Energy Technology Data Exchange (ETDEWEB)
Aguiar, J; Asta, M; Gronbech-Jensen, N; Perlov, A; Milman, V; Gao, S; Pickard, C; Browning, N
2009-06-05
Energy loss spectra from a variety of cubic oxides are compared with ab-initio calculations based on the density functional plane wave method (CASTEP). In order to obtain agreement between experimental and theoretical spectra, unique material specific considerations were taken into account. The spectra were calculated using various approximations to describe core-hole effects and electronic correlations. All the calculations are based on the local spin density approximation to show qualitative agreement with the sensitive oxygen K-edge spectra in ceria, zirconia, and urania. Comparison of experimental and theoretical results let us characterize the main electronic interactions responsible for both the electronic structure and the resulting EEL spectra of the compounds in question.
Platinum nitride with fluorite structure
Energy Technology Data Exchange (ETDEWEB)
Yu, Rong; Zhang, Xiao-Feng
2005-01-31
The mechanical stability of platinum nitride has been studied using first-principles calculations. By calculating the single-crystal elastic constants, we show that platinum nitride can be stabilized in the fluorite structure, in which the nitrogen atoms occupy all the tetrahedral interstitial sites of the metal lattice. The stability is attributed to the pseudogap effect from analysis of the electronic structure.
Giant Mechanocaloric Effects in Fluorite-Structured Superionic Materials
Cazorla, Claudio; Errandonea, Daniel
2016-05-01
Mechanocaloric materials experience a change in temperature when a mechanical stress is adiabatically applied on them. Thus far, only ferroelectrics and superelastic metallic alloys have been considered as potential mechanocaloric compounds to be exploited in solid-state cooling applications. Here we show that giant mechanocaloric effects occur in hitherto overlooked fast ion conductors (FIC), a class of multicomponent materials in which above a critical temperature, Ts, a constituent ionic species undergoes a sudden increase in mobility. Using first-principles and molecular dynamics simulations, we found that the superionic transition in fluorite-structured FIC, which is characterised by a large entropy increase of the order of 100 J/K*Kg, can be externally tuned with hydrostatic, biaxial or uniaxial stresses. In particular, Ts can be reduced several hundreds of degrees through the application of moderate tensile stresses due to the concomitant drop in the formation energy of Frenkel pair defects. We predict that the adiabatic temperature change in CaF2 and PbF2, two archetypal fluorite-structured FIC, close to their critical points are of the order of 100 and 10 K, respectively. This work advocates that FIC constitute a new family of mechanocaloric materials showing great promise for prospective solid-state refrigeration applications.
Energy Technology Data Exchange (ETDEWEB)
Aidhy, Dilpuneet S.; Liu, Bin; Zhang, Yanwen; Weber, William J.
2015-03-01
We study the chemical expansion for neutral and charged oxygen vacancies in fluorite, rocksalt, perovskite and pyrochlores materials using first principles calculations. We show that the neutral oxygen vacancy leads to lattice expansion whereas the charged vacancy leads to lattice contraction. In addition, we show that there is a window of strain within which an oxygen vacancy is stable; beyond that range, the vacancy can become unstable. Using CeO2|ZrO2 interface structure as an example, we show that the concentration of oxygen vacancies can be manipulated via strain, and the vacancies can be preferentially stabilized. These results could serve as guiding principles in predicting oxygen vacancy stability in strained systems and in the design of vacancy stabilized materials.
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, which...... in the actinide dioxides is discussed, and it is found that the dioxide is the most stable oxide for the actinides from Np onward. Our study reveals a strong link between preferred oxidation number and degree of localization which is confirmed by comparing to the ground-state configurations of the corresponding...
Electronic Structures of Silicene Doped with Galium: First Principle study
Directory of Open Access Journals (Sweden)
Pamungkas Mauludi Ariesto
2015-01-01
Full Text Available Following the success of graphene which possesses unique and superior properties, 2D material other than graphene become centre of interest of material scientists.Silicene, which has the same crystal structure as graphene but consist of silicon atoms rather than carbon become intriguing material due to domination of silicon as main material of electronic component. It is common to enhance electronic properties of semiconductor by adding dopant atoms. The electronic properties of Silicene doped with Gallium are investigated using first principle calculation based on density functional theory (DFT.Ga doping changes character of silicene from semimetal to conductor except silicene with Ga doping on S-site (Ga atom substitutes one Si atom which lead to semiconductor.
First-principles structural design of superhard materials.
Zhang, Xinxin; Wang, Yanchao; Lv, Jian; Zhu, Chunye; Li, Qian; Zhang, Miao; Li, Quan; Ma, Yanming
2013-03-21
We reported a developed methodology to design superhard materials for given chemical systems under external conditions (here, pressure). The new approach is based on the CALYPSO algorithm and requires only the chemical compositions to predict the hardness vs. energy map, from which the energetically preferable superhard structures are readily accessible. In contrast to the traditional ground state structure prediction method where the total energy was solely used as the fitness function, here we adopted hardness as the fitness function in combination with the first-principles calculation to construct the hardness vs. energy map by seeking a proper balance between hardness and energy for a better mechanical description of given chemical systems. To allow a universal calculation on the hardness for the predicted structure, we have improved the earlier hardness model based on bond strength by applying the Laplacian matrix to account for the highly anisotropic and molecular systems. We benchmarked our approach in typical superhard systems, such as elemental carbon, binary B-N, and ternary B-C-N compounds. Nearly all the experimentally known and most of the earlier theoretical superhard structures have been successfully reproduced. The results suggested that our approach is reliable and can be widely applied into design of new superhard materials.
Configurational Model for Conductivity of Stabilized Fluorite Structure Oxides
DEFF Research Database (Denmark)
Poulsen, Finn Willy
1981-01-01
The formalism developed here furnishes means by which ionic configurations, solid solution limits, and conductivity mechanisms in doped fluorite structures can be described. The present model differs markedly from previous models but reproduces qualitatively reality. The analysis reported...
First-principles determination of the structure of magnesium borohydride.
Zhou, Xiang-Feng; Oganov, Artem R; Qian, Guang-Rui; Zhu, Qiang
2012-12-14
The energy landscape of Mg(BH(4))(2) under pressure is explored by ab initio evolutionary calculations. Two new tetragonal structures, with space groups P4 and I4(1)/acd, are predicted to be lower in enthalpy by 15.4 and 21.2 kJ/mol, respectively, than the earlier proposed P4(2)nm phase. We have simulated x-ray diffraction spectra, lattice dynamics, and equations of state of these phases. The density, volume contraction, bulk modulus, and simulated x-ray diffraction patterns of I4(1)/acd and P4 structures are in excellent agreement with the experimental results.
Structural and electronic properties of perylene from first principles calculations.
Fedorov, I A; Zhuravlev, Y N; Berveno, V P
2013-03-07
The electronic structure of crystalline perylene has been investigated within the framework of density functional theory including van der Waals interactions. The computations of the lattice parameters and cohesive energy have good agreement with experimental values. We have also calculated the binding distance and energy of perylene dimers, using different schemes, which include van der Waals interactions.
First-Principles Calculation of the Structure of Mercury
Mehl, M J
1995-01-01
Mercury has perhaps the strangest behavior of any of the metals. Although the other metals in column IIB have an $hcp$ ground state, mercury's ground state is the body centered tetragonal $\\beta$Hg phase. The most common phase of mercury is the rhombohedral $\\alpha$Hg phase, which is stable from 79K to the melting point and meta-stable below 79K. Another rhombohedral phase, calculations are used to study the energetics of the various phases of mercury. Even when partial spin-orbit effects are included, the calculations indicate that the hexagonal close packed structure is the ground state. It is suggested that a better treatment of the spin-orbit interaction might alter this result.
First principles based multiparadigm modeling of electronic structures and dynamics
Xiao, Hai
Electronic structures and dynamics are the key to linking the material composition and structure to functionality and performance. An essential issue in developing semiconductor devices for photovoltaics is to design materials with optimal band gaps and relative positioning of band levels. Approximate DFT methods have been justified to predict band gaps from KS/GKS eigenvalues, but the accuracy is decisively dependent on the choice of XC functionals. We show here for CuInSe2 and CuGaSe2, the parent compounds of the promising CIGS solar cells, conventional LDA and GGA obtain gaps of 0.0-0.01 and 0.02-0.24 eV (versus experimental values of 1.04 and 1.67 eV), while the historically first global hybrid functional, B3PW91, is surprisingly the best, with band gaps of 1.07 and 1.58 eV. Furthermore, we show that for 27 related binary and ternary semiconductors, B3PW91 predicts gaps with a MAD of only 0.09 eV, which is substantially better than all modern hybrid functionals, including B3LYP (MAD of 0.19 eV) and screened hybrid functional HSE06 (MAD of 0.18 eV). The laboratory performance of CIGS solar cells (> 20% efficiency) makes them promising candidate photovoltaic devices. However, there remains little understanding of how defects at the CIGS/CdS interface affect the band offsets and interfacial energies, and hence the performance of manufactured devices. To determine these relationships, we use the B3PW91 hybrid functional of DFT with the AEP method that we validate to provide very accurate descriptions of both band gaps and band offsets. This confirms the weak dependence of band offsets on surface orientation observed experimentally. We predict that the CBO of perfect CuInSe2/CdS interface is large, 0.79 eV, which would dramatically degrade performance. Moreover we show that band gap widening induced by Ga adjusts only the VBO, and we find that Cd impurities do not significantly affect the CBO. Thus we show that Cu vacancies at the interface play the key role in
National Research Council Canada - National Science Library
Ding, Yi; Wang, Yanli
2015-01-01
Using first-principles calculations, we investigate the geometric structures and electronic properties of porous silicene and germanene nanosheets, which are the Si and Ge analogues of α−graphyne...
Size of oxide vacancies in fluorite and perovskite structured oxides
DEFF Research Database (Denmark)
Chatzichristodoulou, Christodoulos; Norby, Poul; Hendriksen, Peter Vang
2015-01-01
An analysis of the effective radii of vacancies and the stoichiometric expansion coefficient is performed on metal oxides with fluorite and perovskite structures. Using the hard sphere model with Shannon ion radii we find that the effective radius of the oxide vacancy in fluorites increases...... with increasing ion radius of the host cation and that it is significantly smaller than the radius of the oxide ion in all cases, from 37% smaller for HfO2 to 13 % smaller for ThO2. The perovskite structured LaGaO3 doped with Sr or Mg or both is analyzed in some detail. The results show that the effective radius...... of an oxide vacancy in doped LaGaO3 is only about 6 % smaller than the oxide ion. In spite of this the stoichiometric expansion coefficient (a kind of chemical expansion coefficient) of the similar perovskite, LaCrO3, is significantly smaller than the stoichiometric expansion coefficient of the fluorite...
Crystal structure prediction from first principles: The crystal structures of glycine
Lund, Albert M.; Pagola, Gabriel I.; Orendt, Anita M.; Ferraro, Marta B.; Facelli, Julio C.
2015-04-01
Here we present the results of our unbiased searches of glycine polymorphs obtained using the genetic algorithms search implemented in MGAC, modified genetic algorithm for crystals, coupled with the local optimization and energy evaluation provided by Quantum Espresso. We demonstrate that it is possible to predict the crystal structures of a biomedical molecule using solely first principles calculations. We were able to find all the ambient pressure stable glycine polymorphs, which are found in the same energetic ordering as observed experimentally and the agreement between the experimental and predicted structures is of such accuracy that the two are visually almost indistinguishable.
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...
Stability of Sb-Te layered structures: First-principles study
Govaerts, K.; Sluiter, M.H.F.; Partoens, B.; Lamoen, D.
2012-01-01
Using an effective one-dimensional cluster expansion in combination with first-principles electronic structure calculations we have studied the energetics and electronic properties of Sb-Te layered systems. For a Te concentration between 0 and 60 at. % an almost continuous series of metastable
Bannikov, V. V.; Shein, I. R.; Ivanovskii, A. L.
2010-05-01
First-principles FLAPW-GGA calculations for six possible polymorphs of ruthenium mononitride RuN indicate that the most stable structure is that of zinc blende rather than the rock salt structure recently reported for synthesized RuN samples. The elastic, electronic properties and the features of chemical bonds of zinc-blende RuN polymorph were investigated and discussed in detail.
Crystal structure of Mg3Pd from first-principles calculations
Institute of Scientific and Technical Information of China (English)
DENG Yong-he; WANG Tao-fen; ZHANG Wei-bing; TANG Bi-yu; ZENG Xiao-qin; DING Wen-jiang
2008-01-01
Crystal structure of Mg3Pd alloy was studied by first-principles calculations based on the density functional theory. The total energy, formation heat and cohesive energy of the two types of Mg3Pd were calculated to assess the stability and the preferentiality. The results show that Mg3Pd alloy with Cu3P structure is more stable than Na3As structure, and Mg3Pd alloy is preferential to Cu3P structure. The obtained densities of states and charge density distribution for the two types of crystal structure were analyzed and discussed in combination with experimental findings for further discussion of the Mg3Pd structure.
First-Principles Calculations for Structures and Melting Temperature of Si6 Clusters
Institute of Scientific and Technical Information of China (English)
BAI Yu-Lin; CHEN Xiang-Rong; ZHOU Xiao-Lin; CHENG Xiao-Hong; YANG Xiang-Dong
2006-01-01
@@ We investigate the structures and the melting temperature of the Si6 cluster by using the first-principles pseudopotential method in real space and Langevin molecular dynamics. It is shown that the ground structure of the Si6 cluster is a square bipyramid, and the corresponding melting temperature is about 1923 K. In the heating procedure, the structures of the Si6 cluster change from high symmetry structures containing 5-8 bonds, via prolate structures containing 3-4 bonds, to oblate structures containing 1-2 bonds.
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.
ding,Yi; Wang, Yanli
2015-01-01
Using first-principles calculations, we investigate the geometric structures and electronic properties of porous silicene and germanene nanosheets, which are the Si and Ge analogues of α−graphyne (referred to as silicyne and germanyne). It is found that the elemental silicyne and germanyne sheets are energetically unfavourable. However, after the C-substitution, the hybrid graphyne-like sheets (c-silicyne/c-germanyne) possess robust energetic and dynamical stabilities. Different from silicene...
Mancera, L; Takeuchi, N
2003-01-01
We have studied the structural and electronic properties of YN in rock salt (sodium chloride), caesium chloride, zinc blende and wurtzite structures using first-principles total energy calculations. Rock salt is the calculated ground state structure with a = 4.93 A, B sub 0 = 157 GPa. The experimental lattice constant is a = 4.877 A. There is an additional local minimum in the wurtzite structure with total energy 0.28 eV/unit cell higher. At high pressure (approx 138 GPa), our calculations predict a phase transformation from a NaCl to a CsCl structure.
First principles study of structural, electronic and mechanical properties of alkali nitride-KN
Energy Technology Data Exchange (ETDEWEB)
Murugan, A.; Rajeswarapalanichamy, R., E-mail: rrpalanichamy@gmail.com; Santhosh, M. [Department of Physics, N.M.S.S.V.N college, Madurai, Tamilnadu-625019 (India); Iyakutti, K. [Department of Physics and Nanotechnology, SRM University, Chennai, Tamilnadu-603203 (India)
2015-06-24
The structural, electronic and elastic properties of alkali- metal nitride (KN) is investigated by the first principles calculations based on density functional theory as implemented in Vienna ab-initio simulation package. At ambient pressure KN is stable in the ferromagnetic state with NaCl structure. The calculated lattice parameters are in good agreement with the available results. The electronic structure reveals that the KN is half metallic ferromagnet at normal pressure. A pressure-induced structural phase transition from NaCl to ZB phase is observed in KN. Half metallicity and ferromagnetism is maintained at all pressures.
Bahadur, Amar; Verma, Mohan L.; Mishra, Madhukar
2015-04-01
Using first principle calculation, we investigate the structural, electronic and magnetic properties of silicon doped zigzag boron nitride nanoribbon (ZBNNR). Our results show that the shift in position of silicon doping with respect to the ribbon edge causes change in the structural geometry, electronic structure and magnetization of ZBNNR. The band gap of silicon doped ZBNNR is found to become narrower as compared to that of perfect ZBNNR. We find that band gap and magnetic moment of ZBNNR can be tuned by substitutional silicon doping position and doping concentration.
Structural phase transition and elastic properties of hafnium dihydride: A first principles study
Energy Technology Data Exchange (ETDEWEB)
Santhosh, M., E-mail: rrpalanichamy@gmail.com; Rajeswarapalanichamy, R., E-mail: rrpalanichamy@gmail.com; Sudhapriyanga, G.; Murugan, A.; Chinthia, A. Jemmy [Department of Physics, N.M.S.S.V.N College, Madurai, Tamil Nadu-625019 (India); Kanagaprabha, S. [Department of Physics, Kamaraj College, Tuticorin, Tamil Nadu-628003 (India); Iyakutti, K. [Department of Physics and Nanotechnology, SRM University, Chennai, Tamil Nadu-603203 (India)
2014-04-24
The structural and elastic properties of Hafnium dihydride (HfH{sub 2}) are investigated by first principles calculation based on density functional theory using Vienna ab-initio simulation package (VASP). The calculated lattice parameters are in good agreement with the available results. A pressure induced structural phase transition from CaF{sub 2} to FeS{sub 2} phase is observed in HfH{sub 2} at 10.75 GPa. The calculated elastic constants indicate that this hydride is mechanically stable at ambient condition.
First-principles prediction of the equation of state for TcC with rocksalt structure
Sun, Xiao-Wei; Chu, Yan-Dong; Liu, Zi-Jiang; Song, Ting; Tian, Jun-Hong; Wei, Xiao-Ping
2014-10-01
The equation of state of TcC with rocksalt structure is investigated by means of first-principles density functional theory calculations combined with the quasi-harmonic Debye model in which the phononic effects are considered. Particular attention is paid to the predictions of the compressibility, the isothermal bulk modulus and its first pressure derivative which play a central role in the formulation of approximate equations of state for the first time. The properties of TcC with rocksalt structure are summarized in the pressure range of 0-80 GPa and the temperature up to 2500 K.
First-Principles Study on Electronic Structures and Optical Properties of Doped Ag Crystal
Institute of Scientific and Technical Information of China (English)
CAO Can; CHEN Ling-Na; JIA Shu-Ting; ZHANG Dan; XU Hui
2012-01-01
By using the first-principles calculation based on density functional theory,we investigate the electronic structures and optical properties of Cl-doped Ag crystal. The results show that the electronic structure of Cl-doped Ag crystal depends on the doped concentration and the site of impurity defect.Interestingly,the calculated adsorption spectra of Cl-doped Ag crystal show isotropy or anisotropy coincide with the symmetry of Ag crystal. These features are discussed to provide guidance to experimental efforts for Ag-based nanoeletronic devices.
First-principles calculations of structure and high pressure phase transition in gallium nitride
Institute of Scientific and Technical Information of China (English)
Tan Li-Na; Hu Cui-E; Yu Bai-Ru; Chen Xiang-Rong
2007-01-01
The phase transitions of semiconductor GaN from the Wurtzite (WZ) structure and the zinc-blende (ZB) structure to the rocksalt (RS) structure are investigated by using the first-principles plane-wave pseudopotential density functional method combined with the ultrasoft pseudopotential scheme in the generalized gradient approximation (GGA)correction. It is found that the phase transitions from the WZ structure and the ZB structure to the RS structure occur at pressures of 46.1 GPa and 45.2 GPa, respectively. The lattice parameters, bulk moduli and their pressure derivatives of these structures of GaN are also calculated. Our results are consistent with available experimental and other theoretical results. The dependence of the normalized formula-unit volume V/Vo on pressure P is also successfully obtained.
First-principles prediction of a ground state crystal structure of magnesium borohydride.
Ozolins, V; Majzoub, E H; Wolverton, C
2008-04-04
Mg(BH(4))(2) contains a large amount of hydrogen by weight and by volume, but its promise as a candidate for hydrogen storage is dependent on the currently unknown thermodynamics of H2 release. Using first-principles density-functional theory calculations and a newly developed prototype electrostatic ground state search strategy, we predict a new T=0 K ground state of Mg(BH(4))(2) with I4[over ]m2 symmetry, which is 5 kJ/mol lower in energy than the recently proposed P6(1) structure. The calculated thermodynamics of H(2) release are within the range required for reversible storage.
Indian Academy of Sciences (India)
Mousumi Upadhyay Kahaly; Umesh V Waghmare
2008-06-01
First-principles pseudopotential-based density functional theory calculations of atomic and electronic structures, full phonon dispersions and thermal properties of zigzag single wall carbon nanotubes (SWCNTs) are presented. By determining the correlation between vibrational modes of a graphene sheet and of the nanotube, we understand how rolling of the sheet results in mixing between modes and changes in vibrational spectrum of graphene. We find that the radial breathing mode softens with decreasing curvature. We estimate thermal expansion coefficient of nanotubes within a quasiharmonic approximation and identify the modes that dominate thermal expansion of some of these SWCNTs both at low and high temperatures.
First-principle study on the electronic structure of stressed CrSi2
Institute of Scientific and Technical Information of China (English)
ZHOU ShiYun; XIE Quan; YAN WanJun; CHEN Qian
2009-01-01
The electronic structure of stressed CrSi2 was calculated using the first-principle methods based on plane-wave pseudo-potential theory. The calculated results showed that, under the uniaxial compres-sion, the energy level of CrSi2 shifted toward high energy and its energy gap became wider with the increasing uniaxial stress, while the gap became narrower under the negative uniaxial stress. When the negative uniaxial stress was up to -18.5 Gpa, CrSi2 was converted into a direct-gap semiconductor with the band gap of 0.32 eV.
First-principle study on the electronic structure of stressed CrSi2
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
The electronic structure of stressed CrSi2 was calculated using the first-principle methods based on plane-wave pseudo-potential theory. The calculated results showed that, under the uniaxial compression, the energy level of CrSi2 shifted toward high energy and its energy gap became wider with the increasing uniaxial stress, while the gap became narrower under the negative uniaxial stress. When the negative uniaxial stress was up to -18.5 GPa, CrSi2 was converted into a direct-gap semiconductor with the band gap of 0.32 eV.
Stability and electronic structure of InN nanotubes from first-principles study
Institute of Scientific and Technical Information of China (English)
Chen Li-Juan
2006-01-01
The stability and electronic structure of hypothetical InN nanotubes were studied by first-principles density functional theory.It was found that the strain energies of InN nanotubes are smaller than those of carbon nanotubes of the same radius.Single-wall zigzag InN nanotubes were found to be semiconductors with a direct band gap while the armchair counterparts have an indirect band gap.The band gaps of nanotubes decrease with increasing diameter,similar to the case of carbon nanotubes.
First principles study on the structural, electronic, and elastic properties of Na-As systems
Ozisik, H. B.; Colakoglu, K.; Deligoz, E.; Ozisik, H.
2011-10-01
We have performed the first principles calculation by using the plane-wave pseudopotential approach with the generalized gradient approximation for investigating the structural, electronic, and elastic properties Na-As systems (NaAs in NaP, LiAs and AuCu-type structures, NaAs 2 in MgCu 2-type structure, Na 3As in Na 3As, Cu 3P and Li 3Bi-type structures, and Na 5As 4 in A 5B 4-type structure). The lattice parameters, cohesive energy, formation energy, bulk modulus, and the first derivative of bulk modulus (to fit to Murnaghan's equation of state) of the related structures are calculated. The second-order elastic constants and the other related quantities such as Young's modulus, shear modulus, Poisson's ratio, sound velocities, and Debye temperature are also estimated.
First-principles simulation of Raman spectra and structural properties of quartz up to 5 GPa
Liu, Lei; Lv, Chao-Jia; Zhuang, Chun-Qiang; Yi, Li; Liu, Hong; Du, Jian-Guo
2015-12-01
The crystal structure and Raman spectra of quartz are calculated by using first-principles method in a pressure range from 0 to 5 GPa. The results show that the lattice constants (a, c, and V) decrease with increasing pressure and the a-axis is more compressible than the c axis. The Si-O bond distance decreases with increasing pressure, which is in contrast to experimental results reported by Hazen et al. [Hazen R M, Finger L W, Hemley R J and Mao H K 1989 Solid State Communications 725 507-511], and Glinnemann et al. [Glinnemann J, King H E Jr, Schulz H, Hahn T, La Placa S J and Dacol F 1992 Z. Kristallogr. 198 177-212]. The most striking changes are of inter-tetrahedral O-O distances and Si-O-Si angles. The volume of the tetrahedron decreased by 0.9% (from 0 to 5 GPa), which suggests that it is relatively rigid. Vibrational models of the quartz modes are identified by visualizing the associated atomic motions. Raman vibrations are mainly controlled by the deformation of the tetrahedron and the changes in the Si-O-Si bonds. Vibrational directions and intensities of atoms in all Raman modes just show little deviations when pressure increases from 0 to 5 GPa. The pressure derivatives (dνi/dP) of the 12 Raman frequencies are obtained at 0 GPa-5 GPa. The calculated results show that first-principles methods can well describe the high-pressure structural properties and Raman spectra of quartz. The combination of first-principles simulations of the Raman frequencies of minerals and Raman spectroscopy experiments is a useful tool for exploring the stress conditions within the Earth. Project supported by the Key Laboratory of Earthquake Prediction, Institute of Earthquake Science, China Earthquake Administration (CEA) (Grant No. 2012IES010201) and the National Natural Science Foundation of China (Grant Nos. 41174071 and 41373060).
Structures and magnetic properties of Co-Zr-B magnets studied by first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Zhao, Xin; Ke, Liqin; Nguyen, Manh Cuong; Wang, Cai-Zhuang, E-mail: wangcz@ameslab.gov; Ho, Kai-Ming, E-mail: kmh@ameslab.gov [Ames Laboratory, U.S. DOE and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011 (United States)
2015-06-28
The structures and magnetic properties of Co-Zr-B alloys near the composition of Co{sub 5}Zr with B at. % ≤6% were studied using adaptive genetic algorithm and first-principles calculations. The energy and magnetic moment contour maps as a function of chemical composition were constructed for the Co-Zr-B magnet alloys through extensive structure searches and calculations. We found that Co-Zr-B system exhibits the same structure motif as the “Co{sub 11}Zr{sub 2}” polymorphs, and such motif plays a key role in achieving strong magnetic anisotropy. Boron atoms were found to be able to substitute cobalt atoms or occupy the “interruption” sites. First-principles calculations showed that the magnetocrystalline anisotropy energies of the boron-doped alloys are close to that of the high-temperature rhombohedral Co{sub 5}Zr phase and larger than that of the low-temperature Co{sub 5.25}Zr phase. Our calculations provide useful guidelines for further experimental optimization of the magnetic performances of these alloys.
Li, Xinting; Zhang, Xinyu; Qin, Jiaqian; Zhang, Suhong; Ning, Jinliang; Jing, Ran; Ma, Mingzhen; Liu, Riping
2014-11-01
The structural stability and mechanical properties of WC in WC-, MoC- and NaCl-type structures under high pressure are investigated systematically by first-principles calculations. The calculated equilibrium lattice constants at zero pressure agree well with available experimental and theoretical results. The formation enthalpy indicates that the most stable WC is in WC-type, then MoC-type finally NaCl-type. By the elastic stability criteria, it is predicted that the three structures are all mechanically stable. The elastic constants Cij, bulk modulus B, shear modulus G, Young's modulus E and Poisson's ratio ν of the three structures are studied in the pressure range from 0 to 100 GPa. Furthermore, by analyzing the B/G ratio, the brittle/ductile behavior under high pressure is assessed. Moreover, the elastic anisotropy of the three structures up to 100 GPa is also discussed in detail.
A novel anion interstitial defect structure in zinc-blende materials: A first-principles study
Yin, Yuan; Chen, Guangde; Ye, Honggang; Duan, Xiangyang; Zhu, Youzhang; Wu, Yelong
2016-05-01
The low-formation energy structure of anion interstitial defect in zinc-blende materials is usually identified as the tetrahedron central structure where the anion interstitial atom is surrounded by four countercation atoms. A line-type anion interstitial defect structure AD_il , however, is found to be lower in energy than the tetrahedron central anion interstitial defect structure by first-principles calculations. By analyzing the structural and electronical characters of this line-type defect in relative compounds of zinc-blende materials, we attribute this to the electronegativity shift trends and the bond forming, which lead to the hybridization types varying from sp 3 to sp-like and ending at sp.
Structural, electronic and mechanical properties of rare earth nitride-ErN: A first principles study
Energy Technology Data Exchange (ETDEWEB)
Murugan, A.; Rajeswarapalanichamy, R., E-mail: rajeswarapalanichamy@gmail.com; Santhosh, M.; Priyanga, G. Sudha [Department of physics, N.M.S.S.V.N college, Madurai, Tamilnadu-625019 (India); Kanagaprabha, S. [Department of Physics, Kamaraj College, Tuticorin, Tamil Nadu 628 003 (India); Iyakutti, K. [Department of Physics and Nanotechnology, SRM University, Chennai, Tamilnadu-603203 (India)
2015-06-24
The structural, electronic and mechanical properties of rare earth nitride ErN is investigated by the first principles calculations based on density functional theory using the Vienna ab-initio simulation package. At ambient pressure ErN is stable in the ferromagnetic state with NaCl structure. The calculated lattice parameters are in good agreement with the available results. The electronic structure reveals that ErN is half metallic at normal pressure. A pressure-induced structural phase transition from NaCl (B1) to CsCl (B2) phase is observed in ErN. Ferromagnetic to non magnetic phase transition is predicted in ErN at high pressure.
Electronic Structure and Elastic Properties of Ti3AlC from First-Principles Calculations
Institute of Scientific and Technical Information of China (English)
DU Yu-Lei
2009-01-01
We perform a first-principles study on the electronic structure and elastic properties of Ti3AlC with an antiper-ovskite structure. The absence of band gap at the Fermi level and the finite value of the density of states at the Fermi energy reveal the metallic behavior of this compound. The elastic constants of Ti_3AlC are derived yielding c_(11)=356 GPa, c_(12)= 55 GPa, c_(44)=157 GPa. The bulk modulus B, shear modulus G and Young's modulus E are determined to be 156, 151 and 342 GPa, respectively. These properties are compared with those of Ti_3AlC_2 and Ti_2AlC with a layered structure in the Ti-Al-C system and Fe_3AlC with the same antiperovskite structure.
Structure reconstruction of TiO2-based multi-wall nanotubes: first-principles calculations.
Bandura, A V; Evarestov, R A; Lukyanov, S I
2014-07-28
A new method of theoretical modelling of polyhedral single-walled nanotubes based on the consolidation of walls in the rolled-up multi-walled nanotubes is proposed. Molecular mechanics and ab initio quantum mechanics methods are applied to investigate the merging of walls in nanotubes constructed from the different phases of titania. The combination of two methods allows us to simulate the structures which are difficult to find only by ab initio calculations. For nanotube folding we have used (1) the 3-plane fluorite TiO2 layer; (2) the anatase (101) 6-plane layer; (3) the rutile (110) 6-plane layer; and (4) the 6-plane layer with lepidocrocite morphology. The symmetry of the resulting single-walled nanotubes is significantly lower than the symmetry of initial coaxial cylindrical double- or triple-walled nanotubes. These merged nanotubes acquire higher stability in comparison with the initial multi-walled nanotubes. The wall thickness of the merged nanotubes exceeds 1 nm and approaches the corresponding parameter of the experimental patterns. The present investigation demonstrates that the merged nanotubes can integrate the two different crystalline phases in one and the same wall structure.
First-Principles Study of Structural,Magnetic,Electronic and Elastic Properties of PuC2简
National Research Council Canada - National Science Library
杨荣 唐斌 高涛 敖冰云
2016-01-01
We perform first-principles calculations of crystal structure,magnetism,electronic structure,chemical bonding and elastic properties for PuC2 using the standard local spin-density approximation（LSDA）+U...
Yorulmaz, Uğur; Özden, Ayberk; Perkgöz, Nihan K.; Ay, Feridun; Sevik, Cem
2016-08-01
MXenes, carbides, nitrides and carbonitrides of early transition metals are the new members of two dimensional materials family given with a formula of {{{M}}}n+1 X n . Recent advances in chemical exfoliation and CVD growth of these crystals together with their promising performance in electrochemical energy storage systems have triggered the interest in these two dimensional structures. In this work, we employ first principles calculations for n = 1 structures of Sc, Ti, Zr, Mo and Hf pristine MXenes and their fully surface terminated forms with F and O. We systematically investigated the dynamical and mechanical stability of both pristine and fully terminated MXene structures to determine the possible MXene candidates for experimental realization. In conjunction with an extensive stability analysis, we report Raman and infrared active mode frequencies for the first time, providing indispensable information for the experimental elaboration of MXene field. After determining dynamically stable MXenes, we provide their phonon dispersion relations, electronic and mechanical properties.
Energy Technology Data Exchange (ETDEWEB)
Liu, X.X.; Liu, L.Z. [Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics and Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China); Wu, X.L., E-mail: hkxlwu@nju.edu.cn [Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics and Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China); Department of Physics, NingBo University, NingBo 315301 (China); Chu, Paul K. [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China)
2015-07-03
The defect states and optical absorption enhancement induced by twin boundaries in silicon are investigated by first-principle calculation. The defect states in the forbidden bands are identified and based on the established electronic structures, the dielectric functions and absorption coefficients are derived. An important result of our calculations is that visible light absorption by the twinning configuration is enhanced significantly, indicating that twinning structures possibly play an important role in silicon-based photovoltaic devices. - Highlights: • Defect states and optical absorption enhancement induced by twin boundaries in silicon are investigated theoretically. • Dielectric functions and absorption coefficients are derived. • Enhanced visible light absorption by the twinning configuration is demonstrated. • Twinning structures play an important role in silicon-based photovoltaic devices.
Lithium halide monolayers: Structural, electronic and optical properties by first principles study
Safari, Mandana; Maskaneh, Pegah; Moghadam, Atousa Dashti; Jalilian, Jaafar
2016-09-01
Using first principle study, we investigate the structural, electronic and optical properties of lithium halide monolayers (LiF, LiCl, LiBr). In contrast to graphene and other graphene-like structures that form hexagonal rings in plane, these compounds can form and stabilize in cubic shape interestingly. The type of band structure in these insulators is identified as indirect type and ionic nature of their bonds are illustrated as well. The optical properties demonstrate extremely transparent feature for them as a result of wide band gap in the visible range; also their electron transitions are indicated for achieving a better vision on the absorption mechanism in these kinds of monolayers.
First principle study of the electronic structure of hafnium-doped anatase TiO2
Institute of Scientific and Technical Information of China (English)
Li Lezhong; Yang Weiqing; DingYingchun; Zhu Xinghua
2012-01-01
Crystal structures and electronic structures of hafnium doping anatase TiO2 were calculated by first principles with the plane-wave ultrasoft pseudopotential method based on the density functional theory within the generalized gradient approximation.The calculated results show that the lattice parameters a and c of Hf-doped anatase TiO2 are larger than those of intrinsic TiO2 under the same calculated condition.The calculated band structure and density of states show that the conduction band width of Hf-doped TiO2 is broadened which results in the band gap of Hf-doped being smaller than the band gap of TiO2.
First Principles Study of Electronic Structure and Magnetic Properties of TMH (TM = Cr, Mn, Fe, Co
Directory of Open Access Journals (Sweden)
S. Kanagaprabha
2013-01-01
Full Text Available First principles calculations are performed using a tight-binding linear muffin-tin orbital (TB-LMTO method with local density approximation (LDA and atomic sphere approximation (ASA to understand the electronic properties of transition metal hydrides (TMH (TM = Cr, Mn, Fe, Co. The structural property, electronic structure, and magnetic properties are investigated. A pressure induced structural phase transition from cubic to hexagonal phase is predicted at the pressures of 50 GPa for CrH and 23 GPa for CoH. Also, magnetic phase transition is observed in FeH and CoH at the pressures of 10 GPa and 180 GPa, respectively.
Novel phases of lithium-aluminum binaries from first-principles structural search
Energy Technology Data Exchange (ETDEWEB)
Sarmiento-Pérez, Rafael; Cerqueira, Tiago F. T.; Botti, Silvana; Marques, Miguel A. L., E-mail: marques@tddft.org [Institut Lumière Matière (UMR5306) and ETSF, Université Lyon 1-CNRS, Université de Lyon, F-69622 Villeurbanne Cedex (France); Valencia-Jaime, Irais [Institut Lumière Matière (UMR5306) and ETSF, Université Lyon 1-CNRS, Université de Lyon, F-69622 Villeurbanne Cedex (France); Centro de Investigación y Estudios Avanzados del IPN, MX-76230 Querétaro (Mexico); Amsler, Maximilian; Goedecker, Stefan [Department of Physics, Universität Basel, Klingelbergstr. 82, 4056 Basel (Switzerland); Romero, Aldo H. [Physics Department, West Virginia University, Morgantown, West Virginia 26506-6315 (United States)
2015-01-14
Intermetallic Li–Al compounds are on the one hand key materials for light-weight engineering, and on the other hand, they have been proposed for high-capacity electrodes for Li batteries. We determine from first-principles the phase diagram of Li–Al binary crystals using the minima hopping structural prediction method. Beside reproducing the experimentally reported phases (LiAl, Li{sub 3}Al{sub 2}, Li{sub 9}Al{sub 4}, LiAl{sub 3}, and Li{sub 2}Al), we unveil a structural variety larger than expected by discovering six unreported binary phases likely to be thermodynamically stable. Finally, we discuss the behavior of the elastic constants and of the electric potential profile of all Li–Al stable compounds as a function of their stoichiometry.
A proposal to first principles electronic structure calculation: Symbolic-Numeric method
Kikuchi, Akihito
2012-01-01
This study proposes an approach toward the first principles electronic structure calculation with the aid of symbolic-numeric solving. The symbolic computation enables us to express the Hartree-Fock-Roothaan equation in an analytic form and approximate it as a set of polynomial equations. By use of the Grobner basis technique, the polynomial equations are transformed into other ones which have identical roots. The converted equations take more convenient forms which will simplify numerical procedures, from which we can derive necessary physical properties in order, in an a la carte way. This method enables us to solve the electronic structure calculation, the optimization of any kind, or the inverse problem as a forward problem in a unified way, in which there is no need for iterative self-consistent procedures with trials and errors.
First-principles calculations atomic structure and elastic properties of Ti-Nb alloys
Timoshevskii, A N; Ivasishin, O M
2011-01-01
Elastic properties of Ti based \\beta-alloy were studied by the method of the model structure first principle calculations. Concentrational dependence of Young modulus for the binary \\beta-alloy Ti-Nb was discovered. It is shown that peculiarities visible at 15-18% concentrations can be related to the different Nb atoms distribution. Detailed comparison of the calculation results with the measurement results was done. Young modulus for the set of the ordered structures with different Nb atoms location, which simulate triple \\beta-alloys Ti-29.7%Zr-18.5%Nb and Ti-51.8%Zr-18.5%Nb have been calculated. The results of these calculations allowed us to suggest the concentration region for single-phase ternary \\beta-phase alloys possessing low values of Young's modulus.
Band structure and optical properties of amber studied by first principles
Energy Technology Data Exchange (ETDEWEB)
Rao, Zhi-Fan, E-mail: raozhifan@163.com [Analysis and Testing Center of Yunnan, Kunming University of Science and Technology, Kunming 650093 (China); Zhou, Rong-Feng [Analysis and Testing Center of Yunnan, Kunming University of Science and Technology, Kunming 650093 (China)
2013-03-01
The band structure and density of states of amber is studied by the first principles calculation based on density of functional theory. The complex structure of amber has 214 atoms and the band gap is 5.0 eV. The covalent bond is combined C/O atoms with H atoms. The O 2p orbital is the biggest effect near the Fermi level. The optical properties' results show that the reflectivity is low, and the refractive index is 1.65 in visible light range. The highest absorption coefficient peak is at 172 nm and another higher peak is at 136 nm. These convince that the amber would have a pretty sheen and that amber is a good and suitable crystal for jewelry and ornaments.
Novel phases of lithium-aluminum binaries from first-principles structural search
Sarmiento-Pérez, Rafael; Cerqueira, Tiago F. T.; Valencia-Jaime, Irais; Amsler, Maximilian; Goedecker, Stefan; Romero, Aldo H.; Botti, Silvana; Marques, Miguel A. L.
2015-01-01
Intermetallic Li-Al compounds are on the one hand key materials for light-weight engineering, and on the other hand, they have been proposed for high-capacity electrodes for Li batteries. We determine from first-principles the phase diagram of Li-Al binary crystals using the minima hopping structural prediction method. Beside reproducing the experimentally reported phases (LiAl, Li3Al2, Li9Al4, LiAl3, and Li2Al), we unveil a structural variety larger than expected by discovering six unreported binary phases likely to be thermodynamically stable. Finally, we discuss the behavior of the elastic constants and of the electric potential profile of all Li-Al stable compounds as a function of their stoichiometry.
First-principle study of energy band structure of armchair graphene nanoribbons
Ma, Fei; Guo, Zhankui; Xu, Kewei; Chu, Paul K.
2012-07-01
First-principle calculation is carried out to study the energy band structure of armchair graphene nanoribbons (AGNRs). Hydrogen passivation is found to be crucial to convert the indirect band gaps into direct ones as a result of enhanced interactions between electrons and nuclei at the edge boundaries, as evidenced from the shortened bond length as well as the increased differential charge density. Ribbon width usually leads to the oscillatory variation of band gaps due to quantum confinement no matter hydrogen passivated or not. Mechanical strain may change the crystal symmetry, reduce the overlapping integral of C-C atoms, and hence modify the band gap further, which depends on the specific ribbon width sensitively. In practical applications, those effects will be hybridized to determine the energy band structure and subsequently the electronic properties of graphene. The results can provide insights into the design of carbon-based devices.
Wang, Jinjin; Wang, Zhanyu; Jing, Yueyue; Wang, Songyou; Chou, Che-Fu; Hu, Han; Chiou, Shan-Haw; Tsoo, Chia-Chin; Su, Wan-Sheng
2016-10-01
The structural, mechanical, electronic, and optical properties of B6O were explored by means of first-principles calculations. Such a system is mechanically stable and also a relatively hard material which are derived from obtained elastic constants and bulk moduli. Bulk B6O is a direct-gap semiconductor with a bandgap of about 2.93 eV within G0W0 approximation. Furthermore, the optical properties, such as real and imaginary parts of dielectric functions, refractive index and extinction coefficient, and the comparison of optical properties between the density-functional theory (DFT) and G0W0 Bethe-Salpeter equation (G0W0-BSE) results, were computed and discussed. The results obtained from our calculations open a possibility for expanding its use in device applications.
The structural, electronic and phonon behavior of CsPbI3: A first principles study
Bano, Amreen; Khare, Preeti; Parey, Vanshree; Shukla, Aarti; Gaur, N. K.
2016-05-01
Metal halide perovskites are optoelectronic materials that have attracted enormous attention as solar cells with power conversion efficiencies reaching 20%. The benefit of using hybrid compounds resides in their ability to combine the advantage of these two classes of compounds: the high mobility of inorganic materials and the ease of processing of organic materials. In spite of the growing attention of this new material, very little is known about the electronic and phonon properties of the inorganic part of this compounds. A theoretical study of structural, electronic and phonon properties of metal-halide cubic perovskite, CsPbI3 is presented, using first-principles calculations with planewave pseudopotential method as personified in PWSCF code. In this approach local density approximation (LDA) is used for exchange-correlation potential.
First-principles investigation of the electronic structure and magnetism of eskolaite
Institute of Scientific and Technical Information of China (English)
Shen Jing-Qin; Shi Si-Qi; Ouyang Chu-Ying; Lei Min-Sheng; Tang Wei-Hua
2009-01-01
The electronic structure and magnetism of eskolaite are studied by using first-principles calculations where the on-site Coulomb interaction and the exchange interaction are taken into account and the LSDA+U method is used.The calculated energies of magnetic configurations are very well fitted by the Heisenberg Hamiltonian with interactions in five neighbour shells; interaction with two nearest neighbours is found to be dominant. The Neel temperature is calculated in the spin-3/2 pair-cluster approximation. It is found that the measurements are in good agreement with for the values of U and J that are close to those obtained within the constrained occupation method.The band gap is of the Mott-Hubbard type.
Energy Technology Data Exchange (ETDEWEB)
Desnavi, Sameerah, E-mail: sameerah-desnavi@zhcet.ac.in [Department of Electronic Engineering, ZHCET, Aligarh Muslim University, Aligarh-202002 (India); Chakraborty, Brahmananda; Ramaniah, Lavanya M. [High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai-400085 (India)
2014-04-24
The electronic structure and hydrogen storage capability of Yttrium-doped grapheme has been theoretically investigated using first principles density functional theory (DFT). Yttrium atom prefers the hollow site of the hexagonal ring with a binding energy of 1.40 eV. Doping by Y makes the system metallic and magnetic with a magnetic moment of 2.11 μ{sub B}. Y decorated graphene can adsorb up to four hydrogen molecules with an average binding energy of 0.415 eV. All the hydrogen atoms are physisorbed with an average desorption temperature of 530.44 K. The Y atoms can be placed only in alternate hexagons, which imply a wt% of 6.17, close to the DoE criterion for hydrogen storage materials. Thus, this system is potential hydrogen storage medium with 100% recycling capability.
Structural, electronic, and elastic properties of K-As compounds: a first principles study.
Ozisik, Havva Bogaz; Colakoglu, Kemal; Deligoz, Engin; Ozisik, Haci
2012-07-01
First-principle calculations are performed to investigate the structural, elastic and electronic properties of K-As compounds (KAs in NaP, LiAs and AuCu-type structures, KAs(2) in MgCu(2)-type structure, K(3)As in Na(3)As, Cu(3)P and Li(3)Bi-type structures, and K(5)As(4) in A(5)B(4)-type structure). The lattice parameters, cohesive energy, formation energy, bulk modulus, and the first derivative of bulk modulus (to fit to the Murnaghan's equation of state) of the considered structures are calculated and reasonable agreement is obtained, and the phase transition pressure is also predicted. The repeated calculations on the electronic band structures and the related partial density of states are also given. The calculated second-order elastic constants based on the stress-strain method and the other related quantities such as Young's modulus, shear modulus, Poisson's ratio, sound velocities, Debye temperature, and shear anisotropy factors for considered structures are presented, and trends are discussed.
Structures, phase transitions, and magnetic properties of C o3Si from first-principles calculations
Zhao, Xin; Yu, Shu; Wu, Shunqing; Nguyen, Manh Cuong; Wang, Cai-Zhuang; Ho, Kai-Ming
2017-07-01
C o3Si was recently reported to exhibit remarkable magnetic properties in the nanoparticle form [B. Balasubramanian et al., Appl. Phys. Lett. 108, 152406 (2016)], 10.1063/1.4945987, yet better understanding of this material should be promoted. Here we report a study on the crystal structures of C o3Si using an adaptive genetic algorithm and discuss its electronic and magnetic properties from first-principles calculations. Several competing phases of C o3Si have been revealed from our calculations. We show that the hexagonal C o3Si structure reported in experiments has lower energy in the nonmagnetic state than in the ferromagnetic state at zero temperature. The ferromagnetic state of the hexagonal structure is dynamically unstable with imaginary phonon modes and transforms into a new orthorhombic structure, which is confirmed by our structure searches to have the lowest energy for both C o3Si and C o3Ge . Magnetic properties of the experimental hexagonal structure and the lowest-energy structures obtained from our structure searches are investigated in detail.
Dahmane, F.; Mogulkoc, Y.; Doumi, B.; Tadjer, A.; Khenata, R.; Bin Omran, S.; Rai, D. P.; Murtaza, G.; Varshney, Dinesh
2016-06-01
Using the first-principles density functional calculations, the structural, electronic and magnetic properties of the Fe2XAl (X=Cr, Mn, Ni) compounds in both the Hg2CuTi and Cu2MnAl-type structures were studied by the full-potential linearized augmented plane waves (FP-LAPW) method. The exchange and correlation potential is treated by the generalized-gradient approximation (GGA) where the results show that the Cu2MnAl-type structure is energetically more stable than the Hg2CuTi-type structure for the Fe2CrAl and Fe2MnAl compounds at the equilibrium volume. The full Heusler compounds Fe2XAl (X=Cr, Mn) are half-metallic in the Cu2MnAl-type structure. Fe2NiAl has a metallic character in both CuHg2Ti and AlCu2Mn-type structures. The total magnetic moments of the Fe2CrAl and Fe2MnAl compounds are 1.0 and 2.0 μB, respectively, which are in agreement with the Slater-Pauling rule Mtot=Ztot- 24.
First-principles study of structural and bonding properties of vanadium carbide and niobium carbide
Joshi, K. B.; Paliwal, U.
2009-11-01
An ab initio linear combination of atomic orbitals method founded on density functional theory is applied to study the structural and bonding properties of vanadium carbide and niobium carbide. We present structural properties, namely, first-principles total energies, equilibrium lattice constants, bulk moduli and their pressure derivatives, together with the x-ray structure factors. Two generalized correction schemes—P86 and PW92—are applied to treat correlation. P86 gives a favourable ground state compared with the PW92. The computed equilibrium lattice constants and bulk moduli of the two compounds are compared with available experimental data. The x-ray structure factors for a few reflection planes are also reported. Comparison with experiment could be done only for niobium carbide. More refined measurements on x-ray structure factors for both compounds are required. We also present the autocorrelation functions derived from the ground-state momentum density. The electronic behaviour and bonding properties are discussed in terms of absolute and anisotropies in the directional autocorrelation functions. Our findings on structural and bonding parameters are well in accordance with the experimental data.
First-principles study of structural and bonding properties of vanadium carbide and niobium carbide
Energy Technology Data Exchange (ETDEWEB)
Joshi, K B; Paliwal, U [Department of Physics, University College of Science, M L Sukhadia University, Udaipur - 313001 (India)], E-mail: k_joshi@yahoo.com
2009-11-15
An ab initio linear combination of atomic orbitals method founded on density functional theory is applied to study the structural and bonding properties of vanadium carbide and niobium carbide. We present structural properties, namely, first-principles total energies, equilibrium lattice constants, bulk moduli and their pressure derivatives, together with the x-ray structure factors. Two generalized correction schemes-P86 and PW92-are applied to treat correlation. P86 gives a favourable ground state compared with the PW92. The computed equilibrium lattice constants and bulk moduli of the two compounds are compared with available experimental data. The x-ray structure factors for a few reflection planes are also reported. Comparison with experiment could be done only for niobium carbide. More refined measurements on x-ray structure factors for both compounds are required. We also present the autocorrelation functions derived from the ground-state momentum density. The electronic behaviour and bonding properties are discussed in terms of absolute and anisotropies in the directional autocorrelation functions. Our findings on structural and bonding parameters are well in accordance with the experimental data.
Ceder, Gerbrand
2007-03-01
The prediction of structure is a key problem in computational materials science that forms the platform on which rational materials design can be performed. Finding structure by traditional optimization methods on quantum mechanical energy models is not possible due to the complexity and high dimensionality of the coordinate space. An unusual, but efficient solution to this problem can be obtained by merging ideas from heuristic and ab initio methods: In the same way that scientist build empirical rules by observation of experimental trends, we have developed machine learning approaches that extract knowledge from a large set of experimental information and a database of over 15,000 first principles computations, and used these to rapidly direct accurate quantum mechanical techniques to the lowest energy crystal structure of a material. Knowledge is captured in a Bayesian probability network that relates the probability to find a particular crystal structure at a given composition to structure and energy information at other compositions. We show that this approach is highly efficient in finding the ground states of binary metallic alloys and can be easily generalized to more complex systems.
Structural stability and mechanical properties of Pt–Zr alloys from first-principles
Energy Technology Data Exchange (ETDEWEB)
Pan, Yong, E-mail: y_pan@ipm.com.cn [School of Materials Science and Engineering, Southwest Petroleum University, Chengdu 610500 (China); Lin, Yuanhua, E-mail: yhlin28@163.com [State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500 (China); Wang, Xiaohong; Chen, Songsong; Wang, Lijun; Tong, Chuangchuang; Cao, Zhen [School of Materials Science and Engineering, Southwest Petroleum University, Chengdu 610500 (China)
2015-09-15
Highlights: • The convex hull indicates that Pt{sub 11}Zr{sub 7} is the most stable structure. • Pt{sub 8}Zr has the strongest volume deformation resistance. • Pt{sub 3}Zr has the strongest shear deformation resistance and has highest stiffness. • The high elastic modulus originated from Pt concentration and bond characteristic. - Abstract: The correlation between structural stability and mechanical properties of Pt–Zr alloys is systematically investigated by first-principles calculations. Additionally, the thermodynamic properties and electronic structure are discussed in detail. The convex hull indicates that the Pt{sub 10}Zr{sub 7} with orthorhombic structure is more stable than other Pt–Zr alloys at ground state. The bulk modulus of Pt–Zr alloys increases linearly as Pt concentration increases. Pt{sub 8}Zr has strong volume deformation resistance, which is derived from the high Pt concentration. Pt{sub 3}Zr exhibits strong shear deformation resistance and has high elastic stiffness, which originated from the strong Pt–Pt metallic bond along the b-direction. The trend of Debye temperature is consistent with the variation of shear modulus and Young’s modulus, and the calculated Debye temperature of Pt{sub 3}Zr is 342 K, which is bigger than other Pt–Zr alloys. The results provide a helpful for the design of Pt-based high-temperature structural materials with excellent mechanical properties.
Ding, Li-Ping; Shao, Peng; Zhang, Fang-Hui; Lu, Cheng; Ding, Lei; Ning, Shu Ya; Huang, Xiao Fen
2016-07-18
On the basis of the first-principles techniques, we perform the structure prediction for MoB2. Accordingly, a new ground-state crystal structure WB2 (P63/mmc, 2 fu/cell) is uncovered. The experimental synthesized rhombohedral R3̅m and hexagonal AlB2, as well as theoretical predicted RuB2 structures, are no longer the most favorite structures. By analyzing the elastic constants, formation enthalpies, and phonon dispersion, we find that the WB2 phase is thermodynamically and mechanically stable. The high bulk modulus B, shear modulus G, low Poisson's ratio ν, and small B/G ratio are benefit to its low compressibility. When the pressure is 10 GPa, a phase transition is observed between the WB2-MoB2 and the rhombohedral R3̅m MoB2 phases. By analyzing the density of states and electron density, we find that the strong covalent is formed in MoB2 compounds, which contributes a great deal to its low compressibility. Furthermore, the low compressibility is also correlated with the local buckled structure.
Xu, C.; Li, Q.; Liu, C. M.; Duan, M. Y.; Wang, H. K.
2016-05-01
First-principles calculations are employed to investigate the structural and elastic properties, formation enthalpies and chemical bonding features as well as hardness values of chromium tetraboride (CrB4) with different structures. The lattice parameters, Poisson’s ratio and B/G ratio are also derived. Our calculations indicate that the orthorhombic structure with Pnnm symmetry is the most energetically stable one for CrB4. Except for WB4P63/mmc structure with imaginary frequencies, another six new structures are investigated through the full phonon dispersion calculations. Their mechanical and thermodynamic stabilities are also studied by calculating the elastic constants and formation enthalpies. Our calculations show that the thermodynamic stabilities of all these CrB4 phases can be enhanced under high pressure. The large shear moduli, Young’s moduli and hardness values indicate that these CrB4 phases are potential hard materials. Analyses of the densities of states (DOSs) and electron localization functions (ELFs) provide further understandings of the chemical and physical properties of these CrB4 phases. It is observed that the large occupations and high strengths of the B-B covalent bonds are important for the stabilities, incompressibility and hardnesses of these CrB4 phases.
Owens, Jonathan R.
In this work, we first present two powerful methods for understanding the electronic, structural, conducting, and energetic properties of nano-materials: density functional theory (DFT) and quantum transport. The basics of the theory and background of both methods are discussed thoroughly. After establishing a firm foundation, we turn our attention to using these tools to solve practical problems, often in collaboration with experimental colleagues. The first two projects pertain to nitrogen doping in graphene nanoribbons (GNRs). We study nitrogen doping in two different schema: concentration-based (N_x-doped) and structural based (N_2. {AA}-doped). Concentration based doping is explored in the context of experimental measurements of IV curves on GNRs with differing dopant concentrations. These results show a shift towards semi-conducting behavior with an increase in dopant concentration. We combine first principles calculations (DFT) and transport calculations in the Landauer formalism to compute the density-of-states (DOS) and transport curves for various dopant concentrations (0.46%, 1.39%, 1.89%, and 2.31%), which corroborate the experimental observations. The N_2. {AA}-doped GNR study was inspired by experimental observation of an atomically precise nitrogen doping scheme in bulk graphene. Experimental STM images, combined with simulated STM images, revealed that the majority (80%) of doping sites consist of nitrogen atoms on neighboring sites of the same sublattice (A) in graphene, hence N_2. {AA} doping. We examine this doping scheme applied to zigzag and armchair GNRs under different orientations of the dopants. We present spin-resolved charge densities, energetics, transport, DOS, and simulated STM images for all four systems studied. Our results show the possibility of spin-filtered devices and the STM images provide an aid in helping experimentalist identify the dopant patterns, if these GNRs are fabricated. We next venture to explain different observed
Design of BAs-AlN monolayered honeycomb heterojunction structures: A first-principles study
Energy Technology Data Exchange (ETDEWEB)
Camacho-Mojica, Dulce C.; López-Urías, Florentino, E-mail: flo@ipicyt.edu.mx
2016-04-15
Graphical abstract: Single-layer honeycomb heterojunction structures based on alternated and coupled ribbons of BAs and AlN are investigated using first-principles density functional theory calculations. Optimized geometries, density of states, band-gaps, formation energies, and wave functions are studied for different ribbon widths joined along the zigzag and armchair edges. Optimized heterojunction geometries results revealed that BAs narrow ribbons exhibit a corrugation effect at the interface due to a lattice mismatch. From formation energy calculations, it was found that zigzag heterojunctions are more stable than the armchair heterojunctions. - Highlights: • We design new 2D-semiconductor heterojunction nanostructures. • Monolayers formed by alternated strips (heterojunctions) of aluminum-nitride and boron-arsenide, with graphene-like structure are explored by DFT method. • Due to the lattice mismatch, an effect of corrugation was observed in heterojunctions AlN and BAs. • Electronic band gaps are strongly dependent on width and chirality (zigzag or armchair) of the strips. • Formation energy calculations revealed that zigzag heterojunctions are more stable than the armchair heterojunctions. - Abstract: BAs and AlN are semiconductor materials with an indirect and direct gap respectively in the bulk phase. Recently, electronic calculations have demonstrated that a single-layer or few layers of BAs and AlN exhibit a graphite-like structure with interesting electronic properties. In this work, infinite sheets single-layer heterojunction structures based on alternated strips with honeycomb BAs and AlN layers are investigated using first-principles density functional theory calculations. Optimized geometries, density of states, band-gaps, formation energies, and wave functions are studied for different strip widths joined along zigzag and armchair edges. Results in optimized heterojunction geometries revealed that BAs narrow strips exhibit a corrugation
BabaeiPour, M.; Safari, E. Keshavarz; Shokri, A. A.
2017-02-01
A systematic study has been done on the structural and electronic properties of carbon, boron nitride and aluminum nitride nanotubes with structure consisting of periodically distributed tetragonal (T ≡A2X2), hexagonal (H ≡A3X3) and dodecagonal (D ≡A6X6) (AX=C2, BN, AlN) cycles. The method has been performed using first-principles calculations based on density functional theory (DFT). The optimized lattice parameters, density of state (DOS) curves and band structure of THD-NTs are obtained for (3, 0) and (0, 2) types. Our calculation results indicate that carbon nanotubes of these types (THD-CNTs) behave as a metallic, but the boron nitride nanotubes (THD-BNNTs) (with a band gap of around 4 eV) as well as aluminum nitride nanotubes (THD-AlNNTs) (with a band gap of around 2.6 eV) behave as an semiconductor. The inequality in number of atoms in different directions is affected on structures and diameters of nanotubes and their walls curvature.
First-principles study of structural, elastic, and thermodynamic properties of ZrHf alloy
Institute of Scientific and Technical Information of China (English)
韦昭; 翟东; 邵晓红; 鲁勇; 张平
2015-01-01
Structural parameters, elastic constants, and thermodynamic properties of ordered and disordered solid solutions of ZrHf alloys are investigated through first-principles calculations based on density-functional theory (DFT). The special quasi-random structure (SQS) method is used to model the disordered phase as a single unit cell, and two lamella structures are generated to model the ordered alloys. Small strains are applied to the unit cells to measure the elastic behavior and mechanical stability of ZrHf alloys and to obtain the independent elastic constants by the stress–strain relationship. Phonon dispersions and phonon density of states are presented to verify the thermodynamic stability of the considered phases. Our results show that both the ordered and disordered phases of ZrHf alloys are structurally stable. Based on the obtained phonon frequencies, thermodynamic properties, including Gibbs free energy, entropy, and heat capacity, are predicted within the quasi-harmonic approximation. It is verified that there are no obvious differences in energy between ordered and disordered phases over a wide temperature range.
Electronic Structure of KFe2Se2 from First-Principles Calculations
Institute of Scientific and Technical Information of China (English)
CAO Chao; DAI Jian-Hui
2011-01-01
@@ Electronic structures and magnetic properties for iron-selenide KFe2Se2 axe studied by first-principles calculations.The ground state is collinear antiferromagnetic with calculated 2.26μB magnetic moment on Fe atoms; and the J1 and J2 coupling strengths are calculated to be 0.038eV and 0.029eV.The states around EF are dominated by the Fe 3d orbitals which hybridize noticeably to the Se 4p orbitals.While the band structure of KFe2Se2 is similar to a heavily electron-doped BaFe2As2 or FeSe system,the Fermi surface of KFe2Se2 is much closer to the FeSe system since the electron sheets around M are symmetric with respect to x-y exchange.These features,as well as the absence of Fermi surface nesting,suggest that the parent KFe2Se2 could be regarded as an electron doped FeSe system with possible local moment magnetism.%Electronic structures and magnetic properties for iron-selenide KFe2Se2 are studied by first-principles calculations.The ground state is collinear antiferromagnetic with calculated 2.26μB magnetic moment on Fe atoms; and the J1 and J2 coupling strengths are calculated to be 0.038eV and 0.029eV.The states around EF are dominated by the Fe 3d orbitals which hybridize noticeably to the Se 4p orbitals.While the band structure of KFe2Se2 is similar to a heavily electron-doped BaFe2As2 or FeSe system, the Fermi surface of KFe2Se2 is much closer to the FeSe system since the electron sheets around M are symmetric with respect to x-y exchange.These features, as well as the absence of Fermi surface nesting, suggest that the parent KFe2Se2 could be regarded as an electron doped FeSe system with possible local moment magnetism.
Ying, Chun; Zhao, Erjun; Lin, Lin; Hou, Qingyu
2014-10-01
The structural determination, thermodynamic, mechanical, dynamic and electronic properties of 4d transitional metal diborides MB2 (M = Y-Ag) are systematically investigated by first-principles within the density functional theory (DFT). For each diboride, five structures are considered, i.e. AlB2-, ReB2-, OsB2-, MoB2- and WB2-type structures. The calculated lattice parameters are in good agreement with the previously theoretical and experimental studies. The formation enthalpy increases from YB2 to AgB2 in AlB2-type structure (similar to MoB2- and WB2-type). While the formation enthalpy decreases from YB2 to MoB2, reached minimum value to TcB2, and then increases gradually in ReB2-type structure (similar to OsB2-type), which is consistent with the results of the calculated density of states. The structural stability of these materials relates mainly on electronegative of metals, boron structure and bond characters. Among the considered structures, TcB2-ReB2 (TcB2-ReB2 represents TcB2 in ReB2-type structure, the same hereinafter) has the largest shear modulus (248 GPa), and is the hardest compound. The number of electrons transferred from metals to boron atoms and the calculated densities of states (DOS) indicate that each diboride is a complex mixture of metallic, ionic and covalent characteristics. Trends are discussed.
New crystal structure prediction of fully hydrogenated borophene by first principles calculations
Wang, Zhi-Qiang; Wang, Hui-Qiong; Feng, Yuan Ping; Zheng, Jin-Cheng
2016-01-01
We have studied the structure stability, band structures and mechanical properties of fully hydrogenated borophene (borophane) with different configurations by first principles calculations. Comparing with the Chair-like borophane (C-boropane) that has been reported in literature, we obtained four new conformers with much lower total-energy. The most stable one, Washboard-like borophane (W-borophane), has energy difference about 113.41 meV/atom lower than C-borophane. In W-borophane, B atoms are staggered by zigzag mode along the a direction, and staggered by up and down wrinkle mode along the b direction. Furthermore, we examined the dynamical stability of borophane conformers by calculating phonon dispersions. For the five conformers, no imaginary frequencies along the high-symmetry directions of the Brillouin zone were found, indicating that the five conformers are all dynamically stable. In addition, the band structures of the five conformers all show a Dirac cone along {\\Gamma}-Y or {\\Gamma}-X direction....
First-principles calculations of BC{sub 4}N nanostructures: stability and electronic structure
Energy Technology Data Exchange (ETDEWEB)
Freitas, A.; Azevedo, S. [Universidade Federal da Paraiba, CCEN, Departamento de Fisica, Joao Pessoa, PB (Brazil); Machado, M. [Universidade Federal de Pelotas, Departamento de Fisica, Pelotas, RS (Brazil); Kaschny, J.R. [Instituto Federal da Bahia-Campus Vitoria da Conquista, Vitoria da Conquista, BA (Brazil)
2012-07-15
In this work, we apply first-principles methods to investigate the stability and electronic structure of BC{sub 4}N nanostructures which were constructed from hexagonal graphite layers where substitutional nitrogen and boron atoms are placed at specific sites. These layers were rolled up to form zigzag and armchair nanotubes, with diameters varying from 7 to 12 A, or cut and bent to form nanocones, with 60 and 120 disclination angles. The calculation results indicate that the most stable structures are the ones which maximize the number of B-N and C-C bonds. It is found that the zigzag nanotubes are more stable than the armchair ones, where the strain energy decreases with increasing tube diameter D, following a 1/D {sup 2} law. The results show that the 60 disclination nanocones are the most stable ones. Additionally, the calculated electronic properties indicate a semiconducting behavior for all calculated structures, which is intermediate to the typical behaviors found for hexagonal boron nitride and graphene. (orig.)
First principles calculations of interlayer exchange coupling in bcc Fe/Cu/Fe structures
Energy Technology Data Exchange (ETDEWEB)
Kowalewski, M.; Heninrich, B. [Simon Fraser Univ., Burnaby, British Columbia (Canada); Schulthess, T.C.; Butler, W.H. [Oak Ridge National Lab., TN (United States)
1998-01-01
The authors report on theoretical calculations of interlayer exchange coupling between two Fe layers separated by a modified Cu spacer. These calculations were motivated by experimental investigations of similar structures by the SFU group. The multilayer structures of interest have the general form: Fe/Cu(k)/Fe and Fe/Cu(m)/X(1)/Cu(n)/Fe where X indicates one AL (atomic layer) of foreign atoms X (Cr, Ag, or Fe) and k, m, n represent the number of atomic layers of Cu. The purpose of the experimental and theoretical work was to determine the effect of modifying the pure Cu spacer by replacing the central Cu atomic layer with the atomic layer of foreign atoms X. The first principles calculation were performed using the Layer Korringa-Kohn-Rostoker (LKKR) method. The theoretical thickness dependence of the exchange coupling between two semi-infinite Fe layers was calculated for pure Cu spacer thicknesses in the range of 0 < k < 16. The effect of the foreign atoms X on the exchange coupling was investigated using the structure with 9 AL Cu spacer as a reference sample. The calculated changes in the exchange coupling are in qualitative agreement with experiment.
First-principles calculation on dilute magnetic alloys in zinc blend crystal structure
Energy Technology Data Exchange (ETDEWEB)
Ullah, Hamid, E-mail: hamidullah@yahoo.com [Department of Physics, Government Post Graduate Jahanzeb College, Saidu Sharif Swat (Pakistan); Inayat, Kalsoom [Department of Physics, Government Post Graduate Jahanzeb College, Saidu Sharif Swat (Pakistan); Khan, S.A; Mohammad, S. [Department of Physics, Materials Modeling Laboratory, Hazara University, Mansehra 21300 (Pakistan); Ali, A. [Department of Advanced Materials Science & Engineering, Hanseo University, Seosan-si, Chungnam-do 356-706 (Korea, Republic of); Alahmed, Z.A. [Department of Physics and Astronomy, King Saud University, Riyadh 11451 (Saudi Arabia); Reshak, A.H. [New Technologies-Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia)
2015-07-01
Ab-initio calculations are performed to investigate the structural, electronic and magnetic properties of spin-polarized diluted magnetic alloys in zinc blende structure. The first-principles study is carried out on Mn doped III–V semiconductors. The calculated band structures, electronic properties and magnetic properties of Ga{sub 1−x}Mn{sub x}X (X=P, As) compounds reveal that Ga{sub 0.75}Mn{sub 0.25}P is half metallic turned to be metallic with increasing x to 0.5 and 0.75, whereas substitute P by As cause to maintain the half-metallicity nature in both of Ga{sub 0.75}Mn{sub 0.25}As and Ga{sub 0.5}Mn{sub 0.5}As and tune Ga{sub 0.25}Mn{sub 0.75}As to be metallic. Calculated total magnetic moments and the robustness of half-metallicity of Ga{sub 0.75}Mn{sub 0.25}P, Ga{sub 0.75}Mn{sub 0.25}As and Ga{sub 0.5}Mn{sub 0.5}As with respect to the variation in lattice parameters are also discussed. The predicted theoretical evidence shows that some Mn-doped III–V semiconductors can be effectively used in spintronic devices.
Prediction of new high pressure structural sequence in thorium carbide: A first principles study
Energy Technology Data Exchange (ETDEWEB)
Sahoo, B. D., E-mail: bdsahoo@barc.gov.in; Joshi, K. D.; Gupta, Satish C. [Applied Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India)
2015-05-14
In the present work, we report the detailed electronic band structure calculations on thorium monocarbide. The comparison of enthalpies, derived for various phases using evolutionary structure search method in conjunction with first principles total energy calculations at several hydrostatic compressions, yielded a high pressure structural sequence of NaCl type (B1) → Pnma → Cmcm → CsCl type (B2) at hydrostatic pressures of ∼19 GPa, 36 GPa, and 200 GPa, respectively. However, the two high pressure experimental studies by Gerward et al. [J. Appl. Crystallogr. 19, 308 (1986); J. Less-Common Met. 161, L11 (1990)] one up to 36 GPa and other up to 50 GPa, on substoichiometric thorium carbide samples with carbon deficiency of ∼20%, do not report any structural transition. The discrepancy between theory and experiment could be due to the non-stoichiometry of thorium carbide samples used in the experiment. Further, in order to substantiate the results of our static lattice calculations, we have determined the phonon dispersion relations for these structures from lattice dynamic calculations. The theoretically calculated phonon spectrum reveal that the B1 phase fails dynamically at ∼33.8 GPa whereas the Pnma phase appears as dynamically stable structure around the B1 to Pnma transition pressure. Similarly, the Cmcm structure also displays dynamic stability in the regime of its structural stability. The B2 phase becomes dynamically stable much below the Cmcm to B2 transition pressure. Additionally, we have derived various thermophysical properties such as zero pressure equilibrium volume, bulk modulus, its pressure derivative, Debye temperature, thermal expansion coefficient and Gruneisen parameter at 300 K and compared these with available experimental data. Further, the behavior of zero pressure bulk modulus, heat capacity and Helmholtz free energy has been examined as a function temperature and compared with the experimental data of Danan [J
Prediction of new high pressure structural sequence in thorium carbide: A first principles study
Sahoo, B. D.; Joshi, K. D.; Gupta, Satish C.
2015-05-01
In the present work, we report the detailed electronic band structure calculations on thorium monocarbide. The comparison of enthalpies, derived for various phases using evolutionary structure search method in conjunction with first principles total energy calculations at several hydrostatic compressions, yielded a high pressure structural sequence of NaCl type (B1) → Pnma → Cmcm → CsCl type (B2) at hydrostatic pressures of ˜19 GPa, 36 GPa, and 200 GPa, respectively. However, the two high pressure experimental studies by Gerward et al. [J. Appl. Crystallogr. 19, 308 (1986); J. Less-Common Met. 161, L11 (1990)] one up to 36 GPa and other up to 50 GPa, on substoichiometric thorium carbide samples with carbon deficiency of ˜20%, do not report any structural transition. The discrepancy between theory and experiment could be due to the non-stoichiometry of thorium carbide samples used in the experiment. Further, in order to substantiate the results of our static lattice calculations, we have determined the phonon dispersion relations for these structures from lattice dynamic calculations. The theoretically calculated phonon spectrum reveal that the B1 phase fails dynamically at ˜33.8 GPa whereas the Pnma phase appears as dynamically stable structure around the B1 to Pnma transition pressure. Similarly, the Cmcm structure also displays dynamic stability in the regime of its structural stability. The B2 phase becomes dynamically stable much below the Cmcm to B2 transition pressure. Additionally, we have derived various thermophysical properties such as zero pressure equilibrium volume, bulk modulus, its pressure derivative, Debye temperature, thermal expansion coefficient and Gruneisen parameter at 300 K and compared these with available experimental data. Further, the behavior of zero pressure bulk modulus, heat capacity and Helmholtz free energy has been examined as a function temperature and compared with the experimental data of Danan [J. Nucl. Mater. 57, 280
Gu, Jian-Bing; Wang, Chen-Ju; Zhang, Wang-Xi; Sun, Bin; Liu, Guo-Qun; Liu, Dan-Dan; Yang, Xiang-Dong
2016-12-01
Since knowledge of the structure and elastic properties of Ta at high pressures is critical for addressing the recent controversies regarding the high-pressure stable phase and elastic properties, we perform a systematical study on the high-pressure structure and elastic properties of the cubic Ta by using the first-principles method. Results show that the initial body-centered cubic phase of Ta remains stable even up to 500 GPa and the high-pressure elastic properties are excellently consistent with the available experimental results. Besides, the high-pressure sound velocities of the single- and poly-crystals Ta are also calculated based on the elastic constants, and the predications exhibit good agreement with the existing experimental data. Project supported by the Basic and Frontier Technical Research Project of Henan Province, China (Grant No. 152300410228), the University Innovation Team Project in Henan Province, China (Grant No. 15IRTSTHN004), and the Key Scientific Research Project of Higher Education of Henan Province, China (Grant No. 17A140014).
First-Principles Study of Structural, Magnetic, Electronic and Elastic Properties of PuC2
Yang, Rong; Tang, Bin; Gao, Tao; Ao, Bing-Yun
2016-10-01
We perform first-principles calculations of crystal structure, magnetism, electronic structure, chemical bonding and elastic properties for PuC2 using the standard local spin-density approximation (LSDA)+U scheme. The use of the Hubbard term to describe the 5f electrons of plutonium is discussed according to the lattice parameters, magnetism and densities of states. Our calculated lattice constants and magnetism are in good agreement with the experimental data or other theoretical calculations. It is shown that the total densities of states at the Fermi energy level mainly come from the contribution of narrow f band. The Pu-C bonds of PuC2 have a mixture of covalent character and ionic character, while covalent character is stronger than ionic character. The C1-C2 bonding has strong covalent character because of sp2 hybridization between C atoms. Lastly, the elastic properties of PuC2 are studied. We hope that our results can provide a useful reference for further theoretical and experimental research on PuC2. Supported by the National Natural Science Foundation of China under Grant Nos. 21371160, 21401173, and the Science Challenge Program of China
Chappell, Helen F.; Thom, William; Bowron, Daniel T.; Faria, Nuno; Hasnip, Philip J.; Powell, Jonathan J.
2017-08-01
Ferrihydrite, with a ``two-line'' x-ray diffraction pattern (2L-Fh), is the most amorphous of the iron oxides and is ubiquitous in both terrestrial and aquatic environments. It also plays a central role in the regulation and metabolism of iron in bacteria, algae, higher plants, and animals, including humans. In this study, we present a single-phase model for ferrihydrite that unifies existing analytical data while adhering to fundamental chemical principles. The primary particle is small (20-50 Å) and has a dynamic and variably hydrated surface, which negates long-range order; collectively, these features have hampered complete characterization and frustrated our understanding of the mineral's reactivity and chemical/biochemical function. Near and intermediate range neutron diffraction (NIMROD) and first-principles density functional theory (DFT) were employed in this study to generate and interpret high-resolution data of naturally hydrated, synthetic 2L-Fh at standard temperature. The structural optimization overcomes transgressions of coordination chemistry inherent within previously proposed structures, to produce a robust and unambiguous single-phase model.
Electronic Structure of Cu(tmdt2 Studied with First-Principles Calculations
Directory of Open Access Journals (Sweden)
Kiyoyuki Terakura
2012-08-01
Full Text Available We have studied the electronic structure of Cu(tmdt2, a material related to single-component molecular conductors, by first-principles calculations. The total energy calculations for several different magnetic configurations show that there is strong antiferromagnetic (AFM exchange coupling along the crystal a-axis. The electronic structures are analyzed in terms of the molecular orbitals near the Fermi level of isolated Cu(tmdt2 molecule. This analysis reveals that the system is characterized by the half-filled pdσ(− band whose intermolecular hopping integrals have strong one-dimensionality along the crystal a-axis. As the exchange splitting of the band is larger than the band width, the basic mechanism of the AFM exchange coupling is the superexchange. It will also be shown that two more ligand orbitals which are fairly insensitive to magnetism are located near the Fermi level. Because of the presence of these orbitals, the present calculation predicts that Cu(tmdt2 is metallic even in its AFM state, being inconsistent with the available experiment. Some comments will be made on the difference between Cu(tmdt2 and Cu(dmdt2.
Energy Technology Data Exchange (ETDEWEB)
Li, Xiaowei; Zhang, Dong [Key Laboratory of Marine Materials and Related Technologies, Key Laboratory of Marine Materials and Protective Technologies of Zhejiang Province, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China); Lee, Kwang-Ryeol, E-mail: krlee@kist.re.kr [Computational Science Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Wang, Aiying, E-mail: aywang@nimte.ac.cn [Key Laboratory of Marine Materials and Related Technologies, Key Laboratory of Marine Materials and Protective Technologies of Zhejiang Province, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China)
2016-05-31
First-principles calculation was performed to investigate the effect of metal doping on the structural characteristics of amorphous carbon system, and the 3d transition metals (TM) were particularly selected as representative case. Results showed that the total energy in TM–C systems caused by distorting the bond angles was reduced distinctly for comparison with that in C–C system. Further electronic structure revealed that as the 3d electrons of doped TM increased, the bond characteristic of highest occupied molecular orbital changed from bonding (Sc, Ti) to nonbonding (V, Cr, Mn, Fe) and finally to antibonding (Co, Ni, Cu) between the TM and C atoms. Meanwhile, the TM–C bond presented a mixture of the covalent and ionic characters. The decrease of strength and directionality of TM–C bonds resulted in the total energy change upon bond angle distortion, which demonstrated that the bond characteristics played an important role in reducing residual stress of TM-doped amorphous carbon systems. - Highlights: • The bond characteristics as 3d electrons changed from bonding, nonbonding to antibonding. • The TM–C bond was a mixture of covalent and ionic characters. • Reduced strength and directionality of TM–C bond led to small distortion energy change. • The weak TM–C bond accounted for the reduced compressive stress caused by TM.
Electronic Structures of S-Doped Capped C-SWNT from First Principles Study.
Wang, L; Zhang, Yz; Zhang, Yf; Chen, Xs; Lu, W
2010-04-14
The semiconducting single-walled carbon nanotube (C-SWNT) has been synthesized by S-doping, and they have extensive potential application in electronic devices. We investigated the electronic structures of S-doped capped (5, 5) C-SWNT with different doping position using first principles calculations. It is found that the electronic structures influence strongly on the workfunction without and with external electric field. It is considered that the extended wave functions at the sidewall of the tube favor for the emission properties. With the S-doping into the C-SWNT, the HOMO and LUMO charges distribution is mainly more localized at the sidewall of the tube and the presence of the unsaturated dangling bond, which are believed to enhance workfunction. When external electric field is applied, the coupled states with mixture of localized and extended states are presented at the cap, which provide the lower workfunction. In addition, the wave functions close to the cap have flowed to the cap as coupled states and to the sidewall of the tube mainly as extended states, which results in the larger workfunction. It is concluded that the S-doped C-SWNT is not incentive to be applied in field emitter fabrication. The results are also helpful to understand and interpret the application in other electronic devices.
Electronic Structures of S-Doped Capped C-SWNT from First Principles Study
Directory of Open Access Journals (Sweden)
Chen XS
2010-01-01
Full Text Available Abstract The semiconducting single-walled carbon nanotube (C-SWNT has been synthesized by S-doping, and they have extensive potential application in electronic devices. We investigated the electronic structures of S-doped capped (5, 5 C-SWNT with different doping position using first principles calculations. It is found that the electronic structures influence strongly on the workfunction without and with external electric field. It is considered that the extended wave functions at the sidewall of the tube favor for the emission properties. With the S-doping into the C-SWNT, the HOMO and LUMO charges distribution is mainly more localized at the sidewall of the tube and the presence of the unsaturated dangling bond, which are believed to enhance workfunction. When external electric field is applied, the coupled states with mixture of localized and extended states are presented at the cap, which provide the lower workfunction. In addition, the wave functions close to the cap have flowed to the cap as coupled states and to the sidewall of the tube mainly as extended states, which results in the larger workfunction. It is concluded that the S-doped C-SWNT is not incentive to be applied in field emitter fabrication. The results are also helpful to understand and interpret the application in other electronic devices.
First-principles study on structural stability of 3d transition metal alloying magnesium hydride
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
A first-principles plane-wave pseudopotential method based on the density functional theory was used to investigate the energy and electronic structure of magnesium hydride (MgH2) alloyed by 3d transition metal elements. Through calculations of the negative heat formation of magnesium hydride alloyed by X (X denotes 3d transition metal) element, it is found that when a little X (not including Sc) dissolves into magnesium hydride, the structural stability of alloying systems decreases, which indicates that the dehydrogenation properties of MgH2 can be improved. After comparing the densities of states(DOS) and the charge distribution of MgH2 with or without X alloying, it is found that the improvement for the dehydrogenation properties of MgH2 alloyed by X attributes to the fact that the weakened bonding between magnesium and hydrogen is caused by the stronger interactions between X (not including Cu) and hydrogen. The calculation results of the improvement for the dehydrogenation properties of MgH2-X (X=Ti, V, Mn, Fe, Co,Ni, Cu) systems are in agreement with the experimental results. Hence, the dehydrogenation properties of MgH2 are expected to be improved by addition of Cr, Zn alloying elements.
First-principle studies of electronic structure and magnetic excitations in FeSe monolayer
Bazhirov, Timur; Cohen, Marvin L.
2013-03-01
Recent experimental advances made it possible to study single-layered superconducting systems of iron-based compounds. The results show evidence of significant enhancement of superconducting properties compared to the bulk case. We use first-principle pseudopotential density functional theory techniques and the local spin-density approximation to study the electronic properties of an FeSe monolayer in different spin configurations. The results show that the experimental shape of the Fermi surface is best described by a checkerboard antiferromagnetic (AFM) spin arrangement. To explore the underlying pairing mechanism, we study the evolution of the non-magnetic to the AFM-ordered structures under constrained magnetization, and we estimate the electronic coupling to magnetic excitations involving transfer and increase of iron magnetic moments and compare it to the electron-phonon coupling. Finally, we simulate the substrate-induced interaction by using uniform charge doping and show that the latter can lead to an increase in the density of states at the Fermi level and possibly produce higher superconducting transition temperatures. This work was supported by NSF grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at Lawrence Berkeley National Laboratory's NERSC facility
Energy Technology Data Exchange (ETDEWEB)
Piskunov, Sergei, E-mail: piskunov@lu.l [Faculty of Computing, University of Latvia, 19 Raina blvd., Riga LV-1586 (Latvia); Faculty of Physics and Mathematics, University of Latvia, 8 Zellu Str., Riga LV-1002 (Latvia); Zvejnieks, Guntars; Zhukovskii, Yuri F. [Institute for Solid State Physics, University of Latvia, 8 Kengaraga Str., LV-1063, Riga (Latvia); Bellucci, Stefano [INFN-Laboratori Nazionali di Frascati, Via Enrico Fermi 40, I-00044, Frascati (Italy)
2011-03-31
In this study, we perform first principles simulations on both atomically smooth and nanostructured Ni(111) slabs. The latter contains periodically distributed nickel nanoclusters atop a thin metal film gradually growing from adatoms and serving as a promising catalyst. Applying the generalized gradient approximation within the formalism of the density functional theory we compare the atomic and electronic structures of Ni bulk, as well as both perfect and nanostructured (111) surfaces obtained using two different ab initio approaches: (i) the linear combination of atomic orbitals and (ii) the projector augmented plane waves. The most essential inter-atomic forces between the Ni adatoms upon the substrate have been found to be formed via: (i) attractive pair-wise interactions, (ii) repulsive triple-wise interactions within a triangle and (iii) attractive triple-wise interactions within a line between the nearest adatoms. The attractive interactions surmount the repulsive forces, hence resulting in the formation of stable clusters from Ni adatoms. The magnetic moment and the effective charge (within both Mulliken and Bader approaches) of the outer atoms in Ni nanoparticles increase as compared to those for the smooth Ni(111) surface. The calculated electronic charge redistribution in the Ni nanoclusters features them as possible adsorption centers with increasing catalytic activity, e.g., for further synthesis of carbon nanotubes.
First-principle studies on the electronic structure of Fe3O4(110) surface
Institute of Scientific and Technical Information of China (English)
LI Yan-li; YAO Kai-lun; LIU Zu-li
2007-01-01
The first-principle was employed to study the six possible models for the Fe3O4(110) surface, namely the AB-terminated surface (AB model), the AB-terminated with Fen vacancy (AB-FeA vac model), the AB-terminated with FeB vacancy (AB-FeB vac model), the B-terminated surface (B model), the B-terminated surface with FeB vacancy (B-FeB vac model) and the B-terminated surface with O vacancy (B-O vac model). The stability, the electronic structure and the magnetic properties of the six surface models were also calculated. The results predict that the B-O vac model is more stable than other types of surface models. The half-metallic property remain in the AB and B models, while the other four surface models exhibit metallic properties. At the same time, the AB, AB-FeAvac, AB-FeB vac, B and the B-FeB vac models have ferrimagnetic properties, while the B-O vac model has antiferromagnetic property.
Energy Technology Data Exchange (ETDEWEB)
Mundy, C; Kuo, I W
2005-06-08
successfully applied to studying the complex problems put forth by atmospheric chemists. To date, the majority of the molecular models of atmospherically relevant interfaces have been comprised of two genres of molecular models. The first is based on empirical interaction potentials. The use of an empirical interaction potential suffers from at least two shortcomings. First, empirical potentials are usually fit to reproduce bulk thermodynamic states, or gas phase spectroscopic data. Thus, without the explicit inclusion of charge transfer, it is not at all obvious that empirical potentials can faithfully reproduce the structure at a solid-vapor, or liquid-vapor interface where charge rearrangement is known to occur (see section 5). One solution is the empirical inclusion of polarization effects. These models are certainly an improvement, but still cannot offer insight into charge transfer processes and are usually difficult to parameterize. The other shortcoming of empirical models is that, in general, they cannot describe bond-making/breaking events, i.e. chemistry. In order to address chemistry one has to consider an ab initio (to be referred to as first-principles throughout the remaining text) approach to molecular modeling that explicitly treats the electronic degrees of freedom. First-principles modeling also give a direct link to spectroscopic data and chemistry, but at a large computational cost. The bottle-neck associated with first-principles modeling is usually determined by the level of electronic structure theory that one chooses to study a particular problem. High-level first-principles approaches, such as MP2, provide accurate representation of the electronic degrees of freedom but are only computationally tractable when applied to small system sizes (i.e. 10s of atoms). Nevertheless, this type of modeling has been extremely useful in deducing reaction mechanisms of atmospherically relevant chemistry that will be discussed in this review (see section 4). However
First-principles study and electronic structures of Mn-doped ultrathin ZnO nanofilms
Institute of Scientific and Technical Information of China (English)
E. Salmani; A. Benyoussef; H. Ez-Zahraouy; E. H. Saidi; O. Mounkachi
2012-01-01
The first-principles density functional calculation is used to investigate the electronic structures and magnetic properties of Mn-doped and N-co-doped ZnO nanofilms.The band structure calculation shows that the band gaps of ZnO films with 2,4,and 6 layers are larger than the band gap of the bulk with wurtzite structure and decrease with the increase of film thickness.However,the four-layer ZnO nanofilms exhibit ferromagnetic phases for Mn concentrations less than 24％ and 12％ for Mn-doping performed in the whole layers and two layers of the film respectively,while they exhibit spin glass phases for higher Mn concentrations.It is also found,on the one hand,that the spin glass phase turns into the ferromagnetic one,with the substitution of nitrogen atoms for oxygen atoms,for nitrogen concentrations higher than 16％ and 5％ for Mn-doping performed in the whole layers and two layers of the film respectively.On the other hand,the spin-glass state is more stable for ZnO bulk containing 5％ of Mn impurities,while the ferromagnetic phase is stable by introducing the p-type carriers into the bulk system.Moreover,it is shown that using the effective field theory for ferromagnetic system,the Curie temperature is close to the room temperature for the undamped Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction.
Saikia, Nabanita; Pati, Swapan K.; Deka, Ramesh C.
2012-09-01
One-dimensional nanostructures such as nanowires and nanotubes are stimulating tremendous research interest due to their structural, electronic and magnetic properties. We perform first principles calculation using density functional theory on the structural, and electronics properties of BNNTs adsorbed with isoniazid (INH) drug via noncovalent functionalization using the GGA/PBE functional and DZP basis set implemented in SIESTA program. The band structure, density of states and projected density of states (PDOS) plots suggest that isoniazid prefers to get adsorbed at the hollow site in case of (5,5) BNNT, whereas in (10,0) BNNT it favours the bridge site. The adsorption energy of INH onto (5,5) BNNT is smaller than in (10,0) BNNT which proposes that (10,0) BNNT with a larger radius compared to (5,5) BNNT is more favourable for INH adsorption as the corresponding distortion energy will also be quite lower. Functionalization of (5,5) and (10,0) BNNTs with isoniazid displays the presence of new impurity states (dispersionless bands) within the HOMO-LUMO energy gap of pristine BNNT leading to an increase in reactivity of the INH/BNNT system and lowering of the energy gap of the BNNTs. The PDOS plots show the major contribution towards the dispersionless impurity states is from INH molecule itself rather than from BNNT near the Fermi energy region. To summarize, noncovalent functionalization of BNNTs with isoniazid drug modulates the electronic properties of the pristine BNNT by lowering its energy gap with respect to the Fermi level, as well as demonstrating the preferential site selectivity for adsorption of isoniazid onto the nanotube sidewalls of varying chirality.
Chang, Jing; Zhao, Guo-Ping; Zhou, Xiao-Lin; Liu, Ke; Lu, Lai-Yu
2012-10-15
The structure and mechanical properties of tantalum mononitride (TaN) are investigated at high pressure from first-principles using the plane wave pseudopotential method within the local density approximation. Three stable phases were considered, i.e., two hexagonal phases (ε and θ) and a cubic δ phase. The obtained equilibrium structure parameters and ground state mechanical properties are in excellent agreement with the experimental and other theoretical results. A full elastic tensor and crystal anisotropy of the ultra-incompressible TaN in three stable phases are determined in the wide pressure range. Results indicated that the elastic properties of TaN in three phases are strongly pressure dependent. And the hexagonal θ-TaN is the most ultraincompressible among the consider phases, which suggests that the θ phase of TaN is a potential candidate structure to be one of the ultraincompressible and hard materials. By the elastic stability criteria, it is predicted that θ-TaN is not stable above 53.9 GPa. In addition, the calculated B/G ratio indicated that the ε and δ phases possess brittle nature in the range of pressure from 0 to 100 GPa. While θ phase is brittleness at low pressure (below 8.2 GPa) and is strongly prone to ductility at high pressure (above 8.2 GPa). The calculated elastic anisotropic factors for three phases of TaN suggest that they are elastically highly anisotropic and strongly dependent on the propagation direction.
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.
First Principles Modeling of Phonon Heat Conduction in Nanoscale Crystalline Structures
Energy Technology Data Exchange (ETDEWEB)
Sandip Mazumder; Ju Li
2010-06-30
of optical phonons, and (2) by developing a suite of numerical algorithms for solution of the BTE for phonons. The suite of numerical algorithms includes Monte Carlo techniques and deterministic techniques based on the Discrete Ordinates Method and the Ballistic-Diffusive approximation of the BTE. These methods were applied to calculation of thermal conductivity of silicon thin films, and to simulate heat conduction in multi-dimensional structures. In addition, thermal transport in silicon nanowires was investigated using two different first principles methods. One was to apply the Green-Kubo formulation to an equilibrium system. The other was to use Non-Equilibrium Molecular Dynamics (NEMD). Results of MD simulations showed that the nanowire cross-sectional shape and size significantly affects the thermal conductivity, as has been found experimentally. In summary, the project clarified the role of various phonon modes - in particular, optical phonon - in non-equilibrium transport in silicon. It laid the foundation for the solution of the BTE in complex three-dimensional structures using deterministic techniques, paving the way for the development of robust numerical tools that could be coupled to existing device simulation tools to enable coupled electro-thermal modeling of practical electronic/optoelectronic devices. Finally, it shed light on why the thermal conductivity of silicon nanowires is so sensitive to its cross-sectional shape.
First-principle investigations on the structural dynamics of Ti{sub 2}GaN
Energy Technology Data Exchange (ETDEWEB)
Yang, Z.J., E-mail: yzjscu@163.com [School of Science, Zhejiang University of Technology, Hangzhou 310023 (China); Li, J. [School of Material and Chemical Engineering, Hainan University, Key Laboratory of Ministry of Education for Application Technology of Chemical Materials in Hainan Superior Resources, Haikou 570228 (China); Linghu, R.F. [School of Physics, Guizhou Normal College, Guiyang 550018 (China); Cheng, X.L.; Yang, X.D. [Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China)
2013-10-15
Highlights: •Our calculated lattice parameter of Ti{sub 2}GaN shows that c axis is always stiffer than a axis. •The elastic constants investigations demonstrated that the Ti{sub 2}GaN is meta-stable between 350 and 600 GPa. •We observed an abnormal c-axis expansion behavior within 350–600 GPa resulting from the expansion of the Ti–Ti bond length and the increase of the Ti–Ti bond populations. •Study on the density of states we found that the Ti s and p electrons shift towards higher energies with pressure. -- Abstract: We report a first-principle study on the elastic and electronic properties of the nanolaminate Ti{sub 2}GaN. Our calculated lattice parameter shows that c axis is always stiffer than a axis. The elastic constants investigations demonstrated that Ti{sub 2}GaN is stable over a wide pressure range of 0–1000 GPa with the only exception of 350–600 GPa owing to the elastic softening. The softening behaviors of the Young’s and shear moduli are also found in the same pressure range of 350–600 GPa, indicating a structural metastability. Investigation on the axial compressibility we observed an abnormal c-axis expansion behavior within a pressure range of 350–600 GPa, resulting from the expansion of the Ti–Ti bond length and the increase of the Ti–Ti bond population. Study on the density of states (DOSs) we found that the Ti s and Ti p electrons shift towards higher energies with pressure.
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...... function for molecular hydrogen....
A structured modeling approach for dynamic hybrid fuzzy-first principles models
Lith, van Pascal F.; Betlem, Ben H.L.; Roffel, Brian
2002-01-01
Hybrid fuzzy-first principles models can be attractive if a complete physical model is difficult to derive. These hybrid models consist of a framework of dynamic mass and energy balances, supplemented with fuzzy submodels describing additional equations, such as mass transformation and transfer rate
Importance of surface structure on dissolution of fluorite
DEFF Research Database (Denmark)
Godinho, Jose; Piazolo, Sandra; Balic Zunic, Tonci
2014-01-01
Dissolution rates are usually calculated as a function of surface area, which is assumed to remain constant ignoring the changes occurring on the surface during dissolution. Here we present a study of how topography of natural fluorite surfaces with different orientation changes during up to 3200 h...... of dissolution. Results are analyzed in terms of changes in surface area, surface reactivity and dissolution rates. All surfaces studied present fast changes in topography during the initial 200 h of dissolution. The controlling factors that cause the development of topography are the stability of the step edges...... forming the initial surface and its inclination to the closest stable planes, which are specific for each surface orientation. During an initial dissolution regime dissolution rates decrease significantly, even though the total surface area increases. During a second dissolution regime, some surfaces...
Directory of Open Access Journals (Sweden)
Lihua Xiao
2011-06-01
Full Text Available The electronic structure and the optical performance of YB6 were investigated by first-principles calculations within the framework of density functional theory. It was found that the calculated results are in agreement with the relevant experimental data. Our theoretical studies showed that YB6 is a promising solar radiation shielding material for windows.
Canning, Andrew
2013-03-01
Inorganic scintillation phosphors (scintillators) are extensively employed as radiation detector materials in many fields of applied and fundamental research such as medical imaging, high energy physics, astrophysics, oil exploration and nuclear materials detection for homeland security and other applications. The ideal scintillator for gamma ray detection must have exceptional performance in terms of stopping power, luminosity, proportionality, speed, and cost. Recently, trivalent lanthanide dopants such as Ce and Eu have received greater attention for fast and bright scintillators as the optical 5d to 4f transition is relatively fast. However, crystal growth and production costs remain challenging for these new materials so there is still a need for new higher performing scintillators that meet the needs of the different application areas. First principles calculations can provide a useful insight into the chemical and electronic properties of such materials and hence can aid in the search for better new scintillators. In the past there has been little first-principles work done on scintillator materials in part because it means modeling f electrons in lanthanides as well as complex excited state and scattering processes. In this talk I will give an overview of the scintillation process and show how first-principles calculations can be applied to such systems to gain a better understanding of the physics involved. I will also present work on a high-throughput first principles approach to select new scintillator materials for fabrication as well as present more detailed calculations to study trapping process etc. that can limit their brightness. This work in collaboration with experimental groups has lead to the discovery of some new bright scintillators. Work supported by the U.S. Department of Homeland Security and carried out under U.S. Department of Energy Contract no. DE-AC02-05CH11231 at Lawrence Berkeley National Laboratory.
Sandratskii, L. M.
2017-07-01
The purpose of the paper is to gain deeper insight into microscopic formation of the Dzyaloshinskii-Moriya interaction (DMI). The paper aims at the development of the physical picture able to address apparently contradicting conclusions of recent studies concerning the location of the DMI energy in the real and reciprocal spaces as well as the relation between values of the atomic moments and the DMI strength. The main tools of our study are the first-principles calculations of the energies of the spiral magnetic states with opposite chiralities. We suggest a method of the calculation of the spiral structures with account for the spin-orbit coupling (SOC). It is based on the application of the generalized Bloch theorem and generalized Bloch functions and allows to reduce the consideration of arbitrary incommensurate spiral to small chemical unit cell. The method neglects the anisotropy in the plane orthogonal to the rotation axis of the spirals that does not influence importantly the DMI energy. For comparison, the supercell calculation with full account for the SOC is performed. The concrete calculations are performed for the Co/Pt bilayer. We consider the distribution of the DMI energy in both real and reciprocal spaces and the dependence of the DMI on the number of electrons. The results of the calculations reveal a number of energy compensations in the formation of the DMI. Thus, the partial atomic contributions as functions of the spiral wave vector q are nonmonotonic and have strongly varying slopes. However, in the total DMI energy these atom-related features compensate each other, resulting in a smooth q dependence. The reason for the peculiar form of the partial DMI contributions is a q -dependent difference in the charge distribution between q and -q spirals. The strongly q -dependent relation between atomic contributions shows that the real-space distribution of the DMI energy obtained for a selected q value cannot be considered as a general
Electronic structures of long periodic stacking order structures in Mg: A first-principles study
Energy Technology Data Exchange (ETDEWEB)
Wang, William Yi, E-mail: yuw129@psu.edu [Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802 (United States); State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Shang, Shun Li; Wang, Yi [Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802 (United States); Darling, Kristopher A. [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Kecskes, Laszlo J. [U.S. Army Research Laboratory, Weapons and Materials Research Directorate, RDRL-WMM-B, Aberdeen Proving Ground, MD 21005 (United States); Mathaudhu, Suveen N. [Materials Science Division, U.S. Army Research Office, Research Triangle Park, NC 27709 (United States); Hui, Xi Dong [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Liu, Zi-Kui, E-mail: dr.liu@psu.edu [Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802 (United States)
2014-02-15
Graphical abstract: -- Highlight: • Formation energies of the LPSOs (γ{sub LPSO}) can be scaled with respect to the formation energy of I2. • γ{sub LPSO} depends on the number of fault layers. • Electron structures of the 10H, 14H, 18R and 24R originate from those of I2. • Electron structure and formation energy of the 6H are between those of I1 and I2. -- Abstract: Long period stacking order (LPSO) structures, such as 6H, 10H, 14H, 18R and 24R, play significant roles in enhancing the mechanical properties of Mg alloys and have been largely investigated separately. In the present work, through detailed investigations of deformation electron density, we show that the electron structures of 10H, 14H, 18R and 24R LPSO structures in Mg originate from those of deformation stacking faults in Mg, and their formation energies can be scaled with respect to formation energy and the number of layers of deformation stacking faults, while the electron structure and formation energy of the 6H LPSO structure are between those of deformation and growth stacking faults. The simulated images of high resolution transmission electron microscopy compare well with experimental observed ones. The understanding of LPSO structures in Mg enables future quantitative investigations of effects of alloying elements on properties of LPSO structures and Mg alloys.
Directory of Open Access Journals (Sweden)
Benabadji M.K.
2013-09-01
Full Text Available First-principles calculations have been carried out to investigate the structural properties and electronic structure of the main binary Laves phase YCu2 and YZn2 with C14, C14, C36 and CeCu2 structures in Cu-Y-Zn alloy, respectively. The total energies of Laves phases with various occupations of nonequivalent lattice sites in all four structural forms have been calculated Ab initio by a pseudopotential VASP code. The optimized structural parameters were in very good agreement with the experimental values. The calculated heat of formation showed that the CeCu2-YCu2 and YZn2 Laves phase was of the strongest alloying ability and structural stability. The electronic density of states (DOS and charge density distribution were given.
First-principles study of the structural stability and electronic structures of TaN
Energy Technology Data Exchange (ETDEWEB)
Cao, C.L.; Yuan, G. [School of Information and Engineering, Ocean University of China, QingDao 266100 (China); Hou, Z.F. [Department of Physics, Fudan University, Shanghai 200433 (China)
2008-08-15
Using the plane-wave pseudopotential method within the generalized gradient approximation, we have studied the structural stability and electronic structures for several TaN phases. Our results show CoSn is the calculated ground-state structure of TaN among the five crystallographic structures that have been studied. The order of energetic stability of phase structures of TaN from low to high is: CsCl
Optical properties of Cr3+ in fluorite-structure hosts and in MgF*2
Payne, Stephen A.; Chase, L. L.; Krupke, William F.
1987-03-01
We have examined the optical properties of Cr3+ in MgF2 and in the fluorite-structure hosts: CdF2, CaF2, SrF2, and BaF2. The properties of Cr3+ in MgF2 are similar to those observed for other fluoride crystals that have octahedral substitutional metal sites. Interestingly, Cr3+ is also found to be sixfold coordinated in the fluorite hosts, despite the fact that the metal sites of these crystal lattices are eightfold coordinated. The smaller ionic radius of Cr3+ compared to, say, Ca2+, undoubtedly results in considerable relaxation at the metal site. However, the crystal field stabilization energy present in the 4A2(d3) ground state also provides for the energetic preference of sixfold vs eightfold coordination. The similarity of the observed absorption spectra of Cr3+ in MgF2 and in fluorite give evidence that the ground state is octahedrally coordinated in all of these hosts. The reduction of this electronic stabilization energy in the 4T2(d3) excited state is considered to produce a configurational shift relative to the ground state. This shift may be the reason why Cr3+ luminesces effectively in MgF2 whereas it is largely quenched in the fluorite-structure materials.
Electronic structures of N- and C-doped NiO from first-principles calculations
2010-01-01
The large intrinsic band gap of NiO has hindered severely its potential application under visible-light irradiation. In this study, we have performed first-principles calculations on the electronic properties of N- and C-doped NiO to ascertain if its band gap may be narrowed theoretically. It was found that impurity bands driven by N 2p or C 2p states appear in the band gap of NiO and that some of these locate at the conduction band minimum, which leads to a significant band gap narrowing. Ou...
Experimental and first principle studies on electronic structure of BaTiO{sub 3}
Energy Technology Data Exchange (ETDEWEB)
Sagdeo, Archna, E-mail: archnaj@rrcat.gov.in; Ghosh, Haranath, E-mail: archnaj@rrcat.gov.in; Chakrabarti, Aparna, E-mail: archnaj@rrcat.gov.in; Kamal, C., E-mail: archnaj@rrcat.gov.in; Ganguli, Tapas, E-mail: archnaj@rrcat.gov.in; Deb, S. K. [Indus Synchrotrons Utilization Division, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India); Phase, D. M. [IUC-DAEF, University Campus, Khandwa Road, Indore-452017 (India)
2014-04-24
We have carried out photoemission experiments to obtain valence band spectra of various crystallographic symmetries of BaTiO{sub 3} system which arise as a function of temperature. We also present results of a detailed first principle study of these symmetries of BaTiO{sub 3} using generalized gradient approximation for the exchange-correlation potential. Here we present theoretical results of density of states obtained from DFT based simulations to compare with the experimental valence band spectra. Further, we also perform calculations using post density functional approaches like GGA + U method as well as non-local hybrid exchange-correlation potentials like PBE0, B3LYP, HSE in order to understand the extent of effect of correlation on band gaps of different available crystallographic symmetries (5 in number) of BaTiO{sub 3}.
Energy Technology Data Exchange (ETDEWEB)
Yu, Ching-Feng [Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Cheng, Hsien-Chie, E-mail: hccheng@fcu.edu.tw [Department of Aerospace and Systems Engineering, Feng Chia University, Taichung 40724, Taiwan (China); Chen, Wen-Hwa, E-mail: whchen@pme.nthu.edu.tw [Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan (China)
2015-01-15
Highlights: • The mechanical and thermodynamic properties of AuIn{sub 2} are reported for the first time. • The calculated lattice constants and elastic properties of AuIn{sub 2} are consistent with the literature data. • The results reveal that AuIn{sub 2} demonstrates low elastic anisotropy, low hardness and high ductility. • It is worth to note that the anisotropic AuIn{sub 2} tends to become elastically isotropic as hydrostatic pressure increases. - Abstract: The structural, mechanical and thermodynamic properties of cubic AuIn{sub 2} crystal in the cubic fluorite structure, and also their temperature, hydrostatic pressure and direction dependences are investigated using first-principles calculations based on density functional theory (DFT) within the generalized gradient approximation (GGA). The optimized lattice constants of AuIn{sub 2} single crystal are first evaluated, by which its hydrostatic pressure-dependent elastic constants are also derived. Then, the hydrostatic pressure-dependent mechanical characteristics of the single crystal, including ductile/brittle behavior and elastic anisotropy, are explored according to the characterized angular character of atomic bonding, Zener anisotropy factor and directional Young’s modulus. Moreover, the polycrystalline elastic properties of AuIn{sub 2}, such as bulk modulus, shear modulus and Young’s modulus, and its ductile/brittle and microhardness characteristics are assessed versus hydrostatic pressure. Finally, the temperature-dependent Debye temperature and heat capacity of AuIn{sub 2} single crystal are investigated by quasi-harmonic Debye modeling. The present results reveal that AuIn{sub 2} crystal demonstrates low elastic anisotropy, low hardness and high ductility. Furthermore, its heat capacity strictly follows the Debye T{sup 3}-law at temperatures below the Debye temperature, and reaches the Dulong–Petit limit at temperatures far above the Debye temperature.
First-principles prediction of oxygen octahedral rotations in perovskite-structure EuTiO_{3}
Rushchanskii, Konstantin Z.; Spaldin, Nicola A.; Marjana Le\\ueai\\u
2012-01-01
We present a systematic first-principles study of the structural and vibrational properties of perovskite-structure EuTiO3. Our calculated phonon spectrum of the high-symmetry cubic structural prototype shows strong M-and R-point instabilities, indicating a tendency to symmetry-lowering structural deformations composed of rotations and tilts of the oxygen octahedra. Subsequent explicit study of 14 different octahedral tilt-patterns showed that the I4/mcm, Imma, and R (3) over barc structures,...
Energy Technology Data Exchange (ETDEWEB)
Kanagaprabha, S. [Department of Physics, Kamaraj College, Tuticorin, Tamil nadu-628003 (India); Rajeswarapalanichamy, R., E-mail: rrpalanichamy@gmail.com; Sudhapriyanga, G., E-mail: rrpalanichamy@gmail.com; Murugan, A., E-mail: rrpalanichamy@gmail.com; Santhosh, M., E-mail: rrpalanichamy@gmail.com [Department of Physics, N.M.S.S.V.N College, Madurai, Tamilnadu-625019 (India); Iyakutti, K. [Department of Physics and Nanotechnology, SRM University, Chennai, Tamilnadu-603203 (India)
2014-04-24
The electronic, structural and mechanical properties of ZrH and ZrH{sub 2} are investigated by means of first principles calculation based on density functional theory as implemented in VASP code with generalized gradient approximation. The calculated ground state properties are in good agreement with previous experimental and other theoretical results. Among the six crystallographic structures considered for ZrH, ZB phase is found to be the most stable phase, whereas ZrH{sub 2} is energetically stable in tetragonal structure at ambient condition. A structural phase transition from ZB→NaCl at a pressure 10 GPa is predicted for ZrH.
Phase stability and electronic structure of UMo2Al20: A first-principles study
Liu, Peng-Chuang; Xian, Ya-Jiang; Wang, Xin; Zhang, Yu-Ting; Zhang, Peng-Cheng
2017-09-01
In this paper, the phase stability of UMo2Al20 was explored using cluster formula in combination with first-principles calculations. Cluster formula analysis uncovered that the compound was composed of two principal clusters, i.e. [Mo-Al12] and [U-Al16]. The electronic interactions between U, Mo and Al atoms in this compound were discussed using elastic property, Bader charges and energy-resolved local bonding analysis, as well as the electronic interactions between Mo and Al atoms in [Mo-Al12] cluster and between U and Al atoms in [U-Al16] cluster. It revealed that UMo2Al20 satisfied the mechanical stability criterion for cubic system, and exhibited near ionic bonding character with weak bonding directionality. The calculations within both standard DFT and HSE frameworks demonstrated that U and Al atoms acted as an electron donor while Mo atoms acted as electron acceptor. The intrinsic stability of UMo2Al20 mainly stemmed from the bonding states of Mo-Al bonds and Al-Al bonds in [Mo-Al12] cluster. These calculations provide a further insight on the CeCr2Al20-type ternary compounds.
Energy Technology Data Exchange (ETDEWEB)
Lu, Peng-Xian, E-mail: pengxian_lu@haut.edu.cn; Xia, Yi
2017-05-01
How to further optimize the thermoelectric figure of merit of silicon (Si) nanostructure? Constructing the layered structure composed of two different Si nano morphologies should be viewed an effective approach. The figure of merit of the layered structure could be further optimized by tuning the different contribution from the composed nano morphologies on the electron and phonon transport. In order to reveal the thermoelectric transport mechanism, the electronic structure, the lattice dynamics and the thermoelectric properties of Si nanosphere, Si nanoribbon and the layered structure composed of the two nano morphologies were investigated through first-principles calculation, lattice dynamics simulation and Boltzmann transport theory. The results suggest that the figure of merit of the layered structure is improved significantly in whole although its specific thermoelectric parameters are unsatisfactory as compared to the single nano morphologies. Therefore we provide a complete understanding on the thermoelectric transport of the layered structure and an effective route to further optimize the figure of merit of Si nanostructure.
First-principles prediction of oxygen octahedral rotations in perovskite-structure EuTiO3
Rushchanskii, Konstantin Z.; Spaldin, Nicola A.; Ležaić, Marjana
2012-03-01
We present a systematic first-principles study of the structural and vibrational properties of perovskite-structure EuTiO3. Our calculated phonon spectrum of the high-symmetry cubic structural prototype shows strong M- and R-point instabilities, indicating a tendency to symmetry-lowering structural deformations composed of rotations and tilts of the oxygen octahedra. Subsequent explicit study of 14 different octahedral tilt-patterns showed that the I4/mcm, Imma, and R3¯c structures, all with antiferrodistortive rotations of the octahedra, have significantly lower total energy than the prototype Pm3¯m structure. We discuss the dynamical stability of these structures, and the influence of the antiferrodistortive structural distortions on the vibrational, optical, and magnetic properties of EuTiO3, in the context of recent unexplained experimental observations.
First-principles study of electronic structure, optical and phonon properties of α-ZrW2O8
Li, Jinping; Meng, Songhe; Qin, Liyuan; Lu, Hantao
2016-12-01
ZrW2O8 exhibits isotropic negative thermal expansions over its entire temperature range of stability, yet so far its physical properties and mechanism have not been fully addressed. In this article, the electronic structure, elastic, thermal, optical and phonon properties of α-ZrW2O8 are systematically investigated from first principles. The agreements between the generalized gradient approximation (GGA) calculation and experiments are found to be quite satisfactory. The calculation results can be useful in relevant material designs, e.g., when ZrW2O8 is employed to adjust the thermal expansion coefficient of ceramic matrix composites.
First-principles DFT+\\emph{U} study of structural and electronic properties of PbCrO$_{3}$
Wang, Bao-Tian; Yin, Wen; Li, Wei-Dong; Wang, Fangwei
2010-01-01
We have performed a systematic first-principles investigation to calculate the structural, electronic, and magnetic properties of PbCrO$_{3}$, CrPbO$_{3}$ as well as their equiproportional combination. The local density approximation (LDA)$+U$ and the generalized gradient approximation$+U$ theoretical formalisms have been used to account for the strong on-site Coulomb repulsion among the localized Cr 3d electrons. By choosing the Hubbard \\emph{U} parameter around 4 eV, ferromagnetic, and/or a...
First-Principles Band Calculations on Electronic Structures of Ag-Doped Rutile and Anatase TiO2
Institute of Scientific and Technical Information of China (English)
HOU Xing-Gang; LIU An-Dong; HUANG Mei-Dong; LIAO Bin; WU Xiao-Ling
2009-01-01
The electronic structures of Ag-doped rutile and anatase TiO2 are studied by first-principles band calculations based on density funetionai theory with the full-potentiai linearized-augraented-plane-wave method.New occupied bands ore found between the band gaps of both Ag-doped rutile and anatase TiO2.The formation of these new bands Capri be explained mainly by their orbitals of Ag 4d states mixed with Ti 3d states and are supposed to contribute to their visible light absorption.
Institute of Scientific and Technical Information of China (English)
ZHOU Junzhe; WANG Chongyu
2005-01-01
The effects of Si doping on geometric and electronic structure of closed carbon nanotube (CNT) are studied by, a first-principles method, DMol. It is found that the local density of states at the Fermi level (EF) increases due to the Si-doping and the non-occupied states above the EF go down toward the lower energy range under an external electronic field. In addition, due to the doping of Si, a sub-tip on the CNT cap is formed, which consisted of the Si atom and its neighbor C atoms. From these results it is concluded that Si-doping is beneficial to the CNT field emission properties.
Energy Technology Data Exchange (ETDEWEB)
Kizaki, H., E-mail: hkizaki@aquarius.mp.es.osaka-u.ac.j [Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 567-8531 (Japan); Toyoda, M.; Sato, K. [The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Katayama-Yoshida, H. [Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 567-8531 (Japan); The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)
2009-12-15
Electronic structure of TiO{sub 2} (rutile) based dilute magnetic semiconductors (DMS) are investigated within self-interaction-corrected local density approximation (SIC-LDA) from first-principles calculation. These results are compared with those calculated within standard LDA. It is found that the calculated band-gap energy in the host TiO{sub 2} is different within the LDA and the SIC-LDA. We find that high-spin state is predicted within the SIC-LDA with oxygen vacancy. The calculated density of states within SIC-LDA is in good agreement with photoemission results.
Jiao, Zhen; Liu, Qi-Jun; Liu, Fu-Sheng; Tang, Bin
2017-10-01
The structural, electronic and surface properties of low-index surfaces of tetragonal NbAl3 have been studied with first-principles plane-wave ultrasoft pseudo-potential method based on density functional theory. The atomic relaxations, surface energies and work functions are reported. The calculated atomic relaxations and surface energies suggest that the (111) surface is the most stable stoichiometric surface. Furthermore, the Al-terminated (110) surface is thermodynamically stable than other surfaces in both Al-rich and Nb-rich conditions.
Lin, Jingwu; Wang, Lei; Hu, Zhi; Li, Xiao; Yan, Hong
2017-02-01
The structural, thermodynamic, mechanical and electronic properties of cubic Al2Sm intermetallic compound are investigated by the first-principles method on the basis of density functional theory. In light of the strong on-site Coulomb repulsion between the highly localized 4f electrons of Sm atoms, the local spin density approximation approach paired with additional Hubbard terms is employed to achieve appropriate results. Moreover, to examine the reliability of this study, the experimental value of lattice parameter is procured from the analysis of the TEM image and diffraction pattern of Al2Sm phase in the AZ31 alloy to verify the authenticity of the results originated from the computational method. The value of cohesive energy reveals Al2Sm to be a stable in absolute zero Kelvin. According to the stability criteria, the subject of this work is mechanically stable. Afterward, elastic moduli are deduced by performing Voigt-Reuss-Hill approximation. Furthermore, elastic anisotropy and anisotropy of sound velocity are discussed. Finally, the calculation of electronic density of states is implemented to explore the underlying mechanism of structural stability.
Rong, Ximing; Chen, Jun; Li, Jing-Tian; Zhuang, Jun; Ning, Xi-Jing
2015-12-01
A first-principles calculation of the structural stability and mechanical property of Ni(111)-graphene-Ni(111) layered composite was presented. Three different structural models were considered, and the most stable interfacial structure had been determined with top-fcc structure in both sides of graphene. Stretching calculations demonstrate that the tensile stress of the composite can reach twice of that of pure Ni in the ranges of 0-0.2 strain. The Young’s modulus in triaxial directions are 384 (x), 362 (y), and 303 (z) GPa for the Ni(111)-graphene-Ni(111) structure, and 212 (x), 251 (y), and 273 (z) GPa for pure single-crystal Ni(111).
First-principles study on the adsorption properties of phenylalanine on carbon graphitic structures
Kang, Seoung-Hun; Kwon, Dae-Gyeon; Park, Sora; Kwon, Young-Kyun
2015-12-01
Using ab-initio density functional theory, we investigate the binding properties of phenylalanine, an amino acid, on graphitic carbon structures, such as graphene, nanotubes, and their modified structures. We focus especially on the effect of the adsorbate on the geometrical and the electronic structures of the absorbents. The phenylalanine molecule is found to bind weakly on pristine graphitic structures with a binding energy of 40-70 meV and not to change the electronic configuration of the graphitic structures, implying that the phenylalanine molecule may not be detected on pristine graphitic structures. On the other hand, the phenylalanine molecule exhibits a substantial increase in its binding energy up to ~2.60 eV on the magnesium-decorated boron-doped graphitic structures. We discover that the Fermi level of the system, which was shifted below the Dirac point of the graphitic structures due to p-doping by boron substitution, can be completely restored to the Dirac point because of the amino acid adsorption. This behavior implies that such modified structures can be utilized to detect phenylalanine molecules.
Energy Technology Data Exchange (ETDEWEB)
Chou, M.Y.
1992-04-01
This report discusses the following topics: calculation of the Structural Properties of Yttrium; dynamical and pairing properties of {alpha}-YH{chi}; electronic and structural properties of YH{sub 2} and YH{sub 3}; phase diagram of hydrogen on Ru(000); peierls distortion in hexagonal YH{sub 3}; and study of hydrogen in niobium and palladium.
DEFF Research Database (Denmark)
Damager, Iben; Engelsen, Søren Balling; Blennow, Per Gunnar Andreas
2010-01-01
A study was conducted to demonstrate the synthesis, conformation, and hydration of the α-glucan structures of starch. Starch and glycogen were synthesized by sets of specific enzyme activities that directly determined their molecular structures and physical properties. It was demonstrated that th...
Sahara, Ryoji; Emura, Satoshi; Ii, Seiichiro; Ueda, Shigenori; Tsuchiya, Koichi
2014-06-01
The electronic structures and structural properties of body-centered cubic Ti-Mo alloys were studied by first-principles calculations. The special quasirandom structures (SQS) model was adopted to emulate the solid solution state of the alloys. The valence band electronic structures of Ti-Mo and Ti-Mo-Fe alloys were measured by hard x-ray photoelectron spectroscopy. The structural parameters and valence band photoelectron spectra were calculated using first-principles calculations. The results obtained with the SQS models showed better agreement with the experimental results than those obtained using the conventional ordered structure models. This indicates that the SQS model is effective for predicting the various properties of solid solution alloys by means of first-principles calculations.
Energy Technology Data Exchange (ETDEWEB)
Long, Jianping, E-mail: longjianping@cdut.cn [College of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology, Chengdu 610059 (China); Shu, Chaozhu [The Mineral Resources Chemistry Key Laboratory of Sichuan Higher Education Institutions, Chengdu University of Technology, Chengdu 610059 (China); Yang, Lijun; Yang, Mei [College of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology, Chengdu 610059 (China)
2015-09-25
Graphical abstract: The minimum thermal conductivity as a function of pressure for p-BN. - Highlights: • First-principles calculations were carried out to investigate the physical properties of novel superhard p-BN under pressure. • The calculated Vicker’s hardness of p-BN was 55.4 GPa, which indicates that it is a superhard material. • The elastic constants, polycrystalline modulus and Debye temperature under pressure are obtained. • A new modified Clarke-type equation is used to calculate the minimum thermal conductivity. - Abstract: The first-principles calculations were carried out to investigate the electronic structure, elastic, hardness and thermodynamics properties of novel superhard p-BN under pressure. The calculated lattice parameters are in good agreement with previous theoretical results. The band structure, the density of states and the partial density of states are analyzed, which reveals the insulator character of p-BN. In addition, the elastic constants, polycrystalline modulus and Debye temperature under pressure are also successfully obtained. It is observed that the p-BN should be classified as brittle materials and possesses elastically anisotropic. The calculated Vicker’s hardness of p-BN was 55.4 GPa, which indicates that it is a superhard material. According to the calculated polycrystalline modulus, a new modified Clarke-type equation is used to calculate the minimum thermal conductivity. This work provides a useful guide for designing novel borides materials having excellent mechanical performance.
Settouti, Nadera; Aourag, Hafid
2016-08-01
The structural and mechanical properties of alkali hydrides (LiH, NaH, KH, RbH, and CsH) were investigated via first-principles calculations which cover the optimized structural parameters. The density functional theory in combination with the generalized gradient approximation (GGA) were used in this study. From the present study, one could note that alkali hydrides are brittle materials and mechanically stable. It was found that stiffness and shear resistance are greater in LiH than in other hydrides. It is more brittle in nature, and comparatively harder than the other materials under study; it also presents a high degree of anisotropy. The results were then investigated and analyzed with principal component analysis (PCA), which is one of the most common techniques in multivariate analysis, was used to explore the correlations among material properties of alkali hydrides and to study their trends. The alkali hydrides obtained by the first-principles calculations were also compared with the alkaline-earth metal hydrides (BeH2, MgH2, CaH2, SrH2, and BaH2) and discussed in this work.
First-principles study of structural and electronic properties of different phases of GaAs
Energy Technology Data Exchange (ETDEWEB)
Arabi, H. [Faculty of Science, Department of Physics, University of Birjand, Birjand (Iran, Islamic Republic of)]. E-mail: harabi@birjand.ac.ir; Pourghazi, A. [Faculty of Science, Department of Physics, University of Isfahan, Isfahan (Iran, Islamic Republic of); Ahmadian, F. [Faculty of Science, Department of Physics, University of Birjand, Birjand (Iran, Islamic Republic of); Nourbakhsh, Z. [Faculty of Science, Department of Physics, University of Isfahan, Isfahan (Iran, Islamic Republic of)
2006-03-01
We present a theoretical investigation of structural and electronic properties of the four known structural phases of GaAs (zinc-blende, sc16, cinnabar and Cmcm). We used the full potential linearized augmented plane wave method, within local density approximation, and also within generalized gradient approximation for the exchange correlation potential. The lattice constants, bulk modulus and its pressure derivative are calculated for each of the four phases. The data obtained for the transition pressures between different phases are presented. Band structures and densities of states of the four phases are also given. The results are compared with previous calculations and with experimental results.
First-principles study of structural stabilities of AlH3 under high pressure
Feng, Wenxia; Cui, Shouxin; Feng, Min
2014-07-01
The structural stabilities and electronic properties of AlH3 under high pressure are investigated by using the plane-wave pseudopotential method. Our results demonstrate that the sequence of the pressure-induced phase transition is Fd 3 bar m(β) → cmcm(α ') → R 3 bar c(α) → Pnma(hp 1) → Pm 3 bar n(hp 2), and the transition pressures are 0.49, 0.91, 47, and 70 GPa, respectively. Im 3 bar m , Pnnm(γ) and P63/m structures are not stable in the 0-100 GPa. β, α ', α, and hp1 structures of AlH3 are nonmetals, while Pm 3 bar n structure of AlH3 is metallic, and the pressure-induced metallization is ascribed to phase transition under higher compression.
Liang, Zuozhong; Wang, Wei; Zhang, Min; Wu, Fei; Chen, Jian-Feng; Xue, Chunyu; Zhao, Hong
2017-04-01
The structural, mechanical and thermodynamic properties of ZrO2 polymorphs (namely, monoclinic (P21/c), tetragonal (P42/nmc), cubic (Fm 3 bar m), and orthorhombic (Pbca and Pnma)) are investigated systematically by employing DFT functionals (LDA, PBE and PW91). It is found that the structural parameters of ZrO2 polymorphs calculated by PBE and PW91 functionals are highly consistent with previous experiments with low absolute relative error (ARE). Moreover, all considered structures are mechanically stable according to the Born-Huang criterion and the PBE and PW91 functionals are more accurate than the LDA functional in predicting mechanical and thermodynamic properties. Significantly, we described mechanical and thermodynamic properties of ZrO2 polymorphs by introducing the charge density difference of related surfaces, which provides a better understanding of different behaviors of elastic constants (Cij) in various crystal structures of ZrO2.
First principle investigation of structural and electronic properties of bulk ZnSe
Energy Technology Data Exchange (ETDEWEB)
Khatta, Swati; Tripathi, S. K., E-mail: surya@pu.ac.in; Prakash, Satya [Department of Physics, Center of Advanced Study in Physics, Panjab University, Chandigarh-160 014 (India)
2015-08-28
Electronic and structural properties of ZnSe are investigated using plane-wave self-consistent field method within the framework of density functional theory. The pseudopotential method within the local density approximation is used for the exchange-correlation potential. The equilibrium lattice parameter, static bulk modulus and its pressure derivative are calculated. The electronic band structure, partial density of states and density of states are also obtained. The results are compared with available theoretical calculations and experimental results.
Large-Scale Computations Leading to a First-Principles Approach to Nuclear Structure
Energy Technology Data Exchange (ETDEWEB)
Ormand, W E; Navratil, P
2003-08-18
We report on large-scale applications of the ab initio, no-core shell model with the primary goal of achieving an accurate description of nuclear structure from the fundamental inter-nucleon interactions. In particular, we show that realistic two-nucleon interactions are inadequate to describe the low-lying structure of {sup 10}B, and that realistic three-nucleon interactions are essential.
High pressure structures of "111" type iron-based superconductors predicted from first-principles.
Zhang, Xinxin; Wang, Yanchao; Ma, Yanming
2012-11-21
The high-pressure crystal structures of the "111" type iron-based superconductors: NaFeAs, LiFeP and LiFeAs have been systematically explored by using particle-swarm structural searches. It was found that though these iron-based superconductors are chemically similar, they adopted distinct structural phase transitions: P4/nmm→Cmcm→P3m1 for NaFeAs, P4/nmm→Cmcm→I4mm for LiFeP, and P4/nmm→P3m1 →I4mm→P6(3)/mmc for LiFeAs under high pressure. The high pressure orthorhombic Cmcm phase preserved the structural features of FeX(4)(X = As, P) tetrahedral layers present in the ambient-pressure P4/nmm structure. However, the FeX(4) tetrahedrons in the Cmcm phase were clearly distorted, leading to changes in the electronic behavior around the Fermi level. Under higher pressures, the FeX(4) layered structural features were no longer persistent and three-dimensional crystal structures were stabilized in other P3m1, I4mm, and P6(3)/mmc phases, which featured FeAs(5)/FeAs(6) hexahedron and octahedrons, FeX(5) tetragonal pyramids, and FeAs(6) octahedrons, respectively. Analysis of the electronic density of states suggests that most of the high pressure phases are metallic except for the tetragonal I4mm phase, which possesses a narrow band gap. This semiconducting state might relate to the tetragonal pyramid structure formed by FeX(5) unit, which might be favorable for charge localization.
Magnetism, structure and chemical order in small CoPd clusters: A first-principles study
Energy Technology Data Exchange (ETDEWEB)
Mokkath, Junais Habeeb, E-mail: Junais.Mokkath@kaust.edu.sa
2014-01-15
The structural, electronic and magnetic properties of small Co{sub m}Pd{sub n}(N=m+n=8,m=0−N) nanoalloy clusters are studied in the framework of a generalized-gradient approximation to density-functional theory. The optimized cluster structures have a clear tendency to maximize the number of nearest-neighbor CoCo pairs. The magnetic order is found to be ferromagnetic-like (FM) for all the ground-state structures. Antiferromagnetic-like spin arrangements were found in some low-lying isomers. The average magnetic moment per atom μ{sup ¯}{sub N} increases approximately linearly with Co content. A remarkable enhancement of the local Co moments is observed as a result of Pd doping. This is a consequence of the increase in the number of Co d holes, due to CoPd charge transfer, combined with the reduced local coordination. The influence of spin–orbit interactions on the cluster properties is also discussed. - Highlights: • This work analyses the structural and magnetic properties of CoPd nanoclusters. • The magnetic order is found to be ferromagnetic-like for all the ground-state structures. • The average magnetic moment per atom increases approximately linearly with Co content. • The influence of spin–orbit interactions on the cluster properties is discussed.
First-principles predicted low-energy structures of NaSc(BH4)4
Tran, Huan Doan; Amsler, Maximilian; Botti, Silvana; Marques, Miguel A. L.; Goedecker, Stefan
2014-03-01
According to previous interpretations of experimental data, sodium-scandium double-cation borohydride NaSc(BH4)4 crystallizes in the crystallographic space group Cmcm where each sodium (scandium) atom is surrounded by six scandium (sodium) atoms. A careful investigation of this phase based on ab initio calculations indicates that the structure is dynamically unstable and gives rise to an energetically and dynamically more favorable phase with C2221 symmetry and nearly identical x-ray diffraction pattern. By additionally performing extensive structural searches with the minima-hopping method we discover a class of new low-energy structures exhibiting a novel structural motif in which each sodium (scandium) atom is surrounded by four scandium (sodium) atoms arranged at the corners of either a rectangle with nearly equal sides or a tetrahedron. These new phases are all predicted to be insulators with band gaps of 7.9-8.2 eV. Finally, we estimate the influence of these structures on the hydrogen-storage performance of NaSc(BH4)4.
Energy Technology Data Exchange (ETDEWEB)
Matar, S.F., E-mail: matar@icmcb-bordeaux.cnrs.fr [CNRS, Universite de Bordeaux, ICMCB, 87 avenue du Docteur Albert Schweitzer, F-33608 Pessac (France); Nakhl, M. [Universite Libanaise, Laboratoire de Chimie-Physique des Materiaux LCPM, Fanar (Lebanon); Al Alam, A.F.; Ouaini, N. [Universite Saint-Esprit de Kaslik, Faculte des Sciences et de Genie Informatique, Jounieh (Lebanon); Chevalier, B. [CNRS, Universite de Bordeaux, ICMCB, 87 avenue du Docteur Albert Schweitzer, F-33608 Pessac (France)
2010-11-25
Graphical abstract: Base centered orthorhombic YNiH{sub X} structure. For x = 3, only H1 and H2 are present. Highest hydrogen content YNiH{sub 4} is obtained when H3 are added. - Abstract: Within density functional theory, establishing the equations of states of YNi in two different controversial structures in the literature, leads to determine the orthorhombic FeB-type as the ground state one with small energy difference. For YNiH{sub 3} and YNiH{sub 4} hydrides crystallizing in the orthorhombic CrB-type structure the geometry optimization and the ab initio determination of the H atomic positions show that the stability of hydrogen decreases from the tri- to the tetra- hydride. New states brought by hydrogen within the valence band lead to its broadening and to enhanced localization of metal density of states. The chemical bonding analysis shows a preferential Ni-H bonding versus Y-H.
First-principles study of structural, elastic and thermodynamic properties of AuIn2
Wu, Hai Ying; Chen, Ya Hong; Deng, Chen Rong; Yin, Peng Fei; Cao, Hong
2015-12-01
The structural, elastic and thermodynamic properties of AuIn2 in the CaF2 structure under pressure have been investigated using ab initio plane wave pseudopotential method within the generalized gradient approximation. The calculated structural parameters and equation of state are in excellent agreement with the available experimental and theoretical results. The elastic constants of AuIn2 at ambient condition are calculated, and the bulk modulus obtained from these calculated elastic constants agrees well with the experimental data. The pressure dependence of the elastic constants, bulk modulus, shear modulus and Young’s modulus has also been investigated. The Debye temperature presents a slight increase with pressure. AuIn2 exhibits ductibility and low hardness characteristics, the ductibility increases while the hardness decreases with the increasing of pressure. The pressure effect on the heat capacity and thermal expansion coefficient for AuIn2 is much larger.
DEFF Research Database (Denmark)
Zeng, Zhenhua; Kubal, Joseph; Greeley, Jeffrey Philip
2015-01-01
In the present study, on the basis of detailed density functional theory (DFT) calculations, and using Ni hydroxy(oxide) films on Pt(111) and Au(111) electrodes as model systems, we describe a detailed structural and electrocatalytic analysis of hydrogen evolution (HER) at three-phase boundaries...... of information that is inaccessible by purely experimental means, and these structures, in turn, strongly suggest that a bifunctional reaction mechanism for alkaline HER will be operative at the interface between the films, the metal substrates, and the surrounding aqueous medium. This bifunctionality produces...... important changes in the calculated barriers of key elementary reaction steps, including water activation and dissociation, as compared to traditional monofunctional Pt surfaces. The successful identification of the structures of thin metal films and three-phase boundary catalysts is not only an important...
Structure of a 13-fold superhelix (almost determined from first principles
Directory of Open Access Journals (Sweden)
Guillaume A. Schoch
2015-03-01
Full Text Available Nuclear hormone receptors are cytoplasm-based transcription factors that bind a ligand, translate to the nucleus and initiate gene transcription in complex with a co-activator such as TIF2 (transcriptional intermediary factor 2. For structural studies the co-activator is usually mimicked by a peptide of circa 13 residues, which for the largest part forms an α-helix when bound to the receptor. The aim was to co-crystallize the glucocorticoid receptor in complex with a ligand and the TIF2 co-activator peptide. The 1.82 Å resolution diffraction data obtained from the crystal could not be phased by molecular replacement using the known receptor structures. HPLC analysis of the crystals revealed the absence of the receptor and indicated that only the co-activator peptide was present. The self-rotation function displayed 13-fold rotational symmetry, which initiated an exhaustive but unsuccessful molecular-replacement approach using motifs of 13-fold symmetry such as α- and β-barrels in various geometries. The structure was ultimately determined by using a single α-helix and the software ARCIMBOLDO, which assembles fragments placed by PHASER before using them as seeds for density modification model building in SHELXE. Systematic variation of the helix length revealed upper and lower size limits for successful structure determination. A beautiful but unanticipated structure was obtained that forms superhelices with left-handed twist throughout the crystal, stabilized by ligand interactions. Together with the increasing diversity of structural elements in the Protein Data Bank the results from TIF2 confirm the potential of fragment-based molecular replacement to significantly accelerate the phasing step for native diffraction data at around 2 Å resolution.
Structural and electronic phase transitions of ThS2 from first-principles calculations
Guo, Yongliang; Wang, Changying; Qiu, Wujie; Ke, Xuezhi; Huai, Ping; Cheng, Cheng; Zhu, Zhiyuan; Chen, Changfeng
2016-10-01
Thorium and its compounds have received considerable attention in recent years due to the renewed interest in developing the thorium fuel cycle as an alternative nuclear energy technology. There is pressing current need to explore the physical properties essential to the fundamental understanding and practical application of these materials. Here we report on a computational study of thorium disulfide (ThS2), which plays an important role in the thorium fuel reprocessing cycle. We have employed the density functional theory and evolutionary structure search methods to determine the crystal structures, electronic band structures, phonon dispersions and density of states, and thermodynamic properties of ThS2 under various pressure and temperature conditions. Our calculations identify several crystalline phases of ThS2 and a series of structural phase transitions induced by pressure and temperature. The calculated results also reveal electronic phase transitions from the semiconducting state in the low-pressure phases of ThS2 in the P n m a and F m 3 ¯m symmetry to the metallic state in the high-pressure phases of ThS2 in the P n m a and I 4 /m m m symmetry. These results explain the experimental observation of the thermodynamic stability of the P n m a phase of ThS2 at the ambient conditions and a pressure-induced structural phase transition in ThS2 around 40 GPa. Moreover, the present study reveals considerable additional information on the structural and electronic properties of ThS2 in a wide range of pressure and temperature. Such information provides key insights into the fundamental material behavior and the underlying mechanisms that lay the foundation for further exploration and application of ThS2.
Pasianot, Roberto C.
2016-12-01
We study the structure of several standard and non-standard self-interstitial configurations in a series of hcp metals, by using Density Functional Theory as embodied in the computer codes SIESTA and WIEN2k. The considered metals include Be, Mg, Ti, Zr, Co, Zn, and Cd, thus spanning the whole range of experimental c/a ratios, different kinds of bonding, and even magnetism (Co). The results show the importance of low symmetry configurations, closely related to the non-basal crowdion, in order to rationalize the experimental data on self-interstitial structure and migration.
First-principles study of the structural and electronic properties of III-phosphides
Energy Technology Data Exchange (ETDEWEB)
Ahmed, Rashid [Centre for High Energy Physics, University of the Punjab, Lahore 54590 (Pakistan)], E-mail: rasofi@hotmail.com; Fazal-e-Aleem [Centre for High Energy Physics, University of the Punjab, Lahore 54590 (Pakistan); Hashemifar, S. Javad; Akbarzadeh, Hadi [Department of Physics, Isfahan University of Technology, Isfahan 84156 (Iran, Islamic Republic of)
2008-05-01
We use density functional theory and different forms of the exchange-correlation approximation to calculate the structural and electronic properties of tetrahedrally coordinated III-phosphide semiconductors. The computed results for structural properties using generalized gradient approximation (GGA) agree well with the experimental data. For reliable description of energy band gap values, another form of GGA developed by Engel and Vosko has been applied. As anticipated, boron phosphide was found to be the hardest compound due to the strong B-P covalent bonding.
Energy Technology Data Exchange (ETDEWEB)
Song, T., E-mail: songting_lzjtu@yeah.net [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); School of Material Science and Engineering, Lanzhou University of Technology, Lanzhou 730050 (China); Ma, Q. [School of Material Science and Engineering, Lanzhou University of Technology, Lanzhou 730050 (China); Sun, X.W., E-mail: xsun@carnegiescience.edu [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015 (United States); Liu, Z.J., E-mail: liuzj_lzcu@163.com [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); Department of Physics, Lanzhou City University, Lanzhou 730070 (China); Fu, Z.J. [School of Electrical and Electronic Engineering, Chongqing University of Arts and Sciences, Chongqing 402160 (China); Wei, X.P.; Wang, T.; Tian, J.H. [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China)
2016-09-07
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.
Institute of Scientific and Technical Information of China (English)
Wen Jun; Duan Chang-Kui; Yin Min; Yu.V.Orlovskii; Xia Shang-Da; Zhang Yong-Fan
2012-01-01
The local coordination structures around the doping Yb2+ ions in sodium and potassium halides were calculated by using the first-principles supercell model.Both the cases with and without the charge compensation vacancy in the local environment of the doping Yb2+ were calculated to study the effect of the doping on the local coordination structures of Yb2+.Using the calculated local structures,we obtained the crystal-field parameters for the Yb2+ ions doped in sodium and potassium halides by a method based on the combination of the quantum-chemical calculations and the effective Hamiltonian method.The calculated crystal-field parameters were analyzed and compared with the fitted results.
First-principles study of structural stability and elastic property of pre-perovskite PbTiO3
Institute of Scientific and Technical Information of China (English)
Liu Yong; Ni Li-Hong; Ren Zhao-Hui; Xu Gang; Li Xiang; Song Chen-Lu; Han Gao-Rong
2012-01-01
The structural stability and the elastic properties of a novel structure of lead titanate,which is named preperovskite PbTiO3 (PP-PTO) and is constructed with TiO6 octahedral columns arranged in a one-dimensional manner,are investigated by using first-principles calculations.PP-PTO is energetically unstable compared with conventional perovskite phases,however it is mechanically stable. The equilibrium transition pressures for changing from preperovskite to cubic and tetragonal phases are -0.5 GPa and -1.4 GPa,respectively,with first-order characteristics.Further,the differences in elastic properties between pre-perovskite and conventional perovskite phases are discussed for the covalent bonding network,which shows a highly anisotropic character in PP-PTO.This study provides a crucial insight into the structural stabilities of PP-PTO and conventional perovskite.
First-principles study on adsorption structure and electronic state of stanene on α-alumina surface
Araidai, Masaaki; Kurosawa, Masashi; Ohta, Akio; Shiraishi, Kenji
2017-09-01
The adsorption structure and electronic state of stanene on an α-Al2O3(0001) 1×1 surface were investigated by first-principles calculations. The variation in the electronic state of the adsorbed stanene from that of the free-standing one increased with the stanene-alumina distance, because the strength of the stanene-alumina interaction increased with the distance. The band splitting induced by the Rashba effect was observed in the electronic band structures. It was observed from the band structures with spin-orbit interactions that the degrees of band-gap opening due to the spin-orbit interactions were much lower than that due to the interaction between stanene and the α-alumina surface. By population analyses for chemical bonds, we revealed that the electronic state of stanene on the α-alumina surface was affected by Sn-O bonds with antibonding nature.
First principles calculations of the structural and electronic properties of(CdSe)n clusters
Institute of Scientific and Technical Information of China (English)
WANG Xin-qiang; CHEN Yong
2004-01-01
The structural and electronic properties of (CdSe)n(1≤n≤5) clusters are calculated using density functional theory within the pseudopotential and generalized gradient approximations. The calculated binding energies and highest occupied molecular orbitallowest unoccupied molecular orbital gaps are compared with those obtained within local density approximation.
Structure determination of ultra dense magnesium borohydride: A first-principles study
Fan, Jing; Duan, Defang; Jin, Xilian; Bao, Kuo; Liu, Bingbing; Cui, Tian
2013-06-01
Magnesium borohydride (Mg(BH4)2) is one of the potential hydrogen storage materials. Recently, two experiments [Y. Filinchuk, B. Richter, T. R. Jensen, V. Dmitriev, D. Chernyshov, and H. Hagemann, Angew. Chem., Int. Ed. 50, 11162 (2011);, 10.1002/anie.201100675 L. George, V. Drozd, and S. K. Saxena, J. Phys. Chem. C 113, 486 (2009), 10.1021/jp807842t] found that α-Mg(BH4)2 can irreversibly be transformed to an ultra dense δ-Mg(BH4)2 under high pressure. Its volumetric hydrogen content at ambient pressure (147 g/cm3) exceeds twice of DOE's (U.S. Department of Energy) target (70 g/cm3) and that of α-Mg(BH4)2 (117 g/cm3) by 20%. In this study, the experimentally proposed P42nm structure of δ-phase has been found to be dynamically unstable. A new Fddd structure has been reported as a good candidate of δ-phase instead. Its enthalpy from 0 to 12 GPa is much lower than P42nm structure and the simulated X-ray diffraction spectrum is in satisfied agreement with previous experiments. In addition, the previously proposed P-3m1 structure, which is denser than Fddd, is found to be a candidate of ɛ-phase due to the agreement of Raman shifts.
First-principle simulations of the electronic structure of copper-based oxide superconductors
Yutoh, Y
2003-01-01
The relationship between the transition temperature (T sub c) of an oxide superconductor and strain has been studied by means of experiments, with a focus an specimens that include an interface between a superconductor and a substrate. In the current study, we performed calculations on the bulk and the surface in order to investigate the electronic structures of the above systems. We calculated the electronic structure of La sub 2 CuO sub 4 bulk by employment of three-dimensional boundary conditions and that of a La sub 2 CuO sub 4 surface by employment of two-dimensional boundary conditions. The results for the bulk indicate that a relationship exists between the lattice parameters and T sub c of La sub 2 CuO sub 4. We discuss the calculated results for the bulk and surface on the basis of the results of investigation of the differences in electronic structures. The results indicate that the surface retained the electronic structures of the bulk. (Abstract Copyright [2003], Wiley Periodicals, Inc.)
Structure determination of ultra dense magnesium borohydride: a first-principles study.
Fan, Jing; Duan, Defang; Jin, Xilian; Bao, Kuo; Liu, Bingbing; Cui, Tian
2013-06-07
Magnesium borohydride (Mg(BH4)2) is one of the potential hydrogen storage materials. Recently, two experiments [Y. Filinchuk, B. Richter, T. R. Jensen, V. Dmitriev, D. Chernyshov, and H. Hagemann, Angew. Chem., Int. Ed. 50, 11162 (2011); L. George, V. Drozd, and S. K. Saxena, J. Phys. Chem. C 113, 486 (2009)] found that α-Mg(BH4)2 can irreversibly be transformed to an ultra dense δ-Mg(BH4)2 under high pressure. Its volumetric hydrogen content at ambient pressure (147 g/cm(3)) exceeds twice of DOE's (U.S. Department of Energy) target (70 g/cm(3)) and that of α-Mg(BH4)2 (117 g/cm(3)) by 20%. In this study, the experimentally proposed P4(2)nm structure of δ-phase has been found to be dynamically unstable. A new Fddd structure has been reported as a good candidate of δ-phase instead. Its enthalpy from 0 to 12 GPa is much lower than P4(2)nm structure and the simulated X-ray diffraction spectrum is in satisfied agreement with previous experiments. In addition, the previously proposed P-3m1 structure, which is denser than Fddd, is found to be a candidate of ε-phase due to the agreement of Raman shifts.
Structural and electronic properties of Y2CrS4 from first-principles study
Wang, B.-T.; Yin, W.; Li, W.-D.; Wang, F.
2011-04-01
We systematically study the structural, electronic, and magnetic properties of chromium sulfide Y2CrS4 by using density-functional theory. We find that antiferromagnetic order is more energetically favorable than ferromagnetic state and near the Fermi level the main occupation is from Cr 3 d states.
First principles results of structural and electronic properties of ZnS clusters
Indian Academy of Sciences (India)
D L Lalsare; Anjali Kshirsagar
2012-12-01
We present results of the study of ZnS (1 ≤ ≤ 9) clusters, using the density functional formalism and projector augmented wave method within the generalized gradient approximation. Along with the structural and electronic properties, nature of bonding and overall stability of clusters has been studied.
First principles study of structural and electronic properties of different phases of boron nitride
Energy Technology Data Exchange (ETDEWEB)
Ahmed, Rashid [Centre for High Energy Physics, University of the Punjab, Lahore 54590 (Pakistan)], E-mail: rasofi@hotmail.com; Fazal-e-Aleem [Centre for High Energy Physics, University of the Punjab, Lahore 54590 (Pakistan); Hashemifar, S. Javad; Akbarzadeh, Hadi [Department of Physics, Isfahan University of Technology, 84156 Isfahan (Iran, Islamic Republic of)
2007-11-15
A theoretical study of structural and electronic properties of the four phases of BN (zincblende, wurtzite, hexagonal and rhombohedral) is presented. The calculations are done by full potential (linear) augmented plane wave plus local orbitals (APW+lo) method based on the density functional theory (DFT) as employed in WIEN2k code. Using the local density approximation (LDA) and generalized gradient approximation (GGA-PBE) for the exchange correlation energy functional, we have calculated lattice parameters, bulk modulus, its pressure derivative and cohesive energy. In order to calculate electronic band structure, another form of the generalized gradient approximation proposed by Engel and Vosko (GGA-EV) has been employed along with LDA and GGA-PBE. It is found that all the three approximations exhibit similar band structure qualitatively. However, GGA-EV gives energy band gap values closer to the measured data. Our results for structural and electronic properties are compared with the experimental and other theoretical results wherever these are available.
Poswal, H. K.; Sharma, Surinder M.; Sikka, S. K.
2010-03-01
High-pressure behaviour of superhydrous phase B (high temperature; HT) of Mg10Si3O14(OH)4 (Shy B) is investigated with the help of density functional theory-based first-principles calculations. In addition to the lattice parameters and equation of state, we use these calculations to determine the positional parameters of atoms as a function of pressure. Our results show that the compression induced structural changes involve cooperative distortions in the full geometry of the hydrogen bonds. The bond-bending mechanism proposed by Hofmeister et al. (Vibrational spectra of dense hydrous magnesium silicates at high pressure: Importance of the hydrogen bond angle, Am. Miner. 84 (1999), pp. 454-464) for hydrogen bonds to relieve the heightened repulsion due to short H- - -H contacts is not found to be effective in Shy B. The calculated O-H bond contraction is consistent with the observed blue shift in the stretching frequency of the hydrogen bond. These results establish that one can use first-principles calculations to obtain reliable insights into the pressure-induced bonding changes of complex minerals.
Structure-property relationships of curved aromatic materials from first principles.
Zoppi, Laura; Martin-Samos, Layla; Baldridge, Kim K
2014-11-18
CONSPECTUS: Considerable effort in the past decade has been extended toward achieving computationally affordable theoretical methods for accurate prediction of the structure and properties of materials. Theoretical predictions of solids began decades ago, but only recently have solid-state quantum techniques become sufficiently reliable to be routinely chosen for investigation of solids as quantum chemistry techniques are for isolated molecules. Of great interest are ab initio predictive theories for solids that can provide atomic scale insights into properties of bulk materials, interfaces, and nanostructures. Adaption of the quantum chemical framework is challenging in that no single theory exists that provides prediction of all observables for every material type. However, through a combination of interdisciplinary efforts, a richly textured and substantive portfolio of methods is developing, which promise quantitative predictions of materials and device properties as well as associated performance analysis. Particularly relevant for device applications are organic semiconductors (OSC), with electrical conductivity between that of insulators and that of metals. Semiconducting small molecules, such as aromatic hydrocarbons, tend to have high polarizabilities, small band-gaps, and delocalized π electrons that support mobile charge carriers. Most importantly, the special nature of optical excitations in the form of a bound electron-hole pairs (excitons) holds significant promise for use in devices, such as organic light emitting diodes (OLEDs), organic photovoltaics (OPVs), and molecular nanojunctions. Added morphological features, such as curvature in aromatic hydrocarbon structure, can further confine the electronic states in one or more directions leading to additional physical phenomena in materials. Such structures offer exploration of a wealth of phenomenology as a function of their environment, particularly due to the ability to tune their electronic
Crystal structure analysis and first principle investigation of F doping in LiFePO4
Milović, Miloš; Jugović, Dragana; Cvjetićanin, Nikola; Uskoković, Dragan; Milošević, Aleksandar S.; Popović, Zoran S.; Vukajlović, Filip R.
2013-11-01
This work presents the synthesis of F-doped LiFePO4/C composite by the specific modification of the recently suggested synthesis procedure based on an aqueous precipitation of precursor material in molten stearic acid, followed by a high temperature treatment. Besides the lattice parameters and the primitive cell volume reductions, compared to the undoped sample synthesized under the same conditions, the Rietveld refinement also shows that fluorine ions preferably occupy specific oxygen sites. Particularly, the best refinement is accomplished when fluorine ions occupy O(2) sites exclusively. By means of up-to-date electronic structure and total energy calculations this experimental finding is theoretically confirmed. Such fluorine doping also produces closing of the gap in the electronic structure and consequently better conductivity properties of the doped compound. In addition, the morphological and electrochemical performances of the synthesized powder are fully characterized.
Thermodynamic stability and structures of iron chloride surfaces: A first-principles investigation
Energy Technology Data Exchange (ETDEWEB)
Saraireh, Sherin A. [Physics Department, Faculty of Sciences, Al-Hussein Bin Talal University, Ma' an (Jordan); Altarawneh, Mohammednoor, E-mail: M.Altarawneh@Murdoch.edu.au [School of Engineering and Information Technology, Murdoch University, Perth (Australia)
2014-08-07
In this study, we report a comprehensive density functional theory investigation of the structure and thermodynamic stability of FeCl{sub 2} and FeCl{sub 3} surfaces. Calculated lattice constants and heats of formation for bulk FeCl{sub 2} and FeCl{sub 3} were found to be in relatively good agreement with experimental measurements. We provide structural parameters for 15 distinct FeCl{sub 2} and FeCl{sub 3} surfaces along the three low-index orientations. The optimized geometries for all surfaces are compared with analogous bulk values. Ab initio atomistic thermodynamic calculations have been carried out to assess the relative thermodynamic stability of FeCl{sub 2} and FeCl{sub 3} surfaces under practical operating conditions of temperatures and pressures. The FeCl{sub 2} (100-Cl) surface is found to afford the most stable configuration at all experimentally accessible gas phase conditions.
ACRES: An Efficient Method for First-Principles Electronic Structure Calculations of Complex Systems
Energy Technology Data Exchange (ETDEWEB)
WAGHMARE,R.V.; KIM,HANCHUL; PARK,I.J.; MODINE,NORMAND A.; MARAGAKIS,P.; KAXIRAS,EFTHIMIOS
2000-08-29
The authors discuss their new implementation of the Adaptive Coordinate Real-space Electronic Structure (ACRES) method for studying the atomic and electronic structure of infinite periodic as well as finite systems, based on density functional theory. This improved version aims at making the method widely applicable and efficient, using high performance Fortran on parallel architectures. The scaling of various parts of an ACRES calculation is analyzed and compared to that of plane-wave based methods. The new developments that lead to enhanced performance, and their parallel implementation, are presented in detail. They illustrate the application of ACRES to the study of elemental crystalline solids, molecules and complex crystalline materials, such as blue bronze and zeolites.
First principle calculation of structure and lattice dynamics of Lu2Si2O7
Nazipov, D. V.; Nikiforov, A. E.
2016-12-01
Ab initio calculations of crystal structure and Raman spectra has been performed for single crystal of lutetium pyrosilicate Lu2Si2O7. The types of fundamental vibrations, their frequencies and intensities in the Raman spectrum has been obtained for two polarizations. Calculations were made in the framework of density functional theory (DFT) with hybrid functionals. The isotopic substitution was calculated for all inequivalent ions in cell. The results in a good agreement with experimental data.
First principle calculation of structure and lattice dynamics of Lu2Si2O7
Directory of Open Access Journals (Sweden)
Nazipov D.V.
2017-01-01
Full Text Available Ab initio calculations of crystal structure and Raman spectra has been performed for single crystal of lutetium pyrosilicate Lu2Si2O7. The types of fundamental vibrations, their frequencies and intensities in the Raman spectrum has been obtained for two polarizations. Calculations were made in the framework of density functional theory (DFT with hybrid functionals. The isotopic substitution was calculated for all inequivalent ions in cell. The results in a good agreement with experimental data.
Churakov, Sergey V.
2007-03-01
Edge sites of clay minerals play a key role for pH dependent sorption of ions from solutions of electrolytes. Pyrophyllite, Al 2[Si 4O 10](OH) 2, is an important structural prototype for a variety of 2:1 dioctahedral phyllosilicates but in contrast to the other clays has no permanent structural charge. The structure of thin water films confined between most common edges of 1Tc pyrophyllite: (0 1 0), (1 1 0) and (1 0 0), was analyzed by means of ab initio molecular dynamic simulations. The system setup allowed for a full flexibility of the interfaces and a proton exchange between the edges of pyrophyllite and water molecules in solution. The structure of hydrated surfaces is compared with the recent predictions of static geometry optimizations for edge-vacuum interfaces. All surfaces studied reveal a strong hydrophilic character of edge similar to the hydrated silica surface and the facets of simple layered hydroxides. Spontaneous proton transfer between different surface sites were observed in molecular dynamics simulations of the (0 1 0) interface. The proton bound to the tbnd Si sbnd OH site was found to exchange with the tbnd Al sbnd OH group by the mechanism tbnd Si sbnd OH +tbnd Al sbnd OH ↔tbnd Si sbnd O+tbnd Al sbnd OH 2+. The direction of the proton transfer agrees with the scale of relative proton affinities for surface sites obtained from the static calculations. Alternatively, the proton attached to the tbnd Al sbnd OH 2 site exchanges with the tbnd Al sbnd OH group. In both reactions, the protons are transferred through the chains of hydrogen bonds formed between water molecules in the solution and the surface sites. The observed mechanisms might be one of the basic schemes for the surface proton diffusion in compacted clays. Kinetics of the proton transfer at edge sites is limited by the rate of rearrangements of the water molecules near interface.
Energy Technology Data Exchange (ETDEWEB)
Hao Xianfeng [Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Wu Zhijian [Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Xu Yuanhui [School of Biological Engineering, Changchun University of Technology, Changchun 130012 (China); Zhou Defeng [School of Biological Engineering, Changchun University of Technology, Changchun 130012 (China); Liu Xiaojuan [Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Meng Jian [Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China)
2007-05-16
We investigate the cohesive energy, heat of formation, elastic constant and electronic band structure of transition metal diborides TMB{sub 2} (TM = Hf, Ta, W, Re, Os and Ir, Pt) in the Pmmn space group using the ab initio pseudopotential total energy method. Our calculations indicate that there is a relationship between elastic constant and valence electron concentration (VEC): the bulk modulus and shear modulus achieve their maximum when the VEC is in the range of 6.8-7.2. In addition, trends in the elastic constant are well explained in terms of electronic band structure analysis, e.g., occupation of valence electrons in states near the Fermi level, which determines the cohesive energy and elastic properties. The maximum in bulk modulus and shear modulus is attributed to the nearly complete filling of TM d-B p bonding states without filling the antibonding states. On the basis of the observed relationship, we predict that alloying W and Re in the orthorhombic structure OsB{sub 2} might be harder than alloying the Ir element. Indeed, the further calculations confirmed this expectation.
First-principles study of the structure of water layers on flat and stepped Pb electrodes.
Lin, Xiaohang; Evers, Ferdinand; Groß, Axel
2016-01-01
On the basis of perodic density functional theory (DFT) calculations, we have addressed the geometric structures and electronic properties of water layers on flat and stepped Pb surfaces. In contrast to late d-band metals, on Pb(111) the energy minimum structure does not correspond to an ice-like hexagonal arrangement at a coverage of 2/3, but rather to a distorted structure at a coverage of 1 due to the larger lattice constant of Pb. At stepped Pb surfaces, the water layers are pinned at the step edge and form a complex network consisting of rectangles, pentagons and hexagons. The thermal stability of the water layers has been studied by using ab initio molecular dynamics simulations (AIMD) at a temperature of 140 K. Whereas the water layer on Pb(111) is already unstable at this temperature, the water layers on Pb(100), Pb(311), Pb(511) and Pb(711) exhibit a higher stability because of stronger water-water interactions. The vibrational spectra of the water layers at the stepped surfaces show a characteristic splitting into three modes in the O-H stretch region.
Magnetism, structure and chemical order in small CoPd clusters: A first-principles study
Mokkath, Junais Habeeb
2014-01-01
The structural, electronic and magnetic properties of small ComPdn (N=m+n=8,m=0-N) nanoalloy clusters are studied in the framework of a generalized-gradient approximation to density-functional theory. The optimized cluster structures have a clear tendency to maximize the number of nearest-neighbor CoCo pairs. The magnetic order is found to be ferromagnetic-like (FM) for all the ground-state structures. Antiferromagnetic-like spin arrangements were found in some low-lying isomers. The average magnetic moment per atom μ̄N increases approximately linearly with Co content. A remarkable enhancement of the local Co moments is observed as a result of Pd doping. This is a consequence of the increase in the number of Co d holes, due to CoPd charge transfer, combined with the reduced local coordination. The influence of spin-orbit interactions on the cluster properties is also discussed. © 2013 Elsevier B.V.
Electronic structures and vibrational properties of coronene on Ru(0001): first-principles study
Institute of Scientific and Technical Information of China (English)
Zhang Yu-Yang; Du Shi-Xuan; Gao Hong-Jun
2012-01-01
We calculate the configurations,electronic structures,vibrational properties at the coronene/Ru(0001) interface,and adsorption of a single Pt atom on coronene/Ru(0001) based on density functional theory calculations.The geometric structures and electronic structures of the coronene on Ru(0001) are compared with those of the graphene/Ru(0001).The results show that the coronene/Ru(0001) can be a simplified model system used to describe the interaction between graphene and ruthenium.Further calculations of the vibrational properties of coronene molecule adsorbed on Ru(0001)suggest that the phonon properties of differently corrugated regions of graphene on Ru(0001) are different.This model system is also used to investigate the selective adsorption of Pt atoms on graphene/Ru(0001).The configurations of Pt on coronene/Ru(0001) with the lowest binding energy give clues to explain the experimental observation that a Pt cluster selectively adsorbs on the second highest regions of graphene/Ru(0001).This work provides a simple model for understanding the adsorption properties and vibrational properties of graphene on Ru(0001) substrate.
Kaloni, Thaneshwor P.
2013-11-01
This thesis covers the structural, electronic, magnetic, and vibrational properties of graphene and silicene. In Chapter I, we will start with an introduction to graphene and silicene. In Chapter II, we will briefly discuss about the methodology (i. e. density functional theory)In Chapter III, we will introduce band gap opening in graphene either by introducing defects/doping or by creating superlattices with h-BN substrate. In Chapter IV, we will focus on the structural and electronic properties of K and Ge-intercalated graphene on SiC(0001). In addition, the enhancement of the superconducting transition temperature in Li-decorated graphene supported by h-BN substrate will be discussed. In Chapter V, we will discuss the vibrational properties of free-standing silicene. In addition, superlattices of silicene with h-BN as well as the phase transition in silicene by applying an external electric field will be discussed. The electronic and magnetic properties transition metal decorated silicene will be discussed, in particular the realization of the quantum anomalous Hall effect will be addressed. Furthermore, the structural, electronic, and magnetic properties of Mn decorated silicene supported by h-BN substrate will be discussed. The conclusion is included in Chapters VI. Finally, we will end with references and a list of publications for this thesis.
Yao, Yin; Liu, Anping; Bai, Jianhui; Zhang, Xuanmei; Wang, Rui
2016-12-01
In this paper, we investigate the structural and electronic properties of zigzag silicene nanoribbons (ZSiNRs) with edge-chemistry modified by H, F, OH, and O, using the ab initio density functional theory method and local spin-density approximation. Three kinds of spin polarized configurations are considered: nonspin polarization (NM), ferromagnetic spin coupling for all electrons (FM), ferromagnetic ordering along each edge, and antiparallel spin orientation between the two edges (AFM). The H, F, and OH groups modified 8-ZSiNRs have the AFM ground state. The directly edge oxidized (O1) ZSiNRs yield the same energy and band structure for NM, FM, and AFM configurations, owning to the same s p (2) hybridization. And replacing the Si atoms on the two edges with O atoms (O2) yields FM ground state. The edge-chemistry-modified ZSiNRs all exhibit metallic band structures. And the modifications introduce special edge state strongly localized at the Si atoms in the edge, except for the O1 form. The modification of the zigzag edges of silicene nanoribbons is a key issue to apply the silicene into the field effect transistors (FETs) and gives more necessity to better understand the experimental findings.
First-Principles Study of Electronic Structure of Type I Hybrid Carbon-Silicon Clathrates
Chan, Kwai S.; Peng, Xihong
2016-08-01
A new class of type I hybrid carbon-silicon clathrates has been designed using computational methods by substituting some of the Si atoms in the silicon clathrate framework with carbon atoms. In this work, the electronic structure of hybrid carbon-silicon clathrates with and without alkaline or alkaline-earth metal guest atoms has been computed within the density functional theory framework. The theoretical calculations indicate that a small number of carbon substitutions in the Si46 framework slightly reduces the density of states (DOS) near the band edge and narrows the bandgap of carbon-silicon clathrates. Weak hybridization of the conduction band occurs when alkaline metal (Li, Na, K) atoms are inserted into the structure, while strong hybridization of the conduction band occurs when alkaline-earth metal (Mg, Ca, Ba) atoms are inserted into the hybrid structure. Empty C y Si46- y clathrates within the composition range of 2 ≤ y ≤ 15 can be tuned to exhibit indirect bandgaps of 1.5 eV or less, and may be considered as potential electronic materials.
A first principles study of the electronic structure, elastic and thermal properties of UB2
Jossou, Ericmoore; Malakkal, Linu; Szpunar, Barbara; Oladimeji, Dotun; Szpunar, Jerzy A.
2017-07-01
Uranium diboride (UB2) has been widely deployed for refractory use and is a proposed material for Accident Tolerant Fuel (ATF) due to its high thermal conductivity. However, the applicability of UB2 towards high temperature usage in a nuclear reactor requires the need to investigate the thermomechanical properties, and recent studies have failed in highlighting applicable properties. In this work, we present an in-depth theoretical outlook of the structural and thermophysical properties of UB2, including but not limited to elastic, electronic and thermal transport properties. These calculations were performed within the framework of Density Functional Theory (DFT) + U approach, using Quantum ESPRESSO (QE) code considering the addition of Coulomb correlations on the uranium atom. The phonon spectra and elastic constant analysis show the dynamic and mechanical stability of UB2 structure respectively. The electronic structure of UB2 was investigated using full potential linear augmented plane waves plus local orbitals method (FP-LAPW+lo) as implemented in WIEN2k code. The absence of a band gap in the total and partial density of states confirms the metallic nature while the valence electron density plot reveals the presence of covalent bond between adjacent B-B atoms. We predicted the lattice thermal conductivity (kL) by solving Boltzmann Transport Equation (BTE) using ShengBTE. The second order harmonic and third-order anharmonic interatomic force constants required as input to ShengBTE was calculated using the Density-functional perturbation theory (DFPT). However, we predicted the electronic thermal conductivity (kel) using Wiedemann-Franz law as implemented in Boltztrap code. We also show that the sound velocity along 'a' and 'c' axes exhibit high anisotropy, which accounts for the anisotropic thermal conductivity of UB2.
Surface structure and hole localization in bismuth vanadate: A first principles study
Kweon, Kyoung E.; Hwang, Gyeong S.
2013-09-01
The monoclinic and tetragonal phases of bismuth vanadate (BiVO4) have been found to exhibit significantly different photocatalytic activities for water splitting. To assess a possible surface effect on the phase-dependent behavior, we calculate and compare the geometries and electronic structures of the monoclinic and tetragonal BiVO4 (001) surfaces using hybrid density functional theory. The relaxed atomic configurations of these two surfaces are found to be nearly identical, while an excess hole shows a relatively stronger tendency to localize at the surface than the bulk in both phases. Possible factors for the phase-dependent photocatalytic activity of BiVO4 are discussed.
First Principles Study on Electronic Structures of Mn2+:CdMoO4 Crystals
Institute of Scientific and Technical Information of China (English)
WANG Xi-En; LIU Ting-Yu; ZHANG Qi-Ren; ZHANG Hai-Yan; SONG Min; GUO Xiao-Feng; YIN Ji-Gang
2008-01-01
@@ Electronic structures of the Mn2+:CdMoO4 crystal are studied within the framework of the fully relativistic self-consistent Dirac-Slater theory,using a numerically discrete variation (DV-Xα)method.The calculated results indicate that the 3d states of Mn have donor energy level in the forbidden band of CdMoO4 crystal.The transition energy of O 2p→Mn 3d is 3.12 eV under excitation corresponding electronic transition being O2-+Mn2+ hvex=3.12 eV→ O-+Mn+hvem→O2+Mn2+.
Structural,electronic and elastic properties of YCu from first principles
Institute of Scientific and Technical Information of China (English)
G.U(g)ur; M.(C)ivi; S.U(g)ur; F.Soyalp; R.Ellialtio(g)lu
2009-01-01
The structural,electronic and elastic properties of YCu compound in the B2 (CsC1) phase were investigated using the density functional theory (DFT) within the generalized gradient approximation (GGA).The electronic density of states (DOS) obtained in this way accorded well with the results of a recent study utilizing the full-potential iinearized augmented plane wave (FLAPW) method.We also found that the density of d-states at the Fermi energy was low.The calculated equilibrium properties such as lattice constant,bulk modulus and its first derivative,and the elastic constants were in good agreement with experimental and theoretical results.
Energy Technology Data Exchange (ETDEWEB)
Dabhi, Shweta, E-mail: venu.mankad@gmail.com; Mankad, Venu, E-mail: venu.mankad@gmail.com; Jha, Prafulla K., E-mail: venu.mankad@gmail.com [Department of Physics, Maharaja Krishnakumasinhji Bhavnagar University, Bhavnagar-364001 (India)
2014-04-24
A detailed theoretical study of structural, electronic and Vibrational properties of BeX compound is presented by performing ab-initio calculations based on density-functional theory using the Espresso package. The calculated value of lattice constant and bulk modulus are compared with the available experimental and other theoretical data and agree reasonably well. BeX (X = S,Se,Te) compounds in the ZB phase are indirect wide band gap semiconductors with an ionic contribution. The phonon dispersion curves are represented which shows that these compounds are dynamically stable in ZB phase.
Fast ion conductivity in strained defect-fluorite structure created by ion tracks in Gd2Ti2O7
Aidhy, Dilpuneet S.; Sachan, Ritesh; Zarkadoula, Eva; Pakarinen, Olli; Chisholm, Matthew F.; Zhang, Yanwen; Weber, William J.
2015-11-01
The structure and ion-conducting properties of the defect-fluorite ring structure formed around amorphous ion-tracks by swift heavy ion irradiation of Gd2Ti2O7 pyrochlore are investigated. High angle annular dark field imaging complemented with ion-track molecular dynamics simulations show that the atoms in the ring structure are disordered, and have relatively larger cation-cation interspacing than in the bulk pyrochlore, illustrating the presence of tensile strain in the ring region. Density functional theory calculations show that the non-equilibrium defect-fluorite structure can be stabilized by tensile strain. The pyrochlore to defect-fluorite structure transformation in the ring region is predicted to be induced by recrystallization during a melt-quench process and stabilized by tensile strain. Static pair-potential calculations show that planar tensile strain lowers oxygen vacancy migration barriers in pyrochlores, in agreement with recent studies on fluorite and perovskite materials. In view of these results, it is suggested that strain engineering could be simultaneously used to stabilize the defect-fluorite structure and gain control over its high ion-conducting properties.
Structure and Properties of the Fe/Y2O3 Interface from First Principles Calculations
Energy Technology Data Exchange (ETDEWEB)
Choudhury, Samrat [Los Alamos National Laboratory; Stanek, Christopher R. [Los Alamos National Laboratory; Uberuaga, Blas P. [Los Alamos National Laboratory
2012-07-31
Fundamentals of radiation damage are: (1) Formation of Frenkel pair (interstitial-vacancy pair) defects in the lattice; (2) Concentration of Frenkel pair defects >>> thermal equilibrium thermodynamic concentration; and (3) The radiation damage response of a material is determined by the fate of these excess Frenkel pair defects in the lattice. The objective is to understand the electronic and atomic structure of Fe/Y{sub 2}O{sub 3} interface and segregation behavior of the alloying elements at the interface. The significance of the results of this report are: (1) Provides a science based approach to design new radiation resistant materials. Obtained two controlling parameters - Dislocation density (composition, orientation relationship) and Oxygen partial pressure; (2) Applicable to any other metal/oxide interfaces (both functional and structural properties at the interface) - (a) Nano Catalysts: Oxide-supported metal catalysts Ni/ZrO{sub 2}, (b) Thermal barrier coatings (Ni/Al{sub 2}O{sub 3}), (c) Corrosion of metals and alloys.
Band Structure and Optical Properties of Kesterite Type Compounds: first principle calculations
Palaz, S.; Unver, H.; Ugur, G.; Mamedov, A. M.; Ozbay, E.
2017-02-01
In present work, our research is mainly focused on the electronic structures, optical and magnetic properties of Cu2FeSnZ4 (Z = S, Se) compounds by using ab initio calculations within the generalized gradient approximation (GGA). The calculations are performed by using the Vienna ab-initio simulation package (VASP) based on the density functional theory. The band structure of the Cu2FeSnZ4 ( Z = S, Se) compounds for majority spin (spin-up) and minority spin (spin-down) were calculated. It is seen that for these compounds, the majority spin states cross the Fermi level and thus have the metallic character, while the minority spin states open the band gaps around the Fermi level and thus have the narrow-band semiconducting nature. For better understanding of the electronic states, the total and partial density of states were calculated, too. The real and imaginary parts of dielectric functions and hence the optical functions such as energy-loss function, the effective number of valance electrons and the effective optical dielectric constant for Cu2FeSnZ4 (Z = S, Se) compounds were also calculated.
Structural and electronic properties of wurtzite Bx Al1-x N from first-principles calculations
Zhang, Muwei
2017-06-14
The structural and electronic properties of wurtzite BAlN (0≤x≤1) are studied using density functional theory. The change of lattice parameters with increased B composition shows small bowing parameters and thus slightly nonlinearity. The bandgap exhibits strong dependence on the B composition, where transition from direct to indirect bandgap occurs at a relatively low B composition (x∼0.12) is observed, above which the bandgap of BAlN maintained indirect, thus desirable for low-absorption optical structures. The Γ-A and Γ-K indirect bandgaps are dominant at lower and higher B compositions, respectively. Density of states (DOS) of the valence band is susceptible to the B incorporation. Strong hybridization of Al, B, and N in p-states leads to high DOS near the valence band maximum. The hybridization of Al and B in s-states at lower B compositions and p-states of B at higher B compositions give rise to high DOS near lower end of the upper valence band. Charge density analysis reveals the B-N chemical bond is more covalent than the Al-N bond. This will lead to more covalent crystal with increasing B composition. Dramatic change of the heavy hole effective mass is found due to significant curvature increase of the band by minor B incorporation.
Electronic Structure of Aromatic and Quinoidic Oligothiophenes by First-principles Calculations
Mizuseki, Hiroshi; Kawazoe, Yoshiyuki
2009-03-01
Since the discovery in 1977 that trans-polyacetylene can be made electrically conducting by means of doping[1] several different conjugated polymers with interesting properties in the conducting and semiconducting phases have been discovered. Polythiophene has a typical π-conjugated system, then many polythiophenes are synthesized and several have been well characterized. Calculation systems based on neutral, doubly charged, and highly charged oligomers whose all ring are linked to have linear chains were studied as model for the polaronic defects in doped polythiophenes. The energetics of the aromatic and quinoid structures is investigated using the both ends of neutral oligomers substituted by dimethyl and dimethylen. To estimate the electronic structures, the difference between corresponding bond lengths along the C-C path of neutral, dicationic, and dianionic oligomers, were investigated. Calculations were performed on systems containing 16 monomers, by using B3LYP/6-31G(d) level of theory. References [1] C. K. Chiang et al., Phys. Rev. Lett. 39, 1098 (1977). [2] http://www-lab.imr.edu/˜mizuseki/nanowire.html
Institute of Scientific and Technical Information of China (English)
Ye Xiao-Qiu; Luo De-Li; Sang Ge; Ao Bing-Yun
2011-01-01
The alanates (complex aluminohydrides) have relatively high gravimetric hydrogen densities and are among the most promising solid-state hydrogen-storage materials. In this work, the electronic structures and the formation enthalpies of seven typical aluminum-based deuterides have been calculated by the plane-wave pseudopotential method,these being AID3, LiAID4, Li3AID6, BaAID5, Ba2AID7, LiMg(AID4)3 and LiMgAID6. The results show that all these compounds are large band gap insulators at 0 K with estimated band gaps from 2.31 eV in AID3 to 4.96 eV in LiMg(AID4)3. The band gaps are reduced when the coordination of Al varies from 4 to 6. Two peaks present in the valence bands are the common characteristics of aluminum-based deuterides containing AID4 subunits while three peaks are the common characteristics of those containing AID6 subunits. The electronic structures of these compounds are determined mainly by aluminum deuteride complexes (AID4 or AID6) and their mutual interactions. The predicted formation enthalpies are presented for the studied aluminum-based deuterides.
Kang, Dongdong; Dai, Jiayu; Yuan, Jianmin
2011-07-14
The changes of structure and distribution of dipole moment of water with temperatures up to 2800 K and densities up to 2.2 g/cm(3) are investigated using ab initio molecular dynamics. Along the isochore of 1.0 g/cm(3), the structure of liquid water above 800 K is dramatically different from that at ambient conditions, where the hydrogen-bonds network collapses. Along the isotherm of 1800 K, the transition from the liquid state to an amorphous superionic phase occurs at 2.0 g/cm(3) (32.9 GPa), which is not observed along the isotherm of 2800 K. With increasing temperature, the average dipole moment of water molecules is decreased arising from the weakened polarization by the collapse of the hydrogen-bonds network, while it is contrarily increased with compression due to the strengthening effect upon the polarization of water molecules. Both higher temperature and pressure broaden the distribution of dipole moment of water molecules due to the enhanced intramolecular charge fluctuations.
Electronic structures of Tl-based materials for γ-ray detectors; First-principles study
Song, Jung-Hwan; Jin, Hosub; Freeman, Arthur J.; Johnsen, Simon; Androulakis, John; Sebastian, Peter; Liu, Zhifu; Peter, John A.; Cho, Nam-Ki; Wessels, Bruce; Kanatzidis, Mercouri G.
2011-03-01
For Tl-based semiconductors, investigated to find good candidate materials for γ -ray detectors, we performed ab-initio calculations using the full-potential linearized augmented plane wave (FLAPW) method to find their electronic structures and to estimate their physical properties such as band gaps, effective masses, absorption coefficients, dielectric constants, and work functions. Within the LDA scheme, the underestimation of the band gap is well-known and causes serious problems in obtaining optical properties. Therefore, we adopted the screened-exchange LDA (sX-LDA) scheme and acquired correct gap values close to experimental ones. With the sX-LDA, we found that Tl 6 I4 S and Tl 6 I4 Se have direct band gaps of 2.36 and 1.88 eV, respectively, and they exhibit dispersive bands near the band edges. Based on the calculated and experimental results, we discuss the relationship between atom species/crystal structure and electronic characteristics, and suggest several materials for γ -ray detectors. Supported by NSF (Grant No. ARI-MA CMMI-0938810).
First-principles studies of electric field effects on the electronic structure of trilayer graphene
Wang, Yun-Peng; Li, Xiang-Guo; Fry, James N.; Cheng, Hai-Ping
2016-10-01
A gate electric field is a powerful way to manipulate the physical properties of nanojunctions made of two-dimensional crystals. To simulate field effects on the electronic structure of trilayer graphene, we used density functional theory in combination with the effective screening medium method, which enables us to understand the field-dependent layer-layer interactions and the fundamental physics underlying band gap variations and the resulting band modifications. Two different graphene stacking orders, Bernal (or ABC) and rhombohedral (or ABA), were considered. In addition to confirming the experimentally observed band gap opening in ABC-stacked and the band overlap in ABA-stacked trilayer systems, our results reveal rich physics in these fascinating systems, where layer-layer couplings are present but some characteristics features of single-layer graphene are partially preserved. For ABC stacking, the electric-field-induced band gap size can be tuned by charge doping, while for ABA band the tunable quantity is the band overlap. Our calculations show that the electronic structures of the two stacking orders respond very differently to charge doping. We find that in the ABA stacking hole doping can reopen a band gap in the band-overlapping region, a phenomenon distinctly different from electron doping. The physical origins of the observed behaviors were fully analyzed, and we conclude that the dual-gate configuration greatly enhances the tunability of the trilayer systems.
Wang, Yushan
2007-12-01
The formation and development of quantum theory in the first half of the 20th century has led to a revolution in our understanding of pure and applied physics. Quantum theory has nowadays demonstrated a surprisingly accurate and predictive power in modern science and engineering. In this study, an important branch of quantum theory, density functional theory (DFT), is applied to studies of TiO2 and doped TiO2, which have shown considerable applications in industry. The first chapter is an introduction to the theoretical background of DFT, in which a large quantity of efforts are focused on the analysis of exchange-correlation energy and how to approximate it by using local density approximation (LDA), generalized gradient approximation (GGA), and LDA+U, where the U is the Hubbard coefficient. This is followed in the second chapter by a discussion of practical implementations of the DFT-based calculations. We primarily introduce linearized augmented plane wave (LAPW) and augmented plane wave plus local orbital (APW+LO) methods, both of which are applied in our calculations. In chapter 3, we briefly introduce some fundamental properties of TiO2 and its applications in industry. Chapters 4 through 8 are divided into two categories. Chapters 4 through 6 are mainly concerned with insights into the mechanism of optical excitation in anatase TiO2. Chapters 7 and 8 are concerned with TiO2-based dilute magnetic semiconductors (DMS). Chapter 4 presents detailed calculations on pristine TiO2, including the structural optimization, density of states (DOS), band structure, and optical properties. Our calculations involve both bulk and slab TiO 2, presenting reasonable results without considering inherent drawbacks of the calculation methods involved. Calculations on slab TiO2 provide insight to account for the particular property of TiO2 in nanoscale particles where a significant fraction of atoms are on the surface. In chapter 5, we investigate effects of the non-metal dopants
First principle electronic, structural, elastic, and optical properties of strontium titanate
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Chinedu E. Ekuma
2012-03-01
Full Text Available We report self-consistent ab-initio electronic, structural, elastic, and optical properties of cubic SrTiO3 perovskite. Our non-relativistic calculations employed a generalized gradient approximation (GGA potential and the linear combination of atomic orbitals (LCAO formalism. The distinctive feature of our computations stem from solving self-consistently the system of equations describing the GGA, using the Bagayoko-Zhao-Williams (BZW method. Our results are in agreement with experimental ones where the later are available. In particular, our theoretical, indirect band gap of 3.24 eV, at the experimental lattice constant of 3.91 Å, is in excellent agreement with experiment. Our predicted, equilibrium lattice constant is 3.92 Å, with a corresponding indirect band gap of 3.21 eV and bulk modulus of 183 GPa.
Yelgel, Celal
2016-04-01
We present an extensive density functional theory (DFT) based investigation of the electronic structures of ABC-stacked N-layer graphene. It is found that for such systems the dispersion relations of the highest valence and the lowest conduction bands near the K point in the Brillouin zone are characterised by a mixture of cubic, parabolic, and linear behaviours. When the number of graphene layers is increased to more than three, the separation between the valence and conduction bands decreases up until they touch each other. For five and six layer samples these bands show flat behaviour close to the K point. We note that all states in the vicinity of the Fermi energy are surface states originated from the top and/or bottom surface of all the systems considered. For the trilayer system, N = 3, pronounced trigonal warping of the bands slightly above the Fermi level is directly obtained from DFT calculations.
Institute of Scientific and Technical Information of China (English)
LU Lai-Yu; WEI Dong-Qing; CHEN Xiang-Rong; JI Guang-Fu
2008-01-01
Structures and electronic properties of the pentaerythritol (PE) crystal under volume compression up to 0.85Vo are studied by E - V fitting method using density functional theory (DFT). The compression dependences of the cell volumes, lattice constants, and molecular geometries of solid PE are presented and discussed. It is found that the solid PE presents anisotropy along a- and c-axes, and the c axis is the most compressible. Decreasing anisotropy ratio (c/a) with elevating compression suggests an enhancement of the vdW interaction with increasing compression. The C-C and C-H bonds are significantly reduced under compression, which may be related to the sensitivity. The solid PE has indirect band gap (X - C) in the range of the researched compression and the band gap is decreased with compression.
Structure and Formation of Synthetic Hemozoin: Insights from First Principles Calculations
Marom, Noa; Tkatchenko, Alexandre; Kapishnikov, Sergey; Kronik, Leeor; Leiserowitz, Leslie
2011-03-01
Malaria has reemerged due to parasite resistance to synthetic drugs that act by inhibiting crystallization of the malaria pigment, hemozoin (HZ). Understanding the process of HZ nucleation is therefore vital. The crystal structure of synthetic HZ, β -hematin (β H), has recently been determined via x-ray diffraction. We employ van der Waals (vdW) corrected density functional theory to study the β H crystal and its repeat unit, a heme dimer. We find that vdW interactions play a major role in the binding of the heme dimer and the β H crystal. Accounting for the β H periodicity is a must for obtaining the correct geometry of the heme dimer, due to vdW interactions with adjacent dimers. The different isomers of the heme dimer are close in energy, consistent with the observed pseudo-polymorphism. We use these findings to comment on β H crystallization mechanisms.
Surface structure and hole localization in bismuth vanadate: A first principles study
Energy Technology Data Exchange (ETDEWEB)
Kweon, Kyoung E.; Hwang, Gyeong S. [Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712 (United States)
2013-09-23
The monoclinic and tetragonal phases of bismuth vanadate (BiVO{sub 4}) have been found to exhibit significantly different photocatalytic activities for water splitting. To assess a possible surface effect on the phase-dependent behavior, we calculate and compare the geometries and electronic structures of the monoclinic and tetragonal BiVO{sub 4} (001) surfaces using hybrid density functional theory. The relaxed atomic configurations of these two surfaces are found to be nearly identical, while an excess hole shows a relatively stronger tendency to localize at the surface than the bulk in both phases. Possible factors for the phase-dependent photocatalytic activity of BiVO{sub 4} are discussed.
Dabhi, Shweta D.; Gupta, Sanjay D.; Jha, Prafulla K.
2014-05-01
We report the results of a theoretical study on the structural, electronic, mechanical, and vibrational properties of some graphene oxide models (GDO, a-GMO, z-GMO, ep-GMO and mix-GMO) at ambient pressure. The calculations are based on the ab-initio plane-wave pseudo potential density functional theory, within the generalized gradient approximations for the exchange and correlation functional. The calculated values of lattice parameters, bulk modulus, and its first order pressure derivative are in good agreement with other reports. A linear response approach to the density functional theory is used to derive the phonon frequencies. We discuss the contribution of the phonons in the dynamical stability of graphene oxides and detailed analysis of zone centre phonon modes in all the above mentioned models. Our study demonstrates a wide range of energy gap available in the considered models of graphene oxide and hence the possibility of their use in nanodevices.
Energy Technology Data Exchange (ETDEWEB)
Dabhi, Shweta D. [Department of Physics, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar 364001 (India); Gupta, Sanjay D. [V. B. Institute of Science, Department of Physics, C. U. Shah University, Wadhwan City - 363030, Surendranagar (India); Jha, Prafulla K., E-mail: prafullaj@yahoo.com [Department of Physics, Faculty of Science, The Maharaja Sayajirao University of Baroda, Vadodara-390002 (India)
2014-05-28
We report the results of a theoretical study on the structural, electronic, mechanical, and vibrational properties of some graphene oxide models (GDO, a-GMO, z-GMO, ep-GMO and mix-GMO) at ambient pressure. The calculations are based on the ab-initio plane-wave pseudo potential density functional theory, within the generalized gradient approximations for the exchange and correlation functional. The calculated values of lattice parameters, bulk modulus, and its first order pressure derivative are in good agreement with other reports. A linear response approach to the density functional theory is used to derive the phonon frequencies. We discuss the contribution of the phonons in the dynamical stability of graphene oxides and detailed analysis of zone centre phonon modes in all the above mentioned models. Our study demonstrates a wide range of energy gap available in the considered models of graphene oxide and hence the possibility of their use in nanodevices.
Pressure-induced structural, magnetic and transport transitions in Sr2FeO3 from first-principles
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Ting Jia
2017-05-01
Full Text Available The serial system Srn+1FenO2n+1(n=1,2,3… with the FeO4 square planar motif exhibits abundant phase transitions under pressure. In this work, we investigate the pressure-induced structural, magnetic and transport transitions in Sr2FeO3 from first-principles. Our results show that the system undergoes a structural transition from Immm to Ammm when the volume decreases by 30%, together with a spin-state transition (SST from high-spin (S = 2 to intermediate-spin (S = 1, an antiferromagnetic-to-ferromagnetic transition and an insulator-to-metal transition (IMT. Besides, the IMT here is a bandwidth controlled transition, but little influenced by the SST.
Ma, Chao; Yang, Huaixin; Tian, Huanfang; Shi, Honglong; Wang, Zhiwei; Li, Jianqi
2013-03-20
Using electron energy loss spectroscopy (EELS) measurements and first-principles electronic structure calculations, the significant interlayer hybridization between the insulating layers (ReO or Ba) and the conducting FeAs layers was investigated in the layered iron pnictides, which is quite different from the case in the cuprate superconductors. This interlayer hybridization would result in an increase in the bandwidth near the Fermi level and interorbital charge transfer in the Fe 3d orbitals, which subsequently leads to a decrease in the Fe local moment and the modification of the Fermi surface topology. Therefore, a three-dimensional character of the electronic structure due to the interlayer hybridization is expected, as observed in previous experiments. These findings indicate that reduced dimensionality is no longer a necessary condition in the search for high-T(c) superconductors in iron pnictides.
Wu, Zhijian; Hao, Xianfeng; Liu, Xiaojuan; Meng, Jian
2007-02-01
The structure, elastic, and electronic properties of OsN2 at various space groups: cubic Fm-3m , Pa-3 , and orthorhombic Pnnm were studied by first-principles calculations based on density functional theory. Our calculation indicates that the structure in orthorhombic Pnnm phase is energetically more stable compared with cubic systems. It is metallic, mechanically stable and contains diatomic N-N units with the bond distance 1.418Å . These characters are consistent with experimental facts that OsN2 is orthorhombic and metallic. The calculated bulk modulus 394GPa is also the highest among the considered space groups, slightly larger than previous value 358GPa . The calculated elastic anisotropic factors and directional bulk modulus showed that OsN2 possess high elastic anisotropy.
Songjun, Hou; Sunchao, Huang; Zhi, Zeng
2015-01-01
First principles calculations were performed to study the structural, elastic, and bonding properties of hcp ZrxTi1-x binary alloy. The special quasi- random structure (SQS) method is employed to mimic the random hcp ZrxTi1-x alloy. It is found that Bulk modulus, B, Young's modulus, E, and shear modulus, G, exhibit decreasing trends as increasing the amount of Zr. A ductile behavior ZrxTi1-x is predicted in the whole composition range. In terms of Mulliken charge analisis, we found that the element Ti behaves much more electronegative than Zr in hcp ZrxTi1-x alloy, and the charge transfer of an atom is approximately linear to the amount of other element atom surrounding it.
Structural, electronic, and elastic properties of CuFeS2: first-principles study
Zhou, Meng; Gao, Xiang; Cheng, Yan; Chen, Xiangrong; Cai, Lingcang
2015-03-01
The structural, electronic, and elastic properties of CuFeS2 have been investigated by using the generalized gradient approximation (GGA), GGA + U (on-site Coulomb repulsion energy), the local density approximation (LDA), and the LDA + U approach in the frame of density functional theory. It is shown that when the GGA + U formalism is selected with a U value of 3 eV for the 3d state of Fe, the calculated lattice constants agree well with the available experimental and other theoretical data. Our GGA + U calculations indicate that CuFeS2 is a semiconductor with a band gap of 0.552 eV and with a magnetic moment of 3.64 µB per Fe atom, which are well consistent with the experimental results. Combined with the density of states, the band structure characteristics of CuFeS2 have been analyzed and their origins have been specified, which reveals a hybridization existing between Fe-3d, Cu-3s, and S-3p, respectively. The charge and Mulliken population analyses indicate that CuFeS2 is a covalent crystal. Moreover, the calculated elastic constants prove that CuFeS2 is mechanically stable but anisotropic. The bulk modulus obtained from elastic constants is 87.1 GPa, which agrees well with the experimental value of 91 ± 15 GPa and better than the theoretical bulk modulus 74 GPa obtained from GGA method by Lazewski et al. The obtained shear modulus and Debye temperature are 21.0 GPa and 287 K, respectively, and the latter accords well with the available experimental value. It is expected that our work can provide useful information to further investigate CuFeS2 from both the experimental and theoretical sides.
An approach to first principles electronic structure calculation by symbolic-numeric computation
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Akihito Kikuchi
2013-04-01
Full Text Available There is a wide variety of electronic structure calculation cooperating with symbolic computation. The main purpose of the latter is to play an auxiliary role (but not without importance to the former. In the field of quantum physics [1-9], researchers sometimes have to handle complicated mathematical expressions, whose derivation seems almost beyond human power. Thus one resorts to the intensive use of computers, namely, symbolic computation [10-16]. Examples of this can be seen in various topics: atomic energy levels, molecular dynamics, molecular energy and spectra, collision and scattering, lattice spin models and so on [16]. How to obtain molecular integrals analytically or how to manipulate complex formulas in many body interactions, is one such problem. In the former, when one uses special atomic basis for a specific purpose, to express the integrals by the combination of already known analytic functions, may sometimes be very difficult. In the latter, one must rearrange a number of creation and annihilation operators in a suitable order and calculate the analytical expectation value. It is usual that a quantitative and massive computation follows a symbolic one; for the convenience of the numerical computation, it is necessary to reduce a complicated analytic expression into a tractable and computable form. This is the main motive for the introduction of the symbolic computation as a forerunner of the numerical one and their collaboration has won considerable successes. The present work should be classified as one such trial. Meanwhile, the use of symbolic computation in the present work is not limited to indirect and auxiliary part to the numerical computation. The present work can be applicable to a direct and quantitative estimation of the electronic structure, skipping conventional computational methods.
First-principles structure search for the stable isomers of stoichiometric WS2 nano-clusters
Hafizi, Roohollah; Alaei, Mojtaba; Jangrouei, MohammadReza; Akbarzadeh, Hadi
2016-01-01
In this paper, we employ evolutionary algorithm along with the full-potential density functional theory (DFT) computations to perform a comprehensive search for the stable structures of stoichiometric (WS2)n nano-clusters (n=1-9), within three different exchange-correlation functionals. Our results suggest that n=3, 5, 8 are possible candidates for the low temperature magic sizes of WS2 nano-clusters while at temperatures above 600 Kelvin, n=5 and 7 exhibit higher relative stability among the studied systems. The electronic properties and energy gap of the lowest energy isomers were computed within several schemes, including semilocal PBE and BLYP functionals, hybrid B3LYP functional, many body based DFT+GW approach, and time dependent DFT calculations. Vibrational spectra of the lowest lying isomers, computed by the force constant method, are used to address IR spectra and thermal free energy of the clusters. Time dependent density functional calculation in real time domain is applied to determine the full a...
Li, Kexue; Liu, Lei; Yu, Peter Y.; Chen, Xiaobo; Shen, D. Z.
2016-05-01
By converting the energy of nuclear radiation to excited electrons and holes, semiconductor detectors have provided a highly efficient way for detecting them, such as photons or charged particles. However, for detecting the radiated neutrons, those conventional semiconductors hardly behave well, as few of them possess enough capability for capturing these neutral particles. While the element Gd has the highest nuclear cross section, here for searching proper neutron-detecting semiconductors, we investigate theoretically the Gd chalcogenides whose electronic band structures have never been characterized clearly. Among them, we identify that γ-phase Gd2Se3 should be the best candidate for neutron detecting since it possesses not only the right bandgap of 1.76 eV for devices working under room temperature but also the desired indirect gap nature for charge carriers surviving longer. We propose further that semiconductor neutron detectors with single-neutron sensitivity can be realized with such a Gd-chalcogenide on the condition that their crystals can be grown with good quality.
First-principles study of atomic and electronic structures of kaolinite in soft rock
Institute of Scientific and Technical Information of China (English)
He Man-Chao; Zhao Jian; Fang Zhi-Jie
2012-01-01
Kaolinite is a kind of clay mineral which often causes large deformations in soft-rock tunnel engineering and thus causes safety issues.To deal with these engineering safety issues,the physical/chemical properties of the kaolinite should be studied from basic viewpoints.By using the density-functional theory,in this paper,the atomic and the electronic structures of the kaolinite are studied within the local-density approximation (LDA).It is found that the kaolinite has a large indirect band gap with the conduction band minimum (CBM) and the valence band maximum (VBM) being at the T and the B points,respeetively.The chemical bonding between the cation and the oxygen anion in kaolinite is mainly ionic,accompanied by a minor covalent component.It is pointed that the VBM and the CBM of kaolinite consist of oxygen 2p and cation s states,respectively.The bond lengths between different cations and anions,as well as of the different OH groups,are also compared.
Lu, Xuefeng; Gao, Xu; Li, Cuixia; Ren, Junqiang; Guo, Xin; La, Peiqing
2017-09-01
Using DFT-GGA-PW91 calculations we investigate the electronic structures and optical properties of doped GaP. It is found that the lattice constants and volume increase slightly for Al, In, As and Sb doped systems and EG distinctly decrease after doping. The formation energies are 0.587 and 0.273 eV for As and Sb doped systems, respectively, and lower remarkably than those in other systems, indicating that the stability of the two systems is higher. The direct band gap transition occurs when doped with In, As and Sb elements. The charge density difference images reveal that electron loss near Al atom is observed accompanying the enhancement of covalent bond feature, and then electron enrichment is present around N atom demonstrating that the ionic bond characteristic is obvious. The Sb-doped system has the higher static dielectric constant illustrating the applications in semiconductor devices. The absorption peak value is located at 194.7 nm for Al-doped system and this shows that the system can absorb a large amount of light and displays ;Barrier-type; characteristics in UV region. In the visible region, the doped systems have lower reflectivity coefficient, indicating that the systems all have ;clear-type; properties. This is conducive to fundamentally insights to a tunable band gap semiconductor with enormous potential in device fields.
Bannikov, V. V.; Shein, I. R.; Ivanovskii, A. L.
2012-01-01
The structural, elastic, magnetic and electronic properties of the layered tetragonal phase KCo 2Se 2 have been examined in details by means of the first-principles calculations and analyzed in comparison with the isostructural KFe 2Se 2 as the parent phase for the newest group of ternary superconducting iron-chalcogenide materials. Our data show that KCo 2Se 2 should be characterized as a quasi-two-dimensional ferromagnetic metal with highly anisotropic inter-atomic bonding owing to mixed ionic, covalent, and metallic contributions inside [Co 2Se 2] blocks, and with ionic bonding between the adjacent [Co 2Se 2] blocks and K sheets. This material should behave in a brittle manner, adopt enhanced elastic anisotropy rather in compressibility than in shear, and should show very low hardness.
The structural, electronic and phonon behavior of CsPbI{sub 3}: A first principles study
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Bano, Amreen, E-mail: banoamreen.7@gmail.com; Khare, Preeti; Parey, Vanshree; Shukla, Aarti; Gaur, N. K. [Department of Physics, Barkatullah University, Bhopal-462026 (India)
2016-05-06
Metal halide perovskites are optoelectronic materials that have attracted enormous attention as solar cells with power conversion efficiencies reaching 20%. The benefit of using hybrid compounds resides in their ability to combine the advantage of these two classes of compounds: the high mobility of inorganic materials and the ease of processing of organic materials. In spite of the growing attention of this new material, very little is known about the electronic and phonon properties of the inorganic part of this compounds. A theoretical study of structural, electronic and phonon properties of metal-halide cubic perovskite, CsPbI{sub 3} is presented, using first-principles calculations with planewave pseudopotential method as personified in PWSCF code. In this approach local density approximation (LDA) is used for exchange-correlation potential.
Role of anion doping on electronic structure and magnetism of GdN by first principles calculations
Zhang, Xuejing
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.
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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.
Jiang, Hao; Cao, Guanghan; Cao, Chao
2015-11-01
The electronic structure of quasi-one-dimensional superconductor K2Cr3As3 is studied through systematic first-principles calculations. The ground state of K2Cr3As3 is paramagnetic. Close to the Fermi level, the , dxy, and orbitals dominate the electronic states, and three bands cross EF to form one 3D Fermi surface sheet and two quasi-1D sheets. The electronic DOS at EF is less than 1/3 of the experimental value, indicating a large electron renormalization factor around EF. Despite of the relatively small atomic numbers, the antisymmetric spin-orbit coupling splitting is sizable (≈60 meV) on the 3D Fermi surface sheet as well as on one of the quasi-1D sheets. Finally, the imaginary part of bare electron susceptibility shows large peaks at Γ, suggesting the presence of large ferromagnetic spin fluctuation in the compound.
Jentschura, U D
2014-01-01
It has been a notably elusive task to find a remotely sensical ansatz for a calculation of Sommerfeld's electrodynamic fine-structure constant alpha_QED ~ 1/137.036 based on first principles. However, this has not prevented a number of researchers to invest considerable effort into the problem, despite the formidable challenges, and a number of attempts have been recorded in the literature. Here, we review a possible approach based on the quantum electrodynamic (QED) beta function, and on algebraic identities relating alpha_QED to invariant properties of "internal" symmetry groups, as well as attempts to relate the strength of the electromagnetic interaction to the natural cut-off scale for other gauge theories. Conjectures based on both classical as well as quantum-field theoretical considerations are discussed. We point out apparent strengths and weaknesses of the most prominent attempts that were recorded in the literature. This includes possible connections to scaling properties of the Einstein-Maxwell La...
First-principles studies of phase transition and structural stability of SrC2 under pressure
Lu, Yi-Lin; Zhao, Hui
2014-09-01
Pressure-induced phase transitions in SrC2 are investigated using the first-principles plane wave pseudopotential method within the generalized gradient approximation. The phase transition from monoclinic phase (CaC2-II-type, space group C2/c) to trigonal (CaC2-VII-type, space group R\\bar {3}m) structure is predicted to occur at 10.4 GPa. The high-pressure phase is thermodynamic, mechanically and dynamically stable, as verified by the calculations of its formation energy, elastic stiffness constants and phonon dispersion. Further the electronic analysis predicates this high-pressure phase to be an insulator. When increasing pressure, the ionic bond between C and Sr is strengthened, as well is the covalent bond between C and C, however, the increase of the ionic interaction between Sr and C preponderates over that of the covalent bond interaction, so the gap is narrowed.
Energy Technology Data Exchange (ETDEWEB)
Shi Hongliang [LCP, Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China)] [State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Zhang Ping, E-mail: zhang_ping@iapcm.ac.c [LCP, Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China)] [Center for Applied Physics and Technology, Peking University, Beijing 100871 (China); Li Shushen [State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Sun Bo [LCP, Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China); Wang Baotian [Institute of Theoretical Physics and Department of Physics, Shanxi University, Taiyuan 030006 (China)
2009-09-21
The electronic structure, elastic constants, Poisson's ratio, and phonon dispersion curves of UC have been systematically investigated from the first-principles calculations by the projector-augmented-wave (PAW) method. In order to describe precisely the strong on-site Coulomb repulsion among the localized U 5f electrons, we adopt the local density approximation (LDA)+U and generalized gradient approximation (GGA)+U formalisms for the exchange correlation term. We systematically study how the electronic properties and elastic constants of UC are affected by the different choice of U as well as the exchange-correlation potential. We show that by choosing an appropriate Hubbard U parameter within the GGA+U approach, most of our calculated results are in good agreement with the experimental data. Therefore, the results obtained by the GGA+U with effective Hubbard parameter U chosen around 3 eV for UC are considered to be reasonable.
Wolff-Goodrich, Silas; Hanken, Benjamin E.; Solomon, Jonathan M.; Asta, Mark
2015-07-01
The accuracy of the special quasirandom structure (SQS) approach for modeling the structure and energetics of fluorite-structured oxide solid solutions with aliovalent cation substitutions is assessed in an ionic-pair potential study of urania and ceria based systems mixed with trivalent rare-earth ions. Mixing enthalpies for SQS supercells containing 96 and 324 lattice sites were calculated using ionic pair potentials for U0.5La0.5O1.75, U0.5Y0.5O1.75, Ce0.5La0.5O1.75, Ce0.5Y0.5O1.75, and Ce0.5Gd0.5O1.75, which all have stoichiometries of pyrochlores. The SQS results were compared to benchmark values for random substitutional disorder obtained using large supercell models. The calculations show significant improvement of the mixing enthalpy for the larger 324 site SQS, which is attributed to a better description of the structural distortions, as characterized by the radial distribution functions in relaxed systems.
Energy Technology Data Exchange (ETDEWEB)
Sahoo, B. D., E-mail: bdsahoo@barc.gov.in; Joshi, K. D.; Gupta, Satish C. [Applied Physics Division, Bhabha Atomic Research Centre, Mumbai-400085 (India)
2015-06-24
Structural and lattice dynamical stability of the LaF3 has been analyzed as a function of hydrostatic compression through first principle electronic band structure calculations. The comparison of enthalpies of various plausible structures calculated at various pressures suggests a phase transition from ambient condition tysonite structure (space group P-3c1) to a primitive orthorhombic structure (space group Pmmn) at a pressure of ∼19.5 GPa, in line with the experimental value of 16 GPa. Further, it is predicted that this phase will remain stable up to 100 GPa (the maximum pressure up to which calculations have been performed in the present work). The theoretically determined equation of state displays a good agreement with experimental data. Various physical quantities such as zero pressure equilibrium volume, bulk modulus, and pressure derivative of bulk modulus have been derived from the theoretically determined equation of state and compared with the available experimental data. Our lattice dynamic calculations correctly demonstrate that at zero pressure the tysonite structure is lattice dynamically stable whereas the Pmmn structure is unstable lattice dynamically. Further, at transition pressure the theoretically calculated phonon spectra clearly show that the Pmmn phase emerges as lattice dynamically stable phase whereas the tysonite structure becomes unstable dynamically, supporting our static lattice calculations.
On structural and lattice dynamic stability of LaF3 under high pressure: A first principle study
Sahoo, B. D.; Joshi, K. D.; Gupta, Satish C.
2015-06-01
Structural and lattice dynamical stability of the LaF3 has been analyzed as a function of hydrostatic compression through first principle electronic band structure calculations. The comparison of enthalpies of various plausible structures calculated at various pressures suggests a phase transition from ambient condition tysonite structure (space group P-3c1) to a primitive orthorhombic structure (space group Pmmn) at a pressure of ˜19.5 GPa, in line with the experimental value of 16 GPa. Further, it is predicted that this phase will remain stable up to 100 GPa (the maximum pressure up to which calculations have been performed in the present work). The theoretically determined equation of state displays a good agreement with experimental data. Various physical quantities such as zero pressure equilibrium volume, bulk modulus, and pressure derivative of bulk modulus have been derived from the theoretically determined equation of state and compared with the available experimental data. Our lattice dynamic calculations correctly demonstrate that at zero pressure the tysonite structure is lattice dynamically stable whereas the Pmmn structure is unstable lattice dynamically. Further, at transition pressure the theoretically calculated phonon spectra clearly show that the Pmmn phase emerges as lattice dynamically stable phase whereas the tysonite structure becomes unstable dynamically, supporting our static lattice calculations.
Energy Technology Data Exchange (ETDEWEB)
Dahmane, F., E-mail: fethallah05@gmail.com [Département de SM, Institue des sciences et des technologies, Centre universitaire de Tissemsilt, 38000, Tissemsilt (Algeria); Modelling and Simulation in Materials Science Laboratory, Physics Department, University of Sidi Bel-Abbes, 22000 Sidi Bel-Abbes (Algeria); Mogulkoc, Y. [Department of Engineering Physics, Ankara University, Ankara (Turkey); Doumi, B.; Tadjer, A. [Modelling and Simulation in Materials Science Laboratory, Physics Department, University of Sidi Bel-Abbes, 22000 Sidi Bel-Abbes (Algeria); Khenata, R. [Laboratoire de Physique Quantique de la Matière et de Modélisation Mathématique (LPQ3M), Université de Mascara, 29000 Mascara (Algeria); Bin Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O Box 2455, Riyadh 11451 (Saudi Arabia); Rai, D.P. [Department of Physics, Pachhunga University College, Aizawl-796001 (India); Murtaza, G. [Materials Modeling Lab, Department of Physics, Islamia College University, Peshawar (Pakistan); Varshney, Dinesh [Materials Science Laboratory, School of Physics, Vigyan Bhavan, Devi Ahilya University, Khandwa Road Campus, Indore 452001 (India)
2016-06-01
Using the first-principles density functional calculations, the structural, electronic and magnetic properties of the Fe{sub 2}XAl (X=Cr, Mn, Ni) compounds in both the Hg{sub 2}CuTi and Cu{sub 2}MnAl-type structures were studied by the full-potential linearized augmented plane waves (FP-LAPW) method. The exchange and correlation potential is treated by the generalized-gradient approximation (GGA) where the results show that the Cu{sub 2}MnAl-type structure is energetically more stable than the Hg{sub 2}CuTi-type structure for the Fe{sub 2}CrAl and Fe{sub 2}MnAl compounds at the equilibrium volume. The full Heusler compounds Fe{sub 2}XAl (X=Cr, Mn) are half-metallic in the Cu{sub 2}MnAl-type structure. Fe{sub 2}NiAl has a metallic character in both CuHg{sub 2}Ti and AlCu{sub 2}Mn-type structures. The total magnetic moments of the Fe{sub 2}CrAl and Fe{sub 2}MnAl compounds are 1.0 and 2.0 μ{sub B}, respectively, which are in agreement with the Slater–Pauling rule M{sub tot}=Z{sub tot}− 24.
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
Energy Technology Data Exchange (ETDEWEB)
Liang, Pei, E-mail: plianghust@gmail.com [College of Optical and Electronic Technology, China Jiliang University, Hangzhou 310018 (China); Liu, Yang [College of Optical and Electronic Technology, China Jiliang University, Hangzhou 310018 (China); Hu, Xing-Hua [Huazhong University of Science and Technology, Wuhan 430074 (China); Wang, Le; Dong, Qian-min; Jing, Xu-feng [College of Optical and Electronic Technology, China Jiliang University, Hangzhou 310018 (China)
2014-04-15
We present numerically the ferromagnetic and spin-resolved electronic properties of Ti-doped AlP system by using first principle based on spin density functional theory. It is found that Ti impurities are spin-polarized, and it suggests a 100% polarization of the conduction carriers from the calculated band structures. Besides, the net magnetic moment of about 1 μ{sub B} per Ti is demonstrated. The ferromagnetic state of 115.7 meV per Ti atom, lower than the anti-ferromagnetic state, is obtained by total energy calculation for both GGA and GGA+U method. And the Curie temperature, higher than 599 K, in Ti-doped AlP is predicted using mean-field approximation (MFA) theory. Both double-exchange and p–d hybridization mechanism contribute to the ferromagnetic ground state of Ti-doped AlP, but the former is dominant. Therefore, it is expected that Ti-doped AlP would be a promising dilute magnetic semiconductor for the applications in the field of Spintronics. - Highlights: • It is found that Ti impurities are spin-polarized, and it suggests a 100% polarization of the conduction carriers for Ti doped AlP. • The Curie temperature, higher than 599 K in Ti-doped AlP is predicted using mean-field approximation (MFA) theory and first principles method combinational with Monte Carlo method. • The double-exchange and p–d hybridization mechanism are also used to explain the ferromagnetic ground state of Ti-doped AlP.
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).
Chouhan, Sunil Singh; Pagare, Gitanjali; Rajagopalan, M.; Sanyal, S. P.
2012-08-01
The structural, electronic, elastic and thermal properties of YX (X = Cd, In, Au, Hg and Tl) intermetallic compounds crystallizing in B2-type structure have been studied using first principles density functional theory within generalized gradient approximation (GGA) for the exchange correlation potential. Amongst all the YX compounds, YIn is stable in distorted tetragonal (P4/mmm) CuAu-type structure at ambient pressure with very small energy difference of 0.00681 Ry. but it undergoes to CsCl-type (B2 phase) structure at 23.3 GPa. Rest of the compounds are stable in B2 structure at ambient condition. The values of elastic moduli as a function of pressure are also reported. The ductility of these compounds has been analyzed using the Pugh rule. Our calculated results indicate that YTl is the most ductile amongst all the B2-YX compounds. YAu is the hardest and less compressible compound due to the largest bulk modulus. The elastic properties such as Young's modulus (E), Poisson's ratio (σ) and anisotropic ratio (A) are also predicted. The anisotropic factor is found to be unity for YHg which shows that this compound is isotropic.
First-principle calculation of the electronic structure, DOS and effective mass TlInSe2
Ismayilova, N. A.; Orudzhev, G. S.; Jabarov, S. H.
2017-05-01
The electronic structure, density of states (DOS), effective mass are calculated for tetragonal TlInSe2 from first principle in the framework of density functional theory (DFT). The electronic structure of TlInSe2 has been investigated by Quantum Wise within GGA. The calculated band structure by Hartwigsen-Goedecker-Hutter (HGH) pseudopotentials (psp) shows both the valence band maximum and conduction band minimum located at the T point of the Brillouin zone. Valence band maximum at the T point and the surrounding parts originate mainly from 6s states of univalent Tl ions. Bottom of the conduction band is due to the contribution of 6p-states of Tl and 5s-states of In atoms. Calculated DOS effective mass for holes and electrons are mDOS h∗ = 0.830m e, mDOS h∗ = 0.492m e, respectively. Electron effective masses are fairly isotropic, while the hole effective masses show strong anisotropy. The calculated electronic structure, density of states and DOS effective masses of TlInSe2 are in good agreement with existing theoretical and experimental results.
First-principles study of the crystal structures and physical properties of H18-BN and Rh6-BN
Ren, Xiao-Yan; Zhao, Chun-Xiang; Niu, Chun-Yao; Wang, Jia-Qi; Jia, Yu; Cho, Jun-Hyung
2016-12-01
As the analog of carbon allotropes, new three-dimensional (3D) boron nitride (BN) allotropes have attracted much attention of researchers due to their great importance in fundamental sciences and wide practical applications. Here, based on first-principles density-functional theory calculations, we predict two new stable BN allotropes: One is H18-BN with the P 6 bar m 2 (D3h1) symmetry containing eighteen atoms in the hexagonal unit cell and the other is Rh6-BN with the R 3 bar m (C3v5) symmetry containing six atoms in the rhombohedral primitive unit cell. The dynamic stabilities of the two structures are examined through the phonon spectrum analysis as well as molecular dynamics simulations, whereas the mechanical properties are analyzed by elastic constants, bulk modulus and shear modulus. From the analysis of the enthalpy evolution with respect to pressure, we find that h-BN can be transformed into either H18-BN or RH6-BN structure under a higher pressure of ∼ 15 GPa. We also find that both the H18-BN and Rh6-BN allotropes are brittle materials with indirect band gaps of 2.31 and 4.48 eV, respectively. The simulated XRD spectra provide detailed structural information of H18-BN and Rh6-BN for future experimental examinations. Our findings not only greatly enrich the existing structural family of 3D-BN materials but also stimulate further experiments.
Hu, Yonghong; Wu, Yunyi; Zhang, Shengli
2016-12-01
Defects are inevitably present in materials, and their existence strongly affects the fundamental physical properties of 2D materials. Here, we performed first-principles calculations to study the structural and electronic properties of antimonene with Stone-Wales defects, highlighting the differences in the structure and electronic properties. Our calculations show that the presence of a SW defect in antimonene changes the geometrical symmetry. And the band gap decreases in electronic band structure with the decrease of the SW defect concentration. The formation energy and cohesive energy of a SW defect in antimonene are studied, showing the possibility of its existence and its good stability, respectively. The difference charge density near the SW defect is explored, by which the structural deformations of antimonene are explained. At last, we calculated the STM images for the SW defective antimonene to provide more information and characters for possible experimental observation. These results may provide meaningful references to the development and design of novel nanodevices based on new 2D materials.
Matsushita, Stephane Yu; Takayama, Akari; Kawamoto, Erina; Hu, Chunping; Hagiwara, Satoshi; Watanabe, Kazuyuki; Takahashi, Takashi; Suto, Shozo
2017-09-01
We have studied the electronic band structure of the hydrogen-terminated Si(110)-(1 ×1 ) [H:Si(110)-(1 ×1 )] surface using angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations in the framework of density functional theory with local density approximation (LDA). The bulk-truncated H:Si(110)-(1 ×1 ) surface is a good template to investigate the electronic band structure of the intrinsic Si(110). In the ARPES spectra, seven bulk states and one surface state due to the H-H interaction are observed clearly. The four bulk states consisting of Si 3 px y orbitals exhibit anisotropic band dispersions along the high symmetric direction of Γ ¯-X ¯ and Γ ¯-X¯' directions, where one state shows one-dimensional character. The calculated band structures show a good agreement with the experimental results except the surface state. We discuss the exact nature of electronic band structures and the applicability of LDA. We have estimated the anisotropic effective masses of electrons and holes of Si(110) for device application.
First-principles study of the Pd–Si system and Pd(001)/SiC(001) hetero-structure
Energy Technology Data Exchange (ETDEWEB)
Turchi, P.E.A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Ivashchenko, V.I. [National Academy of Sciences of Ukraine (NASU), Kiev (Ukraine)
2014-11-01
First-principles molecular dynamics simulations of the Pd(001)/3C–SiC(001) nano-layered structure were carried out at different temperatures ranging from 300 to 2100 K. Various PdSi (Pnma, Fm3m, P6m2, Pm3m), Pd_{2}Si (P6⁻2m, P6_{3}/mmc, P3m1, P3⁻1m) and Pd_{3}Si (Pnma, P6_{3}22, Pm3m, I4/mmm) structures under pressure were studied to identify the structure of the Pd/Si and Pd/C interfaces in the Pd/SiC systems at high temperatures. It was found that a large atomic mixing at the Pd/Si interface occurred at 1500–1800 K, whereas the Pd/C interface remained sharp even at the highest temperature of 2100 K. At the Pd/C interface, voids and a graphite-like clustering were detected. Palladium and silicon atoms interact at the Pd/Si interface to mostly form C22-Pd_{2}Si and D0_{11}-Pd_{3}Si fragments, in agreement with experiment.
Stolbov, Sergey; Zuluaga, Sebastian
2013-02-27
We present here results of our first-principles studies of the sulfur doping effects on the electronic and geometric structures of graphitic carbon nitride (g-C(3)N(4)). Using the ab initio thermodynamics approach combined with some kinetic analysis, we reveal the favorable S-doping configurations. By analyzing the valence charge densities of the doped and undoped systems, we find that sulfur partially donates its p(x)- and p(y)- electrons to the system with some back donation to the S p(z)-states. To obtain an accurate description of the excited electronic states, we calculate the electronic structure of the systems using the GW method. The band gap width calculated for g-C(3)N(4) is found to be equal to 2.7 eV, which is in agreement with experiment. We find the S doping causes a significant narrowing of the gap. Furthermore, the electronic states just above the gap become occupied upon doping, making the material a conductor. Analysis of the projected local density of states provides an insight into the mechanism underlying such changes in the electronic structure of g-C(3)N(4) upon S doping. Based on our results, we propose a possible explanation for the S-doping effect on the photocatalytic properties of g-C(3)N(4) observed in experiments.
First-principle study on bulk and (1 1 1) surface of MP (M = K and Rb) in rocksalt structure
Energy Technology Data Exchange (ETDEWEB)
Gao, Qiang; Li, Lei; Xie, Huan-Huan; Lei, Gang; Deng, Jian-Bo; Hu, Xian-Ru, E-mail: huxianru@lzu.edu.cn
2015-08-01
The electronic and magnetic properties of bulk and (1 1 1) surfaces for MP (M = K and Rb) in rocksalt structure have been investigated by employing first-principle calculations. The results reveal that the compounds are half-metallic ferromagnets at the equilibrium lattice constants with large half-metallic band gaps of 0.46 and 0.74 eV. The (1 1 1) surfaces of KP and RbP keep their bulk half-metallic property. We study the stabilities of the bulk compounds and their (1 1 1) surfaces as well. The results show that those bulk compounds are more stable in the rocksalt structure than in the tetragonal structure. In addition, the K- and Rb-terminated surfaces are more stable than their P-terminated surfaces. - Highlights: • The half metallic properties of rocksalt-type KP and RbP are studied. • The Slater-Pauling behaviours, energy levels and fat-bands of them are discussed. • The properties to KP's and RBP's (1 1 1) surfaces have been investigated. • The stabilities of bulk compounds and surfaces are studied.
Nakata, Maho; Shimazaki, Tomomi
2017-06-26
Large-scale molecular databases play an essential role in the investigation of various subjects such as the development of organic materials, in silico drug design, and data-driven studies with machine learning. We have developed a large-scale quantum chemistry database based on first-principles methods. Our database currently contains the ground-state electronic structures of 3 million molecules based on density functional theory (DFT) at the B3LYP/6-31G* level, and we successively calculated 10 low-lying excited states of over 2 million molecules via time-dependent DFT with the B3LYP functional and the 6-31+G* basis set. To select the molecules calculated in our project, we referred to the PubChem Project, which was used as the source of the molecular structures in short strings using the InChI and SMILES representations. Accordingly, we have named our quantum chemistry database project "PubChemQC" ( http://pubchemqc.riken.jp/ ) and placed it in the public domain. In this paper, we show the fundamental features of the PubChemQC database and discuss the techniques used to construct the data set for large-scale quantum chemistry calculations. We also present a machine learning approach to predict the electronic structure of molecules as an example to demonstrate the suitability of the large-scale quantum chemistry database.
Crystal structures and elastic properties of superhard IrN2 and IrN3 from first principles
Wu, Zhi-Jian; Zhao, Er-Jun; Xiang, Hong-Ping; Hao, Xian-Feng; Liu, Xiao-Juan; Meng, Jian
2007-08-01
First principles calculations were performed to investigate the structural, elastic, and electronic properties of IrN2 for various space groups: cubic Fm-3m and Pa-3 , hexagonal P3221 , tetragonal P42/mnm , orthorhombic Pmmn , Pnnm , and Pnn2 , and monoclinic P21/c . Our calculation indicates that the P21/c phase with arsenopyrite-type structure is energetically more stable than the other phases. It is semiconducting (the remaining phases are metallic) and contains diatomic N-N with the bond distance of 1.414Å . These characters are consistent with the experimental facts that IrN2 is in lower symmetry and nonmetallic. Our conclusion is also in agreement with the recent theoretical studies that the most stable phase of IrN2 is monoclinic P21/c . The calculated bulk modulus of 373GPa is also the highest among the considered space groups. It matches the recent theoretical values of 357GPa within 4.3% and of 402GPa within 7.8%, but smaller than the experimental value of 428GPa by 14.7%. Chemical bonding and potential displacive phase transitions are discussed for IrN2 . For IrN3 , cubic skutterudite structure (Im-3) was assumed. Our calculation indicated that it is also promising to be superhard due to the large bulk modulus of 358GPa and shear modulus of 246GPa . The diatomic N-N bond distance is even shorter (1.272Å) .
Ul Islam, A. K. M. Farid; Helal, M. A.; Liton, M. N. H.; Kamruzzaman, M.; Islam, H. M. Tariqul
2017-04-01
The optical properties of BiOCu Ch and their dependency on the electronic structures are investigated using first principles study. Modified Perdew-Burke-Ernzerhof generalized gradient approximation functional for solids are used to optimize lattice parameters. These optimized lattice parameters are used to calculate the electronic energy band, density of state and optical properties. It is observed that the optical constants are dependent on the energy band gap and also on the contribution of Copper and Chalcogen atoms in the formation of electronic band structure. The obtained results reveal that the optical constants are dominated by the inter-band transitions. In the case of higher incident photon energy these materials behave like metal, where optical constants are dominated by the free carriers. The obtained optical band gaps 0.60, 0.56 and 0.55 eV for BiOCuS, BiOCuSe and BiOCuTe, respectively are consistent with available theoretical results. We also calculate the carrier concentration, electrical conductivity, effective mass of the carrier and their temperature dependency using semi-classical BoltzTraP package. Among these three materials BiOCuTe shows higher electrical conductivity. Analyzing their optical properties, we conclude that these materials are useful in the optoelectronic devices such as coating materials, high frequency reflector, infrared radiation detector and emitter and also important to design quantum devices.
First-principles study on electronic structure, magnetic and dielectric properties of Cr-doped Fe3C
Institute of Scientific and Technical Information of China (English)
杨建平; 陈津; 李伟; 韩培德; 郭丽娜
2016-01-01
The first-principles calculations were performed to investigate the electronic structure, magnetic and dielectric properties of Cr-doped Fe3C, in comparison to those of pure Fe3C and Cr3C. The obtained results show that the thermodynamic stability of Cr- doped Fe3C becomes weaker in terms of the larger formation enthalpy, on the contrary, the metallicity and covalency are found to strengthen to some extent. The magnetic moments of Fe3C, Fe11CrC4(g), and Fe11CrC4(s) are respectively 21.36μB/cell, 16.92μB/cell, and 17.62μB/cell, and in Fe11CrC4(g) and Fe11CrC4(s), the Fe of Wyckoff positions of 8d and 4c is substituted by Cr. The local magnetic moment of Cr at 8d site is larger than that at 4c site in the doped structure, which is opposite to that of Fe. In low frequency band, the permittivity follows the ranking of Fe11CrC4(s)>Cr3C>Fe11CrC4(g)>Fe3C. Once exceeding a certain frequency, the sequence will be broken. Besides the electron transition, the polarization of atoms also makes a contribution to the dielectric properties.
Ma, Liang-Cai; Zhang, Jian-Min; Xu, Ke-Wei
2012-02-01
We present a systematic study on the structural and electronic properties of close-packed Cu nanowires encapsulated in a series of zigzag ( n,0) BeONTs using first-principles calculations. The initial shapes (cylindrical CuNWs and BeONTs) are preserved without any visible changes for the Cu m@( n,0) ( m=6 or 8, 8≤ n≤14) combined systems. The most stable combined systems are Cu 6@(10,0) and Cu 8@(11,0) with an optimal tube-wire distance of about 2.8 Å and a simple superposition of the band structures of their components near the Fermi level. A quantum conductance of 3G 0 is obtained for both Cu 6 and Cu 8 nanowires in either free-standing state or filled into BeONTs. The electron transport will occur only through the inner CuNW and the inert outer BeONT serves well as insulating cable sheath. So the Cu 6@(10,0) and Cu 8@(11,0) combined systems is top-priority in the ULSI circuits and MEMS devices that demand steady transport of electrons.
Energy Technology Data Exchange (ETDEWEB)
Ma Liangcai [College of Physics and Information Technology, Shaanxi Normal University, Xian 710062, Shaanxi (China); School of Physics and Electrical Information Engineering, Ningxia University, Yinchuan 750021, Ningxia (China); Zhang Jianmin, E-mail: jianm_zhang@yahoo.com [College of Physics and Information Technology, Shaanxi Normal University, Xian 710062, Shaanxi (China); Xu Kewei [Department of Physics, Xian University of Arts and Science, Xian 710065, Shaanxi (China)
2012-02-15
We present a systematic study on the structural and electronic properties of close-packed Cu nanowires encapsulated in a series of zigzag (n,0) BeONTs using first-principles calculations. The initial shapes (cylindrical CuNWs and BeONTs) are preserved without any visible changes for the Cu{sub m}-(n,0) (m=6 or 8, 8{<=}n{<=}14) combined systems. The most stable combined systems are Cu{sub 6}-(10,0) and Cu{sub 8}-(11,0) with an optimal tube-wire distance of about 2.8 Angstrom-Sign and a simple superposition of the band structures of their components near the Fermi level. A quantum conductance of 3G{sub 0} is obtained for both Cu{sub 6} and Cu{sub 8} nanowires in either free-standing state or filled into BeONTs. The electron transport will occur only through the inner CuNW and the inert outer BeONT serves well as insulating cable sheath. So the Cu{sub 6}-(10,0) and Cu{sub 8}-(11,0) combined systems is top-priority in the ULSI circuits and MEMS devices that demand steady transport of electrons.
Busemeyer, Brian; Dagrada, Mario; Sorella, Sandro; Casula, Michele; Wagner, Lucas K.
2016-07-01
Resolving the interplay between magnetic interactions and structural properties in strongly correlated materials through a quantitatively accurate approach has been a major challenge in condensed-matter physics. Here we apply highly accurate first-principles quantum Monte Carlo (QMC) techniques to obtain structural and magnetic properties of the iron selenide (FeSe) superconductor under pressure. Where comparable, the computed properties are very close to the experimental values. Of potential ordered magnetic configurations, collinear spin configurations are the most energetically favorable over the explored pressure range. They become nearly degenerate in energy with bicollinear spin orderings at around 7 GPa, when the experimental critical temperature Tc is the highest. On the other hand, ferromagnetic, checkerboard, and staggered dimer configurations become relatively higher in energy as the pressure increases. The behavior under pressure is explained by an analysis of the local charge compressibility and the orbital occupation as described by the QMC many-body wave function, which reveals how spin, charge, and orbital degrees of freedom are strongly coupled in this compound. This remarkable pressure evolution suggests that stripelike magnetic fluctuations may be responsible for the enhanced Tc in FeSe and that higher Tc is associated with nearness to a crossover between collinear and bicollinear ordering.
Energy Technology Data Exchange (ETDEWEB)
Adebambo, Paul O. [Univ. of Agriculture. Abeokuta (Nigeria). Dept. of Physics; McPherson Univ., Abeokuta (Nigeria). Dept. of Physical and Computer Sciences; Adetunji, Bamidele I. [Univ. of Agriculture. Abeokuta (Nigeria). Dept. of Physics; Bells Univ. of Technology, Oto (Nigeria). Dept. of Mathematics; Olowofela, Joseph A. [Univ. of Agriculture. Abeokuta (Nigeria). Dept. of Physics; Oguntuase, James A. [Univ. of Agriculture. Abeokuta (Nigeria). Dept. of Mathematics; Adebayo, Gboyega A. [Univ. of Agriculture. Abeokuta (Nigeria). Dept. of Physics; Abdus Salam International Centre for Theoretical Physics, Trieste (Italy)
2016-05-01
In this work, detailed first-principles calculations within the generalised gradient approximation (GGA) of electronic, structural, magnetic, and optical properties of Ni,Ti, and Al-based Heusler alloys are presented. The lattice parameter of C1{sub b} with space group F anti 43m (216) NiTiAl alloys is predicted and that of Ni{sub 2}TiAl is in close agreement with available results. The band dispersion along the high symmetry points W→L→Γ→X→W→K in Ni{sub 2}TiAl and NiTiAl Heusler alloys are also reported. NiTiAl alloy has a direct band gap of 1.60 eV at Γ point as a result of strong hybridization between the d state of the lower and higher valence of both the Ti and Ni atoms. The calculated real part of the dielectric function confirmed the band gap of 1.60 eV in NiTiAl alloys. The present calculations revealed the paramagnetic state of NiTiAl. From the band structure calculations, Ni{sub 2}TiAl with higher Fermi level exhibits metallic properties as in the case of both NiAl and Ni{sub 3}Al binary systems.
Kanagaprabha, S.; Asvinimeenaatci, A. T.; Rajeswarapalanichamy, R.; Iyakutti, K.
2012-01-01
First principles calculation were performed using Vienna ab-initio simulation package within the frame work of density functional theory (DFT) to understand the electronic properties of magnesium hydride. At normal pressure, the most stable structure of MgH 2 is rutile type with a wide band gap of 3.52 eV, which agrees well with the available data. A pressure induced semi-conductor to metallic transition at a pressure of 92.54 GPa is predicted. Our results indicate a sequence of pressure induced structural phase transition in MgH 2. The obtained sequence of phase transition was α→γ→β→δ→ε at a pressure of 0.37 GPa, 3.89 GPa,7.23 GPa and 11.26 GPa, respectively. Thus our results indicate that MgH 2 is one of the best hydrogen storage material and the maximum storage capacity achieved was 7.7%.
Energy Technology Data Exchange (ETDEWEB)
Caliskan, S., E-mail: scaliskan@fatih.edu.tr; Guner, S.
2015-01-15
Highlights: • An atomic configuration joining the electrodes can govern spin resolved transport. • Co position and concentration in ZnO have a crucial effect on electronic behavior. • It is possible to obtain high spin polarization in Al–Co doped ZnO–Al systems. • Al–Co doped ZnO–Al device structures reveal Schottky-like contact at the interface. - Abstract: Employing first principles, Co doped ZnO systems between the Al electrodes were investigated through the Density Functional Theory combined with Non Equilibrium Green’s Function Formalism. Electronic transport properties of these systems, in the presence of spin property, were revealed using substitutional Co atoms in a supercell. Spin resolved electronic behavior was observed to be crucially governed by atomic configuration, defined by doping position and concentration, of the system joining the electrodes. Using this feature, one can manipulate both the electronic transport and magnetic properties of an Al–Co doped ZnO–Al device structure. A nonlinearity was exhibited in current–voltage characteristics for Co doped ZnO systems attached to the Al electrodes, which implies a Schottky-like contact at the interface. The induced magnetic moment and spin polarization in the system, yielding the spin dependent transport, were elucidated.
Ul Islam, A. K. M. Farid; Helal, M. A.; Liton, M. N. H.; Kamruzzaman, M.; Islam, H. M. Tariqul
2016-11-01
The optical properties of BiOCuCh and their dependency on the electronic structures are investigated using first principles study. Modified Perdew-Burke-Ernzerhof generalized gradient approximation functional for solids are used to optimize lattice parameters. These optimized lattice parameters are used to calculate the electronic energy band, density of state and optical properties. It is observed that the optical constants are dependent on the energy band gap and also on the contribution of Copper and Chalcogen atoms in the formation of electronic band structure. The obtained results reveal that the optical constants are dominated by the inter-band transitions. In the case of higher incident photon energy these materials behave like metal, where optical constants are dominated by the free carriers. The obtained optical band gaps 0.60, 0.56 and 0.55 eV for BiOCuS, BiOCuSe and BiOCuTe, respectively are consistent with available theoretical results. We also calculate the carrier concentration, electrical conductivity, effective mass of the carrier and their temperature dependency using semi-classical BoltzTraP package. Among these three materials BiOCuTe shows higher electrical conductivity. Analyzing their optical properties, we conclude that these materials are useful in the optoelectronic devices such as coating materials, high frequency reflector, infrared radiation detector and emitter and also important to design quantum devices.
Dri, Fernando L.; Shang, ShunLi; Hector, Louis G., Jr.; Saxe, Paul; Liu, Zi-Kui; Moon, Robert J.; Zavattieri, Pablo D.
2014-12-01
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 K) of the monoclinic cellulose Iβ lattice parameters, constant pressure heat capacity, Cp, entropy, S, enthalpy, H, the linear thermal expansion components, ξi, and components of the isentropic and isothermal (single crystal) elastic stiffness matrices, CijS (T) and CijT (T) , respectively. Thermodynamic quantities from phonon calculations computed with DFT and the supercell method provided necessary inputs to compute the temperature dependence of cellulose Iβ properties via the quasi-harmonic approach. The notable exceptions were the thermal conductivity components, λi (the prediction of which has proven to be problematic for insulators using DFT) for which the reverse, non-equilibrium molecular dynamics approach with a force field was applied. The extent to which anisotropy of Young's modulus and Poisson's ratio is temperature-dependent was explored in terms of the variations of each with respect to crystallographic directions and preferred planes containing specific bonding characteristics (as revealed quantitatively from phonon force constants for each atomic pair, and qualitatively from charge density difference contours). Comparisons of the predicted quantities with available experimental data revealed reasonable agreement up to 500 K. Computed properties were interpreted in terms of the cellulose Iβ structure and bonding interactions.
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.
Indian Academy of Sciences (India)
SANTOSH SINGH; MADHVENDRA NATH TRIPATHI
2017-07-01
First-principles study based on density functional theory $\\rm{(DFT)}$ of two prominent phases, the rutile and the anatase phases, of titanium dioxide $\\rm{(TiO_2)}$ are reported within the generalized gradient approximation $\\rm{(GGA)}$. Our calculated band structure shows that there is a significant presence of O-2p and Ti-3d hybridization in the valence bands. These bands are well separated from the conduction bands by a direct band gap value of 1.73 eV in the rutile phase and an indirect band gap value of 2.03 eV in the anatase phase, from $\\Gamma$ to $\\rm{X}$. Our calculations reproduced the peaks in the conduction and valence band, are in good agreement with experimental observations.Our structural optimization for the rutile and anatase phase led to lattice parameter values of 4.62 Å and 2.99 Å rutile and 3.80 Å and 9.55 Å for anatase for $a$ and $c$. The static dielectric values 7.0 and 5.1 for the rutile and anatase phases respectively are in excellent agreement with experimental results. Our calculation of optical properties reveals that maximum value of the transmittance in anatase phase of $\\rm{(TiO_2)}$ may be achieved by considering the anisotropic behaviour of the optical spectra in the optical region for transparent conducting application.
Energy Technology Data Exchange (ETDEWEB)
Chou, M.Y.
1993-05-01
First-principles calculations were carried for the hydrogen-yttrium system using the pseudopotential method within the local density functional approximation (LDA). We have studied the nature of hydrogen pairing in the solid solution phase ({alpha}-YH{sub x}.) and identified the connection with electronic structure. The vibrational spectra, diffusion barrier, and migration path were also investigated. We have also studied the binding characteristics for different interstitial sites and the (420)-plane ordering of octahedral hydrogen in {beta}YH{sub 2+x} within the lattice gas model. Temperature-composition phase diagram was calculated by cluster variational method with the multibody interactions extracted from total energies of related ordered structures. Moreover, the discovery of Peierls distortions in YH{sub 3} explained the unusual hydrogen displacements found in neutron diffraction and the possibility of an excitonic insulating ground state was speculated. Several new improvements in the calculational techniques also been developed: Separable nonlocal pseudopotentials, scheme to calculate the full phonon spectrum, and distance dependent tight-binding parameters. The Ru(0001)-H system was also studied.
Mechanical Properties and Electronic Structure of N and Ta Doped TiC: A First-Principles Study
Ma, Shi-Qing; Liu, Ying; Ye, Jin-Wen; Wang, Bin
2014-12-01
The first principles calculations based on density functional theory (DFT) are employed to investigate the mechanical properties and electronic structure of N and Ta doped TiC. The result shows that the co-doping of nitrogen and tantalum dilates the lattice constant and improves the stability of TiC. Nitrogen and tantalum can signiβcantly enhance the elastic constants and elastic moduli of TiC. The results of B/G and C12-C44 indicate tantalum can markedly increase the ductility of TiC. The electronic structure is calculated to describe the bonding characteristic, which revealed the strong hybridization between C-p and Ta-d and between N-p and Ti-d. The hardnessis is estimated by a semi-empirical model that is based on the Mulliken overlap population and bond length. While the weakest bond takes determinative role of the hardness of materials, the addition of Ta sharply reduces the hardness of TiC.
Interfacial bonding and electronic structure of GaN/GaAs interface: A first-principles study
Energy Technology Data Exchange (ETDEWEB)
Cao, Ruyue; Zhang, Zhaofu; Wang, Changhong; Li, Haobo; Dong, Hong; Liu, Hui; Wang, Weichao, E-mail: weichaowang@nankai.edu.cn [College of Electronic Information and Optical Engineering, Nankai University, Tianjin 300071 (China); Xie, Xinjian [College of Materials Science, Hebei Technology University, Tianjin 300401 (China)
2015-04-07
Understanding of GaN interfacing with GaAs is crucial for GaN to be an effective interfacial layer between high-k oxides and III-V materials with the application in high-mobility metal-oxide-semiconductor field effect transistor (MOSFET) devices. Utilizing first principles calculations, here, we investigate the structural and electronic properties of the GaN/GaAs interface with respect to the interfacial nitrogen contents. The decrease of interfacial N contents leads to more Ga dangling bonds and As-As dimers. At the N-rich limit, the interface with N concentration of 87.5% shows the most stability. Furthermore, a strong band offsets dependence on the interfacial N concentration is also observed. The valance band offset of N7 with hybrid functional calculation is 0.51 eV. The electronic structure analysis shows that significant interface states exist in all the GaN/GaAs models with various N contents, which originate from the interfacial dangling bonds and some unsaturated Ga and N atoms. These large amounts of gap states result in Fermi level pinning and essentially degrade the device performance.
Electronic structure and optical properties of prominent phases of TiO2: First-principles study
Singh, Santosh; Tripathi, Madhvendra Nath
2017-07-01
First-principles study based on density functional theory (DFT) of two prominent phases, the rutile and the anatase phases, of titanium dioxide (TiO_2) are reported within the generalized gradient approximation (GGA). Our calculated band structure shows that there is a significant presence of O-2p and Ti-3d hybridization in the valence bands. These bands are well separated from the conduction bands by a direct band gap value of 1.73 eV in the rutile phase and an indirect band gap value of 2.03 eV in the anatase phase, from Γ to X. Our calculations reproduced the peaks in the conduction and valence band, are in good agreement with experimental observations. Our structural optimization for the rutile and anatase phase led to lattice parameter values of 4.62 Å and 2.99 Å rutile and 3.80 Å and 9.55 Å for anatase for a and c. The static dielectric values 7.0 and 5.1 for the rutile and anatase phases respectively are in excellent agreement with experimental results. Our calculation of optical properties reveals that maximum value of the transmittance in anatase phase of TiO_2 may be achieved by considering the anisotropic behaviour of the optical spectra in the optical region for transparent conducting application.
Energy Technology Data Exchange (ETDEWEB)
Zhao Hongsheng [Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi 830011 (China); Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Graduate School of Chinese Academy of Sciences, Beijing 100049 (China); Chang Aimin, E-mail: changam@ms.xjb.ac.c [Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi 830011 (China); Wang Yunlan [Center for High Performance Computing, Northwestern Polytechnical University, Xi' an 710072 (China)
2009-08-01
We investigated the structural, elastic, and electronic properties of the cubic perovskite-type BaHfO{sub 3} using a first-principles method based on the plane-wave basis set. Analysis of the band structure shows that perovskite-type BaHfO{sub 3} is a wide gap indirect semiconductor. The band-gap is predicted to be 3.94 eV within the screened exchange local density approximation (sX-LDA). The calculated equilibrium lattice constant of this compound is in good agreement with the available experimental and theoretical data reported in the literatures. The independent elastic constants (C{sub 11}, C{sub 12}, and C{sub 44}), bulk modules B and its pressure derivatives B{sup '}, compressibility beta, shear modulus G, Young's modulus Y, Poisson's ratio nu, and Lame constants (mu,lambda) are obtained and analyzed in comparison with the available theoretical and experimental data for both the singlecrystalline and polycrystalline BaHfO{sub 3}. The bonding-charge density calculation make it clear that the covalent bonds exist between the Hf and O atoms and the ionic bonds exist between the Ba atoms and HfO{sub 3} ionic groups in BaHfO{sub 3}.
Mahmood, Asad; Tezcan, Fatih; Kardaş, Gülfeza; Karadaǧ, Faruk
2017-09-01
Incorporating impurities in ZnO provide opportunities to manipulate its electronic and optical properties, which can be exploited for optoelectronic device applications. Among various elements doped in ZnO crystal structure, limited attempts have been accounted for the Sr-doped ZnO system. Further, no theoretical evidence has been reported so far to explore the Sr-doped ZnO frameworks. Here, we report first principle study for the pure and Sr-doped ZnO (Zn1-xSrxO) structure. We employed the Perdew-Burke-Ernzerhof exchange-correlation function parameters in generalized gradient approximations. In light of these estimations, we calculated the electronic band gap, density of states, and optical parameters, for example, absorption, dielectric functions, reflectivity, refractive index, and energy-loss. The studies suggested that Sr incorporation expanded the optical band gap of ZnO. In addition, the energy-loss significantly increased with Sr content which might be associated with an increase in the degree of disorder in the crystal lattice with Sr incorporation. Also, significant changes were seen in the optical properties of ZnO with Sr content in the low energy region. The theoretical results were likewise compared with the previously reported experimental data.
Ma, Liang-Cai; Zhang, Yan; Zhang, Jian-Min; Xu, Ke-Wei
2011-09-01
We present a systemic study of the structural and electronic properties of Cu n nanowires ( n=5, 9 and 13) encapsulated in armchair (8,8) gallium nitride nanotubes (GaNNTs) using the first-principles calculations. We find that the formation processes of these systems are all exothermic. The initial shapes are preserved without any visible changes for the Cu 5@(8,8) and Cu 9@(8,8) combined systems, but a quadratic-like cross-section shape is formed for the outer nanotube of the Cu 13@(8,8) combined system due to the stronger attraction between nanowire and nanotube. The electrons of Ga and N atoms in outer GaN sheath affect the electron conductance of the encapsulated metallic nanowire in the Cu 13@(8,8) combined system. But in the Cu 5@(8,8) and Cu 9@(8,8) combined systems, the conduction electrons are distributed only on the copper atoms, so charge transport will occur only in the inner copper nanowire, which is effectively insulated by the outer GaN nanotube. Considering the maximal metal filling ratio in nanotube, we know that the Cu 9@(8,8) combined system is top-priority in the ultra-large-scale integration (ULSI) circuits and micro-electromechanical systems (MEMS) devices that demand steady transport of electrons.
Electronic structures and optical properties of Nb-doped SrTiO3 from first principles
Shujuan, Jiao; Jinliang, Yan; Guipeng, Sun; Yinnü, Zhao
2016-07-01
The n-type Nb-doped SrTiO3 with different doping concentrations were studied by first principles calculations. The effects of Nb concentration on the formation enthalpy, electronic structure and optical property were investigated. Results show that Nb preferentially enters the Ti site in SrTiO3, which is in good agreement with the experimental observation. The Fermi level of Nb-doped SrTiO3 moves into the bottom of the conduction band, and the system becomes an n-type semiconductor. The effect of Nb-doping concentration on the conductivity was discussed from the microscopic point of view. Furthermore, the 1.11 at% Nb-doped SrTiO3 shows strong absorption in the visible light and becomes a very useful material for photo-catalytic activity. The 1.67 at% and 2.5 at% Nb-doped models will be potential transparent conductive materials. Project supported by the National Natural Science Foundation of China (No. 10974077) and the Innovation Project of Shandong Graduate Education, China (No. SDYY13093).
First-principles simulations of CaO and CaSiO3 liquids: structure, thermodynamics and diffusion
Bajgain, Suraj K.; Ghosh, Dipta B.; Karki, Bijaya B.
2015-05-01
We have performed first-principles molecular dynamics simulations of CaO and CaSiO3 liquids over broad ranges of pressure (0-150 GPa) and temperature (2,500-8,000 K) within density-functional theory. The simulated liquid structure changes considerably on compression with the mean cation-anion coordination numbers increasing nearly linearly with volume. The Ca-O coordination number increases from 5 (7) near the ambient pressure to 8 (10) at high pressure for CaO (CaSiO3) liquid. The Si-O coordination number increases from 4 to 6 over the same pressure regime. Our results show that both liquids are much more compressible than their solid counterparts implying the possibility of liquid-solid density crossovers at high pressure. The Grüneisen parameter of both the liquids increases with pressure, which is opposite in case of crystalline phases. The calculated self-diffusion coefficients strongly depend on temperature and pressure, thereby requiring non-Arrhenian representation with variable activation volume. The diffusivity differences between the two liquids tend to be large at low-temperature and low-pressure regime. Also, comparisons with MgSiO3 liquid suggest that network modifier cations Ca and Mg behave similarly though Ca is more coordinated and more mobile as compared to Mg.
The electronic structures and ferromagnetism of Fe-doped GaSb: The first-principle calculation study
Lin, Xue-ling; Niu, Cao-ping; Pan, Feng-chun; Chen, Huan-ming; Wang, Xu-ming
2017-09-01
The electronic structures and the magnetic properties of Fe doped GaSb have been investigated by the first-principles calculation based on the framework of the generalized gradient approximation (GGA) and GGA+U schemes. The calculated results indicated that Fe atoms tend to form the anti-ferromagnetic (AFM) coupling with the nearest-neighbor positions preferentially. Compared with the anti-ferromagnetic coupling, the ferromagnetic interactions occurred at the second nearest-neighbor and third nearest-neighbor sites have a bigger superiority energetically. The effect of strong electron correlation at Fe-d orbit taking on the magnetic properties predicted by GGA+U approach demonstrated that the ferromagnetic (FM) coupling between the Fe ions is even stronger in consideration of the strong electron correlation effect. The ferromagnetism in Fe doped GaSb system predicted by our investigation implied that the doping of Fe into GaSb can be as a vital routine for manufacturing the FM semiconductors with higher Curie temperature.
Zhang, Lei; Ju, Ming-Gang; Liang, WanZhen
2016-08-17
With efficiencies exceeding 20% and low production costs, lead halide perovskite solar cells (PSCs) have become potential candidates for future commercial applications. However, there are serious concerns about their long-term stability and environmental friendliness, heavily related to their commercial viability. Herein, we present a theoretical investigation based on the ab initio molecular dynamics (AIMD) simulations and the first-principles density functional theory (DFT) calculations to investigate the effects of sunlight and moisture on the structures and properties of MAPbI3 perovskites. AIMD simulations have been performed to simulate the impact of a few water molecules on the structures of MAPbI3 surfaces terminated in three different ways. The evolution of geometric and electronic structures as well as the absorption spectra has been shown. It is found that the PbI2-terminated surface is the most stable while both the MAI-terminated and PbI2-defective surfaces undergo structural reconstruction, leading to the formation of hydrated compounds in a humid environment. The moisture-induced weakening of photoabsorption is closely related to the formation of hydrated species, and the hydrated crystals MAPbI3·H2O and MA4PbI6·2H2O scarcely absorb the visible light. The electronic excitation in the bare and water-absorbed MAPbI3 nanoparticles tends to weaken Pb-I bonds, especially those around water molecules, and the maximal decrease of photoexcitation-induced bond order can reach up to 20% in the excited state in which the water molecules are involved in the electronic excitation, indicating the accelerated decomposition of perovskites in the presence of sunlight and moisture. This work is valuable for understanding the mechanism of chemical or photochemical instability of MAPbI3 perovskites in the presence of moisture.
Tu, Bingtian; Liu, Xin; Wang, Hao; Wang, Weimin; Zhai, Pengcheng; Fu, Zhengyi
2016-12-19
The nuclear magnetic resonance (NMR) technique gives insight into the local information in a crystal structure, while Rietveld refinement of powder X-ray diffraction (PXRD) sketches out the framework of a crystal lattice. In this work, first-principles calculations were combined with the solid-state NMR technique and Rietveld refinement to explore the crystal structure of a disordered aluminum oxynitride (γ-alon). The theoretical NMR parameters (chemical shift, δiso, quadrupolar coupling constants, CQ, and asymmetry parameter, η) of Al22.5O28.5N3.5, predicted by the gauge-including projector augmented wave (GIPAW) algorithm, were used to facilitate the analytical investigation of the (27)Al magic-angle spinning (MAS) NMR spectra of the as-prepared sample, whose formula was confirmed to be Al2.811O3.565N0.435 by quantitative analysis. The experimental δiso, CQ, and η of (27)Al showed a small discrepancy compared with theoretical models. The ratio of aluminum located at the 8a to 16d sites was calculated to be 0.531 from the relative integration of peaks in the (27)Al NMR spectra. The occupancies of aluminum at the 8a and 16d positions were determined through NMR investigations to be 0.9755 and 0.9178, respectively, and were used in the Rietveld refinement to obtain the lattice parameter and anion parameter of Al2.811O3.565N0.435. The results from (27)Al NMR investigations and PXRD structural refinement complemented each other. This work provides a powerful and accessible strategy to precisely understand the crystal structure of novel oxynitride materials with multiple disorder.
Electronic structure and magnetism of Ge(Sn)TMXTe1-X (TM = V, Cr, Mn): A first principles study
Liu, Yong; Bose, S. K.; Kudrnovský, J.
2016-12-01
This work presents the results of first principles calculations of the electronic and magnetic properties of the compound SnTe and GeTe in zinc blende (ZB) and rock salt (RS) structures, doped with 3d transition metal V, Cr, and Mn. The present study, initiated from the viewpoint of potential application in spintronics, is motivated by our earlier work involving these two compounds, where the doping was limited to the Sn and Ge sublattices. In view of some discrepancies between our calculated results and the available experimental data, in this work we have examined the effect of the Te-sublattice doping. The case of Mn-doping, where the previous results of calculations seemed to differ most from the experimentally available data, is examined further by looking at the effect of Mn atoms partially occupying interstitial sites as well. From the standpoint of potential application in spintronics, we look for half-metallic (HM) states and tabulate their properties in both rock salt and zinc blende structures. ZB structure is found to be more conducive to HM state in general. Among the binary compounds we identify several HM candidates: VGe, VSn, MnGe, MnSn and MnTe at their equilibrium volumes and all in ZB structure. Estimates of the Curie temperature for the ferromagnetic compounds including the half-metals are presented. It is shown that despite the ferromagnetic (FM) nature of the Mn-Mn interaction for the Te-doped case, a simultaneous doping of both Ge(Sn)- and Te-sublattice with Mn atoms would leave the material predominantly antiferromagnetic (AFM).
Energy Technology Data Exchange (ETDEWEB)
Ganeshraj, C.; Santhosh, P. N., E-mail: santhosh@physics.iitm.ac.in [Low Temperature Physics Laboratory, Department of Physics, Indian Institute of Technology Madras, Chennai 600 036, Tamil Nadu (India)
2014-10-14
We report first-principles study of structural, electronic, vibrational, dielectric, and elastic properties of Ba₂YTaO₆, a pinning material in high temperature superconductors (HTS), by using density functional theory. By using different exchange-correlation potentials, the accuracy of the calculated lattice constants of Ba₂YTaO₆ has been achieved with GGA-RPBE, since many important physical quantities crucially depend on change in volume. We have calculated the electronic band structure dispersion, total and partial density of states to study the band gap origin and found that Ba₂YTaO₆ is an insulator with a direct band gap of 3.50 eV. From Mulliken population and charge density studies, we conclude that Ba₂YTaO₆ have a mixed ionic-covalent character. Moreover, the vibrational properties, born effective charges, and the dielectric permittivity tensor have been calculated using linear response method. Vibrational spectrum determined through our calculations agrees well with the observed Raman spectrum, and allows assignment of symmetry labels to modes. We perform a detailed analysis of the contribution of the various infrared-active modes to the static dielectric constant to explain its anisotropy, while electronic dielectric tensor of Ba₂YTaO₆ is nearly isotropic, and found that static dielectric constant is in good agreement with experimental value. The six independent elastic constants were calculated and found that tetragonal Ba₂YTaO₆ is mechanically stable. Other elastic properties, including bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and elastic anisotropy ratios are also investigated and found that Poisson's ratio and Young's modulus of Ba₂YTaO₆ are similar to that of other pinning materials in HTS.
Ganeshraj, C.; Santhosh, P. N.
2014-10-01
We report first-principles study of structural, electronic, vibrational, dielectric, and elastic properties of Ba2YTaO6, a pinning material in high temperature superconductors (HTS), by using density functional theory. By using different exchange-correlation potentials, the accuracy of the calculated lattice constants of Ba2YTaO6 has been achieved with GGA-RPBE, since many important physical quantities crucially depend on change in volume. We have calculated the electronic band structure dispersion, total and partial density of states to study the band gap origin and found that Ba2YTaO6 is an insulator with a direct band gap of 3.50 eV. From Mulliken population and charge density studies, we conclude that Ba2YTaO6 have a mixed ionic-covalent character. Moreover, the vibrational properties, born effective charges, and the dielectric permittivity tensor have been calculated using linear response method. Vibrational spectrum determined through our calculations agrees well with the observed Raman spectrum, and allows assignment of symmetry labels to modes. We perform a detailed analysis of the contribution of the various infrared-active modes to the static dielectric constant to explain its anisotropy, while electronic dielectric tensor of Ba2YTaO6 is nearly isotropic, and found that static dielectric constant is in good agreement with experimental value. The six independent elastic constants were calculated and found that tetragonal Ba2YTaO6 is mechanically stable. Other elastic properties, including bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and elastic anisotropy ratios are also investigated and found that Poisson's ratio and Young's modulus of Ba2YTaO6 are similar to that of other pinning materials in HTS.
Ding, Yi; Wang, Yanli
2016-08-17
Germanium monochalcogenides, i.e. GeS and GeSe sheets, are isoelectronic analogues of phosphorene, which have been synthesized in recent experiments (P. Ramasamy et al., J. Mater. Chem. C, 2016, 4, 479). Utilizing first-principles calculations, we have investigated their tunable electronic and magnetic properties via light non-metallic atom (B, C, N, O, Si, P, S) functionalization. We find that on these GeS and GeSe sheets O and S adatoms prefer to locate at the top site above the Ge atom, while the other ones like to occupy the anion site, which push the original S/Se atom to the hollow site instead. O and S adatoms slightly affect the semiconducting behaviour of the doped systems, while B, C, N, Si, P ones will drastically modify their band structures and induce versatile spintronic properties. Through the supercell calculations, B and C adatoms are found to induce a bipolar semiconducting behaviour in the decorated systems, while the N/P adatom will cause a spin-gapless-semiconducting/nearly-half-metallic feature in them. The B/C/N/Si/P-substituted GeS/GeSe sheet can be formed by removing the hollow-site S/Se atom from the adatom-decorated structures, which exhibit an opposite semiconducting/metallic behaviour to their phosphorene counterparts. A general odd-even rule is proposed for this phenomenon, which shows that an odd (even) number of valence electron difference between the substitution and host atoms would cause a metallic (semiconducting) feature in the substituted systems. Our study demonstrates that atom functionalization is an efficient way to tailor the properties of GeS and GeSe nanosheets, which have adaptable electronic properties for potential applications in nanoelectronics and spintronics.
Rak, Zs.; O'Brien, C. J.; Brenner, D. W.; Andersson, D. A.; Stanek, C. R.
2016-09-01
The results of recent studies are discussed in which first principles calculations at the atomic level have been used to expand the thermodynamic database for science-based predictive modeling of the chemistry, composition and structure of unwanted oxides that deposit on the fuel rods in pressurized light water nuclear reactors. Issues discussed include the origin of the particles that make up deposits, the structure and properties of the deposits, and the forms by which boron uptake into the deposits can occur. These first principles approaches have implications for other research areas, such as hydrothermal synthesis and the stability and corrosion resistance of other materials under other extreme conditions.
Liu, Jingwei; Yu, Guangtao; Shen, Xiaopeng; Zhang, Hui; Li, Hui; Huang, Xuri; Chen, Wei
2017-03-01
Based on the first-principles DFT computations, we systematically investigated the geometries, stabilities, electronic and magnetic properties of fully and partially hydrogenated Ge nanoribbons (fH-GeNRs and pH-GeNRs) with the zigzag and armchair edges. It is revealed that the chair-like configuration is the lowest-lying one for zigzag/armchair-edged fH-GeNRs. Regardless of the edge chirality, the full hydrogenation can effectively widen the band gap of GeNR, and endow fH-GeNRs with the nonmagnetic (NM) semiconducting behaviors, where the band gap decreases with the increase of ribbon width. Comparatively, independent of hydrogenation ratio, all the pH-GeNRs with zigzag edge are the antiferromagnetic semiconductors while all the pH-GeNRs with armchair edge are NM semiconductors. When increasing the hydrogenation ratio, the band gap of pH-GeNRs can increase, but the variation of band gap can exhibit the intriguing three family behavior for the armchair-edged pH-GeNRs. Especially, all these pH-GeNRs can exhibit the almost same electronic and magnetic properties as the remaining pristine GeNRs without hydrogenation. This may offer a potential strategy to realize the "narrow" GeNRs in large scale. Finally, all these hydrogenated GeNRs can possess high structure stability, indicating a great possibility of their experimental realization. These valuable insights can be advantageous for promoting the Ge-based nanomaterials in the application of multifunctional nanodevice.
Energy Technology Data Exchange (ETDEWEB)
Ivashchenko, V.I.; Scrynskyy, P.L. [Frantsevych Institute for Problems of Material Science, NAS of Ukraine, 3, Krzhyzhanovsky Str., 03142 Kyiv (Ukraine); Dub, S.N. [Bakul Institute for Superhard Materials, NAS of Ukraine, 2, Avtozavodska Str., 04074 Kyiv (Ukraine); Butenko, O.O.; Kozak, A.O.; Sinelnichenko, O.K. [Frantsevych Institute for Problems of Material Science, NAS of Ukraine, 3, Krzhyzhanovsky Str., 03142 Kyiv (Ukraine)
2016-01-29
The Al―Mg―B films were deposited on silicon substrates by direct current magnetron sputtering from the AlMgB{sub 14} target at low discharge power and at substrate temperature ranging from 100 to 500 °C. The deposited films have been annealed at 1000 °C in vacuum, and characterized by X-ray diffraction, atomic force microscopy, Fourier transform infra-red spectroscopy, nano- and micro-indentation, and scratch testing. The films exhibit lower hardness than the bulk AlMgB{sub 14} material, which is due to their amorphous structure in which the strong intra-icosahedron B―B bonds are almost lacking and the weaker B―O bonds are predominant. After the annealing, a reduction of a number of B―O bonds and a formation of crystallites in the films lead to an increase in the nanohardness and elastic modulus. The as-deposited films exhibit a low coefficient of friction of 0.08–0.12. First-principles studies show that the icosahedra in amorphous AlMgB{sub 14}-based materials are not fully developed, which is the reason of their lower mechanical performance. - Highlights: • Al―Mg―B films were deposited at different substrate temperatures. • The as-deposited films were amorphous, whereas the annealed ones were nanostructured. • Mechanical properties were analyzed as functions of substrate and annealing temperatures. • Ab-initio MD simulations of AlMgB{sub 14}-based materials were carried out. • Both experimental and theoretical investigations enabled one to explain film properties.
Xie, RH; Bryant, GW; Jensen, L; Smith, VH
2003-01-01
The structural, electronic, vibrational, and magnetic properties of the C48N12 azafullerene and C-60 are comparatively studied from the first-principles calculations. Full geometrical optimization and Mulliken charge analysis are performed. Electronic structure calculations of C48N12 show that the
Structural and electronic properties of cubic KNbO{sub 3} (0 0 1) surfaces: A first-principles study
Energy Technology Data Exchange (ETDEWEB)
Luo, Bingcheng [State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Wang, Xiaohui, E-mail: wxh@mail.tsinghua.edu.cn [State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Tian, Enke [School of Science, China University of Geosciences, Beijing 100083 (China); Li, Guowu [Crystal Structure Laboratory, National Laboratory of Mineral Materials, China University of Geosciences, Beijing 100083 (China); Li, Longtu [State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China)
2015-10-01
Highlights: • To the best of our knowledge, the (0 0 1) surfaces of SrTiO{sub 3}, BaTiO{sub 3}, CaTiO{sub 3} and PbTiO{sub 3} have been extensively investigated, but few ab initio calculations of structural and electronic properties of cubic KNbO{sub 3} (0 0 1) surface are reported. • The surface energy for the KO terminated was 1.21 eV, higher than the calculated surface energy of 0.75 eV for NbO{sub 2} termination, revealing that it take much less energy to cleave on the NbO{sub 2} plane than on the KO plane. • Mulliken population showed a strong increase in the K−O chemical bonding on the top surface of the KO-terminated slab, while the Nb−O chemical bonding on the top surface of the NbO{sub 2}-terminated slab decreased by 50 me. • The bond populations for K−O were much smaller than that for Nb−O, indicating significant covalency for Nb−O bonding. - Abstract: We present the calculations of the cubic perovskite KNbO{sub 3} (0 0 1) surface with NbO{sub 2} and KO terminations within the first-principles density functional theory. The electronic structure, surface energy, and charge distribution for both termination are calculated. For the case of NbO{sub 2}-terminated surfaces, the largest atomic relaxation is in the first-layer atoms, while for KO terminations in the second-layer atoms. The surface energy for the KO terminated was 1.21 eV, higher than the calculated surface energy of 0.75 eV for NbO{sub 2} termination, revealing that it takes much less energy to cleave on NbO{sub 2} plane than on a KO plane. The band gaps for KO-terminated and NbO{sub 2}-terminated surface are 1.70 and 1.30 eV, respectively. Mulliken population analysis shows the strong increase in the K−O chemical bonding on the top surface of the KO-terminated slab and significant covalency for Nb−O bonding.
Powell, B J; Bernstein, N; Brake, K; McKenzie, Ross H; Meredith, P; Pederson, M R
2016-01-01
We report first principles density functional calculations for hydroquinone (HQ), indolequinone (IQ) and semiquinone (SQ). These molecules are believed to be the basic building blocks of the eumelanins, a class of bio-macromolecules with important biological functions (including photoprotection) and with potential for certain bioengineering applications. We have used the DeltaSCF (difference of self consistent fields) method to study the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), Delta_HL. We show that Delta_HL is similar in IQ and SQ but approximately twice as large in HQ. This may have important implications for our understanding of the observed broad band optical absorption of the eumelanins. The possibility of using this difference in Delta_HL to molecularly engineer the electronic properties of eumelanins is discussed. We calculate the infrared and Raman spectra of the three redox forms from first principles. Each of the molecules ...
Rafique, Muhammad; Shuai, Yong; Tan, He-Ping; Hassan, Muhammad
2017-03-01
We present first-principles density-functional calculations for the structural, electronic and magnetic properties of monolayer graphene doped with 3d (Ti, V, Cr, Fe, Co, Mn and Ni) metal trioxide TMO3 halogen clusters. In this paper we used two approaches for 3d metal trioxide clusters (i) TMO3 halogen cluster was embedded in monolayer graphene substituting four carbon (C) atoms (ii) three C atoms were substituted by three oxygen (O) atoms in one graphene ring and TM atom was adsorbed at the hollow site of O atoms substituted graphene ring. All the impurities were tightly bonded in the graphene ring. In first case of TMO3 doped graphene layer, the bond length between Csbnd O atom was reduced and bond length between TM-O atom was increased. In case of Cr, Fe, Co and Ni atoms substitution in between the O atoms, leads to Fermi level shifting to conduction band thereby causing the Dirac cone to move into valence band, however a band gap appears at high symmetric K-point. In case of TiO3 and VO3 substitution, system exhibits semiconductor properties. Interestingly, TiO3-substituted system shows dilute magnetic semiconductor behavior with 2.00 μB magnetic moment. On the other hand, the substitution of CoO3, CrO3, FeO3 and MnO3 induced 1.015 μB, 2.347 μB, 2.084 μB and 3.584 μB magnetic moment, respectively. In second case of O atoms doped in graphene and TM atoms adsorbed at the hollow site, the O atom bulges out of graphene plane and bond length between TM-O atom is increased. After TM atoms adsorption at the O substituted graphene ring the Fermi level (EF) shifts into conduction band. In case of Cr and Ni adsorption, system displays indirect band gap semiconductor properties with 0.0 μB magnetic moment. Co adsorption exhibits dilute magnetic semiconductor behavior producing 0.916 μB magnetic moment. Fe, Mn, Ti and V adsorption introduces band gap at high symmetric K-point also inducing 1.54 μB, 0.9909 μB, 1.912 μB, and 0.98 μB magnetic moments, respectively
Kaneko, Tomoaki; Tajima, Nobuo; Yamasaki, Takahiro; Ohno, Takahisa
2017-09-01
Using first principles calculations based on a density functional theory, the energetics and electronic properties of a (2 × 1) π-bonded chain structure in several polytypes of SiC surfaces are discussed with special attention to the stacking sequence of SiC bilayers. We found that the stacking sequence of the topmost two SiC bilayers plays a decisive role for the stability and electronic structures of the π-bonded chain structure. We showed that the homo-elemental bonds in π-bonded chain structures cause alterations in the electronic structures of both the Si- and C-faces. The energetics of π-bonded chain structures on other group IV and IV-IV compound semiconductors were also investigated. We also showed that the buckling structure in the monolayer honeycomb lattice reflects the buckling of the topmost two atoms in the π-bonded chain structure observed in Si(111) and Ge(111).
Uchida, T.; Kakehashi, Y.; Kimura, N.
2016-02-01
The magnetic and electronic structures of Mn3Pt and Mn3Rh, which are three-dimensional frustrated itinerant magnets with a Cu3Au-type crystal structure, have been investigated by means of the first-principles Molecular Spin Dynamics (MSD) method. The theory is based on the first-principles tight-binding linear muffin-tin orbital Hamiltonian combined with the functional integral method and the isothermal MSD technique, and allows us to determine automatically the magnetic structures of itinerant magnets at finite temperatures. The MSD calculations using a self-consistent site-dependent effective medium show that below the Néel temperature Mn3Pt with fixed crystal structure (Cu3Au structure) and volume exhibits a second-order transition from a triangular structure to another noncollinear phase with increasing temperature. Mn3Rh, on the other hand, shows no sign of a phase transition up to the Néel temperature. We found that the Mn-Eg DOS peak, which is responsible for the ferromagnetic couplings among the second nearest-neighbor Mn local moments, develops at the Fermi energy (EF) around 350 K for Mn3Pt, while the peak development for Mn3Rh occurs with increasing temperature slightly above EF.
Imran, Muhammad; Hussain, Fayyaz; Rashid, Muhammad; Ullah, Hafeez; Sattar, Atif; Iqbal, Faisal; Ahmad, Ejaz
2016-03-01
The semiconducting two-dimensional (2D) architectures materials have potential applications in electronics and optics. The design and search of new 2D materials have attracted extensive attention recently. In this study, first principle calculation has been done on 2D gallium nitride (GaN) monolayer with respect to its formation and binding energies. The electronic and optical properties are also investigated. It is found that the single isolated GaN sheet is forming mainly ionic GaN bonds despite a slightly weaker GaN interaction as compared with its bulk counterpart. The dielectric constant value of 2D GaN is smaller as compared to 3D GaN due to less effective electronic screening effect in the layer, which is accompanied by lesser optical adsorption range and suggested to be a promising candidate in electronic and optoelectronic devices.
Muñoz García, Ana Belén; Barandiarán, Zoila; Seijo, Luis
2012-01-01
This is an electronic version of an article published in Journal of Materials Chemistry. Muñoz García, A.B., Barandiarán, Z. and Luis Seijo. "Antisite defects in Ce-doped YAG (Y3Al5O12): First-principles study on structures and 4f-5d transitions". Journal of Materials Chemistry 22 (2012): 19888-19897
Bulk Modulus and Electronic Band Structure of ZnGa2X4 (X=S,Se): a First-Principles Study
Institute of Scientific and Technical Information of China (English)
JIANG Xiao-Shu; MI Shu; SUN eeng-Jun; LU Yuan; LIANG Jiu-Qing
2009-01-01
First-principles local density functional calculations are presented for the compounds ZnGa2X4 (X = S, Se). We investigate the bulk moduli and electronic band structures in a defect chalcopyrite structure. The lattice constants and internal parameters axe optimized. The electronic structures are analysed with the help of total and partial density of states. The relation between the cohesive energy and the unit cell volume is obtained by fully relaxed structures. We derive the bulk modulus of ZnGa2X4 by fitting the Birch-Murnaghan's equation of state. The extended Cohen's empirical formula agrees well with our ab initio results.
Akashi, Ryosuke; Kawamura, Mitsuaki; Tsuneyuki, Shinji; Nomura, Yusuke; Arita, Ryotaro
2015-06-01
We calculate the superconducting transition temperatures (Tc) in sulfur hydrides H2S and H3S from first principles using the density functional theory for superconductors. At pressures of ≲150 GPa, the high values of Tc (≥130 K) observed in a recent experiment (A. P. Drozdov, M. I. Eremets, and I. A. Troyan, arXiv:1412.0460) are accurately reproduced by assuming that H2S decomposes into R 3 m H3S and S. For higher pressures, the calculated Tc's for I m 3 ¯m H3S are systematically higher than those for R 3 m H3S and the experimentally observed maximum value (190 K), which suggests the possibility of another higher-Tc phase. We also quantify the isotope effect from first principles and demonstrate that the isotope effect coefficient can be larger than the conventional value (0.5) when multiple structural phases energetically compete.
Institute of Scientific and Technical Information of China (English)
Ryota NAKANISHI; Koji SUEOKA; Seiji SHIBA; Makoto HINO; Koji MURAKAMI; Ken MURAOKA
2009-01-01
A study the with first principles calculation of the interfaces of the Ni layer or Cu layer on the Fe(100) surface formed with metal plating was performed. Ni or Cu atoms were shown to adopt the corresponding position to the bcc structure of the Fe(100) substrate. Other calculations showed that the interfaces of Ni (5 atomic layers)/Fe(100) (5 layers) or Cu (5 atomic layers)/Fe(100) (5 layers) had square lattices. The orientation relationship of Ni/Fe(100) interface corresponds to fcc-Ni(100)//bcc-Fe(100), Ni[011]//Fe[010], and Similar results were obtained for Cu/Fe(100) interfaces. This structure was supported by TEM analysis of plated Ni layer on Fe(100) surfaces. The adhesion strength of the Ni/Fe(100) interface evaluated by first principles calculation was higher than that of the Cu/Fe(100) interface. The experimental results of Hull cell iron plated with Ni or Cu supported the results of the calculation. These results indicate that the first principles calculation, which deals with the ideal interface at the atomic scale, has the potential to evaluate the adhesion strength of metallic material interfaces.
Ferdous, Naheed; Ertekin, Elif
2016-07-01
The epitaxial integration of functional oxides with wide band gap semiconductors offers the possibility of new material systems for electronics and energy conversion applications. We use first principles to consider an epitaxial interface between the correlated metal oxide SrRuO3 and the wide band gap semiconductor TiO2, and assess energy level alignment, interfacial chemistry, and interfacial dipole formation. Due to the ferromagnetic, half-metallic character of SrRuO3, according to which only one spin is present at the Fermi level, we demonstrate the existence of a spin dependent band alignment across the interface. For two different terminations of SrRuO3, the interface is found to be rectifying with a Schottky barrier of ≈1.3-1.6 eV, in good agreement with experiment. In the minority spin, SrRuO3 exhibits a Schottky barrier alignment with TiO2 and our calculated Schottky barrier height is in excellent agreement with previous experimental measurements. For majority spin carriers, we find that SrRuO3 recovers its exchange splitting gap and bulk-like properties within a few monolayers of the interface. These results demonstrate a possible approach to achieve spin-dependent transport across a heteroepitaxial interface between a functional oxide material and a conventional wide band gap semiconductor.
Energy Technology Data Exchange (ETDEWEB)
Li, Li [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics; Civil Aviation Flight Univ. of China, Guanghan (China). Dept. of Physics; Zeng, Zhao-Yi [Chongqing Normal Univ., Chongqing (China). College of Physics and Electronic Engineering; Liang, Ting; Tang, Mei; Cheng, Yan [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics
2017-07-01
The influence of pressure on the elastic and mechanical properties of the hexagonal transition-metal dichalcogenide WS{sub 2} is investigated using the first-principles calculations. With the increase in pressure, the lattice parameters and the volume of WS{sub 2} decrease, which is exactly in agreement with the available experimental data and other calculated results. The elastic constants C{sub ij}, bulk modulus B, shear modulus G, Young's modulus E, and Poisson's ratio σ of WS{sub 2} also increase with pressure. At last, for the first time, the band gaps of energy, the partial density of states, and the total density of states under three different pressures are obtained and analysed. It is found that the band gap of WS{sub 2} decreases from 0.843 to 0 eV when the external pressure varies from 0 to 20 GPa, which implies that WS{sub 2} may transform from semiconductors to semimetal phase at a pressure about 20 GPa.
Energy Technology Data Exchange (ETDEWEB)
Xiang, Huimin; Feng, Zhihai; Li, Zhongping; Zhou, Yanchun, E-mail: yczhou@imr.ac.cn, E-mail: yczhou714@gmail.com [Science and Technology on Advanced Functional Composite Laboratory, Aerospace Research Institute of Materials and Processing Technology, No. 1 South Dahongmen Road, Beijing 100076 (China)
2015-06-14
High temperature mechanical and thermodynamic properties of TiB{sub 2} are important to its applications as ultrahigh temperature ceramic, which were not well understood. In this study, the thermodynamic and mechanical properties of TiB{sub 2} were investigated by the combination of first principle and phonon dispersion calculations. The thermal expansion of TiB{sub 2} was anisotropic, α{sub c}/α{sub a} is nearly constant (1.46) from 300 K to 1500 K, theoretically. The origination of this anisotropy is the anisotropic compressibility. The heat capacity at constant pressure was estimated from the theoretical entropy and fitted the experimental result quite well when higher-order anharmonic effects were considered. Theoretical isentropic elastic constants and mechanical properties were calculated and their temperature dependence agreed with the existed experiments. From room temperature to 1500 K, the theoretical slope is −0.0211 GPa·K{sup −1}, −0.0155 GPa·K{sup −1}, and −0.0384 GPa·K{sup −1} for B, G, and E, respectively. Our theoretical results highlight the suitability of this method in predicting temperature dependent properties of ultrahigh temperature ceramics and show ability in selecting and designing of novel ultrahigh temperature ceramics.
Quesne-Turin, Ambroise; Touzeau, Jeremy; Dappe, Yannick J.; Diawara, Boubakar; Maurel, François; Seydou, Mahamadou
2017-05-01
Graphene-based two-dimensional materials have attracted an increasing attention these last years. Among them, the system formed by molecular adsorption on, aim of modifying the conductivity of graphene and make it semiconducting, is of particular interest. We use here hierarchical first-principles simulations to investigate the energetic and electronic properties of an electron-donor, melamine, and an acceptor, NaphtaleneTetraCarboxylic DiImide (NTCDI), and the assembly of their complexes on graphene surface. In particular, the van der Waals-corrected density functional theory (DFT) method is used to compute the interaction and adsorption energies during assembly. The effect of dispersion interactions on both geometries and energies is investigated. Depending on the surface coverage and the molecular organization, there is a significant local deformation of the graphene surface. Self-assembly is driven by the competition between hydrogen bonds in the building blocks and their adsorption on the surface. The dispersion contribution accounts significantly in both intermolecular and adsorption energies. The electron transfer mechanism and density of states (DOS) calculations show the electron-donor and acceptor characters of melamine and NTCDI, respectively. Molecular adsorption affects differently the energy levels around the Fermi level differently, leading to band gap opening. These results provide information about the new materials obtained by controlling molecular assembly on graphene.
Surface modelling on heavy atom crystalline compounds: HfO{sub 2} and UO{sub 2} fluorite structures
Energy Technology Data Exchange (ETDEWEB)
Evarestov, Robert [Department of Quantum Chemistry, St. Petersburg State University, 26 Universitetsky Prospect, Peterhof, St. Petersburg 198504 (Russian Federation)], E-mail: re1973@re1973.spb.edu; Bandura, Andrei; Blokhin, Eugeny [Department of Quantum Chemistry, St. Petersburg State University, 26 Universitetsky Prospect, Peterhof, St. Petersburg 198504 (Russian Federation)
2009-01-15
The study of the bulk and surface properties of cubic (fluorite structure) HfO{sub 2} and UO{sub 2} was performed using the hybrid Hartree-Fock density functional theory linear combination of atomic orbitals simulations via the CRYSTAL06 computer code. The Stuttgart small-core pseudopotentials and corresponding basis sets were used for the core-valence interactions. The influence of relativistic effects on the structure and properties of the systems was studied. It was found that surface properties of Mott-Hubbard dielectric UO{sub 2} differ from those found for other metal oxides with the closed-shell configuration of d-electrons.
Energy Technology Data Exchange (ETDEWEB)
Dimitrievska, Mirjana; Boero, Federica; Litvinchuk, Alexander P.; Delsante, Simona; Borzone, Gabriella; Perez-Rodriguez, Alejandro; Izquierdo-Roca, Victor
2017-02-27
This work presents detailed structural and vibrational characterization of different Cu2ZnSnS4 (CZTS) polymorphs (space groups: I4-, P4-2c, and P4-2m), using Raman spectroscopy and first-principles calculations. Multiwavelength Raman measurements on bulk crystalline CZTS samples permitted determination of the vibrational modes of each polymorph structure, with frequencies matching well with the results obtained from simulations. The results present Raman spectra fingerprints as well as experimental references for the different polymorph modifications.
Solid oxide fuel cell composite cathodes based on perovskite and fluorite structures
Sadykov, Vladislav; Mezentseva, Natalia; Usoltsev, Vladimir; Sadovskaya, Ekaterina; Ishchenko, Arkady; Pavlova, Svetlana; Bespalko, Yulia; Kharlamova, Tamara; Zevak, Ekaterina; Salanov, Aleksei; Krieger, Tamara; Belyaev, Vladimir; Bobrenok, Oleg; Uvarov, Nikolai; Okhlupin, Yury; Smorygo, Oleg; Smirnova, Alevtina; Singh, Prabhakar; Vlasov, Aleksandr; Korobeynikov, Mikhail; Bryazgin, Aleksandr; Kalinin, Peter; Arzhannikov, Andrei
This work presents the results related to the functionally graded fluorite (F)-perovskite (P) nanocomposite cathodes for IT SOFC. Nanocrystalline fluorites (GDC, ScCeSZ) and perovskites (LSrMn, LSrFNi) were synthesized by Pechini method. Nanocomposites were prepared by the ultrasonic dispersion of F and P powders in isopropanol with addition of polyvinyl butyral. Different techniques for deposition and sintering of functionally graded cathode materials were applied including traditional approaches as well as original methods, such as radiation-thermal sintering under electron beam or microwave radiation. Morphology, microstructure and elemental composition of nanocomposites was characterized by XRD and HRTEM/SEM with EDX. Even for dense composites, the sizes of perovskite and fluorite domains remain in the nanorange providing developed P-F interfaces. Oxygen isotope heteroexchange and conductivity/weight relaxation studies demonstrated that these interfaces provide a path for fast oxygen diffusion. The redistribution of the elements between P and F phases in nanocomposites occurs without formation of insulating zirconate phases. Button-size fuel cells with nanocomposite functionally graded cathodes, thin YSZ layers and anode Ni/YSZ cermet (either bulk or supported on Ni-Al foam substrates) were manufactured. For optimized composition and functionally graded design of P-F nanocomposite cathodes, a stable performance in the intermediate temperature range with maximum power density up to 0.5 W cm -2 at 700 °C in wet H 2/air feeds was demonstrated.
Rameshe, Balasubramaniam; Murugan, Ramaswamy; Palanivel, Balan
2016-12-01
First principle calculations are performed to investigate the electronic structure, structural phase stability, optical and vibrational properties of double perovskite oxide semiconductors namely Ba2ScMO6 (M = Nb, Ta) in the cubic symmetry using WIEN2k. In order to study the ground state properties of these compounds, the total energies are calculated as a function of reduced volumes and fitted with Brich Murnaghan equation. The estimated ground state parameters are comparable with the available experimental data. Calculations of electronic band structure on these compounds reveal that both Ba2ScNbO6 and Ba2ScTaO6 exhibit a semiconducting behavior with a direct energy gap of 2.78 and 3.15 eV, respectively. To explore the optical transitions in these compounds, the real and imaginary parts of the dielectric function, refractive index, extinction coefficient, reflectivity, optical absorption coefficient, real part of optical conductivity and the energy-loss function are calculated at ambient pressure and analyzed. The collective Raman active modes of the atoms of these materials are also calculated in order to understand the structural stability of these compounds.
Institute of Scientific and Technical Information of China (English)
Xu Gui-Gui; Wu Jing; Chen Zhi-Gao; Lin Ying-Bin; Huang Zhi-Gao
2012-01-01
Using first-principles calculations within the generalized gradient approximation (GGA) +U framework,we investigate the effect of C doping on the structural and electronic properties of LiFePO4.The calculated formation energies indicate that C doped at O sites is energetically favoured,and that C dopants prefer to occupy O3 sites.The band gap of the C doped material is much narrow than that of the undoped one,indicating better electro- conductive properties.To maintain charge balance,the valence of the Fe nearest to C appears as Fe3+,and it will be helpful to the hopping of electrons.
Institute of Scientific and Technical Information of China (English)
ZHOU Jing; REN Xiao-Min; HUANG Yong-Qing; WANG Qi; HUANG Hui
2008-01-01
We investigate the electronic structures of new semiconductor alloys BxGa1-x As and Tlx Ga1-x As, employing first-principles calculations within the density-functional theory and the generalized gradient approximation.The calculation results indicate that alloying a small Tl content with GaAs will produce larger modifications of the band structures compared to B. A careful investigation of the internal lattice structure relaxation shows that significant bond-length relaxations takes place in both the alloys, and it turns out that difference between the band-gap bowing behaviours for B and Tl stems from the different impact of atomic relaxation on the electronic structure. The relaxed structure yields electronic-structure results, which are in good agreement with the experimental data. Finally, a comparison of formation enthalpies indicates that the production Tlx Ga1-x As with Tl concentration of at least 8% is possible.
First-principles determination of the ground-state structure of Mg(BH4)(2)
DEFF Research Database (Denmark)
Caputo, R.; Tekin, Adem; Sikora, W.;
2009-01-01
stability of the proposed structures. We combined several computational methods to build and compute the lowest energy structure. We found that the building motif of the crystalline structure of alkali and earth-alkaline metal tetrahydroborates is dictated by the coordination of metal atom. We report here...
Atomic structure of icosahedral B4C boron carbide from a first principles analysis of NMR spectra.
Mauri, F; Vast, N; Pickard, C J
2001-08-20
Density functional theory is demonstrated to reproduce the 13C and 11B NMR chemical shifts of icosahedral boron carbides with sufficient accuracy to extract previously unresolved structural information from experimental NMR spectra. B4C can be viewed as an arrangement of 3-atom linear chains and 12-atom icosahedra. According to our results, all the chains have a CBC structure. Most of the icosahedra have a B11C structure with the C atom placed in a polar site, and a few percent have a B (12) structure or a B10C2 structure with the two C atoms placed in two antipodal polar sites.
Li, Xuejiao; Song, Jia; Shi, Shuping; Yan, Liuming; Zhang, Zhaochun; Jiang, Tao; Peng, Shuming
2017-01-26
The dynamic fluctuation of the U(3+) coordination structure in a molten LiCl-KCl mixture was studied using first principles molecular dynamics (FPMD) simulations. The radial distribution function, probability distribution of coordination numbers, fluctuation of coordination number and cage volume, self-diffusion coefficient and solvodynamic mean radius of U(3+), dynamics of the nearest U-Cl distances, and van Hove function were evaluated. It was revealed that fast exchange of Cl(-) occurred between the first and second coordination shells of U(3+) accompanied with fast fluctuation of coordination number and rearrangement of coordination structure. It was concluded that 6-fold coordination structure dominated the coordination structure of U(3+) in the molten LiCl-KCl-UCl3 mixture and a high temperature was conducive to the formation of low coordinated structure.
First-principles calculations of structural properties of Sc{sub 1-x}In{sub x}N compound
Energy Technology Data Exchange (ETDEWEB)
Perez, William Lopez [Departamento de Matematicas y Fisica, Universidad del Norte, A. A. 1569, Barranquilla (Colombia)]. E-mail: wlopez@uninorte.edu.co; Arbey Rodriguez M, Jairo [Departamento de Fisica, Universidad Nacional de Colombia, A. A. 5997, Bogota (Colombia); Moreno-Armenta, Maria G. [Centro de Ciencias de la Materia Condensada, Universidad Nacional Autonoma de Mexico, A. P. 2681, Ensenada Baja California 22800 (Mexico)
2007-09-01
We have applied the full-potential linearized augmented plane wave method (FP-LAPW) within the density functional theory to investigate the structural properties of Sc{sub 1-x}In{sub x}N compound in sodium chloride and wurtzite structures. We have found that the lattice parameter (a) increases with the increment of the In-composition in both structures, while the bulk modulus diminishes with the increase of the In-composition. The lattice constant and the bulk modulus present a small bowing in both structures. We have also analyzed the relative stability of this ternary compound in the two studied phases. We have found that sodium chloride structure is the ground state phase for a In-composition range 0=
Energy Technology Data Exchange (ETDEWEB)
Je, Minyeong [Department of Materials Science and Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 133-791 (Korea, Republic of); Choi, Heechae [Computational Science Research Center, Korea Institute of Science and Technology, 14-Gil 5, Hwarang-Ro, Seoungbuk-Gu, Seoul (Korea, Republic of); Hwang, Yubin; Yun, Kyung-Han [Department of Materials Science and Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 133-791 (Korea, Republic of); Chung, Yong-Chae, E-mail: yongchae@hanyang.ac.kr [Department of Materials Science and Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 133-791 (Korea, Republic of)
2015-08-31
Perpendicular magnetic anisotropy (PMA) in thin film is the key factor to obtain good properties for high density storage devices. Although the importance of the properties of PMA is well-known for Co/Pd thin film, it is still unclear which surface structure and composition indicate that PMA is present. In this work, the surface structure and magnetic properties of L1{sub 0}-ordered Co/Pd (001) were analyzed using density functional theory calculations. It was confirmed that only Pd-rich A among the facile surface structures indicates PMA properties. However, according to the calculated surface energy, not only Pd-rich A but also Co-rich B is among the most energetically stable structures. The density of states showed a clear distinct electronic structure between Pd-rich A and Co-rich B derived from the structural difference. This result indicates that PMA is not always present in a sandwich structure such as Pd-rich A. The results provide a useful guide to magnetic devices created using L1{sub 0}-ordered Co/Pd (001) on substrate Pd. - Highlights: • Investigation on the possible surface structure of L1{sub 0}-ordered Co/Pd (001) • Using surface phase diagram, the stable structures were Pd-rich A and Co-rich B. • The magnetic property of Pd-rich A and Co-rich B has been measured and discussed. • Pd-rich A only showed perpendicular magnetic anisotropy.
First-principles prediction of disordering tendencies in complex oxides
Energy Technology Data Exchange (ETDEWEB)
Jiang, Chao [Los Alamos National Laboratory; Stanek, Christopher R [Los Alamos National Laboratory; Sickafus, Kurt E [Los Alamos National Laboratory; Uberuaga, Blas P [Los Alamos National Laboratory
2008-01-01
The disordering tendencies of a series of zirconate (A{sub 2}Zr{sub 2}O{sub 7}) , hafnate (A{sub 2}Hf{sub 2}O{sub 7}), titanate (A{sub 2}Ti{sub 2}O{sub 7}), and stannate (A{sub 2} Sn{sub 2}O{sub 7}) pyrochlores are predicted in this study using first-principles total energy calculations. To model the disordered (A{sub 1/2}B{sub 1/2})(O{sub 7/8}/V{sub 1/8}){sub 2} fluorite structure, we have developed an 88-atom two-sublattice special quasirandom structure (SQS) that closely reproduces the most important near-neighbor intra-sublattice and inter-sublattice pair correlation functions of the random alloy. From the calculated disordering energies, the order-disorder transition temperatures of those pyrochlores are further predicted and our results agree well with the existing experimental phase diagrams. It is clearly demonstrated that both size and electronic effects play an important role in determining the disordering tendencies of pyrochlore compounds.
Zhu, X. H.; Chen, X. R.; Liu, B. G.
2016-10-01
Recent temperature-dependent x-ray diffraction and Raman spectroscopy experiment proved that single-crystalline BiMnO3 assumes a centrosymmetric monoclinic structure (C2/c space group). Here we investigate magnetic structure and electronic structure of this centrosymmetric BiMnO3 phase by using the modified Becke-Johnson (mBJ) exchange functional within the density functional theory (DFT). Our mBJ calculated semiconductor gap, magnetic moment, and other aspects of the electronic structure, in contrast with previous DFT results, are in good agreement with recent experimental values. This satisfactory description of the electronic structure and magnetism of the BiMnO3 is because mBJ reasonably captures the kinetic property and correlation of electrons. Our calculated results with mBJ approach are both useful to study such Bi-based perovskite oxide materials for spintronics applications.
Factors controlling the oxide ion conductivity of fluorite and perovskite structured oxides
DEFF Research Database (Denmark)
Mogensen, Mogens Bjerg; Lybye, D.; Bonanos, N.
2004-01-01
for the oxide ion movement, (2) free lattice volume, and (3) average metal-oxide bond energy have been proposed as predictors of high oxide ion conductivity. We discuss how these parameters all depend on ionic radii, and therefore, some of these may be redundant. Furthermore, we explore the interrelations among...... such parameters for fluorite and perovskite oxides by considering their sensitivities to the individual ionic radii. Based on experimental data available in the literature, it is argued that lattice distortion (lattice stress and deviation from cubic symmetry) due to ion radii mismatch determines the ionic...
Institute of Scientific and Technical Information of China (English)
WEN QingBo; YU ShanSheng; ZHENG WeiTao
2009-01-01
Calculations have been made for single-walled zigzag (n, 0) carbon nanotubes containing substitutional boron impurity atoms using ab initio density functional theory. It is found that the formation energies of these nanotubes depend on the tube diameter, as do the electronic properties, and show periodic fea-ture that results from their different π bonding structures compared to those of perfect zigzag carbon nanotubes. When more boron atoms are incorporated into a single-walled zigzag carbon nanotube, the substitutional boron atoms tend to come together to form structure of BC3 nanodomains, and B-doped tubes have striking acceptor states above the top of the valence bands. For the structure of BC3, there are two kinds of configurations with different electronic structures.
Indian Academy of Sciences (India)
Anil Thakur; P K Ahluwalia
2007-10-01
In this paper formulae for partial structure factors have been used to study partial structure factors of compound-forming quaternary liquid alloys by considering Hoshino's m-component hard-sphere mixture, which is based on Percus-Yevic equation of Hiroike. Formulae are applied to NaSn (Na, Sn, NaSn, Na3Sn) which is considered as a quaternary liquid mixture with the formation of two compounds simultaneously. We have compared the total structure factors for ternary and quaternary alloys with experimental total structure factors which are found to be in good agreement. This suggests that, for suitable stoichiometric composition, two compounds are formed simultaneously. The hard-sphere diameters needed have been calculated using Troullier and Martins ab-initio pseudopotentials.
Egger, David A; Kronik, Leeor
2014-08-07
A microscopic picture of structure and bonding in organic-inorganic perovskites is imperative to understanding their remarkable semiconducting and photovoltaic properties. On the basis of a density functional theory treatment that includes both spin-orbit coupling and dispersive interactions, we provide detailed insight into the crystal binding of lead-halide perovskites and quantify the effect of different types of interactions on the structural properties. Our analysis reveals that cohesion in these materials is characterized by a variety of interactions that includes important contributions from both van der Waals interactions among the halide atoms and hydrogen bonding. We also assess the role of spin-orbit coupling and show that it causes slight changes in lead-halide bonding that do not significantly affect the lattice parameters. Our results establish that consideration of dispersive effects is essential for understanding the structure and bonding in organic-inorganic perovskites in general and for providing reliable theoretical predictions of structural parameters in particular.
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
Calculations have been made for single-walled zigzag(n,0) carbon nanotubes containing substitutional boron impurity atoms using ab initio density functional theory.It is found that the formation energies of these nanotubes depend on the tube diameter,as do the electronic properties,and show periodic fea-ture that results from their different π bonding structures compared to those of perfect zigzag carbon nanotubes.When more boron atoms are incorporated into a single-walled zigzag carbon nanotube,the substitutional boron atoms tend to come together to form structure of BC3 nanodomains,and B-doped tubes have striking acceptor states above the top of the valence bands.For the structure of BC3,there are two kinds of configurations with different electronic structures.
Structure and Properties of Semiconductor Microclusters GanPn(n=1-4):A First Principle Study
Institute of Scientific and Technical Information of China (English)
ZHANG Cai-rong; CHEN Hong-shan; WANG Guang-hou
2004-01-01
The possible geometrical structures and relative stabilities of semiconductor microclusters GanPn(n= 1-4) were studied by virtue of density functional calculations with generalized gradient approximation (B3LYP).For the most stable isomers of GanPn(n= 1-4) clusters, the electronic structure, vibrational properties,dipole moment, polarizability and ionization potential were analyzed by means of HF, MP2, CISD and B3LYP methods with different basis sets.
First-principles predicted low-energy structures of NaSc(BH{sub 4}){sub 4}
Energy Technology Data Exchange (ETDEWEB)
Tran, Huan Doan, E-mail: huan.tran@uconn.edu; Amsler, Maximilian; Goedecker, Stefan, E-mail: stefan.goedecker@unibas.ch [Department of Physics, Universität Basel, Klingelbergstrasse 82, 4056 Basel (Switzerland); Botti, Silvana; Marques, Miguel A. L. [Institut Lumière Matière and ETSF, UMR5306 Universite Lyon 1-CNRS, Universitè de Lyon, F-69622 Villeurbanne Cedex (France)
2014-03-28
According to previous interpretations of experimental data, sodium-scandium double-cation borohydride NaSc(BH{sub 4}){sub 4} crystallizes in the crystallographic space group Cmcm where each sodium (scandium) atom is surrounded by six scandium (sodium) atoms. A careful investigation of this phase based on ab initio calculations indicates that the structure is dynamically unstable and gives rise to an energetically and dynamically more favorable phase with C222{sub 1} symmetry and nearly identical x-ray diffraction pattern. By additionally performing extensive structural searches with the minima-hopping method we discover a class of new low-energy structures exhibiting a novel structural motif in which each sodium (scandium) atom is surrounded by four scandium (sodium) atoms arranged at the corners of either a rectangle with nearly equal sides or a tetrahedron. These new phases are all predicted to be insulators with band gaps of 7.9–8.2 eV. Finally, we estimate the influence of these structures on the hydrogen-storage performance of NaSc(BH{sub 4}){sub 4}.
Wu, Xiao-Long; Zhou, Xiao-Lin; Chang, Jing
2014-08-01
The structural and elastic properties of 3d transition metal tetraboride TMB4 (TM = V, Cr, Mn) have been studied by using density functional theory (DFT) within the local density approximation (LDA) and generalized gradient approximation (GGA) for exchange-correlation function. Our results are in agreement well with available experimental data and previous theoretical studies. The full elastic constants and bulk shear modulus of TMB4 (TM = V, Cr, Mn) are obtained in the wide pressure range. Results indicated that these phases of TMB4 (TM = V, Cr, Mn) are strongly pressure dependent. And the CrB4 in Immm structure is the most ultraincompressible among the considered phases at 0 GPa. By the mechanical stability criteria, it is predicted that these phases of TMB4 (TM = V, Cr, Mn) compounds are stable up to 100 GPa. In addition, the calculated B/G ratio indicated that all the structures of TMB4 (TM = V, Cr, Mn) possess brittle nature in the range of pressure from 0 GPa to 100 GPa except the Pnnm structure of MnB4, which is higher than 1.75, indicating that the Pnnm structure of MnB4 is prone to ductility when the pressure is above 73 GPa.
Wei, Zhenyi; Tou, Shushi; Wu, Bo; Bai, Kewu
2016-12-01
ZnZrAl2 is a kind of heterogeneous nucleation to promote the refine of grain of ZA43 alloy. ZnZrAl2 intermetallic is also considered as a candidate for superalloys. The crystal lattice structure, alloy thermodynamics and mechanical properties of ZnZrAl2 intermetallic compound were investigated by ab initio calculations based on density functional theory (DFT). In particular, the site preference of atoms in different sublattices was predicted based on alloy thermodynamics. At ground state, the most stable structure is L12 structure with sublattice model (Zn)1a(Zr0.3333Al0.6667)3c or (Zr)1a(Zn0.3333Al0.6667)3c, and the occupying preferences of Zn, Zr and Al atoms are independent with the increasing temperature. The bulk, shear, Young's modulus and the Poisson's ratio of the L12 structure ZnZrAl2 were calculated based on the site occupying configurations. The results show that ZnZrAl2 is a brittle material in nature. Electronic structures analysis revealed that Al-Zr atoms possess a covalent bonding character, while the Zn-Zr atoms have a metallic bonding character. ZnZrAl2 has stable mechanical properties at high temperature. The grain refinement effect of ZnZrAl2 precipitates in Zn-Al alloys were discussed based on crystal lattice match theory.
Energy Technology Data Exchange (ETDEWEB)
Matar, Samir F., E-mail: samir.matar@icmcb.cnrs.fr; Chevalier, Bernard; Etourneau, Jean
2016-01-01
TbTiGe intermetallic compound is characterized by temperature dimorphism with different but related crystal structures with ferromagnetic high temperature (HT) form versus antiferromagnetic low temperature (LT) form. Such different structure properties and magnetic behaviors have been addressed based on DFT computations of cohesive energies, charge transfers, mechanical and chemical properties of the two structures. This is particularly illustrated by harder and less ductile LT-form with stronger Ti–Ge bond and larger charge transfer from Tb and Ti on one hand and Ge on the other hand. - Highlights: • Temperature induced dimorphism in TbTiGe (LT – HT) leads to different magnetic orders. • Long range ferromagnetic SPF and antiferromagnetic SPAF orders addressed within DFT. • SPAF-LT results from differentiated mechanical and chemical behaviors versus SPF-HT.
Pagare, Gitanjali; Jain, Ekta; Sanyal, S. P.
2016-05-01
Structural, electronic, optical and elastic properties of PtZr have been studied using the full-potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). The energy against volume and enthalpy vs. pressure variation in three different structures i.e. B1, B2 and B3 for PtZr has been presented. The equilibrium lattice parameter, bulk modulus and its pressure derivative have been obtained using optimization method for all the three phases. Furthermore, electronic structure was discussed to reveal the metallic character of the present compound. The linear optical properties are also studied under zero pressure for the first time. Results on elastic properties are obtained using generalized gradient approximation (GGA) for exchange correlation potentials. Ductile nature of PtZr compound is predicted in accordance with Pugh's criteria.
Energy Technology Data Exchange (ETDEWEB)
Pagare, Gitanjali, E-mail: gita-pagare@yahoo.co.in [Department of Physics, Sarojini Naidu Government Girls P. G. Autonomous College, Bhopal-462016 (India); Jain, Ekta, E-mail: jainekta05@gmail.com [Department of Physics, Government M. L. B. Girls P. G. Autonomous College, Bhopal-462002 (India); Sanyal, S. P., E-mail: sps.physicsbu@gmail.com [Department of Physics, Barkatullah University, Bhopal-462026 (India)
2016-05-06
Structural, electronic, optical and elastic properties of PtZr have been studied using the full-potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). The energy against volume and enthalpy vs. pressure variation in three different structures i.e. B{sub 1}, B{sub 2} and B{sub 3} for PtZr has been presented. The equilibrium lattice parameter, bulk modulus and its pressure derivative have been obtained using optimization method for all the three phases. Furthermore, electronic structure was discussed to reveal the metallic character of the present compound. The linear optical properties are also studied under zero pressure for the first time. Results on elastic properties are obtained using generalized gradient approximation (GGA) for exchange correlation potentials. Ductile nature of PtZr compound is predicted in accordance with Pugh’s criteria.
Mitchell, Robert A.; Schumacher, Douglass W.; Chowdhury, Enam A.
2015-11-01
We present our results of a fundamental simulation of a periodic grating structure formation on a copper target during the femtosecond-pulse laser damage process, and compare our results to recent experiment. The particle-in-cell (PIC) method is used to model the initial laser heating of the electrons, a two-temperature model (TTM) is used to model the thermalization of the material, and a modified PIC method is employed to model the atomic transport leading to a damage crater morphology consistent with experimental grating structure formation. This laser-induced periodic surface structure (LIPSS) is shown to be directly related to the formation of surface plasmon polaritons (SPP) and their interference with the incident laser pulse.
Ma, Zi-Qian; Pan, Hui; Wong, Pak Kin
2016-11-01
Organic-inorganic halide perovskites have attracted increasing interest on solar-energy harvesting because of their outstanding electronic properties. In this work, we systematically investigate the structural and electronic properties of Sn-based hybrid perovskites MASnX3 and FASnX3 (X = I, Br) based on density-functional-theory calculations. We find that their electronic properties strongly depend on the organic molecules, halide atoms, and structures. We show that there is a general rule to predict the band gap of the Sn-based hybrid perovskite: its band gap increases as the size of halide atom decreases as well as that of organic molecule increase. The band gap of high temperature phase (cubic structure) is smaller than that of low temperature phase (orthorhombic structure). The band gap of tetragonal structure (medium-temperature phase) may be larger or smaller than that of cubic phase, depending on the orientation of the molecule. Tunable band gap within a range of 0.73-1.53 eV can be achieved by choosing halide atom and organic molecule, and controlling structure. We further show that carrier effective mass also reduces as the size of halide atom increases and that of molecule decreases. By comparing with Pb-based hybrid perovskites, the Sn-based systems show enhanced visible-light absorption and carrier mobility due to narrowed band gap and reduced carrier effective mass. These Sn-based organic-inorganic halide perovskites may find applications in solar energy harvesting with improved performance.
Fedorov, Igor A; Fedorova, Tatyana P; Zhuravlev, Yuriy N
2016-05-26
We studied the structural and electronic properties of pentaerythritol tetranitrate (PETN) and erythritol tetranitrate (ETN) crystals within the framework of density functional theory with van der Waals interactions. The computed lattice parameters have good agreement with experimental data. Electronic and structural properties of the crystals under 0-20 GPa hydrostatic pressure were studied. The parameters of equations of state calculated from the theoretical data show good agreement with experiment within the studied pressure intervals. We have also calculated the detonation velocity and pressure.
Ibrahim, Fatima; Yang, Hongxin; Dieny, Bernard; Chshiev, Mairbek
2015-03-01
Electric-field (EF) control of magnetic anisotropy is promising in the context of establishing low-energy consumption memory devices since it allows EF-assisted switching of magnetization in magnetic tunnel junctions with perpendicular magnetic anisotropy (PMA). Using first-principles calculations, we demonstrate that both the EF and structural strain induce changes of the PMA in Fe/MgO interfaces which originally exhibit strong PMA. Namely, we find that the PMA change in response to strain is much larger than that induced by applied EF. This suggests that the EF control of PMA is caused not only by charge accumulation and depletion mechanism but rather mediated by structural modifications occurring at the interface in agreement with recent experimental reports. In addition, using atomic and orbital-resolved analysis of PMA, we elucidate the effect of both the EF and structural strain on PMA showing in particular that it extends beyond the interfacial layer.
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.
Energy Technology Data Exchange (ETDEWEB)
Chen Aqing; Shao Qingyi, E-mail: qyshao@163.com; Li Zhen [South China Normal University, Laboratory of Quantum Information Technology, School of Physics and Telecommunication Engineering (China)
2011-06-15
Boron (B)/phosphorus (P)-doped single-wall carbon nanotubes (B-PSWNTs) are studied by using the first-principle method based on density function theory. Mayer bond order, band structure, electrons density and density of states are calculated. It concludes that the B-PSWNTs have special band structure, which is quite different from BN nanotubes, and that metallic carbon nanotubes will be converted to semiconductor due to boron/phosphorus co-doping, which breaks the symmetrical structure. The bonding forms in B-PSWNTs are investigated in detail. Besides, Mulliken charge population and the quantum conductance are also calculated to study the quantum transport characteristics of B-PSWNT hetero-junction. It is found that the position of p-n junction in this hetero-junction will be changed as the applied electric field increase and it performs the characteristics of diode.
Energy Technology Data Exchange (ETDEWEB)
Pang Hua, E-mail: hpang@lzu.edu.cn; Fang Yang; Li Fashen [Lanzhou UniversityLanzhou, Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Department of Physics (China)
2011-07-15
The hyperfine parameters of hyperfine fields, electric field gradients and isomer shifts at the Fe site are investigated based on the first-principles calculations of the electronic structures using LDA (GGA)+U method in the low-temperature orthorhombic antiferromagnetic phase of undoped BaFe{sub 2}As{sub 2}. It is fond that the electric field gradient of Fe nucleus is highly related with the electronic structures close to the Fermi level. Though the addition of negative on-site Coulomb interaction to Fe-3d states improves the calculated magnetic moment of Fe atom and the hyperfine parameters of Fe nucleus when U = -0.1 Ry (-0.08 Ry) for GGA+U (LDA+U) method, a negative U correction does not capture the right physics of this system. The calculations prove the strong coupling between the magnetic, structural and electronic properties in antiferromagnetic BaFe{sub 2}As{sub 2} parent.
Ehsanfar, S.; Kanjouri, F.; Tashakori, H.; Esmailian, A.
2017-10-01
Based on first-principles calculations with generalized gradient approximation as exchange-correlation functional, the structural, electronic, mechanical, thermal, and phonon properties of III-phosphide binary compounds, namely BP, AlP, GaP, and InP, with cubic zincblende structure have been investigated. The calculations were performed in the framework of density functional theory and density functional perturbation theory (DFPT) implemented in the Quantum ESPRESSO package. The results obtained for the structural and electronic properties are in good agreement with available theoretical and experimental results. The results of our electronic calculations indicate semiconducting properties for these binary compounds. Furthermore, the frequency bandgaps and phonon density of states were also investigated. The computed mechanical constants predict that BP, AlP, GaP, and InP are elastically stable. Finally, we determined the heat capacity and entropy for these binary compounds within a quasiharmonic Debye model using DFPT for comparison.
Koufos, Alexander P.; Papaconstantopoulos, Dimitrios A.; Mehl, Michael J.
2014-01-01
We have performed density functional theory calculations using the linearized augmented plane wave method (LAPW) with the local density approximation (LDA) functional to study the electronic structure of the iron-based superconductor iron-selenium (FeSe). In our study, we have performed a comprehensive set of calculations involving structural, atomic, and spin configurations. All calculations were executed using the tetragonal lead-oxide or P4/nmm structure, with various volumes, c /a ratios, and internal parameters. Furthermore, we investigated the spin polarization using the LDA functional to assess ferromagnetism in this material. The paramagnetic LDA calculations find the equilibrium configuration of FeSe in the P4/nmm structure to have a volume of 472.5 a.u.3 with a c /a ratio of 1.50 and internal parameter of 0.255, with the ferromagnetic having comparable results to the paramagnetic case. In addition, we calculated total energies for FeSe using a pseudopotential method, and found comparable results to the LAPW calculations. Superconductivity calculations were done using the Gaspari-Gyorffy and the McMillan formalisms and found substantial electron-phonon coupling. Under pressure, our calculations show that the superconductivity critical temperature continues to rise, but underestimates the measured values.
First-principles study of the electronic structure of CdS/ZnSe coupled quantum dots
Ganguli, N.; Acharya, S.; Dasgupta, I.
2014-01-01
We have studied the electronic structure of CdS/ZnSe coupled quantum dots, a novel heterostructure at the nanoscale. Our calculations reveal CdS/ZnSe coupled quantum dots are type II in nature where the anion p states play an important role in deciding the band offset for the highest occupied
First-principles study of atomic structure and electronic properties of Si and F doped anatase TiO2
Directory of Open Access Journals (Sweden)
Li Hongping
2015-09-01
Full Text Available Chemical doping represents one of the most effective ways in engineering electronic structures of anatase TiO2 for practical applications. Here, we investigate formation energies, geometrical structures, and electronic properties of Si-, F-doped and Si/F co-doped anatase TiO2 by using spin-polarized density functional theory calculation. We find that the co-doped TiO2 is thermodynamically more favorable than the Si- and F-doped TiO2- Structural analysis shows that atomic impurity varies crystal constants slightly. Moreover, all the three doped systems show a pronounced narrowing of band gap by 0.33 eV for the F-doped TiO2, 0.17 eV for the Si-doped TiO2, and 0.28 eV for the Si/F-co-doped TiO2, which could account for the experimentally observed redshift of optical absorption edge. Our calculations suggest that the Si/F-co-doping represents an effective way in tailoring electronic structure and optical properties of anatase TiO2.
2016-02-10
1997. [3] Y.G.A. Graham, S. MacGlashan, Peter G. Bruce, Structure of the polymer electrolyte poly( ethylene oxide)6:LiAsF6, Nature 398, 792-794 (1999... chlorine , green; aluminum, pink; magnesium, yellow. 11 Table 1 Ab initio vibrational frequencies for EMImAlCl4 and EMImAl2Cl7
Electronic structure of RScO{sub 3} from x-ray spectroscopies and first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Derks, Christine; Neumann, Manfred [Department of Physics, University of Osnabrueck (Germany); Kuepper, Karsten [Department of Solid State Physics, University of Ulm (Germany); Postnikov, Andree [Laboratoire de Physique des Milieux Denses, Universite Paul Verlaine, Metz (France); Uecker, Reinhard [Institute for Crystal Growth, Berlin (Germany)
2011-07-01
Perovskites of the type RScO{sub 3}, where R represents a trivalent rare-earth metal, are high k materials and belong to the best available thin film substrates for the epitaxial growth of high quality thin films. This allows a so called strain tailoring of ferroelectric, ferromagnetic, or multiferroic perovskite thin films by choosing different RScO{sub 3}. With respect to these interesting properties there is up to now only rare knowledge available about the electronic structure of RScO{sub 3}. In a previous work we have already published a work on the electronic structure of SmScO{sub 3}, GdScO{sub 3}, and DyScO{sub 3}. As far as we know, it is the only work combining XPS, XES and XAS with ab initio electronic structure calculations. We are extending these successful investigations to single crystalline PrScO{sub 3}, NdScO{sub 3}, EuScO{sub 3} and TbScO{sub 3}. A complete electronic structure was obtained and the band gaps could be deduced for all these rare-earth scandates. All the results were found to be in good agreement with LDA+U calculations.
Structural and electronic properties of Sc{sub x}Al{sub 1−x}N: First principles study
Energy Technology Data Exchange (ETDEWEB)
Berkok, Houria [Laboratoire d’analyse et d’application des rayonnements, Department of Physics, Université des Sciences et de la Technologie Mohamed Boudiaf PB 1505 El Mnaouer Oran Algeria (Algeria); Tebboune, Abdelghani, E-mail: tebbouneabdelghani@yahoo.fr [Laboratoire d’analyse et d’application des rayonnements, Department of Physics, Université des Sciences et de la Technologie Mohamed Boudiaf PB 1505 El Mnaouer Oran Algeria (Algeria); Saim, Asmaa; Belbachir, Ahmed H [Laboratoire d’analyse et d’application des rayonnements, Department of Physics, Université des Sciences et de la Technologie Mohamed Boudiaf PB 1505 El Mnaouer Oran Algeria (Algeria)
2013-02-15
The structural and electronic properties of Sc{sub x}Al{sub 1−x}N ternary semiconductor alloys are investigated in the rocksalt, zinc blend and wurtzite structures using the full potential linear muffin tin orbitals (FP-LMTO) method. The local density approximation (LDA) was used for the exchange and correlation energy density functional. In particular, the lattice constant, bulk modulus and band gap energies of ScN and AlN compounds and their ternary alloys Sc{sub x}Al{sub 1−x}N are calculated in rocksalt, zinc blend and wurtzite structures and discussed. A linear relationship has obtained for equilibrium lattice constants versus Sc concentration for rocksalt and zinc blend structures. The band gap is decreased with the increasing of Sc concentration in the rocksalt phase. For ZB-Sc{sub x}Al{sub 1−x}N, the band gap is the largest one at x=0.25 and changes from indirect to direct when x is more than 0.25.
Li, Zhimin; Huang, Huisheng; Zhang, Tonglai; Zhang, Shengtao; Zhang, Jianguo; Yang, Li
2014-01-01
The electric field effects on the structure, decomposition mechanism, and stability of crystalline lead styphnate have been studied using density functional theory. The results indicate that the influence of external electric field on the crystal structure is anisotropic. The electric field effects on the distance of the Pb-O ionic interactions are stronger than those on the covalent interactions. However, the changes of most structural parameters are not monotonically dependent on the increased electric field. This reveals that lead styphnate can undergo a phase transition upon the external electric field. When the applied field is increased to 0.003 a.u., the effective band gap and total density of states vary evidently. And the Franz-Keldysh effect yields larger influence on the band gap than the structural change induced by external electric field. Furthermore, lead styphnate has different initial decomposition reactions in the presence and absence of the electric field. Finally, we find that its sensitivity becomes more and more sensitive with the increasing electric field.
Li, Xiaojun
2017-10-01
In this work, we reported the geometrical structures, electronic and spectral properties of the carborane-containing BODIPYs complexes using the density functional theory calculations. In two structures, the calculated main bond lengths and bond angels of structural framework are consistent with X-ray experiment, and the two BODIPYs complexes are thermodynamically and kinetically stable. The strongest DOS band is mainly dominated by the Bsbnd B and Bsbnd H σ-bonds of carborane fragment, whereas the π-type MOs on the pyrromethene fragment contribute to the high-energy DOS bands. Analysis of the AdNDP chemical bonding indicates that the carborane cage can be stabilized by eleven delocalized 3csbnd 2e and two delocalized 4csbnd 2e σ-bonds, while the pyrromethene fragment corresponds to five delocalized 3csbnd 2e π-bonds. In addition, the main characteristic peaks of the two simulated IR spectra for the BODIPYs complexes are properly assigned. Hopefully, all these results will be helpful for understanding the electronic structures, and further stimulate the study on the biological and medical applications.
Charles, Nenian; Rondinelli, James M.
2016-11-01
Motivated by the resurgence of electronic and optical property design in ordered fluoride and oxyfluoride compounds, we present a density functional theory (DFT) study of 19 materials with structures, ranging from simple to complex, and variable oxygen-to-fluorine ratios. We focus on understanding the accuracy of the exchange-correlation potentials (Vx c) to DFT for the prediction of structural, electronic, and lattice dynamical properties at four different levels of theory, i.e., the local density approximation (LDA), generalized gradient approximation (GGA), metaGGA, and hybrid functional level which includes fractions of exact exchange. We investigate in detail the metaGGA functionals MS2 [Sun et al., Phys. Rev. Lett. 111, 106401 (2013), 10.1103/PhysRevLett.111.106401] and SCAN [Sun et al., Phys. Rev. Lett. 115, 036402 (2015), 10.1103/PhysRevLett.115.036402], and show that although the metaGGAs show improvements over the LDA and GGA functionals in describing the electronic structure and phonon frequencies, the static structural properties of fluorides and oxyfluorides are often more accurately predicted by the GGA-level Perdew-Burke-Ernzerhof functional for solids, PBEsol. Results from LDA calculations are unsatisfactory for any compound, regardless of oxygen concentration. The PBEsol and Heyd-Scuseria-Ernzerhof (HSE06) functionals give good performance in all-oxide or all-fluoride compounds. For the oxyfluorides, PBEsol is consistently more accurate for structural properties across all oxygen concentrations; however, we stress the need for detailed property assessment with various functionals for oxyfluorides with variable composition. The "best" functional is anticipated to be more strongly dependent on the property of interest. Our study provides useful insights in selecting an Vx c that achieves optimal performance compromises, enabling more accurate predictive design of functional fluoride-based materials with density functional theory.
Barannikova, S. A.; Zharmukhambetova, A. M.; Nikonov, A. Yu; Dmitriev, A. V.; Ponomareva, A. V.; Abrikosov, I. A.
2015-01-01
Computer simulations in the framework of the Density Functional Theory have become an established tool for computer simulations of materials properties. In most cases, however, information is obtained at ambient conditions, preventing design of materials for applications at extreme conditions. In this work we employ ab initio calculations to investigate the influence of stresses on structure and stability of Ti-Mo and Zr-Nb alloys, an important class of construction materials. Calculations reproduce known phase stability trends in these systems, and we resolve the controversy regarding the stability of body-centered cubic solid solution in Mo-rich Ti-Mo alloys against the isostructural decomposition. Calculated results are explained in terms of the electronic structure effects, as well as in terms of physically transparent thermodynamic arguments that relate phase stability to deviations of concentration dependence of atomic volume from the linear behavior.
First principles electronic structure and optical properties of the Zintl compound Eu3In2P4
Singh, Nirpendra
2011-05-01
We have performed full-potential calculations of the electronic structure and optical properties of the newly found Zintl compound Eu3In 2P4. Eu3In2P4 turns out to be a small gap semiconductor with an energy gap of 0.42 eV, which is in agreement with the experimental value of 0.452 eV. The peaks of the optical spectra originate mainly from transitions between occupied Eu 4f states in the valence band and unoccupied Eu 5d states in the conduction band. A considerable anisotropy is observed for the parallel and perpendicular components in the frequency dependent optical spectra. The spectral features are explained in terms of the band structure. © 2011 Elsevier B.V. All rights reserved.
Institute of Scientific and Technical Information of China (English)
ZHAO Long; LU Peng-Fei; YU Zhong-Yuan; GUO Xiao-Tao; YE Han; YUAN Gui-Fang; SHEN Yue; LIU Yu-Min
2011-01-01
The electronic structure, magnetic properties, and optical properties of Co-doped AlN are investigated based upon the Perdew-Burke-Ernzerhof form of generalized gradient approximation within the density functional theory. The band gaps narrowing of Al1-xCoxN are found with the increase of Co concentrations. The analyses of the band structures and density of states show that Al1-xCoxN alloys exhibit a half-metallic character. Moreover, we have succeeded in demonstrating that Co doped AlN system in x = 0.125 is always antiferromagnetic, which is in good agreement with the experimental results. Besides, it is shown that the insertion of Co atom leads to redshift of the optical absorption edge.Finally, the optical constants of pure AlN and Al1-xCoxN alloy, such as loss function, refractive index and reflectivity,are discussed.
Electronic structure of RScO{sub 3} from x-ray spectroscopies and first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Derks, Christine; Raekers, Michael; Neumann, Manfred [Department of Physics, University of Osnabrueck, D-49069 Osnabrueck (Germany); Kuepper, Karsten [Departement of Solidstate Physics, Univeristy of Ulm, D-89069 Ulm (Germany); Postnikov, Andree [Laboratoire de Physique des Milieux Denses, Universite Paul Verlaine, Metz (France); Uecker, Reinhard [Institute for Crystal Growth, D-12489 Berlin (Germany)
2010-07-01
Perovskites of the type RScO{sub 3}, where R represents a trivalent rare-earth metal, exhibit an enormous variety of physical properties and can be used for different applications. They are high k materials and belong to the best available thin film substrates for the epitaxial growth of high quality thin films. This allows a so called strain tailoring of ferroelectric, ferromagnetic, or multiferroic perovskite thin films by choosing different RScO{sub 3}. The electronic structures of a series of RScO{sub 3} single crystals are investigated by means of x-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES), X-ray absorption spectroscopy (XAS) and band structure calculations. By combining XES and XAS measurements together with theoretical calculations the band gaps of the compounds can be accurately determined. The presented results will broaden the complete experimental and theoretical picture of the valence bands of RScO{sub 3} series.
Guo, Peng; Wang, Tianxing; Xia, Congxin; Jia, Yu
2016-07-01
Based on density functional theory, we investigated band gap tuning in transition-metal dichalcogenides SnS2 nanosheets by external electric fields applied perpendicular to the layers. We show that the fundamental band gap value of 2H and 4H SnS2 multilayer structures continuously decreases with increasing strength of applied electric fields, eventually rendering them metallic. We interpret our results in the light of the giant Stark effect and obtain a robust relationship, which is essentially characterized by the interlayer spacing, for the rate of band gap change with applied external field. And it is also valid for monolayer structure, though it need very large electric filed to make the gap change.
Energy Technology Data Exchange (ETDEWEB)
Kacimi, S.; Zazoua, F.; Djermouni, M.; Zaoui, A. [Modelling and Simulation in Materials Science Laboratory, Djillali Liabes University of Sidi Bel-Abbes, Sidi Bel-Abbes 22000 (Algeria); Bekkouche, B. [Signals and Systems Laboratory, Abdelhamid Ibn Badis University of Mostaganem, Mostaganem 27000 (Algeria); Boukortt, A. [Elaboration Characterization Physico-Mechanics of Materials and Metallurgical Laboratory ECP3M, Faculty of Sciences and Technology, Abdelhamid Ibn Badis University of Mostaganem, Mostaganem 27000 (Algeria)
2012-07-15
The electronic structure and magnetic behavior of hexagonal rare-earth diboride RB{sub 2} are studied using ab initio density-functional theory in the DFT + U approach. The effect of the spin-orbit coupling is also investigated and it is found to be a necessary requirement for the accurate description of the magnetic moment. In this paper, we study the magnetic phase stability of RB{sub 2} compounds; the band structure and the density of state (DOS) results prove that the coulomb potential and the spin-orbit interaction are keys factors to understand the magnetic properties of these series of materials. In addition, we also explain the behavior of a chemical bond of RB{sub 2} compounds through the analysis of the DOS and of the charge density. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
First-principles study of magnetism, structure and chemical order in small FeRh alloy clusters
Mokkath, Junais Habeeb
2011-01-01
The structural, electronic and magnetic properties of small ${\\rm Fe}_m {\\rm Rh}_n$ clusters having $N = m+n \\leq 8$ atoms are studied in the framework of a generalized-gradient approximation to density-functional theory. The correlation between structure, chemical order, and magnetic behavior is analyzed as a function of size and composition. For $N = m+n \\leq 6$ a thorough sampling of all cluster topologies has been performed, while for N = 7 and 8 only a few representative topologies are considered. In all cases the entire concentration range is systematically investigated. All the clusters show ferromagnetic-like order in the optimized structures. As a result, the average magnetic moment per atom $\\bar\\mu_N$ increases monotonously, which is almost linear over a wide range of concentration with Fe content. A remarkable enhancement of the local Fe moments beyond 3 $\\mu_B$ is observed as result of Rh doping. This is a consequence of the increase in the number of Fe $d$ holes, due to charge transfer from Fe t...
Hamioud, L.; Boumaza, A.; Touam, S.; Meradji, H.; Ghemid, S.; El Haj Hassan, F.; Khenata, R.; Omran, S. Bin
2016-06-01
The present paper aims to study the structural, electronic, optical and thermal properties of the boron nitride (BN) and BAs bulk materials as well as the BNxAs1-x ternary alloys by employing the full-potential-linearised augmented plane wave method within the density functional theory. The structural properties are determined using the Wu-Cohen generalised gradient approximation that is based on the optimisation of the total energy. For band structure calculations, both the Wu-Cohen generalised gradient approximation and the modified Becke-Johnson of the exchange-correlation energy and potential, respectively, are used. We investigated the effect of composition on the lattice constants, bulk modulus and band gap. Deviations of the lattice constants and the bulk modulus from the Vegard's law and the linear concentration dependence, respectively, were observed for the alloys where this result allows us to explain some specific behaviours in the electronic properties of the alloys. For the optical properties, the calculated refractive indices and the optical dielectric constants were found to vary nonlinearly with the N composition. Finally, the thermal effect on some of the macroscopic properties was predicted using the quasi-harmonic Debye model in which the lattice vibrations are taken into account.
Directory of Open Access Journals (Sweden)
Changlong Tan
2016-10-01
Full Text Available MgZnO bulk has attracted much attention as candidates for application in optoelectronic devices in the blue and ultraviolet region. However, there has been no reported study regarding two-dimensional MgZnO monolayer in spite of its unique properties due to quantum confinement effect. Here, using density functional theory calculations, we investigated the phase stability, electronic structure and optical properties of MgxZn1−xO monolayer with Mg concentration x range from 0 to 1. Our calculations show that MgZnO monolayer remains the graphene-like structure with various Mg concentrations. The phase segregation occurring in bulk systems has not been observed in the monolayer due to size effect, which is advantageous for application. Moreover, MgZnO monolayer exhibits interesting tuning of electronic structure and optical properties with Mg concentration. The band gap increases with increasing Mg concentration. More interestingly, a direct to indirect band gap transition is observed for MgZnO monolayer when Mg concentration is higher than 75 at %. We also predict that Mg doping leads to a blue shift of the optical absorption peaks. Our results may provide guidance for designing the growth process and potential application of MgZnO monolayer.
Cheng, Hai-Xia; Wang, Xiao-Xu; Hu, Yao-Wen; Song, Hong-Quan; Huo, Jin-Rong; Li, Lu; Qian, Ping; Song, Yu-Jun
2016-12-01
Ag@ZnO core-shell nanoparticles of around 72 atoms have been investigated by the density functional theory, revealing proving for the first time that the core-shell structure exhibits a shrinkage phenomenon from outer shell in agreement with the other studies in literatures. Our calculations predict that the Ag@ZnO core-shell structure is a ferromagnetic spin polarized state, and the magnetism mainly stems from the spin splitting of 2p electrons of O atoms. In addition, the total and partial DOS of Ag@ZnO indicate that the nanostructure is a half-metallic nanoparticle and has the characters of the p-type semiconductor. Furthermore, the optical properties calculations show that the absorption edge of Ag@ZnO have a red shift and good photocatalysis compare to that of the bulk ZnO. These results of the Ag@ZnO core-shell structure obtain a well agreement with the experimental measurement.
Energy Technology Data Exchange (ETDEWEB)
Rached, H.; Rached, D.; Benalia, S. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université Djillali Liabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Reshak, A.H., E-mail: maalidph@yahoo.co.uk [Institute of Complex Systems, FFPW, CENAKVA, University of South Bohemia in CB, Nove Hrady 37333 (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Rabah, M. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université Djillali Liabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modélisation Mathématique de la Matière (LPQ3M), université de Mascara, Mascara 29000 (Algeria); Bin Omran, S. [Department of Physics and Astronomy, Faculty of Science, King Saud University, Riyadh 11451 (Saudi Arabia)
2013-12-16
The structural stabilities, elastic and electronic properties of 5d transition metal mononitrides (TMNs) XN with (X = Ir, Os, Re, W and Ta) and 5d transition metal monocarbides (TMCs) XC with (X = Ir, Os, Re and Ta) were investigated using the full-potential linear muffin-tin orbital (FP-LMTO) method, in the framework of the density functional theory (DFT) within the local density approximation (LDA) for the exchange correlation functional. The ground state quantities such as the lattice parameter, bulks modulus and its pressure derivatives for the six considered crystal structures, Rock-salt (B1), CsCl (B2), zinc-blend (B3), Wurtzite (B4), NiAs (B8{sub 1}) and the tungsten carbides (B{sub h}) are calculated. The elastic constants of TMNs and TMCs compounds in its different stable phases are determined by using the total energy variation with strain technique. The elastic modulus for polycrystalline materials, shear modulus (G), Young's modulus (E), and Poisson's ratio (ν) are calculated. The Debye temperature (θ{sub D}) and sound velocities (v{sub m}) were also derived from the obtained elastic modulus. The analysis of the hardness of the herein studied compounds classifies OsN – (B4 et B8{sub 1}), ReN – (B8{sub 1}), WN – (B8{sub 1}) and OsC – (B8{sub 1}) as superhard materials. Our results for the band structure and densities of states (DOS), show that TMNs and TMCs compounds in theirs energetically and mechanically stable phase has metallic characteristic with strong covalent nature Metal–Nonmetal elements. - Highlights: • Structural stabilities, elastic, electronic properties of 5d TMNs XN are investigated. • 5d TMCs XC with (X = Ir, Os, Re and Ta) were investigated. • The ground state properties for the six considered crystal structure are calculated. • The elastic constants of TMNs and TMCs in its different stable phases are determined. • The elastic modulus for polycrystalline materials, G, E, and ν are calculated.
Shafi, Shahid P.
This thesis primarily focuses on the systematic understanding of structure-reactivity relationships in two representative systems: bixbyite and related structures as well as indium doped CeO2. Topotactic reaction routes have gained significant attention over the past two decades due to their potential to access kinetically controlled metastable materials. This has contributed substantially to the understanding of solid state reaction pathways and provided first insights into mechanisms. Contrary to the widely used ex-situ methods, in-situ techniques including powder x-ray diffraction and thermogravimetric-differential thermal analysis have been employed extensively throughout this work in order to follow the reaction pathways in real time. Detailed analysis of the AVO3 (A = In, Sc) bixbyite reactivity under oxidative conditions has been carried out and a variety of novel metastable oxygen defect phases have been identified and characterized. The novel metastable materials have oxygen deficient fluorite structures and consequently are potential ion conductors. Structural aspects of the topotactic vs. reconstructive transformations are illustrated with this model system. The structure-reactivity study of AVO3 phases was extended to AVO3 perovskite family. Based on the research methodologies and results from AVO3 bixbyite reactivity studies a generalized mechanistic oxidation pathway has been established with a non-vanadium phase, ScTiO3 bixbyite. However, there is stark contrast in terms of structural stability and features beyond this stability limit during AVO3 and ScTiO3 bixbyite reaction pathways. A series of complex reaction sequences including phase separation and phase transitions were identified during the investigation of ScTiO3 reactivity. The two-step formation pathway for the fluorite-type oxide ion conductor Ce1-xInxO2-delta (0 ≤ x ≤ 0.3) is being reported. The formation of the BaCe1-xInxO 3-delta perovskites and the subsequent CO2-capture reaction
Majumder, Chiranjib; Kulshreshtha, S. K.
2004-12-01
Structural and electronic properties of metal-doped silicon clusters ( MSi10 , M=Li , Be, B, C, Na, Mg, Al, and Si) have been investigated via ab initio molecular dynamics simulation under the formalism of the density functional theory. The exchange-correlation energy has been calculated using the generalized gradient approximation method. Several stable isomers of MSi10 clusters have been identified based on different initial configurations and their relative stabilities have been analyzed. From the results it is revealed that the location of the impurity atom depends on the nature of interaction between the impurity atom and the host cluster and the size of the impurty atom. Whereas Be and B atoms form stable isomers, the impurity atom being placed at the center of the bicapped tetragonal antiprism structure of the Si10 cluster, all other elements diffuse outside the cage of Si10 cluster. Further, to understand the stability and the chemical bonding, the LCAO-MO based all electron calculations have been carried out for the lowest energy isomers using the hybrid B3LYP energy functional. Based on the interaction energy of the M atoms with Si10 clusters it is found that p-p interaction dominates over the s-p interaction and smaller size atoms interact more strongly. Based on the binding energy, the relative stability of MSi10 clusters is found to follow the order of CSi10>BSi10>BeSi10>Si11>AlSi10>LiSi10>NaSi10>MgSi10 , leading one to infer that while the substitution of C, B and Be enhances the stability of the Si11 cluster, others have an opposite effect. The extra stability of the BeSi10 clusters is due to its encapsulated close packed structure and large energy gap between the HOMO and LUMO energy levels.
Institute of Scientific and Technical Information of China (English)
HOU Ming-Xiu; HE Kai-Hua; ZHENG Guang; HOU Shu-En
2008-01-01
The structural, electronic and optical properties of the monoclinic ZrO2 were studied by ab initio calculations based on the density functional theory and pseudopotential method. The calculated lattice parameters and band gap are in agreement with the experimental and other theo- retical values. The evolution of lattice parameters and electronic properties were illustrated under high pressure. Meanwhile, the optical properties, such as adsorption coefficients, imaginary part of dielectric function, and energy loss function, were investigated under both ambient and high pressures.
Energy Technology Data Exchange (ETDEWEB)
Cinthia, Arumainayagam Jemmy; Rajeswarapalanichamy, Ratnavelu [N.M.S.S.V.N. College, Madurai, Tamilnadu (India). Dept. of Physics; Iyakutti, Kombiah [SRM Univ., Chennai, Tamilnadu (India). Dept. of Physics and Nanotechnology
2015-07-01
The ground-state properties, electronic structure, magnetic and mechanical properties of cobalt oxide (CoO) and nickel oxide (NiO) are investigated using generalised gradient approximation parameterised by Perdew-Burke-Ernzerhof (GGA-PBE) and GGA-PBE+U formalisms. These oxides are found to be stable in the antiferromagnetic (AFM) state at normal pressure. The computed lattice parameters are in agreement with the experimental and other theoretical works. Pressure-induced magnetic transition from AFM to ferromagnetic (FM) state is predicted in NiO at a pressure of 84 GPa. Both these compounds are found to be mechanically stable in the AFM state at normal pressure.
Directory of Open Access Journals (Sweden)
Do Duc Cuong
2015-11-01
Full Text Available Strain effect on thermoelectricity of orthorhombic SnSe is studied using density function theory. The Seebeck coefficients are obtained by solving Boltzmann Transport equation (BTE with interpolated band energies. As expected from the crystal structure, calculated Seebeck coefficients are highly anisotropic, and agree well with experiment. Changes in the Seebeck coefficients are presented, when strain is applied along b and c direction with strength from -3% to +3%, where influence by band gaps and band dispersions are significant. Moreover, for compressive strains, the sign change of Seebeck coefficients at particular direction suggests that the bipolar transport is possible for SnSe.
2012-11-29
boundaries. A paper describing the work was published in Nature Materials. {J. Rivnay, L.H. Jimison, J. E. Northrup, M. F. Toney, R. Noriega , S. Lu, T. J...Switzerland.[4] [1] J. Rivnay, R. Noriega , J. E. Northrup, R. J. Kline, M. F. Toney, and A. Salleo, Structural origin of gap states in semicrystalline...1] J. Rivnay, L.H. Jimison, J. E. Northrup, M. F. Toney, R. Noriega , S. Lu, T. J. Marks, A, Facchetti, and A. Salleo, Large modulation of
The first principle study on the atomic and electronic structure of GaN(101-bar 0) surface
Energy Technology Data Exchange (ETDEWEB)
Li Yonghua [Structure Research Laboratory, University of Science and Technology of China, Academia Sinica, Hefei 230026 (China); NSRL, University of Science and Technology of China, Hefei 230029 (China); Xu Pengshou [Structure Research Laboratory, University of Science and Technology of China, Academia Sinica, Hefei 230026 (China) and NSRL, University of Science and Technology of China, Hefei 230029 (China)]. E-mail: psxu@ustc.edu.cn; Pan Haibin [NSRL, University of Science and Technology of China, Hefei 230029 (China); Xu Faqiang [NSRL, University of Science and Technology of China, Hefei 230029 (China)
2005-06-15
In this paper, we have calculated the atomic and electronic structure of GaN(101-bar 0) surface using an augmented plane wave plus local orbital (APW+lo) method. It is found that the surface is characterized by a top-layer bond-length-contracting rotation relaxation. The surface Ga atom moves towards the substrate and tends to form a planar sp{sup 2}-like bonding. While the surface N atom tends to a p{sup 3}-like bonding. Surface relaxation induces the transformation from metallic to semiconducting characterization.
First principles study on electronic structure and elastic properties of LaCd and LaHg
Energy Technology Data Exchange (ETDEWEB)
Devi, Hansa, E-mail: gita-pagare@yahoo.co.in, E-mail: gita-pagare@yahoo.co.in; Pagare, Gitanjali, E-mail: gita-pagare@yahoo.co.in, E-mail: gita-pagare@yahoo.co.in; Chouhan, S. S., E-mail: gita-pagare@yahoo.co.in, E-mail: gita-pagare@yahoo.co.in [Department of Physics, Government M. L. B. Girls P. G. Autonomous College, Bhopal-462002 (India); Sanyal, Sankar P. [Department of Physics, Barkatullah University, Bhopal-462026 (India)
2014-04-24
Full -potential linearized augmented plane wave method (FP- LAPW) has been used for the comparative study of electronic structure and elastic properties of CsCl-type LaCd and LaHg intermetallic compounds using generalized gradient approximation (GGA). The density of states at the Fermi Level, N (E{sub F}), is found to be 0.06 and 3.03 states/eV for LaCd and LaHg respectively. We report elastic constants for these compounds for the first time. The ductility/brittleness of these compounds has been analyzed using Pugh rule and Cauchy’s pressure.
Energy Technology Data Exchange (ETDEWEB)
Cuong, Do Duc; Rhim, S. H., E-mail: sonny@ulsan.ac.kr; Hong, Soon Cheol, E-mail: schong@ulsan.ac.kr [Department of Physics and Energy Harvest Storage Research Center, University of Ulsan, Ulsan, 680-749 (Korea, Republic of); Lee, Joo-Hyong [Department of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju (Korea, Republic of)
2015-11-15
Strain effect on thermoelectricity of orthorhombic SnSe is studied using density function theory. The Seebeck coefficients are obtained by solving Boltzmann Transport equation (BTE) with interpolated band energies. As expected from the crystal structure, calculated Seebeck coefficients are highly anisotropic, and agree well with experiment. Changes in the Seebeck coefficients are presented, when strain is applied along b and c direction with strength from -3% to +3%, where influence by band gaps and band dispersions are significant. Moreover, for compressive strains, the sign change of Seebeck coefficients at particular direction suggests that the bipolar transport is possible for SnSe.
Energy Technology Data Exchange (ETDEWEB)
Sahli, B. [Laboratoire de Génie Physique, Université Ibn Khaldoun, Tiaret, 14000 (Algeria); Laboratoire des Matériaux Magnétiques, Université Djillali Liabés, Sidi Bel-Abbes 22000 (Algeria); Bouafia, H., E-mail: hamza.tssm@gmail.com [Laboratoire de Génie Physique, Université Ibn Khaldoun, Tiaret, 14000 (Algeria); Abidri, B.; Abdellaoui, A. [Laboratoire des Matériaux Magnétiques, Université Djillali Liabés, Sidi Bel-Abbes 22000 (Algeria); Hiadsi, S.; Akriche, A. [Laboratoire de Microscope Electronique et Sciences des Matériaux, Université des Sciences et de la Technologie Mohamed Boudiaf, département de Génie Physique, BP1505 El m’naouar, Oran (Algeria); Benkhettou, N.; Rached, D. [Laboratoire des Matériaux Magnétiques, Université Djillali Liabés, Sidi Bel-Abbes 22000 (Algeria)
2015-06-25
Highlights: • The ground state properties of SrUO{sub 3}-Perovskite were investigated. • Elastic constants and their related parameters were calculated. • Electronic properties are treated using GGA-PBEsol + U approach. - Abstract: In this paper, we investigate bulk properties of the cubic SrUO{sub 3}-Perovskite in their nonmagnetic (NM), antiferromagnetic (AFM) and ferromagnetic (FM) states using all-electron self consistent Full Potential Augmented Plane Waves plus local orbital (FP-(L)APW + lo) method within PBEsol Generalized Gradiant density approximations. Our calculation allowed us to predict that the more stable magnetic state of the cubic SrUO{sub 3}-Perovskite is that of the ferromagnetic (FM). This work is the first prediction of elastic constants and their related parameters (Young modulus, shear modulus, Poisson ratio, Zener anisotropy and the Debye temperature) for this cubic compound using Mehl method. We have employed the GGA(PBEsol) and GGA(PBEsol) + U to investigate the electronic band structure, density of states and electronic charge density of SrUO{sub 3}-Perovskite. The electronic band structure calculations revealed that SrUO{sub 3} exhibits metallic behavior. On the other hand the charge density plots for [1 1 0] direction indicates a strong ionic character along the Sr–O bond while the U–O bond has strong covalent character. Finally, we have analyzed the thermodynamic properties using the quasi-harmonic Debye model to complete the fundamental characterization of cubic SrUO{sub 3}-Perovskite.
Institute of Scientific and Technical Information of China (English)
Z. Ayat; A. Boukraa; B. Daoudi
2016-01-01
We performedab initio calculations of electronic structure and equilibrium properties for the rare earth superstoichiometric dihydride GdH2.25 (with the space groupPm-3m (No. 221)) using the full-potential linearized augmented plane wave method (FP-LAPW) approach within the density functional theory (DFT) in the generalized gradient approximation (GGA) and local density approximation (LDA) as implemented in the WIEN2k simulation code at 0 K. The equilibrium properties were determined, the den-sity of states, electronic density and the energy band structures were studied in details. It was concluded that the GGA optimized lat-tice parameter agreed much better with the experimental findings than the LDA one. The non negligible electronic density of states at the Fermi level confirmed that the GdH2.25 had a metallic character. The Fermi energyEF fell at a level where most of the states were rare-earth 5d-eg conduction states while negligible contributions of both interstitial (tetrahedral and octahedral) H s-states were ob-served nearEF. From electronic density, the bonding between Gd and tetrahedral H atoms was of prominent covalency, while was ionic between Gd and octahedral H atoms.
First-principles study of structural stability and elastic properties of MgPd3 and its hydride
Directory of Open Access Journals (Sweden)
Dong-Hai Wu
2014-06-01
Full Text Available Theoretical study of structural stability and elastic properties of α- and β-MgPd3 intermetallic compounds as well as their hydrides have been carried out based on density functional theory. The results indicate α-MgPd3 is more stable than β phase with increased stability in their hydrides. The calculated elastic constants of α-MgPd3 are overall larger than β phase. After hydrogenation, the elastic constants are enlarged. And the elastic moduli exhibit similar tendency. The anisotropy of α-MgPd3 is larger than β phase, and the hydrides demonstrate larger anisotropy. Their ductility follows the order of α-MgPd3H0.5 < α-MgPd3 < β-MgPd3H < β-MgPd3. Compared with β phase, higher Debye temperature of α-MgPd3 implies stronger covalent interaction, and the Debye temperature of hydrides increases slightly. The electronic structures demonstrate that the Pd–Pd interaction is stronger than Pd–Mg, and Pd–H bonds play a significant role in the phase stability and elastic properties of hydrides.
Milko, Matus; Ambrosch-Draxl, Claudia
2011-08-01
Stability and structural properties of nanopeapods are investigated by means of density-functional theory (DFT) including van der Waals interactions. As a prototypical system of organic π-conjugated molecules embedded into single-wall carbon nanotubes, we study benzene inside zig-zag nanotubes (n,0), with n ranging from 10 to 18. We explore the position and orientation of the molecule inside the cavity and find the optimal tube diameter for encapsulation to be around 1 nm. We compute that, overall, the molecule tends to align its molecular plane parallel to the tube axis. The internal orientation and molecule-wall distance depend, however, quite strongly on the tube diameter. The overall energy minimum is found for a situation in which the benzene ring takes a tilted position inside the (13,0) nanotube. Chirality turns out not to play a role in terms of the energetics. When benzene arrays are confined in nanotubes, the intermolecular distances can differ from those in the gas phase. Intermolecular interactions are important and further stabilize the peapods. As these as well as the molecule-tube interactions are governed by dispersive forces, we critically assess the performance of different DFT-based methods in this respect. Comparing four different computational schemes including both ab initio and semi-empirical treatment of van der Waals interactions, we conclude that vdW-DF is most reliable in terms of energetics and structural properties of these hybrids.
Qawasmeh, Yasmeen; Hamad, Bothina
2012-02-01
Density functional theory (DFT) calculations are performed to investigate the structural, electronic, magnetic, and elastic properties of Ni2MnZ (Z = B, Al, Ga, In) and Ni2FeZ (Z = Al, Ga) full Heusler alloys. The alloys are found to be metallic ferromagnets with total magnetic moments of about 4μB/f.u. and 3μB/f.u for Ni2MnZ and Ni2FeZ alloys, respectively. The Ni2MnAl and Ni2MnIn alloys are found to be stable at L21 phase, while the other alloys are more stable in the tetragonal phase with c/a ratios of 1.38 and 1.27 for Ni2MnB and Ni2MnGa, respectively and 1.35 for both Ni2FeAl and Ni2FeGa. The Ni2MnB alloy exhibits the highest electron spin polarization in its tetragonal phase, which is about 88% greater than that of L21 structure. However, the Ni2MnGa, Ni2FeAl, and Ni2FeGa alloys exhibit lower spin polarizations in their tetragonal phase than those at the L21. The most contribution of the total magnetic moments comes from Mn or Fe atoms, whereas Ni atoms exhibit much smaller magnetic moments. However, Z atoms have small induced magnetic moments, which are coupled antiferromagnetically with Ni, Mn and Fe.
First-principles study of structure and nonlinear optical properties of CdHg(SCN)4 crystal
Institute of Scientific and Technical Information of China (English)
张鹏; 孔垂岗; 郑超; 王新强; 马跃; 冯金波; 矫玉秋; 卢贵武
2015-01-01
The geometric structure, electronic structure, and optical properties of CdHg(SCN)4 crystal are calculated by using the density functional perturbation theory and Green function screening Coulomb interaction approximation. The band gap of CdHg(SCN)4 crystal is calculated to be 3.198 eV, which is in good agreement with the experimental value 3.265 eV. The calculated second-order nonlinear optical coefficients are d14=1.2906 pm/V and d15=5.0928 pm/V, which are in agreement with the experimental results (d14=(1.4 ± 0.6) pm/V and d15=(6.0 ± 0.9) pm/V). Moreover, it is found that the contribution to the valence band mainly comes from Cd-4d, Hg-5d states, and the contributions to the valence band top and the conduction band bottom predominantly come from C-2p, N-2p, and S-3p states. The second-order nonlinear optical effect of CdHg(SCN)4 crystal results mainly from the internal electronic transition of (SCN)−.
Chiang, Han-Hsin; Lu, Jian-Ming; Kuo, Chin-Lung
2016-01-21
We have performed density functional theory calculations and ab initio molecular dynamics to investigate the structures and dynamic properties of the liquid and amorphous LixSi alloys over a range of composition from x = 1.0 - 4.8. Our results show that Si atoms can form a variety of covalently bonded polyanions with diverse local bonding structures in the liquid alloys. Like in c-LiSi, Si atoms can form a continuous bond network in liquid Li1.0Si at 1050 K, while it gradually disintegrates into many smaller Si polyanions as the Li content increases in the alloys. The average sizes of Si polyanions in these liquid alloys were found to be relatively larger than those in their crystalline counterparts, which can even persist in the highly lithiated Li4.81Si alloy at 1500 K. Our results also show that amorphous LixSi alloys have similar local bonding structures but a largely increased short-range order as compared to their liquid counterparts. The differences between the average coordination number of each atomic pair in amorphous solids and that in the liquids are less than 1.1. Furthermore, our calculations reveal that Li and Si atoms can exhibit very distinct dynamic behaviors in the liquids and their diffusivities appear to be largely dependent on the chemical composition of the alloys. The diffusivity of Li was found to increase with the Li content in the alloys primarily because of the reduced interactions between Li and Si atoms, while the Si diffusivity also increases due to the gradual disintegration of the strongly interconnected Si bond network. The diffusivity of Li in amorphous LixSi was predicted to lie in the range between 10(-7) and 10(-9) cm(2)/s at 300 K, which is more than 20-fold larger than that of Si over the composition range considered. Our calculations further show that the diffusivities of both Li and Si can increase by two orders of magnitude as x increases from 1.0 to 3.57 in amorphous LixSi, indicating a more profound dependence on the
Energy Technology Data Exchange (ETDEWEB)
Chiang, Han-Hsin; Kuo, Chin-Lung, E-mail: chinlung@ntu.edu.tw [Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan (China); Lu, Jian-Ming [National Center for High-Performance Computing, Tainan 74147, Taiwan (China)
2016-01-21
We have performed density functional theory calculations and ab initio molecular dynamics to investigate the structures and dynamic properties of the liquid and amorphous Li{sub x}Si alloys over a range of composition from x = 1.0 − 4.8. Our results show that Si atoms can form a variety of covalently bonded polyanions with diverse local bonding structures in the liquid alloys. Like in c-LiSi, Si atoms can form a continuous bond network in liquid Li{sub 1.0}Si at 1050 K, while it gradually disintegrates into many smaller Si polyanions as the Li content increases in the alloys. The average sizes of Si polyanions in these liquid alloys were found to be relatively larger than those in their crystalline counterparts, which can even persist in the highly lithiated Li{sub 4.81}Si alloy at 1500 K. Our results also show that amorphous Li{sub x}Si alloys have similar local bonding structures but a largely increased short-range order as compared to their liquid counterparts. The differences between the average coordination number of each atomic pair in amorphous solids and that in the liquids are less than 1.1. Furthermore, our calculations reveal that Li and Si atoms can exhibit very distinct dynamic behaviors in the liquids and their diffusivities appear to be largely dependent on the chemical composition of the alloys. The diffusivity of Li was found to increase with the Li content in the alloys primarily because of the reduced interactions between Li and Si atoms, while the Si diffusivity also increases due to the gradual disintegration of the strongly interconnected Si bond network. The diffusivity of Li in amorphous Li{sub x}Si was predicted to lie in the range between 10{sup −7} and 10{sup −9} cm{sup 2}/s at 300 K, which is more than 20-fold larger than that of Si over the composition range considered. Our calculations further show that the diffusivities of both Li and Si can increase by two orders of magnitude as x increases from 1.0 to 3.57 in amorphous Li
Wang, Dawei; Salje, Ekhard K. H.; Mi, Shao-Bo; Jia, Chun-Lin; Bellaiche, L.
2013-10-01
An effective Hamiltonian scheme is used to reveal the properties of a multidomain structure in BiFeO3 consisting of alternating domains that are initially made of two phases, namely, R3c (ferroelectric with antiphase oxygen octahedral tilting) versus Pnma (antiferroelectric with in-phase and antiphase oxygen octahedral tiltings). These two types of domains dramatically modify their properties as a result of their cohabitation. The weak ferromagnetic vector and polarization rotate, and significantly change their magnitude, in the R3c-like region, while the Pnma-like region becomes polar along the direction of domain propagation. Moreover, the domain walls possess distinct polar and oxygen octahedral tilting patterns that facilitate the transition between these two regions. The studied multidomain is also predicted to exhibit other anomalous properties, such as its strain adopting several plateaus and steps when increasing the magnitude of an applied electric field.
Electronic structure of BaFe2As2 as obtained from DFT/ASW first-principles calculations
Schwingenschlögl, Udo
2010-07-02
We use ab-initio calculations based on the augmented spherical wave method within density functional theory to study the magnetic ordering and Fermi surface of BaFe2As2, the parent compound of the hole-doped iron pnictide superconductors (K,Ba)Fe2As2, for the tetragonal I4/mmm as well as the orthorhombic Fmmm structure. In comparison to full potential linear augmented plane wave calculations, we obtain significantly smaller magnetic energies. This finding is remarkable, since the augmented spherical wave method, in general, is known for a most reliable description of magnetism. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
First-principles studies of the electric-field effect on the band structure of trilayer graphenes
Wang, Yun-Peng; Li, Xiang-Guo; Cheng, Hai-Ping
Electric-field effects on the electronic structure of trilayer graphene are investigated using the density functional theory in the generalized gradient approximation. Two different stacking orders, namely Bernal and rhombohedral, of trilayer graphene are considered. Our calculations reproduce the experimentally data on band gap opening in Bernal stacking and band overlap in rhombohedral trilayer graphene. In addition, we studied effects of charge doping using dual gate configurations. The size of band gap opening in Bernal trilayer graphene can be tuned by charge doping, and charge doping also causes an electron-hole asymmetry in the density of states. Furthermore, hole-doping can reopen a band gap in the band overlapping region of rhombohedral trilayer grapheme induced by electric fields, which contributes to an extra peak in the optical conductivity spectra. This work is supported by DOE # DE-FG02-02ER45995.
Institute of Scientific and Technical Information of China (English)
Yang Huan; Chang Jing; Li Zhe; Chen Xiang-Rong
2009-01-01
The electronic and the optical properties of the cubic zinc-blende(ZB)BeS under high pressure have been in-vestigated by using ab inztio plane-wave pseudopotential density functional theory method in the generalised gradient approximation(GGA)for exchange-correlation interaction. The electronic band structure and the pressure dependence of the total and partial densities of state under pressure are successfully described. Our calculations show that the ZB BeS has large and indirect band gaps associated with(Γ→X)transitions in ambient conditions. The results obtained are consistent with the experimental data available and other calculations. The optical properties, including dielectric function, energy-loss function, complex refractive index, reflection and absorption spectra, are investigated and analysed at different external pressures. The results suggest that the optical absorption appears moctly in the ultra-violet region and the curve of refractive index shift toward high energies(blue shift)with pressure increasing.
Structural stability and magnetic coupling in CaCu(3)Co(4)O(12) from first principles.
Xiang, H P; Liu, X J; Meng, J; Wu, Z J
2009-01-28
The structural, electronic and magnetic properties of CaCu(3)Co(4)O(12) were studied by use of the full-potential linearized augmented plane wave method. The calculated results indicate that CaCu(3)Co(4)O(12) is stable both thermodynamically and mechanically. Both GGA (generalized gradient approximation) and GGA+U methods predict that CaCu(3)Co(4)O(12) is metallic. The ferromagnetic configuration is only slightly more stable in energy compared with the non-magnetic configuration (3.7 meV), suggesting that they are competitive for being the ground state. Co is in the low spin state (S = 1/2).
High-pressure structural, electronic and optical properties of KMgF{sub 3}: A first-principles study
Energy Technology Data Exchange (ETDEWEB)
Cui Shouxin, E-mail: shouxincui@lcu.edu.c [School of Physics Science and Information Technology, Liaocheng University, Wenhua Road 34, Liaocheng 252059 (China); Feng Wenxia; Hu Haiquan; Feng Zhenbao [School of Physics Science and Information Technology, Liaocheng University, Wenhua Road 34, Liaocheng 252059 (China); Wang Yuanxu [Institute of Computational Materials Science, School of Physics and Electronics, Henan University, Kaifeng 475004 (China)
2009-09-18
We theoretically study the structural, electronic and optical properties of KMgF{sub 3}by using the pseudopotential plane-wave method within the density-functional theory. The calculations show that KMgF{sub 3} is found to be indirect insulator in the pressure range 0-100 GPa. The positive pressure derivative of the indirect band gap energy for KMgF{sub 3} is attributed to the absence of d occupations in the valence bands. There exists ionic interaction between the Mg-F and K-F bond with the analysis of the charge-density distribution. Our calculated equation of state (EOS) is well consistent with the recent experimental results. The refractive index increases with the hydrostatic pressure, which shows agreement with the available experimental results.
Wang, Yun-Peng; Cheng, Hai-Ping
2013-06-01
We investigate the currently debated issue of the existence of the Dirac cone in silicene on an Ag(111) surface, using first-principles calculations based on density functional theory to obtain the band structure. By unfolding the band structure in the Brillouin zone of a supercell to that of a primitive cell, followed by projecting onto Ag and silicene subsystems, we demonstrate that the Dirac cone in silicene on Ag(111) is destroyed. Our results clearly indicate that the linear dispersions observed in both angular-resolved photoemission spectroscopy [P. Vogt , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.108.155501 108, 155501 (2012)] and scanning tunneling spectroscopy [L. Chen , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.109.056804 109, 056804 (2012)] come from the Ag substrate and not from silicene.
rehman Hashmi, Muhammad Raza ur; Zafar, Muhammad; Shakil, M.; Sattar, Atif; Ahmed, Shabbir; Ahmad, S. A.
2016-11-01
First-principles calculations by means of the full-potential linearized augmented plane wave method using the generalized gradient approximation with correlation effect correction (GGA+U) within the framework of spin polarized density functional theory (DFT+U) are used to study the structural, electronic, and magnetic properties of cubic perovskite compounds RbXF3 (X = Mn, V, Co, and Fe). It is found that the calculated structural parameters, i.e., lattice constant, bulk modulus, and its pressure derivative are in good agreement with the previous results. Our results reveal that the strong spin polarization of the 3d states of the X atoms is the origin of ferromagnetism in RbXF3. Cohesive energies and the magnetic moments of RbXF3 have also been calculated. The calculated electronic properties show the half-metallic nature of RbCoF3 and RbFeF3, making these materials suitable for spintronic applications.
Energy Technology Data Exchange (ETDEWEB)
Liu, Chun Mei; Xu, Chao [Wuhan University of Science and Technology (China). Dept. of Applied Physics; Duan, Man Yi [Sichuan Normal Univ., Chengdu (China). College of Physics and Electronic Engineering
2015-07-01
SnS has potential technical applications, but many of its properties are still not well studied. In this work, the structural, thermodynamic, elastic, and electronic properties of α-SnS have been investigated by the plane wave pseudo-potential density functional theory with the framework of generalised gradient approximation. The calculated pressure-dependent lattice parameters agree well with the available experimental data. Our thermodynamic properties of α-SnS, including heat capacity C{sub P}, entropy S, and Gibbs free energy relation of -(G{sub T}-H{sub 0}) curves, show similar growth trends as the experimental data. At T=298.15 K, our C{sub P}=52.31 J/mol.K, S=78.93 J/mol.K, and -(G{sub T}-H{sub 0})=12.03 J/mol all agree very well with experimental data C{sub P}=48.77 J/mol.K and 49.25 J/mol.K, S=76.78 J/mol.K, and -(G{sub T}-H{sub 0})=12.38 J/mol. The elastic constants, together with other elastic properties, are also computed. The anisotropy analyses indicate obvious elastic anisotropy for α-SnS along different symmetry planes and axes. Moreover, calculations demonstrate that α-SnS is an indirect gap semiconductor, and it transforms to semimetal with pressure increasing up to 10.2 GPa. Combined with the density of states, the characters of the band structure have been analysed in detail.
Chelli, S.; Meradji, H.; Amara Korba, S.; Ghemid, S.; El Haj Hassan, F.
2014-12-01
The structural, electronic thermodynamic and thermal properties of BaxSr1-xTe ternary mixed crystals have been studied using the ab initio full-potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). In this approach, the Perdew-Burke-Ernzerhof-generalized gradient approximation (PBE-GGA) was used for the exchange-correlation potential. Moreover, the recently proposed modified Becke Johnson (mBJ) potential approximation, which successfully corrects the band-gap problem was also used for band structure calculations. The ground-state properties are determined for the cubic bulk materials BaTe, SrTe and their mixed crystals at various concentrations (x = 0.25, 0.5 and 0.75). The effect of composition on lattice constant, bulk modulus and band gap was analyzed. Deviation of the lattice constant from Vegard's law and the bulk modulus from linear concentration dependence (LCD) were observed for the ternary BaxSr1-xTe alloys. The microscopic origins of the gap bowing were explained by using the approach of Zunger and co-workers. On the other hand, the thermodynamic stability of these alloys was investigated by calculating the excess enthalpy of mixing, ΔHm as well as the phase diagram. It was shown that these alloys are stable at high temperature. Thermal effects on some macroscopic properties of BaxSr1-xTe alloys were investigated using the quasi-harmonic Debye model, in which the phononic effects are considered.
Jiang, Hong
2011-05-28
Early transition metal dichalcogenides (TMDC), characterized by their quasi-two-dimensional layered structure, have attracted intensive interest due to their versatile chemical and physical properties, but a comprehensive understanding of their structural and electronic properties from a first-principles point of view is still lacking. In this work, four simple TMDC materials, MX(2) (M = Zr and Hf, X = S and Se), are investigated by the Kohn-Sham density functional theory (KS-DFT) with different local or semilocal exchange-correlation (xc) functionals and many-body perturbation theory in the GW approximation. Although the widely used Perdew-Burke-Ernzelhof (PBE) generalized gradient approximation (GGA) xc functional overestimates the interlayer distance dramatically, two newly developed GGA functionals, PBE-for-solids (PBEsol) and Wu-Cohen 2006 (WC06), can reproduce experimental crystal structures of these TMDC materials very well. The GW method, currently the most accurate first-principles approach for electronic band structures of extended systems, gives the fundamental band gaps of all these materials in good agreement with the experimental values obtained from optical absorption. The minimal direct gaps from GW are systematically larger than those measured from thermoreflectance by about 0.1-0.3 eV, implying that excitonic effects may be stronger than previously estimated. The calculated density of states from GW quasi-particle band energies agrees very well with photo-emission spectroscopy data. Ionization potentials of these materials are also computed by combining PBE calculations based on the slab model and GW quasi-particle corrections. The calculated absolute band energies with respect to the vacuum level indicate that that ZrS(2) and HfS(2), although having suitable band gaps for visible light absorption, cannot be used for overall water splitting as a result of mismatch of the conduction band minimum with the redox potential of H(+)/H(2).
Electronic Structures of S/C-Doped TiO2 Anatase (101 Surface: First-Principles Calculations
Directory of Open Access Journals (Sweden)
Qili Chen
2014-01-01
Full Text Available The electronic structures of sulfur (S or carbon (C-doped TiO2 anatase (101 surfaces have been investigated by density functional theory (DFT plane-wave pseudopotential method. The general gradient approximation (GGA + U (Hubbard coefficient method has been adopted to describe the exchange-correlation effects. All the possible doping situations, including S/C dopants at lattice oxygen (O sites (anion doping, S/C dopants at titanium (Ti sites (cation doping, and the coexisting of anion and cation doping, were studied. By comparing the formation energies, it was found that the complex of anion and cation doping configuration forms easily in the most range of O chemical potential for both S and C doping. The calculated density of states for various S/C doping systems shows that the synergistic effects of S impurities at lattice O and Ti sites lead a sharp band gap narrowing of 1.35 eV for S-doped system comparing with the pure TiO2 system.
Fatma, Shaheen; Bishnoi, Abha; Singh, Vineeta; Al-Omary, Fatmah A. M.; El-Emam, Ali A.; Pathak, Shilendra; Srivastava, Ruchi; Prasad, Onkar; Sinha, Leena
2016-04-01
Quantum chemical calculations of geometrical structure, energy and vibrational wavenumbers of a novel functionalized pyrido-pyrimidine compound (a prospective antibacterial agent), chemically known as 6-Methyl,13,14,15-Trihydro-14-(4-Nitrophenyl)pyrido[1,2-a:1‧,2‧-a‧] pyrido[2″,3″-d:6″,5″-d‧]dipyrimidine-13,15-dione (C24H16N6O4), were carried out, using B3LYP/6311++G(d,p) method. Comprehensive interpretation of the infrared and Raman spectra of the compound under study is based on potential energy distribution. A good coherence between experimental and theoretical wavenumbers shows the preciseness of the assignments. NLO properties like the dipole moment, polarizability, first static hyperpolarizability and molecular electrostatic potential surface have been calculated to get a better cognizance of the properties of the title compound. Molecular docking results reveal that the title compound exhibit inhibitory activity against Staphylococcus aureus.
Gao, Xiang; Zhou, Meng; Cheng, Yan; Ji, Guangfu
2016-01-01
The structural, elastic, electronic and thermodynamic properties of the rhombohedral topological insulator Bi2Se3 are investigated by the generalized gradient approximation (GGA) with the Wu-Cohen (WC) exchange-correlation functional. The calculated lattice constants agree well with the available experimental and other theoretical data. Our GGA calculations indicate that Bi2Se3 is a 3D topological insulator with a band gap of 0.287 eV, which are well consistent with the experimental value of 0.3 eV. The pressure dependence of the elastic constants Cij, bulk modulus B, shear modulus G, Young's modulus E, and Poisson's ratio σ of Bi2Se3 are also obtained successfully. The bulk modulus obtained from elastic constants is 53.5 GPa, which agrees well with the experimental value of 53 GPa. We also investigate the shear sound velocity VS, longitudinal sound velocity VL, and Debye temperature ΘE from our elastic constants, as well as the thermodynamic properties from quasi-harmonic Debye model. We obtain that the heat capacity Cv and the thermal expansion coefficient α at 0 GPa and 300 K are 120.78 J mol-1 K-1 and 4.70 × 10-5 K-1, respectively.
First-principles study of the band structure and optical absorption of CuGaS2
Aguilera, Irene; Vidal, Julien; Wahnón, Perla; Reining, Lucia; Botti, Silvana
2011-08-01
CuGaS2 is the most promising chalcopyrite host for intermediate-band thin-film solar cells. Standard Kohn-Sham density functional theory fails in describing the band structure of chalcopyrite materials, due to the strong underestimation of the band gap and the poor description of p-d hybridization, which makes it inadvisable to use this approach to study the states in the gap induced by doping. We used a state-of-the-art restricted self-consistent GW approach to determine the electronic states of CuGaS2: in the energy range of interest for optical absorption, the GW corrections shift the Kohn-Sham bands almost rigidly, as we proved through analysis of the effective masses, bandwidths, and relative position of the conduction energy valleys. Furthermore, starting from the GW quasiparticle bands, we calculated optical absorption spectra using different approximations. We show that the time-dependent density functional theory can be an efficient alternative to the solution of the Bethe-Salpeter equation when the exchange-correlation kernels derived from the Bethe-Salpeter equation are employed. This conclusion is important for further studies of optical properties of supercells including dopants.
Sahariah, Munima B; Ghosh, Subhradip; Singh, Chabungbam S; Gowtham, S; Pandey, Ravindra
2013-01-16
The structural stabilities, elastic, electronic and magnetic properties of the Heusler-type shape memory alloy Ni(2)FeGa are calculated using density functional theory. The volume conserving tetragonal distortion of the austenite Ni(2)FeGa find an energy minimum at c/a = 1.33. Metastable behaviour of the high temperature cubic austenite phase is predicted due to elastic softening in the [110] direction. Calculations of the total and partial magnetic moments show a dominant contribution from Fe atoms of the alloy. The calculated density of states shows a depression in the minority spin channel of the cubic Ni(2)FeGa just above the Fermi level which gets partially filled up in the tetragonal phase. In contrast to Ni(2)MnGa, the transition metal spin-down states show partial hybridization in Ni(2)FeGa and there is a relatively high electron density of states near the Fermi level in both phases.
Park, Hanjin; Kim, Cheol-Woon; Lee, Hyung-June; Song, Hosin; Kwon, Young-Kyun
Using ab initio density functional theory, we investigate the structural properties and their phase transition mechanism of the crystalline and amorphous phases of Ge-Sb-Te (GST) based phase change materials, which would be utilized for phase change random access memory. Among various stochiometries of GST, we focus on compositions along the (GeTe)n(Sb2Te3)m pseudo-binary line, denoted simply by (n , m) with integer n and m. We explore various GST materials corresponding (n , m) sets including (1,0), (0,1), (1,1), (2,1) and (1,2) by modeling their both phases. Especially, their amorphous phases can be constructed based on experimental data available or molecular dynamics (MD) simulations performing melt-quench processes. To understand the phase transition mechanism, we evaluate their coordination numbers, radial distribution functions, and angle distribution functions, which enables us to identify the characteristic local geometry representing each phase. We further investigate the thermal properties of various phases by evaluating their phonon densities of states obtained by Fourier-transforming the velocity autocorrelation functions calculated directly from our MD simulation.
Institute of Scientific and Technical Information of China (English)
Yildirim A; Koc H; Deligoz E
2012-01-01
The structural,elastic,electronic,optical,and vibrational properties of the orthorhombic Pd2Ga compound are investigated using the norm-conserving pseudopotentials within the local density approximation in the frame of density functional theory.The calculated lattice parameters have been compared with the experimental values and found to be in good agreement with these results.The second-order elastic constants and the other relevant quantities,such as the Young's modulus,shear modulus,Poisson's ratio,anisotropy factor,sound velocity,and Debye temperature,have been calculated. It is shown that this compound is mechanically stable after analysing the calculated elastic constants. Furthermore,the real and imaginary parts of the dielectric function and the optical constants,such as the optical dielectric constant and the effective number of electrons per unit cell,are calculated and presented.The phonon dispersion curves are derived using the direct method.The present results demonstrate that this compound is dynamically stable.
Sahariah, Munima B.; Ghosh, Subhradip; Singh, Chabungbam S.; Gowtham, S.; Pandey, Ravindra
2013-01-01
The structural stabilities, elastic, electronic and magnetic properties of the Heusler-type shape memory alloy Ni2FeGa are calculated using density functional theory. The volume conserving tetragonal distortion of the austenite Ni2FeGa find an energy minimum at c/a = 1.33. Metastable behaviour of the high temperature cubic austenite phase is predicted due to elastic softening in the [110] direction. Calculations of the total and partial magnetic moments show a dominant contribution from Fe atoms of the alloy. The calculated density of states shows a depression in the minority spin channel of the cubic Ni2FeGa just above the Fermi level which gets partially filled up in the tetragonal phase. In contrast to Ni2MnGa, the transition metal spin-down states show partial hybridization in Ni2FeGa and there is a relatively high electron density of states near the Fermi level in both phases.
Nold, Andreas; Sibley, David N.; Goddard, Benjamin D.; Kalliadasis, Serafim
2014-11-01
Predicting the fluid structure at a three-phase contact line of macroscopic drops is of interest from a fundamental fluid dynamics point of view. However, exact computations for very small scales are prohibitive. As a consequence, coarse-grained quantities such as interface height and disjoining pressure profiles are used to model the interface shape. Here, we evaluate such coarse-grained models within a rigorous and self-consistent framework based on statistical mechanics, in particular with a Density Functional Theory (DFT) approach. We examine the nanoscale behavior of an equilibrium three-phase contact line in the presence of long-ranged intermolecular forces by employing DFT together with fundamental measure theory. Our analysis also enables us to evaluate the predictive quality of effective Hamiltonian models in the vicinity of the contact line. We compare the results for mean field effective Hamiltonians with disjoining pressures defined through the adsorption isotherm for a planar liquid film, and the normal force balance at the contact line [Phys. Fluids, 26, 072001, 2014]. Results are given for a variety of contact angles. An accurate description of the small-scale behavior of a three-phase conjunction is a prerequisite to understanding dynamic wetting phenomena.
First-principles study of the structural and electronic properties of graphene/MoS2 interfaces
Hieu, Nguyen Ngoc; Phuc, Huynh Vinh; Ilyasov, Victor V.; Chien, Nguyen D.; Poklonski, Nikolai A.; Van Hieu, Nguyen; Nguyen, Chuong V.
2017-09-01
In this paper, we study the structural and electronic properties of graphene adsorbed on MoS2 monolayer (G/MoS2) with different stacking configurations using dispersion-corrected density functional theory. Our calculations show that the interaction between graphene and MoS2 monolayer is a weak van der Waals interaction in all four stacking configurations with the binding energy per carbon atom of -30 meV. In the presence of MoS2 monolayer, the linear bands on the Dirac cone of graphene at the interfaces are slightly split. A band gap about 3 meV opens in G/MoS2 interfaces due to the breaking of sublattice symmetry by the intrinsic interface dipole, and it could be effectively modulated by the stacking configurations. Furthermore, we found that an n-type Schottky contact is formed at the G/MoS2 interface in all four stacking configurations with a small Schottky barrier about 0.49 eV. The appearance of the non-zero band gap in graphene has opened up new possibilities for its application in electronic devices such as graphene field-effect transistors.
Energy Technology Data Exchange (ETDEWEB)
Bannikov, V.V.; Shein, I.R. [Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, 620990 Ekaterinburg (Russian Federation); Ivanovskii, A.L., E-mail: ivanovskii@ihim.uran.ru [Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, 620990 Ekaterinburg (Russian Federation)
2012-08-25
Highlights: Black-Right-Pointing-Pointer Silicide arsenides and germanide arsenides of Ti, Zr, Hf are probed from first principles. Black-Right-Pointing-Pointer Structural, elastic, electronic properties and stability trends are evaluated. Black-Right-Pointing-Pointer Bulk moduli of HfCuSiAs and HfCuGeAs are the largest among all 1111-like phases. Black-Right-Pointing-Pointer Chemical bonding is analyzed. - Abstract: The tetragonal (s.g. I4/nmm; no. 129) silicide arsenide ZrCuSiAs is well known as a structural type of the broad family of so-called 1111-like quaternary phases which includes now more than 150 representatives. These materials demonstrate a rich variety of outstanding physical properties (from p-type transparent semiconductors to high-temperature Fe-based superconductors) and attracted a great interest as promising candidates for a broad range of applications. At the same time, the data about the electronic and elastic properties of the ZrCuSiAs phase itself, as well as of related silicide arsenides and germanide arsenides are still very limited. Here for a series of six isostructural and isoelectronic 1111-like phases which includes both synthesized (ZrCuSiAs, HfCuSiAs, ZrCuGeAs, and HfCuGeAs) and hypothetical (TiCuSiAs and TiCuGeAs) materials, systematical studies of their structural, elastic, electronic properties and stability trends are performed by means of first-principles calculations.
Singh, R. P.; Singh, R. K.; Shalu; Rajagopalan, M.
2012-03-01
First principle study on structural, elastic and electronic properties of binary copper and zinc based rare earth intermetallics have been carried out using the full-potential augmented plane waves plus local orbital (APW+ lo) within density functional theory (DFT). Results on elastic properties are obtained using generalized gradient approximation (GGA) for exchange correlation potentials. The equilibrium lattice parameter, bulk modulus and its pressure derivative have been obtained using optimization method. Young's modulus, shear modulus, Poisson ratio, sound velocities for longitudinal and shear waves, Debye average velocity, Debye temperature and Grüneisen parameters have been calculated. From electronic calculations, it has been found that electronic conduction in copper and zinc based rare earth intermetallics is mainly attributed to 3d-orbital electrons of Cu and Zn.
Yang, Kun; He, Yanqing; Cheng, Yi; Che, Li; Yao, Li
2017-03-01
First-principles density functional theory (DFT) calculations have been used to investigate the structural and electronic properties of the cubic KCaF3 and NaCaF3 (001) surfaces with MF (M = K or Na) and CaF2 terminations. For both KCaF3 and NaCaF3 (001) surfaces, the MF termination has stronger surface rumpling than the CaF2 termination. All the computed band gaps for the KCaF3 and NaCaF3 (001) surfaces are smaller than those of the bulks. Furthermore, separated bands that originate from surface layer F p states are introduced at the top of the valance band of MF-terminated surfaces, indicating the emergence of the surface states. The calculated surface energies show that the MF-terminated surface is energetically more favorable than the CaF2-terminated surface.
Energy Technology Data Exchange (ETDEWEB)
Bannikov, V.V.; Shein, I.R. [Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, 620990 Ekaterinburg (Russian Federation); Ivanovskii, A.L., E-mail: ivanovskii@ihim.uran.ru [Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, 620990 Ekaterinburg (Russian Federation)
2012-01-15
The structural, elastic, magnetic and electronic properties of the layered tetragonal phase KCo{sub 2}Se{sub 2} have been examined in details by means of the first-principles calculations and analyzed in comparison with the isostructural KFe{sub 2}Se{sub 2} as the parent phase for the newest group of ternary superconducting iron-chalcogenide materials. Our data show that KCo{sub 2}Se{sub 2} should be characterized as a quasi-two-dimensional ferromagnetic metal with highly anisotropic inter-atomic bonding owing to mixed ionic, covalent, and metallic contributions inside [Co{sub 2}Se{sub 2}] blocks, and with ionic bonding between the adjacent [Co{sub 2}Se{sub 2}] blocks and K sheets. This material should behave in a brittle manner, adopt enhanced elastic anisotropy rather in compressibility than in shear, and should show very low hardness.
Bounab, S.; Bentabet, A.; Bouhadda, Y.; Belgoumri, Gh.; Fenineche, N.
2017-08-01
We have investigated the structural and electronic properties of the BAs x Sb 1- x , AlAs x Sb 1- x , GaAs x Sb 1- x and InAs x Sb 1- x semiconductor alloys using first-principles calculations under the virtual crystal approximation within both the density functional perturbation theory and the pseudopotential approach. In addition the optical properties have been calculated by using empirical methods. The ground state properties such as lattice constants, both bulk modulus and derivative of bulk modulus, energy gap, refractive index and optical dielectric constant have been calculated and discussed. The obtained results are in reasonable agreement with numerous experimental and theoretical data. The compositional dependence of the lattice constant, bulk modulus, energy gap and effective mass of electrons for ternary alloys show deviations from Vegard's law where our results are in agreement with the available data in the literature.
Energy Technology Data Exchange (ETDEWEB)
Ventelon, L
2008-11-15
The various methods appropriate for the simulation of dislocations within first-principles calculations have been set up, improved and compared between them. They have been applied to study screw dislocations in body-centered cubic iron using the SIESTA code. A non-degenerate core structure is obtained; its detailed analysis reveals a dilatation effect. Taking it into account in an anisotropic elasticity model, allows explaining the cell-size dependence of the energetics, obtained within the dipole approach. The Peierls potential obtained in ab initio suggests that the metastable core configuration at halfway position in the Peierls barrier, predicted by empirical potential, does not exist. We show how to construct tri-periodic cells optimized to study kinked dislocations. Using empirical potential, we demonstrate the feasibility of ab initio calculations of Peierls stress and kink formation. (author)
Zhang, Delin; Yan, Binghai; Wu, Shu-Chun; Kübler, Jürgen; Kreiner, Guido; Parkin, Stuart S P; Felser, Claudia
2013-05-22
We investigate the structural stability and magnetic properties of the cubic, tetragonal and hexagonal phases of Mn3Z (Z=Ga, Sn and Ge) Heusler compounds using first-principles density-functional theory. We propose that the cubic phase plays an important role as an intermediate state in the phase transition from the hexagonal to the tetragonal phases. Consequently, Mn3Ga and Mn3Ge behave differently from Mn3Sn, because the relative energies of the cubic and hexagonal phases are different. This result agrees with experimental observations for these three compounds. The weak ferromagnetism of the hexagonal phase and the perpendicular magnetocrystalline anisotropy of the tetragonal phase obtained in our calculations are also consistent with experiment.
Zhang, Delin; Yan, Binghai; Wu, Shu-Chun; Kübler, Jürgen; Kreiner, Guido; Parkin, Stuart S. P.; Felser, Claudia
2013-05-01
We investigate the structural stability and magnetic properties of the cubic, tetragonal and hexagonal phases of Mn3Z (Z=Ga, Sn and Ge) Heusler compounds using first-principles density-functional theory. We propose that the cubic phase plays an important role as an intermediate state in the phase transition from the hexagonal to the tetragonal phases. Consequently, Mn3Ga and Mn3Ge behave differently from Mn3Sn, because the relative energies of the cubic and hexagonal phases are different. This result agrees with experimental observations for these three compounds. The weak ferromagnetism of the hexagonal phase and the perpendicular magnetocrystalline anisotropy of the tetragonal phase obtained in our calculations are also consistent with experiment.
Energy Technology Data Exchange (ETDEWEB)
Arul Mary, J. [Catalysis and Nanomaterials Research Laboratory, Department of Chemistry Loyola College, Chennai 600 034 (India); Judith Vijaya, J., E-mail: jjvijayaloyola@yahoo.co.in [Catalysis and Nanomaterials Research Laboratory, Department of Chemistry Loyola College, Chennai 600 034 (India); Bououdina, M. [Departments of Physics, College of Science, University of Bahrain, PO Box 32038 Kingdom of Bahrain (Bahrain); John Kennedy, L. [Materials Division, School of Advanced Sciences, Vellore Institute of Technology (VIT) University, Chennai Campus, Chennai 600 127 (India); Daie, J.H.; Song, Y. [School of Materials Science and Engineering, Harbin Institute of Technology at Weihai, 2 West Wenhua Road, Weiahi 264209 (China)
2015-01-01
We report on the synthesis of ((Zn{sub 1−2x}Ce{sub x}Fe{sub x}) O (x=0.00, 0.01, 0.02, 0.03, 0.04 and 0.05)) nanoparticles via microwave combustion by using urea as a fuel. To understand how the dopant influenced the structural, magnetic and optical properties of nanoparticles, it was characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectra and vibrating sample magnetometer (VSM). The stability and magnetic properties of Ce and Fe co-doped ZnO were probed by first principle calculations. From the analysis of X-ray diffraction, the samples are identified with the wurtzite crystal structure. The change in lattice parameters, micro-strain, and a small shift in XRD peaks confirms the substitution of co dopants into the ZnO lattice. Morphological investigation of the products revealed the existence of irregular shapes, such as spherical, spherodial and hexagonal. DRS measurements showed a decrease in the energy gap with increasing dopants contents, probably due to an increase in the lattice parameters. PL spectra consist of visible emission, due to the electronic defects, which are related to deep level emissions, such as oxide antisite (O{sub Zn}), interstitial zinc (Zn{sub i}), interstitial oxygen (O{sub i}) and zinc vacancy (V{sub Zn}). Magnetic measurements showed a ferromagnetic behavior for all the doped samples at room temperature. The first principle calculation results showed that the Ce governs the stability, while the Fe adjusts the magnetic characteristics in the Ce and Fe co-doped ZnO.
Arul Mary, J.; Judith Vijaya, J.; Bououdina, M.; John Kennedy, L.; Daie, J. H.; Song, Y.
2015-01-01
We report on the synthesis of ((Zn1-2xCexFex) O (x=0.00, 0.01, 0.02, 0.03, 0.04 and 0.05)) nanoparticles via microwave combustion by using urea as a fuel. To understand how the dopant influenced the structural, magnetic and optical properties of nanoparticles, it was characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectra and vibrating sample magnetometer (VSM). The stability and magnetic properties of Ce and Fe co-doped ZnO were probed by first principle calculations. From the analysis of X-ray diffraction, the samples are identified with the wurtzite crystal structure. The change in lattice parameters, micro-strain, and a small shift in XRD peaks confirms the substitution of co dopants into the ZnO lattice. Morphological investigation of the products revealed the existence of irregular shapes, such as spherical, spherodial and hexagonal. DRS measurements showed a decrease in the energy gap with increasing dopants contents, probably due to an increase in the lattice parameters. PL spectra consist of visible emission, due to the electronic defects, which are related to deep level emissions, such as oxide antisite (OZn), interstitial zinc (Zni), interstitial oxygen (Oi) and zinc vacancy (VZn). Magnetic measurements showed a ferromagnetic behavior for all the doped samples at room temperature. The first principle calculation results showed that the Ce governs the stability, while the Fe adjusts the magnetic characteristics in the Ce and Fe co-doped ZnO.
Energy Technology Data Exchange (ETDEWEB)
Li Jia, E-mail: jiali@hebut.edu.cn; Zhang Zhidong; Ji Qing; Zhang Hui; Luo Hongzhi
2012-10-05
Highlights: Black-Right-Pointing-Pointer Reproduce of band gap for XSi(X = Fe,Ru,Os) with gap of {approx}10{sup -1} eV. Black-Right-Pointing-Pointer Using the mBJ + LDA first principles in comparison with GGA and LDA. Black-Right-Pointing-Pointer Theoretical optical conductivity is in agreement with the measurement. - Abstract: The electronic structure, optical reflectivity spectra and optical conductivity of semiconducting transition-metal silicides FeSi, RuSi and OsSi have been investigated by using first principles calculation within the recent developed modified Becke-Johnson exchange potential plus local-density approximation (mBJ + LDA). The electronic structures produced by mBJ + LDA, generalized gradient approximation (GGA) and LDA are rather similar although the band gap has been enlarged more or less by the mBJ + LDA compared to the GGA and LDA for the three compounds. The mBJ + LDA, GGA and LDA all have overestimated the band gap for FeSi and OsSi compared to the experiment. For RuSi, the theoretical gap values are basically close to the experimental values and the improvement of gap by mBJ + LDA is only 0.04 eV in comparison with the GGA. The mBJ + LDA and GGA also produce similar results with respect to their optical properties including the reflectivity spectra and optical conductivity except that for the reflectivity spectra of FeSi, the GGA result is little better consistent with the experimental measurement than the mBJ + LDA result. The optical conductivity calculated by mBJ + LDA and GGA both exhibits the absorption edge, in well correspondence to the optical measurement.
Energy Technology Data Exchange (ETDEWEB)
Rajeswarapalanichamy, R., E-mail: rrpalanichamy@gmail.com [Department of Physics, N.M.S.S.V.N College, Madurai, Tamil Nadu 625 019 (India); Priyanga, G. Sudha; Murugan, A.; Santhosh, M.; Cinthia, A. Jemmy [Department of Physics, N.M.S.S.V.N College, Madurai, Tamil Nadu 625 019 (India); Kanagaprabha, S. [Department of Physics, Kamaraj College, Tuticorin, Tamil Nadu 628 003 (India); Iyakutti, K. [Department of Physics and Nanotechnology, SRM University, Chennai, Tamil Nadu 603 203 (India)
2013-12-15
Highlights: •Electronic, structural and elastic properties of group IB nitrides are investigated. •A pressure induced structural phase transition is predicted under high pressure. •Electronic structure reveals that these materials exhibit metallic behavior. •Computed elastic moduli obey traditional mechanical stability condition. •The Debye temperature values are computed for Group IB metal mono and di-nitrides. -- Abstract: The structural, electronic and elastic properties of group IB transition metal nitrides (TMN{sub x}: TM = Cu, Ag, Au and x = 1, 2) are investigated by first principles calculation using the Vienna ab initio simulation package. The lattice constants, cohesive energy, bulk modulus, band structures and the density of states are obtained. The calculated lattice parameters are in good agreement with the available results. The electronic structure reveals that these materials exhibit metallic behaviour. A pressure-induced structural phase transition from NaCl to CsCl phase in AgN at 6 GPa, NaCl to ZB phase in AuN at 34.2 GPa and ZB to NaCl phase in CuN at 36.2 GPa is observed. In group IB metal di-nitrides, CaF{sub 2} to AlB{sub 2} phase transition is predicted. The computed elastic constants indicate that these nitrides are mechanically stable at ambient pressure. The calculated Debye temperature values are in good agreement with experimental and other theoretical results.
Energy Technology Data Exchange (ETDEWEB)
Liu, Yanjun [Key Laboratory of Oil and Gas Equipment of Ministry of Education, Southwest Petroleum University, Chengdu, Sichuan 610500 (China); Huang, Huawei [National Key Laboratory for Nuclear Fuel and Materials, Nuclear Power of China, Chengdu, Sichuan 610041 (China); Pan, Yong, E-mail: yongpanyn@163.com [State Key Laboratory of Advanced Technologies for Comprehensive Utilization of Platinum Metals, Kunming 650106 (China); Zhao, Guanghui; Liang, Zheng [Key Laboratory of Oil and Gas Equipment of Ministry of Education, Southwest Petroleum University, Chengdu, Sichuan 610500 (China)
2014-06-01
Highlights: • The phase transition of Pt{sub 3}Al alloys occurs at 60 GPa. • The elastic modulus of Pt{sub 3}Al alloys increase with increasing pressure. • The cubic structure has good resistance to volume deformation under high pressure. • The pressure enhances the hybridization between Pt atom and Al atom. - Abstract: The phase transition, formation enthalpies, elastic properties and electronic structure of Pt{sub 3}Al alloys are studied using first-principle approach. The calculated results show that the pressure leads to phase transition from tetragonal structure to cubic structure at 60 GPa. With increasing pressure, the elastic constants, bulk modulus and shear modulus of these Pt{sub 3}Al alloys increase linearly and the bond lengths of Pt–Al metallic bonds and the peak at E{sub F} decrease. The cubic Pt{sub 3}Al alloy has excellent resistance to volume deformation under high pressure. We suggest that the phase transition is derived from the hybridization between Pt and Al atoms for cubic structure is stronger than that of tetragonal structure and forms the strong Pt–Al metallic bonds under high pressure.
Hu, Wen-Cheng; Liu, Yong; Li, De-Jiang; Li, Ke; Jin, Hua-Lan; Xu, Ying-Xuan; Xu, Chun-Shui; Zeng, Xiao-Qin
2014-12-01
Structural stability and electronic properties of polar intermetallic CaZn2 and SrZn2 in both CeCu2-type and MgZn2-type structures have been investigated using first-principles method. The calculated equilibrium lattice parameters agree closely with the available experimental and other theoretical results. In terms of formation enthalpy, it is discovered that the present compounds with CeCu2-type structure are energetically more stable than that with MgZn2-type. They are all mechanically stable according to the criteria of elastic stability. In particular, we have investigated the pressure effect on the compressive behaviour and structural stability of each compound. Subsequently, the bulk modulus, shear modulus, Young's modulus, theoretical hardness, Poisson's ratio and Debye temperature in the ground state can be estimated using Voigt-Reuss-Hill homogenization method. Mechanical anisotropy is characterized by the anisotropic factors and direction-dependent Young's modulus. Finally, the electronic structures are determined to reveal the bonding characteristics of considered phases.
Institute of Scientific and Technical Information of China (English)
粟劲苍; 周广; 裴勇; 杨振华; 王先友
2015-01-01
NaxCoO2 is a commonly used cathode material for sodium ion batteries because of its easy synthesis, high reversible capacity and good cyclability. The structural and electrochemical properties of NaxCoO2 during sodium ion insertion/extraction process are studied based on first principles calculations. The calculation results of crystal structure parameters and average intercalation voltage are in good agreement with experiment data. Through calculation of the geometric structure and charge transfer in charging and discharging processes of NaxCoO2, it is found that the oxygen atom surrounding Co of the CoO6 octahedral screens the coulomb potential produced by sodium vacancy in NaxCoO2, and the charge is removed from the entire Co−O layer instead of the Co atom adjacent to sodium vacancy when sodium ions are extracted from the NaCoO2 lattice. Thus, during the insertion/extraction of sodium ion from NaCoO2, the CoO6 octahedral structure undergoes small lattice distortion, which makes the local structure quite stable and is beneficial to the cycling stability of the material for the application of sodium ion batteries.
Le Roux, Sébastien; Bouzid, Assil; Kim, Kye Yeop; Han, Seungwu; Zeidler, Anita; Salmon, Philip S.; Massobrio, Carlo
2016-08-01
The structure of glassy GeSe9 was investigated by combining neutron diffraction with density-functional-theory-based first-principles molecular dynamics. In the simulations, three different models of N = 260 atoms were prepared by sampling three independent temporal trajectories, and the glass structures were found to be substantially different from those obtained for models in which smaller numbers of atoms or more rapid quench rates were employed. In particular, the overall network structure is based on Sen chains that are cross-linked by Ge(Se4)1/2 tetrahedra, where the latter are predominantly corner as opposed to edge sharing. The occurrence of a substantial proportion of Ge-Se-Se connections does not support a model in which the material is phase separated into Se-rich and GeSe2-rich domains. The appearance of a first-sharp diffraction peak in the Bhatia-Thornton concentration-concentration partial structure factor does, however, indicate a non-uniform distribution of the Ge-centered structural motifs on an intermediate length scale.
Directory of Open Access Journals (Sweden)
Mingye Yang
2015-06-01
Full Text Available By using first-principles calculations, we investigate the structural stability of nitrogen-doped (N-doped graphene with graphitic-N, pyridinic-N and pyrrolic-N, and the transition metal (TM atoms embedded into N-doped graphene. The structures and energetics of TM atoms from Sc to Ni embedded into N-doped graphene are studied. The TM atoms at N4V 2 forming a 4N-centered structure shows the strongest binding and the binding energies are more than 7 eV. Finally, we investigate the catalytic performance of N-doped graphene with and without TM embedding for O2 dissociation, which is a fundamental reaction in fuel cells. Compared to the pyridinic-N, the graphitic-N is more favorable to dissociate O2 molecules with a relatively low reaction barrier of 1.15 eV. However, the catalytic performance on pyridinic-N doped structure can be greatly improved by embedding TM atoms, and the energy barrier can be reduced to 0.61 eV with V atom embedded. Our results provide the stable structure of N-doped graphene and its potential applications in the oxygen reduction reactions.
Joo, Paul H; Behtash, Maziar; Yang, Kesong
2016-01-14
We studied the defect formation energies, oxidation states of the dopants, and electronic structures of Bi-doped NaTaO3 using first-principles hybrid density functional theory calculations. Three possible structural models, including Bi-doped NaTaO3 with Bi at the Na site (Bi@Na), with Bi at the Ta site (Bi@Ta), and with Bi at both Na and Ta sites [Bi@(Na,Ta)], are constructed. Our results show that the preferred doping sites of Bi are strongly related to the preparation conditions of NaTaO3. It is energetically more favorable to form a Bi@Na structure under Na-poor conditions, to form a Bi@Ta structure under Na-rich conditions, and to form a Bi@(Na,Ta) structure under mildly Na-rich conditions. The Bi@Na doped model shows an n-type conducting character along with an expected blueshift of the optical absorption edge, in which the Bi atoms exist as Bi(3+) (6s(2)6p(0)). The Bi@Ta doped model has empty gap states consisting of Bi 6s states in its band gap, which can lead to visible-light absorption via the electron transition among the valence band, the conduction band, and the gap states. The Bi dopant is present as a Bi(5+) ion in this model, consistent with the experimental results. In contrast, the Bi@(Na,Ta) doped model has occupied gap states consisting of Bi 6s states in its band gap, and thus visible-light absorption is also expected in this system due to electron excitation from these occupied states to the conduction band, in which the Bi dopants exist as Bi(3+) ions. Our first-principles electronic structure calculations revealed the relationship between the Bi doping sites and the material preparation conditions, and clarified the oxidation states of Bi dopants in NaTaO3 as well as the origin of different visible-light photocatalytic hydrogen evolution behaviors in Bi@Ta and Bi@(Na,Ta) doped NaTaO3. This work can provide a useful reference for preparing a Bi-doped NaTaO3 photocatalyst with desired doping sites.
Escamilla, R.; Carvajal, E.; Cruz-Irisson, M.; Romero, M.; Gómez, R.; Marquina, V.; Galván, D. H.; Durán, A.
2016-12-01
The structural, elastic, vibrational, thermodynamic and electronic properties of the Mo2B intermetallic under pressure are assessed using first-principles calculations based on the generalized gradient approximation (GGA) proposed by Perdew-Wang (PW91). Our results show that the calculated structural parameters at a pressure of zero GPa are in good agreement with the available experimental data. The effect of high pressures on the lattice constants shows that the compression along the c-axis and along the a-axis are similar. The elastic constants were calculated using the static finite strain technique, and the bulk shear moduli are derived from the ideal polycrystalline aggregate. We find that the elastic constants, elastic modulus and hardness monotonically increase as a function of pressure; consequently, the structure is dynamically stable and tends from brittle to ductile behavior under pressure. The Debye temperature θD increases and the so-called Gru¨ neisen constant γ decreases due to stiffening of the crystal structure. The phonon dispersion curves were obtained using the direct method. Additionally, the internal energy (ΔE), the Helmholtz free energy (ΔF), the entropy (S) and the lattice contribution to the heat capacity Cv were calculated and analyzed with the help of the phonon dispersion curves. The N(EF) and the electron transfer between the B and Mo atoms increase as a function of pressure.
Rajgaria, R.; Wei, Y.; Floudas, C. A.
2010-01-01
An integer linear optimization model is presented to predict residue contacts in β, α + β, and α/β proteins. The total energy of a protein is expressed as sum of a Cα – Cα distance dependent contact energy contribution and a hydrophobic contribution. The model selects contacts that assign lowest energy to the protein structure while satisfying a set of constraints that are included to enforce certain physically observed topological information. A new method based on hydrophobicity is proposed to find the β-sheet alignments. These β-sheet alignments are used as constraints for contacts between residues of β-sheets. This model was tested on three independent protein test sets and CASP8 test proteins consisting of β, α + β, α/β proteins and was found to perform very well. The average accuracy of the predictions (separated by at least six residues) was approximately 61%. The average true positive and false positive distances were also calculated for each of the test sets and they are 7.58 Å and 15.88 Å, respectively. Residue contact prediction can be directly used to facilitate the protein tertiary structure prediction. This proposed residue contact prediction model is incorporated into the first principles protein tertiary structure prediction approach, ASTRO-FOLD. The effectiveness of the contact prediction model was further demonstrated by the improvement in the quality of the protein structure ensemble generated using the predicted residue contacts for a test set of 10 proteins. PMID:20225257
Mizutani, U.; Asahi, R.; Sato, H.; Noritake, T.; Takeuchi, T.
2008-07-01
The first-principles FLAPW (full potential linearized augmented plane wave) electronic structure calculations were performed for the Ag5Li8 gamma-brass, which contains 52 atoms in a unit cell and has been known for many years as one of the most structurally complex alloy phases. The calculations were also made for its neighboring phase AgLi B2 compound. The main objective in the present work is to examine if the Ag5Li8 gamma-brass is stabilized at the particular electrons per atom ratio e/a = 21/13 in the same way as some other gamma-brasses like Cu5Zn8 and Cu9Al4, obeying the Hume-Rothery electron concentration rule. For this purpose, the e/a value for the Ag5Li8 gamma-brass as well as the AgLi B2 compound was first determined by means of the FLAPW-Fourier method we have developed. It proved that both the gamma-brass and the B2 compound possess an e/a value equal to unity instead of 21/13. Moreover, we could demonstrate why the Hume-Rothery stabilization mechanism fails for the Ag5Li8 gamma-brass and proposed a new stability mechanism, in which the unique gamma-brass structure can effectively lower the band-structure energy by forming heavily populated bonding states near the bottom of the Ag-4d band.
Lizárraga, Raquel
2016-11-01
A structural and magnetic characterization of Gd-based bulk metallic glasses, GdFe2, GdCo2, and GdNi2, was performed. Models for the amorphous structures for two magnetic configurations, ferromagnetic and ferrimagnetic, were obtained by means of a first-principles-based method, the stochastic quenching. In all three cases, the ferrimagnetic configuration was energetically more stable than the ferromagnetic one, in perfect agreement with experiments. In the structural analysis, radial and angle distribution functions as well as calculations of bond lengths and average coordination numbers were included. Structural properties are in good agreement with experiments and do not depend on the magnetic configuration. The distribution of magnetic moments shows that amorphous GdFe2 and GdCo2 are both ferrimagnets, with antiparallel alignment of the magnetic moments of the two magnetic sublattices, whereas Ni nearly loses its magnetic moment in amorphous GdNi2, similar to the situation in its crystalline counterpart.
Rajgaria, R; Wei, Y; Floudas, C A
2010-06-01
An integer linear optimization model is presented to predict residue contacts in beta, alpha + beta, and alpha/beta proteins. The total energy of a protein is expressed as sum of a C(alpha)-C(alpha) distance dependent contact energy contribution and a hydrophobic contribution. The model selects contact that assign lowest energy to the protein structure as satisfying a set of constraints that are included to enforce certain physically observed topological information. A new method based on hydrophobicity is proposed to find the beta-sheet alignments. These beta-sheet alignments are used as constraints for contacts between residues of beta-sheets. This model was tested on three independent protein test sets and CASP8 test proteins consisting of beta, alpha + beta, alpha/beta proteins and it was found to perform very well. The average accuracy of the predictions (separated by at least six residues) was approximately 61%. The average true positive and false positive distances were also calculated for each of the test sets and they are 7.58 A and 15.88 A, respectively. Residue contact prediction can be directly used to facilitate the protein tertiary structure prediction. This proposed residue contact prediction model is incorporated into the first principles protein tertiary structure prediction approach, ASTRO-FOLD. The effectiveness of the contact prediction model was further demonstrated by the improvement in the quality of the protein structure ensemble generated using the predicted residue contacts for a test set of 10 proteins.
Garcia-Diaz, Reyes; Cocoletzi, Gregorio H.; Mandru, Andrada-Oana; Wang, Kangkang; Smith, Arthur R.; Takeuchi, Noboru
2017-10-01
Using first principles total energy calculations within the periodic spin polarized density functional theory, we have investigated the structural, electronic, and magnetic properties of manganese gallium (MnGa) alloys. Specifically, we explore the MnGa(111)-1 × 2 and 2 × 2 reconstructions. The surface formation energies reveal that selected substitutions occur under Mn (Ga) rich growth conditions. Structures with top layers missing all Mn (Ga) atoms and two layers deep substitutions are also investigated. However, the formation energy shows that these structures are less favorable. For the stable structures, the magnetic properties per layer are proportional to the Mn:Ga ratio. Also, the density of states shows that the MnGa surfaces are metallic. The projected density of states shows that the electronic states in the vicinity of the Fermi level are due mainly to the manganese 3d orbitals. However charge density plots reveal that Mn 3d electrons are closer to the nucleus than Ga sp electrons. Consequently, experimental scanning tunneling microscopy images reveal periodically-arranged bright features, corresponding to the Ga atoms.
Sarkar, Tanmay; Kumar, Parveen; Bharadwaj, Mridula Dixit; Waghmare, Umesh
2016-04-14
A double layer δ-NH4V4O10, due to its high energy storage capacity and excellent rate capability, is a very promising cathode material for Li-ion and Na-ion batteries for large-scale renewable energy storage in transportation and smart grids. While it possesses better stability, and higher ionic and electronic conductivity than the most widely explored V2O5, the mechanisms of its cyclability are yet to be understood. Here, we present a theoretical cyclic voltammetry as a tool based on first-principles calculations, and uncover structural transformations that occur during Li(+)/Na(+) insertion (x) into (Lix/Nax)NH4V4O10. Structural distortions associated with single-phase and multi-phase structural changes during the insertion of Li(+)/Na(+), identified through the analysis of voltage profile and theoretical cyclic voltammetry are in agreement with the reported experimental electrochemical measurements on δ-NH4V4O10. We obtain an insight into its electronic structure with a lower band gap that is responsible for the high rate capability of (Lix/Nax) δ-NH4V4O10. The scheme of theoretical cyclic voltammetry presented here will be useful for addressing issues of cyclability and energy rate in other electrode materials.
Energy Technology Data Exchange (ETDEWEB)
Ciftci, Yasemin Oe. [Gazi University Teknikokullar, Department of Physics, Faculty of Sciences, Ankara (Turkey); Evecen, Meryem; Aldirmaz, Emine [Amasya University, Department of Physics, Faculty of Arts and Sciences, Amasya (Turkey)
2017-01-15
First-principles calculations for the structural, elastic, electronic and vibrational properties of BeGeAs{sub 2} with chalcopyrite structure have been reported in the frame work of the density functional theory. The calculated ground state properties are in good agreement with the available data. By considering the electronic band structure and electronic density of states calculation, it is found that this compound is a semiconductor which confirmed the previous work. Single-crystal elastic constants and related properties such as Young's modulus, Poisson ratio, shear modulus and bulk modulus have been predicted using the stress-finite strain technique. It can be seen from the calculated elastic constants that this compound is mechanically stable in the chalcopyrite structure. Pressure dependences of elastic constants and band gap are also reported. Finally, the phonon dispersion curves and total and partial density of states were calculated and discussed. The calculated phonon frequencies BeGeAs{sub 2} are positive, indicating the dynamical stability of the studied compound. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Kocak, B. [Gazi University, Department of Physics, Teknikokullar, 06500 Ankara (Turkey); Ciftci, Y.O., E-mail: yasemin@gazi.edu.tr [Gazi University, Department of Physics, Teknikokullar, 06500 Ankara (Turkey); Colakoglu, K. [Gazi University, Department of Physics, Teknikokullar, 06500 Ankara (Turkey); Deligoz, E. [Aksaray University, Department of Physics, 68100 Aksaray (Turkey)
2012-02-01
The structural, phase transition, elastic, lattice dynamic and thermodynamic properties of rare-earth compounds PrP and PrAs with NaCl (B1), CsCl (B2), ZB (B3), WC (B{sub h}) and CuAu (L1{sub 0}) structures are investigated using the first principles calculations within the generalized gradient approximation (GGA). For the total-energy calculation, we have used the projected augmented plane-wave (PAW) implementation of the Vienna Ab-initio Simulation Package (VASP). Specifically, some basic physical parameters, e.g. lattice constants, bulk modulus, elastic constants, shear modulus, Young's modulus and Poison's ratio, are predicted. The obtained equilibrium structure parameters are in excellent agreement with the experimental and theoretical data. The temperature and pressure variations of the volume, bulk modulus, thermal expansion coefficient, heat capacity and Debye temperature are calculated in wide pressure and temperature ranges. The phonon dispersion curves and corresponding one-phonon density of states (DOS) for both compounds are also computed in the NaCl (B1) structure.
Kocak, B.; Ciftci, Y. O.; Colakoglu, K.; Deligoz, E.
2012-02-01
The structural, phase transition, elastic, lattice dynamic and thermodynamic properties of rare-earth compounds PrP and PrAs with NaCl (B1), CsCl (B2), ZB (B3), WC (B h) and CuAu (L1 0) structures are investigated using the first principles calculations within the generalized gradient approximation (GGA). For the total-energy calculation, we have used the projected augmented plane-wave (PAW) implementation of the Vienna Ab-initio Simulation Package (VASP). Specifically, some basic physical parameters, e.g. lattice constants, bulk modulus, elastic constants, shear modulus, Young's modulus and Poison's ratio, are predicted. The obtained equilibrium structure parameters are in excellent agreement with the experimental and theoretical data. The temperature and pressure variations of the volume, bulk modulus, thermal expansion coefficient, heat capacity and Debye temperature are calculated in wide pressure and temperature ranges. The phonon dispersion curves and corresponding one-phonon density of states (DOS) for both compounds are also computed in the NaCl (B1) structure.
Kabita, Kh; Maibam, Jameson; Indrajit Sharma, B.; Brojen Singh, R. K.; Thapa, R. K.
2016-01-01
We report first principles phase transition, elastic properties and electronic structure for cadmium telluride (CdTe) under induced pressure in the light of density functional theory using the local density approximation (LDA), generalised gradient approximation (GGA) and modified Becke-Johnson (mBJ) potential. The structural phase transition of CdTe from a zinc blende (ZB) to a rock salt (RS) structure within the LDA calculation is 2.2 GPa while that within GGA is found to be at 4 GPa pressure with a volume collapse of 20.9%. The elastic constants and parameters (Zener anisotropy factor, Shear modulus, Poisson’s ratio, Young’s modulus, Kleinmann parameter and Debye’s temperature) of CdTe at different pressures of both the phases have been calculated. The band diagram of the CdTe ZB structure shows a direct band gap of 1.46 eV as predicted by mBJ calculation which gives better results in close agreement with experimental results as compared to LDA and GGA. An increase in the band gap of the CdTe ZB phase is predicted under induced pressure while the metallic nature is retained in the CdTe RS phase.
Phase Transition and Thermodynamic Properties of Magnesium Fluoride by First Principles
Zhang, Tian; Cheng, Yan; Lv, Zhen-Long; Ji, Guang-Fu; Gong, Min
2014-12-01
The structural stabilities, phase transitions and thermodynamic properties of MgF2 under high pressure and temperature are investigated by first-principles calculations based on plane-wave pseudopotential density functional theory method within the local density approximation. The calculated lattice parameters of MgF2 in all four phases under zero pressure and zero temperature are in good agreement with the existing experimental data and other theoretical results. Our results demonstrate that MgF2 undergoes a series of structural phase transitions from rutile (P42/mnm)→CaCl2-type (Pnnm)→modified fluorite (Pa-3)→cotunnite (Pnam) under high pressure and the obtained transition pressures are in fairly good agreement with the experimental results. The temperature-dependent volume and thermodynamic properties of MgF2 in the rutile phase at 0 GPa are presented and the thermodynamic properties of MgF2 in the rutile, CaCl2-type, modified fluorite and cotunnite phases at 300 K are also predicted using the quasi-harmonic approximation model (QHA) and the quasi-harmonic Debye model (QHD), respectively. Moreover, the partial density of states and the electronic density of the four phases under the phase transition are also investigated.
Bentouaf, Ali; Hassan, Fouad H.; Reshak, Ali H.; Aïssa, Brahim
2017-01-01
We report on the investigation of the structural and physical properties of the Co2VZ (Z = Al, Ga) Heusler alloys, with L21 structure, through first-principles calculations involving the full potential linearized augmented plane-wave method within density functional theory. These physical properties mainly revolve around the electronic, magnetic and thermodynamic properties. By using the Perdew-Burke-Ernzerhof generalized gradient approximation, the calculated lattice constants and spin magnetic moments were found to be in good agreement with the experimental data. Furthermore, the thermal effects using the quasi-harmonic Debye model have been investigated in depth while taking into account the lattice vibrations, the temperature and the pressure effects on the structural parameters. The heat capacities, the thermal expansion coefficient and the Debye temperatures have also been determined from the non-equilibrium Gibbs functions. An application of the atom in molecule theory is presented and discussed in order to analyze the bonding nature of the Heusler alloys. The focus is on the mixing of the metallic and covalent behavior of Co2VZ (Z = Al, Ga) Heusler alloys.
Energy Technology Data Exchange (ETDEWEB)
Benkabou, M. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Rached, H. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Département de Physique, Faculté des Sciences, Université Hassiba Benbouali, Chlef 02000 (Algeria); Abdellaoui, A. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Rached, D., E-mail: rachdj@yahoo.fr [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modélisation Mathématique de la Matière, (LPQ3M), Université de Mascara, Mascara 29000 (Algeria); and others
2015-10-25
First-principle calculations are performed to predict the electronic structure and elastic and magnetic properties of CoRhMnZ (Z = Al, Ga, Ge and Si) Heusler alloys. The calculations employ the full-potential linearized augmented plane wave. The exchange-correlations are treated within the generalized gradient approximation of Perdew–Burke and Ernzerhof (GGA-PBE). The electronic structure calculations show that these compounds exhibit a gap in the minority states band and are clearly half-metallic ferromagnets, with the exception of the CoRhMnAl and CoRhMnGa, which are simple ferromagnets that are nearly half metallic in nature. The CoRhMnGe and CoRhMnSi compounds and their magnetic moments are in reasonable agreement with the Slater-Pauling rule, which indicates the half metallicity and high spin polarization for these compounds. At the pressure transitions, these compounds undergo a structural phase transition from the Y-type I → Y-type II phase. We have determined the elastic constants C{sub 11}, C{sub 12} and C{sub 44} and their pressure dependence, which have not previously been established experimentally or theoretically. - Highlights: • Based on DFT calculations, CoRhMnZ (Z = Al, Ga, Ge and Si) Heusler alloys were investigated. • The magnetic phase stability was determined from the total energy calculations. • The mechanical properties were investigated.
Wang, Mingliang; Chen, Zhe; Chen, Dong; Xia, Cunjuan; Wu, Yi
2016-12-01
The structural, elastic and thermodynamic properties of the A15 structure V3Ir, V3Pt and V3Au were studied using first-principles calculations based on the density functional theory (DFT) within generalized gradient approximation (GGA) and local density approximation (LDA) methods. The results have shown that both GGA and LDA methods can process the structural optimization in good agreement with the available experimental parameters in the compounds. Furthermore, the elastic properties and Debye temperatures estimated by LDA method are typically larger than the GGA methods. However, the GGA methods can make better prediction with the experimental values of Debye temperature in V3Ir, V3Pt and V3Au, signifying the precision of the calculating work. Based on the E-V data derived from the GGA method, the variations of the Debye temperature, coefficient of thermal expansion and heat capacity under pressure ranging from 0 GPa to 50 GPa and at temperature ranging from 0 K to 1500 K were obtained and analyzed for all compounds using the quasi-harmonic Debye model.
Dridi, Z; Ruterana, P; Aourag, H
2002-01-01
First-principles calculations have been used to study the effect of vacancies on the structural and electronic properties in substoichiometric TiC sub x and TiN sub x. The effect of vacancies on equilibrium volumes, bulk moduli, electronic band structures and density of states of the substoichiometric phases was studied using a full-potential linear augmented plane-wave method. A model structure of eight-atom supercells with ordered vacancies within the carbon and nitrogen sublattices is used. We find that the lattice parameters of the studied stoichiometries in both TiC sub x and TiN sub x are smaller than that of ideal stoichiometric TiC and TiN. Our results for the variation of the lattice parameters and the bulk moduli for TiC sub x are found to be in good agreement with experiment. The variation of the energy gaps with the atomic concentration ratio shows that these compounds present the same trends. Results for TiC sub x are compared to a recent full-potential calculation with relaxed 16-atom supercells...
Directory of Open Access Journals (Sweden)
Xianfeng Li
2017-06-01
Full Text Available The pressure dependent behaviors on the structural, elastic and electronic properties of the A15 structure Nb3Ir and Nb3Pt were studied using first-principles calculations based on the density functional theory within generalized gradient approximation and local density approximation methods. Initially, the optimized lattice constants of Nb3Ir and Nb3Pt are consistent with the available experimental and theoretical results. Furthermore, Nb3Ir is found to be more thermodynamically stable than Nb3Pt due to its lower formation enthalpy and higher melting temperature. In addition, the elastic constants of Nb3Ir and Nb3Pt show an increasing tendency, and keep mechanically stable structures under pressures to 40 GPa. Besides, the increasing Cauchy pressures and B/G values have indicated that higher pressures can improve their ductility in both Nb3Ir and Nb3Pt. Finally, the pressure-dependent behaviors on the density of states, Mulliken charges and bond lengths are discussed for both compounds.
Energy Technology Data Exchange (ETDEWEB)
Liu, Qi-Jun, E-mail: qijunliu@home.swjtu.edu.cn [Bond and Band Engineering Group, Institute of High Temperature and High Pressure Physics, School of Physical Science and Technology, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Zhang, Ning-Chao; Liu, Fu-Sheng [Bond and Band Engineering Group, Institute of High Temperature and High Pressure Physics, School of Physical Science and Technology, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Liu, Zheng-Tang [State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an, Shaanxi 710072 (China)
2014-03-15
Highlights: • OsTM and TMOs{sub 2} compounds have no superhard character. • These compounds are mechanically stable and behave in ductile manner. • OsTM has a mixture of covalent-ionic and metallic character. -- Abstract: The first-principles calculations have been performed to study the structural, elastic, mechanical and electronic properties of cubic OsTM (TM = Ti, Zr, and Hf) and hexagonal TMOs{sub 2} compounds. The calculated structural parameters are in good agreement with the available experimental data. To the best of our knowledge, the elastic constants of OsTM and TMOs{sub 2} compounds have been obtained for the first time. The calculated elastic and mechanical properties show that these compounds have no superhard character. These compounds are mechanically stable and behave in ductile manner. The electronic band structures and densities of states of OsTM and TMOs{sub 2} compounds have been analysed. OsTM has a mixture of covalent-ionic and metallic character, and TMOs{sub 2} has strong metallic nature.
Energy Technology Data Exchange (ETDEWEB)
Tavana, Ali, E-mail: tavana@uma.ac.ir [Chair of Atomistic Modelling and Design of Materials, Montanuniversität Leoben, Franz-Josef-Straße 18, A-8700 Leoben (Austria); Advanced Materials Design and Simulation Lab., Department of Physics, University of Mohaghegh Ardabili, Ardabil (Iran, Islamic Republic of); Akhavan, Mohammad [Magnet Research Laboratory (MRL), Department of Physics, Sharif University of Technology, P.O. Box 11365-9161, Tehran (Iran, Islamic Republic of); Draxl, Claudia [Chair of Atomistic Modelling and Design of Materials, Montanuniversität Leoben, Franz-Josef-Straße 18, A-8700 Leoben (Austria); Physics Department and IRIS Adlershof, Humboldt-Universität zu Berlin, Zum Großen Windkanal 6, D-12489 Berlin (Germany)
2015-10-15
Highlights: • Investigating the lattice instability by obtaining the phonon dispersion in whole Brillouin zone from first-principles. • Describing the structural phase transitions by doping and pressure, based on soft phonon modes. • Showing that the “x = 1/8 puzzle” may be answered without invoking strong correlations. - Abstract: We present linear-response density-functional theory calculations for the high-T{sub c} superconductor La{sub 2−x}Ba{sub x}CuO{sub 4} to study the doping dependence of phonon dispersion. Using the virtual crystal approximation, the doping range up to x = 0.20 is investigated. We find unstable phonon modes that soften around high-symmetry points of the Brillouin zone. These branches are analyzed as a function of doping and pressure. The structural distortions related to these phonons are in accordance with the observed phase transitions from the high-temperature tetragonal (HTT) phase to the low-temperature orthorhombic (LTO) and the low-temperature tetragonal (LTT) phases. The calculated tilting angles of the CuO{sub 6} octahedra corresponding to these phases are in good agreement with experiment. Our findings confirm that strong electron correlations have only minor impact on the structural properties of high-T{sub c} cuprates.
Saeed, Yasir
2010-10-01
We report a first-principles study of structural, electronic and magnetic properties of crystalline alloys Zn1-xTMxS (TM = Fe, Co and Ni) at x = 0.25. Structural properties are computed from the total ground state energy convergence and it is found that the cohesive energies of Zn 1-xTMxS are greater than that of zincblende ZnS. We also study the spin-polarized electronic band structures, total and partial density of states and the effect of TM 3d states. Our results exhibit that Zn 0.75Fe0.25S, Zn0.75Co0.25S and Zn0.75Ni0.25S are half-metallic ferromagnetic with a magnetic moment of 4μB, 3μB and 2μB, respectively. Furthermore, we calculate the TM 3d spin-exchange-splitting energies Δx (d), Δx (x-d), exchange constants N0α and N0β, crystal field splitting (ΔEcrystEt2g-Eeg), and find that p-d hybridization reduces the local magnetic moment of TM from its free space charge value. Moreover, robustness of Zn1-xTMxS with respect to the variation of lattice constants is also discussed. © 2010 Elsevier B.V. All rights reserved.
Energy Technology Data Exchange (ETDEWEB)
Zhang Xiaochao; Zhao Lijun [Institute of Clean Technique for Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024 (China); Fan Caimei, E-mail: fancm@163.com [Institute of Clean Technique for Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024 (China); Liang Zhenhai [Institute of Clean Technique for Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024 (China); Han Peide [College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024 (China)
2012-11-01
We performed first-principles calculation to investigate the bonding behavior, electronic structure and visible light absorption of Mn{sub x}Bi{sub 1-x}OCl (x=0, 0.0625, 0.09375 and 0.125) using density functional theory (DFT) within a plane-wave ultrasoft pseudopotential scheme. The relaxed structural parameters are consistent with the experimental results. The bonding behavior, bond orders, Mulliken charges and bond populations as well as formation energies are obtained. The calculated band structures and density of states show that Mn incorporation results in some impurity energy levels of Mn 3d states in forbidden band as well as valence band and conduction band, and that Mn 3d states, for the modest Mn doping concentration, not only can act as the capture center of excited electrons under longer wavelength light irradiation, but also may trap the photo-excited holes, improving the transfer of photo-excited carriers to the reactive sites. Our calculated optical absorption spectra exhibit that the spectral absorption edge is obviously red-shifted and extends to the visible, red and infrared light region due to the incorporation of Mn. Our calculated absorption spectra are in excellent agreement with the experimental results of Mn-doped BiOCl photocatalyst.
Yadav, Sushma; Choudhary, Ashu; Chandra, Amalendu
2017-09-15
A first-principles molecular dynamics study is presented for the structural, dynamical, vibrational, and dipolar properties of the solvation shell of a nitrate ion in deuterated water. A detailed description of the anisotropic structure of the solvation shell is presented through calculations of various structural distributions in different conical shells around the perpendicular axis of the ion. The nitrate ion-water dimer potential energies are also calculated for many different orientations of water. The average vibrational stretch frequency of OD modes in the solvation shell is found to be higher than that of other OD modes in the bulk, which signifies a weakening of hydrogen bonds in the hydration shell. A splitting of the NO stretch frequencies and an associated fast spectral diffusion of the solute are also observed in the current study. The dynamics of rotation and hydrogen bond relaxation are found to be faster in the hydration shell than that in the bulk water. The residence time of water in the hydration shell is, however, found to be rather long. The nitrate ion is found to have a dipole moment of 0.9 D in water which can be attributed to its fluctuating interactions with the surrounding water.
Institute of Scientific and Technical Information of China (English)
G Sudha Priyanga; R Rajeswarapalanichamy; K Iyakutti
2015-01-01
The structural, electronic, elastic and magnetic properties of cerium, praseodymium and their hydrides REHx (RE=Ce, Pr andx=2, 3) were investigated by the first principles calculations based on density functional theory using the Viennaab-initio simula-tion package. At zero pressure all the hydrides were stable in the ferromagnetic state. The calculated lattice parameters were in good agreement with the experimental results. The bulk modulus decreased with the increase in the hydrogen content for these hydrides. The electronic structure revealed that di-hydrides were metallic whereas trihydrides were half metallic at zero pressure. A pres-sure-induced structural phase transition from cubic to hexagonal phase was predicted in these hydrides. The computed elastic con-stants indicated that these hydrides were mechanically stable at zero pressure. The calculated Debye temperature values were in good agreement with experimental and other theoretical results. A half metallic to metallic transition was also observed in REH3under high pressure. Ferromagnetism was quenched in these hydrides at high pressures.
Institute of Scientific and Technical Information of China (English)
Zhang Wei; Tong Pei-Qing
2013-01-01
The structural and elastic properties of multiferroic Ca3Mn2O7 with ferroelectric orthorhombic (O-phase) and paraelectric tetragonal structures (T-phase) have been studied by first-principles calculations within the generalized gradient approximation (GGA) and the GGA plus Hubbard U approaches (GGA + U).The calculated theoretical structures are in good agreement with the experimental values.The T-phase is found to be antiferromagnetic (AFM) and the AFM O-phase is more stable than the T-phase,which also agree with the experiments.On these bases,the single-crystal elastic constants (Cijs) and elastic properties of polycrystalline aggregates are investigated for the two phases.Our elasticity calculations indicate Ca3Mn2O7 is mechanically stable against volume expansions.The AFM O-phase is found to be a ductile material,while the AFM T-phase shows brittle nature and tends to be elastically isotropic.We also investigate the influence of strong correlation effects on the elastic properties,qualitatively consistent results are obtained in a reasonable range of values of U.Finally,the ionicity is discussed by Bader analysis.Our work provides useful guidance for the experimental elasticity measurements of Ca3Mn2O7,and makes the strain energy calculation in multiferroic Ca3Mn2O7 thin films possible.
Energy Technology Data Exchange (ETDEWEB)
Schiffmann, Florian; Hutter, Juerg; VandeVondele, Joost [Physical Chemistry Institute, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich (Switzerland)
2008-02-13
The acetonitrile/anatase(101) interface can be considered a prototypical interface between an oxide and a polar aprotic liquid, and is common in dye sensitized solar cells. Using first principles molecular dynamics simulations of a slab of TiO{sub 2} in contact with neat acetonitrile (MeCN), the liquid structure near this interface has been characterized. Furthermore, in order to investigate properties that require extensive sampling, a classical force field to describe the MeCN/TiO{sub 2} interaction has been optimized, and we show that this force field accurately describes the structure near the interface. We find a surprisingly strong interaction of MeCN with TiO{sub 2}, which leads to an ordered first MeCN layer displaying a significantly enhanced molecular dipole. The strong dipolar interactions between solvent molecules lead to pronounced layering further away from the interface, each successive layer having an alternate orientation of the molecular dipoles. At least seven distinct solvent layers (approximately 12 A) can be discerned in the orientational distribution function. The observed structure also strongly suppresses diffusion parallel to the interface in the first nanometer of the liquid. These results show that the properties of the liquid near the interface differ from those in the bulk, which suggests that solvation near the interface will be distinctly different from solvation in the bulk.
Shabara, Reham M.; Aly, Samy H.
2017-02-01
The elastic, magnetic, and structural properties of PrX2 (X=Fe, Mn, Co) alloys, of the cubic Laves structure (MgCu2), have been evaluated by first-principles density functional theory using both local spin density (LSDA) and generalized gradient (GGA) approximations. The lattice constant, magnetic moment, density of states, band structure, bulk modulus and its first pressure derivative are calculated. At zero pressure, the total magnetic moments of PrFe2, PrCo2, and PrMn2 using GGA are 4.515, 1.05, and 4.79 μB respectively. The bulk moduli using LSDA are higher than those using GGA approximation. The evaluated Bulk moduli of PrFe2, PrMn2 and PrCo2 using GGA approximation are 48.1, 42.98, and 72.23 GPa respectively. The lattice constant and magnetic moment of PrFe2 using GGA approximation are 7.2 Ǻ and 4.51 μB respectively in good agreement with experimental results.
Energy Technology Data Exchange (ETDEWEB)
Liu, Hong-Xia [Department of Materials Science and Engineering, Lanzhou University of Technology, State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals, Lanzhou 730050 (China); Tang, Fu-Ling, E-mail: tfl03@mails.tsinghua.edu.cn [Department of Materials Science and Engineering, Lanzhou University of Technology, State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals, Lanzhou 730050 (China); Xue, Hong-Tao; Zhang, Yu [Department of Materials Science and Engineering, Lanzhou University of Technology, State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals, Lanzhou 730050 (China); Feng, Yu-Dong [Science and Technology on Surface Engineering Laboratory, Lanzhou Institute of Physics, Lanzhou 730000 (China)
2015-10-01
Graphical abstract: The atomic structure, bonding energy and electronic properties of the perfect WZ-CIS (1 0 0)/MoS{sub 2} (−1 0 0) interface with a lattice mismatch less than 3.5% are studied using the first principles calculation. - Highlights: • The degree of lattice mismatch of WZ-CuInS{sub 2} (1 0 0)/MoS{sub 2} (−1 0 0) is about 3.5%. • The interface bonding energy is −0.65 J/m{sup 2}, the interface has better stability. • On the interface there are some interface states near the Fermi level mainly caused by In-5s and S-3p orbital. • Difference charge density and Bader charges analysis find that the atoms near the interface have strong charge transfer. • A lot of atomic orbital hybridizations appear on the interface enhanced the interface stability and conductivity. - Abstract: Using first-principles plane-wave calculations within density functional theory, we theoretically studied the perfect WZ-CIS (1 0 0)/MoS{sub 2} (−1 0 0) interface, including the atomic structure, bonding energy and electronic properties. After relaxation the atomic positions and the bond lengths change slightly on the interface. The WZ-CIS/MoS{sub 2} interface can exist stably with the interface bonding energy about −0.65 J/m{sup 2}. Via analysis density of states, difference charge density and Bader charges we find that the electrons are largely redistributed on the interface, and there are some interface states near the Fermi level, which are mainly caused by In-5s orbital in the WZ-CIS region and S-3p orbital in the MoS{sub 2} region. On the interface the orbital hybridizations of different interfacial atoms highly enhance the bonding ability of the atoms. Electron transformation and orbital hybridization together promote the bonding between atoms and increase the adhesion energy of the interface.
Geng, Wei; Tong, Chuan-Jia; Liu, Jiang; Zhu, Wenjun; Lau, Woon-Ming; Liu, Li-Min
2016-02-05
Methylammonium lead iodide perovskite, CH3NH3PbI3, has attracted particular attention due to its fast increase in efficiency in dye sensitization TiO2 solid-state solar cells. We performed first-principles calculations to investigate several different types of CH3NH3PbI3/TiO2 interfaces. The interfacial structures between the different terminated CH3NH3PbI3 and phase TiO2 are thoroughly explored, and the calculated results suggest that the interfacial Pb atoms play important roles in the structure stability and electronic properties. A charge transfer from Pb atoms to the O atoms of TiO2 lead to the band edge alignment of Pb-p above Ti-d about 0.4 eV, suggesting a better carries separation. On the other hand, for TiO2, rutile (001) is the better candidate due to the better lattice and atoms arrangement match with CH3NH3PbI3.
Parvin, R.; Parvin, F.; Ali, M. S.; Islam, A. K. M. A.
2016-08-01
The electronic properties (Fermi surface, band structure, and density of states (DOS)) of Al-based alloys AlM 3 (M = Zr and Cu) and AlCu2Zr are investigated using the first-principles pseudopotential plane wave method within the generalized gradient approximation (GGA). The structural parameters and elastic constants are evaluated and compared with other available data. Also, the pressure dependences of mechanical properties of the compounds are studied. The temperature dependence of adiabatic bulk modulus, Debye temperature, specific heat, thermal expansion coefficient, entropy, and internal energy are all obtained for the first time through quasi-harmonic Debye model with phononic effects for T = 0 K-100 K. The parameters of optical properties (dielectric functions, refractive index, extinction coefficient, absorption spectrum, conductivity, energy-loss spectrum, and reflectivity) of the compounds are calculated and discussed for the first time. The reflectivities of the materials are quite high in the IR-visible-UV region up to ˜ 15 eV, showing that they promise to be good coating materials to avoid solar heating. Some of the properties are also compared with those of the Al-based Ni3Al compound.
Hattabi, I.; Abdiche, A.; Moussa, R.; Riane, R.; Hadji, K.; Soyalp, F.; Varshney, Dinesh; Syrotyuk, S. V.; Khenata, R.
2016-09-01
In this article, we present results of the first-principle study of the structural, electronic, and optical properties of the InN, InP binary compounds and their related ternary alloy InNxP1-x in the zinc-blend (ZB) phase within a nonrelativistic full potential linearised augmented plan wave (FP-LAPW) method using Wien2k code based on the density functional theory (DFT). Different approximations of exchange-correlation energy were used for the calculation of the lattice constant, bulk modulus, and first-order pressure derivative of the bulk modulus. Whereas the lattice constant decreases with increasing nitride composition x. Our results present a good agreement with theoretical and experimental data. The electronic band structures calculated using Tran-Blaha-modified Becke-Johnson (TB-mBJ) approach present a direct band gap semiconductor character for InNxP1-x compounds at different x values. The electronic properties were also calculated under hydrostatic pressure for (P=0.00, 5.00, 10.0, 15.0, 20.0, 25.0 GPa) where it is found that the InP compound change from direct to indirect band gap at the pressure P≥7.80 GPa. Furthermore, the pressure effect on the dielectric function and the refractive index was carried out. Results obtained in our calculations present a good agreement with available theoretical reports and experimental data.
Indian Academy of Sciences (India)
S Bendaif; A Boumaza; O Nemiri; K Boubendira; H Meradji; S Ghemid; F El Haj Hassan
2015-04-01
First-principle calculations were performed to study the structural, electronic, thermodynamic and thermal properties of ZnSxSe1−x ternary alloys using the full potential-linearized augmented plane wave method (FP-LAPW) within the density functional theory (DFT). In this approach the Wu–Cohen generalized gradient approximation (WC-GGA) and Perdew–Wang local density approximation (LDA) were used for the exchange–correlation potential. For band structure calculations, in addition to WC-GGA approximation, both Engel–Vosko (EV-GGA) generalized gradient approximation and recently proposed modified Becke–Johnson (mBJ) potential approximation have been used. Our investigation on the effect of composition on lattice constant, bulk modulus and band gap for ternary alloys shows a linear dependence on alloy composition with a small deviation. The microscopic origins of the gap bowing were explained using the approach of Zunger and co-workers. Besides, a regular-solution model was used to investigate the thermodynamic stability of the alloys which mainly indicates a phase miscibility gap. Finally, the quasi-harmonic Debye model was applied to see how the thermal properties vary with temperature at different pressures.
Liu, Shuai; Zhan, Yongzhong; Wu, Junyan; Wei, Xuanchen
2015-11-01
The structural, phase stabilities, mechanical, electronic and thermodynamic properties of intermetallic phases in Zr-Sn system are investigated by using first-principles method. The equilibrium lattice constants, enthalpy of formation (ΔHform) and elastic constants are obtained and compared with available experimental and theoretical data. The configuration of Zr4Sn is measured with reasonable precision. The ΔHform of five hypothetical structures are obtained in order to find possible metastable phase for Zr-Sn system. The mechanical properties, including bulk modulus, shear modulus, Young's modulus and Poisson's ratio, are calculated by Voigt-Reuss-Hill approximation and the Zr5Sn4 and Zr5Sn3 show excellent mechanical properties. The electronic density of states for Zr5Sn4, Zr5Sn3 and cP8-Zr3Sn are calculated to further investigate the stability of intermetallic compounds. Through the quasi-harmonic Debye model, the Debye temperature, heat capacity and thermal expansion coefficient under temperature of 0-300 K and pressure of 0-50 GPa for Zr5Sn3 and Zr5Sn4 are deeply investigated.
Shein, I. R.; Bannikov, V. V.; Ivanovskii, A. L.
2008-01-01
First principle total energy calculations using the full potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA) for the exchange-correlation potential were performed to investigate the systematic trends for structural, elastic and electronic properties of the family of superconducting anti-perovskites MCNi 3 depending from the type of M cations (M are Mg, Zn and Cd). In result the optimized lattice parameters, independent elastic constants ( C11, C12 and C44), bulk modulus B, compressibility β, shear modulus G and tetragonal shear modulus G‧ are evaluated. Further, for the first time the numerical estimates of a set of elastic parameters (bulk and shear modulus, Young’s modulus Y, Poisson’s ratio ( ν), Lamé’s coefficients ( μ, λ)) of the polycrystalline superconducting MCNi 3 ceramics (in framework of the Voigt-Reuss-Hill approximation) were performed. Besides, the band structures, densities of states (DOS), total and site-projected l-decomposed DOS at the Fermi level, the shapes of the Fermi surfaces, the Sommerfeld’s coefficients and the molar Pauli paramagnetic susceptibility for these anti-perovskites were obtained and analyzed in comparison with the available theoretical and experimental data.
Energy Technology Data Exchange (ETDEWEB)
Hattabi, I. [Ibn Khaldoun Univ. de Tiaret (Algeria). Lab. Synthese et Catalyse; Abdiche, A.; Riane, R. [Sidi-bel-Abbes Univ. (Algeria). Applied Materials Lab.; Moussa, R. [Sidi-bel-Abbes Univ. (Algeria). Physic Dept.; Hadji, K. [Ibn Khaldoun Univ. de Tiaret (Algeria). Science and Technology Dept.; Soyalp, F. [Yuezuencue Yil Univ., Van (Turkey). Dept. of Physics; Varshney, Dinesh [Devi Ahilya Univ., Indore (India). Materials Science Lab.; Syrotyuk, S.V. [National Univ. ' Lviv Polytechnic' , Lviv (Ukraine). Semiconductor Electronics Dept.; Khenata, R. [Mascara Univ. (Algeria). Lab. de Physique Quantique et de Modelisation Mathematique (LPQ3M)
2016-07-01
In this article, we present results of the first-principle study of the structural, electronic, and optical properties of the InN, InP binary compounds and their related ternary alloy InN{sub x}P{sub 1-x} in the zinc-blend (ZB) phase within a nonrelativistic full potential linearised augmented plan wave (FP-LAPW) method using Wien2k code based on the density functional theory (DFT). Different approximations of exchange-correlation energy were used for the calculation of the lattice constant, bulk modulus, and first-order pressure derivative of the bulk modulus. Whereas the lattice constant decreases with increasing nitride composition x. Our results present a good agreement with theoretical and experimental data. The electronic band structures calculated using Tran-Blaha-modified Becke-Johnson (TB-mBJ) approach present a direct band gap semiconductor character for InN{sub x}P{sub 1-x} compounds at different x values. The electronic properties were also calculated under hydrostatic pressure for (P=0.00, 5.00, 10.0, 15.0, 20.0, 25.0 GPa) where it is found that the InP compound change from direct to indirect band gap at the pressure P≥7.80 GPa. Furthermore, the pressure effect on the dielectric function and the refractive index was carried out. Results obtained in our calculations present a good agreement with available theoretical reports and experimental data.
Wang, Yanli; Ding, Yi
2016-09-01
Utilizing first-principles calculations, we have investigated the structural, electronic and topological properties of binary SnSi and SnGe nanosheets as well as their H-/F-derivatives. It is found that all these systems have chair-like buckled configurations with robust structural stabilities. Unlike the elemental group-IV sheets, SnSi and SnGe sheets are narrow-band-gap semiconductors, which have a gapped Dirac cone with massive Fermions. Under the strains, a direct-to-indirect band gap transition and a semiconductor-to-metal transition would occur in these systems. Although these binary systems are trivial band insulators with ℤ2 = 0, their topological features can be altered by the surface decorations. Particularly, the fluorinated SiGe sheet becomes a topological insulator with ℤ2 = 1, and such non-trivial state can also be found in the strained fluorinated SnSi and hydrogenated SnGe sheets. Large non-trivial SOC band gaps of 0.09-0.17 eV are obtained in these 2D topological insulating systems, which will be beneficial for realizing the room-temperature quantum spin Hall effect. Our study demonstrates that binary Sn-based nanomaterials possess tunable electronic and topological properties, which have potential applications in low-power nano-electrics and devices.
Zhou, Hai Yang; Chen, Xiang Ming
2017-04-01
The structural distortions, orbital ordering, magnetic and electronic properties of double perovskite R2CoMnO6 (R = rare-earth element) have been systematically calculated by first-principles. Structural distortions, including Co–O and Mn–O bond length splitting, the antiferroelectric motions of R ions, the tilting of octahedral (the resulted Co–O–Mn bond angle) are obviously affected by the rare-earth ions’ radius. The bond length splitting behavior of Co–O and Mn–O are rather different because of the Jahn–Teller active ion Co2+ and the Jahn–Teller nonactive ion Mn4+. Taking Gd2CoMnO6 as an example, the t 2g orbitals of Co ions are predicted to be orbital ordered. That is, the spin down channel of d xz orbital for one Co ion and d yz orbital for another Co ion are basically vacant. Finally, the physical properties, including the magnetic Curie temperature and electronic band gap of R2CoMnO6 are almost linear dependent on the average value of cos2 θ (θ is the Co–O–Mn exchange-angle).
Xiao, Jiusan; Jiang, Bo; Huang, Kai; Jiao, Shuqiang; Zhu, Hongmin
2016-09-01
A series of TiC x N y O z solid solutions were synthesized via solid-state reaction and XRD patterns exhibited a single phase of FCC structure over the whole concentration range. The structural and thermodynamic properties of TiC x N y O z solid solutions were studied using experimental method and first-principles calculations. The difference between the calculated and experimental lattice parameters could be attributed to the vacancies segregated in TiO part. The fitting formulae for lattice parameters and mixing enthalpies were firstly given for TiC x N y O z solid solution over the whole concentration range. The obtained thermodynamic data for TiC x N y O z solid solution properly explained the reaction sequence of the carbothermal reduction of TiO2, providing theoretical foundation for TiC x N y O z solid solution as a kind of prospective material for consuming anode utilized in USTB titanium electrolysis process.
Ma, Dongwei; Lu, Zhansheng; Ju, Weiwei; Tang, Yanan
2012-04-11
BN sheets with absorbed transition metal (TM) single atoms, including Fe, Co, and Ni, and their dimers have been investigated by using a first-principles method within the generalized gradient approximation. All of the TM atoms studied are found to be chemically adsorbed on BN sheets. Upon adsorption, the binding energies of the Fe and Co single atoms are modest and almost independent of the adsorption sites, indicating the high mobility of the adatoms and isolated particles to be easily formed on the surface. However, Ni atoms are found to bind tightly to BN sheets and may adopt a layer-by-layer growth mode. The Fe, Co, and Ni dimers tend to lie (nearly) perpendicular to the BN plane. Due to the wide band gap of the pure BN sheet, the electronic structures of the BN sheets with TM adatoms are determined primarily by the distribution of TM electronic states around the Fermi level. Very interesting spin gapless semiconductors or half-metals can be obtained in the studied systems. The magnetism of the TM atoms is preserved well on the BN sheet, very close to that of the corresponding free atoms and often weakly dependent on the adsorption sites. The present results indicate that BN sheets with adsorbed TM atoms have potential applications in fields such as spintronics and magnetic data storage due to the special spin-polarized electronic structures and magnetic properties they possess.
Wong, D. F.; Young, K.; Ng, K. Y. S.
2016-12-01
The c/a unit-cell aspect ratios of CaCu5-structured AB5 and C14 Laves phase AB2 metal hydride alloy families are generally correlated to pressure-concentration-temperature hysteresis and degree of alloy pulverization. Structures of substituted LaNi4 X and C14 Ti4Mn7 X compositions and their hydrides in the α-phase were calculated by first principles using density functional theory to look at the c/a ratio and its relationship to initial lattice expansion. Lattice expansion with respect to the lattice parameters and lattice volume in the α-phase hydrides were analyzed, and a general trend in lattice expansion in the direction of higher resistance to elastic deformation was observed to correlate well to the trends in hysteresis measured in AB5 and C14 AB2 type alloys. Lattice expansion is noted to induce microstrains within the crystal lattice, and the anisotropy in the LaNi4 X and Ti4Mn7 X alloys played a role in determining the direction of higher resistance to deformation. Lattice expansions both measured and calculated have been linked to capacity degradation measurements as well as to hysteresis (a measure of irreversible energy losses due to lattice plastic deformation), which may be related to the dislocations and defects formed during hydrogenation.
Cadars, Sylvian; Brouwer, Darren H; Chmelka, Bradley F
2009-03-21
Subtle structural details of siliceous zeolites are probed by using two-bond scalar (J) coupling constants to characterize covalently bonded 29Si-O-29Si site pairs and local framework order. Solid-state two-dimensional (2D) 29Si{29Si} NMR measurements and first-principles calculations of 2J(29Si-O-29Si) couplings shed insights on both the local structures of siliceous zeolites Sigma-2 and ZSM-12, as well as the sensitivity of J couplings for detailed characterization analyses. DFT calculations on a model linear silicate dimer show that 2J(Si-O-Si) couplings have complicated multiple angular dependencies that make semi-empirical treatments impractical, but which are amenable to cluster approaches for accurate J-coupling calculations in zeolites. DFT calculations of 2J(29Si-O-29Si) couplings of the siliceous zeolite Sigma-2, whose framework structure is known to high accuracy from single-crystal X-ray diffraction studies, yield excellent agreement between calculated and experimentally measured 2J(Si-O-Si) couplings. For the siliceous zeolite ZSM-12, calculated 2J(29Si-O-29Si) couplings based on less-certain powder X-ray diffraction analyses deviate significantly from experimental values, while a refined structure based on 29Si chemical-shift-tensor analyses shows substantially improved agreement. 29Si J-coupling interactions can be used as sensitive probes of local structures of zeolitic frameworks and offer new opportunities for refining and solving complicated structures, in combination with complementary scattering, modeling, and other nuclear spin interactions.
Energy Technology Data Exchange (ETDEWEB)
Wang, Guangtao, E-mail: wangtao@henannu.edu.cn; Shi, Xianbiao
2016-06-15
Highlights: • Study the electronic and magnetic properties of LaFe{sub 2}Ge{sub 2} and LaFe{sub 2}Si{sub 2}. • Find LaFe{sub 2}Ge{sub 2} and LaFe{sub 2}Si{sub 2} share similar electronic structures and magnetism properties. • The band structure and Fermi surfaces exhibit significantly three dimensional character and very similar in shape to that of YFe{sub 2}Ge{sub 2}. • Both LaFe{sub 2}Ge{sub 2} and LaFe{sub 2}Si{sub 2} were suggested nearness to a magnetic quantum critical point (QCP). - Abstract: Inspired by the recent discovery of superconductivity in YFe{sub 2}Ge{sub 2}, we report first-principles calculations on the electronic structure and magnetic properties of LaFe{sub 2}Ge{sub 2} and LaFe{sub 2}Si{sub 2}. We found that LaFe{sub 2}Ge{sub 2} and LaFe{sub 2}Si{sub 2} share similar electronic structure and magnetism properties. In the nonmagnetic state, the density of states at the Fermi level are mostly derived from the d{sub xy}, d{sub yz}, and d{sub zx} orbits, just like the Fe-pnictide superconductors. The band structure and Fermi surfaces exhibit significantly three dimensional character. Our calculations indicate that the ground state of LaFe{sub 2}Ge{sub 2} and LaFe{sub 2}Si{sub 2} is the stripe antiferromagnetic configuration in the a-b plane and stacked antiparallel along the c-axis direction. The overestimate magnetic tendency within calculation indicates these systems nearness to a magnetic quantum critical point (QCP).
Poineau, Frederic; Hartmann, Thomas; Weck, Philippe F; Kim, Eunja; Silva, G W Chinthaka; Jarvinen, Gordon D; Czerwinski, Kenneth R
2010-02-15
The structural properties of Tc-Zr binary alloys were investigated using combined experimental and computational approaches. The Tc(2)Zr and Tc(6)Zr samples were characterized by X-ray diffraction analysis, scanning electron microscopy, electron probe microanalysis, and transmission electron microscopy. Our XRD results show that Tc(6)Zr crystallizes in the cubic alpha-Mn-type structure (I43m space group) with a variable stoichiometry of Tc(6.25-x)Zr (0 Tc(2)Zr has a hexagonal crystal lattice with a MgZn(2)-type structure (P6(3)/mmc space group). Rietveld analysis of the powder XRD patterns and density functional calculations of the "Tc(6)Zr" phase show a linear increase of the lattice parameter when moving from Tc(6.25)Zr to Tc(4..80)Zr compositions, similar to previous observations in the Re-Zr system. This variation of the composition of "Tc(6)Zr" is explained by the substitution of Zr for Tc atoms in the 2a site of the alpha-Mn-type structure. These results suggest that the width of the "Tc(6)Zr" phase needs to be included when constructing the Tc-Zr phase diagram. The bonding character and stability of the various Tc-Zr phases were also investigated from first principles. Calculations indicate that valence and conduction bands near the Fermi level are dominated by electrons occupying the 4d orbital. In particular, the highest-lying molecular orbitals of the valence band of Tc(2)Zr are composed of d-d sigma bonds, oriented along the normal axis of the (110) plane and linking the Zr network to the Tc framework. Strong d-d bonds stabilizing the Tc framework in the hexagonal unit cell are also in the valence band. In the cubic structures of Tc-Zr phases, only Tc 4d orbitals are found to significantly contribute near the Fermi level.
Energy Technology Data Exchange (ETDEWEB)
Zhou, Zhaobo [Key Laboratory of Advanced Materials of Yunnan Province & Key Laboratory of Advanced Materials of Non-Ferrous and Precious Rare Metals Ministry of Education, Kunming University of Science and Technology, Kunming 650093 (China); Zhou, Xiaolong, E-mail: kmzxlong@163.com [Key Laboratory of Advanced Materials of Yunnan Province & Key Laboratory of Advanced Materials of Non-Ferrous and Precious Rare Metals Ministry of Education, Kunming University of Science and Technology, Kunming 650093 (China); Zhang, Kunhua [State Key Laboratory of Rare Precious Metals Comprehensive Utilization of New Technologies, Kunming Institute of Precious Metals, Kunming 650106 (China)
2016-12-15
First-principle calculations were performed to investigate the structural, phase stability, electronic, elastic properties and hardness of monoclinic structure IrN{sub 2} (m-IrN{sub 2}), orthorhombic structure IrN{sub 2} (o-IrN{sub 2}) and zinc blende structure IrN (ZB IrN). The results show us that only m-IrN{sub 2} is both thermodynamic and dynamic stability. The calculated band structure and density of states (DOS) curves indicate that o-IrN{sub 2} and ZB Ir-N compounds we calculated have metallic behavior while m-IrN{sub 2} has a small band gap of ~0.3 eV, and exist a common hybridization between Ir-5d and N-2p states, which forming covalent bonding between Ir and N atoms. The difference charge density reveals the electron transfer from Ir atom to N atom for three Ir-N compounds, which forming strong directional covalent bonds. Notable, a strong N-N bond appeared in m-IrN{sub 2} and o-IrN{sub 2}. The ratio of bulk to shear modulus (B/G) indicate that three Ir-N compounds we calculated are ductile, and ZB IrN possesses a better ductility than two types IrN{sub 2}. m-IrN{sub 2} has highest Debye temperature (736 K), illustrating it possesses strongest covalent bonding. The hardness of three Ir-N compounds were also calculated, and the results reveal that m-IrN{sub 2} (18.23 GPa) and o-IrN{sub 2} (18.02 GPa) are ultraincompressible while ZB IrN has a negative value, which may be attributed to phase transition at ca. 1.98 GPa.
Huang, Meng-Li; Wang, Chong-Yu
2016-10-01
The effects of boron and carbon on the structural, elastic, and electronic properties of both Ni solution and Ni3Al intermetallics are investigated using first-principles calculations. The results agree well with theoretical and experimental data from previous studies and are analyzed based on the density of states and charge density. It is found that both boron and carbon are inclined to occupy the Ni-rich interstices in Ni3Al, which gives rise to a cubic interstitial phase. In addition, the interstitial boron and carbon have different effects on the elastic moduli of Ni and Ni3Al. The calculation results for the G/B and Poisson’s ratios further demonstrate that interstitial boron and carbon can both reduce the brittleness of Ni, thereby increasing its ductility. Meanwhile, boron can also enhance the ductility of the Ni3Al while carbon hardly has an effect on its brittleness or ductility. Project supported by the National Basic Research Program of China (Grant No. 2011CB606402).
Allaf Behbahani, Marzieh; Moradi, Mahmood; Rostami, Mohammad; Davatolhagh, Saeed
2016-05-01
First-principle calculations based on the density functional theory for new half-Heusler IrCrZ (Z=Ge, As, Sn and Sb) alloys are performed. It is found that the half-Heusler IrCrGe and IrCrSn compounds have an antiferromagnetic ground state while the ferromagnetic state is more stable than the antiferromagnetic and non-magnetic states for both IrCrAs and IrCrSb compounds. IrCrAs and IrCrSb exhibit half-metallic property with integer magnetic moments of 2.00 μB per formula unit and half-metallic gaps of 0.28 and 0.27 eV at their equilibrium volume, respectively. In addition, the density of states (DOSs) and band structures of IrCrAs and IrCrSb compounds are studied and the origin of their half-metallic gaps are discussed in detail. The estimation of Curie temperatures of IrCrAs and IrCrSb compounds is performed within the mean field approximation (MFA). The Curie temperatures of IrCrAs and IrCrSb are estimated to be 1083 and 1470 K, respectively. The stability of the half-metallicity in IrCrAs and IrCrSb compounds with the variation of lattice constant are also investigated.
Lahiji, Mohammadreza Askaripour; Ziabari, Ali Abdolahzadeh
2016-11-01
The structural, elastic, electronic, and optical properties of undoped and Cu-doped ZnS nanostructured layers have been studied in the zincblende (ZB) phase, by first-principle approach. Density functional theory (DFT) has been employed to calculate the fundamental properties of the layers using full-potential linearized augmented plane-wave (FPLAPW) method. Mechanical analysis revealed that the bulk modulus increases with the increase of Cu content. Cu doping was found to reduce the band gap value of the material. In addition, DOS effective mass of the electrons and heavy holes was evaluated. Adding Cu caused the decrement/increment of transmission/reflectance of nanolayers in the UV-vis region. The substitution by Cu increased the intensity of the peaks, and a slight red shift was observed in the absorption peak. Moreover, the static dielectric constant, and static refractive index increased with Cu content. The optical conductivity also followed a similar trend to that of the dielectric constants. Energy loss function of the modeled compounds was also evaluated. All calculated parameters were compared with the available experimental and other theoretical results.
Institute of Scientific and Technical Information of China (English)
Ouyang Chu-Ying; Xiong Zhi-Hua; Uuyang Qi-Zhen; Liu Guo-Dong; Ye Zhi-Qing; Lei Min-Sheng
2006-01-01
The electronic and optical properties of zincblende ZnX(X=S, Se, Te) and ZnX:Co are studied from density functional theory (DFT) based first principles calculations. The local crystal structure changes around the Co atoms in the lattice are studied after Co atoms are doped. It is shown that the Co-doped materials have smaller lattice constant (about 0.6%-0.9%). This is mainly due to the shortened Co-X bond length. The (partial) density of states (DOS) is calculated and differences between the pure and doped materials are studied. Results show that for the Co-doped materials, the valence bands are moving upward due to the existence of Co 3d electron states while the conductance bands are moving downward due to the reduced lattice constants. This results in the narrowed band gap of the doped materials. The complex dielectric indices and the absorption coefficients are calculated to examine the influences of the Co atoms on the optical properties. Results show that for the Co-doped materials, the absorption peaks in the high wavelength region are not as sharp and distinct as the undoped materials, and the absorption ranges are extended to even higher wavelength region.
Wang, Qi; Yu, Hai-Tao; Xie, Ying; Li, Ming-Xia; Yi, Ting-Feng; Guo, Chen-Feng; Song, Qing-Shan; Lou, Ming; Fan, Shan-Shan
2016-07-01
The thermodynamic stabilities, surface morphologies, and electronic structures of the LiTi2O4 compound were investigated by the first-principles methods. The formation enthalpies and lattice constants of LixTi2O4 decrease at first and then increase again. This phenomenon is related to the balance between Lisbnd O attractions and Lisbnd Li repulsions. Population analysis revealed that pure ionic and strong covalent bonds are formed respectively between lithium and oxygen and between titanium and oxygen in LiTi2O4 material. These interactions are very crucial for the thermodynamic stability of the compounds. The surface stability was considered as functions of the chemical potentials, and five terminations, (100)-Ti2O4, (110)-Ti2O4, (210)-Ti2O4, (111)-LiTiO4, and (310)-Ti2O8ones, are dominant in the stability diagram. Our calculation showed that a particle morphology with mono (110) facet can be obtained at Ti- and/or O-moderate conditions, and this morphology will be very helpful for improving the rate performance of the material via reduction of the lithium diffusion distance. Furthermore, partially filled electronic states at the Fermi energy were confirmed for bulk LiTi2O4 and some of the surfaces, and they are responsible for the excellent electronic conductivity of the material. Further calculations showed that the work functions are sensitive to the stoichiometry of the surfaces.
Energy Technology Data Exchange (ETDEWEB)
Li Chenliang [School of Astronautics, Harbin Institute of Technology, Harbin (China); Wang Biao [School of Physics and Engineering, Sun Yat-Sen University, Guangzhou (China); Li Yuanshi [Department of Cardiology, First Clinical College, Harbin Medical University, Harbin (China); Wang Rui, E-mail: lichenliang1980@yahoo.com.c [Department of Applied Chemistry, Harbin Institute of Technology, Harbin (China)
2009-03-21
We calculated the mechanical properties, electronic structure, theoretical hardness and optical properties of V{sub 4}AlC{sub 3} using the first-principles method. The results show that V{sub 4}AlC{sub 3} shows a better performance of the resistance to shape change and against uniaxial tensions and has a slight anisotropy on elasticity. Moreover, it is more brittle than {alpha}-Nb{sub 4}AlC{sub 3} and Ta{sub 4}AlC{sub 3}. The chemical bonding of V{sub 4}AlC{sub 3} is a combination of covalent, ionic and metallic nature. The calculated theoretical hardness is 9.33 GPa, and the weaker covalent bonding of Al-V is responsible for the low hardness of V{sub 4}AlC{sub 3}. The optical properties (dielectric function, absorption spectrum, conductivity, energy-loss spectrum and reflectivity) are discussed in detail. It is shown that V{sub 4}AlC{sub 3} has the potential to be used as a promising dielectric material and coating to avoid solar heating.
Directory of Open Access Journals (Sweden)
Zagrebin Mikhail
2015-01-01
Full Text Available The composition dependences of crystal lattice parameters, bulk moduli, magnetic moments, magnetic exchange parameters, and Curie temperatures in FexNi2-xMn1+yAl1-y (0.2 ≤ x ≤ 1.8; 0.0 ≤ y ≤ 0.6 Heusler alloys are investigated with the help of first principles and Monte Carlo calculations. It is shown that equilibrium lattice parameters and MnY-MnZ magnetic exchange interactions increase with increasing Fe content (x. A crossover from ferromagnetic to antiferromagnetic interaction between nearest neighbors MnY and MnZ atoms was observed in compositions with x ≥ 1.4 and 0.2 ≤ y ≤ 0.6. Such magnetic competitive behavior points to a complex magnetic structure in FexNi2-xMn1+yAl1-y. Calculated values of lattice parameters, magnetic moments, and Curie temperatures are in a good agreement with other theoretical results and available experimental data.
Kong, Yuanyuan; Duan, Yonghua; Ma, Lishi; Li, Runyue
2016-10-01
By performing first-principles calculations within the generalized gradient approximation, the phase stability, elastic constant and anisotropy, and density of states of cubic C15-type MAl2 (M = Mg, Ca, Sr and Ba) Laves phases have been investigated. Optimized equilibrium lattice parameters and formation enthalpies agree well with the available experimental data. Elastic constants C ij have been evaluated, and these C15-type MAl2 Laves phases are mechanically stable due to the meeting of C ij to the mechanical stability criteria. Polycrystalline elastic moduli have been deduced from elastic constants by Voigt-Reuss-Hill approximation. Plastic properties were characterized via values of B/G, Poisson’s ratio ν and Cauchy pressure (C 12-C 44). The elastic anisotropy has been considered by several anisotropy indexes (A U , A Z , A shear and A comp), anisotropy of shear modulus, and 3D surface constructions of bulk and Young’s moduli. Additionally, the sound velocity anisotropy and Debye temperature were predicted. Finally, electronic structures were carried out to reveal the underlying phase stability mechanism of these Laves phases.
Energy Technology Data Exchange (ETDEWEB)
Zhou, J. [Tianjin Key Laboratory of Film Electronic & Communicate Devices, School of Electronics Information Engineering, Tianjin University of Technology, Tianjin 300191 (China); Wang, X.C., E-mail: wangxccn@126.com [Tianjin Key Laboratory of Film Electronic & Communicate Devices, School of Electronics Information Engineering, Tianjin University of Technology, Tianjin 300191 (China); Chen, G.F. [School of Material Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); Yang, B.H. [Tianjin Key Laboratory of Film Electronic & Communicate Devices, School of Electronics Information Engineering, Tianjin University of Technology, Tianjin 300191 (China)
2015-12-15
The electronic structure and magnetism of Co{sub 14}Ti{sub 2}O{sub 15} systems are investigated by first-principles calculations. CoO is an antiferromagnetic insulator. The Ti doped CoO at positions 9 and 11 shows a half-metallic character. The O vacancy near Ti has a great effect on Ti magnetic moment due to the electron transfer. When the O vacancy at position 6 or 9, the Ti magnetic moment is very small and the systems are magnetic insulator. As the O vacancy locates at position 1, the Ti magnetic moment is smaller than that in Co{sub 14}Ti{sub 2}O{sub 16} system, showing a metallic character that makes its conductivity enhanced. The system with O vacancy at position 2 shows a half-metallic character due to the strong hybridization between Ti and Co atoms. The system with O vacancy at position 5 shows a metallic character; the system with O vacancy at position 13 or 14 shows a half-metallic character. - Highlights: • When the O vacancies at 6 position and 9, the systems are magnetic insulator. • The system with O vacancy at position 5 shows the metallic characteristic. • The system with O vacancy at position 2, 13 or 14 shows a half-metallic character.
Mahata, Partha; Raghunathan, Rajamani; Banerjee, Debamalya; Sen, Diptiman; Ramasesha, S; Bhat, S V; Natarajan, S
2009-06-01
Two new three-dimensional metal-organic frameworks (MOFs) [Mn(2)(mu(3)-OH)(H(2)O)(2)(BTC)] x 2 H(2)O, I, and [NaMn(BTC)], II (BTC = 1,2,4-benzenetricarboxylate = trimellitate) were synthesized and their structures determined by single-crystal X-ray diffraction (XRD). In I, the Mn(4) cluster, [Mn(4)(mu(3)-OH)(2)(H(2)O)(4)O(12)], is connected with eight trimellitate anions and each trimellitate anion connects to four different Mn(4) clusters, resulting in a fluorite-like structure. In II, the Mn(2)O(8) dimer is connected with two Na(+) ions through carboxylate oxygen to form mixed-metal distorted Kagome-related two-dimensional -M-O-M- layers, which are pillared by the trimellitate anions forming the three-dimensional structure. The extra-framework water molecules in I are reversibly adsorbed and are also corroborated by powder XRD studies. The formation of octameric water clusters involving free and coordinated water molecules appears to be new. Interesting magnetic behavior has been observed for both compounds. Electron spin resonance (ESR) studies indicate a broadening of the signal below the ordering temperature and appear to support the findings of the magnetic studies.
Wen, Jun; Ning, Lixin; Duan, Chang-Kui; Zhan, Shengbao; Huang, Yucheng; Zhang, Jie; Yin, Min
2015-07-23
In the present work, geometric structures, electronic properties, and 4f → 5d transitions of γ-Ca2SiO4:Ce(3+) phosphors have been investigated by using first-principles calculations. Four categories of typical substitutions (i.e., the doping of the Ce(3+) without the neighboring dopants/defects and with the neighboring VO(••), AlSi', and VCa″) are taken into account to simulate local environments of the Ce(3+) located at two crystallographically different calcium sites in the γ-Ca2SiO4. Density functional theory (DFT) geometry optimization calculations are first performed on the constructed supercells to obtain the information about the local structures and preferred sites for the Ce(3+). On the basis of the optimized crystal structures, the electronic properties of γ-Ca2SiO4:Ce(3+) phosphors are calculated with the Heyd-Scuseria-Ernzerhof screened hybrid functional, and the energies and relative oscillator strengths of the 4f → 5d transitions of the Ce(3+) are derived from the ab initio embedded cluster calculations at the CASSCF/CASPT2/RASSI-SO level. A satisfactory agreement with the available experimental results is thus achieved. Moreover, the relationships between the dopants/defects and the electronic as well as spectroscopic properties of γ-Ca2SiO4:Ce(3+) phosphors have been explored. Such information is vital, not least for the design of Ce(3+)-based phosphors for the white light-emitting diodes (w-LEDs) with excellent performance.
Zhao, Li-Juan; Tian, Wen-Juan; Ou, Ting; Xu, Hong-Guang; Feng, Gang; Xu, Xi-Ling; Zhai, Hua-Jin; Li, Si-Dian; Zheng, Wei-Jun
2016-03-28
We present a combined photoelectron spectroscopy and first-principles theory study on the structural and electronic properties and chemical bonding of B3O3 (-/0) and B3O3H(-/0) clusters. The concerted experimental and theoretical data show that the global-minimum structures of B3O3 and B3O3H neutrals are very different from those of their anionic counterparts. The B3O3 (-) anion is characterized to possess a V-shaped OB-B-BO chain with overall C2 v symmetry (1A), in which the central B atom interacts with two equivalent boronyl (B≡O) terminals via B-B single bonds as well as with one O atom via a B=O double bond. The B3O3H(-) anion has a Cs (2A) structure, containing an asymmetric OB-B-OBO zig-zag chain and a terminal H atom interacting with the central B atom. In contrast, the C2 v (1a) global minimum of B3O3 neutral contains a rhombic B2O2 ring with one B atom bonded to a BO terminal and that of neutral B3O3H (2a) is also of C2 v symmetry, which is readily constructed from C2 v (1a) by attaching a H atom to the opposite side of the BO group. The H atom in B3O3H(-/0) (2A and 2a) prefers to interact terminally with a B atom, rather than with O. Chemical bonding analyses reveal a three-center four-electron (3c-4e) π hyperbond in the B3O3H(-) (2A) cluster and a four-center four-electron (4c-4e) π bond (that is, the so-called o-bond) in B3O3 (1a) and B3O3H (2a) neutral clusters.
Ikuhara, Yuichi
2011-01-01
Grain boundaries and interfaces of crystals have peculiar electronic structures, caused by the disorder in periodicity, providing the functional properties, which cannot be observed in a perfect crystal. In the vicinity of the grain boundaries and interfaces, dopants or impurities are often segregated, and they play a crucial role in deciding the properties of a material. Spherical aberration (Cs)-corrected scanning transmission electron microscopy (STEM), allowing the formation of sub-angstrom-sized electron probes, can directly observe grain boundary-segregated dopants. On the other hand, ceramic materials are composed of light elements, and these light elements also play an important role in the properties of ceramic materials. Recently, annular bright-field (ABF)-STEM imaging has been proposed, which is now known to be a very powerful technique in producing images showing both light- and heavy-element columns simultaneously. In this review, the atomic structure determination of ceramic grain boundaries and direct observation of grain boundary-segregated dopants and light elements in ceramics were shown to combine with the theoretical calculations. Examples are demonstrated for well-defined grain boundaries in rare earth-doped Al(2)O(3) and ZnO ceramics, CeO(2) and SrTiO(3) grain boundary, lithium battery materials and metal hydride, which were characterized by Cs-corrected high-angle annular dark-field and ABF-STEM. It is concluded that the combination of STEM characterization and first-principles calculation is very useful in interpreting the structural information and in understanding the origin of the properties in various ceramics.
Electronic structures of anatase (TiO2)1-x(TaON)x solid solutions: a first-principles study.
Dang, Wenqiang; Chen, Hungru; Umezawa, Naoto; Zhang, Junying
2015-07-21
Sensitizing wide band gap photo-functional materials under visible-light irradiation is an important task for efficient solar energy conversion. Although nitrogen doping into anatase TiO2 has been extensively studied for this purpose, it is hard to increase the nitrogen content in anatase TiO2 because of the aliovalent nitrogen substituted for oxygen, leading to the formation of secondary phases or defects that hamper the migration of photoexcited charge carriers. In this paper, electronic structures of (TiO2)1-x(TaON)x (0 ≤ x ≤ 1) solid solutions, in which the stoichiometry is satisfied with the co-substitution of Ti for Ta along with O for N, are investigated within the anatase crystal structure using first-principles calculations. Our computational results show that the solid solutions have substantially narrower band gaps than TiO2, without introducing any localized energy states in the forbidden gap. In addition, in comparison with the pristine TiO2, the solid solution has a direct band gap when the content of TaON exceeds 0.25, which is advantageous to light absorption. The valence band maximum (VBM) of the solid solutions, which is mainly composed of N 2p states hybridized with O 2p, Ti 3d or Ta 5d orbitals, is higher in energy than that of pristine anatase TiO2 consisting of non-bonding O 2p states. On the other hand, incorporating TaON into TiO2 causes the formation of d-d bonding states through π interactions and substantially lowers the conduction band minimum (CBM) because of the shortened distance between some metal atoms. As a result, the anatase (TiO2)1-x(TaON)x is expected to become a promising visible-light absorber. In addition, some atomic configurations are found to possess exceptionally narrow band gaps.
Structural, Electronic and Optical Properties of KTa0.5Nb0.5O3 Surface: A First-Principles Study
Institute of Scientific and Technical Information of China (English)
SUN Hong-Guo; ZHOU Zhong-Xiang; YUAN Cheng-Xun; YANG Wen-Long; WANG He
2012-01-01
The crystal surface properties of potassium tantalite niobate,KTa0.5Nb0.5O3 (KTN),are studied with firstprinciples calculation based on the density functional theory (DFT).Generalized gradient approximation (GGA) functional analysis is also employed by using CASTEP software.The explanations for the differences of the ferroelectric and piezoelectric properties between the bulk and surface of the material are provided.The DFT with GGA is used to determine the structure and to calculate the electronic and optical properties of the chemically ordered KTa0.5Nb0.5O3 crystal (100),(110) and (111) surfaces.The results show that the surface properties are different from the bulk properties.The data obtained agree with the expected values and can serve as guidance for future experimental studies in the fields of photorefraction and nonlinear optics.%The crystal surface properties of potassium tantalite niobate, Ktao.5Nbo.5O3 (KTN), are studied with first-principles calculation based on the density functional theory (DFT). Generalized gradient approximation (GGA) functional analysis is also employed by using CASTEP software. The explanations for the differences of the ferroelectric and piezoelectric properties between the bulk and surface of the material are provided. The DFT with GGA is used to determine the structure and to calculate the electronic and optical properties of the chemically ordered Ktao.sNbo.5O3 crystal (100), (110) and (111) surfaces. The results show that the surface properties are different from the bulk properties. The data obtained agree with the expected values and can serve as guidance for future experimental studies in the Gelds of photorefraction and nonlinear optics.
Zhang, Lei; Zhang, Ying; Lu, Guang-Hong
2013-03-06
We have studied the atomic structure and energetic stability of helium (He) and He-vacancy clusters in an iron (Fe) Σ5(310)/[001] grain boundary (GB) using a first-principles method. The He and He-vacancy clusters in the Fe GB are shown to exhibit high-symmetry structures. The equilibrium He-He distance in the clusters is ~1.70 Å, much smaller than 2.80 Å in the vacuum or 2.94 Å in a face centred cubic (fcc) crystal, indicating the attractive interaction between the He atoms due to the presence of Fe. The charge density surrounding He is demonstrated to decrease with an increasing number of He atoms in the clusters, leading to a positive binding energy of a He atom to the clusters. This suggests He and He-vacancy clusters can energetically trap more He atoms, which is responsible for the growth of the He-related clusters (He and He-vacancy clusters) and thus the He bubbles in the GB. The binding energy of an interstitial He atom to the He-related clusters is found generally lower in the GB than in a bcc crystal. Besides, the binding strengths of small He clusters to the GB and to a vacancy in a bcc matrix are compared, and the latter shows greater trapping strength to an interstitial He and a He(2) cluster. The magnetism of the Fe atoms near the GB as well as its variation caused by the He-related clusters is also investigated. The local magnetic moment variation of the Fe atoms in the system is enhanced to a different extent, depending on the size of the He-related clusters.
氨硼烷低温和室温结构的第一性原理计算%First-principles Study of Structure of Ammonia Borane
Institute of Scientific and Technical Information of China (English)
刘超仁; 胡青苗; 王平
2011-01-01
Two kinds of crystal structures (Pmn21 and P42cm) of (ammonia borane) are studied using first-principles plane wave pseudopotential method based on density functional theory in this paper. It was found that the Pmn21 structure is energetically more stable than the P42cm structure at 0 K.This agrees well with the experimental observation, that lower temperature phase is the Pmn21 structure whereas the room temperature phase is P42cm structure. The structure difference between Pmn21 and P42cm phases manifests itself mainly by the variation of intermolecular bond length whereas the intramolecular bond length remains almost unchanged. Electronic state of density was calculated to identify the bonding nature of ammonia borane. The XRD and FTIR patterns of the P42cm structure were calculated, results agree well with the experimental results of AB at room temperature.%采用第-性原理平面波赝暖势方法研究了两种氨硼烷结构(Pmn21及P42cm)的晶格参数、电子结构以及动力学性质.结果表明,Pmn21结构的能量低于P42cm结构,与实验观测结果相符,即低温相为Pmn21结构而室温相为P42cm结构.Pmn21到P42cm相变所引起的结构变化主要体现为氨硼烷分子间双氢键键长显著增加,而分子内部化学键键长变化不大.根据电子态密度分析了氨硼烷的成键状态.氨硼烷室温相的XRD图谱和FTIR图谱的理论预测结果与实验结果符合得较好.
Structural optimization and physical properties of TcB3 and MoB3 at high-pressure: First-principles
Ying, Chun; Bai, Xiaowan; Du, Yungang; Zhao, Erjun; Lin, Lin; Hou, Qingyu
2016-06-01
The thermodynamic, mechanical and dynamic properties of TcB3 and MoB3 are systematically investigated at high-pressure by first-principles within density functional theory (DFT). The calculated formation enthalpies are negative for TcB3 with considered structures under the pressure range from 0 to 100 GPa. Triboride hP4-TcB3 (i.e., TcB3 in hP4-OsB3 type structure) has the lowest formation enthalpy of -1.44 eV under ambient condition. The largest shear modulus of 240 GPa and smallest Poisson’s ratio of 0.20 for oP16-TcB3 are comparable to those of 267 GPa and 0.15 for ReB2. The calculated elastic constants show that MB3 (M=Tc and Mo) are mechanically stable at ambient conditions, except for mP8-MoB3. The estimated high hardness of 33.4 and 33.1 GPa for oP16-TcB3 and hP4-TcB3, respectively, are reported for the first time. The calculated lattice parameters for MoB3 are in good agreement with the previously theoretical and experimental studies. Below 13 GPa, hP16-MoB3 and hR24-MoB3 are thermodynamically more favorable than MoB3 in other structures. A pressure-induced phase transition is predicted at 13 GPa from hP16-MoB3 and hR24-MoB3 to hP4-MoB3. Above 13 GPa, hP4-MoB3 becomes the thermodynamically most stable phase among MoB3 in considered structures. All compounds with considered structures are metallic, and the electronic structures of MB3 are governed by a strong hybridization between M-4d and B-2p states. The strong and directional covalent bonding between M-4d and B-2p as well as the strong interlayer interactions of boron layers are correlated to the high hardness of 38.0 and 38.4 GPa for hP16-MoB3 and hR24-MoB3, respectively.
Yang, Jian; Huang, Jihua; Fan, Dongyu; Chen, Shuhai; Zhao, Xingke
2016-05-01
First-principle calculations have been performed to investigate the structural, mechanical, thermo-physical and electronic properties of η‧-(CuNi)6Sn5 intermetallic compounds. The results indicated that, the doped Ni atom can not only enhance the stability of the η‧-Cu6Sn5, but also improve the mechanical and thermo-physical properties, which are more dependent on the Ni atom doping number than the doping position. In all the η‧-(CuNi)6Sn5, Cu3Ni3Sn5 (Cu1+Cu3 site) shows the best stability, the most excellent deformation resistance and the highest hardness. The Cu6Sn5, Cu3Ni3Sn5, Cu4Ni2Sn5, Cu1Ni5Sn5 and Ni6Sn5 are ductile while the Cu5Ni1Sn5 and Cu4Ni2Sn5 are brittle. The anisotropies of η‧-(CuNi)6Sn5 are all mainly due to the uneven distribution of Young's modulus at (001) planes, moreover, the anisotropy of Cu1Ni5Sn5 (Cu1+Cu2+Cu4 site) is the strongest while that of Ni6Sn5 is the weakest. The calculated Debye temperature and heat capacity showed that Cu4Ni2Sn5 (Cu2 site) possesses the best thermal conductivity (ΘD = 356.9 K) and Cu2Ni4Sn5 (Cu1+Cu2 site) possesses the largest heat capacity. From the electronic property analysis results, the Ni s and Ni p states can replace the Cu s and Cu p states to hybridize with Sn s states at -7.98 eV. Moreover, with the increasing number of the doped Ni atom, the hybridization between Cu d states at different positions is receded, while that between Ni d states is enhanced gradually.
Huang, Wenqi; Cheng, Buwen; Xue, Chunlai; Liu, Zhi
2015-10-01
Experiments and calculations performed in previous studies indicate that compressive strain will increase (100)-strained GeSn's need for Sn to realize a direct bandgap when it is pseudomorphically grown on Ge buffers. To eliminate this negative effect, we systematically investigate the band structures of biaxial (100)-, (110)-, and (111)-strained GeSn using a first-principle calculation combined with supercell models and the GGA+U approach. This method has proven to be efficient and accurate for calculating the properties of GeSn. The calculated lattice constants and elastic constants of Ge and Sn are in good agreement with the experimental results. The crossover value of Sn concentration which is required to change the bandgap of unstrained GeSn from indirect to direct is found to be 8.5%, which is very close to the recent experimental result of 9%. The calculated bandgaps of strained GeSn show that the moving rate of the Γ valley is higher than those of the L and X valleys in (100)- and (110)-strained GeSn. However, the moving rate of the L valley is higher than those of Γ and X valleys in (111)-strained GeSn. Tensile strain has a positive effect on the transition of (100)- and (110)-strained GeSn, changing the bandgap from indirect to direct, whereas compressive strain has a positive effect for (111)-strained GeSn. The use of the (111) orientation can reduce GeSn's need for Sn and greatly increase the energy difference between the L valley and Γ valley. Thus, for strained GeSn grown on Ge buffers, the (111) orientation is a good choice to take advantage of compressive strain.
Guo, San-Dong
2016-05-01
To identify thermoelectric materials containing abundant, low-cost and non-toxic elements, we have studied the electronic structures and thermoelectric properties of (Mg2X)2/ (Mg2Y)2 (X, Y = Si, Ge, Sn) superlattices with state-of-the-art first-principles calculations using a modified Becke and Johnson (mBJ) exchange potential. Our results show that (Mg2Ge)2/ (Mg2Sn)2 and (Mg2Si)2/ (Mg2Sn)2 are semi-metals using mBJ plus spin-orbit coupling (mBJ + SOC), while (Mg2Si)2/ (Mg2Ge)2 is predicted to be a direct-gap semiconductor with a mBJ gap value of 0.46 eV and mBJ + SOC gap value of 0.44 eV. Thermoelectric properties are predicted by through solving the Boltzmann transport equations within the constant scattering time approximation. It is found that (Mg2Si)2/ (Mg2Ge)2 has a larger Seebeck coefficient and power factor than (Mg2Ge)2/ (Mg2Sn)2 and (Mg2Si)2/ (Mg2Sn)2 for both p-type and n-type doping. The detrimental influence of SOC on the power factor of p-type (Mg2X)2/ (Mg2Y)2 (X, Y = Si, Ge, Sn) is analyzed as a function of the carrier concentration, but there is a negligible SOC effect for n-type. These results can be explained by the influence of SOC on their valence and conduction bands near the Fermi level.
Xie, Ling-Yun; Zhang, Jian-Min
2016-10-01
The spin-polarized first-principles calculations are performed to study the electronic structures and magnetic properties of a single or double identical transition metal (TM) atoms X (X = Mn, Fe, Co and Ni) doped monolayer WS2 systems. Although the pristine monolayer WS2 system is a nonmagnetic semiconductor with a direct band gap of 1.820 eV, a single Mn, Fe, Co or Ni doped WS2 systems exhibit the magnetic half-metallic (HM) characters with the total magnetic moments Mtot of 1, 2, 3 and 4 μB and the smaller spin-down gaps Eg of 1.262, 1.154, 1.407 and 1.073 eV, respectively. For double identical TM atoms doped monolayer WS2 systems, except for the cases of two Ni atoms doped at the first (0,1), second (0,2) and third (0,3) nearest-neighbor cation configuration which are antiferromagnetic (AFM), ferromagnetic (FM) and FM metals, respectively, the other cases are all HM ferromagnets, and the total magnetic moment Mtot increases not only for double identical TM dopants Mn, Fe, Co and Ni (except for (0,1) AFM case) successively at the same nearest-neighbor cation configuration but also for each of the double identical TM dopants at the first (0,1), second (0,2) and third (0,3) nearest-neighbor cation configurations successively. These results provide a theoretical guide to choose new two-dimensional HM ferromagnetic materials in spintronic applications.
Energy Technology Data Exchange (ETDEWEB)
Hu, Hai [Institute for Structure and Function, Chongqing University, 401331 (China); Wu, Xiaozhi, E-mail: xiaozhiwu@cqu.edu.cn [Institute for Structure and Function, Chongqing University, 401331 (China); College of Materials Science and Engineering, Chongqing University, 400044 (China); Wang, Rui, E-mail: rcwang@cqu.edu.cn [Institute for Structure and Function, Chongqing University, 401331 (China); Jia, Zhihong [College of Materials Science and Engineering, Chongqing University, 400044 (China); Li, Weiguo [College of Aerospace Engineering, Chongqing University, 400044 (China); Liu, Qing [College of Materials Science and Engineering, Chongqing University, 400044 (China)
2016-05-05
The structural stability of D0{sub 22} TiAl{sub 3} alloyed with Zn, Cu and Ag are systematically investigated using first-principles calculations. There is a phase transition from D0{sub 22} to L1{sub 2} with the increasing of the concentrations of Zn, Cu and Ag, respectively. Based on the predicted elastic constants and Pugh's ratio, the ductility of TiAl{sub 3} are improved due to the phase transition. The generalized stacking fault energies and cleavage energies are also presented. The reduced unstable stacking fault energy and antiphase boundary energy of 〈110〉{001} slip systems may weaken the stability of D0{sub 22} TiAl{sub 3}. Furthermore, Rice and Zhou–Carlsson–Thomson criterions are used to reveal the brittle/ductile mechanism, which is in agreement with Pugh's view. Finally, the electronic properties are also presented. The DOS suggests that weakened p–d interactions between Al and Ti atoms but enhanced d–d interactions between Ti and alloying atoms in TiAl{sub 3} result in the improvement of ductility. - Highlights: • There is a phase transition from D022 to L12 with Zn, Cu and Ag. • The ductility of TiAl{sub 3} are improved due to the phase transition. • The phase stability maybe weakened by the reduction of stacking fault energy. • Density of states are used to reveal mechanical properties of TiAl{sub 3}.
Energy Technology Data Exchange (ETDEWEB)
Maeda, T., E-mail: tmaeda@ad.ryukoku.ac.jp; Wada, T.
2015-05-01
We studied the features of CuSbS{sub 2} (CAS) and CuSbSe{sub 2} (CASe), two proposed photovoltaic compounds, and clarified their electronic structures by first-principles calculations and compared them to the chalcopyrite-type CuInSe{sub 2} results. For both CAS and CASe, the calculated enthalpies of formation of the chalcostibite phases were considerably lower than those of the chalcopyrite phases. Therefore, we considered that the chalcostibite phase is more stable for CAS and CASe. In their band structure calculated with the HSE06 hybrid functional, the valence band maxima of CAS and CASe were located at the Γ-point, and the conduction band minima were located at the R-point. Their second lowest conduction band was located at the Γ-point, whose energy level nearly equaled the R-point. For CAS (CASe), the partial density of the states shows the character of the Cu 3d and S 3p (Se 4p) orbitals at the top of the valence bands and the Sb 5p and S 3p (Se 4p) orbitals at the bottom of the conduction bands. The conduction bands of CAS and CASe have a p-orbital character (Sb 5p) that differs from the s-orbital character (In 5s) of CuInSe{sub 2}. It is for the reason that CAS and CASe do not have a chalcopyrite structure but a chalcostibite-type structure. The calculated absorption coefficient of CuSbS{sub 2} (10{sup 4}-10{sup 5} cm{sup −1}) is comparable to that of CuInSe{sub 2}. - Highlights: • We studied the features of CuSbS{sub 2} and CuSbSe{sub 2}, newly proposed photovoltaic compounds. • Chalcostibite phase is more stable in CuSbS{sub 2} and CuSbSe{sub 2}. • Band structures of CuSbS{sub 2} and CuSbS{sub 2} were calculated with HSE06 hybrid functional. • Absorption coefficient of chalcostibite-type CuSbS{sub 2} is comparable to that of CuInSe{sub 2}.
Aqueous solvation of methane from first principles
Rossato, Lorenzo; Silvestrelli, Pier Luigi
2012-01-01
Structural, dynamical, bonding, and electronic properties of water molecules around a soluted methane molecule are studied from first principles. The results are compatible with experiments and qualitatively support the conclusions of recent classical Molecular Dynamics simulations concerning the controversial issue on the presence of "immobilized" water molecules around hydrophobic groups: the hydrophobic solute slightly reduces (by a less than 2 factor) the mobility of many surrounding water molecules rather than immobilizing just the few ones which are closest to methane, similarly to what obtained by previous first-principles simulations of soluted methanol. Moreover, the rotational slowing down is compatible with that one predicted on the basis of the excluded volume fraction, which leads to a slower Hydrogen bond-exchange rate. The analysis of simulations performed at different temperatures suggests that the target temperature of the soluted system must be carefully chosen, in order to avoid artificial ...
Yan, Zhang; Li, Duan; Vincent, Ji; Ke-Wei, Xu
2016-05-01
The structural, electronic, and magnetic properties of double perovskite Sr2FeReO6 containing eight different imperfections of FeRe or ReFe antisites, Fe1-Re1 or Fe1-Re4 interchanges, VFe, VRe, VO or VSr vacancies have been studied by using the first-principles projector augmented wave (PAW) within generalized gradient approximation as well as taking into account the on-site Coulomb repulsive interaction (GGA+U). No obvious structural changes are observed for the imperfect Sr2FeReO6 containing FeRe or ReFe antisites, Fe1-Re1 or Fe1-Re4 interchanges, or VSr vacancy defects. However, the six (eight) nearest oxygen neighbors of the vacancy move away from (close to) VFe or VRe (VO) vacancies. The half-metallic (HM) character is maintained for the imperfect Sr2FeReO6 containing FeRe or ReFe antisites, Fe1-Re4 interchange, VFe, VO or VSr vacancies, while it vanishes when the Fe1-Re1 interchange or VRe vacancy is presented. So the Fe1-Re1 interchange and the VRe vacancy defects should be avoided to preserve the HM character of Sr2FeReO6 and thus usage in spintronic devices. In the FeRe or ReFe antisites, Fe1-Re1 or Fe1-Re4 interchanges cases, the spin moments of the Fe (Re) cations situated on Re (Fe) antisites are in an antiferromagnetic coupling with those of the Fe (Re) cations on the regular sites. In the VFe, VRe, VO, or VSr vacancies cases, a ferromagnetic coupling is obtained within each cation sublattice, while the two cation sublattices are coupled antiferromagnetically. The total magnetic moments μ tot (μ B/f.u.) of the imperfect Sr2FeReO6 containing eight different defects decrease in the sequence of VSr vacancy (3.50), VRe vacancy (3.43), FeRe antisite (2.74), VO vacancy (2.64), VFe vacancy (2.51), ReFe antisite (2.29), Fe1-Re4 interchange (1.96), Fe1-Re1 interchange (1.87), and the mechanisms of the saturation magnetization reduction have been analyzed. Project supported by the National Natural Science Foundation of China (Grant No. 51501017).
Energy Technology Data Exchange (ETDEWEB)
Li, Jia; Zhang, Shengli [Division of Molecule and Materials Simulation, State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029 (China); Huang, Shiping, E-mail: huangsp@mail.buct.edu.cn [Division of Molecule and Materials Simulation, State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029 (China); Wang, Peng; Tian, Huiping [Research Institute of Petroleum Processing, SINOPEC , Beijing 100083 (China)
2013-02-15
R{sub 3}ZnH{sub 5} (R=K, Rb, Cs) series have been investigated with respect to the crystal structure, electronic and thermodynamic properties using first-principle methods based on density functional theory with generalized gradient approximation. The optimized structures and atomic coordinates are in good agreement with the experimental data. The strong covalent interactions are obtained between Zn and H atoms in the 18-electron [ZnH{sub 4}]{sup 2-} complex, while an ionic interaction is found between [ZnH{sub 4}]{sup 2-} and R atom. The formation enthalpies show that the formations of R{sub 3}ZnH{sub 5} hydrides are all exothermic at 298 K. The vibration free energies of R{sub 3}ZnH{sub 5} show that the thermodynamic stabilities of R{sub 3}ZnH{sub 5} hydrides decrease with the increasing diameter of R atom. Two possible decomposition reactions of R{sub 3}ZnH{sub 5} series have been suggested in our work. One (reaction one) is that R{sub 3}ZnH{sub 5} hydrides decomposes to elements directly, and the other (reaction two) is that R{sub 3}ZnH{sub 5} hydrides decomposes to RH hydride. The results show that the first decomposition reaction is more favorable one. The spontaneous decomposition reaction of K{sub 3}ZnH{sub 5} hydrides occur upon 465 K via reaction one, and 564 K via reaction two, respectively. - Graphical abstract: Total charge density of K{sub 3}ZnH{sub 5}. Highlights: Black-Right-Pointing-Pointer Electronic and thermodynamic properties of R{sub 3}ZnH{sub 5} (R=K, Rb, Cs) were calculated. Black-Right-Pointing-Pointer The formations of R{sub 3}ZnH{sub 5} hydrides are all exothermic at 298 K. Black-Right-Pointing-Pointer The thermodynamic stabilities decrease with the increasing diameter of R atom. Black-Right-Pointing-Pointer Two possible decomposition pathways of R{sub 3}ZnH{sub 5} were investigated.
Chiang, Han-Hsin; Kuo, Chin-Lung
2017-02-14
We have performed a comparative first-principles study on the structural and electronic properties of the liquid Li1-xSix and Li1-xGex alloys over a range of composition from x = 0.09 to 0.50. Our calculations showed that Si and Ge atoms can exhibit very distinct local bonding characteristics as they were alloyed with the Li atoms in the liquid state, where Si atoms tended to form a variety of covalent bonding configurations while Ge atoms predominantly appeared as the isolated anions in the liquid alloys. These differences in bonding characteristics were reflected in their electronic density of states, in which the liquid Li1-xGex alloys have a lower degree of s-p hybridization with narrower distributions of the 3s and 3p states than the liquid Li1-xSix alloys. Our calculations also showed that the optical conductivities of these two liquid alloys can undergo a transition from the Drude-like metallic nature to the semiconductor-like character as the Si/Ge content increases from 0.09 to 0.22. However, as the Si/Ge content further increases to 0.50, the liquid Li1-xGex alloys may transit to exhibit the Drude-like metallic nature, while the liquid Li1-xSix alloys can still hold the semiconductor-like character. Moreover, our calculations revealed that the dc conductivities of these liquid alloys are predominantly determined by the number of total electronic states at the Fermi level. As the liquid Li1-xSix alloys are within the composition range between 0.20 and 0.50, the increment of the states at the Fermi level with increasing the Si content is nearly identical to the amount of the Li states decreased, leading to an almost unchanged number of total electronic states at the Fermi level. However, since Ge atoms do not favor forming covalent bonding in the liquid alloys to keep the Fermi level at a minimum of the density of states, the liquid Li1-xGex alloys would have more electronic states at the Fermi level and thereby higher dc conductivities than the liquid Li1
Energy Technology Data Exchange (ETDEWEB)
Zhao, Fangfang; Liu, Chuan [Division of Molecule and Materials Simulation, State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029 (China); Wang, Peng [Research Institute of Petroleum Processing, SINOPEC, Beijing 100083 (China); Huang, Shiping, E-mail: huangsp@mail.buct.edu.cn [Division of Molecule and Materials Simulation, State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029 (China); Tian, Huiping [Research Institute of Petroleum Processing, SINOPEC, Beijing 100083 (China)
2013-11-15
Highlights: •Magnetic properties of Pt{sub 13−n}Ni{sub n} clusters are performed by DFT calculations. •Ni 3d orbitals make mainly contribution to the magnetism of Pt{sub 13−n}Ni{sub n} clusters. •Magnetic moments of Pt{sub 13−n}Ni{sub n} clusters are as a function of Ni concentration. •Binding energies of Pt{sub 13−n}Ni{sub n} clusters decrease with increasing Ni concentration. -- Abstract: First-principles method based on the density functional theory has been utilized to calculate the structural, electronic and magnetic properties of Pt{sub 13−n}Ni{sub n} (n = 0–13) clusters. For Pt{sub 13−n}Ni{sub n} clusters, Ni atoms are mainly found in the cluster core and Pt atoms are segregated to the cluster surface. The calculated binding energies of Pt{sub 13−n}Ni{sub n} clusters decrease with increasing Ni concentration. Through the bader charge and difference charge density analyses, it is observed that the small charge transfer is from Ni to Pt. In the total and partial density of states of Pt{sub 13−n}Ni{sub n} clusters, Pt 5d and Ni 3d orbitals make the main contribution to the electronic states and play an important role in determining the magnetism of Pt{sub 13−n}Ni{sub n} clusters. From n ⩾ 2, the calculated magnetic moments of Pt{sub 13−n}Ni{sub n} clusters increase to the maximum (8.34 μ{sub B}) in Pt{sub 2}Ni{sub 11} cluster as a function of Ni concentration and then decrease slightly. The variation in the magnetic behavior of Pt{sub 13−n}Ni{sub n} clusters can be attributed to the exchange splitting of the energy bands near the Fermi level.
Barreda-Argüeso, J. A.; López-Moreno, S.; Sanz-Ortiz, M. N.; Aguado, F.; Valiente, R.; González, J.; Rodríguez, F.; Romero, A. H.; Muñoz, A.; Nataf, L.; Baudelet, F.
2013-12-01
We report a complete structural study of CoF2 under pressure. Its crystal structure and vibrational and electronic properties have been studied both theoretically and experimentally using first-principles density functional theory (DFT) methods, x-ray diffraction, x-ray absorption at Co K-edge experiments, Raman spectroscopy, and optical absorption in the 0-80 GPa range. We have determined the structural phase-transition sequence in CoF2 and corresponding transition pressures. The results are similar to other transition-metal difluorides such as FeF2 but different to ZnF2 and MgF2, despite that the Co2+ size (ionic radius) is similar to Zn2+ and Mg2+. We found that the complete phase-transition sequence is tetragonal rutile (P42/mnm) → CaCl2 type (orthorhombic Pnnm) → distorted PdF2 (orthorhombic Pbca)+PdF2 (cubic Pa3¯) in coexistence → fluorite (cubic Fm3¯m) → cotunnite (orthorhombic Pnma). It was observed that the structural phase transition to the fluorite at 15 GPa involves a drastic change of coordination from sixfold octahedral to eightfold cubic with important modifications in the vibrational and electronic properties. We show that the stabilization of this high-pressure cubic phase is possible under nonhydrostatic conditions since ideal hydrostaticity would stabilize the distorted-fluorite structure (tetragonal I4/mmm) instead. Although the first rutile → CaCl2-type second-order phase transition is subtle by Raman spectroscopy, it was possible to define it through the broadening of the Eg Raman mode which is split in the CaCl2-type phase. First-principles DFT calculations are in fair agreement with the experimental Raman mode frequencies, thus providing an accurate description for all vibrational modes and elastic properties of CoF2 as a function of pressure.
Lei, Xiang; Yu, Ke; Li, Honglin; Tang, Zheng; Guo, Bangjun; Li, Jinzhu; Fu, Hao; Zhang, Qingfeng; Zhu, Ziqiang
2016-04-01
In this work, we report the First-principle investigation and synthesis of MoS2@SnO2 heterostructure as high-performance humidity sensor by a two-step hydrothermal method. The first-principles calculations were performed to explain water molecule adsorption mechanism by applying density of state model to simulate the interaction between water molecule and sensing base material. The higher specific surface and the lower adsorption energy theoretically predicted the improvement on humidity sensing performance, which was confirmed by experiments testing. The MoS2@SnO2 heterostructure exhibited promoted humidity sensing characteristics on response time of 53 s and recovery time of 21 s, while switching the humidity between 11% relative humidity (RH) and 95% RH. The corresponding humidity sensing mechanisms of MoS2@SnO2 were elaborately interpreted. This work could bring forward a new design method on practical humidity sensing devices with an excellent stability and fast response by using MoS2@SnO2 heterostructure.
Energy Technology Data Exchange (ETDEWEB)
Santhosh, M.; Rajeswarapalanichamy, R.; Priyanga, G. Sudha; Murugan, A. [Department of Physics, N.M.S.S.V.N college, Madurai, Tamilnadu-625019 (India); Kanagaprabha, S. [Department of Physics, Kamaraj College, Tuticorin, Tamil Nadu 628 003 (India); Iyakutti, K. [Department of physics and Nanotechnology, SRM University, Chennai, Tamilnadu-603203 (India)
2015-06-24
Ab initio calculations are performed to investigate the structural stability, electronic structure and mechanical properties of ABeH{sub 3} (A = Li, Na) for three different crystal structures, namely orthorhombic (Pnma), monoclinic (P2{sub 1}/c) and triclinic (P-1) phase. Among the considered structures monoclinic (P2{sub 1}/c) phase is found to be the most stable one for all the three hydrides at ambient condition. The electronic structure reveals that these materials are wide band gap semiconductors. The calculated elastic constants indicate that these materials are mechanically stable at ambient condition.
Energy Technology Data Exchange (ETDEWEB)
Santhosh, M.; Rajeswarapalanichamy, R., E-mail: rajeswarapalanichamy@gmail.com; Priyanga, G. Sudha; Cinthia, A. Jemmy [Department of physics, N.M.S.S.V.N college, Madurai, Tamilnadu-625019 (India); Kanagaprabha, S. [Department of Physics, Kamaraj College, Tuticorin, Tamil Nadu 628003 (India); Iyakutti, K. [Department of Physics and Nanotechnology, SRM University, Chennai, Tamilnadu-603203 (India)
2015-06-24
Ab initio calculations are performed to investigate the structural stability, electronic structure and mechanical properties of BeAlH{sub 5} for monoclinic crystal structures with two different types of space group namely P2{sub 1} and C{sub 2}/c. Among the considered structures monoclinic (P2{sub 1}) phase is found to be the most stable at ambient condition. The structural phase transition from monoclinic (P2{sub 1}) to monoclinic (C{sub 2}/c) phase is observed in BeAlH{sub 5}. The electronic structure reveals that this compound is insulator. The calculated elastic constants indicate that this material is mechanically stable at ambient condition.
Water orientation and hydrogen-bond structure at the fluorite/water interface
Khatib, Rémi; Bonn, Mischa; Perez-Haro, María-José; Gaigeot, Marie-Pierre; Sulpizi1, Marialore
2016-01-01
Water in contact with mineral interfaces is important for a variety of different processes. Here, we present a combined theoretical-experimental study which provides a quantitative, molecular-level understanding of the ubiquitous and important flourite-water interface. Our results show that, at low pH, the surface is positively charged, causing a substantial degree of water ordering. The surface charge originates primarily from the dissolution of fluoride ions, rather than from adsorption of protons to the surface. At high pH we observe the presence of Ca-OH species pointing into the water. These OH groups interact remarkably weakly with the surrounding water, and are responsible for the free OH signature in the SFG spectrum, which can be explained from local electronic structure effects. The quantification of the surface termination, near-surface ion distribution and water arrangement is enabled by a combination of advanced phase-resolved Vibrational Sum Frequency Generation spectra of flourite-water interfa...
Mao, Fei; Hou, Qingyu; Zhao, Chunwang; Guo, Shaoqiang; Zhang, Yue
2014-01-01
Based on the first-principles plane wave ultra-soft pseudo potential (USP) method of density function theory pure N and Ce doped and Ce-N codoping anatase TiO2 supercell models were established, respectively, and calculated their energy in this paper. The calculated results show that the three doping systems compared to the pure anatase TiO2 band gap narrowed which results in red-shift of the optical absorption edges and Ce-N codoped anatase TiO2 have the most obvious visible effect. Meanwhile, synergy is very effective for the separation of electron-hole pairs and the electrons have a better lifespan. Research found that the trend of the donor's movements at the shallow level of Ce-N codoped anatase TiO2 is not obvious. This is due to its very thick shell, resulting in shielding effect of the outer layer of the Ce-4f.
Energy Technology Data Exchange (ETDEWEB)
González-Hernández, Rafael, E-mail: rhernandezj@uninorte.edu.co [Grupo de Investigación en Física Aplicada, Departamento de Física, Universidad del Norte, Barranquilla (Colombia); Martínez, Gustavo; López-Perez, William [Grupo de Investigación en Física Aplicada, Departamento de Física, Universidad del Norte, Barranquilla (Colombia); Rodriguez, Jairo Arbey [Grupo de Estudio de Materiales, Departamento de Física, Universidad Nacional de Colombia, Bogotá (Colombia)
2014-01-01
First-principles calculations based on density-functional theory have been implemented to study the scandium (Sc) adsorption and incorporation on nonpolar GaN (112{sup ¯}0) and (101{sup ¯}0) surfaces. It is found that Sc adatom prefers to reside at bridge positions, between the hollow and top sites, on both GaN nonpolar surfaces. In addition, calculating the relative surface energy of several Sc configurations, we constructed a phase diagram showing the energetically most stable surfaces as a function of the Ga chemical potentials. Based on these results, we have found that incorporation of Sc adatoms in the Ga-substitutional site is energetically more favorable compared with the adsorption on the top layers. This effect leads to the formation of ScN interlayers on nonpolar GaN (112{sup ¯}0) and (101{sup ¯}0) surfaces, which reduces the dislocation densities between GaN and ScN.
Institute of Scientific and Technical Information of China (English)
Liu Hai-Tao; Li Jia-Ming
2005-01-01
We present results of first-principle study for both neutral and anionic onion-like [As@Ni12@As20]. The groundstates of singly-charged and doubly-charged anions deviate from ideal Ih symmetrical geometry because of Jahn-Teller effect, whereas the triply-charged singlet and neutral quartet have similar stable geometries of Ih symmetry. The infrared and Raman spectra may provide a way to determine various charge states of this molecule with the same symmetry.Based on our systematical calculations, we suggest additional experimental measurements in order to determine the appropriate functional with great confidence, which should be important in the research for future quantum dot devices.
Energy Technology Data Exchange (ETDEWEB)
Babamoradi, Mohsen, E-mail: babamoradi@iust.ac.ir [Department of Physics, Iran University of Science and Technology, Narmak, 16846-13114 Tehran (Iran, Islamic Republic of); Liyai, Mohammad Reza [Department of Physics, Iran University of Science and Technology, Narmak, 16846-13114 Tehran (Iran, Islamic Republic of); Azimirad, Rouhollah, E-mail: azimirad@yahoo.com [Malek-Ashtar University of Technology, Tehran (Iran, Islamic Republic of); Salehi, Hamdollah, E-mail: salehi_h@scu.ac.ir [Department of Physics, Faculty of Science, Shahid Chamran University of Ahvaz, Ahvaz (Iran, Islamic Republic of)
2017-04-15
In this paper, we have investigated the electronic structure and optical properties of the single crystal and two-dimensional (2D) structure of cadmium tungstate (CdWO{sub 4}). This investigation includes calculation of the density of states (DOS), dielectric tensor elements and reflectivity. All the calculations have been done by full potential augmented plane waves plus local orbitals (FP-APW+lo) with Wien2k code. The calculated band gaps for the single crystal and 2D structure along [010] direction are 4.2 and 5.02 eV, respectively. The results show that in the 2D structure of CdWO{sub 4}, the electron density of the surface oxygen atoms is much more than the electron density of the inside oxygen atoms. This difference in the density has the main role in the optical properties. The results of the dielectric tensor elements and reflectivity for the single crystal are in good agreement with the experimental values. The results of the dielectric tensor elements and reflectivity for the 2D structure in comparison with the single crystal have shown that the intensity and place of the calculated peaks reduced and shifted, respectively. These results can be related to the surface oxygen atoms and thickness of the 2D structure.
Energy Technology Data Exchange (ETDEWEB)
Nejatipour, Hajar, E-mail: nejatipour.h@lu.ac.ir; Dadsetani, Mehrdad, E-mail: dadsetani.m@lu.ac.ir
2015-08-15
Highlights: • Zn K-edges of ZnX (X = O and S) in bulk and nanosheet structures exhibit different properties. • The presence of sp{sup 2} hybridization in nanosheets results in a π{sup *} structure at the onset of K-edge and a σ{sup *} structure beyond the onset which this is the characteristic behavior of sp{sup 2} hybridized materials and it is absent in bulk structures. • The main contributions in L{sub 2,3}-edge of ZnX bulks and nanosheets can be attributed to transition to mostly d-symmetry states and the hybridized p-d orbitals. • As a result of the smaller bond lengths in the nanosheet structures, all the ELNES spectra in nanosheets, including Zn K- and L{sub 2,3}-edges, and O and S K-edges have a shift to the higher energies. • Whereas the momentum dependency, and therefore, the anisotropy features of the spectra are small for the Zn L{sub 2,3} ELNES, they are important in the K edge ELNES spectra of ZnX nanosheets. - Abstract: This paper tries to study the core energy loss spectra of zinc based nanosheets (ZnO and ZnS) in density functional theory using the FPLAPW method. We have calculated the energy loss near edge structure (ELNES) spectra of zinc K- and L{sub 2,3}-edges, and oxygen and sulfur K-edges in ZnO and ZnS nanosheet at magic angle conditions and compare to those of ZnO and ZnS wurtzite bulk structures. As a result of the smaller bond lengths in the nanosheet structures, all the ELNES spectra in nanosheets, including Zn K- and L{sub 2,3}-edges, and O and S K-edges show a shift to the higher energies. The calculations reveal that in comparison to Zn edges in ZnO structures, all the ELNES spectra of ZnS structures including the bulk and sheet show a shift to lower energy region. This is a result of larger bond lengths in ZnS structures, and that it can be used to fingerprint each structure. The comparison of ELNES spectra and unoccupied symmetry-projected density of states (local DOS) confirms that Zn K-edges of both ZnO and Zn
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.
Mattsson, Thomas R.
2011-11-01
Significant progress has over the last few years been made in high energy density physics (HEDP) by executing high-precision multi-Mbar experiments and performing first-principles simulations for elements ranging from carbon [1] to xenon [2]. The properties of water under HEDP conditions are of particular importance in planetary science due to the existence of ice-giants like Neptune and Uranus. Modeling the two planets, as well as water-rich exoplanets, requires knowing the equation of state (EOS), the pressure as a function of density and temperature, of water with high accuracy. Although extensive density functional theory (DFT) simulations have been performed for water under planetary conditions [3] experimental validation has been lacking. Accessing thermodynamic states along planetary isentropes in dynamic compression experiments is challenging because the principal Hugoniot follows a significantly different path in the phase diagram. In this talk, we present experimental data for dynamic compression of water up to 700 GPa, including in a regime of the phase-diagram intersected by the Neptune isentrope and water-rich models for the exoplanet GJ436b. The data was obtained on the Z-accelerator at Sandia National Laboratories by performing magnetically accelerated flyer plate impact experiments measuring both the shock and re-shock in the sample. The high accuracy makes it possible for the data to be used for detailed model validation: the results validate first principles based thermodynamics as a reliable foundation for planetary modeling and confirm the fine effect of including nuclear quantum effects on the shock pressure. 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. Department of Energy's National Nuclear Security Administration under Contract No. DE-AC04-94AL85000. [4pt] [1] M.D. Knudson, D.H. Dolan, and M.P. Desjarlais, SCIENCE
Energy Technology Data Exchange (ETDEWEB)
Huang, Wenchao [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China); Wang, Xiaofang, E-mail: wxiaof66@mail.sitp.ac.cn [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China); Chen, Xiaoshuang, E-mail: xschen@mail.sitp.ac.cn [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China); Lu, Wei [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China); Damewood, L.; Fong, C.Y. [Department of Physics, University of California, Davis, CA 95616-8677 (United States)
2015-03-01
First principles calculations with spin polarization based on density functional theory have been performed on half-Heusler alloys PtXBi, with X=Mn, Fe, Co and Ni, in three different atomic configurations (i.e. α, β, and γ phases). For each configuration, their optimized lattice constants are determined. Electronic and magnetic properties are also investigated. The differences reflect the atomic arrangements of the three phases and varied transition metal elements X. Meanwhile, the possibility of having the integer magnetic moment for each phase is explored. PtMnBi in α phase show half-metallic (HM) properties when its lattice constant is reduced from −3.0% to −11.2% with magnetic moment consistent with the values given by the modified Slater–Pauling rule. Additionally, we examined the effects of the spin–orbit (S–O) interaction on half-metal PtMnBi by comparing the relative shifts of the valence bands and the indirect semiconducting gap with respect to the spin polarized results.
Huang, Wenchao; Wang, Xiaofang; Chen, Xiaoshuang; Lu, Wei; Damewood, L.; Fong, C. Y.
2015-03-01
First principles calculations with spin polarization based on density functional theory have been performed on half-Heusler alloys PtXBi, with X=Mn, Fe, Co and Ni, in three different atomic configurations (i.e. α, β, and γ phases). For each configuration, their optimized lattice constants are determined. Electronic and magnetic properties are also investigated. The differences reflect the atomic arrangements of the three phases and varied transition metal elements X. Meanwhile, the possibility of having the integer magnetic moment for each phase is explored. PtMnBi in α phase show half-metallic (HM) properties when its lattice constant is reduced from -3.0% to -11.2% with magnetic moment consistent with the values given by the modified Slater-Pauling rule. Additionally, we examined the effects of the spin-orbit (S-O) interaction on half-metal PtMnBi by comparing the relative shifts of the valence bands and the indirect semiconducting gap with respect to the spin polarized results.
Liu, Hong-Xia; Tang, Fu-Ling; Xue, Hong-Tao; Zhang, Yu; Cheng, Yu-Wen; Feng, Yu-Dong
2016-12-01
Using the first-principles plane-wave calculations within density functional theory, the perfect bi-layer and monolayer terminated WZ-CIS (100)/WZ-CdS (100) interfaces are investigated. After relaxation the atomic positions and the bond lengths change slightly on the two interfaces. The WZ-CIS/WZ-CdS interfaces can exist stably, when the interface bonding energies are -0.481 J/m2 (bi-layer terminated interface) and -0.677 J/m2 (monolayer terminated interface). Via analysis of the density of states, difference charge density and Bader charges, no interface state is found near the Fermi level. The stronger adhesion of the monolayer terminated interface is attributed to more electron transformations and orbital hybridizations, promoting stable interfacial bonds between atoms than those on a bi-layer terminated interface. Project supported by the National Natural Science Foundation of China (Grant Nos. 11164014 and 11364025) and the Gansu Science and Technology Pillar Program, China (Grant No. 1204GKCA057).
First Principles Calculation of Structural Parameters of Si Crystal%Si晶体结构参数的第一性原理计算
Institute of Scientific and Technical Information of China (English)
林传金; 郭莉莉
2013-01-01
The total energy of Si crystal were calculated in different lattice constant by first principles, which based on the density functional theory. The calculated data were gotten by the Birch-Muranghan third-order equation, then the related parameters were obtained. The Si crystal’s specific form of Birch-Muranghan third equation was also deduced with these parameters. The lattice constant and elastic modulus of Si crystal in the steady state were also calculated, which were quite consistent with the experimental values.%本文采用基于密度泛函理论的第一性原理计算不同晶格常数下 Si 晶体的总能，用计算所得出的数据通过 Brich-Muranghan三阶状态方程进行拟合得到相关的参数，获得 Si晶体的 Brich-Muranghan三阶状态方程具体形式，并通过计算获得Si在稳定状态下的晶格常数和体弹性模量，结果与实验数值相符。
Bajgain, S. K.; Karki, B. B.; Ghosh, D. B.
2014-12-01
We have performed first principles molecular dynamics simulations of CaO and CaSiO3 liquids overbroad ranges of pressure (0 to 150 GPa) and temperature (2500 to 8000 K) within density functionaltheory. They show that both liquids are much more compressible than their solid counterpartsimplying possible liquid-solid density crossover. The liquid Grüneisen parameter increases onpressure, which is opposite of crystalline phases. Our analysis shows that the liquid structurechanges considerably on compression, with the mean cation-anion coordination numbers increasingnearly linearly with volume. The Ca-O coordination number increases from 7 (5) near the ambientpressure to 9 (7) at high pressure for CaSiO3 (CaO) liquid. The Si-O coordination number increasesfrom 4 to 6 over the same pressure regime. The calculated self-diffusion coefficients are stronglydependent on temperature and pressure and require non-Arrhenian representation with variableactivation volume. The diffusivity differences between the two liquids are considerable in low-temperature and low-pressure regime. Also, comparisons with MgSiO3 liquid suggest that networkmodifier cations Ca and Mg behave similarly though Ca is more coordinated and more mobile ascompared with Mg.
Institute of Scientific and Technical Information of China (English)
Shi Si-Qi; Tanaka Shingo; Kohyama Masanori
2008-01-01
In this paper first-principles calculations of Ni (111)/α-Al2O3 (0001) interfaces have been performed, and are compared with the preceding results of the Cu (111)/α-Al2O3 (0001) interface [2004 Phil. Mag. Lett. 84 425]. The Al-terminated and O-terminated interfaces have quite different adhesion mechanisms, which are similar to the Cu (111)/α-Al2O3 (0001) interface. For the O-terminated interface, the adhesion is caused by the strong O-2p/Ni-3d orbital hybridization and ionic interactions. On the other hand, the adhesion nature of the Al-terminated interface is the image-like electrostatic and Ni-Al hybridization interactions, the latter is substantial and cannot be neglected. Charge transfer occurs from Al2O3 to Ni, which is opposite to that in the O-terminated interface. The charge transfer direction for the Al-terminated and O-terminated Ni (111)/α-Al2O3 (0001) interfaces is similar to that in the corresponding Cu (111)/α-Al2O3 (0001) interface, but there exist the larger charge transfer quantity and consequent stronger adhesion nature, respectively.
First principles studies on anatase surfaces
Selcuk, Sencer
TiO2 is one of the most widely studied metal oxides from both the fundamental and the technological points of view. A variety of applications have already been developed in the fields of energy production, environmental remediation, and electronics. Still, it is considered to have a high potential for further improvement and continues to be of great interest. This thesis describes our theoretical studies on the structural and electronic properties of anatase surfaces, and their (photo)chemical behavior. Recently much attention has been focused on anatase crystals synthesized by hydrofluoric acid assisted methods. These crystals exhibit a high percentage of {001} facets, generally considered to be highly reactive. We used first principles methods to investigate the structure of these facets, which is not yet well understood. Our results suggest that (001) surfaces exhibit the bulk-terminated structure when in contact with concentrated HF solutions. However, 1x4-reconstructed surfaces, as observed in UHV, become always more stable at the typical temperatures used to clean the as-prepared crystals in experiments. Since the reconstructed surfaces are only weakly reactive, we predict that synthetic anatase crystals with dominant {001} facets should not exhibit enhanced photocatalytic activity. Understanding how defects in solids interact with external electric fields is important for technological applications such as memristor devices. We studied the influence of an external electric field on the formation energies and diffusion barriers of the surface and the subsurface oxygen vacancies at the anatase (101) surface from first principles. Our results show that the applied field can have a significant influence on the relative stabilities of these defects, whereas the effect on the subsurface-to-surface defect migration is found to be relatively minor. Charge carriers play a key role in the transport properties and the surface chemistry of TiO2. Understanding their
Iron diffusion from first principles calculations
Wann, E.; Ammann, M. W.; Vocadlo, L.; Wood, I. G.; Lord, O. T.; Brodholt, J. P.; Dobson, D. P.
2013-12-01
The cores of Earth and other terrestrial planets are made up largely of iron1 and it is therefore very important to understand iron's physical properties. Chemical diffusion is one such property and is central to many processes, such as crystal growth, and viscosity. Debate still surrounds the explanation for the seismologically observed anisotropy of the inner core2, and hypotheses include convection3, anisotropic growth4 and dendritic growth5, all of which depend on diffusion. In addition to this, the main deformation mechanism at the inner-outer core boundary is believed to be diffusion creep6. It is clear, therefore, that to gain a comprehensive understanding of the core, a thorough understanding of diffusion is necessary. The extremely high pressures and temperatures of the Earth's core make experiments at these conditions a challenge. Low-temperature and low-pressure experimental data must be extrapolated across a very wide gap to reach the relevant conditions, resulting in very poorly constrained values for diffusivity and viscosity. In addition to these dangers of extrapolation, preliminary results show that magnetisation plays a major role in the activation energies for diffusion at low pressures therefore creating a break down in homologous scaling to high pressures. First principles calculations provide a means of investigating diffusivity at core conditions, have already been shown to be in very good agreement with experiments7, and will certainly provide a better estimate for diffusivity than extrapolation. Here, we present first principles simulations of self-diffusion in solid iron for the FCC, BCC and HCP structures at core conditions in addition to low-temperature and low-pressure calculations relevant to experimental data. 1. Birch, F. Density and composition of mantle and core. Journal of Geophysical Research 69, 4377-4388 (1964). 2. Irving, J. C. E. & Deuss, A. Hemispherical structure in inner core velocity anisotropy. Journal of Geophysical
First-principles determination of magnetic properties
Energy Technology Data Exchange (ETDEWEB)
Wu Ruqian; Yang Zongxian; Hong Jisang [Department of Physics, University of California, Irvine, CA (United States)
2003-02-12
First-principles density functional theory calculations have achieved great success in the exciting field of low-dimension magnetism, in explaining new phenomena observed in experiments as well as in predicting novel properties and materials. As known, spin-orbit coupling (SOC) plays an extremely important role in various magnetic properties such as magnetic anisotropy, magnetostriction, magneto-optical effects and spin-dynamics. Using the full potential linearized augmented plane wave approach, we have carried out extensive investigations for the effects of SOC in various materials. Results of selected examples, such as structure and magnetic properties of Ni/Cu(001), magnetism and magnetic anisotropy in magnetic Co/Cu(001) thin films, wires and clusters, magnetostriction in FeGa alloys and magneto-optical effects in Fe/Cr superlattices, are discussed.
Tunable hydrogen storage in magnesium-transition metal compounds: First-principles calculations
Er, Süleyman; Tiwari, Dhirendra; de Wijs, Gilles A.; Brocks, Geert
2009-01-01
Magnesium dihydride (MgH2) stores 7.7wt% hydrogen but it suffers from a high thermodynamic stability and slow (de)hydrogenation kinetics. Alloying Mg with lightweight transition metals (TM) (=Sc,Ti,V,Cr) aims at improving the thermodynamic and kinetic properties. We study the structure and stability of MgxTM1-xH2 compounds, x=[0-1] , by first-principles calculations at the level of density functional theory. We find that the experimentally observed sharp decrease in hydrogenation rates for x≳0.8 correlates with a phase transition of MgxTM1-xH2 from a fluorite to a rutile phase. The stability of these compounds decreases along the series Sc, Ti, V, and Cr. Varying the TM and the composition x , the formation enthalpy of MgxTM1-xH2 can be tuned over the substantial range of 0-2 eV/f.u. Assuming however that the alloy MgxTM1-x does not decompose upon dehydrogenation, the enthalpy associated with reversible hydrogenation of compounds with a high magnesium content (x=0.75) is close to that of pure Mg.
Babu, K Ramesh; Vaitheeswaran, G.
2013-01-01
We report density functional theory calculations on the crystal structure, elastic, lattice dynamics and electronic properties of iso-structural layered monoclinic alkali azides, LiN3 and NaN3. The effect of van der Waals interactions on the ground- state structural properties is studied by using various dispersion corrected density functionals. Based on the equilibrium crystal structure, the elastic constants, phonon dispersion and phonon density of states of the compounds are calculated. Th...
Energy Technology Data Exchange (ETDEWEB)
Chou, M.Y.
1992-04-01
This report discusses the following topics: calculation of the Structural Properties of Yttrium; dynamical and pairing properties of {alpha}-YH{chi}; electronic and structural properties of YH{sub 2} and YH{sub 3}; phase diagram of hydrogen on Ru(000); peierls distortion in hexagonal YH{sub 3}; and study of hydrogen in niobium and palladium.
Energy Technology Data Exchange (ETDEWEB)
Puvaneswari, S. [Department of Physics, E.M.G. Yadava Women’s College, Madurai, Tamilnadu-625014 (India); Priyanga, G. Sudha; Rajeswarapalanichamy, R., E-mail: rajeswarapalanichamy@gmail.com; Santhosh, M. [Department of Physics, N.M.S.S.V.N college, Madurai, Tamilnadu-625019 (India)
2015-06-24
The structural, electronic, elastic and magnetic properties of the perovskite structure of RuFe{sub 3}N, and OsFe{sub 3}N have been reported using the VASP within the gradient generalized approximation. Total energy calculations are performed using both spin and non-spin polarized calculations and it is found that, at ambient pressure both RuFe{sub 3}N and OsFe{sub 3}N are stable in ferromagnetic phase. The electronic structure reveals that both RuFe{sub 3}N and OsFe{sub 3}N are metallic in nature at ambient pressure.
Indian Academy of Sciences (India)
N Boukhris; H Meradji; S Amara Korba; S Drablia; S Ghemid; F El Haj Hassan
2014-08-01
The structural, electronic and thermal properties of lead chalcogenides PbS, PbSe and BeTe using full-potential linear augmented plane wave (FP-LAPW) method are investigated. The exchange–correlation energy within the local density approximation (LDA) and the generalized gradient approximation (GGA) are described. The calculated structural parameters are in reasonable agreement with the available experimental and theoretical data. The electronic band structure shows that the fundamental energy gap is direct (L–L) for all the compounds. Thermal effects on some macroscopic properties of these compounds are predicted using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. The variations of the lattice constant, bulk modulus, heat capacity, volume expansion coefficient and Debye temperature with temperature and pressure are obtained successfully. The effect of spin–orbit interaction is found to be negligible in determining the thermal properties and leads to a richer electronic structure.
High Pressure Hydrogen from First Principles
Morales, M. A.
2014-12-01
Typical approximations employed in first-principles simulations of high-pressure hydrogen involve the neglect of nuclear quantum effects (NQE) and the approximate treatment of electronic exchange and correlation, typically through a density functional theory (DFT) formulation. In this talk I'll present a detailed analysis of the influence of these approximations on the phase diagram of high-pressure hydrogen, with the goal of identifying the predictive capabilities of current methods and, at the same time, making accurate predictions in this important regime. We use a path integral formulation combined with density functional theory, which allows us to incorporate NQEs in a direct and controllable way. In addition, we use state-of-the-art quantum Monte Carlo calculations to benchmark the accuracy of more approximate mean-field electronic structure calculations based on DFT, and we use GW and hybrid DFT to calculate the optical properties of the solid and liquid phases near metallization. We present accurate predictions of the metal-insulator transition on the solid, including structural and optical properties of the molecular phase. This work was supported by the U.S. Department of Energy at the Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and by LDRD Grant No. 13-LW-004.
Energy Technology Data Exchange (ETDEWEB)
Murugan, A.; Priyanga, G. Sudha [Department of Physics, N.M.S.S.V.N College, Madurai, Tamil Nadu 625019 (India); Rajeswarapalanichamy, R., E-mail: rajeswarapalanichamy@gmail.com [Department of Physics, N.M.S.S.V.N College, Madurai, Tamil Nadu 625019 (India); Santhosh, M. [Department of Physics, N.M.S.S.V.N College, Madurai, Tamil Nadu 625019 (India); Iyakutti, K. [Department of Physics and Nanotechnology, SRM University, Chennai, Tamil Nadu 603203 (India)
2016-09-15
The electronic, structural, mechanical and magnetic properties of Actinide nitrides AnN (An = U, Np and Pu) are investigated in three cubic phases, namely, NaCl (B1), CsCl (B2) and zinc blende (B3). At normal pressure, UN is stable in antiferromagnetic state while the other two nitrides are stable in the ferromagnetic state with NaCl (B1) structure. A pressure induced structural phase transition from B1 to B3 phase is predicted in these nitrides. The electronic structure reveals that these nitrides are metallic in nature. The magnetic phase transition from antiferromagnetic to non-magnetic state is observed in UN at a pressure of 127 GPa while ferromagnetic to non-magnetic state is observed in NpN and PuN at the pressures of 67 GPa and 102.3 GPa respectively. The computed structural parameters, bulk modulus density of states and charge density distributions are compared with experimental and other theoretical calculations.
Xu-Hui, Zhu; Xiang-Rong, Chen; Bang-Gui, Liu
2016-05-01
The electronic structures, the effective masses, and optical properties of spinel CdCr2S4 are studied by using the full-potential linearized augmented planewave method and a modified Becke-Johnson exchange functional within the density-functional theory. Most importantly, the effects of the spin-orbit coupling (SOC) on the electronic structures and carrier effective masses are investigated. The calculated band structure shows a direct band gap. The electronic effective mass and the hole effective mass are analytically determined by reproducing the calculated band structures near the BZ center. SOC substantially changes the valence band top and the hole effective masses. In addition, we calculated the corresponding optical properties of the spinel structure CdCr2S4. These should be useful to deeply understand spinel CdCr2S4 as a ferromagnetic semiconductor for possible semiconductor spintronic applications. Project supported by the Joint Fund of the National Natural Science Foundation of China and the China Academy of Engineering Physics (Grant Nos. U1430117 and U1230201).
Li, Jia
2016-03-01
We have systematically investigated the influence of oxygen vacancy defects on the structural, electronic and magnetic properties of La(1-x)Sr(x)MnO3 (x = 1/3) film by means of ab initio calculations using bare GGA as well as GGA+U formalism, in the latter of which, the on-site Coulombic repulsion parameter U for Mn 3d orbital has been determined by the linear response theory. It is revealed that the introduction of the vacancy defects causes prominent structural changes including the distortion of MnO6 octahedra and local structural deformation surrounding the oxygen vacancy. The GGA+U formalism yields a significantly larger structural change than the bare GGA method, surprisingly in contrast with the general notion that the inclusion of Hubbard U parameter exerts little influence on structural properties. The distortion of MnO6 octahedra leads to a corresponding variation in the hybridization between Mn 3d and O 2p, which gets strengthened if the Mn-O distance becomes smaller and vice versa. The magnetic moments of the Mn atoms located in three typical sites of the vacancy-containing supercell are all larger than those in the pristine system. We have characterized the O-vacancy defect as a hole-type defect that forms a negative charge center, attracting electrons.
Murugan, A.; Priyanga, G. Sudha; Rajeswarapalanichamy, R.; Santhosh, M.; Iyakutti, K.
2016-09-01
The electronic, structural, mechanical and magnetic properties of Actinide nitrides AnN (An = U, Np and Pu) are investigated in three cubic phases, namely, NaCl (B1), CsCl (B2) and zinc blende (B3). At normal pressure, UN is stable in antiferromagnetic state while the other two nitrides are stable in the ferromagnetic state with NaCl (B1) structure. A pressure induced structural phase transition from B1 to B3 phase is predicted in these nitrides. The electronic structure reveals that these nitrides are metallic in nature. The magnetic phase transition from antiferromagnetic to non-magnetic state is observed in UN at a pressure of 127 GPa while ferromagnetic to non-magnetic state is observed in NpN and PuN at the pressures of 67 GPa and 102.3 GPa respectively. The computed structural parameters, bulk modulus density of states and charge density distributions are compared with experimental and other theoretical calculations.
Energy Technology Data Exchange (ETDEWEB)
Escaño, Mary Clare Sison, E-mail: mcescano@u-fukui.ac.jp [Graduate School of Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui 910-8507 (Japan); Arevalo, Ryan Lacdao [Department of Precision Science and Technology and Applied Physics, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan); Gyenge, Elod [Department of Chemical and Biological Engineering, The University of British Columbia, Vancouver, BC, Canada V6T 1Z3 (Canada); Kasai, Hideaki [Department of Precision Science and Technology and Applied Physics, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan)
2013-12-15
Highlights: ► Difference in Pt, Os electronic structures lead to different borohydride structures. ► Promotion of B–H bond breaking on Os due to water effects. ► Control of borohydride structure on Os catalyst using electric field. -- Abstract: Periodic density functional theory calculations are performed to investigate the nature of the BH{sub 4ad} and its interaction with H{sub 2}O{sub ad} in the presence of homogenous electric field. We observed a significant charge polarity of BH{sub 4ad} on Os(1 1 1) and such property could explain the electrostatic interaction with water monomer (H{sub ad}) with its HOH plane parallel to the surface. This interaction changes the BH{sub ad} molecular structure to BH{sub 3ad} + H{sub ad}. In the presence of homogenous electric field, the water co-adsorption effect is reduced due to the stabilization of H{sub 2}O{sub ad} on the surface and the deviation of the O–H bond from the plane, decreasing the electrostatic interaction between BH{sub 4ad} and H{sub 2}O{sub ad}. These fundamental findings imply accessible control of borohydride structures on an electrode surface, which could be relevant for direct borohydride fuel cell (DBFC) and reversible hydrogen storage/release applications.
Energy Technology Data Exchange (ETDEWEB)
Guemou, M., E-mail: guemoumhamed7@gmail.com [Engineering Physics Laboratory, University Ibn Khaldoun of Tiaret, BP 78-Zaaroura, Tiaret 14000 (Algeria); Bouhafs, B. [Modelling and Simulation in Materials Science Laboratory, Physics Department, University of Sidi Bel-Abbes, 22000 Sidi Bel-Abbes (Algeria); Abdiche, A. [Applied Materials Laboratory, Research Center, University of Sidi Bel Abbes, 22000 Sidi Bel Abbes (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modelisation Mathematique (LPQ3M), Departement de Technologie, Universite de Mascara, 29000 Mascara (Algeria); Al Douri, Y. [Institute of Nano Electronic Engineering, Universiti Malaysia Perlis, Perlis (Malaysia); Bin Omran, S. [Department of Physics and Astronomy, Faculty of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia)
2012-04-15
Density functional calculations are performed to study the structural, electronic and optical properties of technologically important B{sub x}Ga{sub 1-x}As ternary alloys. The calculations are based on the total-energy calculations within the full-potential augmented plane-wave (FP-LAPW) method. For exchange-correlation potential, local density approximation (LDA) and the generalized gradient approximation (GGA) have been used. The structural properties, including lattice constants, bulk modulus and their pressure derivatives, are in very good agreement with the available experimental and theoretical data. The electronic band structure, density of states for the binary compounds and their ternary alloys are given. The dielectric function and the refractive index are also calculated using different models. The obtained results compare very well with previous calculations and experimental measurements.
Tu, Qing; Lange, Björn; Parlak, Zehra; Lopes, Joao Marcelo J; Blum, Volker; Zauscher, Stefan
2016-07-26
Interfaces and subsurface layers are critical for the performance of devices made of 2D materials and heterostructures. Facile, nondestructive, and quantitative ways to characterize the structure of atomically thin, layered materials are thus essential to ensure control of the resultant properties. Here, we show that contact-resonance atomic force microscopy-which is exquisitely sensitive to stiffness changes that arise from even a single atomic layer of a van der Waals-adhered material-is a powerful experimental tool to address this challenge. A combined density functional theory and continuum modeling approach is introduced that yields sub-surface-sensitive, nanomechanical fingerprints associated with specific, well-defined structure models of individual surface domains. Where such models are known, this information can be correlated with experimentally obtained contact-resonance frequency maps to reveal the (sub)surface structure of different domains on the sample.
Energy Technology Data Exchange (ETDEWEB)
Zhao, Erjun [State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun (China); Graduate School, Chinese Academy of Sciences, Beijing (China); Wang, Jinping [Department of Applied Chemistry, Qingdao Agricultural University, Qingdao (China); Wu, Zhijian [State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun (China)
2010-05-15
The structural stability, electronic, and mechanical properties of MoN were investigated by use of the density functional theory. Nine structures were considered, i.e., hexagonal {delta}{sub 1}-MoN, {delta}{sub 2}-MoN, {delta}'{sub 2}-MoN, {delta}{sub 3}-MoN, {delta}{sub 4}-MoN, and wurtzite ZnS structures, cubic NaCl, zincblende, and CsCl structures. The calculated results indicated that {delta}{sub 3}-MoN is the ground state among the considered structures. The second-order displacive phase transition has been found from {delta}{sub 3}-MoN to {delta}'{sub 2}-MoN with increase in pressure, in agreement with the experimental observation. {delta}'{sub 2}-MoN has the largest calculated bulk and shear moduli among the considered structures, followed by {delta}{sub 3}-MoN. The estimated hardness of {delta}'{sub 2}-MoN and {delta}{sub 3}-MoN is 34 and 29 GPa, respectively. Both of them are thermodynamically and mechanically stable. The compressibility along the c-axis for both compounds is smaller than that for diamond and cubic boron nitride (c-BN). The ideal strengths of {delta}'{sub 2}-MoN were discussed. The stress-strain relationship for {delta}'{sub 2}-MoN shows that the ideal tensile strength of 107.0 GPa along the left angle 0001 right angle direction is very large, which might have potential technological and industrial applications. (Abstract Copyright [2010], Wiley Periodicals, Inc.)
Energy Technology Data Exchange (ETDEWEB)
Liu, Chuan; Zhang, Shengli [Division of Molecule and Materials Simulation, State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029 (China); Huang, Shiping, E-mail: huangsp@mail.buct.edu.cn [Division of Molecule and Materials Simulation, State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029 (China); Wang, Peng; Tian, Huiping [Research Institute of Petroleum Processing, SINOPEC, Beijing 100083 (China)
2013-02-05
Highlights: Black-Right-Pointing-Pointer Structural stability and thermodynamic properties of K{sub 2}ZnH{sub 4} hydride are analyzed. Black-Right-Pointing-Pointer Decomposition temperature of two-step reactions is predicted based on free energy. Black-Right-Pointing-Pointer Orthorhombic structure of K{sub 2}ZnH{sub 4} hydride is much more stable. - Abstract: Density functional theory calculations have been used to investigate the structural stability, electronic characteristics and thermodynamic properties of K{sub 2}ZnH{sub 4} hydride. We find that the orthorhombic structure of K{sub 2}ZnH{sub 4} is more stable than the tetragonal structure base on the total energy and phonon density of states. The calculated lattice parameters of the orthorhombic structure of K{sub 2}ZnH{sub 4} are in good agreement with the experimental data. Analysis of the electronic characteristic suggests that K{sub 2}ZnH{sub 4} crystal is an insulating material with a band gap of 4.010 eV. The calculated average H site energy is 4.540 eV/H, demonstrating that strong covalent bond exist between Zn and H atom. The formation enthalpy of K{sub 2}ZnH{sub 4} is found to be -1.318 eV/f.u at 298 K. Hydrogen desorption from K{sub 2}ZnH{sub 4} takes place via a two-step process, firstly forming KH, Zn and H{sub 2}, and then K and H{sub 2}. The first decomposition reaction is predicted at 524 K, and the second decomposition reaction is at 505 K. The reaction enthalpy is estimated to be 49.164 kJ/mol at 524 K for the first decomposition reaction, and 62.523 kJ/mol at 505 K for the second decomposition reaction.
First-principles calculations on structure and properties of amorphous Li5P4O8N3 (LiPON)
Sicolo, Sabrina; Albe, Karsten
2016-11-01
The structural, electronic and ion transport properties of an amorphous member of the LiPON family with non-trivial composition and cross-linking are studied by means of electronic structure calculations within Density Functional Theory. By a combination of an evolutionary algorithm followed by simulated annealing and alternatively by a rapid quenching protocol, structural models of disordered Li5P4O8N3 are generated, which are characterized by a local demixing in Li-rich and Li-poor layers. These structures have a composition close to what is found experimentally in thin films and contain all the expected diversely coordinated atoms, namely triply- and doubly-coordinated nitrogens and bridging and non-bridging oxygens. The issue of ionic conductivity is addressed by calculating defect formation energies and migration barriers of neutral and charged point defects. Li+ interstitials are energetically much preferred over vacancies, both when the lithium reservoir is metallic lithium and LiCoO2. The competitive formation of neutral Li interstitials when LiPON is contacted with metallic Li results in the chemical reduction of LiPON and the disruption of the network, as recently observed in experiments.
Moon, Chang-Youn; Kang, Hanhim; Jang, Bo Gyu; Shim, Ji Hoon
2015-12-01
We investigate the evolution of the electronic structure of NiS2 -xSex alloys with varying temperature and composition x by using the combined approach of density-functional theory and dynamical mean-field theory. Adopting realistic alloy structures containing S and Se dimers, we map their electronic correlation strength on the phase diagram and observe the metal-insulator transition (MIT) at the composition x =0.5 , which is consistent with the experimental measurements. The temperature dependence of the local magnetic susceptibility is found to show a typical Curie-Weiss-like behavior in the insulating phase while it shows a constant Pauli-like behavior in the metallic phase. A comparison of the electronic structures for NiS2 and NiSe2 in different lattice structures suggests that the MIT in this alloy system can be classified as of bandwidth-control type, where the change in the hybridization strength between Ni d and chalcogen p orbitals is the most important parameter.
Olovsson, Weine; Magnuson, Martin
2016-01-01
The local structure and chemical bonding in two-phase amorphous Cr$_{1-x}$C$_{x}$ nanocomposite thin films are investigated by Cr $K$-edge ($1s$) X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies in comparison to theory. By utilizing the computationally efficient \\textit{stochastic quenching} (SQ) technique, we reveal the complexity of different Cr-sites in the transition metal carbides, highlighting the need for large scale averaging to obtain theoretical XANES and EXAFS spectra for comparison with measurements. As shown in this work, it is advantageous to use \\textit{ab initio} theory as an assessment to correctly model and fit experimental spectra and investigate the trends of bond lengths and coordination numbers in complex amorphous materials. With sufficient total carbon content ($\\geq$ 30 at\\%), we find that the short-range coordination in the amorphous carbide phase exhibit similarities to that of a Cr$_{7}$C$_{3\\pm{}y}$ structure, while e...
Energy Technology Data Exchange (ETDEWEB)
Khan, Wilayat, E-mail: walayat76@gmail.com [New Technologies-Research Center, University of West Bohemia, Univerzitní 8, 306 14 Plzeň (Czech Republic); Reshak, A.H. [New Technologies-Research Center, University of West Bohemia, Univerzitní 8, 306 14 Plzeň (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia)
2015-01-15
The electronic structure, electronic charge density and linear optical properties of the metallic Li{sub 7}MnN{sub 4} compound, having cubic symmetry, are calculated using the full potential linearized augmented plane wave (FP-LAPW) method. The calculated band structure and density of states using the local density, generalized gradient and Engel–Vosko approximations, depict the metallic nature of the cubic Li{sub 7}MnN{sub 4} compound. The bands crossing the Fermi level in the calculated band structure are mainly from the Mn-d states with small support of N-p states. In addition, the Mn-d states at the Fermi level enhance the density of states, which is very useful for the electronic transport properties. The valence electronic charge density depicts strong covalent bond between Mn and two N atoms and polar covalent bond between Mn and Li atoms. The frequency dependent linear optical properties like real and imaginary part of the dielectric function, optical conductivity, reflectivity and energy loss function are calculated on the basis of the computed band structure. Both intra-band and inter-band transitions contribute to the calculated optical parameters. Using the BoltzTraP code, the thermoelectric properties like electrical and thermal conductivity, Seebeck coefficient, power coefficient and heat capacity of the Li{sub 7}MnN{sub 4} are also calculated as a function of temperature and studied.
Zhang, S. H.; Beyerlein, I. J.; Legut, D.; Fu, Z. H.; Zhang, Z.; Shang, S. L.; Liu, Z. K.; Germann, T. C.; Zhang, R. F.
2017-06-01
Taking pure Mg, Mg-Al, and Mg-Zn as prototypes, the effects of strain on the stacking fault energies (SFEs), dislocation core structure, and Peierls stress were systematically investigated by means of density functional theory and the semidiscrete variational Peierls-Nabarro model. Our results suggest that volumetric strain may significantly influence the values of SFEs of both pure Mg and its alloys, which will eventually modify the dislocation core structure, Peierls stress, and preferred slip system, in agreement with recent experimental results. The so-called "strain factor" that was previously proposed for the solute strengthening could be justified as a major contribution to the strain effect on SFEs. Based on multivariate regression analysis, we proposed universal exponential relationships between the dislocation core structure, the Peierls stress, and the stable or unstable SFEs. Electronic structure calculations suggest that the variations of these critical parameters controlling strength and ductility under strain can be attributed to the strain-induced electronic polarization and redistribution of valence charge density at hollow sites. These findings provide a fundamental basis for tuning the strain effect to design novel Mg alloys with both high strength and ductility.
Medeiros, Subenia; Araujo, Maeva
2015-03-01
The structural, electronic, vibrational, and optical properties of perovskite CaTiO3 in the cubic, orthorhombic, and tetragonal phase are calculated in the framework of density functional theory (DFT) with different exchange-correlation potentials by CASTEP package. The calculated band structure shows an indirect band gap of 1.88 eV at the Γ-R points in the Brillouin zone to the cubic structure, a direct band gap of 2.41 eV at the Γ- Γ points to the orthorhombic structure, and an indirect band gap of 2.31 eV at theM - Γ points to the tetragonal phase. It is still known that the CaTiO3 has a static dielectric constant that extrapolates to a value greater than 300 at zero temperature, and the dielectric response is dominated by low frequency (ν ~ 90cm-1) polar optical modes in which cation motion opposes oxygen motion. Our calculated lattice parameters, elastic constants, optical properties, and vibrational frequencies are found to be in good agreement with the available theoretical and experimental values. The results for the effective mass in the electron and hole carriers are also presented in this work.
Liebscher, C H; Freysoldt, C; Dennenwaldt, T; Harzer, T P; Dehm, G
2016-07-12
Metastable Cu-Cr alloy thin films with nominal thickness of 300nm and composition of Cu67Cr33 (at%) are obtained by co-evaporation using molecular beam epitaxy. The microstructure, chemical phase separation and electronic structure are investigated by transmission electron microscopy (TEM). The thin film adopts the body-centered cubic crystal structure and consists of columnar grains with ~50nm diameter. Aberration-corrected scanning TEM in combination with energy dispersive X-ray spectroscopy confirms compositional fluctuations within the grains. Cu- and Cr-rich domains with composition of Cu85Cr15 (at%) and Cu42Cr58 (at%) and domain size of 1-5nm are observed. The alignment of the interface between the Cu- and Cr-rich domains shows a preference for {110}-type habit plane. The electronic structure of the Cu-Cr thin films is investigated by electron energy loss spectroscopy (EELS) and is contrasted to an fcc-Cu reference sample. The experimental EEL spectra are compared to spectra computed by density functional theory. The main differences between bcc-and fcc-Cu are related to differences in van Hove singularities in the electron density of states. In Cu-Cr solid solutions with bcc crystal structure a single peak after the L3-edge, corresponding to a van Hove singularity at the N-point of the first Brillouin zone is observed. Spectra computed for pure bcc-Cu and random Cu-Cr solid solutions with 10at% Cr confirm the experimental observations. The calculated spectrum for a perfect Cu50Cr50 (at%) random structure shows a shift in the van Hove singularity towards higher energy by developing a Cu-Cr d-band that lies between the delocalized d-bands of Cu and Cr.
Energy Technology Data Exchange (ETDEWEB)
Irshad, Zainab [Pakistan Institute of Engineering and Applied Sciences (PIEAS), P.O. Nilore, Islamabad 45650 (Pakistan); Shah, S.H., E-mail: shafqatshah@gmail.com [Pakistan Institute of Engineering and Applied Sciences (PIEAS), P.O. Nilore, Islamabad 45650 (Pakistan); Theoretical Physics Division, PINSTECH, Nilore, Islamabad (Pakistan); National Centre for Physics (NCP), Quaid-i-Azam University, Islamabad (Pakistan); Rafiq, M.A.; Hasan, M.M. [Pakistan Institute of Engineering and Applied Sciences (PIEAS), P.O. Nilore, Islamabad 45650 (Pakistan)
2015-03-05
Highlights: • Standard xc functionals give correct geometry but incorrect electronic structure. • The calculated bandgap using PBE-GGA + U is 2.1 eV. • Varying degree of hybridization between Fe–O and Bi–O atoms is observed. • Exchange and crystal field splittings are vital in the electronic structure of Bi{sub 2}Fe{sub 4}O{sub 9}. • Magnetism of Bi{sub 2}Fe{sub 4}O{sub 9} is due to Fe{sup 3+} ions which induce magnetic moment in neighboring atoms. - Abstract: The structural, electronic, and magnetic properties of ferromagnetic bismuth ferrate (Bi{sub 2}Fe{sub 4}O{sub 9}) are investigated using density functional theory (DFT). Different exchange–correlation (xc) functionals (LSDA, PBE-GGA, PBEsol-GGA and WC-GGA) are tested to calculate various properties of Bi{sub 2}Fe{sub 4}O{sub 9}. All the exchange correlation functionals accurately describe the structural properties of Bi{sub 2}Fe{sub 4}O{sub 9} but fail to calculate its correct band structure. The calculated band structure improves when DFT + U method is employed. The PBE-GGA + U calculations predict a bandgap of 2.1 eV for the ferromagnetic Bi{sub 2}Fe{sub 4}O{sub 9} in close agreement with the experiment. The calculated density of states shows appreciable hybridization between Fe-3d states and O-2p states along with minor overlap between Bi-6p and O-2p states. The magnetic properties of Bi{sub 2}Fe{sub 4}O{sub 9} are primarily due to Fe{sup 3+} ions, each of which has a non-integer magnetic moment of approximately 3.9 μ{sub B}. The values of the induced magnetic moments at the other atomic sites depend on their local environments.
Energy Technology Data Exchange (ETDEWEB)
Jiang Huitian [Department of Physics, Michigan Technological University, Houghton, MI 49931 (United States); Orlando, Roberto [Dipartimento di Scienze e Tecnologie Avanzate, Universita del Piemonte Orientale, C. so Borsalino 54, I-15100 Alessandria (Italy); Blanco, Miguel A [Departamento de QuImica Fisica y Analitica, Universidad de Oviedo, 33006-Oviedo (Spain); Pandey, Ravindra [Department of Physics, Michigan Technological University, Houghton, MI 49931 (United States)
2004-05-12
The results of electronic structure calculations for PbF{sub 2} in ambient and high-pressure phases are reported here. We employ the linear combination of atomic orbital-density functional theory approximation using the CRYSTAL program package whose capabilities were expanded to include the so-called soft-core pseudopotentials with higher-order components (e.g. d, f, and g) of the angular momentum terms for heavier atoms in the periodic table. The band structure and density of states of the cubic, orthorhombic, and hexagonal phases were calculated. A direct band gap at X is predicted for the cubic phase, whereas an indirect band gap is predicted for the high-pressure phases. The density of states reveals hybridization features involving Pb s and F p orbitals in the upper valence band of PbF{sub 2}.
First-principles theory of electronic structure and magnetism of Cr nano-islands on Pd(1 1 1)
Carvalho de Melo Rodrigues, Debora; Pereiro, Manuel; Bergman, Anders; Eriksson, Olle; Burlamaqui Klautau, Angela
2017-01-01
We report on the electronic structure, magnetic moments and exchange interactions of one- and two-dimensional Cr clusters on a Pd(1 1 1) substrate, using a real-space method based on density functional theory in the local spin density approximation. We find in general that for the investigated clusters, the magnetic moments are sizeable and almost entirely of spin-character. We demonstrate that the interactions in general are dominated by nearest-neighbor antiferrom