrogen Storage: A First-Principle Study.
Liu, Tingting; Chen, Yuhong; Wang, Haifeng; Zhang, Meiling; Yuan, Lihua; Zhang, Cairong
2017-12-07
The hydrogen storage properties of pristine β 12 -borophene and Li-decorated β 12 -borophene are systemically investigated by means of first-principles calculations based on density functional theory. The adsorption sites, adsorption energies, electronic structures, and hydrogen storage performance of pristine β 12 -borophene/H₂ and Li- β 12 -borophene/H₂ systems are discussed in detail. The results show that H₂ is dissociated into Two H atoms that are then chemisorbed on β 12 -borophene via strong covalent bonds. Then, we use Li atom to improve the hydrogen storage performance and modify the hydrogen storage capacity of β 12 -borophene. Our numerical calculation shows that Li- β 12 -borophene system can adsorb up to 7 H₂ molecules; while 2Li- β 12 -borophene system can adsorb up to 14 H₂ molecules and the hydrogen storage capacity up to 10.85 wt %.
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.
First-Principles Study on the Adsorption Properties of Transition-Metal Atoms on CaO(001) Surfaces
Energy Technology Data Exchange (ETDEWEB)
Yu, Byung Deok [University of Seoul, Seoul (Korea, Republic of); Jang, Young-Rok [Incheon National University, Incheon (Korea, Republic of)
2017-03-15
By using first-principles electronic-structure calculations based on the density functional theory, we systematically investigated the adsorption properties of transition-metal (TM) adatoms on CaO(001) surfaces. Optimized adsorption structures and energetics of TM adatoms on CaO(001) are reported for various adsorption structures. The results are different from those of TM adatoms on MgO(001). Concomitantly, this suggests different dynamical properties of TM adatoms on CaO(001) surfaces as compared with TM adatoms on MgO(001) surfaces. Also performed was an analysis of the electronic structures of the TM adatoms on CaO(001) by using the energy positions of the adsorbate states with respect to the valence band maximum of CaO. The results are discussed in connection with the charge states of the TM adatoms on doped CaO(001).
International Nuclear Information System (INIS)
Song, T.; Ma, Q.; Sun, X.W.; Liu, Z.J.; Fu, Z.J.; Wei, X.P.; Wang, T.; Tian, J.H.
2016-01-01
The phase transition, electronic band structure, and equation of state (EOS) of cubic TcN are investigated by first-principles pseudopotential method based on density-functional theory. The calculated enthalpies show that TcN has a transformation between zincblende and rocksalt phases and the pressure determined by the relative enthalpy is 32 GPa. The calculated band structure indicates the metallic feature and it might make cubic TcN a better candidate for hard materials. Particular attention is paid to the predictions of volume, bulk modulus and its pressure derivative which play a central role in the formulation of approximate EOSs using the quasi-harmonic Debye model. - Highlights: • The phase transition pressure and electronic band structure for cubic TcN are determined. • Particular attention is paid to investigate the equation of state parameters for cubic TcN. • The thermodynamic properties up to 80 GPa and 3000 K are successfully predicted.
Chegeni, Mahdieh; Beiranvand, Razieh; Valedbagi, Shahoo
2017-04-01
Using first-principles approach, we theoretically study the effect of anion/cation vacancies on structural and electro-magnetic properties of zigzag AlN nanoribbons (ZAlNNRs). Calculations were performed using a full spin-polarized method within the density functional theory (DFT). Our findings shed light on how the edge states combined with vacancy engineering can affect electro-magnetic properties of ZAlNNRs. We found that depending on the nature and number of vacancies, ZAlNNRs can design as half-metal or semiconductor. Our results reveal a significant amount of spin magnetic moment for ZAlNNR with Al vacancies (VAl). These results may open new applications of AlN nano-materials in spintronics.
First-principles study of Ga-vacancy induced magnetism in β-Ga2O3.
Yang, Ya; Zhang, Jihua; Hu, Shunbo; Wu, Yabei; Zhang, Jincang; Ren, Wei; Cao, Shixun
2017-11-01
First principles calculations based on density functional theory were performed to study the electronic structure and magnetic properties of β-Ga 2 O 3 in the presence of cation vacancies. We investigated two kinds of Ga vacancies at different symmetry sites and the consequent structural distortion and defect states. We found that both the six-fold coordinated octahedral site and the four-fold coordinated tetrahedral site vacancies can lead to a spin polarized ground state. Furthermore, the calculation identified a relationship between the spin polarization and the charge states of the vacancies, which might be explained by a molecular orbital model consisting of uncompensated O 2- 2p dangling bonds. The calculations for the two vacancy systems also indicated a potential long-range ferromagnetic order which is beneficial for spintronics application.
International Nuclear Information System (INIS)
Spanos, G.; Geltmacher, A.B.; Lewis, A.C.; Bingert, J.F.; Mehl, M.; Papaconstantopoulos, D.; Mishin, Y.; Gupta, A.; Matic, P.
2007-01-01
This paper provides a brief overview of a multidisciplinary effort at the Naval Research Laboratory aimed at developing a computationally-based methodology to assist in the design of advanced Naval steels. This program uses multiple computational techniques ranging from the atomistic length scale to continuum response. First-principles electronic structure calculations using density functional theory were employed, semi-empirical angular dependent potentials were developed based on the embedded atom method, and these potentials were used as input into Monte-Carlo and molecular dynamics simulations. Experimental techniques have also been applied to a super-austenitic stainless steel (AL6XN) to provide experimental input, guidance, verification, and enhancements to the models. These experimental methods include optical microscopy, scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction, and serial sectioning in conjunction with computer-based three-dimensional reconstruction and quantitative analyses. The experimental results are also used as critical input into mesoscale finite element models of materials response
Yan, Hai-Yan; Zhang, Mei-Guang; Huang, Duo-Hui; Wei, Qun
2013-04-01
The first-principles study on the elastic properties, elastic anisotropy and thermodynamic properties of the orthorhombic OsB4 is reported using density functional theory method with the ultrasoft pseudopotential scheme in the frame of the generalized gradient approximation. The calculated equilibrium parameters are in good agreement with the available theoretical data. A complete elastic tensor and crystal anisotropies of the ultra-incompressible OsB4 are determined in the pressure range of 0-50 GPa. By the elastic stability criteria, it is predicted that the orthorhombic OsB4 is stable below 50 GPa. By using the quasi-harmonic Debye model, the heat capacity, the coefficient of thermal expansion, and the Grüneisen parameter of OsB4 are also successfully obtained in the present work.
Behzad, Somayeh
2018-04-01
Effects of strain on the electronic and optical properties of graphene on monolayer boron nitride (BN) substrate are investigated using first-principle calculations based on density functional theory. Strain-free graphene/BN has a small band gap of 97 meV at the K point. The magnitude of band gap increases with in-plane biaxial strain while it decreases with the perpendicular uniaxial strain. The ɛ2 (ω ) spectrum of graphene/BN bilayer for parallel polarization shows red and blue shifts by applying the in-plane tensile and compressive strains, respectively. Also the positions of peaks in the ɛ2 (ω ) spectrum are not significantly changed under perpendicular strain. The calculated results indicate that graphene on the BN substrate has great potential in microelectronic and optoelectronic applications.
International Nuclear Information System (INIS)
Liu Qijun; Liu Zhengtang; Feng Liping; Tian Hao
2010-01-01
We have performed ab-initio total energy calculations using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT) to study structural parameters, mechanical, electronic, chemical bonding and optical properties of cubic BaHfO 3 . The calculated lattice parameter and independent elastic constants are in good agreement with previous theoretical and experimental work. The bulk, shear and Young's modulus, Poisson coefficient, compressibility and Lame constants are obtained using Voigt-Reuss-Hill method and the Debye temperature is estimated using Debye-Grueneisen model, which are consistent with previous results. Electronic and chemical bonding properties have been studied from the calculations of band structure, density of states and charge densities. Furthermore, in order to clarify the mechanism of optical transitions of cubic BaHfO 3 , the complex dielectric function, refractive index, extinction coefficient, reflectivity, absorption efficient, loss function and complex conductivity function are calculated. Then, we have explained the origins of spectral peaks on the basis of the theory of crystal-field and molecular-orbital bonding.
First principles study of pentacene on Au(111)
Stokbro, Kurt; Smidstrup, Søren
2013-01-01
We investigate the atomic and electronic structure of a single layer of pentacene on the Au(111) surface using density functional theory. To find the candidate structures we strain match the pentacene crystal geometry with the Au(111) surface, in this way we find pentacene overlayer structures with a low strain. We show that the geometries obtained with this approach has lower energy than previous proposed surface geometries of pentacene on Au(111). We also show that the geometry and workfunc...
Engineering drawing from first principles using AutoCAD
Maguire, Dennis E
1998-01-01
Engineering Drawing From First Principles is a guide to good draughting for students of engineering who need to learn how to produce technically accurate and detailed designs to British and International Standards. Written by Dennis Maguire, an experienced author and City and Guilds chief examiner, this text is designed for use on Further Education and University courses where a basic understanding of draughtsmanship and CAD is necessary. Although not written as an AutoCAD tutor, the book will be a useful introduction to good CAD practice.Part of the Revision and Self-Assessmen
First-principles study of Frenkel pair recombination in tungsten
International Nuclear Information System (INIS)
Qin, Shi-Yao; Jin, Shuo; Li, Yu-Hao; Zhou, Hong-Bo; Zhang, Ying; Lu, Guang-Hong
2017-01-01
The recombination of one Frenkel pair in tungsten has been investigated through first-principles simulation. Two different recombination types have been identified: instantaneous and thermally activated. The small recombination barriers for thermally activated recombination cases indicate that recombination can occur easily with a slightly increased temperature. For both of the two recombination types, recombination occurs through the self-interstitial atom moving towards the vacancy. The recombination process can be direct or through replacement sequences, depending on the vertical distance between the vacancy and the 〈1 1 1〉 line of self-interstitial atom pair.
First principle study of cubic ScGaN ternaries
International Nuclear Information System (INIS)
Adli, W.; Mecheref, R.; Sekkal, N.; Tair, F.; Amrani, B.
2008-08-01
The electronic properties of the Sc x Ga1- x N ternary alloy are investigated. The transition from rocksalt (B1) to zinc blende (B3) structure is found to occur rapidly after incorporating just a small fraction (less than 1%) of Ga. In the present paper, the first principles method the full potential linear muffin-tin orbitals method (FPLMTO) in its atomic sphere approximation (ASA) coupled to the technique of the empty spheres is employed. Our results concerning the electronic properties are different from those reported in literature. (author)
Parallelization for first principles electronic state calculation program
International Nuclear Information System (INIS)
Watanabe, Hiroshi; Oguchi, Tamio.
1997-03-01
In this report we study the parallelization for First principles electronic state calculation program. The target machines are NEC SX-4 for shared memory type parallelization and FUJITSU VPP300 for distributed memory type parallelization. The features of each parallel machine are surveyed, and the parallelization methods suitable for each are proposed. It is shown that 1.60 times acceleration is achieved with 2 CPU parallelization by SX-4 and 4.97 times acceleration is achieved with 12 PE parallelization by VPP 300. (author)
Tao, Yehan; Xue, Qingzhong; Liu, Zilong; Shan, Meixia; Ling, Cuicui; Wu, Tiantian; Li, Xiaofang
2014-06-11
First-principle density functional theory (DFT) calculation and molecular dynamic (MD) simulation are employed to investigate the hydrogen purification performance of two-dimensional porous graphene material (PG-ESX). First, the pore size of PG-ES1 (3.2775 Å) is expected to show high selectivity of H2 by DFT calculation. Then MD simulations demonstrate the hydrogen purification process of the PG-ESX membrane. The results indicate that the selectivity of H2 over several other gas molecules that often accompany H2 in industrial steam methane reforming or dehydrogenation of alkanes (such as N2, CO, and CH4) is sensitive to the pore size of the membrane. PG-ES and PG-ES1 membranes both exhibit high selectivity for H2 over other gases, but the permeability of the PG-ES membrane is much lower than the PG-ES1 membrane because of the smaller pore size. The PG-ES2 membrane with bigger pores demonstrates low selectivity for H2 over other gases. Energy barrier and electron density have been used to explain the difference of selectivity and permeability of PG-ESX membranes by DFT calculations. The energy barrier for gas molecules passing through the membrane generally increase with the decreasing of pore sizes or increasing of molecule kinetic diameter, due to the different electron overlap between gas and a membrane. The PG-ES1 membrane is far superior to other carbon membranes and has great potential applications in hydrogen purification, energy clean combustion, and making new concept membrane for gas separation.
Roondhe, Basant; Dabhi, Shweta D.; Jha, Prafulla K.
2018-05-01
To understand the underlying physics behind the interaction of biomolecules with the nanomaterials to use them practically as bio-nanomaterials is very crucial. A first principles calculation under the frame work of density functional theory is executed to investigate the electronic structures and binding properties of alkaloids (Caffeine and Nicotine) over single walled boron nitride nanotube (BNNT) and boron nitride nanoribbon (BNNR) to determine their suitability towards filtration or sensing of these molecules. We have also used GGA-PBE scheme with the inclusion of Van der Waals (vdW) interaction based on DFT-D2. Increase in the accuracy by incorporating the dispersion correction in the calculation is observed for the long range Van der Waals interaction. Binding energy range of BNNT and BNNR with both alkaloids have been found to be -0.35 to -0.76 eV and -0.45 to -0.91 eV respectively which together with the binding distance shows physisorption binding of these molecules to the both nanostructures. The transfer of charge between the BN nanostructures and the adsorbed molecule has also been analysed by using Lowdin charge analysis. The sensitivity of both nanostructures BNNT and BNNR towards both alkaloids is observed through electronic structure calculations, density of states and quantum conductance. The binding of both alkaloids with BNNR is stronger. The analysis of the calculated properties suggests absence of covalent interaction between the considered species (BNNT/BNNR) and alkaloids. The study may be useful in designing the boron nitride nanostructure based sensing device for alkaloids.
A first-principles study on gas sensing properties of graphene and Pd-doped graphene
International Nuclear Information System (INIS)
Ma, Ling; Zhang, Jian-Min; Xu, Ke-Wei; Ji, Vincent
2015-01-01
Graphical abstract: - Highlights: • Optimized configurations for CO, NH 3 , O 2 and NO 2 adsorbed on PG ((a)–(d)) and Pd-G ((e)–(h)). The green, red, orange and blue balls represent the carbon, oxygen, nitrogen and palladium atoms, respectively. • Sensitivity of PG and Pd-G toward CO, NH 3 , O 2 and NO 2 has been investigated. • Pd dopants enhance interaction of gas molecules with the Pd-G sheet. • The electrical conductivity of Pd-G dramatically changes after gas adsorption. • Pd-G is more suitable for gas molecules detection compared with PG. - Abstract: Sensitivity of pristine graphene (PG) and Pd-doped graphene (Pd-G) toward a series of small gas molecules (CO, NH 3 , O 2 and NO 2 ) has been investigated by first-principles based on density functional theory (DFT). The most stable adsorption configuration, adsorption energy, charge transfer, density of states and magnetic moment of these molecules on PG and Pd-G are thoroughly discussed. It is found that four gas molecules are weakly adsorbed on PG with low adsorption energy of 0.08–0.24 eV, and the electronic properties of PG are only sensitive to the presence of O 2 and NO 2 molecules. In contrast, doping graphene with Pd dopants significantly enhances the strength of interaction between adsorbed molecules and the modified substrate. The dramatically increased adsorption energy and charge transfer of these systems are expected to induce significant changes in the electrical conductivity of the Pd-G sheet. The results reveals that the sensitivity of graphene-based chemical gas sensors could be drastically improved by introducing the Pd dopants, so Pd-G is more suitable for gas molecules detection compared with PG
Directory of Open Access Journals (Sweden)
Samah Al-Qaisi
Full Text Available First-principles investigations of the Terbium oxide TbO are performed on structural, elastic, mechanical and thermodynamic properties. The investigations are accomplished by employing full potential augmented plane wave FP-LAPW method framed within density functional theory DFT as implemented in the WIEN2k package. The exchange-correlation energy functional, a part of the total energy functional, is treated through Perdew Burke Ernzerhof scheme of the Generalized Gradient Approximation PBEGGA. The calculations of the ground state structural parameters, like lattice constants a0, bulk moduli B and their pressure derivative B′ values, are done for the rock-salt RS, zinc-blende ZB, cesium chloride CsCl, wurtzite WZ and nickel arsenide NiAs polymorphs of the TbO compound. The elastic constants (C11, C12, C13, C33, and C44 and mechanical properties (Young’s modulus Y, Shear modulus S, Poisson’s ratio σ, Anisotropic ratio A and compressibility β, were also calculated to comprehend its potential for valuable applications. From our calculations, the RS phase of TbO compound was found strongest one mechanically amongst the studied cubic structures whereas from hexagonal phases, the NiAs type structure was found stronger than WZ phase of the TbO. To analyze the ductility of the different structures of the TbO, Pugh’s rule (B/SH and Cauchy pressure (C12–C44 approaches are used. It was found that ZB, CsCl and WZ type structures of the TbO were of ductile nature with the obvious dominance of the ionic bonding while RS and NiAs structures exhibited brittle nature with the covalent bonding dominance. Moreover, Debye temperature was calculated for both cubic and hexagonal structures of TbO in question by averaging the computed sound velocities. Keywords: DFT, TbO, Elastic properties, Thermodynamic properties
Spin theory of the density functional: reduced matrices and density functions
International Nuclear Information System (INIS)
Pavlov, R.; Delchev, Y.; Pavlova, K.; Maruani, J.
1993-01-01
Expressions for the reduced matrices and density functions of N-fermion systems of arbitrary order s (1<=s<=N) are derived within the frame of rigorous spin approach to the density functional theory (DFT). Using the local-scale transformation method and taking into account the particle spin it is shown that the reduced matrices and density functions are functionals of the total one-fermion density. Similar dependence is found for the distribution density of s-particle aggregates. Generalization and applicability of DFT to the case of s-particle ensembles and aggregates is discussed. 14 refs
Rational Density Functional Selection Using Game Theory.
McAnanama-Brereton, Suzanne; Waller, Mark P
2018-01-22
Theoretical chemistry has a paradox of choice due to the availability of a myriad of density functionals and basis sets. Traditionally, a particular density functional is chosen on the basis of the level of user expertise (i.e., subjective experiences). Herein we circumvent the user-centric selection procedure by describing a novel approach for objectively selecting a particular functional for a given application. We achieve this by employing game theory to identify optimal functional/basis set combinations. A three-player (accuracy, complexity, and similarity) game is devised, through which Nash equilibrium solutions can be obtained. This approach has the advantage that results can be systematically improved by enlarging the underlying knowledge base, and the deterministic selection procedure mathematically justifies the density functional and basis set selections.
First-principles calculation on oxygen ion migration in alkaline-earth doped La2GeO5
International Nuclear Information System (INIS)
Thuy Linh, Tran Phan; Sakaue, Mamoru; Aspera, Susan Meñez; Alaydrus, Musa; Wungu, Triati Dewi Kencana; Hoang Linh, Nguyen; Kasai, Hideaki; Mohri, Takahiro; Ishihara, Tatsumi
2014-01-01
By using first-principles calculations based on the density functional theory, we investigated the doping effects of alkaline-earth metals (Ba, Sr and Ca) in monoclinic lanthanum germanate La 2 GeO 5 on its oxygen ion conduction. Although the lattice parameters of the doped systems changed due to the ionic radii mismatch, the crystal structures remained monoclinic. The contribution of each atomic orbital to electronic densities of states was evaluated from the partial densities of states and partial charge densities. It was confirmed that the materials behaved as ionic crystals comprising of cations of La and dopants and anions of oxygen and covalently formed GeO 4 . The doping effect on the activation barrier for oxygen hopping to the most stable oxygen vacancy site was investigated by the climbing-image nudged elastic band method. By tracing the charge density change during the hopping, it was confirmed that the oxygen motion is governed by covalent interactions. The obtained activation barriers showed excellent quantitative agreements with an experiment for the Ca- and Sr-doped systems in low temperatures as well as the qualitative trend, including the Ba-doped system. (paper)
Liang, Wenkel; Isborn, Christine M.; Li, Xiaosong
2009-11-01
The calculation of doubly excited states is one of the major problems plaguing the modern day excited state workhorse methodology of linear response time dependent Hartree-Fock (TDHF) and density function theory (TDDFT). We have previously shown that the use of a resonantly tuned field within real-time TDHF and TDDFT is able to simultaneously excite both the α and β electrons to achieve the two-electron excited states of minimal basis H2 and HeH+ [C. M. Isborn and X. Li, J. Chem. Phys. 129, 204107 (2008)]. We now extend this method to many electron systems with the use of our Car-Parrinello density matrix search (CP-DMS) with a first-principles fictitious mass method for wave function optimization [X. Li, C. L. Moss, W. Liang, and Y. Feng, J. Chem. Phys. 130, 234115 (2009)]. Real-time TDHF/TDDFT is used during the application of the laser field perturbation, driving the electron density toward the doubly excited state. The CP-DMS method then converges the density to the nearest stationary state. We present these stationary state doubly excited state energies and properties at the HF and DFT levels for H2, HeH+, lithium hydride, ethylene, and butadiene.
Hu, S X; Collins, L A; Boehly, T R; Kress, J D; Goncharov, V N; Skupsky, S
2014-04-01
Thermal conductivity (κ) of both the ablator materials and deuterium-tritium (DT) fuel plays an important role in understanding and designing inertial confinement fusion (ICF) implosions. The extensively used Spitzer model for thermal conduction in ideal plasmas breaks down for high-density, low-temperature shells that are compressed by shocks and spherical convergence in imploding targets. A variety of thermal-conductivity models have been proposed for ICF hydrodynamic simulations of such coupled and degenerate plasmas. The accuracy of these κ models for DT plasmas has recently been tested against first-principles calculations using the quantum molecular-dynamics (QMD) method; although mainly for high densities (ρ > 100 g/cm3), large discrepancies in κ have been identified for the peak-compression conditions in ICF. To cover the wide range of density-temperature conditions undergone by ICF imploding fuel shells, we have performed QMD calculations of κ for a variety of deuterium densities of ρ = 1.0 to 673.518 g/cm3, at temperatures varying from T = 5 × 103 K to T = 8 × 106 K. The resulting κQMD of deuterium is fitted with a polynomial function of the coupling and degeneracy parameters Γ and θ, which can then be used in hydrodynamic simulation codes. Compared with the "hybrid" Spitzer-Lee-More model currently adopted in our hydrocode lilac, the hydrosimulations using the fitted κQMD have shown up to ∼20% variations in predicting target performance for different ICF implosions on OMEGA and direct-drive-ignition designs for the National Ignition Facility (NIF). The lower the adiabat of an imploding shell, the more variations in predicting target performance using κQMD. Moreover, the use of κQMD also modifies the shock conditions and the density-temperature profiles of the imploding shell at early implosion stage, which predominantly affects the final target performance. This is in contrast to the previous speculation that κQMD changes mainly the
Pressure induced structural phase transition in solid oxidizer KClO3: A first-principles study
Yedukondalu, N.; Ghule, Vikas D.; Vaitheeswaran, G.
2013-05-01
High pressure behavior of potassium chlorate (KClO3) has been investigated from 0 to 10 GPa by means of first principles density functional theory calculations. The calculated ground state parameters, transition pressure, and phonon frequencies using semiempirical dispersion correction scheme are in excellent agreement with experiment. It is found that KClO3 undergoes a pressure induced first order phase transition with an associated volume collapse of 6.4% from monoclinic (P21/m) → rhombohedral (R3m) structure at 2.26 GPa, which is in good accord with experimental observation. However, the transition pressure was found to underestimate (0.11 GPa) and overestimate (3.57 GPa) using local density approximation and generalized gradient approximation functionals, respectively. Mechanical stability of both the phases is explained from the calculated single crystal elastic constants. In addition, the zone center phonon frequencies have been calculated using density functional perturbation theory at ambient as well as at high pressure and the lattice modes are found to soften under pressure between 0.6 and 1.2 GPa. The present study reveals that the observed structural phase transition leads to changes in the decomposition mechanism of KClO3 which corroborates with the experimental results.
Versatile Density Functionals for Computational Surface Science
DEFF Research Database (Denmark)
Wellendorff, Jess
Density functional theory (DFT) emerged almost 50 years ago. Since then DFT has established itself as the central electronic structure methodology for simulating atomicscale systems from a few atoms to a few hundred atoms. This success of DFT is due to a very favorable accuracy-to-computational c......Density functional theory (DFT) emerged almost 50 years ago. Since then DFT has established itself as the central electronic structure methodology for simulating atomicscale systems from a few atoms to a few hundred atoms. This success of DFT is due to a very favorable accuracy...... resampling techniques, thereby systematically avoiding problems with overfitting. The first ever density functional presenting both reliable accuracy and convincing error estimation is generated. The methodology is general enough to be applied to more complex functional forms with higher-dimensional fitting...
Kroonblawd, Matthew; Goldman, Nir
First principles molecular dynamics using highly accurate density functional theory (DFT) is a common tool for predicting chemistry, but the accessible time and space scales are often orders of magnitude beyond the resolution of experiments. Semi-empirical methods such as density functional tight binding (DFTB) offer up to a thousand-fold reduction in required CPU hours and can approach experimental scales. However, standard DFTB parameter sets lack good transferability and calibration for a particular system is usually necessary. Force matching the pairwise repulsive energy term in DFTB to short DFT trajectories can improve the former's accuracy for chemistry that is fast relative to DFT simulation times (Contract DE-AC52-07NA27344.
Kroonblawd, Matthew; Goldman, Nir
2017-06-01
First principles molecular dynamics using highly accurate density functional theory (DFT) is a common tool for predicting chemistry, but the accessible time and space scales are often orders of magnitude beyond the resolution of experiments. Semi-empirical methods such as density functional tight binding (DFTB) offer up to a thousand-fold reduction in required CPU hours and can approach experimental scales. However, standard DFTB parameter sets lack good transferability and calibration for a particular system is usually necessary. Force matching the pairwise repulsive energy term in DFTB to short DFT trajectories can improve the former's accuracy for reactions that are fast relative to DFT simulation times (Contract DE-AC52-07NA27344.
Density functional theory for field emission from carbon nano-structures.
Li, Zhibing
2015-12-01
Electron field emission is understood as a quantum mechanical many-body problem in which an electronic quasi-particle of the emitter is converted into an electron in vacuum. Fundamental concepts of field emission, such as the field enhancement factor, work-function, edge barrier and emission current density, will be investigated, using carbon nanotubes and graphene as examples. A multi-scale algorithm basing on density functional theory is introduced. We will argue that such a first principle approach is necessary and appropriate for field emission of nano-structures, not only for a more accurate quantitative description, but, more importantly, for deeper insight into field emission. Copyright © 2015 The Author. Published by Elsevier B.V. All rights reserved.
Defects in boron carbide: First-principles calculations and CALPHAD modeling
International Nuclear Information System (INIS)
Saengdeejing, Arkapol; Saal, James E.; Manga, Venkateswara Rao; Liu Zikui
2012-01-01
The energetics of defects in B 4+x C boron carbide and β-boron are studied through first-principles calculations, the supercell phonon approach and the Debye–Grüneisen model. It is found that suitable sublattice models for β-boron and B 4+x C are B 101 (B,C) 4 and B 11 (B,C) (B,C,Va) (B,Va) (B,C,Va), respectively. The thermodynamic properties of B 4+x C, β-boron, liquid and graphite are modeled using the CALPHAD approach based on the thermochemical data from first-principles calculations and experimental phase equilibrium data in the literature. The concentrations of various defects are then predicted as a function of carbon composition and temperature.
Energy Technology Data Exchange (ETDEWEB)
Bondi, Robert J., E-mail: rjbondi@sandia.gov; Desjarlais, Michael P.; Thompson, Aidan P.; Brennecka, Geoff L.; Marinella, Matthew J. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)
2013-11-28
We apply first-principles density-functional theory (DFT) calculations, ab-initio molecular dynamics, and the Kubo-Greenwood formula to predict electrical conductivity in Ta{sub 2}O{sub x} (0 ≤ x ≤ 5) as a function of composition, phase, and temperature, where additional focus is given to various oxidation states of the O monovacancy (V{sub O}{sup n}; n = 0,1+,2+). In the crystalline phase, our DFT calculations suggest that V{sub O}{sup 0} prefers equatorial O sites, while V{sub O}{sup 1+} and V{sub O}{sup 2+} are energetically preferred in the O cap sites of TaO{sub 7} polyhedra. Our calculations of DC conductivity at 300 K agree well with experimental measurements taken on Ta{sub 2}O{sub x} thin films (0.18 ≤ x ≤ 4.72) and bulk Ta{sub 2}O{sub 5} powder-sintered pellets, although simulation accuracy can be improved for the most insulating, stoichiometric compositions. Our conductivity calculations and further interrogation of the O-deficient Ta{sub 2}O{sub 5} electronic structure provide further theoretical basis to substantiate V{sub O}{sup 0} as a donor dopant in Ta{sub 2}O{sub 5}. Furthermore, this dopant-like behavior is specific to the neutral case and not observed in either the 1+ or 2+ oxidation states, which suggests that reduction and oxidation reactions may effectively act as donor activation and deactivation mechanisms, respectively, for V{sub O}{sup n} in Ta{sub 2}O{sub 5}.
First-principles Study of the Electronic Structure and Optical Properties of MgH2
Alford, Ashley; Chou, Mei-Yin
2003-03-01
It has been noticed that magnesium might play an interesting role in recently discovered switchable-mirror systems. For example, the films of rare earth and magnesium alloys are found to be superior to the pure rare-earth samples in maximum transparency and mirror-state reflectivity [1]. Moreover, the magnesium-rich Ni-Mg alloy films turned out to be a switchable-mirror system without rare earths [2]. In both cases, pure transparent MgH2 is reversibly formed when these alloys take up hydrogen. In order to model the optical properties of these films, we need to know the electronic and optical properties of MgH2. In this work, we investigate its bonding characteristics, band structure, and dielectric properties with first-principles theoretical methods. The stability of the crystal and the bonding are studied using density functional theory and pseudopotential methods. The excited state properties (the quasiparticle spectra) are studied by many-body perturbation theory within the so-called GW approximation in which the electronic self-energy is approximated by the full Green's function (G) times the screened Coulomb interaction (W). We will report the results for both the rutile-structured alpha-MgH2 and the low-symmetry gamma-MgH2. [1] P. van der Sluis, M. Ouwerkerk, and P. A. Duine, Appl. Phys. Lett. 70, 3356 (1997). [2] T. J. Richardson, J. L. Slack, R. D. armitage, R. Kostecki, B. Farangis, and M. D. Rubin, Appl. Phys. Lett. 78, 3047 (2001).
Degradation of Alkali-Based Photocathodes from Exposure to Residual Gases: A First-Principles Study
International Nuclear Information System (INIS)
Wang, Gaoxue; Batista, Enrique R.
2017-01-01
Photocathodes are a key component in the production of electron beams in systems such as X-ray free-electron lasers and X-ray energy-recovery linacs. Alkali-based materials display high quantum efficiency (QE), however, their QE undergoes degradation faster than metal photocathodes even in the high vacuum conditions where they operate. The high reactivity of alkali-based surfaces points to surface reactions with residual gases as one of the most important factors for the degradation of QE. In order to advance the understanding on the degradation of the QE, we investigated the surface reactivity of common residual gas molecules (e.g., O 2 , CO 2 , CO, H 2 O, N 2 , and H 2 ) on one of the best-known alkali-based photocathode materials, cesium antimonide (Cs 3 Sb), using first-principles calculations based on density functional theory. Furthermore, the reaction sites, adsorption energy, and effect in the local electronic structure upon reaction of these molecules on (001), (110), and (111) surfaces of Cs 3 Sb were computed and analyzed. The adsorption energy of these molecules on Cs3Sb follows the trend of O 2 (-4.5 eV) > CO 2 (-1.9 eV) > H 2 O (-1.0 eV) > CO (-0.8 eV) > N 2 (-0.3 eV) ≈ H 2 (-0.2 eV), which agrees with experimental data on the effect of these gases on the degradation of QE. The interaction strength is determined by the charge transfer from the surfaces to the molecules. The adsorption and dissociation of O containing molecules modify the surface chemistry such as the composition, structure, charge distribution, surface dipole, and work function of Cs 3 Sb, resulting in the degradation of QE with exposure to O 2 , CO 2 , H 2 O, and CO.
Nonlocal kinetic-energy-density functionals
International Nuclear Information System (INIS)
Garcia-Gonzalez, P.; Alvarellos, J.E.; Chacon, E.
1996-01-01
In this paper we present nonlocal kinetic-energy functionals T[n] within the average density approximation (ADA) framework, which do not require any extra input when applied to any electron system and recover the exact kinetic energy and the linear response function of a homogeneous system. In contrast with previous ADA functionals, these present good behavior of the long-range tail of the exact weight function. The averaging procedure for the kinetic functional (averaging the Fermi momentum of the electron gas, instead of averaging the electron density) leads to a functional without numerical difficulties in the calculation of extended systems, and it gives excellent results when applied to atoms and jellium surfaces. copyright 1996 The American Physical Society
Half-metallicity in a BiFeO3/La2/3Sr1/3MnO3 superlattice: A first-principles study
Jiwuer, Jilili
2013-06-01
We present first-principles results for the electronic, magnetic, and optical properties of the heterostructure as obtained by spin-polarized calculations using density functional theory. The electronic states of the heterostructure are compared to those of the bulk compounds. Structural relaxation turns out to have only a minor impact on the chemical bonding, even though the oxygen octahedra in develop some distortions due to the interface strain. While a small charge transfer affects the heterointerfaces, our results demonstrate that the half-metallic character of is fully maintained. © EPLA, 2013.
Saidi, F.; Sebaa, N.; Mahmoudi, A.; Aourag, H.; Merad, G.; Dergal, M.
2018-06-01
We performed first-principle calculations to investigate structural, phase stability, electronic and mechanical properties for the Laves phases YM2 (M = Mn, Fe, Co) with C15, C14 and C36 structures. We used the density functional theory within the framework of both pseudo-potentials and plane wave basis using VASP (Vienna Ab Initio Software Package). The calculated equilibrium structural parameters are in accordance with available theoretical values. Mechanical properties were calculated, discussed, and analyzed with data mining approach in terms of structure stability. The results reveal that YCo2 is harder than YFe2 and YMn2.
Energy Technology Data Exchange (ETDEWEB)
Migaou, Amani; Guiltat, Mathilde; Payen, Kevin; Landa, Georges; Hémeryck, Anne, E-mail: anne.hemeryck@laas.fr [LAAS-CNRS, Université de Toulouse, CNRS, UPS, Toulouse (France); Sarpi, Brice; Daineche, Rachid; Vizzini, Sébastien [Aix Marseille University, IM2NP, Fac Sci St. Jérôme, F-13397 Marseille (France)
2016-05-21
First principles calculations, scanning tunneling microscopy, and Auger spectroscopy experiments of the adsorption of Mg on Ag(111) substrate are conducted. This detailed study reveals that an atomic scale controlled deposition of a metallic Mg monolayer perfectly wets the silver substrate without any alloy formation at the interface at room temperature. A liquid-like behavior of the Mg species on the Ag substrate is highlighted as no dot formation is observed when coverage increases. Finally a layer-by-layer growth mode of Mg on Ag(111) can be predicted, thanks to density functional theory calculations as observed experimentally.
Periodic subsystem density-functional theory
International Nuclear Information System (INIS)
Genova, Alessandro; Pavanello, Michele; Ceresoli, Davide
2014-01-01
By partitioning the electron density into subsystem contributions, the Frozen Density Embedding (FDE) formulation of subsystem Density Functional Theory (DFT) has recently emerged as a powerful tool for reducing the computational scaling of Kohn–Sham DFT. To date, however, FDE has been employed to molecular systems only. Periodic systems, such as metals, semiconductors, and other crystalline solids have been outside the applicability of FDE, mostly because of the lack of a periodic FDE implementation. To fill this gap, in this work we aim at extending FDE to treat subsystems of molecular and periodic character. This goal is achieved by a dual approach. On one side, the development of a theoretical framework for periodic subsystem DFT. On the other, the realization of the method into a parallel computer code. We find that periodic FDE is capable of reproducing total electron densities and (to a lesser extent) also interaction energies of molecular systems weakly interacting with metallic surfaces. In the pilot calculations considered, we find that FDE fails in those cases where there is appreciable density overlap between the subsystems. Conversely, we find FDE to be in semiquantitative agreement with Kohn–Sham DFT when the inter-subsystem density overlap is low. We also conclude that to make FDE a suitable method for describing molecular adsorption at surfaces, kinetic energy density functionals that go beyond the GGA level must be employed
Periodic subsystem density-functional theory
Genova, Alessandro; Ceresoli, Davide; Pavanello, Michele
2014-11-01
By partitioning the electron density into subsystem contributions, the Frozen Density Embedding (FDE) formulation of subsystem Density Functional Theory (DFT) has recently emerged as a powerful tool for reducing the computational scaling of Kohn-Sham DFT. To date, however, FDE has been employed to molecular systems only. Periodic systems, such as metals, semiconductors, and other crystalline solids have been outside the applicability of FDE, mostly because of the lack of a periodic FDE implementation. To fill this gap, in this work we aim at extending FDE to treat subsystems of molecular and periodic character. This goal is achieved by a dual approach. On one side, the development of a theoretical framework for periodic subsystem DFT. On the other, the realization of the method into a parallel computer code. We find that periodic FDE is capable of reproducing total electron densities and (to a lesser extent) also interaction energies of molecular systems weakly interacting with metallic surfaces. In the pilot calculations considered, we find that FDE fails in those cases where there is appreciable density overlap between the subsystems. Conversely, we find FDE to be in semiquantitative agreement with Kohn-Sham DFT when the inter-subsystem density overlap is low. We also conclude that to make FDE a suitable method for describing molecular adsorption at surfaces, kinetic energy density functionals that go beyond the GGA level must be employed.
Chandran, Mahesh; Lee, S. C.; Shim, Jae-Hyeok
2018-02-01
A disordered configuration of atoms in a multicomponent solid solution presents a computational challenge for first-principles calculations using density functional theory (DFT). The challenge is in identifying the few probable (low energy) configurations from a large configurational space before DFT calculation can be performed. The search for these probable configurations is possible if the configurational energy E({\\boldsymbol{σ }}) can be calculated accurately and rapidly (with a negligibly small computational cost). In this paper, we demonstrate such a possibility by constructing a machine learning (ML) model for E({\\boldsymbol{σ }}) trained with DFT-calculated energies. The feature vector for the ML model is formed by concatenating histograms of pair and triplet (only equilateral triangle) correlation functions, {g}(2)(r) and {g}(3)(r,r,r), respectively. These functions are a quantitative ‘fingerprint’ of the spatial arrangement of atoms, familiar in the field of amorphous materials and liquids. The ML model is used to generate an accurate distribution P(E({\\boldsymbol{σ }})) by rapidly spanning a large number of configurations. The P(E) contains full configurational information of the solid solution and can be selectively sampled to choose a few configurations for targeted DFT calculations. This new framework is employed to estimate (100) interface energy ({σ }{{IE}}) between γ and γ \\prime at 700 °C in Alloy 617, a Ni-based superalloy, with composition reduced to five components. The estimated {σ }{{IE}} ≈ 25.95 mJ m-2 is in good agreement with the value inferred by the precipitation model fit to experimental data. The proposed new ML-based ab initio framework can be applied to calculate the parameters and properties of alloys with any number of components, thus widening the reach of first-principles calculation to realistic compositions of industrially relevant materials and alloys.
First principles simulation of amorphous InSb
Los, Jan H.; Kühne, Thomas D.; Gabardi, Silvia; Bernasconi, Marco
2013-05-01
Ab initio molecular dynamics simulations based on density functional theory have been performed to generate a model of amorphous InSb by quenching from the melt. The resulting network is mostly tetrahedral with a minor fraction (10%) of atoms in a fivefold coordination. The structural properties are in good agreement with available x-ray diffraction and extended x-ray-absorption fine structure data and confirm the proposed presence of a sizable fraction of homopolar In-In and Sb-Sb bonds whose concentration in our model amounts to about 20% of the total number of bonds.
Substitutional Co dopant on the GaAs(110) surface: A first principles study
Energy Technology Data Exchange (ETDEWEB)
Fang, Zhou; Yi, Zhijun, E-mail: zhijunyi@cumt.edu.cn
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.
First-principles calculation of the structural stability of 6d transition metals
International Nuclear Information System (INIS)
Oestlin, A.; Vitos, L.
2011-01-01
The phase stability of the 6d transition metals (elements 103-111) is investigated using first-principles electronic-structure calculations. Comparison with the lighter transition metals reveals that the structural sequence trend is broken at the end of the 6d series. To account for this anomalous behavior, the effect of relativity on the lattice stability is scrutinized, taking different approximations into consideration. It is found that the mass-velocity and Darwin terms give important contributions to the electronic structure, leading to changes in the interstitial charge density and, thus, in the structural energy difference.
A first principles investigation of the electronic structure of actinide oxides
DEFF Research Database (Denmark)
Petit, Leon; Svane, Axel; Szotek, Zdzislawa
2010-01-01
The ground state electronic structures of the actinide oxides AO, A2O3 and AO2 (A=U, Np, Pu, Am, Cm, Bk, Cf) are determined from first-principles calculations using the selfinteraction corrected local spin-density approximation. Our study reveals a strong link between preferred oxidation number...... and degree of localization. The ionic nature of the actinide oxides emerges from the fact that those oxides where the ground state is calculated to be metallic do not exist in nature, as the corresponding delocalized f-states favour the accommodation of additional O atoms into the crystal lattice....
Effect of contact deformation on contact electrification: a first-principles calculation
International Nuclear Information System (INIS)
Zhang, Yuanyue; Shao, Tianmin
2013-01-01
The effect of contact deformation on contact electrification of metallic materials was studied by the first-principles method. The results of charge population and the densities of states of the deformed contact models demonstrated that the magnitude of the transferred charge increased with deformation. The mechanism of the effect of deformation was investigated by studying the electronic properties of the deformed surface slabs. The results showed that crystal deformation led to a change in the electrostatic potential of the metal, where the number of nearly free electrons and unoccupied orbitals for charge transfer increased, and their energy barrier decreased. (paper)
Prospects for first-principle calculations of scintillator properties
International Nuclear Information System (INIS)
Derenzo, Stephen E.; Weber, Marvin J.
1999-01-01
Several scintillation processes can be modeled from first principles using quantum chemistry cluster calculations and recently available high-performance computers. These processes include the formation of excitons and trapping centers, the diffusion of ionization energy (electrons and holes) through a host crystal, and the efficient capture of these carriers by an activator atom to form a luminous, non-quenched excited state. As examples of such calculations, results are presented for (1) hole transport in the known scintillator host crystal CsI, (2) hole trapping in the non-scintillator PbF 2 , (3) hole transport in the experimentally unexplored PbF 4 , and (4) the electronic nature of excited states of CsI : Tl and CsI : Na
Multiphysics modeling using COMSOL a first principles approach
Pryor, Roger W
2011-01-01
Multiphysics Modeling Using COMSOL rapidly introduces the senior level undergraduate, graduate or professional scientist or engineer to the art and science of computerized modeling for physical systems and devices. It offers a step-by-step modeling methodology through examples that are linked to the Fundamental Laws of Physics through a First Principles Analysis approach. The text explores a breadth of multiphysics models in coordinate systems that range from 1D to 3D and introduces the readers to the numerical analysis modeling techniques employed in the COMSOL Multiphysics software. After readers have built and run the examples, they will have a much firmer understanding of the concepts, skills, and benefits acquired from the use of computerized modeling techniques to solve their current technological problems and to explore new areas of application for their particular technological areas of interest.
The first principle calculation of two-dimensional Dirac materials
Lu, Jin
2017-12-01
As the size of integrated device becoming increasingly small, from the last century, semiconductor industry is facing the enormous challenge to break the Moore’s law. The development of calculation, communication and automatic control have emergent expectation of new materials at the aspect of semiconductor industrial technology and science. In spite of silicon device, searching the alternative material with outstanding electronic properties has always been a research point. As the discovery of graphene, the research of two-dimensional Dirac material starts to express new vitality. This essay studied the development calculation of 2D material’s mobility and introduce some detailed information of some approximation method of the first principle calculation.
Molecular electronics: insight from first-principles transport simulations.
Paulsson, Magnus; Frederiksen, Thomas; Brandbyge, Mads
2010-01-01
Conduction properties of nanoscale contacts can be studied using first-principles simulations. Such calculations give insight into details behind the conductance that is not readily available in experiments. For example, we may learn how the bonding conditions of a molecule to the electrodes affect the electronic transport. Here we describe key computational ingredients and discuss these in relation to simulations for scanning tunneling microscopy (STM) experiments with C60 molecules where the experimental geometry is well characterized. We then show how molecular dynamics simulations may be combined with transport calculations to study more irregular situations, such as the evolution of a nanoscale contact with the mechanically controllable break-junction technique. Finally we discuss calculations of inelastic electron tunnelling spectroscopy as a characterization technique that reveals information about the atomic arrangement and transport channels.
First principles studies of electron tunneling in proteins
Hayashi, Tomoyuki; Stuchebrukhov, Alexei A.
2014-01-01
A first principles study of electronic tunneling along the chain of seven Fe/S clusters in respiratory complex I, a key enzyme in the respiratory electron transport chain, is described. The broken-symmetry states of the Fe/S metal clusters calculated at both DFT and semi-empirical ZINDO levels were utilized to examine both the extremely weak electronic couplings between Fe/S clusters and the tunneling pathways, which provide a detailed atomistic-level description of the charge transfer process in the protein. One-electron tunneling approximation was found to hold within a reasonable accuracy, with only a moderate induced polarization of the core electrons. The method is demonstrated to be able to calculate accurately the coupling matrix elements as small as 10−4 cm−1. A distinct signature of the wave properties of electrons is observed as quantum interferences of multiple tunneling pathways. PMID:25383312
First Principles Modelling of Shape Memory Alloys Molecular Dynamics Simulations
Kastner, Oliver
2012-01-01
Materials sciences relate the macroscopic properties of materials to their microscopic structure and postulate the need for holistic multiscale research. The investigation of shape memory alloys is a prime example in this regard. This particular class of materials exhibits strong coupling of temperature, strain and stress, determined by solid state phase transformations of their metallic lattices. The present book presents a collection of simulation studies of this behaviour. Employing conceptually simple but comprehensive models, the fundamental material properties of shape memory alloys are qualitatively explained from first principles. Using contemporary methods of molecular dynamics simulation experiments, it is shown how microscale dynamics may produce characteristic macroscopic material properties. The work is rooted in the materials sciences of shape memory alloys and covers thermodynamical, micro-mechanical and crystallographical aspects. It addresses scientists in these research fields and thei...
Predicting catalysis: Understanding ammonia synthesis from first-principles calculations
DEFF Research Database (Denmark)
Hellmann, A.; Baerends, E.J.; Biczysko, M.
2006-01-01
. Furthermore, our studies provide new insight into several related fields, for instance, gas-phase and electrochemical ammonia synthesis. The success of predicting the outcome of a catalytic reaction from first-principles calculations supports our point of view that, in the future, theory will be a fully......Here, we give a full account of a large collaborative effort toward an atomic-scale understanding of modern industrial ammonia production over ruthenium catalysts. We show that overall rates of ammonia production can be determined by applying various levels of theory (including transition state...... for any given point along an industrial reactor, and the kinetic results can be integrated over the catalyst bed to determine the industrial reactor yield. We find that, given the present uncertainties, the rate of ammonia production is well-determined directly from our atomic-scale calculations...
Quantum theory from first principles an informational approach
D'Ariano, Giacomo Mauro; Perinotti, Paolo
2017-01-01
Quantum theory is the soul of theoretical physics. It is not just a theory of specific physical systems, but rather a new framework with universal applicability. This book shows how we can reconstruct the theory from six information-theoretical principles, by rebuilding the quantum rules from the bottom up. Step by step, the reader will learn how to master the counterintuitive aspects of the quantum world, and how to efficiently reconstruct quantum information protocols from first principles. Using intuitive graphical notation to represent equations, and with shorter and more efficient derivations, the theory can be understood and assimilated with exceptional ease. Offering a radically new perspective on the field, the book contains an efficient course of quantum theory and quantum information for undergraduates. The book is aimed at researchers, professionals, and students in physics, computer science and philosophy, as well as the curious outsider seeking a deeper understanding of the theory.
Directory of Open Access Journals (Sweden)
Hui Niu
2012-09-01
Full Text Available Systematic first-principles calculations based on density functional theory were performed on a wide range of Ln2TiO5 compositions (Ln = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy and Y in order to investigate their structural, elastic, electronic, and thermal properties. At low temperature, these compounds crystallize in orthorhombic structures with a Pnma symmetry, and the calculated equilibrium structural parameters agree well with experimental results. A complete set of elastic parameters including elastic constants, Hill's bulk moduli, Young's moduli, shear moduli and Poisson's ratio were calculated. All Ln2TiO5 are ductile in nature. Analysis of densities of states and charge densities and electron localization functions suggests that the oxide bonds are highly ionic with some degree of covalency in the Ti-O bonds. Thermal properties including the mean sound velocity, Debye temperature, and minimum thermal conductivity were obtained from the elastic constants.
First-principle Simulations of Heavy Fermion Materials
Dong, Ruanchen
Heavy fermion materials, one of the most challenging topics in condensed matter physics, pose a variety of interesting properties and have attracted extensive studies for decades. Although there has been great success in explaining many ground- state properties of solids, the well-known theoretical calculations based on density functional theory (DFT) in its popular local density approximation (LDA) fail to describe heavy fermion materials due to improper treatment of many-body correlation effects. Here with the implementations of dynamical mean-field theory (DMFT) and the Gutzwiller variational method, the computational simulation of the heavy fermion materials is explored further and better compared with experimental data. In this dissertation, first, the theoretical background of DMFT and LDA+G methods is described in detail. The rest is the application of these techniques and is basically divided into two parts. First, the continuous-time quantum Monte Carlo (CT-QMC) method combined with DMFT is used to calculate and compare both the periodic Anderson model (PAM) and the Kondo lattice model (KLM). Different parameter sets of both models are connected by the Schrieffer-Wolff transformation. For spin and orbital degeneracy N = 2 case, a special particle-hole symmetric case of PAM at half-filling which always fixes one electron per impurity site is compared with the results of the KLM. We find a good mapping between PAM and KLM in the limit of large on-site Hubbard interaction U for different properties like self-energy, quasiparticle residue and susceptibility. This allows us to extract quasiparticle mass renormalizations for the f-electrons directly from KLM. The method is further applied to higher degenerate cases and to the realistic heavy fermion system CeRhIn5 in which the estimate of the Sommerfeld coefficient is proven to be close to the experimental value. Second, a series of Cerium based heavy fermion materials is studied using a combination of local
Optoelectronics and defect levels in hydroxyapatite by first-principles
Avakyan, Leon A.; Paramonova, Ekaterina V.; Coutinho, José; Öberg, Sven; Bystrov, Vladimir S.; Bugaev, Lusegen A.
2018-04-01
Hydroxyapatite (HAp) is an important component of mammal bones and teeth, being widely used in prosthetic implants. Despite the importance of HAp in medicine, several promising applications involving this material (e.g., in photo-catalysis) depend on how well we understand its fundamental properties. Among the ones that are either unknown or not known accurately, we have the electronic band structure and all that relates to it, including the bandgap width. We employ state-of-the-art methodologies, including density hybrid-functional theory and many-body perturbation theory within the dynamically screened single-particle Green's function approximation, to look at the optoelectronic properties of HAp. These methods are also applied to the calculation of defect levels. We find that the use of a mix of (semi-)local and exact exchange in the exchange-correlation functional brings a drastic improvement to the band structure. Important side effects include improvements in the description of dielectric and optical properties not only involving conduction band (excited) states but also the valence. We find that the highly dispersive conduction band bottom of HAp originates from anti-bonding σ* states along the ⋯OH-OH-⋯ infinite chain, suggesting the formation of a conductive 1D-ice phase. The choice of the exchange-correlation treatment to the calculation of defect levels was also investigated by using the OH-vacancy as a testing model. We find that donor and acceptor transitions obtained within semi-local density functional theory (DFT) differ from those of hybrid-DFT by almost 2 eV. Such a large discrepancy emphasizes the importance of using a high-quality description of the electron-electron interactions in the calculation of electronic and optical transitions of defects in HAp.
First Principles Study of Electron Tunneling through Ice
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.
First Principles Study of Electron Tunneling through Ice
Cucinotta, Clotilde S.; Rungger, Ivan; Sanvito, Stefano
2012-01-01
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.
A generalized Poisson solver for first-principles device simulations
Energy Technology Data Exchange (ETDEWEB)
Bani-Hashemian, Mohammad Hossein; VandeVondele, Joost, E-mail: joost.vandevondele@mat.ethz.ch [Nanoscale Simulations, ETH Zürich, 8093 Zürich (Switzerland); Brück, Sascha; Luisier, Mathieu [Integrated Systems Laboratory, ETH Zürich, 8092 Zürich (Switzerland)
2016-01-28
Electronic structure calculations of atomistic systems based on density functional theory involve solving the Poisson equation. In this paper, we present a plane-wave based algorithm for solving the generalized Poisson equation subject to periodic or homogeneous Neumann conditions on the boundaries of the simulation cell and Dirichlet type conditions imposed at arbitrary subdomains. In this way, source, drain, and gate voltages can be imposed across atomistic models of electronic devices. Dirichlet conditions are enforced as constraints in a variational framework giving rise to a saddle point problem. The resulting system of equations is then solved using a stationary iterative method in which the generalized Poisson operator is preconditioned with the standard Laplace operator. The solver can make use of any sufficiently smooth function modelling the dielectric constant, including density dependent dielectric continuum models. For all the boundary conditions, consistent derivatives are available and molecular dynamics simulations can be performed. The convergence behaviour of the scheme is investigated and its capabilities are demonstrated.
First-principles study on ferrite/TiC heterogeneous nucleation interface
International Nuclear Information System (INIS)
Yang, Jian; Zhang, Pengfei; Zhou, Yefei; Guo, Jing; Ren, Xuejun; Yang, Yulin; Yang, Qingxiang
2013-01-01
Highlights: ► Interface stability of ferrite (1 0 0)/TiC (1 0 0) was studied. ► The effectiveness of TiC as the heterogeneous nuclei of ferrite was analyzed. ► Ti-termination and C-termination are the two binding modes for ferrite/TiC interface. ► Interfacial energy of the Ti-termination is larger than that of the C-termination. ► On C-termination, ability of TiC promotes ferrite heterogeneous nucleation is strong. -- Abstract: Interface atomic structure, bonding character, cohesive energy and interfacial energy of ferrite (1 0 0)/TiC (1 0 0) were studied using a first-principles density functional plane-wave ultrasoft pseudopotential method. Meanwhile, the effectiveness of TiC as the heterogeneous nuclei of ferrite was analyzed. The results indicated that, TiC bonding is dominated by the C-2p, C-2s and Ti-3d electrons, which exhibits high covalency. With increase of the atomic layers, the interfacial energies of ferrite and TiC are both declined rapidly and stabilized gradually. There are two binding modes for TiC as the heterogeneous nuclei of ferrite, which are Fe atoms above the Ti atoms (Ti-termination) and Fe atoms above the C atoms (C-termination). Interfacial energy of the Ti-termination is larger than that of the C-termination, which means that for Fe atoms above the C atoms, the ability of TiC promotes ferrite heterogeneous nucleation on its surface is larger than that for Fe atoms above the Ti atoms
First principles calculation of mixing enthalpy of β-Ti with transition elements
International Nuclear Information System (INIS)
Chandran, Mahesh; Subramanian, P.R.; Gigliotti, Michael F.
2013-01-01
Highlights: ► Compares the accuracy of SQS with parametric method to determine ΔH for binary alloys which has not been done before. ► Trends in ΔH for β-Ti–X alloys where X is 3d-, 4d- and 5d-transition series are presented. ► The design space for new β-Ti alloys is determined by combining ΔH with Hume-Rothery rules. - Abstract: The mixing enthalpy ΔH mix (x) of body-centered cubic (BCC) β-Ti with transition elements was calculated using first-principles methods based on density functional theory (DFT). The solid solution effect was treated by two different approaches, viz. special quasi-random structures (SQS) and the parametric method. The SQS-N method uses direct DFT to calculate energy of structures containing N atoms which approximate the correlation of an ideal solid solution up to some distance, whereas the parametric method employs a polynomial representation for ΔH mix (x) and the coefficients are calculated using DFT. Comparison of the two methods shows fair agreement for most alloys though differences as high as 40% can also be seen among some of the alloys. The trends in ΔF mix (x), obtained by adding entropy contribution from ideal solution model to ΔH mix (x) for 3d-, 4d- and 5d-transition series were analyzed in terms of e/a, the ratio of number of valence electrons to atoms. The early transition elements, between Group 4–7, was found to have very small ΔF mix (x) over a wide range of concentration. Stability of the alloys is analyzed by combining ΔF mix (x) with Hume-Rothery rules.
Carbyne from first principles: chain of C atoms, a nanorod or a nanorope.
Liu, Mingjie; Artyukhov, Vasilii I; Lee, Hoonkyung; Xu, Fangbo; Yakobson, Boris I
2013-11-26
We report an extensive study of the properties of carbyne using first-principles calculations. We investigate carbyne's mechanical response to tension, bending, and torsion deformations. Under tension, carbyne is about twice as stiff as the stiffest known materials and has an unrivaled specific strength of up to 7.5 × 10(7) N·m/kg, requiring a force of ∼10 nN to break a single atomic chain. Carbyne has a fairly large room-temperature persistence length of about 14 nm. Surprisingly, the torsional stiffness of carbyne can be zero but can be "switched on" by appropriate functional groups at the ends. Further, under appropriate termination, carbyne can be switched into a magnetic semiconductor state by mechanical twisting. We reconstruct the equivalent continuum elasticity representation, providing the full set of elastic moduli for carbyne, showing its extreme mechanical performance (e.g., a nominal Young's modulus of 32.7 TPa with an effective mechanical thickness of 0.772 Å). We also find an interesting coupling between strain and band gap of carbyne, which is strongly increased under tension, from 2.6 to 4.7 eV under a 10% strain. Finally, we study the performance of carbyne as a nanoscale electrical cable and estimate its chemical stability against self-aggregation, finding an activation barrier of 0.6 eV for the carbyne-carbyne cross-linking reaction and an equilibrium cross-link density for two parallel carbyne chains of 1 cross-link per 17 C atoms (2.2 nm).
Density-functional expansion methods: Grand challenges.
Giese, Timothy J; York, Darrin M
2012-03-01
We discuss the source of errors in semiempirical density functional expansion (VE) methods. In particular, we show that VE methods are capable of well-reproducing their standard Kohn-Sham density functional method counterparts, but suffer from large errors upon using one or more of these approximations: the limited size of the atomic orbital basis, the Slater monopole auxiliary basis description of the response density, and the one- and two-body treatment of the core-Hamiltonian matrix elements. In the process of discussing these approximations and highlighting their symptoms, we introduce a new model that supplements the second-order density-functional tight-binding model with a self-consistent charge-dependent chemical potential equalization correction; we review our recently reported method for generalizing the auxiliary basis description of the atomic orbital response density; and we decompose the first-order potential into a summation of additive atomic components and many-body corrections, and from this examination, we provide new insights and preliminary results that motivate and inspire new approximate treatments of the core-Hamiltonian.
Electronic Structure and Transport in Solids from First Principles
Mustafa, Jamal Ibrahim
The focus of this dissertation is the determination of the electronic structure and trans- port properties of solids. We first review some of the theory and computational methodology used in the calculation of electronic structure and materials properties. Throughout the dissertation, we make extensive use of state-of-the-art software packages that implement density functional theory, density functional perturbation theory, and the GW approximation, in addition to specialized methods for interpolating matrix elements for extremely accurate results. The first application of the computational framework introduced is the determination of band offsets in semiconductor heterojunctions using a theory of quantum dipoles at the interface. This method is applied to the case of heterojunction formed between a new metastable phase of silicon, with a rhombohedral structure, and cubic silicon. Next, we introduce a novel method for the construction of localized Wannier functions, which we have named the optimized projection functions method (OPFM). We illustrate the method on a variety of systems and find that it can reliably construct localized Wannier functions with minimal user intervention. We further develop the OPFM to investigate a class of materials called topological insulators, which are insulating in the bulk but have conductive surface states. These properties are a result of a nontrivial topology in their band structure, which has interesting effects on the character of the Wannier functions. In the last sections of the main text, the noble metals are studied in great detail, including their electronic properties and carrier dynamics. In particular, we investigate, the Fermi surface properties of the noble metals, specifically electron-phonon scattering lifetimes, and subsequently the transport properties determined by carriers on the Fermi surface. To achieve this, a novel sampling technique is developed, with wide applicability to transport calculations
Density functional theory of polydisperse fluid interfaces
International Nuclear Information System (INIS)
Baus, M.; Bellier-Castella, L.; Xu, H.
2002-01-01
Most colloids usually exhibit one or several polydispersities. A natural framework for the theoretical description of polydisperse systems is provided by the extension of density functional theory to 'continuous' mixtures. This will be illustrated here by the study of both the bulk and interfacial properties of a simple van der Waals model for a polydisperse colloidal fluid. (author)
Chemical hardness and density functional theory
Indian Academy of Sciences (India)
Unknown
RALPH G PEARSON. Chemistry Department, University of California, Santa Barbara, CA 93106, USA. Abstract. The concept of chemical hardness is reviewed from a personal point of view. Keywords. Hardness; softness; hard & soft acids bases (HSAB); principle of maximum hardness. (PMH) density functional theory (DFT) ...
Density functional and neural network analysis
DEFF Research Database (Denmark)
Jalkanen, K. J.; Suhai, S.; Bohr, Henrik
1997-01-01
Density functional theory (DFT) calculations have been carried out for hydrated L-alanine, L-alanyl-L-alanine and N-acetyl L-alanine N'-methylamide and examined with respect to the effect of water on the structure, the vibrational frequencies, vibrational absorption (VA) and vibrational circular...
First-principles modeling of hafnia-based nanotubes.
Evarestov, Robert A; Bandura, Andrei V; Porsev, Vitaly V; Kovalenko, Alexey V
2017-09-15
Hybrid density functional theory calculations were performed for the first time on structure, stability, phonon frequencies, and thermodynamic functions of hafnia-based single-wall nanotubes. The nanotubes were rolled up from the thin free layers of cubic and tetragonal phases of HfO 2 . It was shown that the most stable HfO 2 single-wall nanotubes can be obtained from hexagonal (111) layer of the cubic phase. Phonon frequencies have been calculated for different HfO 2 nanolayers and nanotubes to prove the local stability and to find the thermal contributions to their thermodynamic functions. The role of phonons in stability of nanotubes seems to be negligible for the internal energy and noticeable for the Helmholtz free energy. Zone folding approach has been applied to estimate the connection between phonon modes of the layer and nanotubes and to approximate the nanotube thermodynamic properties. It is found that the zone-folding approximation is sufficiently accurate for heat capacity, but less accurate for entropy. The comparison has been done between the properties of TiO 2 , ZrO 2 , and HfO 2 . © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.
Epoxide reduction with hydrazine on graphene: a first principles study.
Kim, Min Chan; Hwang, Gyeong S; Ruoff, Rodney S
2009-08-14
Mechanisms for epoxide reduction with hydrazine on a single-layer graphene sheet are examined using quantum mechanical calculations within the framework of gradient-corrected spin-polarized density-functional theory. We find that the reduction reaction is mainly governed by epoxide ring opening which is initiated by H transfer from hydrazine or its derivatives. In addition, our calculations suggest that the epoxide reduction by hydrazine may predominantly follow a direct Eley-Rideal mechanism rather than a Langmuir-Hinshelwood mechanism. We also discuss the generation of various hydrazine derivatives during the reduction of graphene oxide with hydrazine and their potential contribution to lowering the barrier height of epoxide ring opening.
Chlorination of zirconium (0001) surface: A first-principles study.
Energy Technology Data Exchange (ETDEWEB)
Kim, Eunja [Univ. of Nevada, Las Vegas, NV (United States). Dept. of Physics and Astronomy; Weck, Philippe F [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Borjas, Rosendo [Univ. of Nevada, Las Vegas, NV (United States). Dept. of Chemistry; Poineau, Frederic [Univ. of Nevada, Las Vegas, NV (United States). Dept. of Chemistry
2017-01-01
Here, the mechanisms and energetics of Zr(0001) surface chlorination by dissociative adsorption of gaseous Cl_{2}, and associated speciation and surface degradation processes, have been investigated within the framework of density functional theory. Chlorination of Zr(0001) is predicted to be exothermic by ~3 eV/Cl for dissociative adsorption of a single Cl_{2} molecule, followed by exothermic chlorination to 1ML and 2 ML under Cl-rich conditions, with respective energy gains of 1.93 and 2.79 eV/Cl. Calculations also show that exfoliation of the top Cl-Zr-Cl sandwich layers is exothermic and most energetically favorable, and can thus be considered as a leading mechanism for Zr(0001) surface dissolution. Consistent with experimental findings, formation of ZrCl_{4} molecular products is also found to be dominant during Zr(0001) chlorination.
Chlorination of zirconium (0001) surface: A first-principles study
Energy Technology Data Exchange (ETDEWEB)
Kim, E. [Univ. of Nevada, Las Vegas, NV (United States). Department of Physics and Astronomy; Weck, Philippe F [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Poineau, F. [Univ. of Nevada, Las Vegas, NV (United States). Department of Chemistry; Paviet, P. [Dept. of Energy (DOE), Washington DC (United States)
2016-12-13
The mechanisms and energetics of Zr(0001) surface chlorination by dissociative adsorption of gaseous Cl_{2}, and associated speciation and surface degradation processes, have been investigated within the framework of density functional theory. Chlorination of Zr(0001) is predicted to be exothermic by 3 eV/Cl for dissociative adsorption of a single Cl_{2} molecule, followed by exothermic chlorination to 1ML and 2 ML under Cl-rich conditions, with respective energy gains of 1.93 and 2.79 eV/Cl. Calculations also show that exfoliation of the top Cl-Zr-Cl sandwich layers is exothermic and most energetically favorable, and can thus be considered as a leading mechanism for Zr(0001) surface dissolution. Finally, consistent with experimental findings, formation of ZrCl_{4} molecular products is also found to be dominant during Zr(0001) chlorination.
Spectral function from Reduced Density Matrix Functional Theory
Romaniello, Pina; di Sabatino, Stefano; Berger, Jan A.; Reining, Lucia
2015-03-01
In this work we focus on the calculation of the spectral function, which determines, for example, photoemission spectra, from reduced density matrix functional theory. Starting from its definition in terms of the one-body Green's function we derive an expression for the spectral function that depends on the natural occupation numbers and on an effective energy which accounts for all the charged excitations. This effective energy depends on the two-body as well as higher-order density matrices. Various approximations to this expression are explored by using the exactly solvable Hubbard chains.
Intrinsic and extrinsic spin-orbit torques from first principles
International Nuclear Information System (INIS)
Geranton, Guillaume
2017-01-01
This thesis attempts to shed light on the microscopic mechanisms underlying the current-induced magnetic torques in ferromagnetic heterostructures. We have developed first principles methods aiming at the accurate and effcient calculation of the so-called spin-orbit torques (SOTs) in magnetic thin films. The emphasis of this work is on the impurity-driven extrinsic SOTs. The main part of this thesis is dedicated to the development of a formalism for the calculation of the SOTs within the Korringa-Kohn-Rostoker (KKR) method. The impurity-induced transitions rates are obtained from first principles and their effect on transport properties is treated within the Boltzmann formalism. The developed formalism provides a mean to compute the SOTs beyond the conventional constant relaxation time approximation. We first apply our formalism to the investigation of FePt/Pt and Co/Cu bilayers in the presence of defects and impurities. Our results hint at a crucial dependence of the torque on the type of disorder present in the films, which we explain by a complex interplay of several competing Fermi surface contributions to the SOT. Astonishingly, specific defect distributions or doping elements lead respectively to an increase or a sign change of the torque, which can not be explained on the basis of simple models. We also compute the intrinsic SOT induced by electrical and thermal currents within the full potential linearized augmented plane-wave method. Motivated by recent experimental works, we then investigate the microscopic origin of the SOT in a Ag_2Bi-terminated Ag film grown on ferromagnetic Fe(110). We find that the torque in that system can not be explained solely by the spin-orbit coupling in the Ag_2Bi alloy, and instead results from the spin-orbit coupling in all regions of the film.Finally, we predict a large SOT in Fe/Ge bilayers and suggest that semiconductor substrates might be a promising alternative to heavy metals for the development of SOT-based magnetic
Intrinsic and extrinsic spin-orbit torques from first principles
Energy Technology Data Exchange (ETDEWEB)
Geranton, Guillaume
2017-09-01
This thesis attempts to shed light on the microscopic mechanisms underlying the current-induced magnetic torques in ferromagnetic heterostructures. We have developed first principles methods aiming at the accurate and effcient calculation of the so-called spin-orbit torques (SOTs) in magnetic thin films. The emphasis of this work is on the impurity-driven extrinsic SOTs. The main part of this thesis is dedicated to the development of a formalism for the calculation of the SOTs within the Korringa-Kohn-Rostoker (KKR) method. The impurity-induced transitions rates are obtained from first principles and their effect on transport properties is treated within the Boltzmann formalism. The developed formalism provides a mean to compute the SOTs beyond the conventional constant relaxation time approximation. We first apply our formalism to the investigation of FePt/Pt and Co/Cu bilayers in the presence of defects and impurities. Our results hint at a crucial dependence of the torque on the type of disorder present in the films, which we explain by a complex interplay of several competing Fermi surface contributions to the SOT. Astonishingly, specific defect distributions or doping elements lead respectively to an increase or a sign change of the torque, which can not be explained on the basis of simple models. We also compute the intrinsic SOT induced by electrical and thermal currents within the full potential linearized augmented plane-wave method. Motivated by recent experimental works, we then investigate the microscopic origin of the SOT in a Ag{sub 2}Bi-terminated Ag film grown on ferromagnetic Fe(110). We find that the torque in that system can not be explained solely by the spin-orbit coupling in the Ag{sub 2}Bi alloy, and instead results from the spin-orbit coupling in all regions of the film.Finally, we predict a large SOT in Fe/Ge bilayers and suggest that semiconductor substrates might be a promising alternative to heavy metals for the development of SOT
First-principles modeling of localized d states with the GW@LDA+U approach
Jiang, Hong; Gomez-Abal, Ricardo I.; Rinke, Patrick; Scheffler, Matthias
2010-07-01
First-principles modeling of systems with localized d states is currently a great challenge in condensed-matter physics. Density-functional theory in the standard local-density approximation (LDA) proves to be problematic. This can be partly overcome by including local Hubbard U corrections (LDA+U) but itinerant states are still treated on the LDA level. Many-body perturbation theory in the GW approach offers both a quasiparticle perspective (appropriate for itinerant states) and an exact treatment of exchange (appropriate for localized states), and is therefore promising for these systems. LDA+U has previously been viewed as an approximate GW scheme. We present here a derivation that is simpler and more general, starting from the static Coulomb-hole and screened exchange approximation to the GW self-energy. Following our previous work for f -electron systems [H. Jiang, R. I. Gomez-Abal, P. Rinke, and M. Scheffler, Phys. Rev. Lett. 102, 126403 (2009)10.1103/PhysRevLett.102.126403] we conduct a systematic investigation of the GW method based on LDA+U(GW@LDA+U) , as implemented in our recently developed all-electron GW code FHI-gap (Green’s function with augmented plane waves) for a series of prototypical d -electron systems: (1) ScN with empty d states, (2) ZnS with semicore d states, and (3) late transition-metal oxides (MnO, FeO, CoO, and NiO) with partially occupied d states. We show that for ZnS and ScN, the GW band gaps only weakly depend on U but for the other transition-metal oxides the dependence on U is as strong as in LDA+U . These different trends can be understood in terms of changes in the hybridization and screening. Our work demonstrates that GW@LDA+U with “physical” values of U provides a balanced and accurate description of both localized and itinerant states.
First-principles electronic structure of Mn-doped GaAs, GaP, and GaN semiconductors
Energy Technology Data Exchange (ETDEWEB)
Schulthess, T C [Computer Science and Mathematics Division and Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6164 (United States); Temmerman, W M [Daresbury Laboratory, Daresbury, Warrington WA4 4AD (United Kingdom); Szotek, Z [Daresbury Laboratory, Daresbury, Warrington WA4 4AD (United Kingdom); Svane, A [Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark); Petit, L [Computer Science and Mathematics Division and Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6164 (United States)
2007-04-23
We present first-principles electronic structure calculations of Mn-doped III-V semiconductors based on the local spin-density approximation (LSDA) as well as the self-interaction corrected local spin-density method (SIC-LSD). We find that it is crucial to use a self-interaction free approach to properly describe the electronic ground state. The SIC-LSD calculations predict the proper electronic ground state configuration for Mn in GaAs, GaP, and GaN. Excellent quantitative agreement with experiment is found for the magnetic moment and p-d exchange in (GaMn)As. These results allow us to validate commonly used models for magnetic semiconductors. Furthermore, we discuss the delicate problem of extracting binding energies of localized levels from density functional theory calculations. We propose three approaches to take into account final state effects to estimate the binding energies of the Mn d levels in GaAs. We find good agreement between computed values and estimates from photoemission experiments.
First-principles calculations of structural, electronic and optical properties of CdxZn1-xS alloys
Noor, Naveed Ahmed
2010-10-01
Structural, electronic and optical properties of ternary alloy system CdxZn1-xS have been studied using first-principles approach based on density functional theory. Electronic structure, density of states and energy band gap values for CdxZn1-xS are estimated in the range 0 ≤ x ≤ 1 using both the standard local density approximation (LDA) as well as the generalized gradient approximations (GGA) of Wu-Cohen (WC) for the exchange-correlation potential. It is observed that the direct band gap EgΓ-Γ of CdxZn1-xS decreases nonlinearly with the compositional parameter x, as observed experimentally. It is also found that Cd s and d, S p and Zn d states play a major role in determining the electronic properties of this alloy system. Furthermore, results for complex dielectric constant ε(ω), refractive index n(ω), normal-incidence reflectivity R(ω), absorption coefficient α(ω) and optical conductivity σ(ω) are also described in a wide range of the incident photon energy and compared with the existing experimental data. © 2010 Elsevier B.V. All rights reserved.
First-principles study of the structure properties of Al(111)/6H-SiC(0001) interfaces
Wu, Qingjie; Xie, Jingpei; Wang, Changqing; Li, Liben; Wang, Aiqin; Mao, Aixia
2018-04-01
This paper presents a systematic study on the energetic and electronic structure of the Al(111)/6H-SiC(0001) interfaces by using first-principles calculation with density functional theory (DFT). There are all three situations for no-vacuum layer of Al/SiC superlattics, and two cases of C-terminated and Si-terminated interfaces are compared and analyzed. Through the density of states analysis, the initial information of interface combination is obtained. Then the supercells are stretched vertically along the z-axis, and the fracture of the interface is obtained, and it is pointed out that C-terminated SiC and Al interfaces have a better binding property. And, the fracture positions of C-terminated and Si-terminated interfaces are different in the process of stretching. Then, the distance variation in the process of stretching, the charge density differences, and the distribution of the electrons near the interface are analyzed. Al these work makes the specific reasons for the interface fracture are obtained at last.
First-principles electronic structure of Mn-doped GaAs, GaP, and GaN semiconductors
International Nuclear Information System (INIS)
Schulthess, T C; Temmerman, W M; Szotek, Z; Svane, A; Petit, L
2007-01-01
We present first-principles electronic structure calculations of Mn-doped III-V semiconductors based on the local spin-density approximation (LSDA) as well as the self-interaction corrected local spin-density method (SIC-LSD). We find that it is crucial to use a self-interaction free approach to properly describe the electronic ground state. The SIC-LSD calculations predict the proper electronic ground state configuration for Mn in GaAs, GaP, and GaN. Excellent quantitative agreement with experiment is found for the magnetic moment and p-d exchange in (GaMn)As. These results allow us to validate commonly used models for magnetic semiconductors. Furthermore, we discuss the delicate problem of extracting binding energies of localized levels from density functional theory calculations. We propose three approaches to take into account final state effects to estimate the binding energies of the Mn d levels in GaAs. We find good agreement between computed values and estimates from photoemission experiments
Zeng, Huadong; Cheng, Xinlu; Wang, Wei
2018-03-01
The adsorption behaviors and properties of hydrazine (N2H4) molecules on pristine and Li-decorated graphene sheets were investigated by means of first-principles based on density functional theory. We systematically analyzed the optimal geometry, average binding energy, charge transfer, charge density difference and density of states of N2H4 molecules adsorbed on pristine and Li-decorated graphene sheets. It is found that the interaction between single N2H4 molecule and pristine graphene is weak physisorption with the low binding energy of -0.026 eV, suggesting that the pristine graphene sheet is insensitive to the presence of N2H4 molecule. However, it is markedly enhanced after lithium decoration with the high binding energy of -1.004 eV, verifying that the Li-decorated graphene sheet is significantly sensitive to detect N2H4 molecule. Meanwhile, the effects of the concentrations of N2H4 molecules on two different substrates were studied detailedly. For pristine graphene substrate, the average binding energy augments apparently with increasing the number of N2H4 molecules, which is mainly attributed to the van der Waals interactions and hydrogen bonds among N2H4 clusters. Li-decorated graphene sheet has still a strong affinity to N2H4 molecules despite the corresponding average binding energy emerges a contrary tendency. Overall, Li-decorated graphene sheet could be considered as a potential gas sensor in field of hydrazine molecules.
Magnetism, microstructure and First Principles calculations of atomized and annealed Ni3Al
International Nuclear Information System (INIS)
García-Escorial, A.; Crespo, P.; Hernando, A.; Lieblich, M.; Marín, P.; Velasco, V.; Ynduráin, F.
2014-01-01
Highlights: • The microstructure and order of as-atomized Ni 3 Al powder change with annealing. • The change of the magnetic properties shows the influence of the chemical order. • First Principles calculations show the effect of the density of states to the order. - Abstract: In this work Ni 3 Al powder particles obtained by atomization were characterized magnetically and microstructurally in as-atomized state and after annealing. Upon annealing the X-ray diffraction patterns show a noticeable increase of the signal of the ordered phase γ′-Ni 3 Al, L1 2 , phase and the microstructure evolves from a lamellar and dendrite to a large grain microstructure. The Curie temperature of the as-atomized powder particles is 85 K and decreases after annealing down to 50 K. First Principles calculations were carried out to correlate the experimental observations with local order of Ni and Al atoms and illustrate the importance of the local order in the density of states at the Fermi level, showing how the magnetic moment depends on the Ni and Al atomic position
Magnetism, microstructure and First Principles calculations of atomized and annealed Ni{sub 3}Al
Energy Technology Data Exchange (ETDEWEB)
García-Escorial, A., E-mail: age@cenim.csic.es [CENIM-CSIC, Avda. Gregorio del Amo, 8, 28040 Madrid (Spain); Crespo, P.; Hernando, A. [Instituto de Magnetismo Aplicado, IMA-UCM, P.O. Box 155, 28230 Madrid (Spain); Lieblich, M. [CENIM-CSIC, Avda. Gregorio del Amo, 8, 28040 Madrid (Spain); Marín, P.; Velasco, V. [Instituto de Magnetismo Aplicado, IMA-UCM, P.O. Box 155, 28230 Madrid (Spain); Ynduráin, F. [Dpto. de Física de la Materia Condensada, UAM, Cantoblanco, 28049 Madrid (Spain)
2014-12-05
Highlights: • The microstructure and order of as-atomized Ni{sub 3}Al powder change with annealing. • The change of the magnetic properties shows the influence of the chemical order. • First Principles calculations show the effect of the density of states to the order. - Abstract: In this work Ni{sub 3}Al powder particles obtained by atomization were characterized magnetically and microstructurally in as-atomized state and after annealing. Upon annealing the X-ray diffraction patterns show a noticeable increase of the signal of the ordered phase γ′-Ni{sub 3}Al, L1{sub 2}, phase and the microstructure evolves from a lamellar and dendrite to a large grain microstructure. The Curie temperature of the as-atomized powder particles is 85 K and decreases after annealing down to 50 K. First Principles calculations were carried out to correlate the experimental observations with local order of Ni and Al atoms and illustrate the importance of the local order in the density of states at the Fermi level, showing how the magnetic moment depends on the Ni and Al atomic position.
Building a universal nuclear energy density functional
International Nuclear Information System (INIS)
Bertsch, G F
2007-01-01
This talk describes a new project in SciDAC II in the area of low-energy nuclear physics. The motivation and goals of the SciDAC are presented as well as an outline of the theoretical and computational methodology that will be employed. An important motivation is to have more accurate and reliable predictions of nuclear properties including their binding energies and low-energy reaction rates. The theoretical basis is provided by density functional theory, which the only available theory that can be systematically applied to all nuclei. However, other methodologies based on wave function methods are needed to refine the functionals and to make applications to dynamic processes
Two dimensional layered materials: First-principle investigation
Tang, Youjian
Two-dimensional layered materials have emerged as a fascinating research area due to their unique physical and chemical properties, which differ from those of their bulk counterparts. Some of these unique properties are due to carriers and transport being confined to 2 dimensions, some are due to lattice symmetry, and some arise from their large surface area, gateability, stackability, high mobility, spin transport, or optical accessibility. How to modify the electronic and magnetic properties of two-dimensional layered materials for desirable long-term applications or fundamental physics is the main focus of this thesis. We explored the methods of adsorption, intercalation, and doping as ways to modify two-dimensional layered materials, using density functional theory as the main computational methodology. Chapter 1 gives a brief review of density functional theory. Due to the difficulty of solving the many-particle Schrodinger equation, density functional theory was developed to find the ground-state properties of many-electron systems through an examination of their charge density, rather than their wavefunction. This method has great application throughout the chemical and material sciences, such as modeling nano-scale systems, analyzing electronic, mechanical, thermal, optical and magnetic properties, and predicting reaction mechanisms. Graphene and transition metal dichalcogenides are arguably the two most important two-dimensional layered materials in terms of the scope and interest of their physical properties. Thus they are the main focus of this thesis. In chapter 2, the structure and electronic properties of graphene and transition metal dichalcogenides are described. Alkali adsorption onto the surface of bulk graphite and metal intecalation into transition metal dichalcogenides -- two methods of modifying properties through the introduction of metallic atoms into layered systems -- are described in chapter 2. Chapter 3 presents a new method of tuning
First-Principle Characterization for Singlet Fission Couplings.
Yang, Chou-Hsun; Hsu, Chao-Ping
2015-05-21
The electronic coupling for singlet fission, an important parameter for determining the rate, has been found to be too small unless charge-transfer (CT) components were introduced in the diabatic states, mostly through perturbation or a model Hamiltonian. In the present work, the fragment spin difference (FSD) scheme was generalized to calculate the singlet fission coupling. The largest coupling strength obtained was 14.8 meV for two pentacenes in a crystal structure, or 33.7 meV for a transition-state structure, which yielded a singlet fission lifetime of 239 or 37 fs, generally consistent with experimental results (80 fs). Test results with other polyacene molecules are similar. We found that the charge on one fragment in the S1 diabatic state correlates well with FSD coupling, indicating the importance of the CT component. The FSD approach is a useful first-principle method for singlet fission coupling, without the need to include the CT component explicitly.
A first principle approach for encapsulated type composite detectors
International Nuclear Information System (INIS)
Kshetri, R
2012-01-01
A first principle approach is presented for modeling a composite detector consisting of several high-purity germanium detector modules. Without making assumptions, if we consider the full energy peak counts from single and multiple detector module interactions, and the decomposition of background counts to counts corresponding to the escaping γ-rays and counts for γ-rays which could be recovered in addback mode, it is observed that the addback mode of a composite detector could be described in terms of four probability amplitudes only. Expressions for peak-to-total and peak-to-background ratios are obtained. Considering details of the scattering and absorption processes in a composite detector, a formalism is introduced for understanding the probability amplitudes. Detailed investigation has been performed on the effect of shape and size of composite detectors on peak-to-total and peak-to-background ratios. In accordance with isoperimetric inequality for hexagonal shapes, we have discussed about the optimal design of detector layout for extremely large values of detector modules. Using experimental data on relative single crystal efficiency, addback factor and peak-to-total ratio at 1332 keV for cluster detector, the peak-to-total and peak-to-background ratios have been calculated for several composite detectors.
Safeguards First Principles Initiative at the Nevada Test Site
International Nuclear Information System (INIS)
Johnson, Geneva
2007-01-01
The Material Control and Accountability (MC and A) program at the Nevada Test Site (NTS) was selected as a test bed for the Safeguards First Principles Initiative (SFPI). The implementation of the SFPI is evaluated using the system effectiveness model and the program is managed under an approved MC and A Plan. The effectiveness model consists of an evaluation of the critical elements necessary to detect, deter, and/or prevent the theft or diversion of Special Nuclear Material (SNM). The modeled results indicate that the MC and A program established under this variance is still effective, without creating unacceptable risk. Extensive performance testing is conducted through the duration of the pilot to ensure the protection system is effective and no material is at an unacceptable risk. The pilot was conducted from January 1, 2007, through May 30, 2007. This paper will discuss the following activities in association with SFPI: (1) Development of Timeline; (2) Crosswalk of DOE Order and SFPI; (3) Peer Review; (4) Deviation; (5) MC and A Plan and Procedure changes; (6) Changes implemented at NTS; (7) Training; and (8) Performance Test
Automated first-principles mapping for phase-change materials.
Esser, Marc; Maintz, Stefan; Dronskowski, Richard
2017-04-05
Plotting materials on bi-coordinate maps according to physically meaningful descriptors has a successful tradition in computational solid-state science spanning more than four decades. Equipped with new ab initio techniques introduced in this work, we generate an improved version of the treasure map for phase-change materials (PCMs) as introduced previously by Lencer et al. which, other than before, charts all industrially used PCMs correctly. Furthermore, we suggest seven new PCM candidates, namely SiSb 4 Te 7 , Si 2 Sb 2 Te 5 , SiAs 2 Te 4 , PbAs 2 Te 4 , SiSb 2 Te 4 , Sn 2 As 2 Te 5 , and PbAs 4 Te 7 , to be used as synthetic targets. To realize aforementioned maps based on orbital mixing (or "hybridization") and ionicity coordinates, structural information was first included into an ab initio numerical descriptor for sp 3 orbital mixing and then generalized beyond high-symmetry structures. In addition, a simple, yet powerful quantum-mechanical ionization measure also including structural information was introduced. Taken together, these tools allow for (automatically) generating materials maps solely relying on first-principles calculations. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.
First principles study of lithium insertion in bulk silicon
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.
Monolayer II-VI semiconductors: A first-principles prediction
Zheng, Hui; Chen, Nian-Ke; Zhang, S. B.; Li, Xian-Bin
A systematic study of 32 honeycomb monolayer II-VI semiconductors is carried out by first-principles methods. It appears that BeO, MgO, CaO, ZnO, CdO, CaS, SrS, SrSe, BaTe, and HgTe honeycomb monolayers have a good dynamic stability which is revealed by phonon calculations. In addition, from the molecular dynamic (MD) simulation of other unstable candidates, we also find two extra monolayers dynamically stable, which are tetragonal BaS and orthorhombic HgS. The honeycomb monolayers exist in form of either a planar perfect honeycomb or a low-buckled 2D layer, all of which possess a band gap and most of them are in the ultraviolet region. Interestingly, the dynamically stable SrSe has a gap near visible light, and displays exotic electronic properties with a flat top of the valence band, and hence has a strong spin polarization upon hole doping. The honeycomb HgTe has been reported to achieve a topological nontrivial phase under appropriate in-plane tensile strain and spin-orbital coupling (SOC). Some II-VI partners with less than 5% lattice mismatch may be used to design novel 2D heterojunction devices. If synthesized, potential applications of these 2D II-VI families could include optoelectronics, spintronics, and strong correlated electronics. Distinguished Student (DS) Program of APS FIP travel funds.
Leptogenesis from first principles in the resonant regime
International Nuclear Information System (INIS)
Garny, Mathias; Kartavtsev, Alexander; Hohenegger, Andreas
2011-12-01
The lepton asymmetry generated by the out-of-equilibrium decays of heavy Majorana neutrinos with a quasi-degenerate mass spectrum is resonantly enhanced. In this work, we study this scenario within a first-principle approach. The quantum field theoretical treatment is applicable for mass splittings of the order of the width of the Majorana neutrinos, for which the enhancement is maximally large. The non-equilibrium evolution of the mixing Majorana neutrino fields is described by a formal analytical solution of the Kadanoff-Baym equations, that is obtained by neglecting the back-reaction. Based on this solution, we derive approximate analytical expressions for the generated asymmetry and compare them to the Boltzmann result. We find that the resonant enhancement obtained from the Kadanoff-Baym approach is smaller compared to the Boltzmann approach, due to additional contributions that describe coherent transitions between the Majorana neutrino species. We also discuss corrections to the masses and widths of the degenerate pair of Majorana neutrinos that are relevant for very small mass splitting, and compare the approximate analytical result for the lepton asymmetry with numerical results. (orig.)
Leptogenesis from first principles in the resonant regime
Energy Technology Data Exchange (ETDEWEB)
Garny, Mathias [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Kartavtsev, Alexander [Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany); Hohenegger, Andreas [Ecole Polytechnique Federale de Lausanne (Switzerland)
2011-12-15
The lepton asymmetry generated by the out-of-equilibrium decays of heavy Majorana neutrinos with a quasi-degenerate mass spectrum is resonantly enhanced. In this work, we study this scenario within a first-principle approach. The quantum field theoretical treatment is applicable for mass splittings of the order of the width of the Majorana neutrinos, for which the enhancement is maximally large. The non-equilibrium evolution of the mixing Majorana neutrino fields is described by a formal analytical solution of the Kadanoff-Baym equations, that is obtained by neglecting the back-reaction. Based on this solution, we derive approximate analytical expressions for the generated asymmetry and compare them to the Boltzmann result. We find that the resonant enhancement obtained from the Kadanoff-Baym approach is smaller compared to the Boltzmann approach, due to additional contributions that describe coherent transitions between the Majorana neutrino species. We also discuss corrections to the masses and widths of the degenerate pair of Majorana neutrinos that are relevant for very small mass splitting, and compare the approximate analytical result for the lepton asymmetry with numerical results. (orig.)
Accurate line intensities of methane from first-principles calculations
Nikitin, Andrei V.; Rey, Michael; Tyuterev, Vladimir G.
2017-10-01
In this work, we report first-principle theoretical predictions of methane spectral line intensities that are competitive with (and complementary to) the best laboratory measurements. A detailed comparison with the most accurate data shows that discrepancies in integrated polyad intensities are in the range of 0.4%-2.3%. This corresponds to estimations of the best available accuracy in laboratory Fourier Transform spectra measurements for this quantity. For relatively isolated strong lines the individual intensity deviations are in the same range. A comparison with the most precise laser measurements of the multiplet intensities in the 2ν3 band gives an agreement within the experimental error margins (about 1%). This is achieved for the first time for five-atomic molecules. In the Supplementary Material we provide the lists of theoretical intensities at 269 K for over 5000 strongest transitions in the range below 6166 cm-1. The advantage of the described method is that this offers a possibility to generate fully assigned exhaustive line lists at various temperature conditions. Extensive calculations up to 12,000 cm-1 including high-T predictions will be made freely available through the TheoReTS information system (http://theorets.univ-reims.fr, http://theorets.tsu.ru) that contains ab initio born line lists and provides a user-friendly graphical interface for a fast simulation of the absorption cross-sections and radiance.
Quasiballistic heat removal from small sources studied from first principles
Vermeersch, Bjorn; Mingo, Natalio
2018-01-01
Heat sources whose characteristic dimension R is comparable to phonon mean free paths display thermal resistances that exceed conventional diffusive predictions. This has direct implications to (opto)electronics thermal management and phonon spectroscopy. Theoretical analyses have so far limited themselves to particular experimental configurations. Here, we build upon the multidimensional Boltzmann transport equation (BTE) to derive universal expressions for the apparent conductivity suppression S (R ) =κeff(R ) /κbulk experienced by radially symmetric 2D and 3D sources. In striking analogy to cross-plane heat conduction in thin films, a distinct quasiballistic regime emerges between ballistic (κeff˜R ) and diffusive (κeff≃κbulk ) asymptotes that displays a logarithmic dependence κeff˜ln(R ) in single crystals and fractional power dependence κeff˜R2 -α in alloys (with α the Lévy superdiffusion exponent). Analytical solutions and Monte Carlo simulations for spherical and circular heat sources in Si, GaAs, Si0.99Ge0.01 , and Si0.82Ge0.18 , all carried out from first principles, confirm the predicted generic tendencies. Contrary to the thin film case, common approximations like kinetic theory estimates κeff≃∑Sωgreyκω and modified Fourier temperature curves perform relatively poorly. Up to threefold deviations from the BTE solutions for sub-100 nm sources underline the need for rigorous treatment of multidimensional nondiffusive transport.
Wang, Xiao Hua; Wang, Da Wei; Yang, Ai Jun; Koratkar, Nikhil; Chu, Ji Feng; Lv, Pin Lei; Rong, Ming Zhe
2018-02-07
Tellurene is a new member of the two-dimensional (2D) materials' family, whose existence has been recently confirmed by first principles calculation and experimental work. Tellurene is also the first 2D mono-elemental material of group-VI predicted by scientists, and investigations of its basic properties are still in their infancy. In this study, we use first principles calculation based on density functional theory to investigate the adsorption of nineteen typical adatoms (Li, Na, K, Ca, Fe, Co, Ni, Cu, Zn, Ag, Au, Pd, Pt, B, N, O, Si, Cl, and Al), and five typical gas molecules (H 2 , O 2 , H 2 O, NO 2 , and NH 3 ) on α-phase as well as β-phase tellurene sheets. Our calculations shows that most adatoms are chemisorbed on tellurene sheets with large adsorption energies. Moreover, some of the adatoms are observed to give rise to distinct structural deformations and even local reconstructions. We report that a variety of electronic states are induced by the adatoms, which implies that different electronic structures can be engineered by the adsorption of adatoms. In fact, n-type doping, p-type doping, half-metal, and spin-gapless semiconductor features can be acquired by doping adatoms on tellurene sheets. Our calculations also show that the five gas molecules are all physisorbed on tellurene sheets, and no splitting behaviors are observed. Therefore, the adsorption of the five gas molecules has a weak effect on the electronic properties of tellurene. To conclude, our results indicate that adatom engineering may be used to greatly expand the potential applications of 2D tellurene.
Energy Technology Data Exchange (ETDEWEB)
Vazhappilly, Tijo, E-mail: tijoj@barc.gov.in [Theoretical Chemistry Section, Chemistry Group, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Ghanty, Tapan K., E-mail: tapang@barc.gov.in [Theoretical Chemistry Section, Chemistry Group, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400094 (India); Jagatap, B.N. [Theoretical Chemistry Section, Chemistry Group, Bhabha Atomic Research Centre, Mumbai 400 085 (India)
2017-07-15
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. - Graphical abstract: The adsorption of radioactive fission gases Xe and Kr on pristine/doped graphene is an interesting topic in the context of nuclear waste management. Previous experimental and computational studies about Xe/Kr adsorption on graphene were limited to only on pristine graphene. The doping by hetero atom changes the electronic properties of graphene and creates active sites in the lattice. Based
Energy Technology Data Exchange (ETDEWEB)
Sun, Fei [Key Laboratory of Liquid Structure and Heredity of Materials, Ministry of Education, Shandong University, Jinan 250061 (China); Mao, Shengcheng [Institute of Microstructure and Property of Advanced Materials, Beijing University of Technology, Beijing 100124 (China); Zhang, Jianxin, E-mail: jianxin@sdu.edu.cn [Key Laboratory of Liquid Structure and Heredity of Materials, Ministry of Education, Shandong University, Jinan 250061 (China)
2014-10-15
The impurity formation energies of the σ and γ phases of Ni-based single crystal superalloys doped with W, Cr and Co in different sublattices have been investigated using first-principles based on the density functional theory. The bonding characteristics of the doped σ phase were analyzed with the valence charge densities and the density of the states. The results of the calculations indicated that the typical refractory element W, which has a large atomic size, preferentially partitions into the σ phase due to the nature of the bonding and the unique crystal structure with close-packed planes and large interstitial spaces. In addition, the site preference of refractory elements in γ phase was in the order of W, Cr and Co. - Highlights: • A reasonable σ phase model was adopted in our calculation. • The site preference of refractory elements in σ and γ phases was investigated. • The bonding characteristic was analyzed on the basis of electronic microstructures.
Optimization of smart Heusler alloys from first principles
Energy Technology Data Exchange (ETDEWEB)
Entel, Peter, E-mail: entel@thp.uni-duisburg.de [Faculty of Physics and Center for Nanointegration, CeNIDE, University of Duisburg-Essen, 47048 Duisburg (Germany); Siewert, Mario; Gruner, Markus E. [Faculty of Physics and Center for Nanointegration, CeNIDE, University of Duisburg-Essen, 47048 Duisburg (Germany); Chakrabarti, Aparna [Faculty of Physics and Center for Nanointegration, CeNIDE, University of Duisburg-Essen, 47048 Duisburg (Germany); Raja Ramanna Centre for Advanced Technology, Indore 452013, Madhya Pradesh (India); Barman, Sudipta R. [UGC-DAE Consortium for Scientific Research, Khandwa Road, Indore 452001, Madhya Pradesh (India); Sokolovskiy, Vladimir V.; Buchelnikov, Vasiliy D. [Condensed Matter Physics Department, Chelyabinsk State University, 454001, Chelyabinsk (Russian Federation)
2013-11-15
Highlights: ► We investigate the tensile deformation of single crystalline Ni–Mn–Ga stripes by DIC. ► Mechanical constraints (fixation, bending) determine the type of twin boundary formed during training in a magnetic field. ► Orientation of strain bands (45° or 84° inclination) depends on the type of twin boundary. ► The twinning stress is lower for twin boundaries inclined by 84° compared to the case of 45°. -- Abstract: The strong magnetoelastic interaction in ternary X{sub 2}YZ Heusler alloys is reponsible for the appearance of magnetostructural phase transitions and related functional properties such as the magnetocaloric and magnetic shape-memory effects. Here, X and Y are transition metal elements and Z is usually an element from the III–V group. In order to discuss possibilities to optimize the multifunctional effects, we use density functional theory calculations from which the martensitic driving forces of the magnetic materials can be derived. We find that the electronic contribution arising from the band Jahn–Teller effect is one of the major driving forces. The ab initio calculations also give a hint of how to design new intermetallics with higher martensitic transformation temperatures compared to the prototype alloy system Ni–Mn–Ga. As an example, we discuss quarternary Pt{sub x}Ni{sub 2−x}MnGa alloys which have properties very similar to Ni–Mn–Ga but exhibit a higher maximal eigenstrain of 14%.
Linear scaling of density functional algorithms
International Nuclear Information System (INIS)
Stechel, E.B.; Feibelman, P.J.; Williams, A.R.
1993-01-01
An efficient density functional algorithm (DFA) that scales linearly with system size will revolutionize electronic structure calculations. Density functional calculations are reliable and accurate in determining many condensed matter and molecular ground-state properties. However, because current DFA's, including methods related to that of Car and Parrinello, scale with the cube of the system size, density functional studies are not routinely applied to large systems. Linear scaling is achieved by constructing functions that are both localized and fully occupied, thereby eliminating the need to calculate global eigenfunctions. It is, however, widely believed that exponential localization requires the existence of an energy gap between the occupied and unoccupied states. Despite this, the authors demonstrate that linear scaling can still be achieved for metals. Using a linear scaling algorithm, they have explicitly constructed localized, almost fully occupied orbitals for the quintessential metallic system, jellium. The algorithm is readily generalizable to any system geometry and Hamiltonian. They will discuss the conceptual issues involved, convergence properties and scaling for their new algorithm
First principles simulation on the K0.8Fe2Se2 high-temperature structural superconductor
International Nuclear Information System (INIS)
Guo, Rui; Yang, Shizhong; Khosravi, Ebrahim; Zhao, Guang-Lin; Bagayoko, Diola
2013-01-01
Highlights: • The superconductor K 0.8 Fe 2 Se 2 super cell size, shape, and atomic positions are fully optimized using first principles density functional theory method. • Each K atom donates 0.8 |e| with K vacancies in the supercell, each Fe atom donates 0.4 |e|, while each Se atom gains 0.7 |e| ∼ 0.8 |e|. • Fe atoms show magnetic moment fluctuation and possible strong spin-orbital coupling. -- Abstract: Since the synthesis of the first ones in 2008, iron-based high temperature superconductors have been the subject of many studies. This great interest is partly due to their higher, upper magnetic field, smaller Fermi surface around the Γ point, and a larger coherence length. This work is focused on A x Fe 2 Se 2 structural superconductor (FeSe, 11 hierarchy; A = K, Cs) as recently observed. ARPES data show novel, electronic structure and a hole-free Fermi surface which is different from previously observed Fermi surface images. We use ab initio density functional theory method to simulate the electronic structure of the novel superconductor A x Fe 2 Se 2 . We compare this electronic structure with those of other Fe-based superconductors
International Nuclear Information System (INIS)
Qi, Lei; Jin, Yuchun; Zhao, Yuhong; Yang, Xiaomin; Zhao, Hui; Han, Peide
2015-01-01
Highlights: • Structural, elastic, electronic properties and Debye temperature under pressure. • Higher hardness of Ni 3 Mo compound may be obtained when pressure increases. • Proper pressure can improve the ductility but excess pressure was just the opposite. • Ni 3 Mo compound has no structural phase transformation under pressure up to 30 GPa. • Debye temperatures increase with increasing pressure. - Abstract: With the help of first principles method based on density functional theory, the structural, elastic, electronic properties and Debye temperature of Ni 3 Mo binary compound under pressure are investigated. Our calculated structural parameters are in good agreement with experimental and previous theoretical results. The obtained elastic constants show that Ni 3 Mo compound is mechanically stable. Elastic properties such as bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio υ are calculated by the Voigt–Reuss–Hill method. The results of B/G under various pressures show that proper pressure can improve the ductility of Ni 3 Mo but excess pressure will make the ductility decrease. In addition, the density of states as a function of pressure is analyzed. The Debye temperature Θ D calculated from elastic constants increases along with the pressure
First-principles calculations of two cubic fluoropervskite compounds: RbFeF3 and RbNiF3
Mubarak, A. A.; Al-Omari, Saleh
2015-05-01
We present first-principles calculations of the structural, elastic, electronic, magnetic and optical properties for RbFeF3 and RbNiF3. The full-potential linear augmented plan wave (FP-LAPW) method within the density functional theory was utilized to perform the present calculations. We employed the generalized gradient approximation as exchange-correlation potential. It was found that the calculated analytical lattice parameters agree with previous studies. The analysis of elastic constants showed that the present compounds are elastically stable and anisotropic. Moreover, both compounds are classified as a ductile compound. The calculations of the band structure and density functional theory revealed that the RbFeF3 compound has a half-metallic behavior while the RbNiF3 compound has a semiconductor behavior with indirect (M-Γ) band gap. The ferromagnetic behavior was studied for both compounds. The optical properties were calculated for the radiation of up to 40 eV. A beneficial optics technology is predicted as revealed from the optical spectra.
First-principles calculations of two cubic fluoropervskite compounds: RbFeF3 and RbNiF3
International Nuclear Information System (INIS)
Mubarak, A.A.; Al-Omari, Saleh
2015-01-01
We present first-principles calculations of the structural, elastic, electronic, magnetic and optical properties for RbFeF 3 and RbNiF 3 . The full-potential linear augmented plan wave (FP-LAPW) method within the density functional theory was utilized to perform the present calculations. We employed the generalized gradient approximation as exchange-correlation potential. It was found that the calculated analytical lattice parameters agree with previous studies. The analysis of elastic constants showed that the present compounds are elastically stable and anisotropic. Moreover, both compounds are classified as a ductile compound. The calculations of the band structure and density functional theory revealed that the RbFeF 3 compound has a half-metallic behavior while the RbNiF 3 compound has a semiconductor behavior with indirect (M–Γ) band gap. The ferromagnetic behavior was studied for both compounds. The optical properties were calculated for the radiation of up to 40 eV. A beneficial optics technology is predicted as revealed from the optical spectra. - Highlights: • RbFeF 3 and RbNiCl 3 compounds are elastically stable. • RbFeF 3 and RbNiCl 3 compounds are classified as a ductile compound. • The RbFeF 3 compound has a half-metallic behavior while the RbNiF 3 compound has a semiconductor behavior. • The optical properties were calculated for the radiation of up to 40 eV
da Silva, Thiago H.; Nelson, Eric B.; Williamson, Izaak; Efaw, Corey M.; Sapper, Erik; Hurley, Michael F.; Li, Lan
2018-05-01
First-principles density functional theory-based calculations were performed to study θ-phase Al2Cu, S-phase Al2CuMg surface stability, as well as their interactions with water molecules and chloride (Cl-) ions. These secondary phases are commonly found in aluminum-based alloys and are initiation points for localized corrosion. Density functional theory (DFT)-based simulations provide insight into the origins of localized (pitting) corrosion processes of aluminum-based alloys. For both phases studied, Cl- ions cause atomic distortions on the surface layers. The nature of the distortions could be a factor to weaken the interlayer bonds in the Al2Cu and Al2CuMg secondary phases, facilitating the corrosion process. Electronic structure calculations revealed not only electron charge transfer from Cl- ions to alloy surface but also electron sharing, suggesting ionic and covalent bonding features, respectively. The S-phase Al2CuMg structure has a more active surface than the θ-phase Al2Cu. We also found a higher tendency of formation of new species, such as Al3+, Al(OH)2+, HCl, AlCl2+, Al(OH)Cl+, and Cl2 on the S-phase Al2CuMg surface. Surface chemical reactions and resultant species present contribute to establishment of local surface chemistry that influences the corrosion behavior of aluminum alloys.
International Nuclear Information System (INIS)
Soni, Himadri R.; Mankad, Venu; Gupta, Sanjeev K.; Jha, Prafulla K.
2012-01-01
Highlights: ► We present spin dependent bandstructure, structural and magnetic moment of FeN/CoN. ► The PDC, PHDOS, spin effect on phonons suggests ZB is preferred at ambient pressure. ► Spin calculation offers an opportunity to understand the role of spin on phonons. - Abstract: Using first principles density functional theoretical calculations, the present paper reports a systematic nonspin and spin polarized total energy calculations of the lattice dynamical and a number of other properties such as band structure, structural and magnetic moment of two mononitrides FeN and CoN. The phonon dispersion curves and phonon density of states in the case of FeN and CoN have been determined for the first time and discussed. The structural and dynamical calculations suggest that the zinc blende structure is preferred at ambient pressure for both compounds. The rocksalt FeN has a nonzero magnetic moment while for FeN in zinc blende phase, it is either zero or very small. The zinc blende phase for both compounds is nonmagnetic. The spin calculation offers an intensive opportunity to understand the role of spin on the phonon properties of two mononitrides. Majority of the modes are sensitive to the effect of spin due to the modification of lattice constant. In this work we reveal that spin modifies the interionic interactions and local structure and leads to a flexible lattice which can be used for the functional materials design.
First-principles study on silicon atom doped monolayer graphene
Rafique, Muhammad; Shuai, Yong; Hussain, Nayyar
2018-01-01
This paper illustrates the structural, electronic and optical properties of individual silicon (Si) atom-doped single layer graphene using density functional theory method. Si atom forms tight bonding with graphene layer. The effect of doping has been investigated by varying the concentration of Si atoms from 3.125% to 9.37% (i.e. From one to three Si atoms in 4 × 4 pure graphene supercell containing 32 carbon atoms), respectively. Electronic structure, partial density of states (PDOS) and optical properties of pure and Si atom-doped graphene sheet were calculated using VASP (Vienna ab-initio Simulation Package). The calculated results for pure graphene sheet were then compared with Si atom doped graphene. It is revealed that upon Si doping in graphene, a finite band gap appears at the high symmetric K-point, thereby making graphene a direct band gap semiconductor. Moreover, the band gap value is directly proportional to the concentration of impurity Si atoms present in graphene lattice. Upon analyzing the optical properties of Si atom-doped graphene structures, it is found that, there is significant change in the refractive index of the graphene after Si atom substitution in graphene. In addition, the overall absorption spectrum of graphene is decreased after Si atom doping. Although a significant red shift in absorption is found to occur towards visible range of radiation when Si atom is substituted in its lattice. The reflectivity of graphene improves in low energy region after Si atom substitution in graphene. These results can be useful for tuning the electronic structure and to manipulate the optical properties of graphene layer in the visible region.
Teaching Density Functional Theory Through Experiential Learning
International Nuclear Information System (INIS)
Narasimhan, Shobhana
2015-01-01
Today, quantum mechanical density functional theory is often the method of choice for performing accurate calculations on atomic, molecular and condensed matter systems. Here, I share some of my experiences in teaching the necessary basics of solid state physics, as well as the theory and practice of density functional theory, in a number of workshops held in developing countries over the past two decades. I discuss the advantages of supplementing the usual mathematically formal teaching methods, characteristic of graduate courses, with the use of visual imagery and analogies. I also describe a successful experiment we carried out, which resulted in a joint publication co-authored by 67 lecturers and students participating in a summer school. (paper)
Density functional theory a practical introduction
Sholl, David
2009-01-01
Demonstrates how anyone in math, science, and engineering can master DFT calculations Density functional theory (DFT) is one of the most frequently used computational tools for studying and predicting the properties of isolated molecules, bulk solids, and material interfaces, including surfaces. Although the theoretical underpinnings of DFT are quite complicated, this book demonstrates that the basic concepts underlying the calculations are simple enough to be understood by anyone with a background in chemistry, physics, engineering, or mathematics. The authors show how the widespread availability of powerful DFT codes makes it possible for students and researchers to apply this important computational technique to a broad range of fundamental and applied problems. Density Functional Theory: A Practical Introduction offers a concise, easy-to-follow introduction to the key concepts and practical applications of DFT, focusing on plane-wave DFT. The authors have many years of experience introducing DFT to studen...
The problem of the universal density functional and the density matrix functional theory
International Nuclear Information System (INIS)
Bobrov, V. B.; Trigger, S. A.
2013-01-01
The analysis in this paper shows that the Hohenberg-Kohn theorem is the constellation of two statements: (i) the mathematically rigorous Hohenberg-Kohn lemma, which demonstrates that the same ground-state density cannot correspond to two different potentials of an external field, and (ii) the hypothesis of the existence of the universal density functional. Based on the obtained explicit expression for the nonrel-ativistic particle energy in a local external field, we prove that the energy of the system of more than two non-interacting electrons cannot be a functional of the inhomogeneous density. This result is generalized to the system of interacting electrons. It means that the Hohenberg-Kohn lemma cannot provide justification of the universal density functional for fermions. At the same time, statements of the density functional theory remain valid when considering any number of noninteracting ground-state bosons due to the Bose condensation effect. In the framework of the density matrix functional theory, the hypothesis of the existence of the universal density matrix functional corresponds to the cases of noninteracting particles and to interaction in the Hartree-Fock approximation.
Structural and electronic properties of LaPd2As2 superconductor: First-principle calculations
Singh, Birender; Kumar, Pradeep
2017-05-01
In present work we have studied electronic and structural properties of superconducting LaPd2As2 compound having collapsed tetragonal structure using first-principle calculations. The band structure calculations show that the LaPd2As2 is metallic consistent with the reported experimental observation, and the density of states plots clearly shows that at the Fermi level major contribution to density of states arises from Pd 4d and As 4p states, unlike the Fe-based superconductors where major contribution at the Fermi level comes from Fe 3d states. The estimated value of electron-phonon coupling is found to be 0.37, which gives the upper bound of superconducting transition temperature of 5K, suggesting the conventional nature of this superconductor.
Site-specific electronic structure analysis by channeling EELS and first-principles calculations.
Tatsumi, Kazuyoshi; Muto, Shunsuke; Yamamoto, Yu; Ikeno, Hirokazu; Yoshioka, Satoru; Tanaka, Isao
2006-01-01
Site-specific electronic structures were investigated by electron energy loss spectroscopy (EELS) under electron channeling conditions. The Al-K and Mn-L(2,3) electron energy loss near-edge structure (ELNES) of, respectively, NiAl2O4 and Mn3O4 were measured. Deconvolution of the raw spectra with the instrumental resolution function restored the blunt and hidden fine features, which allowed us to interpret the experimental spectral features by comparing with theoretical spectra obtained by first-principles calculations. The present method successfully revealed the electronic structures specific to the differently coordinated cationic sites.
A density functional approach to ferrogels
Cremer, P.; Heinen, M.; Menzel, A. M.; Löwen, H.
2017-07-01
Ferrogels consist of magnetic colloidal particles embedded in an elastic polymer matrix. As a consequence, their structural and rheological properties are governed by a competition between magnetic particle-particle interactions and mechanical matrix elasticity. Typically, the particles are permanently fixed within the matrix, which makes them distinguishable by their positions. Over time, particle neighbors do not change due to the fixation by the matrix. Here we present a classical density functional approach for such ferrogels. We map the elastic matrix-induced interactions between neighboring colloidal particles distinguishable by their positions onto effective pairwise interactions between indistinguishable particles similar to a ‘pairwise pseudopotential’. Using Monte-Carlo computer simulations, we demonstrate for one-dimensional dipole-spring models of ferrogels that this mapping is justified. We then use the pseudopotential as an input into classical density functional theory of inhomogeneous fluids and predict the bulk elastic modulus of the ferrogel under various conditions. In addition, we propose the use of an ‘external pseudopotential’ when one switches from the viewpoint of a one-dimensional dipole-spring object to a one-dimensional chain embedded in an infinitely extended bulk matrix. Our mapping approach paves the way to describe various inhomogeneous situations of ferrogels using classical density functional concepts of inhomogeneous fluids.
Risk reduction and the privatization option: First principles
International Nuclear Information System (INIS)
Bjornstad, D.J.; Jones, D.W.; Russell, M.; Cummings, R.C.; Valdez, G.; Duemmer, C.L.
1997-01-01
The Department of Energy's Office of Environmental Restoration and Waste Management (EM) faces a challenging mission. To increase efficiency, EM is undertaking a number of highly innovative initiatives--two of which are of particular importance to the present study. One is the 2006 Plan, a planning and budgeting process that seeks to convert the clean-up program from a temporally and fiscally open-ended endeavor to a strictly bounded one, with firm commitments over a decade-long horizon. The second is a major overhauling of the management and contracting practices that define the relationship between the Department and the private sector, aimed at cost reduction by increasing firms' responsibilities and profit opportunities and reducing DOE's direct participation in management practices and decisions. The goal of this paper is to provide an independent perspective on how EM should create new management practices to deal with private sector partners that are motivated by financial incentives. It seeks to ground this perspective in real world concerns--the background of the clean-up effort, the very difficult technical challenges it faces, the very real threats to environment, health and safety that have now been juxtaposed with financial drivers, and the constraints imposed by government's unique business practices and public responsibilities. The approach is to raise issues through application of first principles. The paper is targeted at the EM policy officer who must implement the joint visions of the 2006 plan and privatization within the context of the tradeoff between terminal risk reduction and interim risk management
First principle active neutron coincidence counting measurements of uranium oxide
Energy Technology Data Exchange (ETDEWEB)
Goddard, Braden, E-mail: goddard.braden@gmail.com [Nuclear Security Science and Policy Institute, Texas A and M University, College Station, Texas 77843 (United States); Charlton, William [Nuclear Security Science and Policy Institute, Texas A and M University, College Station, Texas 77843 (United States); Peerani, Paolo [European Commission, EC-JRC-ITU, Ispra (Italy)
2014-03-01
Uranium is present in most nuclear fuel cycle facilities ranging from uranium mines, enrichment plants, fuel fabrication facilities, nuclear reactors, and reprocessing plants. The isotopic, chemical, and geometric composition of uranium can vary significantly between these facilities, depending on the application and type of facility. Examples of this variation are: enrichments varying from depleted (∼0.2 wt% {sup 235}U) to high enriched (>20 wt% {sup 235}U); compositions consisting of U{sub 3}O{sub 8}, UO{sub 2}, UF{sub 6}, metallic, and ceramic forms; geometries ranging from plates, cans, and rods; and masses which can range from a 500 kg fuel assembly down to a few grams fuel pellet. Since {sup 235}U is a fissile material, it is routinely safeguarded in these facilities. Current techniques for quantifying the {sup 235}U mass in a sample include neutron coincidence counting. One of the main disadvantages of this technique is that it requires a known standard of representative geometry and composition for calibration, which opens up a pathway for potential erroneous declarations by the State and reduces the effectiveness of safeguards. In order to address this weakness, the authors have developed a neutron coincidence counting technique which uses the first principle point-model developed by Boehnel instead of the “known standard” method. This technique was primarily tested through simulations of 1000 g U{sub 3}O{sub 8} samples using the Monte Carlo N-Particle eXtended (MCNPX) code. The results of these simulations showed good agreement between the simulated and exact {sup 235}U sample masses.
Risk reduction and the privatization option: First principles
Energy Technology Data Exchange (ETDEWEB)
Bjornstad, D.J.; Jones, D.W.; Russell, M. [Joint Inst. for Energy and Environment, Knoxville, TN (United States); Cummings, R.C.; Valdez, G. [Georgia State Univ., Atlanta, GA (United States); Duemmer, C.L. [Hull, Duemmer and Garland (United States)
1997-06-25
The Department of Energy`s Office of Environmental Restoration and Waste Management (EM) faces a challenging mission. To increase efficiency, EM is undertaking a number of highly innovative initiatives--two of which are of particular importance to the present study. One is the 2006 Plan, a planning and budgeting process that seeks to convert the clean-up program from a temporally and fiscally open-ended endeavor to a strictly bounded one, with firm commitments over a decade-long horizon. The second is a major overhauling of the management and contracting practices that define the relationship between the Department and the private sector, aimed at cost reduction by increasing firms` responsibilities and profit opportunities and reducing DOE`s direct participation in management practices and decisions. The goal of this paper is to provide an independent perspective on how EM should create new management practices to deal with private sector partners that are motivated by financial incentives. It seeks to ground this perspective in real world concerns--the background of the clean-up effort, the very difficult technical challenges it faces, the very real threats to environment, health and safety that have now been juxtaposed with financial drivers, and the constraints imposed by government`s unique business practices and public responsibilities. The approach is to raise issues through application of first principles. The paper is targeted at the EM policy officer who must implement the joint visions of the 2006 plan and privatization within the context of the tradeoff between terminal risk reduction and interim risk management.
First principles characterisation of brittle transgranular fracture of titanium hydrides
International Nuclear Information System (INIS)
Olsson, Pär A.T.; Mrovec, Matous; Kroon, Martin
2016-01-01
In this work we have studied transgranular cleavage and the fracture toughness of titanium hydrides by means of quantum mechanical calculations based on density functional theory. The calculations show that the surface energy decreases and the unstable stacking fault energy increases with increasing hydrogen content. This is consistent with experimental findings of brittle behaviour of titanium hydrides at low temperatures. Based on Griffith-Irwin theory we estimate the fracture toughness of the hydrides to be of the order of 1 MPa⋅m"1"/"2, which concurs well with experimental data. To investigate the cleavage energetics, we analyse the decohesion at various crystallographic planes and determine the traction-separation laws based on the Rose's extended universal binding energy relation. The calculations predict that the peak stresses do not depend on the hydrogen content of the phases, but it is rather dependent on the crystallographic cleavage direction. However, it is found that the work of fracture decreases with increasing hydrogen content, which is an indication of hydrogen induced bond weakening in the material.
Understanding the behavior of buried Bi nanostructures from first principles
Sims, Hunter; Pantelides, Sokrates; Song, Jiaming; Hudak, Bethany; Lupini, Andrew; Snijders, Paul
Bismuth dopants in silicon provide several advantages over other n-type options such as phosphorus for usage as quantum bits (qubits). Self-assembled Bi nanolines on Si (100) surfaces may provide a means of introducing these dopants with greater control over placement and with less damage to the host system than is possible using ion implantation. However, these structures have thus far only been observed in vacuum, limiting their usefulness for application. We examine Bi nanolines overgrown with amorphous Si using density functional theory, comparing our findings with observations from scanning tunneling microscopy (STM) and atomic-resolution scanning transmission electron microscopy (STEM) in order to better understand the way in which the Si surface is influenced by both the Bi ad-dimers and the capping layer. We compare the thermodynamic stability of the generally accepted haiku defect core to the modified core that we observe and offer insight from total energy calculations into how the overgrowth process affects the nanolines. Supported by Department of Energy Grant DE-FG02- 09ER46554 (VU) and by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy (ORNL).
First principles study of edge carboxylated graphene quantum dots
Abdelsalam, Hazem; Elhaes, Hanan; Ibrahim, Medhat A.
2018-05-01
The structure stability and electronic properties of edge carboxylated hexagonal and triangular graphene quantum dots are investigated using density functional theory. The calculated binding energies show that the hexagonal clusters with armchair edges have the highest stability among all the quantum dots. The binding energy of carboxylated graphene quantum dots increases by increasing the number of carboxyl groups. Our study shows that the total dipole moment significantly increases by adding COOH with the highest value observed in triangular clusters. The edge states in triangular graphene quantum dots with zigzag edges produce completely different energy spectrum from other dots: (a) the energy gap in triangular zigzag is very small as compared to other clusters and (b) the highest occupied molecular orbital is localized at the edges which is in contrast to other clusters where it is distributed over the cluster surface. The enhanced reactivity and the controllable energy gap by shape and edge termination make graphene quantum dots ideal for various nanodevice applications such as sensors. The infrared spectra are presented to confirm the stability of the quantum dots.
Phase stability in yttria-stabilized zirconia from first principles
Energy Technology Data Exchange (ETDEWEB)
Carbogno, Christian; Scheffler, Matthias [Materials Department, University of California, Santa Barbara, CA (United States); Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin (Germany); Levi, Carlos G.; Van de Walle, Chris G. [Materials Department, University of California, Santa Barbara, CA (United States)
2012-07-01
Zirconia based ceramics are of pivotal importance for a variety of industrial technologies, e.g., for thermal barrier coatings in gas and airplane turbines. Naturally, the stability of such coatings at elevated temperatures plays a critical role in these applications. It is well known that an aliovalent doping of tetragonal ZrO{sub 2} with yttria, which induces oxygen vacancies due to charge conservation, increases its thermodynamic stability. However, the atomistic mechanisms that determine the phase stability of such yttria-stabilized Zirconia (YSZ) coatings are not yet fully understood. In this work, we use density functional theory calculations to assess the electronic structure of the different YSZ polymorphs at various levels of doping. With the help of population analysis schemes, we are able to unravel the intrinsic mechanisms that govern the interaction in YSZ and that can so explain the relative stabilities of the various polymorphs. We critically compare our results to experimental measurements and discuss the implications of our findings with respect to other oxides.
International Nuclear Information System (INIS)
Capelle, K.; Gross, E.
1997-01-01
It is shown that the exchange-correlation functional of spin-density functional theory is identical, on a certain set of densities, with the exchange-correlation functional of current-density functional theory. This rigorous connection is used to construct new approximations of the exchange-correlation functionals. These include a conceptually new generalized-gradient spin-density functional and a nonlocal current-density functional. copyright 1997 The American Physical Society
Miao, Yurun; Li, Huayang; Wang, Hongjuan; He, Kaihua; Wang, Qingbo
2018-02-01
First principles and quasi-harmonic Debye model have been used to study the thermodynamic properties, enthalpies, electronic and optical properties of MgO up to the core-mantle boundary (CMB) condition (137 GPa and 3700 K). Thermodynamic properties calculation includes thermal expansion coefficient and capacity, which have been studied up to the CMB pressure (137 GPa) and temperature (3700 K) by the Debye model with generalized gradient approximation (GGA) and local-density approximation (LDA). First principles with hybrid functional method (PBE0) has been used to calculate the electronic and optical properties under pressure up to 137 GPa and 0 K. Our results show the Debye model with LDA and first principles with PBE0 can provide accurate thermodynamic properties, enthalpies, electronic and optical properties. Calculated enthalpies show that MgO keep NaCl (B1) structure up to 137 GPa. And MgO is a direct bandgap insulator with a 7.23 eV calculated bandgap. The bandgap increased with increasing pressure, which will induce a blue shift of optical properties. We also calculated the density of states (DOS) and discussed the relation between DOS and band, optical properties. Equations were used to fit the relations between pressure and bandgaps, absorption coefficient (α(ω)) of MgO. The equations can be used to evaluate pressure after careful calibration. Our calculations can not only be used to identify some geological processes, but also offer a reference to the applications of MgO in the future.
A density functional theory study of new boron nanotubes
Energy Technology Data Exchange (ETDEWEB)
Chen, Zhao-Hua [Shijiazhuang Institute of Technology, Shijiazhuang (China); Xie, Zun [Hebei Normal Univ., Shijiazhuang (China). College of Physics Science and Information Engineering and Hebei Advanced Thin Films Lab.
2017-07-01
Using first-principles calculations, a series of new boron nanotubes (BNTs), which show various electronic properties, were theoretically predicted. Stable nanotubes with various chiral vectors and diameters can be formed by rolling up the boron sheet with relative stability [H. Tang and S. I. Beigi, Phys. Rev. B 82, 115412 (2010).]. By increasing the diameter for BNT, the stability is enhanced. The calculated density of states and band structures demonstrate that all the predicted BNTs are metallic, regardless of their diameter and chirality. The multicentre chemical bonds of the relatively stable boron sheet and BNTs are analysed using the deformation electron density. Within our study, the BNTs all have metallic conductive characteristics, in addition to having a low effective quality and high carrier concentration, which are very good nanoconductive material properties and could be combined to form high-power electrodes for lithium-ion batteries such as those used in many modern electronics.
Extended screened exchange functional derived from transcorrelated density functional theory.
Umezawa, Naoto
2017-09-14
We propose a new formulation of the correlation energy functional derived from the transcorrelated method in use in density functional theory (TC-DFT). An effective Hamiltonian, H TC , is introduced by a similarity transformation of a many-body Hamiltonian, H, with respect to a complex function F: H TC =1FHF. It is proved that an expectation value of H TC for a normalized single Slater determinant, D n , corresponds to the total energy: E[n] = ⟨Ψ n |H|Ψ n ⟩/⟨Ψ n |Ψ n ⟩ = ⟨D n |H TC |D n ⟩ under the two assumptions: (1) The electron density nr associated with a trial wave function Ψ n = D n F is v-representable and (2) Ψ n and D n give rise to the same electron density nr. This formulation, therefore, provides an alternative expression of the total energy that is useful for the development of novel correlation energy functionals. By substituting a specific function for F, we successfully derived a model correlation energy functional, which resembles the functional form of the screened exchange method. The proposed functional, named the extended screened exchange (ESX) functional, is described within two-body integrals and is parametrized for a numerically exact correlation energy of the homogeneous electron gas. The ESX functional does not contain any ingredients of (semi-)local functionals and thus is totally free from self-interactions. The computational cost for solving the self-consistent-field equation is comparable to that of the Hartree-Fock method. We apply the ESX functional to electronic structure calculations for a solid silicon, H - ion, and small atoms. The results demonstrate that the TC-DFT formulation is promising for the systematic improvement of the correlation energy functional.
First-principles investigation of the electronic states at perovskite and pyrite hetero-interfaces
Nazir, Safdar
2012-09-01
Oxide heterostructures are attracting huge interest in recent years due to the special functionalities of quasi two-dimensional quantum gases. In this thesis, the electronic states at the interface between perovskite oxides and pyrite compounds have been studied by first-principles calculations based on density functional theory. Optimization of the atomic positions are taken into account, which is considered very important at interfaces, as observed in the case of LaAlO3/SrTiO3. The creation of metallic states at the interfaces thus is explained in terms of charge transfer between the transition metal and oxygen atoms near the interface. It is observed that with typical thicknesses of at least 10-12 °A the gases still extend considerably in the third dimension, which essentially determines the magnitude of quantum mechanical effects. To overcome this problem, we propose incorporation of highly electronegative cations (such as Ag) in the oxides. A fundamental interest is also the thermodynamic stability of the interfaces due to the possibility of atomic intermixing in the interface region. Therefore, different cation intermixed configurations are taken into account for the interfaces aiming at the energetically stable state. The effect of O vacancies is also discussed for both polar and non-polar heterostructures. The interface metallicity is enhanced for the polar system with the creation of O vacancies, while the clean interface at the non-polar heterostructure exhibits an insulating state and becomes metallic in presence of O vacancy. The O vacancy formation energies are calculated and explained in terms of the increasing electronegativity and effective volume of A the side cation. Along with these, the electronic and magnetic properties of an interface between the ferromagnetic metal CoS2 and the non-magnetic semiconductor FeS2 is investigated. We find that this contact shows a metallic character. The CoS2 stays quasi half metallic at the interface, while the
International Nuclear Information System (INIS)
Ganeshan, S.; Hector, L.G.; Liu, Z.-K.
2011-01-01
Research highlights: → Implemented the eight frequency model for impurity diffusion in hexagonal metals. → Model inputs were energetics/vibrational properties from first princples. → Predicted diffusion coefficients for Al, Ca, Zn and Sn impurity diffusion in Mg. → Successful prediction of partial correlation factors and jump frequencies. → Good agreement between calculated and experimental results. - Abstract: Diffusion in dilute Mg-X alloys, where X denotes Al, Zn, Sn and Ca impurities, was investigated with first-principles density functional theory in the local density approximation. Impurity diffusion coefficients were computed as a function of temperature using the 8-frequency model which provided the relevant impurity and solvent (Mg) jump frequencies and correlation factors. Minimum energy pathways for impurity diffusion and associated saddle point structures were computed with the climbing image nudged elastic band method. Vibrational properties were obtained with the supercell (direct) method for lattice dynamics. Calculated diffusion coefficients were compared with available experimental data. For diffusion between basal planes, we find D Mg-Ca > D Mg-Zn > D Mg-Sn > D Mg-Al, where D is the diffusion coefficient. For diffusion within a basal plane, the same trend holds except that D Mg-Zn overlaps with D Mg-Al at high temperatures and D Mg-Sn at low temperatures. These trends were explored with charge density contours in selected planes of each Mg-X alloy, the variation of the activation energy for diffusion with the atomic radius of each impurity and the electronic density of states. The theoretical methodology developed herein can be applied to impurity diffusion in other hexagonal materials.
Functional derivative of noninteracting kinetic energy density functional
International Nuclear Information System (INIS)
Liu Shubin; Ayers, Paul W.
2004-01-01
Proofs from different theoretical frameworks, namely, the Hohenbergh-Kohn theorems, the Kohn-Sham scheme, and the first-order density matrix representation, have been presented in this paper to show that the functional derivative of the noninteracting kinetic energy density functional can uniquely be expressed as the negative of the Kohn-Sham effective potential, arbitrary only to an additive orbital-independent constant. Key points leading to the current result as well as confusion about the quantity in the literature are briefly discussed
International Nuclear Information System (INIS)
Yanagisawa, Susumu; Okuma, Koji; Inaoka, Takeshi; Hamada, Ikutaro
2015-01-01
Highlights: • Review of theoretical studies on organic solids with the density-functional methods. • van der Waals (vdW)-inclusive methods to predict cohesive properties of oligoacenes. • A variant of the vdW density functional describes the structures accurately. • The molecular configuration and conformation crucially affects the band dispersion. - Abstract: We review recent studies on electronic properties of the organic solids with the first-principles electronic structure methods, with the emphasis on the roles of the intermolecular van der Waals (vdW) interaction in electronic properties of the organic semiconductors. After a brief summary of the recent vdW inclusive first-principle theoretical methods, we discuss their performance in predicting cohesive properties of oligoacene crystals as examples of organic crystals. We show that a variant of the van der Waals density functional describes structure and energetics of organic crystals accurately. In addition, we review our recent study on the zinc phthalocyanine crystal and discuss the importance of the intermolecular distance and orientational angle in the band dispersion. Finally, we draw some general conclusions and the future perspectives.
Energy Technology Data Exchange (ETDEWEB)
Yanagisawa, Susumu, E-mail: shou@sci.u-ryukyu.ac.jp [Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213 (Japan); Okuma, Koji; Inaoka, Takeshi [Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213 (Japan); Hamada, Ikutaro, E-mail: Hamada.Ikutaro@nims.go.jp [International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Tsukuba 305-0044 (Japan)
2015-10-01
Highlights: • Review of theoretical studies on organic solids with the density-functional methods. • van der Waals (vdW)-inclusive methods to predict cohesive properties of oligoacenes. • A variant of the vdW density functional describes the structures accurately. • The molecular configuration and conformation crucially affects the band dispersion. - Abstract: We review recent studies on electronic properties of the organic solids with the first-principles electronic structure methods, with the emphasis on the roles of the intermolecular van der Waals (vdW) interaction in electronic properties of the organic semiconductors. After a brief summary of the recent vdW inclusive first-principle theoretical methods, we discuss their performance in predicting cohesive properties of oligoacene crystals as examples of organic crystals. We show that a variant of the van der Waals density functional describes structure and energetics of organic crystals accurately. In addition, we review our recent study on the zinc phthalocyanine crystal and discuss the importance of the intermolecular distance and orientational angle in the band dispersion. Finally, we draw some general conclusions and the future perspectives.
International Nuclear Information System (INIS)
Raji, Abdulrafiu T.; Lombardi, Enrico B.
2015-01-01
We report a first-principles investigation of the structural, electronic and magnetic properties of cobalt–vacancy defect complexes in graphene, within the framework of density-functional theory (DFT), incorporating DFT+U. Specifically, we consider the interactions of cobalt and vacancies in graphene, at varying separations and sub-lattices. We show that it is energetically favorable for substitutional Co in graphene to trap an additional vacancy in graphene, forming a Co–vacancy complex. In all the configurations considered, the most stable configuration is when the Co atom is embedded in a divacancy. The magnetic moment induced on the cobalt atom varies as the vacancy–cobalt separation changes, depending not only on the separation, but also on the sub-lattice of the vacancy relative to cobalt. Furthermore, for each separation and sub-lattice considered, the linear density of states of graphene is modified such that Dirac point is either not discernible or has shifted above the Fermi energy. Since individual vacancies or transition metal (TM) atoms, such as cobalt in graphene, have mostly been studied in isolation up to now, ignoring possible transition metal–vacancy interactions, these results have important implications to the fundamental understanding of TM–vacancy defect interactions in graphene
Institute of Scientific and Technical Information of China (English)
高恩强; 黄福祥; 陈志谦; 王兰兰; 张照超
2016-01-01
The effects of applied pressure on the structural, mechanical, and electronic properties of LaAg5 compound were investi-gated employing the first-principles method based on the density functional theory. The mechanical results demonstrated that bulk modulus, shear modulus and Young’s modulus presented the linearly increasing dependences on the external pressure; theB/G and Poisson’s ratio indicated that LaAg5 compound was a ductile material with central forces in interatomic under pressure from 0 to 40 GPa; the universal anisotropic index was performed to investigate the elastic anisotropic of LaAg5. Additionally, the pressure de-pendence of the density of states and Mulliken charge were also discussed. The bonding characterization in LaAg5 was composed of metallic, covalent and ionic. The metallic component was derived from free-electron transferring from Ag-s and Ag-d to Ag-p, and from La-s to La-d. The ionic component was due to the charge movement from La to Ag. The covalent was owing to Ag-p-La-d bonding hybridization and Ag-s-Ag-p in the Ag atomic chains. The covalent and ionic bonds were stronger under pressure but there was no significant change in metallic nature.