First Principles Calculations for X-ray Resonant Spectra and Elastic Properties
International Nuclear Information System (INIS)
Yongbin Lee
2006-01-01
In this thesis, we discuss applications of first principles methods to x-ray resonant spectra and elastic properties calculation. We start with brief reviews about theoretical background of first principles methods, such as density functional theory, local density approximation (LDA), LDA+U, and the linear augmented plane wave (LAPW) method to solve Kohn-Sham equations. After that we discuss x-ray resonant scattering (XRMS), x-ray magnetic circular dichroism (XMCD) and the branching problem in the heavy rare earths Ledges. In the last chapter we discuss the elastic properties of the second hardest material AlMgB 14
AELAS: Automatic ELAStic property derivations via high-throughput first-principles computation
Zhang, S. H.; Zhang, R. F.
2017-11-01
The elastic properties are fundamental and important for crystalline materials as they relate to other mechanical properties, various thermodynamic qualities as well as some critical physical properties. However, a complete set of experimentally determined elastic properties is only available for a small subset of known materials, and an automatic scheme for the derivations of elastic properties that is adapted to high-throughput computation is much demanding. In this paper, we present the AELAS code, an automated program for calculating second-order elastic constants of both two-dimensional and three-dimensional single crystal materials with any symmetry, which is designed mainly for high-throughput first-principles computation. Other derivations of general elastic properties such as Young's, bulk and shear moduli as well as Poisson's ratio of polycrystal materials, Pugh ratio, Cauchy pressure, elastic anisotropy and elastic stability criterion, are also implemented in this code. The implementation of the code has been critically validated by a lot of evaluations and tests on a broad class of materials including two-dimensional and three-dimensional materials, providing its efficiency and capability for high-throughput screening of specific materials with targeted mechanical properties. Program Files doi:http://dx.doi.org/10.17632/f8fwg4j9tw.1 Licensing provisions: BSD 3-Clause Programming language: Fortran Nature of problem: To automate the calculations of second-order elastic constants and the derivations of other elastic properties for two-dimensional and three-dimensional materials with any symmetry via high-throughput first-principles computation. Solution method: The space-group number is firstly determined by the SPGLIB code [1] and the structure is then redefined to unit cell with IEEE-format [2]. Secondly, based on the determined space group number, a set of distortion modes is automatically specified and the distorted structure files are generated
Kong, Ge-Xing; Ma, Xiao-Juan; Liu, Qi-Jun; Li, Yong; Liu, Zheng-Tang
2018-03-01
Using first-principles calculations method based on density functional theory (DFT) with the Perdew-Burke-Ernzerhof (PBE) implementation of the generalized gradient approximation (GGA), we investigate the structural, elastic and thermodynamic properties of gold-copper intermetallic compounds (Au-Cu ICs). The calculated lattice parameters are in excellent agreement with experimental data. The elastic constants show that all the investigated Au-Cu alloys are mechanically stable. Elastic properties, including the shear modulus, Young's modulus, Poisson's ratio and Pugh's indicator, of the intermetallic compounds are evaluated and discussed, with special attention to the remarkable anisotropy displayed by Au-Cu ICs. Thermodynamic and transport properties including the Debye temperature, thermal conductivity and melting point are predicted from the averaged sound velocity and elastic moduli, using semi-empirical formulas.
Thermodynamics and elastic properties of Ir from first-principle calculations
International Nuclear Information System (INIS)
Li Qiang; Huang Duohui; Cao Qilong; Wang Fanhou
2013-01-01
Within the framework of the quasiharmonic approximation, the thermodynamics and elastic properties, including phonon dispersion curves, equation of state, linear thermal expansion coefficient and temperature-dependent entropy, enthalpy, heat capacity, elastic constants, bulk modulus, shear modulus, Young's modulus of Ir have been studied using first-principles projector-augmented wave method. The results revealed that the predicted phonon dispersion curves of Ir are in agreement with the experimental measurements by neutron diffractions. Considering the thermal electronic contribution to Helmholtz free energy, the calculated entropy, enthalpy, heat capacity and linear thermal expansion co- efficient from the first-principle are consistent well with the experimental data. At 2600 K, the electronic heat capacity accounts for 17% of the total heat capacity at constant pressure, thus the thermal electronic contribution to Helmholtz free energy is very important. The predicted elastic constants, bulk modulus, shear modulus and Young's modulus at room temperature are also in agreement with the available measurements and increase with the increasing temperature. (authors)
Electronic, elastic and thermal properties of SrCu2As2 via first principles calculation
International Nuclear Information System (INIS)
Lv, Zhen-Long; Cheng, Yan; Chen, Xiang-Rong; Ji, Guang-Fu
2013-01-01
Highlights: •Electronic properties, Fermi surface and non-magnetic property of SrCu 2 As 2 are investigated. •Elastic constants and elasticity-related properties are calculated. •Elastic anisotropy is visually shown and analyzed. •Thermal properties are calculated, consisting well with the experimental data. -- Abstract: ThCr 2 Si 2 -type crystal has a large family member, most of which have certain unusual properties. In this work, the electronic, elastic and thermal properties of the recently re-synthesized SrCu 2 As 2 are investigated by employing first principles calculation. The characters of the band structure and the partial density of states (PDOS) of SrCu 2 As 2 are analyzed, which shows that SrCu 2 As 2 is a metallic crystal with no magnetism. The calculated elastic constants reveal that SrCu 2 As 2 is mechanically stable but anisotropic; the anisotropy is further illustrated by the direction-dependent linear compressibility and Young’s modulus. By analyzing, we find that the corresponding shear deformation is most easy to take place when the shear stresses are imposed on the vertical {1 0 0} planes along the horizontal 〈1 0 0〉 directions. Besides these, other elasticity-relevant properties, including the bulk modulus, shear modulus, the Poisson ratio, the velocities of acoustic waves and the Debye temperature, are also derived. The specific heat C V and C P as functions of temperature (T) are obtained from quasi-harmonic Debye model, the curve of Cp–T consists well with the experimental data. Meanwhile, the thermal expansion coefficient α is also predicted
The first-principles calculations for the elastic properties of Zr2Al under compression
International Nuclear Information System (INIS)
Yuan Xiaoli; Wei Dongqing; Chen Xiangrong; Zhang Qingming; Gong Zizheng
2011-01-01
Graphical abstract: The calculated elastic constants C ij as a function of pressure P. Display Omitted Research highlights: → It is found that the five independent elastic constants increase monotonically with pressure. C 11 and C 33 vary rapidly as pressure increases, C 13 and C 12 becomes moderate. However, C 44 increases comparatively slowly with pressure. Figure shows excellent satisfaction of the calculated elastic constants of Zr 2 Al to these equations and hence in our calculation, the Zr 2 Al is mechanically stable at pressure up to 100 GPa. - Abstract: The first-principles calculations were applied to investigate the structural, elastic constants of Zr 2 Al alloy with increasing pressure. These properties are based on the plane wave pseudopotential density functional theory (DFT) method within the generalized gradient approximation (GGA) for exchange and correlation. The result of the heat of formation of Zr 2 Al crystal investigated is in excellent consistent with results from other study. The anisotropy, the shear modulus, and Young's modulus for the ideal polycrystalline Zr 2 Al are also studied. It is found that (higher) pressure can significantly improve the ductility of Zr 2 Al. Moreover, the elastic constants of Zr 2 Al increase monotonically and the anisotropies decrease with the increasing pressure. Finally, it is observed that Zr d electrons are mainly contributed to the density of states at the Fermi level.
Moon, Juhyuk
2012-06-04
The structure and elasticity of tricalcium aluminate (C 3A) have been experimentally and theoretically studied. From high-pressure X-ray diffraction experiments, the bulk modulus of 102(6) and 110(3) GPa were obtained by fitting second- and third-order finite strain equation of state, respectively. First-principles calculations with a generalized gradient approximation gave an isotropic bulk modulus of 102.1 GPa and an isothermal bulk modulus of 106.0 GPa. The static calculations using the exchange-correlation functional show an excellent agreement with the experimental measurements. Based on the agreement, accurate elastic constants and other elastic moduli were computed. The slight difference of behavior at high pressure can be explained by the infiltration of pressure-transmitting silicone oil into structural holes in C 3A. The computed elastic and mechanical properties will be useful in understanding structural and mechanical properties of cementitious materials, particularly with the increasing interest in the advanced applications at the nanoscale. © 2012 The American Ceramic Society.
International Nuclear Information System (INIS)
Briquet, Ludovic G.V.; Philipp, Patrick
2013-01-01
Highlights: ► Full electronic structure description. ► Elastic properties. ► Phonon band structure and DOS. ► Analysis of vibration modes. -- Abstract: Interest in tungsten disilicide is growing due to its use as protective coatings and non-volatile memory devices but fundamental investigations on tungsten disilicide vibrational properties are lacking in literature. In particular, the phonon vibration modes have never been described. This paper presents a first-principles investigation of the vibrational properties of WSi 2 crystals. The elastic and electronic properties are considered as well. First, the electron band structure is computed. Extra electronic levels for the valence electrons as compared to previously published results are found, highlighting the need for state-of-the-art DFT calculations. It is shown that the ionicity plays only a little role in the W–Si bonding. Instead, a strong degree of covalency is found. The elastic constants are computed in good agreement with the available experimental data. The complete phonon density of state as well as band structure are presented and all vibration modes are described. The phonon vibrations are also correlated to IR and Raman investigations available in the literature
International Nuclear Information System (INIS)
Hua Manyu; Li Yimin; Long Chunguang; Li Xia
2012-01-01
The structural, electronic and elastic properties of potassium hexatitanate (K 2 Ti 6 O 13 ) whisker were investigated using first-principles calculations. The calculated cell parameters of K 2 Ti 6 O 13 including lattice constants and atomic positions are in good agreement with the experimental data. The obtained formation enthalpy (-61.1535 eV/atom) and cohesive energy (-137.4502 eV/atom) are both negative, showing its high structural stability. Further analysis of the electronic structures shows that the potassium hexatitanate is a wide-band semiconductor. Within K 2 Ti 6 O 13 crystal, the Ti---O bonding interactions are stronger than that of K---O, while no apparent K---Ti bonding interactions can be observed. The structural stability of K 2 Ti 6 O 13 was closely associated with the covalent bond interactions between Ti (d) and O (p) orbits. Further calculations on elastic properties show that K 2 Ti 6 O 13 is a high stiffness and brittle material with small anisotropy in shear and compression.
Ekuma, Chinedu E.; Bagayoko, Diola; Jarrell, Mark; Moreno, Juana
2012-09-01
We utilized a simple, robust, first principle method, based on basis set optimization with the BZW-EF method, to study the electronic and related properties of transition metal mono-nitrides: ScN and YN. We solved the KS system of equations self-consistently within the linear combination of atomic orbitals (LCAO) formalism. It is shown that the band gap and low energy conduction bands, as well as elastic and structural properties, can be calculated with a reasonable accuracy when the LCAO formalism is used to obtain an optimal basis. Our calculated, indirect electronic band gap (E^Γ -X_g) is 0.79 (LDA) and 0.88 eV (GGA) for ScN. In the case of YN, we predict an indirect band gap (E^Γ -X_g) of 1.09 (LDA) and 1.15 eV (GGA). We also calculated the equilibrium lattice constants, the bulk moduli (Bo), effective masses, and elastic constants for both systems. Our calculated values are in excellent agreement with experimental ones where the latter are available.
Directory of Open Access Journals (Sweden)
Chinedu E. Ekuma
2012-09-01
Full Text Available We utilized a simple, robust, first principle method, based on basis set optimization with the BZW-EF method, to study the electronic and related properties of transition metal mono-nitrides: ScN and YN. We solved the KS system of equations self-consistently within the linear combination of atomic orbitals (LCAO formalism. It is shown that the band gap and low energy conduction bands, as well as elastic and structural properties, can be calculated with a reasonable accuracy when the LCAO formalism is used to obtain an optimal basis. Our calculated, indirect electronic band gap (EΓ−Xg is 0.79 (LDA and 0.88 eV (GGA for ScN. In the case of YN, we predict an indirect band gap (EΓ−Xg of 1.09 (LDA and 1.15 eV (GGA. We also calculated the equilibrium lattice constants, the bulk moduli (Bo, effective masses, and elastic constants for both systems. Our calculated values are in excellent agreement with experimental ones where the latter are available.
Directory of Open Access Journals (Sweden)
Samah Al-Qaisi
Full Text Available First-principles investigations of the Terbium oxide TbO are performed on structural, elastic, mechanical and thermodynamic properties. The investigations are accomplished by employing full potential augmented plane wave FP-LAPW method framed within density functional theory DFT as implemented in the WIEN2k package. The exchange-correlation energy functional, a part of the total energy functional, is treated through Perdew Burke Ernzerhof scheme of the Generalized Gradient Approximation PBEGGA. The calculations of the ground state structural parameters, like lattice constants a0, bulk moduli B and their pressure derivative Bâ² values, are done for the rock-salt RS, zinc-blende ZB, cesium chloride CsCl, wurtzite WZ and nickel arsenide NiAs polymorphs of the TbO compound. The elastic constants (C11, C12, C13, C33, and C44 and mechanical properties (Youngâs modulus Y, Shear modulus S, Poissonâs ratio Ï, Anisotropic ratio A and compressibility Î², were also calculated to comprehend its potential for valuable applications. From our calculations, the RS phase of TbO compound was found strongest one mechanically amongst the studied cubic structures whereas from hexagonal phases, the NiAs type structure was found stronger than WZ phase of the TbO. To analyze the ductility of the different structures of the TbO, Pughâs rule (B/SH and Cauchy pressure (C12âC44 approaches are used. It was found that ZB, CsCl and WZ type structures of the TbO were of ductile nature with the obvious dominance of the ionic bonding while RS and NiAs structures exhibited brittle nature with the covalent bonding dominance. Moreover, Debye temperature was calculated for both cubic and hexagonal structures of TbO in question by averaging the computed sound velocities. Keywords: DFT, TbO, Elastic properties, Thermodynamic properties
Xiao-Lin, Zhang; Yuan-Yuan, Wu; Xiao-Hong, Shao; Yong, Lu; Ping, Zhang
2016-05-01
The high pressure behaviors of Th4H15 and ThH2 are investigated by using the first-principles calculations based on the density functional theory (DFT). From the energy-volume relations, the bct phase of ThH2 is more stable than the fcc phase at ambient conditions. At high pressure, the bct ThH2 and bcc Th4H15 phases are more brittle than they are at ambient pressure from the calculated elastic constants and the Poisson ratio. The thermodynamic stability of the bct phase ThH2 is determined from the calculated phonon dispersion. In the pressure domain of interest, the phonon dispersions of bcc Th4H15 and bct ThH2 are positive, indicating the dynamical stability of these two phases, while the fcc ThH2 is unstable. The thermodynamic properties including the lattice vibration energy, entropy, and specific heat are predicted for these stable phases. The vibrational free energy decreases with the increase of the temperature, and the entropy and the heat capacity are proportional to the temperature and inversely proportional to the pressure. As the pressure increases, the resistance to the external pressure is strengthened for Th4H15 and ThH2. Project supported by the Long-Term Subsidy Mechanism from the Ministry of Finance and the Ministry of Education of China.
ShunLi Shang; Louis G. Hector Jr.; Paul Saxe; Zi-Kui Liu; Robert J. Moon; Pablo D. Zavattieri
2014-01-01
Anisotropy and temperature dependence of structural, thermodynamic and elastic properties of crystalline cellulose Iβ were computed with first-principles density functional theory (DFT) and a semi-empirical correction for van der Waals interactions. Specifically, we report the computed temperature variation (up to 500...
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.
Elastic properties of Ni2MnGa from first-principles calculations
International Nuclear Information System (INIS)
Ozdemir Kart, S.; Cagin, T.
2010-01-01
Research highlights: In this study, we have performed spin-polarized total energy calculations aiming to develop microscopic understanding of magnetic shape memory behavior of Ni 2 MnGa. This paper is devoted to determine the mechanical properties of Ni 2 MnGa in both austenitic and martensitic structures. To the best of our knowledge, this work presents the elastic constants of Ni 2 MnGa in the structure of 5M martensite, for the first time. We have also re-calculated elastic constants for cubic and nonmodulated (NM) structures by using the potential with e/a = 7.5. The elastic constants are predicted by straining the cubic L2 1 , 5M pseudo-tetragonal and NM tetragonal martensitic structures. Because of the special significance of the isotropic bulk modulus, shear modulus, Young's modulus and Poisson's ratio for technological applications, we have also calculated these quantities from the elastic constants. - Abstract: Elastic properties of Ni 2 MnGa in both austenitic and martensitic structures are determined by using ab initio methods based on density functional theory (DFT) within the spin-polarized generalized-gradient approximation. The tetragonal shear elastic constant C' takes a very small value in the austenitic phase, indicating the elastic instability results in a phase transition to martensitic structure. Isotropic mechanical properties such as bulk modulus, shear modulus, Young's modulus and Poisson's ratio are predicted. The trend of the Debye temperatures calculated for three structures of Ni 2 MnGa is comparable with that of the experiment.
Energy Technology Data Exchange (ETDEWEB)
Lakel, S., E-mail: s.lakel@yahoo.fr [Laboratory of physical materials - University of LAGHOUAT – BP 37G, Laghouat (Algeria); Laboratoire de Matériaux Semi Conducteurs et Métalliques «LMSM», Université de Biskra (Algeria); Okbi, F. [Laboratoire de Sciences Fondamentales, Université Amar Telidji de Laghouat, BP 37G, Laghouat 03000 (Algeria); Ibrir, M. [Laboratoire de Sciences Fondamentales, Université Amar Telidji de Laghouat, BP 37G, Laghouat 03000 (Algeria); Département de physique, Université de M' sila (Algeria); Almi, K. [Laboratoire de Matériaux Semi Conducteurs et Métalliques «LMSM», Université de Biskra (Algeria)
2015-03-30
We have performed first-principles calculations to investigate the behavior under hydrostatic pressure of the structural, elastic and lattice dynamics properties of aluminum phosphide crystal (AlP), in both zinc-blende (B3) and nickel arsenide (B8) phases. Our calculated structural and electronic properties are in good agreement with previous theoretical and experimental results. The elastic constants, bulk modulus (B), shear modulus (G), and Young's modulus (E), Born effective charge and static dielectric constant ε{sub 0}, were calculated with the generalized gradient approximations and the density functional perturbation theory (DFPT). Our results in the pressure behavior of the elastic and dielectric properties of both phases are compared and contrasted with the common III–V materials. The Born effective charge ZB decreases linearly with pressure increasing, while the static dielectric constant decreases quadratically with the increase of pressure.
First-Principles Calculations for Elastic Properties of ZnS under Pressure
International Nuclear Information System (INIS)
Xiang-Rong, Chen; Cui-E, Hu; Zhao-Yi, Zeng; Ling-Cang, Cai
2008-01-01
The pressure dependence of elastic properties of ZnS in zinc-blende (ZB) and wurtzite (WZ) structures are investigated by the generalized gradient approximation (GGA) within the plane-wave pseudopotential density functional theory (DFT). Our results are in good agreement with the available experimental data and other theoretical results. From the high-pressure elastic constants obtained, we find that the ZB and WZ structures of ZnS are unstable when the applied pressures are larger than 15.8 GPa and 21.3 GPa, respectively. The sound velocities along different directions for the two structures are also obtained. It is shown that as pressure increases, the sound velocities of the shear wave decrease, and those of all the longitudinal waves increase. An analysis has been made to reveal the anisotropy and highly noncentral forces in ZnS
First-principles study of structural stability and elastic property of pre-perovskite PbTiO3
International Nuclear Information System (INIS)
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 pre- perovskite PbTiO 3 (PP-PTO) and is constructed with TiO 6 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 pre- perovskite 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. (condensed matter: structural, mechanical, and thermal properties)
First-principles study of electronic and elastic properties of LuAl{sub 3}
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Shukla, Pushplata, E-mail: pujashukla50@gmail.com; Shrivastava, Deepika; Sanyal, Sankar P. [Department of Physics, Barkatullah university, Bhopal 462026 (India)
2016-05-06
A systematic theoretical study of electronic structure of rare earth intermetallic LuAl{sub 3} has been carried out using full potential linearized augmented plane wave (FP-LAPW) method based on density functional theory (DFT) within the generalized gradient approximation(GGA) for exchange and correlation potential. The ground state properties such as lattice constant (a{sub o}), bulk modulus (B) and pressure derivative of bulk modulus (B′) were evaluated. LuAl{sub 3} has the cubic AuCu{sub 3} type crystal structure. The electronic properties of this compound have been analyzed quantatively from band structure and DOS. It is clear from band structure that this compound is metallic in nature. The calculated elastic constants infer that this compound is mechanically stable.
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.
First principle electronic, structural, elastic, and optical properties of strontium titanate
Directory of Open Access Journals (Sweden)
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.
First principle electronic, structural, elastic, and optical properties of strontium titanate
Ekuma, Chinedu E.; Jarrell, Mark; Moreno, Juana; Bagayoko, Diola
2012-03-01
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.
International Nuclear Information System (INIS)
Thore, A.; Dahlqvist, M.; Alling, B.; Rosén, J.
2014-01-01
In this paper, we report the by first-principles predicted properties of the recently discovered magnetic MAX phase Mn 2 GaC. The electronic band structure and vibrational dispersion relation, as well as the electronic and vibrational density of states, have been calculated. The band structure close to the Fermi level indicates anisotropy with respect to electrical conductivity, while the distribution of the electronic and vibrational states for both Mn and Ga depend on the chosen relative orientation of the Mn spins across the Ga sheets in the Mn–Ga–Mn trilayers. In addition, the elastic properties have been calculated, and from the five elastic constants, the Voigt bulk modulus is determined to be 157 GPa, the Voigt shear modulus 93 GPa, and the Young's modulus 233 GPa. Furthermore, Mn 2 GaC is found relatively elastically isotropic, with a compression anisotropy factor of 0.97, and shear anisotropy factors of 0.9 and 1, respectively. The Poisson's ratio is 0.25. Evaluated elastic properties are compared to theoretical and experimental results for M 2 AC phases where M = Ti, V, Cr, Zr, Nb, Ta, and A = Al, S, Ge, In, Sn.
Predicting elastic properties of β-HMX from first-principles calculations.
Peng, Qing; Rahul; Wang, Guangyu; Liu, Gui-Rong; Grimme, Stefan; De, Suvranu
2015-05-07
We investigate the performance of van der Waals (vdW) functions in predicting the elastic constants of β cyclotetramethylene tetranitramine (HMX) energetic molecular crystals using density functional theory (DFT) calculations. We confirm that the accuracy of the elastic constants is significantly improved using the vdW corrections with environment-dependent C6 together with PBE and revised PBE exchange-correlation functionals. The elastic constants obtained using PBE-D3(0) calculations yield the most accurate mechanical response of β-HMX when compared with experimental stress-strain data. Our results suggest that PBE-D3 calculations are reliable in predicting the elastic constants of this material.
Elastic, dynamical, and electronic properties of LiHg and Li3Hg: First-principles study
Wang, Yan; Hao, Chun-Mei; Huang, Hong-Mei; Li, Yan-Ling
2018-04-01
The elastic, dynamical, and electronic properties of cubic LiHg and Li3Hg were investigated based on first-principles methods. The elastic constants and phonon spectral calculations confirmed the mechanical and dynamical stability of the materials at ambient conditions. The obtained elastic moduli of LiHg are slightly larger than those of Li3Hg. Both LiHg and Li3Hg are ductile materials with strong shear anisotropy as metals with mixed ionic, covalent, and metallic interactions. The calculated Debye temperatures are 223.5 K and 230.6 K for LiHg and Li3Hg, respectively. The calculated phonon frequency of the T2 g mode in Li3Hg is 326.8 cm-1. The p states from the Hg and Li atoms dominate the electronic structure near the Fermi level. These findings may inspire further experimental and theoretical study on the potential technical and engineering applications of similar alkali metal-based intermetallic compounds.
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.
International Nuclear Information System (INIS)
Sharma, V.; Pilania, G.
2013-01-01
Using first principles computations, we have investigated the structural, electronic, magnetic, optical and elastic properties of Fe 2 YAl (Y=Ti, V and Cr) Heusler alloys. The present study reveals that for the majority-spin state, Fe 2 CrAl compound has high density of states and shows a 100% spin polarization in the vicinity of the Fermi level. Our results also suggest that both the electronic and magnetic properties and also the Fermi surface of the Fe 2 CrAl are intrinsically related to the appearance of the minority-spin gap. The origin of energy gap in the minority-spin states is discussed in terms of the d–d hybridization between the Fe and Cr atoms. The Fermi surface structure and optical properties are explored within the framework of the full potential linearized augmented plane wave (FP-LAPW) method. The origin of Fermi surface structure is discussed in terms of energy bands in the majority-spin states near the Fermi level. The calculated dielectric functions and other optical properties are found to be in good agreement with earlier experimental results. In addition, the independent elastic constants of these Heusler alloys are also derived from the derivative of total energy as a function of lattice strain in full detail. The analysis of the ratio between the bulk and shear moduli confirms that all three compounds are found to be brittle in nature. Furthermore, as a representative case, we have also carried out the spin-polarized relativistic Korringa–Kohn–Rostoker (SPR-KKR) method based on calculations to obtain the magnetic Compton profiles (MCPs) for momentum transfer along [100], [110], and [111] principal directions and also investigated the anisotropy in the spin-dependent Compton profiles. - Highlights: • We report the electronic, magnetic, optical and elastic properties of some Heusler alloys. • The Fermi surface is discussed in terms of energy bands in the vicinity of Fermi level. • The anisotropy in the directional magnetic
Energy Technology Data Exchange (ETDEWEB)
Zhang, Yun; Wang, Zhe [Department of Physics, Xiangtan University, Xiangtan, 411105 Hunan (China); Cao, Juexian, E-mail: jxcao@xtu.edu.cn [Department of Physics, Xiangtan University, Xiangtan, 411105 Hunan (China); Beijing Computational Science Reasearch Center, 100084 Beijing (China)
2014-11-15
Using the first-principles full-potential linearized augmented plane-wave method, we investigated the stability, elastic and magnetostrictive properties of γ-Fe{sub 4}C and its derivatives. From the formation energy, we show that the most preferable configuration for MFe{sub 3}C (M=Pd, Pt, Rh, Ir) is that the M atom occupies the corner 1a position rather than 3c position. These derivatives are ductile due to high B/G values except for IrFe{sub 3}C. The calculated tetragonal magnetostrictive coefficient λ{sub 001} value for γ-Fe{sub 4}C is −380 ppm, which is larger than the value of Fe{sub 83}Ga{sub 17} (+207 ppm). Due to the strong SOC coupling strength constant (ξ) of Pt, the calculated λ{sub 001} of PtFe{sub 3}C is −691 ppm, which is increased by 80% compared to that of γ-Fe{sub 4}C. We demonstrate the origin of giant magnetostriction coefficient in terms of electronic structures and their responses to the tetragonal lattice distortion. - Highlights: • The most preferable site for M atom of MFe{sub 3}C (M=Pd, Pt, Rh, Ir) is the corner position. • The magnetostrictive coefficient for γ-Fe{sub 4}C is −380 ppm, larger than the value of Fe{sub 83}Ga{sub 17}. • The calculated λ{sub 001} of PtFe{sub 3}C is −691 ppm, which is increased by 80% compared to that of γ-Fe{sub 4}C.
First-principle calculations of structural, electronic, optical, elastic ...
Indian Academy of Sciences (India)
S CHEDDADI
2017-11-28
Nov 28, 2017 ... Abstract. First-principle calculations on the structural, electronic, optical, elastic and thermal properties of the chalcopyrite MgXAs2 (X = Si, Ge) have been performed within the density functional theory (DFT) using the full- potential linearized augmented plane wave (FP-LAPW) method. The obtained ...
Energy Technology Data Exchange (ETDEWEB)
Wang, Chenju [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics; Institute of Fluid Physics, Sichuan (China). National Key Laboratory of Shock Wave and Detonation Physics; Gu, Jianbing [Institute of Fluid Physics, Sichuan (China). National Key Laboratory of Shock Wave and Detonation Physics; Sichuan Univ., Chengdu (China). College of Physical Science and Technology; Kuang, Xiaoyu [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics; Xiang, Shikai [Institute of Fluid Physics, Sichuan (China). National Key Laboratory of Shock Wave and Detonation Physics
2015-10-01
Nonlinear elastic properties of diamond-cubic silicon and germanium have not been investigated sufficiently to date. Knowledge of these properties not only can help us to understand nonlinear mechanical effects but also can assist us to have an insight into the related anharmonic properties, so we investigate the nonlinear elastic behaviour of single silicon and germanium by calculating their second- and third-order elastic constants. All the results of the elastic constants show good agreement with the available experimental data and other theoretical calculations. Such a phenomenon indicates that the present values of the elastic constants are accurate and can be used to further study the related anharmonic properties. Subsequently, the anharmonic properties such as the pressure derivatives of the second-order elastic constants, Grueneisen constants of long-wavelength acoustic modes, and ultrasonic nonlinear parameters are explored. All the anharmonic properties of silicon calculated in the present work also show good agreement with the existing experimental results; this consistency not only reveals that the calculation method of the anharmonic properties is feasible but also illuminates that the anharmonic properties obtained in the present work are reliable. For the anharmonic properties of germanium, since there are no experimental result and other theoretical data till now, we hope that the anharmonic properties of germanium first offered in this work would serve as a reference for future studies.
First-principles study on mechanical and elastic properties of BxAl1-xP alloys
Directory of Open Access Journals (Sweden)
Huihui Ma
2017-06-01
Full Text Available Based on density functional theory calculations, systematic calculations of the structural properties, elastic anisotropy and mechanical properties of boron alloying aluminum phosphide (BxAl1-xP ternary mixed crystal have been presented. The results of the lattice parameters, band gaps, elastic constants and elastic modulus accord with the experimental and others published data well. The band structure which is described by CASTEP method indicates they are direct gap semiconductors for the composition x = 0.25, 0.50 and 0.75. Beyond that, we studied the Debye temperatures together with the acoustic velocities for all the BxAl1-xP alloys using the obtained elastic modulus. Finally, we depicted the three dimensional surface constructions to explain the elastic anisotropy using several calculated different anisotropic indexes in our work.
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.
Fernando L. Dri; Louis G. Jr. Hector; Robert J. Moon; Pablo D. Zavattieri
2013-01-01
In spite of the significant potential of cellulose nanocrystals as functional nanoparticles for numerous applications, a fundamental understanding of the mechanical properties of defect-free, crystalline cellulose is still lacking. In this paper, the elasticity matrix for cellulose IÃ with hydrogen bonding network A was calculated using ab initio...
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.
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.
Qing, Lu; Huai-Yong, Zhang; Yan, Cheng; Xiang-Rong, Chen; Guang-Fu, Ji
2016-02-01
The phase transition, elastic and electronic properties of three phases (phase I, II, and III) of Sb2Te3 are investigated by using the generalized gradient approximation (GGA) with the PBESOL exchange-correlation functional in the framework of density-functional theory. Some basic physical parameters, such as lattice constants, bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, acoustic velocity, and Debye temperature Θ are calculated. The obtained lattice parameters under various pressures are consistent with experimental data. Phase transition pressures are 9.4 GPa (I → II) and 14.1 GPa (II → III), which are in agreement with the experimental results. According to calculated elastic constants, we also discuss the ductile or brittle characters and elastic anisotropies of three phases. Phases I and III are brittle, while phase II is ductile. Of the three phases, phase II has the most serious degree of elastic anisotropy and phase III has the slightest one. Finally, we investigate the partial densities of states (PDOSs) of three phases and find that the three phases possess some covalent features. Project supported by the National Natural Science Foundation of China (Grant Nos. 11204192 and 11174214) and Jointly supported by the National Natural Science Foundation of China and the China Academy of Engineering Physics (NSAF) (Grant No. U1430117).
A first principle study of the pressure dependent elastic properties of monazite LaPO{sub 4}
Energy Technology Data Exchange (ETDEWEB)
Ali, Kawsar, E-mail: ali.ksr71@gmail.com; Arya, A.; Ghosh, P. S.; Dey, G. K. [Material Science Division, Bhabha Atomic Research centre, Mumbai 400085 (India)
2016-05-06
DFT based ab-initio simulations have been performed to study the effect of pressure on the elastic properties of monazite LaPO{sub 4} which is a promising host material for immobilization of high level nuclear waste. The phase is found to be stable up to 30 GPa. The calculated polycrystalline bulk, shear and Young moduli show an increasing trend as a function of pressure. The ductility and anisotropy in shear modulus of the material have been found to increase with pressure; whilethe bulk modulus anisotropy decreases with pressure.
Energy Technology Data Exchange (ETDEWEB)
Liu, Na; Wang, Xueye, E-mail: wxueye@xtu.edu.cn; Wan, Yali
2015-07-15
The effects of pressure on the structural, elastic and electronic properties of Ir{sub 3}Zr are investigated by means of the first-principles calculations based on the density functional theory with generalized gradient approximation and local density approximation methods. The calculated lattice parameters and elastic modulus of Ir{sub 3}Zr at zero pressure are in good agreement with available experimental and theoretical results. The values of elastic constants (C{sub 11}, C{sub 12}, C{sub 44}), bulk modulus (B), shear modulus (G), Young modulus (E), Poisson's ratio (υ), anisotropy index (A) and Debye temperature (T{sub D}) present the linearly increasing dependences on the external pressure. Additionally, the B/G values exhibit an upward trend with increasing pressure, which means that higher pressure can improve its ductility. Ir{sub 3}Zr exhibits a brittle characteristic at zero pressure. When the pressure reaches 10 GPa, the Cauchy pressure and B/G value show ductile feature. In addition, the pressure-dependence behavior of density of states, Mulliken charge and bond length are analyzed. - Graphical abstract: Display Omitted - Highlights: • The elastic and electronic properties of Ir{sub 3}Zr under pressure are investigated. • The elastic constants, elastic moduli increase with the pressure increasing. • When the pressure reaches 10 GPa, Ir{sub 3}Zr changes from brittle to ductile. • Ir{sub 3}Zr remains as a stable structure and no structural transition under pressure.
Energy Technology Data Exchange (ETDEWEB)
Li, Li; Wang, Y.-J. [College of Mathematics and Physics, Chongqing University of Posts and Telecommunications, 2 Chongwen Road, Nan' an District, Chongqing 400065 (China); Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland); Liu, D.-X.; Ma, C.-G. [College of Mathematics and Physics, Chongqing University of Posts and Telecommunications, 2 Chongwen Road, Nan' an District, Chongqing 400065 (China); Brik, M.G., E-mail: mikhail.brik@ut.ee [College of Mathematics and Physics, Chongqing University of Posts and Telecommunications, 2 Chongwen Road, Nan' an District, Chongqing 400065 (China); Institute of Physics, University of Tartu, W. Ostwald Str. 1, Tartu 50411 (Estonia); Institute of Physics, Jan Długosz University, Armii Krajowej 13/15, PL-42200 Częstochowa (Poland); Suchocki, A. [College of Mathematics and Physics, Chongqing University of Posts and Telecommunications, 2 Chongwen Road, Nan' an District, Chongqing 400065 (China); Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland); Institute of Physics, Kazimierz Wielki University, Weyssenhoffa 11, 85-072 Bydgoszcz (Poland); Piasecki, M. [Institute of Physics, Jan Długosz University, Armii Krajowej 13/15, PL-42200 Częstochowa (Poland); Reshak, A.H. [New Technologies – Research Centre, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia)
2017-02-15
Three fluoroperovskites with the general formula XCaF{sub 3} (X = K, Rb, Cs) have been systematically studied using the first-principles methods. The structural, electronic, optical, elastic and thermodynamic properties of these three compounds were calculated at the ambient and elevated hydrostatic pressure. Variation of all these properties with pressure was analyzed; it was shown that the structural and elastic constants change linearly with increased pressure, whereas the calculated band gaps follow the quadratic dependence on pressure. Influence of the first cation variation (K – Rb – Cs) on these properties was discussed. Elastic anisotropy (directional dependence of the Young moduli) of these compounds was modeled and analyzed for the first time. - Highlights: • Three cubic perovskites XCaF{sub 3} (X = K, Rb, Cs) were studied by ab initio methods. • Systematic variation of physical properties with the first cation change was traced. • Pressure effects on physical properties were calculated and modeled. • Debye temperature and Grüneisen constant for all materials were calculated for the first time. • Elastic anisotropy was visualized by plotting Young moduli directional dependences.
Saadaoui, Fatiha; Driss Khodja, Fatima Zohra; Kadoun, Abd-Ed-Daïm; Driss Khodja, Mohammed; Elias, Abdelkader; Boudali, Abdelkader
2015-12-01
We have performed first-principles calculations of structural, elastic, thermodynamic, and electronic properties of anti-perovskites AIIICNi3 (AIII = Al, Ga, In), by using the full-potential linearized augmented plane wave (FP-LAPW) method combined with the quasi-harmonic Debye model. We carried out our calculations within the local density approximation (LDA) and the generalized gradient approximation (GGA-PBE and GGA-PBEsol functionals). Our results constitute interesting first predictions in the case of many elastic parameters of the anti-perovskites AIIICNi3, among them elastic parameters of AlCNi3 and GaCNi3 and some polycrystalline elastic parameters of InCNi3. We also report for the first time calculated values, at ambient conditions, of Grüneisen parameter, thermal expansion coefficient, specific heat at constant pressure, specific heat at constant volume, isothermal bulk modulus, and adiabatic bulk modulus for AlCNi3, GaCNi3, and InCNi3. Band structure, total and partial densities of states, and charge density have been obtained and analyzed. Electronic structure results show metallic behavior for the three compounds. Ni 3 d states play dominant role near the Fermi level and there is a strong hybridization between Ni 3 d and C 2 p states. In addition, as AIIICNi3 synthesized samples are expected to be carbon-deficient, we calculated structural, elastic, and thermodynamic properties of sub-stoichiometric AlC x Ni3 materials.
Directory of Open Access Journals (Sweden)
C. Li
2015-07-01
Full Text Available In this paper, the basic electronic structures and elastic properties of Ni3Al doping with alloying elements (Re, Cr, and Mo under different pressures have been investigated using first-principles calculations based on density functional theory. It is shown that both alloying elements and external applied pressure contribute positively to the elastic properties of Ni3Al, and the configurations of the compounds remain almost unchanged. The calculated elastic constants and moduli increase linearly with the pressure increasing from 0 and 40 GPa. Among the alloying elements studied in the present work, Re exhibits the most significant effect compared with the other elements, showing its practical importance. Especially, if both alloying elements doping and pressure effects are considered simultaneously, which has not been considered previously, the studied compounds exhibit an even better elastic property than the simple superposition of the two influences. Such synergistic effect demonstrates promising applications of Ni-based single crystal superalloys in possible extreme mechanical environments.
Liu, Lili
2014-05-22
We present theoretical studies for the third-order elastic constants (TOECs) of superconducting antiperovskites MNNi 3 (M = Zn, Cd, Mg, Al, Ga, and In) using the density functional theory (DFT) and homogeneous deformation method. From the nonlinear least-square fitting, the elastic constants are extracted from a polynomial fit to the calculated strain-energy data. Calculated second-order elastic constants (SOECs) are compared with the previous theoretical calculations, and a very good agreement was found. The nonlinear effects often play an important role when the finite strains are larger than approximately 2.5 %. Besides, we have computed the pressure derivatives of SOECs and provided rough estimations for the Grüneisen constants of long-wavelength acoustic modes by using the calculated TOECs. © 2014 Springer Science+Business Media New York.
International Nuclear Information System (INIS)
Pan, Y.; Zheng, W.T.; Guan, W.M.; Zhang, K.H.; Fan, X.F.
2013-01-01
The structural formation, elastic properties, hardness and electronic structure of TMB 4 (TM=Cr, Re, Ru and Os) compounds are investigated using first-principles approach. The value of C 22 for these compounds is almost two times bigger than the C 11 and C 33 . The intrinsic hardness, shear modulus and Young's modulus are calculated to be in a sequence of CrB 4 >ReB 4 >RuB 4 >OsB 4 , and the Poisson's ratio and B/G ratio of TMB 4 follow the order of CrB 4 4 4 4 . The intrinsic hardness of CrB 4 and ReB 4 by LDA is bigger than 40 GPa. The high hardness of TMB 4 compounds is derived from the feature of B–B bonds cage and higher C 22 value. The B–B covalent bonds as bonds cage enhances the resistance to shear deformation and improve the hardness. We predict that the TMB 4 compounds with CrB 4 -type are the potential superhard materials. - Graphical abstract: The first-principles calculations show that the intrinsic hardness of CrB 4 and ReB 4 are bigger than 40 GPa, which are the potential superhard materials due to the B–B bonds cage structure. Display Omitted - Highlights: • The intrinsic hardness of CrB 4 and ReB 4 is bigger than 40 GPa. • The hardness of TMB 4 is calculated to be in a sequence of CrB 4 >ReB 4 >RuB 4 >OsB 4 . • The trend of hardness for TMB 4 is consistent with the variation of elastic modulus. • The C 22 value of TMB 4 is bigger than that of C 11 and C 33 . • The high hardness of TMB 4 is originated from the B–B bonds cage
Cheddadi, S.; Boubendira, K.; Meradji, H.; Ghemid, S.; Hassan, F. El Haj; Lakel, S.; Khenata, R.
2017-12-01
First-principle calculations on the structural, electronic, optical, elastic and thermal properties of the chalcopyrite MgXAs2 (X=Si, Ge) have been performed within the density functional theory (DFT) using the full-potential linearized augmented plane wave (FP-LAPW) method. The obtained equilibrium structural parameters are in good agreement with the available experimental data and theoretical results. The calculated band structures reveal a direct energy band gap for the interested compounds. The predicted band gaps using the modified Becke-Johnson (mBJ) exchange approximation are in fairly good agreement with the experimental data. The optical constants such as the dielectric function, refractive index, and the extinction coefficient are calculated and analysed. The independent elastic parameters namely, C_{11}, C_{12}, C_{13}, C_{33}, C_{44} and C_{66 } are evaluated. The effects of temperature and pressure on some macroscopic properties of MgSiAs2 and MgGeAs2 are predicted using the quasiharmonic Debye model in which the lattice vibrations are taken into account.
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)
Pandech, Narasak; Limpijumnong, Sukit, E-mail: sukit@sut.ac.th [School of Physics and NANOTEC-SUT Center of Excellence on Advanced Functional Nanomaterials, Suranaree University of Technology, Nakhon Ratchasima 30000 (Thailand); Synchrotron Light Research Institute, Nakhon Ratchasima 30000 (Thailand); Thailand Center of Excellence in Physics (ThEP Center), Commission on Higher Education, Bangkok 10400 (Thailand); Sarasamak, Kanoknan [College of Nanotechnology, King Mongkut' s Institute of Technology Ladkrabang, Bangkok 10520 (Thailand)
2015-05-07
The mechanical properties of perovskite oxides depend on two metal oxide lattices that are intercalated. This provides an opportunity for separate tuning of hardness, Poisson's ratio (transverse expansion in response to the compression), and shear strength. The elastic constants of series of perovskite oxides were studied by first principles approach. Both A-site and B-site cations were systematically varied in order to see their effects on the elastic parameters. To study the effects of A-site cations, we studied the elastic properties of perovskite ATiO{sub 3} for A being Be, Mg, Ca, Sr, or Ba, one at a time. Similarly, for B-site cations, we studied the elastic properties of PbBO{sub 3} for B being Ti, Zr, or Hf, one at a time. The density functional first principles calculations with local density approximation (LDA) and generalized gradient approximation (GGA) were employed. It is found that the maximum C{sub 11} elastic constant is achieved when the atomic size of the cations at A-site and B-site are comparable. We also found that C{sub 12} elastic constant is sensitive to B-site cations while C{sub 44} elastic constant is more sensitive to A-site cations. Details and explanations for such dependencies are discussed.
International Nuclear Information System (INIS)
Pandech, Narasak; Limpijumnong, Sukit; Sarasamak, Kanoknan
2015-01-01
The mechanical properties of perovskite oxides depend on two metal oxide lattices that are intercalated. This provides an opportunity for separate tuning of hardness, Poisson's ratio (transverse expansion in response to the compression), and shear strength. The elastic constants of series of perovskite oxides were studied by first principles approach. Both A-site and B-site cations were systematically varied in order to see their effects on the elastic parameters. To study the effects of A-site cations, we studied the elastic properties of perovskite ATiO 3 for A being Be, Mg, Ca, Sr, or Ba, one at a time. Similarly, for B-site cations, we studied the elastic properties of PbBO 3 for B being Ti, Zr, or Hf, one at a time. The density functional first principles calculations with local density approximation (LDA) and generalized gradient approximation (GGA) were employed. It is found that the maximum C 11 elastic constant is achieved when the atomic size of the cations at A-site and B-site are comparable. We also found that C 12 elastic constant is sensitive to B-site cations while C 44 elastic constant is more sensitive to A-site cations. Details and explanations for such dependencies are discussed
Wang, Yun-Jiang; Wang, Chong-Yu
2009-10-01
A model system consisting of Ni[001](100)/Ni3Al[001](100) multi-layers are studied using the density functional theory in order to explore the elastic properties of single crystal Ni-based superalloys. Simulation results are consistent with the experimental observation that rafted Ni-base superalloys virtually possess a cubic symmetry. The convergence of the elastic properties with respect to the thickness of the multilayers are tested by a series of multilayers from 2γ'+2γ to 10γ'+10γ atomic layers. The elastic properties are found to vary little with the increase of the multilayer's thickness. A Ni/Ni3Al multilayer with 10γ'+10γ atomic layers (3.54 nm) can be used to simulate the mechanical properties of Ni-base model superalloys. Our calculated elastic constants, bulk modulus, orientation-dependent shear modulus and Young's modulus, as well as the Zener anisotropy factor are all compatible with the measured results of Ni-base model superalloys R1 and the advanced commercial superalloys TMS-26, CMSX-4 at a low temperature. The mechanical properties as a function of the γ' phase volume fraction are calculated by varying the proportion of the γ and γ' phase in the multilayers. Besides, the mechanical properties of two-phase Ni/Ni3Al multilayer can be well predicted by the Voigt-Reuss-Hill rule of mixtures.
Directory of Open Access Journals (Sweden)
H.Y. Wang
2012-03-01
Full Text Available The density-functional theory (DFT and density-functional perturbation theory (DFPT are employed to study the pressure dependence of elastic and dynamical properties of zinc-blende ZnS and ZnSe. The calculated elastic constants and phonon spectra from 0 GPa to 15 GPa are compared with the available experimental data. Generally, our calculated values are overestimated with experimental data, but agree well with recent other theoretical values. The discrepancies with experimental data are due to the use of local density approximation (LDA and effect of temperature. In this work, in order to compare with experimental data, we calculated and discussed the pressure derivatives of elastic constants, the pressure dependence of dynamical effect charge, and mode Grüneisen parameter at Γ.
First-principles study of thermal properties of borophene.
Sun, Hongyi; Li, Qingfang; Wan, X G
2016-06-01
Very recently, a new single-element two-dimensional (2D) material borophene was successfully grown on a silver surface under pristine ultrahigh vacuum conditions which attracts tremendous interest. In this paper, the lattice thermal conductivity, phonon lifetimes, thermal expansion and temperature dependent elastic moduli of borophene are systematically studied by using first-principles. Our simulations show that borophene possesses unique thermal properties. Strong phonon-phonon scattering is found in borophene, which results in its unexpectedly low lattice thermal conductivity. Thermal expansion coefficients along both the armchair and zigzag directions of borophene show impressive negative values. More strikingly, the elastic moduli are sizably strengthened as temperature increases, and the negative in-plane Poisson's ratios are found along both the armchair and zigzag directions at around 120 K. The mechanisms of these unique thermal properties are also discussed in this paper.
Energy Technology Data Exchange (ETDEWEB)
Sajjad, M. [School of Electronic Engineering, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Alay-e-Abbas, S.M. [Department of Physics, University of Sargodha, Sargodha 40100 (Pakistan); Department of Physics, Government College University, Faisalabad, Allama Iqbal Road, Faisalabad 38000 (Pakistan); Zhang, H.X. [School of Electronic Engineering, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Beijing Key Laboratory of Work Safety Intelligent Monitoring (Beijing University of Posts and Telecommunications), Beijing 100876 (China); Noor, N.A. [Centre for High Energy Physics, University of the Punjab, Quaid-e-Azam Campus, 54590 Lahore (Pakistan); Saeed, Y. [Department of Physics, Government College University, Faisalabad, Allama Iqbal Road, Faisalabad 38000 (Pakistan); Shakir, Imran [Deanship of scientific research, College of Engineering, King Saud University, P. O. BOX 800, Riyadh 11421 (Saudi Arabia); Shaukat, A., E-mail: schaukat@gmail.com [Department of Physics, University of Sargodha, Sargodha 40100 (Pakistan)
2015-09-15
We investigate zinc-blende phase Al{sub 0.75}Mn{sub 0.25}Y (Y=N, P, As) compounds using full-potential linear-augmented-plane wave plus local-orbital method. For computing structural and elastic properties the Generalized Gradient Approximation (GGA) has been used; whereas the electronic and magnetic properties are examined at the optimized GGA lattice parameters by employing modified Becke and Johnson local density approximation. All these compounds are found to be stable in ferromagnetic ordering in the zinc-blende structure which is supported by the computed elastic constants. The nature of electronic band structure are calculated and the nature of band gaps in the doped system is analyzed. The results are examined to identify exchange mechanism which is the main source of introducing ferromagnetism in the compounds under investigation. Spin charge density contour plots in the (1 1 0) plane and the evaluation of s–p and p–d exchange constants (N{sub 0}α and N{sub 0}β) are evaluated for understanding bonding and exchange splitting process, respectively. - Highlights: • Spin-polarized DFT investigation Mn-doped AlN, AlP and AlAs is reported. • Structrual and elastic properites are computed for evaluating stability. • mBJLDA used for appropriate treatment of d states of Mn for electronic properties. • Half metallicity, ferromagnetic stability and exchange constants are evaluated.
International Nuclear Information System (INIS)
Brik, M.G.
2011-01-01
Detailed ab initio calculations of the structural, electronic, optical and elastic properties of two crystals - magnesite (MgCO 3 ) and calcite (CaCO 3 ) - are reported in the present paper. Both compounds are important natural minerals, playing an important role in the carbon dioxide cycling. The optimized crystal structures, band gaps, density of states diagrams, elastic constants, optical absorption spectra and refractive indexes dependence on the wavelength all have been calculated and compared, when available, with literature data. Both crystals are indirect band compounds, with calculated band gaps of 5.08 eV for MgCO 3 and 5.023 eV for CaCO 3 . Both values are underestimated by approximately 1.0 eV with respect to the experimental data. Although both crystals have the same structure, substitution of Mg by Ca ions leads to certain differences, which manifest themselves in noticeable change in the electronic bands profiles and widths, shape of the calculated absorption spectra, and values of the elastic constants. Response of both crystals to the applied hydrostatic pressure was analyzed in the pressure range of phase stability, variations of the lattice parameters and characteristic interionic distances were considered. The obtained dependencies of lattice constants and calculated band gap on pressure can be used for prediction of properties of these two hosts at elevated pressures that occur in the Earth's mantle. -- Research highlights: → Ab initio calculations of physical properties of MgCO 3 and CaCO 3 were performed. → Changes of the calculated properties with replacement of Mg by Ca were followed. → Pressure dependence of the structural and electronic properties was analyzed. → Good agreement with experimental data was demonstrated.
International Nuclear Information System (INIS)
Fatmi, M; Ghebouli, B; Ghebouli, M A; Hieba, Z K
2011-01-01
We have applied the pseudo-potential plane wave method to study the structural, elastic, electronic, lattice dynamic and optical properties of GaN and AlN in the wurtzite lattice and BN with zinc-blende structure. We have found that all elastic constants depend strongly on hydrostatic pressure, except for C 44 in wurtzite AlN and GaN that shows a weaker dependence. AlN and GaN present a direct band gap Γ-Γ, whereas BN has an indirect band gap Γ-X. The indirect Γ-K band gap in AlN occurs at about 35 GPa. The top of the valence bands reflects the p electronic character for all structures. There is a gap between optical and acoustic modes only for wurtzite phases AlN and GaN. All peaks in the imaginary part of the dielectric function for the wurtzite lattice GaN and AlN move towards lower energies, while those in the zinc-blende BN structure shift towards higher energies with increasing pressure. The decrease of the static dielectric constant and static refractive index in zinc-blende BN is weaker and it can be explained by its higher elastic constants.
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.
International Nuclear Information System (INIS)
Ghebouli, B.; Ghebouli, M.A.; Fatmi, M.; Chihi, T.; Boucetta, S.
2010-01-01
Research highlights: → The range of compositions for which the alloy is lattice matched to AlP is determined. → We study the variation of elastic constants, the optical phonon frequencies (ω TO and ω LO ), the high-frequency dielectric coefficient ε(∞) and the dynamic effective charge Z * with P concentration. - Abstract: Information on the energy band gaps, the lattice parameters and the lattice matching to available substrates is a prerequisite for many practical applications. A pseudopotential plane-wave method as implemented in the ABINIT code is used to the As x P y N 1-x-y Al quaternary alloys lattice matched to AlP substrate to predict their energy band gaps and optical properties. The range of compositions for which the alloy is lattice-matched to AlP is determined. Very good agreement is obtained between the calculated values and the available experimental data. The Debye temperature increase when the bulk modulus is enhanced. We study the variation of elastic constants, the optical phonon frequencies (ω TO and ω LO ), the static and high-frequency dielectric coefficient ε(0) and ε(∞) and the dynamic effective charge Z * with P concentration (y).
Thermophysical properties of paramagnetic Fe from first principles
Ehteshami, Hossein; Korzhavyi, Pavel A.
2017-12-01
A computationally efficient, yet general, free-energy modeling scheme is developed based on first-principles calculations. Finite-temperature disorder associated with the fast (electronic and magnetic) degrees of freedom is directly included in the electronic structure calculations, whereas the vibrational free energy is evaluated by a proposed model that uses elastic constants to calculate average sound velocity of the quasiharmonic Debye model. The proposed scheme is tested by calculating the lattice parameter, heat capacity, and single-crystal elastic constants of α -, γ -, and δ -iron as functions of temperature in the range 1000-1800 K. The calculations accurately reproduce the well-established experimental data on thermal expansion and heat capacity of γ - and δ -iron. Electronic and magnetic excitations are shown to account for about 20% of the heat capacity for the two phases. Nonphonon contributions to thermal expansion are 12% and 10% for α - and δ -Fe and about 30% for γ -Fe. The elastic properties predicted by the model are in good agreement with those obtained in previous theoretical treatments of paramagnetic phases of iron, as well as with the bulk moduli derived from isothermal compressibility measurements [N. Tsujino et al., Earth Planet. Sci. Lett. 375, 244 (2013), 10.1016/j.epsl.2013.05.040]. Less agreement is found between theoretically calculated and experimentally derived single-crystal elastic constants of γ - and δ -iron.
Benyelloul, Kamel; Seddik, Larbi; Bouhadda, Youcef; Bououdina, Mohamed; Aourag, Hafid; Khodja, Khadidja
2017-12-01
The effect of pressure on structural stability, elastic properties and Debye temperature of face centered cubic Mg7TMH16 (TM = Sc, Ti, V, Y, Zr and Nb) hydrides, was investigated by first-principles calculations based on density functional theory (DFT) with the generalized gradient approximation (GGA). The obtained equilibrium lattice parameters and elastic properties at zero pressure for MgH2 and Mg7TMH16 hydrides, are in good agreement with other experimental and theoretical values. The calculations of the bulk modulus and the ductility factors (B/G) show that mixing (MgH2) with small amount of transition metal (TM = Sc, Ti, V, Y, Zr and Nb) can enhance the resistance to volume change and transform it from a brittle to a ductile material (brittle → ductile). The elastic constants, bulk modulus, shear modulus, Young's modulus, anisotropy factor and hardness have been studied under pressure. These mechanical quantities are found to increase with increasing pressure. While the B/G and Poisson's ratios (v) undergo an inverse behaviour. In addition to that, the studied hydrides are found stable with a ductile behaviour under a pressure between 0 and 20 GPa. Furthermore, the effect of pressure on Debye temperature and sound velocity, was also investigated and discussed.
Energy Technology Data Exchange (ETDEWEB)
Thakur, Anil, E-mail: anil-t2001@yahoo.com; Kashyap, Rajinder [Department of Physics, Govt. P. G. College Solan-173212, Himachal Pradesh (India); Sharma, Nalini; Ahluwalia, P. K. [Department of Physics, Himachal Pradesh University Shimla-171005, Himachal Pradesh (India)
2014-04-24
Study of atomic motions in the binary liquid alloys have been studied in terms of dynamical variables like velocity auto correlation, power spectrum and mean square displacement. Elastic constants and isothermal bulk modulus have been calculated to see the effeectiveness of ab-initio pseudopotentials which has been used in this paper. This appraoch is free from the fitting parameters and results obtained using this appraoch have been found very close to the average values.
First-principle calculations of structural, electronic, optical, elastic ...
Indian Academy of Sciences (India)
S CHEDDADI
2017-11-28
Nov 28, 2017 ... The predicted band gaps using the modified Becke–Johnson. (mBJ) exchange approximation are in fairly good agreement with the experimental data. The optical constants such as the dielectric function, refractive index, and the extinction coefficient are calculated and analysed. The independent elastic ...
He, Li-Zhi; Zhu, Jun; Zhang, Lin
2018-02-01
Phase transition of TiCr2 in C15 (MgCu2), C36 (MgNi2), C14 (MgZn2) structures have been studied by using the projector augmented wave method. It is found that C15-type is the most stable structure, which agrees with the results of Chen et al. At 0 K, the phase boundary of C15 to C36 is 207.79 GPa, and the phase transition from C36 to C14 is 265.61 GPa. Both the transition pressures decrease with increasing temperature. Phonon dispersion and elastic constants are calculated and found that C15-type TiCr2 is mechanically stable according to the elastic stability criteria and phonon dispersion analysis. Moreover, the pressure and temperature dependence of the specific heat, Debye temperature and thermal expansion coefficient are discussed, among them our calculated Debye temperature is consistent with the report of A. sari et al., however, it is far from the results of B. Mayer et al. and Chen et al.
Energy Technology Data Exchange (ETDEWEB)
Boudrifa, O. [Laboratory for Developing New Materials and their Characterization, University of Setif 1, 19000 Setif (Algeria); Bouhemadou, A., E-mail: a_bouhemadou@yahoo.fr [Laboratory for Developing New Materials and their Characterization, University of Setif 1, 19000 Setif (Algeria); Guechi, N. [Department of Physics, Faculty of Science, University of Setif 1, 19000 Setif (Algeria); Bin-Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Department of Physics, Faculty of Science and Humanitarian Studies, Salman Bin Abdalaziz University, Alkharj 11942 (Saudi Arabia); Al-Douri, Y. [Institute of Nano Electronic Engineering, Universiti Malaysia Perlis, 01000 Kangar, Perlis (Malaysia); Khenata, R. [Laboratoire de Physique Quantique et de Modélisation Mathématique (LPQ3M), Département de Technologie, Université de Mascara, 29000 Mascara (Algeria)
2015-01-05
Highlights: • Some physical properties of the quaternary nitride Li{sub 4}Sr{sub 3}Ge{sub 2}N{sub 6} have been predicted. • Elastic parameters reveal that Li{sub 4}Sr{sub 3}Ge{sub 2}N{sub 6} is mechanically stable but anisotropi. • Li{sub 4}Sr{sub 3}Ge{sub 2}N{sub 6} is an indirect semiconductor. • The fundamental indirect band gap changes to direct one under pressure effect. • The optical properties exhibit noticeable anisotropy. - Abstract: Structural parameters, elastic constants, thermodynamic properties, electronic structure and optical properties of the monoclinic Li{sub 4}Sr{sub 3}Ge{sub 2}N{sub 6} quaternary nitride are investigated theoretically for the first time using the pseudopotential plane-wave based first-principles calculations. The calculated structural parameters are in excellent agreement with the experimental data. This serves as a proof of reliability of the used theoretical method and gives confidence in the predicted results on aforementioned properties of Li{sub 4}Sr{sub 3}Ge{sub 2}N{sub 6}. The predicted elastic constants C{sub ij} reveal that Li{sub 4}Sr{sub 3}Ge{sub 2}N{sub 6} is mechanically stable but anisotropic. The elastic anisotropy is further illustrated by the direction-dependent of the linear compressibility and Young’s modulus. Macroscopic elastic parameters, including the bulk and shear moduli, the Young’s modulus, the Poisson ratio, the velocities of elastic waves and the Debye temperature are numerically estimated. The pressure and temperature dependence of the unit cell volume, isothermal bulk modulus, volume expansion coefficient, specific heat and Debye temperature are investigated through the quasiharmonic Debye model. The band structure and the density of states of Li{sub 4}Sr{sub 3}Ge{sub 2}N{sub 6} are analyzed, which reveals the semiconducting character of Li{sub 4}Sr{sub 3}Ge{sub 2}N{sub 6}. The complex dielectric function, refractive index, extinction coefficient, absorption coefficient, reflectivity
Branicio, Paulo S.; Vastola, Guglielmo; Jhon, Mark H.; Sullivan, Michael B.; Shenoy, Vivek B.; Srolovitz, David J.
2016-10-01
The deformation of graphene due to the chemisorption of hydrogen atoms on its surface and the long-range elastic interaction between hydrogen atoms induced by these deformations are investigated using a multiscale approach based on first principles, empirical interactions, and continuum modeling. Focus is given to the intrinsic low-temperature structure and interactions. Therefore, all calculations are performed at T =0 , neglecting possible temperature or thermal fluctuation effects. Results from different methods agree well and consistently describe the local deformation of graphene on multiple length scales reaching 500 Å . The results indicate that the elastic interaction mediated by this deformation is significant and depends on the deformation of the graphene sheet both in and out of plane. Surprisingly, despite the isotropic elasticity of graphene, within the linear elastic regime, atoms elastically attract or repel each other depending on (i) the specific site they are chemisorbed; (ii) the relative position of the sites; (iii) and if they are on the same or on opposite surface sides. The interaction energy sign and power-law decay calculated from molecular statics agree well with theoretical predictions from linear elasticity theory, considering in-plane or out-of-plane deformations as a superposition or in a coupled nonlinear approach. Deviations on the exact power law between molecular statics and the linear elastic analysis are evidence of the importance of nonlinear effects on the elasticity of monolayer graphene. These results have implications for the understanding of the generation of clusters and regular formations of hydrogen and other chemisorbed atoms on graphene.
ABINIT: First-principles approach to material and nanosystem properties
Gonze, X.; Amadon, B.; Anglade, P.-M.; Beuken, J.-M.; Bottin, F.; Boulanger, P.; Bruneval, F.; Caliste, D.; Caracas, R.; Côté, M.; Deutsch, T.; Genovese, L.; Ghosez, Ph.; Giantomassi, M.; Goedecker, S.; Hamann, D. R.; Hermet, P.; Jollet, F.; Jomard, G.; Leroux, S.; Mancini, M.; Mazevet, S.; Oliveira, M. J. T.; Onida, G.; Pouillon, Y.; Rangel, T.; Rignanese, G.-M.; Sangalli, D.; Shaltaf, R.; Torrent, M.; Verstraete, M. J.; Zerah, G.; Zwanziger, J. W.
2009-12-01
ABINIT [ http://www.abinit.org] allows one to study, from first-principles, systems made of electrons and nuclei (e.g. periodic solids, molecules, nanostructures, etc.), on the basis of Density-Functional Theory (DFT) and Many-Body Perturbation Theory. Beyond the computation of the total energy, charge density and electronic structure of such systems, ABINIT also implements many dynamical, dielectric, thermodynamical, mechanical, or electronic properties, at different levels of approximation. The present paper provides an exhaustive account of the capabilities of ABINIT. It should be helpful to scientists that are not familiarized with ABINIT, as well as to already regular users. First, we give a broad overview of ABINIT, including the list of the capabilities and how to access them. Then, we present in more details the recent, advanced, developments of ABINIT, with adequate references to the underlying theory, as well as the relevant input variables, tests and, if available, ABINIT tutorials. Program summaryProgram title: ABINIT Catalogue identifier: AEEU_v1_0 Distribution format: tar.gz Journal reference: Comput. Phys. Comm. Programming language: Fortran95, PERL scripts, Python scripts Computer: All systems with a Fortran95 compiler Operating system: All systems with a Fortran95 compiler Has the code been vectorized or parallelized?: Sequential, or parallel with proven speed-up up to one thousand processors. RAM: Ranges from a few Mbytes to several hundred Gbytes, depending on the input file. Classification: 7.3, 7.8 External routines: (all optional) BigDFT [1], ETSF IO [2], libxc [3], NetCDF [4], MPI [5], Wannier90 [6] Nature of problem: This package has the purpose of computing accurately material and nanostructure properties: electronic structure, bond lengths, bond angles, primitive cell size, cohesive energy, dielectric properties, vibrational properties, elastic properties, optical properties, magnetic properties, non-linear couplings, electronic and
First-principles investigations of the physical properties of RCd (R=Ce, La, Pr, Nd)
Long, Jianping
2012-12-01
The crystal structural, electronic, elastic and the thermodynamic properties of RCd are investigated by using the first-principles plane-wave pseudopotential density function theory within the generalized gradient approximation (GGA). The calculated equilibrium lattice parameters for RCd are in good agreement with the available experimental data. Furthermore, the optical properties, namely the dielectric function, refractive index and electron energy loss are reported for radiation up to 30 eV. Finally, the elastic properties, the bulk modulus and the Debye temperature of RCd are given for reference.
First-principles investigations of the physical properties of RCd (R=Ce, La, Pr, Nd)
Energy Technology Data Exchange (ETDEWEB)
Long Jianping, E-mail: jianpinglong@cdut.cn [College of Materials and Chemistry and Chemical Engineering, Chengdu University of Technology, Chengdu 610059 (China)
2012-12-15
The crystal structural, electronic, elastic and the thermodynamic properties of RCd are investigated by using the first-principles plane-wave pseudopotential density function theory within the generalized gradient approximation (GGA). The calculated equilibrium lattice parameters for RCd are in good agreement with the available experimental data. Furthermore, the optical properties, namely the dielectric function, refractive index and electron energy loss are reported for radiation up to 30 eV. Finally, the elastic properties, the bulk modulus and the Debye temperature of RCd are given for reference.
Nonlinear Elasticity of Borocarbide Superconductor YNi2B2C: A First-Principles Study
Directory of Open Access Journals (Sweden)
Lili Liu
2017-01-01
Full Text Available First-principles calculations combined with homogeneous deformation methods are used to investigate the second- and third-order elastic constants of YNi2B2C with tetragonal structure. The predicted lattice constants and second-order elastic constants of YNi2B2C agree well with the available data. The effective second-order elastic constants are obtained from the second- and third-order elastic constants for YNi2B2C. Based on the effective second-order elastic constants, Pugh’s modulus ratio, Poisson’s ratio, and Vickers hardness of YNi2B2C under high pressure are further investigated. It is shown that the ductility of YNi2B2C increases with increasing pressure.
International Nuclear Information System (INIS)
Wang Rui; Wang Shaofeng; Wu Xiaozhi; Liang Xiao
2010-01-01
The method of homogeneous deformation is combined with first-principles total-energy calculations on determining third-order elastic constants and internal relaxation for monolayer graphene. We employ density functional theory (DFT) within generalized-gradient-approximation (GGA). The elastic constants are obtained from a polynomial fitted to the calculations of strain-energy and strain-stress relations. Our results agree well with recent calculations by DFT calculations, tight-binding atomistic simulations, and experiments with an atomic force microscope. The internal relaxation displacement has also been determined from ab initio calculations. The details of internal lattice relaxation by first principles are basically consistent with the previous molecular dynamics (MD) simulation. But for tiny deformation, there is an anomalous region in which the behavior of internal relaxation is backward action. In addition, we have also demonstrated that the symmetry of the relationship between the internal displacement and the infinitesimal stains can be satisfied.
First-principles study of dielectric properties of cerium oxide
International Nuclear Information System (INIS)
Yamamoto, Takenori; Momida, Hiroyoshi; Hamada, Tomoyuki; Uda, Tsuyoshi; Ohno, Takahisa
2005-01-01
We have theoretically investigated the dielectric properties of fluorite CeO 2 as well as hexagonal and cubic Ce 2 O 3 by using first-principles pseudopotentials techniques within the local density approximation. Calculated electronic and lattice dielectric constants of CeO 2 are in good agreement with previous theoretical and experimental results. For Ce 2 O 3 , the hexagonal phase has a lattice dielectric constant comparable to that of CeO 2 , whereas the cubic phase has a much smaller one. We have concluded that the enhancement of the dielectric constant in CeO 2 epitaxially grown on Si is not due to its lattice expansion experimentally observed nor regular formation of oxygen vacancies in CeO 2
Piezoelectric, Mechanical and Acoustic Properties of KNaNbOF5 from First-Principles Calculations
Directory of Open Access Journals (Sweden)
Han Han
2015-12-01
Full Text Available Recently, a noncentrosymmetric crystal, KNaNbOF5, has attracted attention due to its potential to present piezoelectric properties. Although α- and β-KNaNbOF5 are similar in their stoichiometries, their structural frameworks, and their synthetic routes, the two phases exhibit very different properties. This paper presents, from first-principles calculations, comparative studies of the structural, electronic, piezoelectric, and elastic properties of the α and the β phase of the material. Based on the Christoffel equation, the slowness surface of the acoustic waves is obtained to describe its acoustic prosperities. These results may benefit further applications of KNaNbOF5.
Directory of Open Access Journals (Sweden)
Bidai K.
2017-06-01
Full Text Available First-principles density functional theory calculations have been performed to investigate the structural, elastic and thermodynamic properties of rubidium telluride in cubic anti-fluorite (anti-CaF2-type structure. The calculated ground-state properties of Rb2Te compound such as equilibrium lattice parameter and bulk moduli are investigated by generalized gradient approximation (GGA-PBE that are based on the optimization of total energy. The elastic constants, Young’s and shear modulus, Poisson ratio, have also been calculated. Our results are in reasonable agreement with the available theoretical and experimental data. The pressure dependence of elastic constant and thermodynamic quantities under high pressure are also calculated and discussed.
First principles evaluation of the photocatalytic properties of cuprous oxide
Bendavid, Leah Isseroff
Cuprous oxide (Cu2O) is a semiconductor attractive for use as a photocatalyst in renewable fuel production, but has thus far exhibited low efficiencies in solar energy technologies. A thorough understanding of its photocatalytically relevant properties is needed to develop improved cuprous oxide-based photocatalysts. This dissertation uses first principles calculations founded in quantum mechanics to study the physical, optical, electronic, and chemical properties of cuprous oxide and to optimize its performance in solar energy applications. The key properties that affect efficiency include electronic excitations, the band gap, band edge positions, charge transport, defect trap states, catalyst stability, and surface chemistry. The band gap of Cu 2O, which defines the efficiency of solar energy absorption, is first calculated with hybrid density functional theory (DFT) followed by a single GW perturbation. We also design methods to calculate optical excitations using embedded correlated wavefunction theory. The low-index surfaces are characterized using DFT+U, where we identify the (111) surface as the most stable. This surface is employed in the derivation of the band edges of Cu2O, which demonstrate that Cu2O can provide the thermodynamic overpotential needed to drive water splitting and the reduction of CO2 to methanol. We also identify the adsorption mechanisms of weakly physisorbed CO2 and the more strongly adsorbed H2O on the Cu2O(111) surface. Effective charge transport is needed so that photoexcited carriers can reach the surface active sites prior to recombination. We study electron and hole transport in Cu2O using the small polaron model, and show that its localized description is inappropriate for carrier transport, which is better modeled using band theory. We then use an approach founded in band theory to analyze the cause of intrinsic trap states, which promote carrier recombination. We conclude that doping with Li can prevent trap state formation and
First-Principles Study of the Nonlinear Elasticity of Rare-Earth Hexaborides REB6 (RE = La, Ce
Directory of Open Access Journals (Sweden)
Xianshi Zeng
2017-10-01
Full Text Available The complete set of independent second- and third-order elastic constants of rare-earth hexaborides LaB 6 and CeB 6 are determined by the combination method of first-principles calculations and homogeneous deformation theory. The ground-state lattice parameters, second-order elastic constants, and bulk modulus are in reasonable agreement with the available experimental data. The third-order elastic constant of longitudinal mode C 111 has a larger absolute value than other shear modes, showing the contribution to lattice vibrations from longitudinal modes to be greater. The pressure derivatives of the second-order elastic constants related to the third-order elastic constants are calculated to be positive for the two hexaborides, which are consistent with those of their polycrystalline bulk modulus and shear modulus. Furthermore, the effect of pressure on the structural stability, mechanical property, and elastic anisotropy of the two hexaborides are investigated, showing a reduction in mechanical stability and an increase in ductility and anisotropy with increasing pressure.
High-temperature thermophysical properties of γ - and δ -Mn from first principles
Ehteshami, Hossein; Ruban, Andrei V.
2018-03-01
Thermophysical properties of γ - and δ -Mn phases have been investigated using first-principles calculations in their thermodynamically stable temperature range. An adiabatic approximation is used for partitioning of the Helmholtz free energy into electronic, magnetic, and vibrational contributions from the corresponding temperature induced excitations, where the fastest degree of freedom has been included in the slower ones. Namely, electronic excitations (on a one-electron level) have been included directly in the first-principles calculations at the corresponding temperatures. Magnetic excitations in the paramagnetic state then have been taken into consideration in the two opposite limits: localized, considering only transverse spin fluctuations (TSF), and itinerant, allowing for the full coupling of transverse and longitudinal spin fluctuations (LSF). Magnetic contribution to the free energy has been included in the calculations of the vibrational one, which has been obtained within the Debye-Grüneisen model. The calculated thermophysical properties such as lattice constance, thermal lattice expansion, and heat capacity are in good agreement with available experimental data, especially in the case when the itinerant magnetic model is chosen. We also present our results for elastic properties at high temperatures.
Directory of Open Access Journals (Sweden)
Wang J.
2017-01-01
Full Text Available Systematic first-principles calculations of the single crystal elastic stiffness constants (cij’s and the polycrystalline aggregates including bulk modulus (B, shear modulus (G, Young’s modulus (E have been performed for series binary and ternary Al compounds at 0 K. In addition, the temperature-dependent elastic properties for some technologically important phases are calculated. The cij’s are calculated by means of an efficient strain-stress method. Phonon density of states or Debye model is employed to calculate the linear thermal expansion, which is then used to calculate the temperature dependence of elastic properties. The calculated temperature-dependent elastic properties are compiled in the format of CALPHAD (CALculation of PHAse Diagram type formula. The presently computed elastic properties for Al compounds are needed for simulation of microstructure evolution of commercial Al alloys during series of processing route.
International Nuclear Information System (INIS)
Ledbetter, H.M.
1983-01-01
This chapter investigates the following five aspects of engineering-material solid-state elastic constants: general properties, interrelationships, relationships to other physical properties, changes during cooling from ambient to near-zero temperature, and near-zero-temperature behavior. Topics considered include compressibility, bulk modulus, Young's modulus, shear modulus, Poisson's ratio, Hooke's law, elastic-constant measuring methods, thermodynamic potentials, higher-order energy terms, specific heat, thermal expansivity, magnetic materials, structural phase transitions, polymers, composites, textured aggregates, and other-phenomena correlations. Some of the conclusions concerning polycrystalline elastic properties and their temperature dependence are: elastic constants are physical, not mechanical, properties which relate thermodynamically to other physical properties such as specific heat and thermal expansivity; elastic constants at low temperatures are nearly temperature independent, as required by the third law of thermodynamics; and elastic constants can be used to study directional properties of materials, such as textured aggregates and composites
Physical Properties of Superhard Diamond-Like BC5 from a First-Principles Study
Alp, Irem O.; Ciftci, Yasemin O.
2018-01-01
The first-principles calculations are carried out to investigate the structural, elastic, electronic, optical, vibrational and thermodynamic properties of superhard diamond-like BC5 (d-BC5). The structural stability of BC5 is examined for previously proposed and several probable phases including F-43m, P6/mmm, Cmcm, Pnma, P-1, P3m1, Imm2, I-4m2 and Pmma. The most energetically stable phase is predicted to be Pmma. Computed bulk modulus B, shear modulus G, elastic constant C 44 and theoretical Vickers hardness H confirm that BC5 is an ultra-incompressible and superhard material. The electronic character analysis reveals the metallicity of BC5, indicating that a strong covalent bond network through sp 3 hybridization is the origin of its excellent mechanical properties. However, P-1 is found to be dynamically stable, contrary to the other study. Therefore, the phonon, thermodynamic and electronic properties of P-1 which are not available in the literature are discussed. The calculated physical parameters are in good agreement with the theoretical and experimental results. This work is expected to provide a useful guide for designing novel boride materials having superior mechanical performance.
Polymorphism and Elastic Response of Molecular Materials from First Principles: How Hard Can it Be?
Reilly, Anthony; Tkatchenko, Alexandre
2014-03-01
Molecular materials are of great fundamental and applied importance in science and industry, with numerous applications in pharmaceuticals, electronics, sensing, and catalysis. A key challenge for theory has been the prediction of their stability, polymorphism and response to perturbations. While pairwise models of van der Waals (vdW) interactions have improved the ability of density functional theory (DFT) to model these systems, substantial quantitative and even qualitative failures remain. In this contribution we show how a many-body description of vdW interactions can dramatically improve the accuracy of DFT for molecular materials, yielding quantitative description of stabilities and polymorphism for these challenging systems. Moreover, the role of many-body vdW interactions goes beyond stabilities to response properties. In particular, we have studied the elastic properties of a series of molecular crystals, finding that many-body vdW interactions can account for up to 30% of the elastic response, leading to quantitative and qualitative changes in elastic behavior. We will illustrate these crucial effects with the challenging case of the polymorphs of aspirin, leading to a better understanding of the conflicting experimental and theoretical studies of this system.
Studying the properties of a predicted tetragonal silicon by first principles
Xue, Han-Yu; Zhang, Can; Pang, Dong-Dong; Huang, Xue-Qian; Lv, Zhen-Long; Duan, Man-Yi
2018-03-01
Silicon is a very important material in many technological fields. It also has a complicated phase diagram of scientific interest. Here we reported a new allotrope of silicon obtained from crystal structure prediction. We studied its electronic, vibrational, dielectric, elastic and hardness properties by first-principles calculations. The results indicate that it is an indirect narrow-band-gap semiconductor. It is dynamically stable with a doubly degenerate infrared-active mode at its Brillouin zone center. Born effective charges of the constituent element are very small, resulting in a negligible ionic dielectric contribution. Calculated elasticity-related quantities imply that it is mechanically stable but anisotropic. There exist slowly increasing stages in the stress-strain curves of this crystal, which make it difficult to estimate the hardness of the crystal by calculating its ideal strengths. Taking advantage of the hardness model proposed by Šimůnek, we obtained a value of 12.0 GPa as its hardness. This value is lower than that of the cubic diamond-structural Si by about 5.5%.
New crystal structure and physical properties of TcB from first-principles calculations
Zhang, Gang-Tai; Bai, Ting-Ting; Yan, Hai-Yan; Zhao, Ya-Ru
2015-10-01
By combining first-principles calculations with the particle swarm optimization algorithm, we predicted a hexagonal structure for TcB, which is energetically more favorable than the previously reported WC-type and Cmcm structures. The new phase is mechanically and dynamically stable, as confirmed by its phonon and elastic constants calculations. The calculated mechanical properties show that it is an ultra-incompressible and hard material. Meanwhile, the elastic anisotropy is investigated by the shear anisotropic factors and ratio of the directional bulk modulus. Density of states analysis reveals that the strong covalent bonding between Tc and B atoms plays a leading role in forming a hard material. Additionally, the compressibility, bulk modulus, Debye temperature, Grüneisen parameter, specific heat, and thermal expansion coefficient of TcB are also successfully obtained by using the quasi-harmonic Debye model. Project supported by the Science Foundation of Baoji University of Arts and Sciences of China (Grant No. ZK11061) and the Natural Science Foundation of the Education Committee of Shaanxi Province, China (Grant Nos. 2013JK0637, 2013JK0638, and 2014JK1044).
Mechanical, dynamical and thermodynamic properties of Al-3wt%Mg from first principles
Energy Technology Data Exchange (ETDEWEB)
Yang, Rong [Chongqing Jiaotong Univ., Chongqing (China). College of Materials Science and Engineering; Tang, Bin [Chongqing City Management College, Chongqing (China). Inst. of Finance and Trade; Gao, Tao [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics
2017-09-01
The mechanical, dynamical and thermodynamic properties of Al-3wt%Mg have been investigated using the first-principles method. The calculated structural parameter is in good agreement with previous works. Results for the elastic modulus, stress-strain relationships, ideal tensile and shear strengths are presented. Al-3wt%Mg is found to have larger moduli and higher strengths than Al, which is consistent with its exploitation in Al precipitate-hardening mechanisms. The partial density of states (PDOS) show that the partly covalent-like bonding through Al p-Mg s hybridization is the origin of excellent mechanical properties of Al-3wt%Mg. The phonon dispersion curves indicate that Al-3wt%Mg is dynamically stable at ambient pressure and 0 K. Furthermore, the Helmholtz free energy ΔF, the entropy S, the constant-volume specific heat C{sub V} and the phonon contribution to the internal energy ΔE are predicted using the phonon density of states. We expect that our work can provide useful guidance to help with the performance of Al-3wt%Mg.
Mechanical, dynamical and thermodynamic properties of Al-3wt%Mg from first principles
International Nuclear Information System (INIS)
Yang, Rong; Tang, Bin; Gao, Tao
2017-01-01
The mechanical, dynamical and thermodynamic properties of Al-3wt%Mg have been investigated using the first-principles method. The calculated structural parameter is in good agreement with previous works. Results for the elastic modulus, stress-strain relationships, ideal tensile and shear strengths are presented. Al-3wt%Mg is found to have larger moduli and higher strengths than Al, which is consistent with its exploitation in Al precipitate-hardening mechanisms. The partial density of states (PDOS) show that the partly covalent-like bonding through Al p-Mg s hybridization is the origin of excellent mechanical properties of Al-3wt%Mg. The phonon dispersion curves indicate that Al-3wt%Mg is dynamically stable at ambient pressure and 0 K. Furthermore, the Helmholtz free energy ΔF, the entropy S, the constant-volume specific heat C V and the phonon contribution to the internal energy ΔE are predicted using the phonon density of states. We expect that our work can provide useful guidance to help with the performance of Al-3wt%Mg.
Sun, Xinjun; Liu, Changdong; Guo, Yongliang; Sun, Deyan; Ke, Xuezhi
2018-03-01
The structural and thermodynamic properties of titanium nitride (TiN) have been investigated by merging first-principles calculations and particle-swarm algorithm. The three phases are identified for TiN, including the B1, the P63 / mmc, and the B2 phases. A new phase of anti-TiP structure with the space group P63 / mmc has been predicted. The calculated phase transition from the B1 to the P63 / mmc occurs at 270 GPa. The vibrational, elastic, and thermodynamic properties for the three phases have been calculated and discussed.
Structural and Mechanical Properties of TiN-TiC-TiO System: First Principle Study
Farhadizadeh, Ali Reza; Amadeh, Ahmad Ali; Ghomi, Hamidreza
2017-11-01
Mechanical and structural properties of ternary system of TiN-TiO-TiC are investigated using first principle methods. 70 different compositions of Ti 100 (NOC) 100 with cubic structure are examined in order to illustrate the trend of properties variations. The geometry of compounds is optimized, and then, their chemical stability is assessed. Afterward, shear, bulk and young moduli, Cauchy pressure, Zener ratio, hardness and {H}3/{E}2 ratio are computed based on elastic constants. Graphical ternary diagram is used to represent the trend of such properties when the content of nitrogen, oxygen and carbon varies. The results show that incorporation of oxygen into the system decreases the hardness and {H}3/{E}2 ratio while subsequently ductility increases due to positive Cauchy pressure. It is revealed that the maximum {H}3/{E}2 ratio occurs when both nitrogen and carbon with a little amount of oxygen are incorporated. Ti 100 N 30 C 70 owns the highest hardness and {H}3/{E}2 ratio equal to 39.5 and 0.2 GPa, respectively. In addition, the G/B of this compound, which is about 0.9, shows it is brittle. It is also observed that the solid solutions have better mechanical properties with respect to titanium nitride and titanium carbide. The obtained results could be used to enhance monolayer coatings as well as to design multilayers with specific mechanical properties. The authors would like to acknowledge the financial support of University of Tehran Science and Technology Park for this research under Grant No. 94061
International Nuclear Information System (INIS)
Nyawere, P.W.O.; Makau, N.W.; Amolo, G.O.
2014-01-01
All the elastic constants of cubic, orthorhombic and hexagonal phases of BaF 2 have been calculated using first principles methods. We have employed density-functional theory within generalized gradient approximation (GGA) using a plane-wave pseudopotentials method and a plane-wave basis set. The calculated elastic constant values for a cubic phase compare well with recent theoretical and experimental calculations. The bulk modulus derived from the elastic constant calculations of orthorhombic phase of BaF 2 is 94.5 GPa and those of hexagonal phase is 161 GPa. These values are in good agreement with experimental data available. Stability of these phases of BaF 2 is also estimated in different crystallographic directions
Energy Technology Data Exchange (ETDEWEB)
Tayran, Ceren; Aydin, Sezgin [Department of Physics, Sciences Faculty, Gazi University, 06500, Ankara (Turkey)
2017-05-15
The structural, elastic, mechanical, and electronic properties of lithium aluminum tetraboride (LiAlB{sub 4}) under hydrostatic pressure have been investigated by using first-principles density functional theory calculations. The effects of pressure on the lattice parameters, volume, and bond lengths are studied. It is indicated from the calculated elastic constants that LiAlB{sub 4} compound is mechanically stable on 0-40 GPa pressure range. And, by means of these elastic constants set, some mechanical properties such as bulk, shear and Young's moduli, and then Poisson's ratio are determined as a function of pressure. Also, the ductile or brittle nature of LiAlB{sub 4} is examined. Additionally, using the first-principles data obtained from the geometry optimizations, the hardness of LiAlB{sub 4} is calculated, and its nature is investigated under pressure. Furthermore, in order to reveal the effects of pressure on the electronic and binding behavior of the compound, band structures, total and partial density of states, charge densities, Mulliken atomic charges, and bond overlap populations are searched as a function of pressure. To check the stability of the compound, phonon dispersion curves are calculated. And, the results are compared with the other convenient borides. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Forecast of Piezoelectric Properties of Crystalline Materials from First Principles Calculation
International Nuclear Information System (INIS)
Zheng Yanqing; Shi Erwei; Chen Jianjun; Zhang Tao; Song Lixin
2006-01-01
In this paper, forecast of piezoelectric tensors are presented. Piezo crystals including quartz, quartz-like crystals, known and novel crystals of langasite-type structure are treated with density-functional perturb theory (DFPT) using plane-wave pseudopotentials method, within the local density approximation (LDA) to the exchange-correlation functional. Compared with experimental results, the ab initio calculation results have quantitative or semi-quantitative accuracy. It is shown that first principles calculation opens a door to the search and design of new piezoelectric material. Further application of first principles calculation to forecast the whole piezoelectric properties are also discussed
First-principles elastic constants and phonons of delta-Pu
DEFF Research Database (Denmark)
Söderlind, P.; Landa, A.; Sadigh, B.
2004-01-01
Elastic constants and zone-boundary phonons of delta-plutonium have been calculated within the density-functional theory. The paramagnetic state of delta-Pu is modeled by disordered magnetism utilizing either the disordered local moment or the special quasirandom structure techniques...
First-principles investigation of elastic anomalies in niobium at high pressure and temperature
Wang, Yi X.; Geng, Hua Y.; Wu, Q.; Chen, Xiang R.; Sun, Y.
2017-12-01
Niobium does not show any structure transition up to very high pressures. Nonetheless, by using density functional theory, we demonstrate in this work that it exhibits striking softening in elastic moduli C44 and C' at a pressure from 20 to 150 GPa. A novel anomaly softening in C44 from 275 to 400 GPa is also predicted. The physics behind these two anomalies is elaborated by electronic structure calculations, which revealed that they are actually different—first one directly relates to an underlying rhombohedral distortion whereas the latter originates in an electronic topological transition. The large magnitude of the softening leads to a remarkable elastic anisotropy in both the shear and the Young's moduli of Nb. Further investigation shows that thermo-electrons have an important role in these anomalies. This effect has not been noticed before. With increased electronic temperature, it is found that all anomalies (both the elastic softening and anisotropy) in Nb are gradually diminished, effectively giving rise to a temperature-induced hardening phenomenon.
Directory of Open Access Journals (Sweden)
Carlos Mario Ruiz
2011-06-01
Full Text Available Las propiedades elásticas de la familia de los minerales isoestructurales Cu3VSe4, Cu3NbSe4 y Cu3TaSe4 han sido calculadas por primera vez usandoel estado del arte en cálculos atomísticos de primeros-principios, utilizandola Teoría de los Funcionales de la Densidad y la Aproximación del Gradiente Generalizado para el funcional de la energía de intercambio-correlación. Laspropiedades elásticas calculadas son el módulo volumétrico (B, las constantes elásticas (c11, c12 y c44, el factor de anisotropía de Zener (A, el módulo de cizalladura isotrópico (G, el módulo de Young (Y, y la razón de Poisson(ν. A través de estas cantidades también hemos calculado otras propiedades termodinámicas tales como la velocidad promedio del sonido transversal (st y longitudinal (sl y la temperatura de Debye (ΘD. Los valores calculados de B, c11, c12 y c44, G, Y , y ν nos llevan a la conclusión que estos compuestosson compresibles, frágiles y quebradizos.The elastic properties of the family of isostructural minerals Cu3VSe4, Cu3NbSe4 and Cu3TaSe4 have been calculated for the first time using the state of the art in first-principles atomistic calculations, using Density Functional Theory and the Generalized Gradient Approximation for the exchangecorrelation energy functional. The elastic properties calculated are bulk modulus (B, the elastic constants (c11, c12 and c44, the Zener anisotropy factor (A, the isotropic shear modulus (G, the Young modulus (Y , and the Poisson ratio (. By means of these quantities we also computed other thermodynamic properties such as the average transversal (st and longitudinal (sl sound velocities and the Debye temperature (D. The calculated values of B, c11, c12 and c44, G, Y and lead us to the conclusion that these compounds are compressible, fragile and brittle.
Zhou, Jiawei; Liao, Bolin; Chen, Gang
2016-04-01
The transport properties of semiconductors are key to the performance of many solid-state devices (transistors, data storage, thermoelectric cooling and power generation devices, etc). An understanding of the transport details can lead to material designs with better performances. In recent years simulation tools based on first-principles calculations have been greatly improved, being able to obtain the fundamental ground-state properties of materials (such as band structure and phonon dispersion) accurately. Accordingly, methods have been developed to calculate the transport properties based on an ab initio approach. In this review we focus on the thermal, electrical, and thermoelectric transport properties of semiconductors, which represent the basic transport characteristics of the two degrees of freedom in solids—electronic and lattice degrees of freedom. Starting from the coupled electron-phonon Boltzmann transport equations, we illustrate different scattering mechanisms that change the transport features and review the first-principles approaches that solve the transport equations. We then present the first-principles results on the thermal and electrical transport properties of semiconductors. The discussions are grouped based on different scattering mechanisms including phonon-phonon scattering, phonon scattering by equilibrium electrons, carrier scattering by equilibrium phonons, carrier scattering by polar optical phonons, scatterings due to impurities, alloying and doping, and the phonon drag effect. We show how the first-principles methods allow one to investigate transport properties with unprecedented detail and also offer new insights into the electron and phonon transport. The current status of the simulation is mentioned when appropriate and some of the future directions are also discussed.
International Nuclear Information System (INIS)
Zhao, P.; Wang, P.J.; Zhang, Z.; Liu, D.S.
2010-01-01
We have studied the electronic transport properties of a new kind of optical molecular switch with two single-walled carbon nanotube (SWCNT) electrodes using first-principles transport calculations. It is shown that the enol form shows an overall higher conductance than the keto form at low-bias voltage, which is independent of the SWCNTs' chirality. Meantime, it is possible to tune the conductance of the molecular switch by changing the chirality of the SWCNTs.
Physical properties of the tetragonal CuMnAs: A first-principles study
Czech Academy of Sciences Publication Activity Database
Máca, František; Kudrnovský, Josef; Drchal, Václav; Carva, K.; Baláž, P.; Turek, I.
2017-01-01
Roč. 96, č. 9 (2017), s. 1-8, č. článku 094406. ISSN 2469-9950 R&D Projects: GA ČR GB14-37427G Grant - others:GA MŠk(CZ) LM2015042 Institutional support: RVO:68378271 Keywords : first- principles calculations * defects * CuMnAs * transport properties Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 3.836, year: 2016
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.
Energy Technology Data Exchange (ETDEWEB)
Zhao, P., E-mail: ss_zhaop@ujn.edu.c [School of Science, University of Jinan, Jinan 250022 (China); Liu, D.S. [School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China); Department of Physics, Jining University, Qufu 273155 (China); Wang, P.J.; Zhang, Z. [School of Science, University of Jinan, Jinan 250022 (China); Fang, C.F.; Ji, G.M. [School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China)
2011-02-15
By applying non-equilibrium Green's function (NEGF) formalism combined with first-principles density functional theory (DFT), we have investigated the electronic transport properties of the anthraquinone-based molecular switch. The molecule that comprises the switch can be converted between the hydroquinone (HQ) and anthraquinone (AQ) forms via redox reactions. The transmission spectra of these two forms are remarkably distinctive. Our results show that the current through the HQ form is significantly larger than that through the AQ form, which suggests that this system has attractive potential application in future molecular switch technology.
International Nuclear Information System (INIS)
Zhao, P.; Liu, D.S.; Wang, P.J.; Zhang, Z.; Fang, C.F.; Ji, G.M.
2011-01-01
By applying non-equilibrium Green's function (NEGF) formalism combined with first-principles density functional theory (DFT), we have investigated the electronic transport properties of the anthraquinone-based molecular switch. The molecule that comprises the switch can be converted between the hydroquinone (HQ) and anthraquinone (AQ) forms via redox reactions. The transmission spectra of these two forms are remarkably distinctive. Our results show that the current through the HQ form is significantly larger than that through the AQ form, which suggests that this system has attractive potential application in future molecular switch technology.
First-principles investigation of the physical properties of cubic and orthorhombic phase Na3UO4
Chen, Haichuan; Tian, Wenyan
2017-11-01
The anisotropic elastic properties, Vickers hardness, Debye temperature and the minimum thermal conductivity of c-Na3UO4 and o-Na3UO4 have been investigated by means of the first principles calculations. The lattice parameters are in good agreement with the available experimental data and the theoretical results. The elastic constants satisfy the mechanical stability criteria show that both of them are mechanically stable. The value of B / G and Cauchy pressure reveal that the c-Na3UO4 holds a ductile behavior while the o-Na3UO4 behaves a brittle manner. The elastic anisotropy of c-Na3UO4 is less weak than that of o-Na3UO4. The hardness shows that both of them can be classified as ;soft materials;. Finally, the Debye temperature is 452.6 K and 388.4 K, and the minimum thermal conductivities kmin is 0.883 W m-1 K-1 and 0.753 W m-1 K-1 of c-Na3UO4 and o-Na3UO4, respectively. Due to relatively lower thermal conductivity, and thereby they are suitable to be used as thermal insulating materials.
Directory of Open Access Journals (Sweden)
Vivek Dixit
2017-11-01
Full Text Available We investigated the effect of substitution of various ions at the Fe sites on magnetic properties of strontium hexaferrite (SrFe12O19 using first principles method based on density functional theory. The site occupancies of substituted atoms were estimated by calculating the substitution energies of different configurations. The formation probabilities of configurations were used to calculate magnetic properties of substituted strontium hexaferrite. A total of 21 elements (M were screened for their possible substitution in strontium hexaferrite, SrFe12−xMxO19 with x = 0.5. In each case the site preference of the substituted atom and the magnetic properties were calculated. We found that Bi, Sb, Sn, and Sc can effectively increase the magnetization and P, Co, Al, Ga, and Ti can enhance the anisotropy field when substituted into strontium hexaferrite.
Near-infrared radiation absorption properties of covellite (CuS using first-principles calculations
Directory of Open Access Journals (Sweden)
Lihua Xiao
2016-08-01
Full Text Available First-principles density functional theory was used to investigate the electronic structure, optical properties and the origin of the near-infrared (NIR absorption of covellite (CuS. The calculated lattice constant and optical properties are found to be in reasonable agreement with experimental and theoretical findings. The electronic structure reveals that the valence and conduction bands of covellite are determined by the Cu 3d and S 3p states. By analyzing its optical properties, we can fully understand the potential of covellite (CuS as a NIR absorbing material. Our results show that covellite (CuS exhibits NIR absorption due to its metal-like plasma oscillation in the NIR range.
Mechanical Properties and Electronic Structure of N and Ta Doped TiC: A First-Principles Study
International Nuclear Information System (INIS)
Ma Shi-Qing; Liu Ying; Ye Jin-Wen; Wang Bin
2014-01-01
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 C 12 –C 44 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. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Yang, Hua
2012-01-01
Electronic structure and optical properties of α-FeMO 3 systems (M = Sc, Ti, V, Cr, Cu, Cd or In) have been investigated using first principles calculations. All of the FeMO 3 systems have a large net magnetic moment. The ground state of pure α-Fe 2O 3 is an antiferromagnetic insulator. For M = Cu or Cd, the systems are half-metallic. Strong absorption in the visible region can be observed in the Cu and Cd-doped systems. Systems with M = Sc, Ti, V, Cr or In are not half-metallic and are insulators. The strongest peaks shift toward shorter wavelengths in the absorption spectra. It is concluded that transition metal doping can modify the electronic structure and optical properties of α-FeMO 3 systems. This journal is © 2012 The Royal Society of Chemistry.
The electronic and transport properties of borophane with defects: A first principles study
Sun, Jie; Zhang, Yujin; Leng, Jiancai; Ma, Hong
2018-03-01
Recent works well confirm the stability of hydrogenated borophene, known as borophane. Here, first principles studies have performed on the electronic and transport properties of borophane with defects. The calculations indicate that the introduction of defects results in different behavior of charges redistribution along x and y directions. The intrinsic electronic structure of borophane with Dirac cone is destroyed in various degrees by each type of defect. The inducing defect states lead to the occurrence of flat bands, which are not benefit for the electronic transport properties. According to the transmission spectra and I-V characteristics, these defects decrease the transmission intensity and the current value both along two directions. However, the transport anisotropy can be efficiently tuned by defect, which may contribute to the design of functional device.
Properties of half-Heusler compounds TaIrGe by using first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Wei, JunHong [Henan Normal University, College of Physics and Information Engineering, Xinxiang, Henan (China); Henan Institute of Science and Technology, School of Mechanical and Electrical Engineering, Xinxiang, Henan (China); Wang, Guangtao [Henan Normal University, College of Physics and Information Engineering, Xinxiang, Henan (China)
2017-05-15
The electronic structures, optical and thermoelectric properties of ternary half-Heusler compound TaIrGe were investigated by using the first-principles and Boltzmann transport theory. Spin-orbit coupling (SOC) removed the degeneracy of VBM, and then decreased the Seebeck coefficients and power factor. From the compressive to tensile strain, the band gap gradually increases from 0.96 to 1.11 eV, accompanied by the absorption coefficient peak red-shift. The effective mass (m{sup *}{sub DOS}) of VBM and CBM gradually increases from the compressive to tensile strain, which enhances the Seebeck coefficient and power factor. Our results indicate that the electronic structures, optical and thermoelectric properties of TaIrGe can be effectively tuned by the strain and TaIrGe can be used as an important photoelectric and thermoelectric material in the future. (orig.)
Hydrogen and fluorine co-decorated silicene: A first principles study of piezoelectric properties
International Nuclear Information System (INIS)
Noor-A-Alam, Mohammad; Kim, Hye Jung; Shin, Young-Han
2015-01-01
A low-buckled silicene monolayer being centrosymmetric like graphene, in contrast to a piezoelectric hexagonal boron nitride (h-BN), is not intrinsically piezoelectric. However, based on first principles calculations, we show that chemical co-decoration of hydrogen (H) and fluorine (F) on opposite sides of silicene (i.e., one side is decorated with H, while the other one is with F) breaks the centrosymmetry. Redistributing the charge density due to the electronegativity difference between the atoms, non-centrosymmetric co-decoration induces an out-of-plane dipolar polarization and concomitant piezoelectricity into non-piezoelectric silicene monolayer. Our piezoelectric coefficients are comparable with other known two-dimensional piezoelectric materials (e.g., hydrofluorinated graphene/h-BN) and some bulk semiconductors, such as wurtzite GaN and wurtzite BN. Moreover, because of silicene's lower elastic constants compared to graphene or h-BN, piezoelectric strain constants are found significantly larger than those of hydrofluorinated graphene/h-BN. We also predict that a wide range of band gaps with an average of 2.52 eV can be opened in a low-buckled gapless semi-metallic silicene monolayer by co-decoration of H and F atoms on the surface
Zhang, Chuanzhao; Kuang, Xiaoyu; Jin, Yuanyuan; Lu, Cheng; Zhou, Dawei; Li, Peifang; Bao, Gang; Hermann, Andreas
2015-12-09
We present results of an unbiased structure search for stable ruthenium silicide compounds with various stoichiometries, using a recently developed technique that combines particle swarm optimization algorithms with first-principles calculations. Two experimentally observed structures of ruthenium silicides, RuSi (space group P2(1)3) and Ru2Si3 (space group Pbcn), are successfully reproduced under ambient pressure conditions. In addition, a stable RuSi2 compound with β-FeSi2 structure type (space group Cmca) was found. The calculations of the formation enthalpy, elastic constants, and phonon dispersions demonstrate the Cmca-RuSi2 compound is energetically, mechanically, and dynamically stable. The analysis of electronic band structures and densities of state reveals that the Cmca-RuSi2 phase is a semiconductor with a direct band gap of 0.480 eV and is stabilized by strong covalent bonding between Ru and neighboring Si atoms. On the basis of the Mulliken overlap population analysis, the Vickers hardness of the Cmca structure RuSi2 is estimated to be 28.0 GPa, indicating its ultra-incompressible nature.
Structural and electronic properties of LaPd2As2 superconductor: First-principle calculations
Singh, Birender; Kumar, Pradeep
2017-05-01
In present work we have studied electronic and structural properties of superconducting LaPd2As2 compound having collapsed tetragonal structure using first-principle calculations. The band structure calculations show that the LaPd2As2 is metallic consistent with the reported experimental observation, and the density of states plots clearly shows that at the Fermi level major contribution to density of states arises from Pd 4d and As 4p states, unlike the Fe-based superconductors where major contribution at the Fermi level comes from Fe 3d states. The estimated value of electron-phonon coupling is found to be 0.37, which gives the upper bound of superconducting transition temperature of 5K, suggesting the conventional nature of this superconductor.
First-principles study on electronic structures and magnetic properties of Eu-doped phosphorene
Luan, Zhaohui; Zhao, Lei; Chang, Hao; Sun, Dan; Tan, Changlong; Huang, Yuewu
2017-11-01
The structural, electronic and magnetic properties of Eu-doped phosphorene with different doping concentrations were investigated by first-principles calculations for the first time. The calculations show that Eu-doped phosphorene systems are stable and have the large magnetic moments of more than 6 μB by 2.7, 6.25 and 12.5 at.% doping concentrations. The major contribution to the magnetic moment stems from the 4f states of Eu-doped atom. Meanwhile, Eu-doped atom introduces the impurity bands which can be changed by different doping concentrations. In order to determine the magnetic interaction, the different configurations for two Eu atoms doping in 3 × 3 × 1 phosphorene supercell were studied, which reveals that all of the configurations tend to form ferromagnetic. These results can provide references for inducing large magnetism of two-dimensional phosphorene, which are valuable for their applications in spintronic devices and novel semiconductor materials.
International Nuclear Information System (INIS)
Noh, Seunghyo; Kwak, Dohyun; Lee, Juseung; Kang, Joonhee; Han, Byungchan
2014-01-01
We utilized first-principles density-functional-theory (DFT) calculations to evaluate the thermodynamic feasibility of a pyroprocessing methodology for reducing the volume of high-level radioactive materials and recycling spent nuclear fuels. The thermodynamic properties of transuranium elements (Pu, Np and Cm) were obtained in electrochemical equilibrium with a LiCl-KCl molten salt as ionic phases and as adsorbates on a W(110) surface. To accomplish the goal, we rigorously calculated the double layer interface structures on an atomic resolution, on the thermodynamically most stable configurations on W(110) surfaces and the chemical activities of the transuranium elements for various coverages of those elements. Our results indicated that the electrodeposition process was very sensitive to the atomic level structures of Cl ions at the double-layer interface. Our studies are easily expandable to general electrochemical applications involving strong redox reactions of transition metals in non-aqueous solutions.
First-principles calculations of mechanical and electronic properties of silicene under strain
Directory of Open Access Journals (Sweden)
Rui Qin
2012-06-01
Full Text Available We perform first-principles calculations of mechanical and electronic properties of silicene under strains. The in-plane stiffness of silicene is much smaller than that of graphene. The yielding strain of silicene under uniform expansion in the ideal conditions is about 20%. The homogeneous strain can introduce a semimetal-metal transition. The semimetal state of silicene, in which the Dirac cone locates at the Fermi level, can only persist up to tensile strain of 7% with nearly invariant Fermi velocity. For larger strains, silicene changes into a conventional metal. The work function is found to change significantly under biaxial strain. Our calculations show that strain tuning is important for applications of silicene in nanoelectronics.
First-principles study on electron transport properties of carbon-silicon mixed chains
Hu, Wei; Zhou, Qinghua; Liang, Yan; Liu, Wenhua; Wang, Tao; Wan, Haiqing
2018-03-01
In this paper, the transport properties of carbon-silicon mixed chains are studied by using the first-principles. We studied five atomic chain models. In these studies, we found that the equilibrium conductances of atomic chains appear to oscillate, the maximum conductance and the minimum conductance are more than twice the difference. Their I-V curves are linear and show the behavior of metal resistance, M5 system and M2 system current ratio is the largest in 0.9 V, which is 3.3, showing a good molecular switch behavior. In the case of bias, while the bias voltage increases, the transmission peaks move from the Fermi level. The resonance transmission peak height is reduced near the Fermi level. In the higher energy range, a large resonance transmission peak reappears, there is still no energy cut-off range.
First-principles study of the structural and electronic properties of ultrathin silver nanowires
Ma, Liang-Cai; Ma, Ling; Lin, Xue-Ling; Yang, You-Zhen; Zhang, Jian-Min
2015-12-01
By using first-principles calculations based on density-functional theory, we have systematically investigated the equilibrium structure, stability and electronic properties of silver nanowires (AgNWs) with dimer, triangular, square, pentagonal and hexagonal cross-section. It is found that, using the string tension criterion, for the triangular and square AgNWs with small diameters the preferred structures should be the hollow one with staggered configuration, while for the pentagonal and hexagonal AgNWs with bigger diameters the preferred structures should be the staggered ones which contain a linear chain along the wire axis passes through the center of the polygons, where each chain atom is just located at a point equidistant from the planes of polygons. Electronic band structures and density of states calculations show that the AgNWs with different structures exhibit metallic behavior. Charge density contours show that there is an enhanced interatomic interaction in AgNWs compared with Ag bulk.
Directory of Open Access Journals (Sweden)
Biao Li
2015-01-01
Full Text Available Using the first principles calculations, we have studied the atomic and electronic structures of single Co atom incorporated with divacancy in armchair graphene nanoribbon (AGNR. Our calculated results show that the Co atom embedded in AGNR gives rise to significant impacts on the band structures and the FM spin configuration is the ground state. The presence of the Co doping could introduce magnetic properties. The calculated results revealed the arising of spin gapless semiconductor characteristics with doping near the edge in both ferromagnetic (FM and antiferromagnetic (AFM magnetic configurations, suggesting the robustness for potential application of spintronics. Moreover, the electronic structures of the Co-doped AGNRs are strongly dependent on the doping sites and the edge configurations.
First-principles study of electronic and magnetic properties of BiNiO3
Cai, M. Q.; Yang, G. W.; Cao, Y. L.; Yu, W. H.; Wang, L. L.; Wang, Y. G.
2007-06-01
First-principles calculations on the electronic and magnetic properties of BiNiO3 reveal that the G-type antiferromagnetic structure with the insulating ground state is more stable than other possible configurations. The hybridization of Ni-O and Bi-O leads to the reduction of the spin magnetic moment to 1.67μB in comparison with the Ni2+ d8 configuration of 2μB. The band gap of the antiferromagnetic insulating ground state is predicted to be 0.68eV. The antiferromagnetic interaction induces the localized spins to be S =1 in the G-antiferromagnetic structure of BiNiO3.
Structural, dynamical and thermodynamic properties of CdXP2 (X = Si, Ge) from first principles
Hou, H. J.; Zhu, H. J.; Li, S. P.; Li, T. J.; Tian, L.; Yang, J. W.
2018-03-01
The structural, elastic, dynamical and thermodynamic properties of CdXP2 (X = Si, Ge) with chalcopyrite semiconductors have been calculated by using the projector augmented wave method within the generalized gradient approximation. The obtained lattice constants and elastic constants of CdXP2 (X = Si, Ge) are compared with the available experimental and other theoretical results, and the agreements between them are quite well. Also, the elastic anisotropy of CdXP2 (X = Si, Ge) have been evaluated. In addition, the phonon dispersion curves and the corresponding phonon density of states of CdXP2 (X = Si, Ge) have been determined by virtue of a linear response approach to density functional perturbation theory method successfully. Finally, the Helmholtz free energy F, internal energy E, entropy S and the constant volume specific heat C V have also been predicted based on quasi-harmonic approximation.
Electronic and optical properties of bilayer PbI2: a first-principles study
Shen, Chenhai; Wang, Guangtao
2018-01-01
By employing first-principles methods, we investigate the effects of stacking patterns and interlayer coupling on the electronic structures and optical properties of bilayer (BL) PbI2. For optical properties, excitonic effects are considered. The results show that crystal-type BL PbI2 stacking pattern is the most stable bilayer structures with the equilibrium interlayer distance of 3.27 Å and a direct band structure. Moreover, for all considered patterns, the interlayer coupling can induce the band structures to transform from indirect to direct and also the band gap values to vary from 2.56 eV to 2.62 eV. In addition, our calculations show that the exciton binding energy of the most stable pattern is 0.81 eV, and excitonic effects have obvious influences on optical responses of BL PbI2. These results may be useful to future experimental studies on optoelectronic properties of two-dimensional BL PbI2 nanosheets.
Zhou, Wenzhe; Zou, Hui; Xiong, Xiang; Zhou, Yu; Liu, Rutie; Ouyang, Fangping
2017-10-01
On the basis of first-principles density functional theory, the different electronic structures of marginal or central doped armchair phosphorene nanoribbons with various species were calculated. It was found that the bonds between the foreign atoms and the adjacent P atoms are energetically more stable for central doping. The electronic properties of the doped ribbons are strongly related to the valence electron number of foreign atoms. B-, N-, F-, Al-doped (type Ⅰ) armchair phosphorene nanoribbons remain nonmagnetic semiconductors. The bandgap of the central doped nanoribbons is larger than that of the marginal doped nanoribbons. C, O, Si, S doping (type Ⅱ) at the edge introduce about 1 μB delocalized magnetic moment, while significantly decreasing for central doping, which is associated with electron transferring from foreign atoms to neighboring P atoms. The magnetism introduced by type Ⅱ dopants is provided by multiple orbits between the foreign atoms and the adjacent P atoms and delocalized on the edge for marginal doping. These results prove that the presence and the location of isolated electrons are both important factors for modulation of magnetic properties of armchair phosphorene nanoribbons through substitutional doping.
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 and germanene, c-silicyne is a flat sheet, and c-germanyne is buckled with a distinct half-hilled conformation. Such asymmetric buckling structure causes the semiconducting behaviour into c-germanyne. While in c-silicyne, the semimetallic Dirac-like property is kept at the nonmagnetic state, but a spontaneous antiferromagnetism produces the massive Dirac fermions and opens a sizeable gap between Dirac cones. A tensile strain can further enhance the antiferromagnetism, which also linearly modulates the gap value without altering the direct-bandgap feature. Through strain engineering, c-silicyne can form a type-II band alignment with the MoS 2 sheet. The combined c-silicyne/MoS 2 nanostructure has a high power conversion efficiency beyond 20% for photovoltaic solar cells, enabling a fascinating utilization in the fields of solar energy and nano-devices.
First principles calculation of thermodynamic properties of NaAlSi ternary
International Nuclear Information System (INIS)
Qin Jining; Lu Weijie; Zhang Di; Fan Tongxiang
2012-01-01
PbFCl-type NaAlSi ternary is a corrosion compound found in aluminum, which is used as a sealing material in sodium sulfur battery. To understand and control the corrosion process, it is important to predict its quantitative properties. In this study, a first-principles calculation has been carried out to calculate its equilibrium lattice parameters, bulk modulus and pressure derivative of bulk modulus by both all-electron full-potential linear augmented plane wave scheme and pseudopotential plane wave scheme within the generalized gradient approximation. The theoretical results show good agreement with the available experimental data. The thermodynamic properties, including the specific heat capacity and entropy with pressure up to 9 GPa, have been investigated for the first time by coupling of density functional perturbation theory and quasiharmonic approximation. The volume and linear thermal expansion coefficients were estimated and the results show that the linear thermal expansion on c-axis is nearly twice as large as that on a-axis within the calculated temperature.
Cantele, Giovanni; Ninno, Domenico
2017-06-01
Few layer bismuth nanofilms with (111) orientation have shown striking electronic properties, especially as building blocks of novel two-dimensional heterostructures. In this paper we present state-of-the-art first principles calculations, based on both density functional theory and maximally localized Wannier functions, that encompass electronic and structural properties of free-standing Bi(111) nanofilms. We accurately evaluate both the in-plane lattice constant and, by including the van der Waals interaction between bismuth bilayers, the intra/interlayer distances. Interestingly and somehow unexpectedly, the in-plane lattice constant is predicted to shrink by about 5% going from the thickest investigated nanofilm (˜80 Å ) to single bilayer Bi(111), entailing a thickness dependent lattice mismatch in complex heterostructures involving ultrathin Bi(111). Moreover, quantum confinement effects, that would be expected to rule the electronic structure at this size range, compete with surface states that appear close to and across the Fermi level. The implication is that not only all but the thinnest films have a metallic band structure but also that such surface states might play a role in either the formation of interfaces with other materials or for sensing applications. Finally, the calculated electronic structure compares extremely well with ARPES measurements.
Calculations of thermodynamic properties of PuO2 by the first-principles and lattice vibration
International Nuclear Information System (INIS)
Minamoto, Satoshi; Kato, Masato; Konashi, Kenji; Kawazoe, Yoshiyuki
2009-01-01
Plutonium dioxide (PuO 2 ) is a key compound of mixed oxide fuel (MOX fuel). To predict the thermal properties of PuO 2 at high temperature, it is important to understand the properties of MOX fuel. In this study, thermodynamic properties of PuO 2 were evaluated by coupling of first-principles and lattice dynamics calculation. Cohesive energy was estimated from first-principles calculations, and the contribution of lattice vibration to total energy was evaluated by phonon calculations. Thermodynamic properties such as volume thermal expansion, bulk modulus and specific heat of PuO 2 were investigated up to 1500 K
Mechanical, electronic, and optical properties of β-B{sub 6}O. First-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Yang, Ruike; Ma, Shaowei; Wei, Qun [Xidian Univ., Shaanxi (China). School of Physics and Optoelectronic Engineering; Du, Zheng [National Supercomputing Center in Shenzhen, Shenzhen (China)
2017-07-01
The mechanical, electronic, and optical properties of β-B{sub 6}O are calculated by first-principles. The structural optimization and all properties are calculated by the method of generalized gradient approximation - Perdew, Burke and Ernzerhof (PBE). The hardness of β-B{sub 6}O is 39 GPa under a pressure of 0 GPa, which indicates that it belongs to a hard material. The band gap is indirect with a value of 1.836 eV, showing that β-B{sub 6}O is a semiconductor. The research of the electron localization function shows that the bonds of β-B{sub 6}O are covalent bonds, which can increase the stability of the compound. The phonon dispersion curves present the dynamical stability of β-B{sub 6}O under pressures of 0 and 50 GPa. The optical properties of β-B{sub 6}O are also calculated. In the energy range from 0 to 18 eV, β-B{sub 6}O presents high reflectivity; it has a strong absorption in the energy range from 3 to 18 eV. The refractive index results show that light propagates through the β-B{sub 6}O in a difficult manner in the energy range from 6.9 to 16.5 eV. In addition, the energy of the plasma frequency for β-B{sub 6}O is 16.6 eV and the peak value of the loss function is 13.6. These properties provide the basis for the development and application of β-B{sub 6}O.
First-principles calculations of the electronic and structural properties of GaSb
Energy Technology Data Exchange (ETDEWEB)
Castaño-González, E.-E. [Universidad del Norte, Grupo de Investigación en Física Aplicada, Departamento de Física (Colombia); Seña, N. [Universidad Nacional de Colombia-Colombia, Departamento de Física, Grupo de Materiales Nanoestructurados y sus Aplicaciones (Colombia); Mendoza-Estrada, V.; González-Hernández, R., E-mail: rhernandezj@uninorte.edu.co [Universidad del Norte, Grupo de Investigación en Física Aplicada, Departamento de Física (Colombia); Dussan, A. [Universidad Nacional de Colombia-Colombia, Departamento de Física, Grupo de Materiales Nanoestructurados y sus Aplicaciones (Colombia); Mesa, F., E-mail: fredy.mesa@urosario.edu.co [Universidad del Rosario, Grupo NanoTech, Facultad de Ciencias Naturales y Matemáticas (Colombia)
2016-10-15
In this paper, we carried out first-principles calculations in order to investigate the structural and electronic properties of the binary compound gallium antimonide (GaSb). This theoretical study was carried out using the Density Functional Theory within the plane-wave pseudopotential method. The effects of exchange and correlation (XC) were treated using the functional Local Density Approximation (LDA), generalized gradient approximation (GGA): Perdew–Burke–Ernzerhof (PBE), Perdew-Burke-Ernzerhof revised for solids (PBEsol), Perdew-Wang91 (PW91), revised Perdew–Burke–Ernzerhof (rPBE), Armiento–Mattson 2005 (AM05) and meta-generalized gradient approximation (meta-GGA): Tao–Perdew–Staroverov–Scuseria (TPSS) and revised Tao–Perdew–Staroverov–Scuseria (RTPSS) and modified Becke-Johnson (MBJ). We calculated the densities of state (DOS) and band structure with different XC potentials identified and compared them with the theoretical and experimental results reported in the literature. It was discovered that functional: LDA, PBEsol, AM05 and RTPSS provide the best results to calculate the lattice parameters (a) and bulk modulus (B{sub 0}); while for the cohesive energy (E{sub coh}), functional: AM05, RTPSS and PW91 are closer to the values obtained experimentally. The MBJ, Rtpss and AM05 values found for the band gap energy is slightly underestimated with those values reported experimentally.
First principles study of the electronic structure and magnetic properties of YFeO3 oxide
Stoeffler, D.; Chaker, Z.
2017-11-01
The electronic structure and the magnetic properties of the multiferroic YFeO3 perovskite are investigated using two different first principles methods based on the Density Functional Theory with the so-called Hubbard correction. The results obtained with both the Projector Augmented Wave method implemented into the Vienna Ab inito Simulation Package and the Full-potential Linearized Augmented Plane Wave method implemented into FLEUR are compared to investigate the impact of the use of large Hubbard parameter UFe values allowing to get a reasonable bandgap. It is shown that both approaches lead to very similar results as long as the majority spin Fe d states remain hybridized with the O p states; this being the case up to UFe values around 4 eV. For larger UFe values, when the majority spin Fe d states are strongly localized and weakly hybridized with the O states, different crystal field splittings behaviors are obtained leading us to the conclusion that such large UFe values should be use with care. In addition, including the Spin-Orbit coupling contribution, the weakly canted antiferromagnetic structure is investigated and it is shown that the canting decreases when UFe is increased. Finally, the comparison with a method, taking the self-energy of the electrons (the GW approximation) into account, shows that even using small UFe values results in large distortion of the occupied part of the band structure for this particular system.
First-principles studies of electronic, transport and bulk properties of pyrite FeS2
Banjara, Dipendra; Malozovsky, Yuriy; Franklin, LaShounda; Bagayoko, Diola
2018-02-01
We present results from first principle, local density approximation (LDA) calculations of electronic, transport, and bulk properties of iron pyrite (FeS2). Our non-relativistic computations employed the Ceperley and Alder LDA potential and the linear combination of atomic orbitals (LCAO) formalism. The implementation of the LCAO formalism followed the Bagayoko, Zhao, and Williams (BZW) method, as enhanced by Ekuma and Franklin (BZW-EF). We discuss the electronic energy bands, total and partial densities of states, electron effective masses, and the bulk modulus. Our calculated indirect band gap of 0.959 eV (0.96), using an experimental lattice constant of 5.4166 Å, at room temperature, is in agreement with the measured indirect values, for bulk samples, ranging from 0.84 eV to 1.03 ± 0.05 eV. Our calculated bulk modulus of 147 GPa is practically in agreement with the experimental value of 145 GPa. The calculated, partial densities of states reproduced the splitting of the Fe d bands to constitute the dominant upper most valence and lower most conduction bands, separated by the generally accepted, indirect, experimental band gap of 0.95 eV.
First-principles studies of electronic, transport and bulk properties of pyrite FeS2
Directory of Open Access Journals (Sweden)
Dipendra Banjara
2018-02-01
Full Text Available We present results from first principle, local density approximation (LDA calculations of electronic, transport, and bulk properties of iron pyrite (FeS2. Our non-relativistic computations employed the Ceperley and Alder LDA potential and the linear combination of atomic orbitals (LCAO formalism. The implementation of the LCAO formalism followed the Bagayoko, Zhao, and Williams (BZW method, as enhanced by Ekuma and Franklin (BZW-EF. We discuss the electronic energy bands, total and partial densities of states, electron effective masses, and the bulk modulus. Our calculated indirect band gap of 0.959 eV (0.96, using an experimental lattice constant of 5.4166 Å, at room temperature, is in agreement with the measured indirect values, for bulk samples, ranging from 0.84 eV to 1.03 ± 0.05 eV. Our calculated bulk modulus of 147 GPa is practically in agreement with the experimental value of 145 GPa. The calculated, partial densities of states reproduced the splitting of the Fe d bands to constitute the dominant upper most valence and lower most conduction bands, separated by the generally accepted, indirect, experimental band gap of 0.95 eV.
Electronic and magnetic properties of nonmetal atoms doped blue phosphorene: First-principles study
Energy Technology Data Exchange (ETDEWEB)
Zheng, Huiling; Yang, Hui [Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), Department of Physics, Jilin University, Changchun 130012 (China); Wang, Hongxia [College of Mathematics, Physics and Information Science, Zhejiang Ocean University, Zhoushan 316000 (China); Du, Xiaobo [Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), Department of Physics, Jilin University, Changchun 130012 (China); Yan, Yu, E-mail: yanyu@jlu.edu.cn [Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), Department of Physics, Jilin University, Changchun 130012 (China)
2016-06-15
Using first-principles calculations, we study the geometrical structure, electronic structure and magnetic properties of substitutionally doped blue phosphorene with a series of nonmetallic atoms, including F, Cl, B, N, C, Si and O. The calculated formation energies and molecular dynamics simulations indicate that F, Cl, B, N, C, Si and O doped blue phosphorene are stable. Moreover, the substitutional doping of F, Cl, B and N cannot induce the magnetism in blue phosphorene due to the saturation or pairing of the valence electron of dopant and its neighboring P atoms. In contrast, ground states of C, Si and O doped blue phosphorene are spin-polarized and the magnetic moments induced by a doping atom are all 1.0 μ{sub B}, which is attributed to the appearance of an unpaired valence electron of C and Si and the formation of a nonbonding 3p electron of a neighboring P atom around O. Furthermore, the magnetic coupling between the moments induced by two C, Si and O are found to be long-range anti-ferromagnetic and the origin of the coupling can be attributed to the p–p hybridization interaction involving polarized electrons. - Highlights: • F, Cl, B, N, C, Si and O doped blue phosphorene are stable. • Substitutional doping of C, Si and O can produce the magnetism in blue phosphorene. • Magnetic coupling between two C, Si and O is long-range anti-ferromagnetic.
Magnetic and electronic properties of Cu1-xFexO from first principles calculations
Yang, Hua
2013-01-01
Magnetic and electronic properties of Cu1-xFexO systems with x = 6.25% and 12.5% have been investigated using first principles calculations. The ground state of CuO is an antiferromagnetic insulator. At x = 6.25%, Cu1-xFexO systems with Fe on 2 and 4 substitution positions are half-metallic due to the strong hybridization among Fe, the nearest O and Cu atoms, which may come from the double exchange coupling between Fe2+-O2--Cu2+. At x = 12.5%, Cu 1-xFexO system with Fe on 9-11 position has a strong spin polarization near the Fermi level and the system energy is lowest when the doped two Fe atoms form ferromagnetic configuration. This indicates the two doped Fe atoms prefer to form ferromagnetic configuration in Fe2+-O 2--Cu2+-O2--Fe2+ chains. While in the Fe on 7-11 position, the spin-down Fe-11 3d states have a large spin polarization near the Fermi level when the two doped Fe atoms form antiferromagnetic configuration. It is concluded that the transition metal doping can modify the magnetism and electronic structures of Cu 1-xFexO systems. This journal is © The Royal Society of Chemistry 2013.
Magnetic and electronic properties of Fe3O4/graphene heterostructures: First principles perspective
Mi, Wenbo
2013-02-27
Magnetic and electronic properties of Fe3O4(111)/graphene heterostructures are investigated by first principles calculations. Different structural models have been considered, which differ in the interface termination of Fe3O4(111) surface with respect to the same monolayer graphene. In three models, the magnetic moment of Fe(A) has a major change due to less O atoms surrounding Fe(A) atoms than Fe(B). Magnetic moment is enhanced by 8.5%, 18.5%, and 8.7% for models (a), (b), and (c), respectively. Furthermore, the spin polarization of models (a) and (c) is lowered due to the simultaneous occurrence of density of states of spin-up Fe(A) and spin-down Fe(B) at Fermi lever. The spin polarization of model (b) remains the same as that of bulk Fe3O4. Our results suggest that different interface terminations and Fe(A) play an important role in determining the magnetism strength and spin polarization.
Shimada, Kazuhiro
2018-03-01
We perform first-principles calculations to investigate the crystal structure, elastic and piezoelectric properties, and spontaneous polarization of orthorhombic M2O3 (M = Al, Ga, In, Sc, Y) with Pna21 space group based on density functional theory. The lattice parameters, full elastic stiffness constants, piezoelectric stress and strain constants, and spontaneous polarization are successfully predicted. Comparison with available experimental and computational results indicates the validity of our computational results. Detailed analysis of the results clarifies the difference in the bonding character and the origin of the strong piezoelectric response and large spontaneous polarization.
Li, Chun-Mei; Hu, Yan-Fei
2017-12-01
The composition-dependent properties and their correlation with the phase stability of Fe75+xPd25-x (- 10.0 ≤x ≤10.0 ) alloys are systematically investigated by using first-principles exact muffin-tin orbitals (EMTO)-coherent potential approximation (CPA) calculations. It is shown that the martensitic transformation (MT) from L 12 to body-centered-tetragonal (bct) occurs in the ordered alloys with about -5.0 ≤x ≤10.0 . In both the L 12 and bct phases, the evaluated a and c/a agree well with the available experimental data; the average magnetic moment per atom increases whereas the local magnetic moments of Fe atoms, dependent on both their positions and the structure of the alloy, decrease with increasing x. The tetragonal shear elastic constant of the L 12 phase ( C ' ) decreases whereas that of the bct phase (Cs) increases with x. The tetragonality of the martensite ( |1 -c /a | ) increases whereas its energy relative to the austenite with a negative value decreases with Fe addition. All these effects account for the increase of MT temperature (TM) with x. The MT from L 12 to bct is finally confirmed originating from the splitting of Fe 3d Eg and T2 g bands upon tetragonal distortion due to the Jahn-Teller effect.
Energy Technology Data Exchange (ETDEWEB)
Masuda-Jindo, K. [Department of Materials Science and Engineering, Tokyo Institute of Technology, Nagatsuta 4259, Midori-ku, Yokohama 226-8503 (Japan)], E-mail: kmjindo@issp.u-tokyo.ac.jp; Vu Van Hung; Hoa, N.T. [Department of Physics, Hanoi National Pedagogic University, km8 Hanoi-Sontay Highway, Hanoi (Viet Nam); Turchi, P.E.A. [Lawrence Livermore National Laboratory, PO Box 808, L-353 LLNL, Livermore, CA 94551 (United States)
2008-03-06
The thermodynamic quantities of high temperature metals and alloys are studied using the statistical moment method, going beyond the quasi-harmonic approximations. Including the power moments of the atomic displacements up to the fourth order, the Helmholtz free energies and the related thermodynamic quantities are derived explicitly in closed analytic forms. The configurational entropy term is taken into account by using the tetrahedron cluster approximation of the cluster variation method (CVM). The energetics of the binary (Ta-W and Mo-Ta) alloys are treated within the framework of the first-principles TB-LMTO (tight-binding linear muffin tin orbital) method coupled to CPA (coherent potential approximation) and GPM (generalized perturbation method). The equilibrium phase diagrams are calculated for the refractory Ta-W and Mo-Ta bcc alloys. In addition, the mechanical properties, i.e., temperature dependence of the elastic moduli C{sub 11}, C{sub 12} and C{sub 44} and those of the ideal tensile and shear strengths of the bcc Ta-W and Ta-Mo alloys have been also studied.
First-principles theory of Ta up to 10 Mbar pressure: Structural and mechanical properties
Söderlind, Per; Moriarty, John A.
1998-05-01
Fundamental high-pressure structural and mechanical properties of Ta have been investigated theoretically over a wide pressure range, 0-10 Mbar, by means of ab initio electronic-structure calculations. The calculations are fully relativistic and use a state-of-the-art treatment of gradient corrections to the exchange-correlation potential and energy within density-functional theory. The calculated zero-temperature equation of state for bcc Ta is in good agreement with diamond-anvil-cell measurements up to 750 kbar and with reduced shock data to 2.3 Mbar. The crystal-structure stability among bcc, fcc, hcp, and A15 phases has been studied as a function of compression and the observed ambient-pressure bcc phase is found to be thermodynamically stable throughout the entire 0-10 Mbar range. At the upper end of this range, a metastable fcc phase develops with positive elastic moduli and a decreasing fcc-bcc energy difference, suggesting that at even higher pressures above 10 Mbar, fcc Ta will become stable over the bcc phase. Elastic constants, the H- and N-point zone-boundary phonons, and the ideal shear strength have also been calculated for bcc Ta up to 10 Mbar pressure. The elastic moduli and phonons are in good agreement with experiment at ambient pressure and remain real and positive for all compressions studied, demonstrating that the bcc phase is mechanically stable in this regime. The calculated elastic constants validate the assumed pressure scaling of the shear modulus in the Steinberg-Guinan strength model of Ta, while the calculated values of ideal shear strength provide an upper bound to the high-pressure yield stress.
A first-principles study on the magnetic properties of nonmetal atom doped phosphorene monolayers.
Zheng, Huiling; Zhang, Jianmin; Yang, Baishun; Du, Xiaobo; Yan, Yu
2015-07-07
In order to induce magnetism in two-dimensional semiconductors for their applications in spintronic devices and novel chemical and electronic properties of semiconducting phosphorene, the geometrical structure, electronic and magnetic properties of doped phosphorene monolayers with a series of nonmetal atoms, including H, F, Cl, Br, I, B, C, Si, N, As, O, S and Se, were systematically investigated using first-principles calculations. The results show that although the substitutional doping of H, F, Cl, Br, I, B, N, O, S or Se results in large structural deformation at the doping sites of phosphorene monolayers, all neutral nonmetal atom doped systems are stable. The calculated formation energies reveal that the substitutional doping of numerous nonmetal atoms in phosphorene monolayer are possible under appropriate experimental conditions, and the charged dopants C(-), Si(-), S(+) and Se(+) are stable. Moreover, the substitutional doping of H, F, Cl, Br, I, B, N, As, C(-), Si(-), S(+) or Se(+) cannot induce magnetism in phosphorene monolayer due to the saturation or pairing of valence electrons of dopant and its neighboring P atoms, whereas ground states of neutral C, Si, O, S or Se doped systems are magnetic due to the appearance of an unpaired valence electron of C and Si or the formation of a nonbonding 3p electron of a neighboring P atom around O, S and Se. Furthermore, the magnetic coupling between the moments induced by two Si, O, S or Se are long-range anti-ferromagnetic and the coupling can be attributed to the hybridization interaction involving polarized electrons, whereas the coupling between the moments induced by two C is weak.
First principles study of magneto-optical properties of Fe-doped ZnO
Energy Technology Data Exchange (ETDEWEB)
Shaoqiang, Guo [College of Science, Inner Mongolia University of Technology, Hohhot 010051 (China); Qingyu, Hou, E-mail: by0501119@126.com [College of Science, Inner Mongolia University of Technology, Hohhot 010051 (China); Zhenchao, Xu [College of Science, Inner Mongolia University of Technology, Hohhot 010051 (China); Chunwang, Zhao [College of Science, Inner Mongolia University of Technology, Hohhot 010051 (China); College of Arts and Sciences, Shanghai Maritime University, Shanghai 201306 (China)
2016-12-15
Studies on optical band gaps and absorption spectra of Fe-doped ZnO have conflicting conclusions, such as contradictory redshifted and blueshifted spectra. To solve this contradiction, we constructed models of un-doped and Fe-doped ZnO using first-principles theory and optimized the geometry of the three models. Electronic structures and absorption spectra were also calculated using the GGA+U method. Higher doping content of Fe resulted in larger volume of doped system, and higher total energy resulted in lower stability. Higher formation energy also led to more difficult doping. Meanwhile, the band gaps broadened and the absorption spectra exhibited an evident blue shift. The calculations were in good agreement with the experimental results. Given the unipolar structure of ZnO, four possible magnetic coupling configurations for Zn{sub 14}Fe{sub 2}O{sub 16} were calculated to investigate the magnetic properties. Results suggest that Fe doping can improve ferromagnetism in the ZnO system and that ferromagnetic stabilization was mediated by p–d exchange interaction between Fe-3d and O-2p orbitals. Therefore, the doped system is expected to obtain high stability and high Curie temperature of diluted magnetic semiconductor material, which are useful as theoretical bases for the design and preparation of the Fe-doped ZnO system’s magneto-optical properties. - Highlights: • A biomonitoring tool for the freshwater zone of template estuaries. • Water quality characterization related to nutrients and organic matter enrichment. • The percentage of a group of 24 tolerant species were capable of detecting the impairment of the water quality. • Characterization of morpho-functional traits of the selected tolerant species.
Hoffmann, Martin; Marmodoro, Alberto; Nurmi, Eero; Kokko, Kalevi; Vitos, Levente; Ernst, Arthur; Hergert, Wolfram
2012-09-01
We investigate the elastic properties of the binary alloy Ag-Pd. The lattice constant of this system shows significant deviations from the linear behavior anticipated by the semi-empirical Vegard's rule. This effect was formerly studied by assuming total substitutional disorder, and described by the coherent potential approximation (CPA). Theoretical phase diagram investigations have however suggested three ordered phases at low temperatures, and we extend our first-principles investigation to include such scenarios through the adoption of an extended unit cell representation and a recently developed multisublattice generalization of the original CPA. This allows us to explore equilibrium lattice constant and bulk modulus within a unified approach even in the presence of partial long-range order. We obtain significant variations of the bulk modulus in comparison to the totally disordered picture, and again very rich deviations from more intuitive predictions of a simple linear behavior. We follow former suggestions to analyze the different regimes in connection with topological transitions of the Fermi surface, examined through Bloch spectral function calculations.
Energy Technology Data Exchange (ETDEWEB)
Ekuma, C.E., E-mail: panaceamee@yahoo.com [Department of Physics and Astronomy and Center for Computation and Technology, Louisiana State University (LSU) Baton Rouge, Louisiana 70803 (United States); Jarrell, M.; Moreno, J. [Department of Physics and Astronomy and Center for Computation and Technology, Louisiana State University (LSU) Baton Rouge, Louisiana 70803 (United States); Franklin, L.; Zhao, G.L.; Wang, J.T.; Bagayoko, D. [Department of Physics, Southern University and A and M College in Baton Rouge (SUBR) Baton Rouge, Louisiana 70813 (United States)
2012-10-15
The electronic structure of the ferroelectric crystal, NaNO{sub 2}, is studied by means of first-principles, local density calculations. Our ab-initio, non-relativistic calculations employed a local density functional approximation (LDA) potential and the linear combination of atomic orbitals (LCAO). Following the Bagayoko, Zhao, Williams, method, as enhanced by Ekuma and Franklin (BZW-EF), we solved self-consistently both the Kohn-Sham equation and the equation giving the ground state charge density in terms of the wave functions of the occupied states. We found an indirect band gap of 2.83 eV, from W to R. Our calculated direct gaps are 2.90, 2.98, 3.02, 3.22, and 3.51 eV at R, W, X, {Gamma}, and T, respectively. The band structure and density of states show high localization, typical of a molecular solid. The partial density of states shows that the valence bands are formed only by complex anionic states. These results are in excellent agreement with experiment. So are the calculated densities of states. Our calculated electron effective masses of 1.18, 0.63, and 0.73 m{sub o} in the {Gamma}-X, {Gamma}-R, and {Gamma}-W directions, respectively, show the highly anisotropic nature of this material. -- Highlights: Black-Right-Pointing-Pointer Ferro-NaNO{sub 2} has been studied using the BZW-EF method. Black-Right-Pointing-Pointer For the valence states, polarization has primacy over spherical symmetry. Black-Right-Pointing-Pointer The optimal basis set is verified to be complete for the ground state of NaNO{sub 2}. Black-Right-Pointing-Pointer Computed electronic and related properties are in agreement with experiment.
First-principle study on magnetic properties of Mn/Fe codoped ZnS
Energy Technology Data Exchange (ETDEWEB)
Chen Hongxia, E-mail: chenhongxia1@sina.com [College of Physical Science and Electronic Techniques, Yancheng Teachers University, Yancheng 224002 (China); Department of Physics, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China)
2012-07-15
We studied the magnetic properties of Mn/Fe codoped ZnS comparatively with and without defects using first-principle calculation. The calculated results indicate that the Mn/Fe codoped ZnS system tends to stabilize in a ferrimagnetic (FiM) configuration. To obtain a ferromagnetic (FM) configuration, we consider the doped system with defects, such as S or Zn vacancy. The calculated results indicate that the doped system with Zn vacancy favors FiM states. Although the FM states of the doped system with S vacancy are more stable than the FiM states in negative charge states, the FM states are not stable enough to exist. Finally, we replaced an S atom by a C atom in the doped system. The C atom prefers to substitute the S atom connecting Mn and Fe atoms. The formation energy of this defect is -0.40 eV, showing that Mn/Fe/C codoped ZnS can be fabricated easily by experiments. Furthermore, the FM state was lower in energy than the FiM state by 114 meV. Such a large energy difference between the FM and FiM states implies that room temperature ferromagnetism could be expected in such a system. - Highlights: Black-Right-Pointing-Pointer Mn/Fe codoped ZnS system tends to stabilize in a ferrimagnetic configuration with or without defects. Black-Right-Pointing-Pointer By additional C codoping, the doped system tends to stabilize in a ferromagnetic configuration. Black-Right-Pointing-Pointer Energy difference between ferrimagnetic and ferromagnetic states is 114 meV. Black-Right-Pointing-Pointer This indicates room temperature ferromagnetism can be likely in such a system.
First principles study of optical properties of molybdenum disulfide: From bulk to monolayer
Hieu, Nguyen N.; Ilyasov, Victor V.; Vu, Tuan V.; Poklonski, Nikolai A.; Phuc, Huynh V.; Phuong, Le T. T.; Hoi, Bui D.; Nguyen, Chuong V.
2018-03-01
In this paper, we theoretically study the optical properties of both bulk and monolayer MoS2 using first-principles calculations. The optical characters such as: dielectric function, optical reflectivity, and electron energy-loss spectrum of MoS2 are observed in the energy region from 0 to 15 eV. At equilibrium state the dielectric constant in the parallel E∥ x and perpendicular E∥ z directions are of 15.01 and 8.92 for bulk while they are 4.95 and 2.92 for monolayer MoS2, respectively. In the case of bulk MoS2, the obtained computational results for both real and imaginary parts of the dielectric constant are in good agreement with the previous experimental data. In the energy range from 0 to 6 eV, the dielectric functions have highly anisotropic, whereas they become isotropic when the energy is larger than 7 eV. For the adsorption spectra and optical reflectivity, both the collective plasmon resonance and (π + σ) electron plasmon peaks are observed, in which the transition in E∥ x direction is accordant with the experiment data more than the transition in E∥ z direction is. The refractive index, extinction index, and electron energy-loss spectrum are also investigated. The observed prominent peak at 23.1 eV in the energy-loss spectra is in good agreement with experiment value. Our results may provide a useful potential application for the MoS2 structures in electronic and optoelectronic devices.
A first-principles study of the properties of four predicted novel phases of AlN
Yang, Ruike; Zhu, Chuanshuai; Wei, Qun; Du, Zheng
2017-05-01
Structural, elastic, thermodynamic, electronic and optical properties of four predicted novel AlN phases (Pmn21-AlN, Pbam-AlN, Pbca-AlN and Cmcm-AlN) are calculated using first-principles according to density function theory (DFT). These phases were found using the CALYPSO method but have not yet been synthesized experimentally. Here we predict some of their properties. The properties are analyzed by means of GGA-PBE and PBE0 respectively. The more precision results are obtained by PBE0. Cmcm-AlN owns better plasticity and it's Young's modulus has clearer anisotropy than Pmn21-AlN, Pbam-AlN and Pbca-AlN. The Debye temperature, under higher temperature, shows weak temperature dependence and approach to a constant value. The Dulong-Petit limit of all four novel AlN phases and wz-AlN is about 48 J mol-1 K-1 and they have almost the same temperature law. The band structures show that the four AlN are the wide direct band gap semiconductors, which band gaps are 5.95 (Pmn21-AlN), 5.99 (Pbam-AlN), 5.88 (Pbca-AlN) and 5.59 eV (Cmcm-AlN). The bonding behaviors are the combination of covalent and ionic nature. The dielectric constants, refractive index, reflectivity, absorption, loss spectra, conductivity and Raman spectra are also calculated in detail. All four phases have a lower plasma frequency than of wz-AlN.
Haskins, Justin B.; Lawson, John W.
2017-05-01
We present a procedure to determine temperature-dependent thermodynamic properties of crystalline materials from density functional theory molecular dynamics (DFT-MD). Finite temperature properties (structural, thermal, and mechanical properties) of the phases (ground state monoclinic B33, martensitic B19', and austenitic B2) of the shape memory alloy NiTi are investigated. Fluctuation formulas and numerical derivatives are used to evaluate mechanical and thermal properties. A modified version of thermodynamic upsampling is used to predict properties in the high DFT convergence threshold limit from low threshold simulations. DFT convergence thresholds. In addition, a thermodynamic integration expression is developed to compute free energies from isobaric DFT-MD simulations that accounts for volume changes. Structural parameters, elastic constants, volume expansion, and specific heats as a function of temperature are evaluated. Phase transitions between B2 and B19' and between B19' and B33 are characterized according to their thermal energy, entropy, and free energy differences as well as their latent heats. Anharmonic effects are shown to play a large role in both stabilizing the austenite B2 phase and suppressing the martensitic phase transition. The quasiharmonic approximation to the free energy results in large errors in estimating the martensitic transition temperature by neglecting these large anharmonic components.
A first principle study on electronic property of bismuth nano tubes
International Nuclear Information System (INIS)
Su Changrong; Li Jiaming
2002-01-01
A first principle molecular dynamics with density functional theory and ultra-soft pseudopotential has been performed on the bismuth nano tubes. The strain energies are found to follow the classical 1/R 2 strain law. The bismuth nano tubes are expected as semi-conductor with the band gaps around 0.7-0.8 eV
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.
Lattice dynamic properties of BaSi 2 and BaGe 2 from first principle calculations
Peng, H.; Wang, C. L.; Li, J. C.; Zhang, R. Z.; Wang, M. X.; Wang, H. C.; Sun, Y.; Sheng, M.
2010-08-01
First principle calculations have been performed to study the lattice vibration of Ba X2 ( X = Si, Ge). A rigid-unit vibrational mode has been observed, and this mode confines and scatters acoustic phonon modes, leading to a low thermal conductivity. Their stability is analyzed from the calculations of thermodynamic properties.
Lattice dynamic properties of BaSi{sub 2} and BaGe{sub 2} from first principle calculations
Energy Technology Data Exchange (ETDEWEB)
Peng, H., E-mail: penghua@mail.sdu.edu.c [School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China); Wang, C.L.; Li, J.C.; Zhang, R.Z.; Wang, M.X.; Wang, H.C.; Sun, Y.; Sheng, M. [School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China)
2010-08-09
First principle calculations have been performed to study the lattice vibration of BaX{sub 2} (X = Si, Ge). A rigid-unit vibrational mode has been observed, and this mode confines and scatters acoustic phonon modes, leading to a low thermal conductivity. Their stability is analyzed from the calculations of thermodynamic properties.
First principle investigations of the physical properties of hydrogen-rich MgH2
Zarshenas, Mohammed
2013-11-28
Hydrogen being a cleaner energy carrier has increased the importance of hydrogen-containing light metal hydrides, in particular those with large gravimetric hydrogen density like magnesium hydride (MgH2). In this study, density functional and density functional perturbation theories are combined to investigate the structural, elastic, thermodynamic, electronic and optical properties of MgH2. Our structural parameters calculated with those proposed by Perdew, Burke and Ernzerof generalized gradient approximation (PBE-GGA) and Wu-Cohen GGA (WC-GGA) are in agreement with experimental measurements, however the underestimated band gap values calculated using PBE-GGA and WC-GGA were greatly improved with the GGA suggested by Engle and Vosko and the modified Becke-Johnson exchange correlation potential by Trans and Blaha. As for the thermodynamic properties the specific heat values at low temperatures were found to obey the T3 rule and at higher temperatures Dulong and Petit\\'s law. Our analysis of the optical properties of MgH2 also points to its potential application in optoelectronics. © 2013 The Royal Swedish Academy of Sciences.
First-principles calculation of the magnetic properties of paramagnetic fcc iron
International Nuclear Information System (INIS)
Johnson, D.D.; Gyorffy, B.L.; Pinski, F.J.; Staunton, J.; Stocks, G.M.
1985-01-01
Using the disordered local moment picture of itinerant magnetism, we present calculations of the temperature and volume dependence of the magnetic moment and spin-spin correlations for fcc Fe in the paramagnetic state. These calculations are based on the parameter-free, first principles approach of local spin density functional theory and the coherent potential approximation is used to treat the disorder associated with the random orientation of the local moments
Electronic, thermodynamics and mechanical properties of LaB6 from first-principles
Ivashchenko, V. I.; Turchi, P. E. A.; Shevchenko, V. I.; Medukh, N. R.; Leszczynski, Jerzy; Gorb, Leonid
2018-02-01
Up to date, the electronic structure properties of amorphous lanthanum hexaboride, a-LaB6, were not yet investigated, and the thermodynamic and mechanical properties of crystalline lanthanum hexaboride (c-LaB6) were studied incompletely. The goal of this work was to fill these gaps in the study of lanthanum hexaborides. The electronic and phonon structures, thermodynamic and mechanical properties of both crystalline and amorphous lanthanum hexaborides (c-LaB6, a-LaB6, respectively) were investigated within the density functional theory. An amorphyzation of c-LaB6 gives rise to the metal - semiconductor transition. The thermal conductivity decreases on going from c-LaB6 to a-LaB6. The elastic moduli, hardness, ideal tensile and shear strengths of a-LaB6 are significantly lower compared to those of the crystalline counterpart, despite the formation of the icosahedron-like boron network in the amorphous phase. For c-LaB6, the stable boron octahedrons are preserved after the failure under tensile and shear strains. The peculiarity in the temperature dependence of heat capacity, Cp(T), at 50 K is explained by the availability of a sharp peak at 100 cm-1 in the phonon density of states of c-LaB6. An analysis of the Fermi surface indicates that this peak is not related to the shape of the Fermi surface, and is caused by the vibration of lanthanum atoms. In the phonon spectrum of a-LaB6, the peak at 100 cm-1 is significantly broader than in the spectrum of c-LaB6, for which reason the anomaly in the Cp(T) dependence of a-LaB6 does not appear. The calculated characteristics are in good agreement with the available experimental data.
Pan, Hui; Zhang, Yong-Wei; Shenoy, Vivek B; Gao, Huajian
2011-01-01
Abstract The magnetic properties of metal-functionalized graphitic carbon nitride nanotubes were investigated based on first-principles calculations. The graphitic carbon nitride nanotube can be either ferromagnetic or antiferromagnetic by functionalizing with different metal atoms. The W- and Ti-functionalized nanotubes are ferromagnetic, which are attributed to carrier-mediated interactions because of the coupling between the spin-polarized d and p electrons and the formation of the impurit...
Wobbled electronic properties of lithium clusters: Deterministic approach through first principles
Kushwaha, Anoop Kumar; Nayak, Saroj Kumar
2018-03-01
The innate tendency to form dendritic growth promoted through cluster formation leading to the failure of a Li-ion battery system have drawn significant attention of the researchers towards the effective destabilization of the cluster growth through selective implementation of electrolytic media such as acetonitrile (MeCN). In the present work, using first principles density functional theory and continuum dielectric model, we have investigated the origin of oscillatory nature of binding energy per atom of Lin (n ≤ 8) under the influence of MeCN. In the gas phase, we found that static mean polarizability is strongly correlated with binding energy and shows oscillatory nature with cluster size due to the open shell of Lin cluster. However, in acetonitrile medium, the binding energy has been correlated with electrostatic Lin -MeCN interaction and it has been found that both of them possess wobbled behavior characterized by the cluster size.
Lee, Joohwi; Ikeda, Yuji; Tanaka, Isao
2017-11-01
Martensitic transformation with good structural compatibility between parent and martensitic phases are required for shape memory alloys (SMAs) in terms of functional stability. In this study, first-principles-based materials screening is systematically performed to investigate the intermetallic compounds with the martensitic phases by focusing on energetic and dynamical stabilities as well as structural compatibility with the parent phase. The B2, D03, and L21 crystal structures are considered as the parent phases, and the 2H and 6M structures are considered as the martensitic phases. In total, 3384 binary and 3243 ternary alloys with stoichiometric composition ratios are investigated. It is found that 187 alloys survive after the screening. Some of the surviving alloys are constituted by the chemical elements already widely used in SMAs, but other various metallic elements are also found in the surviving alloys. The energetic stability of the surviving alloys is further analyzed by comparison with the data in Materials Project Database (MPD) to examine the alloys whose martensitic structures may cause further phase separation or transition to the other structures.
First-principles calculation of transport property in nano-devices under an external magnetic field
International Nuclear Information System (INIS)
Chen Jingzhe; Zhang Jin; Han Rushan
2008-01-01
The mesoscopic quantum interference phenomenon (QIP) can be observed and behaves as the oscillation of conductance in nano-devices when the external magnetic field changes. Excluding the factor of impurities or defects, specific QIP is determined by the sample geometry. We have improved a first-principles method based on the matrix Green's function and the density functional theory to simulate the transport behaviour of such systems under a magnetic field. We have studied two kinds of QIP: universal conductance fluctuation (UCF) and Aharonov–Bohm effect (A–B effect). We find that the amplitude of UCF is much smaller than the previous theoretical prediction. We have discussed the origin of difference and concluded that due to the failure of ergodic hypothesis, the ensemble statistics is not applicable, and the conductance fluctuation is determined by the flux-dependent density of states (DOSs). We have also studied the relation between the UCF and the structure of sample. For a specific structure, an atomic circle, the A–B effect is observed and the origin of the oscillation is also discussed
Das, Pratik Kumar; Mandal, Nibir; Arya, Ashok
2016-04-01
Cassiterite (SnO2) is the most important ore mineral used for extraction of metal tin. Using DFT calculations we investigate the pressure-dependent variations of elastic anisotropy in the following SnO2 phases: rutile-type (tetragonal; P42/mnm), CaCl2-type (orthorhombic; Pnnm)-, α-PbO2-type (orthorhombic; Pbcn)-, and fluorite-type (cubic; Fm-3m). We estimate the shear anisotropy (A1 and A3) on {100} and {001} crystallographic planes of the tetragonal phase, and (A1, A2 and A3) on {100}, {010} and {001} crystallographic planes of the orthorhombic phases. The rutile-type phase shows strongest shear anisotropy on the {001} planes (A2 > 4.8), and the degree of anisotropy increases nonlinearly with pressure. Conversely, the anisotropy is almost absent on the {100} planes (i.e. A1 ˜ 1) irrespective of the pressure. The CaCl2-type phase exhibits similar shear anisotropy behavior preferentially on {001} (A3 > 5), while A1 and A2 remain close to 1. The α-PbO2-type phase shows strikingly different elastic anisotropy characterized by a reversal in anisotropy (A3 > 1 to type structure at 40 GPa exhibits multi-peaked structure of the valence band which is indicative of underlying layered structure, which corresponds to the anisotropy reversal. Our study also analyzes the directional Young's moduli for the tetragonal and orthorhombic phases as a function of pressure. The rutile-type SnO2 phase is the stiffest material due to its high Young's modulus, while fluorite-type SnO2has the lowest stiffness. The directional Young's moduli of both rutile -type and CaCl2 -type, is very pressure sensitive along the diagonals in {001} plane. Furthermore, in the case of α-PbO2, the Young's modulus is pressure sensitive on {100} and {010}, rather than {001}. Bibliography E. Deligoz, K. Colakoglu, Y.O. Cliftci, J. Phys. Chem. Solids 69 (2008) 859. P. Ravindran, L. Fast, P.A. Korzhavyi, B. Johnnsson, J. Wills, O. Eriksson, J. Appl. Phys. 84 (1998) 4891. R. A. Casali, J. Lasave, M. A
First principles calculations of optical properties of the armchair SiC ...
Indian Academy of Sciences (India)
Dao-Bang Lu
2018-02-13
principles; optical properties; ... quality graphene, a single layer carbon sheet with a honeycomb structure, quasi-one-dimensional nanoma ... electron mobility, excellent mechanical properties, etc., are expected to be ideal materials for ...
Wang, Jing-Jing; Hermann, Andreas; Kuang, Xiao-Yu; Jin, Yuan-Yuan; Lu, Cheng; Zhang, Chuan-Zhao; Ju, Meng; Si, Meng-Ting; Iitaka, Toshiaki
2015-01-01
To understand the structural stability, physical properties, and hardness of the Rh–Si system, we have performed systematic first-principles crystal structure searches for various stoichiometries of rhodium silicides, utilizing the particle swarm optimization method. A new stable stoichiometry, Rh4Si5 with space group P21/m, has been found at atmospheric pressure, complementing the three well-known rhodium silicides of Rh2Si (Pnma), Rh5Si3 (Pbam), and RhSi (Pnma). Our calculations of the stru...
A first-principles study of electronic properties of H and F-terminated zigzag BNC nanoribbons
Energy Technology Data Exchange (ETDEWEB)
Alaal, Naresh [IITB-Monash Research Academy, Old CSE Building 2 nd Floor, IIT Bombay, Powai, Mumbai 400076, India. (India); Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India. (India); Department of Materials Engineering, Monash University, Clayton, Victoria -3800, Australia. (Australia); Medhekar, Nikhil [Department of Materials Engineering, Monash University, Clayton, Victoria -3800, Australia. (Australia); Shukla, Alok, E-mail: shukla@phy.iitb.ac.in [Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India. (India)
2016-05-06
Nanoribbons are quasi one-dimensional structures which have interesting electronic properties on the basis of their edge geometries, and width. We studied the electronic properties of hydrogen and fluorine-terminated zigzag BNC nanoribbons (BNCNRs) using a first-principles based density functional theory approach. We considered BNCNRs that were composed of an equal number of C-C and B-N dimers; one of the edges ends with an N atom and opposite edge ends with a C atom. These two edge atoms are passivated by H or F atoms. Our results suggest that hydrogen-terminated BNCNRs (H-BNCNRs) and flourine-terminated BNCNRs (F-BNCNRs) have different electronic properties. H-BNCNRs exhibit intrinsic half-metallic behavior while F-BNCNRs are indirect band gap semiconductors. Chemical functionalization of BNCNRs with H and F atoms show that BNCNRs have a diverse range of electronic properties.
Order-of-magnitude physics of neutron stars. Estimating their properties from first principles
Energy Technology Data Exchange (ETDEWEB)
Reisenegger, Andreas; Zepeda, Felipe S. [Pontificia Universidad Catolica de Chile, Instituto de Astrofisica, Facultad de Fisica, Macul (Chile)
2016-03-15
We use basic physics and simple mathematics accessible to advanced undergraduate students to estimate the main properties of neutron stars. We set the stage and introduce relevant concepts by discussing the properties of ''everyday'' matter on Earth, degenerate Fermi gases, white dwarfs, and scaling relations of stellar properties with polytropic equations of state. Then, we discuss various physical ingredients relevant for neutron stars and how they can be combined in order to obtain a couple of different simple estimates of their maximum mass, beyond which they would collapse, turning into black holes. Finally, we use the basic structural parameters of neutron stars to briefly discuss their rotational and electromagnetic properties. (orig.)
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.
Nagarajan, V.; Chandiramouli, R.
2018-03-01
The electronic properties of antimonene nanotubes and nanoribbons hydrogenated along the zigzag and armchair borders are investigated with the help of density functional theory (DFT) method. The structural stability of antimonene nanostructures is confirmed with the formation energy. The electronic properties of hydrogenated zigzag and armchair antimonene nanostructures are studied in terms of highest occupied molecular orbital (HOMO) & lowest unoccupied molecular orbital (LUMO) gap and density of states (DOS) spectrum. Moreover, due to the influence of buckled orientation, hydrogen passivation and width of antimonene nanostructures, the HOMO-LUMO gap widens in the range of 0.15-0.41 eV. The findings of the present study confirm that the electronic properties of antimonene nanostructures can be tailored with the influence of width, orientation of the edges, passivation with hydrogen and morphology of antimonene nanostructures (nanoribbons, nanotubes), which can be used as chemical sensor and for spintronic devices.
Nagarajan, V.; Chandiramouli, R.
2017-09-01
The electronic properties of arsenene nanotubes and nanoribbons with hydrogenation along the zigzag and armchair edges are studied using density functional theory (DFT) technique. The structural stability of hydrogenated zigzag and armchair arsenene nanostructures are confirmed with formation energy. The electronic properties of arsenene nano-conformers are described in terms of energy band structure and projected density of states spectrum. Furthermore, owing to the influence of hydrogen passivation, buckled orientation and width of arsenene nanostructures, the band gap widens in the range of 0.38-1.13 eV. The findings of the present work confirm that the electronic properties of arsenene nanomaterial, can be fine-tuned with the influence of passivation with hydrogen, zigzag or armchair border shapes and effect of the width of nanoribbons or nanotubes, which can be utilized as spintronic device and chemical sensor.
Saeed, Yasir
2014-05-11
Thermoelectric materials can convert waste heat into electric power and thus provide a way to reduce the dependence on fossil fuels. Our aim is to model the underlying materials properties and, in particular, the transport as controlled by electrons and lattice vibrations. The goal is to develop an understanding of the thermoelectric properties of selected materials at a fundamental level. The structural, electronic, optical, and phononic properties are studied in order to tune the transport, focusing on KxRhO2, NaxRhO2, PtSb2 and Bi2Se3. The investigations are based on density functional theory as implemented in the all electron linearized augmented plane wave plus local orbitals WIEN2k and pseudo potential Quantum-ESPRESSO codes. The thermoelectric properties are derived from Boltzmann transport theory under the constant relaxation time approximation, using the BoltzTraP code. We will discuss first the changes in the electronic band structure under variation of the cation concentration in layered KxRhO2 in the 2H phase and NaxRhO2 in the 3R phase. We will also study the hydrated phase. The deformations of the RhO6 octahedra turn out to govern the thermoelectric properties, where the high Seebeck coefficient results from ”pudding mold" bands. We investigate the thermoelectric properties of electron and hole doped PtSb2, which is not a layered material but shares “pudding mold" bands. PtSb2 has a high Seebeck coefficient at room temperature, which increases significantly under As alloying by bandgap opening and reduction of the lattice thermal conductivity. Bi2Se3 (bulk and thin film) has a larger bandgap then the well-known thermoelectric material Bi2Te3, which is important at high temperature. The structural stability, electronic structure, and transport properties of one to six quintuple layers of Bi2Se3 will be discussed. We also address the effect of strain on a single quintuple layer by phonon band structures. We will analyze the electronic and transport
First principles results of structural and electronic properties of ZnS
Indian Academy of Sciences (India)
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 results of structural and electronic properties of ZnS ...
Indian Academy of Sciences (India)
and electronic properties, nature of bonding and overall stability of clusters has been studied. Keywords. Projector augmented wave .... of each molecular orbital (MO) to the total charge density. It can be used to discuss the nature of ..... η, the global hardness parameter, and is found to be high- est for Zn3S3. The second ...
Shi, Guangsha
Solar electricity is a reliable and environmentally friendly method of sustainable energy production and a realistic alternative to conventional fossil fuels. Moreover, thermoelectric energy conversion is a promising technology for solid-state refrigeration and efficient waste-heat recovery. Predicting and optimizing new photovoltaic and thermoelectric materials composed of Earth-abundant elements that exceed the current state of the art, and understanding how nanoscale structuring and ordering improves their energy conversion efficiency pose a challenge for materials scientists. I approach this challenge by developing and applying predictive high-performance computing methods to guide research and development of new materials for energy-conversion applications. Advances in computer-simulation algorithms and high-performance computing resources promise to speed up the development of new compounds with desirable properties and significantly shorten the time delay between the discovery of new materials and their commercial deployment. I present my calculated results on the extraordinary properties of nanostructured semiconductor materials, including strong visible-light absorbance in nanoporous silicon and few-layer SnSe and GeSe. These findings highlight the capability of nanoscale structuring and ordering to improve the performance of Earth-abundant materials compared to their bulk counterparts for solar-cell applications. I also successfully identified the dominant mechanisms contributing to free-carrier absorption in n-type silicon. My findings help evaluate the impact of the energy loss from this absorption mechanism in doped silicon and are thus important for the design of silicon solar cells. In addition, I calculated the thermoelectric transport properties of p-type SnSe, a bulk material with a record thermoelectric figure of merit. I predicted the optimal temperatures and free-carrier concentrations for thermoelectric energy conversion, as well the
Tian, Y. L.; Hua, H. L.; Yue, W. W.; Chen, M. N.; Hu, G. C.; Ren, J. F.; Yuan, X. B.
2017-12-01
Adsorption properties of chloroform molecule (CHCl3) on graphene surface are studied experimentally and theoretically. Based on the density functional theory (DFT) calculations, effects of different adsorption configurations and different adsorption distances on the system’s conductivity properties are discussed, and the comparisons with the experimental results are made. It is found that band gap appears when the adsorption distance is 1.0 Å, which is about 0.32 eV near the Fermi level. However, the band gap is nearly zero when the adsorption distance is increased to 1.5 Å, so the conductivity of the system will be increased with the increasing of the adsorption distances. The density of states, the adsorption energy and the effective masses are also calculated and the analyses are consistent with the experimental results. Our results reveal that graphene could be used to build sensors or as a catalyst for molecular adsorption.
Choudhury, Koushik; Majumder, Chiranjib
2017-05-01
Here we present the structural and electronic properties of free and tin substituted copper Cun-mSnm (n=10, 13; m=0, 1, 2) clusters. The ground state properties have been calculated using plane wave based pseudopotential approach under the spin-polarized density functional theory. The results show that Cu13 cluster favors a stacked layer structure over the spherically symmetric icosahedron structure. The substitution of Cu atoms by Sn changes the relative stability pattern of the Cu13 isomers. Moreover, Sn atoms favor to substitute the surface Cu atoms than Cu atom at the center. Thus it is predicted that for bimetallic Cu-Sn nanoclusters, segregation of Sn atoms to the outer surface will lead to significant change in the chemical reactivity.
Ahmad, Faozan
2016-01-01
We have performed DFT calculations of electronic structure, optical properties and photocatalytic potential of the low-index surfaces of CuO. Photocatalytic reaction on the surface of semiconductor requires the appropriate band edge of the semiconductor surface to drive redox reactions. The calculation begins with the electronic structure of bulk system; it aims to determine realistic input parameters and band gap prediction. CuO is an antiferromagnetic material with strong electronic correla...
Vibrational and thermodynamic properties of β-HMX: a first-principles investigation.
Wu, Zhongqing; Kalia, Rajiv K; Nakano, Aiichiro; Vashishta, Priya
2011-05-28
Thermodynamic properties of β-HMX crystal are investigated using the quasi-harmonic approximation and density functional theory within the local density approximation (LDA), generalized gradient approximation (GGA), and GGA + empirical van der Waals (vdW) correction. It is found that GGA well describes the thermal expansion coefficient and heat capacity but fails to produce correct bulk modulus and equilibrium volume. The vdW correction improves the bulk modulus and volume, but worsens the thermal expansion coefficient and heat capacity. In contrast, LDA describes all thermodynamic properties with reasonable accuracy, and overall is a good exchange-correlation functional for β-HMX molecular crystal. The results also demonstrate significant contributions of phonons to the equation of state. The static calculation of equilibrium volume for β-HMX differs from the room-temperature value incorporating lattice vibrations by over 5%. Therefore, for molecular crystals, it is essential to include phonon contributions when calculated equation of state is compared with experimental data at ambient condition. © 2011 American Institute of Physics
Nagarajan, V; Chandiramouli, R
2017-05-01
The electronic properties of borophane nanosheet and adsorption behavior of three distinct alcohol vapors namely methanol, ethanol and 1-propanol on borophane nanosheet is studied using density functional theory method for the first time. The state-of-the-art provides insights on to the development of new two dimensional materials with the surface passivation on boron nanostructures. The density of states spectrum provides a clear perception on charge transfer upon adsorption of alcohol vapors on borophane nanosheets. The monolayer of borophane band gap widens upon adsorption of alcohol vapors, which can be used for the detection for volatile organic vapors. The adsorption properties of alcohol vapors on borophane base material are analyzed in terms of natural bond orbital, average energy gap variation, adsorption energy and energy gap. The most suitable adsorption sites of methanol, ethanol and 1-propanol molecules on borophane nanosheet are investigated in atomistic level. The adsorption of alcohol molecules on borophane nanosheet is found to be more favorable. The findings suggest that the monolayer borophane nanosheet can be utilized to detect the presence of alcohol vapors in the atmosphere. Copyright © 2017 Elsevier Inc. All rights reserved.
Energy Technology Data Exchange (ETDEWEB)
Ahmad, Sardar [Center for Computational Materials Science, University of Malakand, Chakdara, 18800 Pakistan (Pakistan); Department of Chemistry, University of Malakand, Chakdara, 18800 Pakistan (Pakistan); Ahmad, Rashid, E-mail: rashmad@gmail.com [Center for Computational Materials Science, University of Malakand, Chakdara, 18800 Pakistan (Pakistan); Department of Chemistry, University of Malakand, Chakdara, 18800 Pakistan (Pakistan); Jalali-Asadabadi, S. [Department of Physics, Faculty of Sciences, University of Isfahan (UI), Hezar Gerib Avenue, Isfahan 81746-73441 (Iran, Islamic Republic of); Ali, Zahid [Center for Computational Materials Science, University of Malakand, Chakdara, 18800 Pakistan (Pakistan); Department of Physics, University of Malakand, Chakdara, 18800 Pakistan (Pakistan); Ahmad, Iftikhar [Center for Computational Materials Science, University of Malakand, Chakdara, 18800 Pakistan (Pakistan); Vice Chancellor, Abbott Abad University of Science and Technology, Abbott Abad (Pakistan)
2017-01-15
In this article we explore the electronic and magnetic properties of RAu intermetallics (R=Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) for the first time. These properties are calculated by using GGA, GGA+U and hybrid density functional theory (HF) approaches. Our calculations show that HF provides superior results, consistent to the experimentally reported data. The chemical bonding between rare-earth and gold atoms within these compounds are explained on the basis of spin dependent electronic clouds in different planes, which shows predominantly ionic and metallic nature between Au and R atoms. The Cohesive energies of RAu compounds show direct relation with the melting points. Spin-dependent electronic band structure demonstrates that all these compounds are metallic in nature. The magnetic studies show that HoAu and LuAu are stable in non-magnetic structure, PrAu is stable in ferromagnetic phase and CeAu, NdAu, SmAu, GdAu, TbAu, DyAu, ErAu, TmAu, YbAu are anti-ferromagnetic materials.
International Nuclear Information System (INIS)
Zhang Yonghui; Chen Yabin; Zhou Kaige; Liu Caihong; Zeng Jing; Zhang Haoli; Peng Yong
2009-01-01
The interactions between four different graphenes (including pristine, B- or N-doped and defective graphenes) and small gas molecules (CO, NO, NO 2 and NH 3 ) were investigated by using density functional computations to exploit their potential applications as gas sensors. The structural and electronic properties of the graphene-molecule adsorption adducts are strongly dependent on the graphene structure and the molecular adsorption configuration. All four gas molecules show much stronger adsorption on the doped or defective graphenes than that on the pristine graphene. The defective graphene shows the highest adsorption energy with CO, NO and NO 2 molecules, while the B-doped graphene gives the tightest binding with NH 3 . Meanwhile, the strong interactions between the adsorbed molecules and the modified graphenes induce dramatic changes to graphene's electronic properties. The transport behavior of a gas sensor using B-doped graphene shows a sensitivity two orders of magnitude higher than that of pristine graphene. This work reveals that the sensitivity of graphene-based chemical gas sensors could be drastically improved by introducing the appropriate dopant or defect.
Surface structure and properties of functionalized nanodiamonds: a first-principles study
Energy Technology Data Exchange (ETDEWEB)
Datta, Aditi; Kirca, Mesut; Fu Yao; To, Albert C, E-mail: albertto@pitt.edu [Department of Mechanical Engineering and Materials Science and Department of Civil and Environmental Engineering, University of Pittsburgh, Pittsburgh, PA 15261 (United States)
2011-02-11
The goal of this work is to gain fundamental understanding of the surface and internal structure of functionalized detonation nanodiamonds (NDs) using quantum mechanics based density functional theory (DFT) calculations. The unique structure of ND assists in the binding of different functional groups to its surface which in turn facilitates binding with drug molecules. The ability to comprehensively model the surface properties, as well as drug-ND interactions during functionalization, is a challenge and is the problem of our interest. First, the structure of NDs of technologically relevant size ({approx}5 nm) was optimized using classical mechanics based molecular mechanics simulations. Quantum mechanics based density functional theory (DFT) was then employed to analyse the properties of smaller relevant parts of the optimized cluster further to address the effect of functionalization on the stability of the cluster and reactivity at its surface. It is found that functionalization is preferred over reconstruction at the (100) surface and promotes graphitization in the (111) surface for NDs functionalized with the carbonyl oxygen (C = O) group. It is also seen that the edges of ND are the preferred sites for functionalization with the carboxyl group (-COOH) vis-a-vis the corners of ND.
Pressure induced electronic and optical properties of rutile SnO2 by first principle calculations
Bakht, Khush; Mahmood, Tariq; Ahmed, Maqsood; Abid, Kamran
2016-02-01
Tin dioxide (SnO2) is the most important semiconductor material due to its large number of technological applications. In this work we carried out the electronic and optical properties under pressure of rutile SnO2. The ultra-soft pseudopotential method is used by employing the local density approximation functional proposed by Ceperley-Alder and Perdew-Zunger to calculate the exchange correlation potential within the framework of density functional theory. Firstly we optimized the structure to obtain the ground state energy of the system with the increase of cutoff energy (Fig. 1 (b)). The investigated band structure and density of states show that energy bandgap is increasing with the increase of pressure due to the movement of valence bands from higher to low energy levels and the conduction bands from lower to higher energy levels respectively (Fig. 1 (a)). The effect of pressure on lattice constants demonstrates the increase in lattice constants. Optical properties, comprising refractive index, dielectric function, absorption and energy loss spectrum are investigated. The obtained results are in good agreement with the previous reported theoretical and experimental results.
Surface structure and properties of functionalized nanodiamonds: a first-principles study
International Nuclear Information System (INIS)
Datta, Aditi; Kirca, Mesut; Fu Yao; To, Albert C
2011-01-01
The goal of this work is to gain fundamental understanding of the surface and internal structure of functionalized detonation nanodiamonds (NDs) using quantum mechanics based density functional theory (DFT) calculations. The unique structure of ND assists in the binding of different functional groups to its surface which in turn facilitates binding with drug molecules. The ability to comprehensively model the surface properties, as well as drug-ND interactions during functionalization, is a challenge and is the problem of our interest. First, the structure of NDs of technologically relevant size (∼5 nm) was optimized using classical mechanics based molecular mechanics simulations. Quantum mechanics based density functional theory (DFT) was then employed to analyse the properties of smaller relevant parts of the optimized cluster further to address the effect of functionalization on the stability of the cluster and reactivity at its surface. It is found that functionalization is preferred over reconstruction at the (100) surface and promotes graphitization in the (111) surface for NDs functionalized with the carbonyl oxygen (C = O) group. It is also seen that the edges of ND are the preferred sites for functionalization with the carboxyl group (-COOH) vis-a-vis the corners of ND.
International Nuclear Information System (INIS)
Benkabou, M.; Rached, H.; Abdellaoui, A.; Rached, D.; Khenata, R.
2015-01-01
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 11 , C 12 and C 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
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.
Role of Boron Element on the Electronic Properties of α-Nb5Si3: A First-Principle Study
Pan, Yong; Lin, Yuanhua
2018-03-01
Transition metal silicides (TMSis) are attracting increasing interest from the microelectronics and nanoelectronic industries. In this paper, we use the first-principles method to investigate the B-doped mechanism and the influence of B on the electronic properties of α-Nb5Si3. The calculated results show that B-doped Nb5Si3 is thermodynamically stable at the ground state. The calculated electronic structure shows that the thermodynamically stable B-doped Nb5Si3 is attributed to the 3D-network B-Si bonds and B-Nb bond. In particular, B element prefers to occupy B -IT4 site in comparison to other sites. Moreover, the calculated band structure indicates that Nb5Si3 exhibits metallic behavior at the ground state. We find that B-doping can improve charge overlap between conduction band and the valence band, which effectively improves the electronic properties of Nb5Si3.
Xu, Yuanfeng; Zhang, Hao; Shao, Hezhu; Ni, Gang; Li, Jing; Lu, Hongliang; Zhang, Rongjun; Peng, Bo; Zhu, Yongyuan; Zhu, Heyuan; Soukoulis, Costas M.
2017-12-01
The extraordinary properties and the novel applications of black phosphorene induce the research interest in the monolayer group-IV monochalcogenides. Here using first-principles calculations, we systematically investigate the electronic, transport, and optical properties of monolayer α - and β -GeSe, revealing a direct band gap of 1.61 eV for monolayer α -GeSe and an indirect band gap of 2.47 eV for monolayer β -GeSe. For monolayer β -GeSe, the electronic/hole transport is anisotropic, with an extremely high electron mobility of 2.93 ×104cm2/Vs along the armchair direction, comparable to that of black phosphorene. Furthermore, for β -GeSe, robust band gaps nearly independent of the applied tensile strain along the armchair direction are observed. Both monolayer α - and β -GeSe exhibit anisotropic optical absorption in the visible spectrum.
Hernández Rosas, J J; Ramírez Gutiérrez, R E; Escobedo-Morales, A; Chigo Anota, Ernesto
2011-05-01
The electrical and chemical properties of graphene (C(24)H(12)), graphane (C(24)H(24)) and graphene oxide (C(54)H(17)+O+(OH)(3)+COOH) were studied through the density functional theory (DFT) at level of Local Density Approximation (LDA) using a model C(n)H(m) like. The optimized geometry, energy gap and chemical reactivity for the proposed carbon 2D models are reported. It was found that while the graphene and graphane structures have semiconductor behavior, the graphene oxide behaves as semi-metal. However, a transition from semi-mental to semiconductor is predicted if the carboxyl group (COOH) is removed from such structure. The chemically active sites are analyzed on the basis of the electrophilic Fukui functions for each structure.
Thermo-Physical Properties of Ammonium Azide under High Pressure from First-Principles
Landerville, Aaron; Steele, Brad; Oleynik, Ivan
2013-03-01
Polynitrogen compounds offer tremendous promise for use as insensitive high-explosives or propellants. While the existence of such compounds have been observed in Diamond Anvil Cells (DAC) under high pressure, recovery to ambient pressure and temperature has proven problematic. A current thrust towards the recovery, and ultimate manufacture, of materials rich in polymeric nitrogen has brought renewed attention to various nitrogen-rich compounds, particularly crystalline azides, as possible precursors. We investigate the thermo-physical properties and Raman spectra of one azide candidate - ammonium azide - under hydrostatic compression using density functional theory with an empirical van der Waals correction. Additionally, we perform structural minima searches to discern possible polymorphs that may help to elucidate dynamical processes leading to the production of a material rich in polymeric nitrogen, as well as its recovery from DAC.
Structural and electronic properties of sodium azide at high pressure: A first principles study
Zhang, Meiguang; Yin, Ketao; Zhang, Xinxin; Wang, Hui; Li, Quan; Wu, Zhijian
2013-05-01
The structural and electronic properties of NaN3 at high pressures were studied through ab initio calculations. Three new phases with I4/mcm, P6/m and C2/m structure were found to be stable at pressures of 6.5, 58 and 152 GPa, respectively. Similarity of the Raman spectra revealed that the experimental post-α phase should adopt the I4/mcm structure. The calculated insulator-metal transition at 58 GPa directly explained the observed darkening of NaN3 sample at above 50 GPa. The three proposed structures contain azide, N6 hexagon and polymeric nitrogen, respectively. Our finding of the novel N6 hexagon in NaN3 at moderate pressures provides a new view of the pressure-induced polymerization process of metal azides.
Yadav, Priya; Nautiyal, Shashank; Verma, U. P.
2018-04-01
Ternary skutterudites materials exhibit good electronic properties due to the unpaired d- and f- electrons of the transition and rare-earth metals, respectively. In this communication, we have performed the structural optimization of Pr-based filled skutterudite (PrCo4P12) for the first time and obtained the electronic band structure, density of states and magnetic moments by using the full-potential linearized augmented plane wave (FP-LAPW) method based on density functional theory (DFT). Our obtained magnetic moment of PrCo4P12 is ˜ 1.8 µB in which main contribution is due to Pr atom. Behavior of this material is metallic and it is most stable in body centered cubic (BCC) structure.
Electronic and optical properties of antiferromagnetic iron doped NiO - A first principles study
Petersen, John E.; Twagirayezu, Fidele; Scolfaro, Luisa M.; Borges, Pablo D.; Geerts, Wilhelmus J.
2017-05-01
Antiferromagnetic NiO is a candidate for next generation high-speed and scaled RRAM devices. Here, electronic and optical properties of antiferromagnetic NiO: Fe 25% in the rock salt structure are studied and compared to intrinsic NiO. From density of states and complex dielectric function analysis, the first optical transition is found to be at lower frequency than intrinsic NiO due to an Fe impurity level being the valence band maximum. The resulting effects on refractive index, reflectivity, absorption, optical conductivity and loss function for Fe-doped NiO are compared to those of intrinsic NiO, and notable differences are analyzed. The electronic component of the static dielectric constant of NiO: Fe 25% is calculated to be about 2% less than that of intrinsic NiO.
A first-principles study of the piezoelectric properties of Niobium and Tantalum Pentoxides
Directory of Open Access Journals (Sweden)
Olga M. Giraldo-Giraldo
2017-09-01
Full Text Available Nb2O5 and Ta2O5 are wide-bandgap semiconductor oxides that have attracted great interest in recent years due to their technological applications, such as in electronics, telecommunications or photocatalysis. Because of this, we present a study based on firstprinciples calculations of the piezoelectric properties of the Z and β phases of Ta2O5 as well as the Z and P phases of Nb2O5 by using the Density Functional Theory and the Generalized Gradient Approximation with PBEsol parameterization. Once the equilibrium geometry was determined for each of these phases, we made a calculation using the linear response theory to determine the piezoelectric tensor associated with each phase. We discovered that the Z phase of both compounds presents good piezoelectric response. Additionally, β-Ta2O5 does not show such response.
First-principles studies on infrared properties of semiconducting graphene monoxide
Pu, H. H.; Mattson, E. C.; Rhim, S. H.; Gajdardziksa-Josifovska, M.; Hirschmugl, C. J.; Weinert, M.; Chen, J. H.
2013-10-01
Graphene monoxide (GMO), a recently proposed 2D crystalline material in the graphene family, is attractive for next-generation nanoelectronics because of its predicted tunable band gap. As a guide to GMO experimental characterization, we calculate the vibrational properties and obtain three infrared active vibration modes (B1u, B2u, and B3u) and six Raman active modes (B1g, B2g, 2B3g, and 2Ag) for intrinsic GMO. The frequencies of the infrared active modes depend on both local structural deformations and interactions between adjacent GMO layers. These results are consistent with experimental observations and provide a means of estimating the number of layers in intrinsic GMO.
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.
International Nuclear Information System (INIS)
Dabhi, Shweta D.; Gupta, Sanjay D.; Jha, Prafulla K.
2014-01-01
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.
First-principles study of the surface properties of U-Mo system
Energy Technology Data Exchange (ETDEWEB)
Mei, Zhi-Gang; Liang, Linyun; Yacout, Abdellatif M.
2018-02-01
U-Mo alloys are promising fuels for future high-performance research reactors with low enriched uranium. Surface properties, such as surface energy, are important inputs for mesoscale simulations (e.g., phase field method) of fission gas bubble behaviors in irradiated nuclear fuels. The lack of surface energies of U-Mo alloys prevents an accurate modeling of the morphology of gas bubbles and gas bubble-induced fuel swelling. To this end, we study the surface properties of U-Mo system, including bcc Mo, alpha-U, gamma-U, and gamma U-Mo alloys. All surfaces up to a maximum Miller index of three and two are calculated for cubic Mo and gamma-U and non-cubic alpha-U, respectively. The equilibrium crystal shapes of bcc Mo, alpha-U and gamma-U are constructed using the calculated surface energies. The dominant surface orientations and the area fraction of each facet are determined from the constructed equilibrium crystal shape. The disordered gamma U-Mo alloys are simulated using the Special Quasirandom Structure method. The (1 1 0) and (1 0 0) surface energies of gamma U-7Mo and U-10Mo alloys are predicted to lie between those of gamma-U and bcc Mo, following a linear combination of the two constituents' surface energies. To better compare with future measurements of surface energies, the area fraction weighted surface energies of alpha-U, gamma-U and gamma U-7Mo and U-10Mo alloys are also predicted. (C) 2017 Published by Elsevier B.V.
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.
A first principles approach to the electronic properties of liquid and supercritical CO{sub 2}
Energy Technology Data Exchange (ETDEWEB)
Cabral, Benedito J. Costa, E-mail: ben@cii.fc.ul.pt [Grupo de Física Matemática da Universidade de Lisboa, Av. Professor Gama Pinto 2, 1649-003 Lisboa (Portugal); Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa (Portugal); Instituto de Física da Universidade de São Paulo, CP 66318, 05314-970 São Paulo, SP (Brazil); Rivelino, Roberto [Instituto de Física da Universidade Federal da Bahia, Campus Universitário de Ondina, CEP 40210-340 Salvador, Bahia (Brazil); Coutinho, Kaline; Canuto, Sylvio [Instituto de Física da Universidade de São Paulo, CP 66318, 05314-970 São Paulo, SP (Brazil)
2015-01-14
The electronic absorption spectra of liquid and supercritical CO{sub 2} (scCO{sub 2}) are investigated by coupling a many-body energy decomposition scheme to configurations generated by Born-Oppenheimer molecular dynamics. A Frenkel exciton Hamiltonian formalism was adopted and the excitation energies were calculated with time dependent density functional theory. A red-shift of ∼ 0.2 eV relative to the gas-phase monomer is observed for the first electronic absorption maximum in liquid and scCO{sub 2}. The origin of this shift, which is not very dependent on deviations from the linearity of the CO{sub 2} molecule, is mainly related to polarization effects. However, the geometry changes of the CO{sub 2} monomer induced by thermal effects and intermolecular interactions in condensed phase lead to the appearance of an average monomeric electric dipole moment 〈μ〉 = 0.26 ± 0.04 D that is practically the same at liquid and supercritical conditions. The predicted average quadrupole moment for both liquid and scCO{sub 2} is 〈Θ〉 = − 5.5 D Å, which is increased by ∼ −0.9 D Å relative to its gas-phase value. The importance of investigating the electronic properties for a better understanding of the role played by CO{sub 2} in supercritical solvation is stressed.
Thermodynamic properties of copper compounds with oxygen and hydrogen from first principles
International Nuclear Information System (INIS)
Korzhavyi, P.A.; Johansson, B.
2010-02-01
We employ quantum-mechanical calculations (based on density functional theory and linear response theory) in order to test the mechanical and chemical stability of several solid-state configurations of Cu 1+ , Cu 2+ , O 2- , H 1- , and H 1+ ions. We begin our analysis with cuprous oxide (Cu 2 O, cuprite structure), cupric oxide (CuO, tenorite structure), and cuprous hydride (CuH, wurtzite and sphalerite structures) whose thermodynamic properties have been studied experimentally. In our calculations, all these compounds are found to be mechanically stable configurations. Their formation energies calculated at T = 0 K (including the energy of zero-point and thermal motion of the ions) and at room temperature are in good agreement with existing thermodynamic data. A search for other possible solid-state conformations of copper, hydrogen, and oxygen ions is then performed. Several candidate structures for solid phases of cuprous oxy-hydride (Cu 4 H 2 O) and cupric hydride (CuH 2 ) have been considered but found to be dynamically unstable. Cuprous oxy-hydride is found to be energetically unstable with respect to decomposition onto cuprous oxide and cuprous hydride. Metastability of cuprous hydroxide (CuOH) is established in our calculations. The free energy of CuOH is calculated to be some 50 kJ/mol higher than the average of the free energies of Cu 2 O and water. Thus, cuprite Cu 2 O is the most stable of the examined Cu(I) compounds
A First-Principles Study on the Vibrational and Electronic Properties of Zr-C MXenes
Wang, Chang-Ying; Guo, Yong-Liang; Zhao, Yuan-Yuan; Zeng, Guang-Li; Zhang, Wei; Ren, Cui-Lan; Han, Han; Huai, Ping
2018-03-01
Within the framework of density functional theory calculations, the structural, vibrational, and electronic properties of Zr n C n - 1 (n = 2, 3, and 4) and their functionalized MXenes have been investigated. We find that the most stable configurations for Zr-C MXene are the ones that the terminal groups F, O, and OH locate on the common hollow site of the superficial Zr layer and its adjacent C layer. F and OH-terminated Zr 3 C 2 and Zr 4 C 3 have small imaginary acoustic phonon branches around Γ point while the others have no negative phonon modes. The pristine MXenes (Zr 2 C, Zr 3 C 2 and Zr 4 C 3 ) are all metallic with large DOS contributed by the Zr atom at the Fermi energy. When functionalized by F, O and OH, new hybridization states appear and the DOS at the Fermi level are reduced. Moreover, we find that their metallic characteristic increases with an increase in n. For (Zr n C n - 1 )O 2, Zr 2 CO 2 is a semiconductor, Zr 3C2O2 is a semimetal, and Zr 4 C 3O2 becomes a metal. Supported by the National Natural Science Foundation of China under Grant Nos. 11605273, 21571185, U1404111, 11504089, 21501189, 21676291, the Shanghai Municipal Science and Technology Commission 16ZR1443100, the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA02040104)
Xie, Congwei; Oganov, Artem R; Li, Duan; Debela, Tekalign Terfa; Liu, Ning; Dong, Dong; Zeng, Qingfeng
2016-04-28
Interstitial carbides are able to maintain structural stability even with a high concentration of carbon vacancies. This feature provides them with tunable properties through the design of carbon vacancies, and thus making it important to reveal how carbon vacancies affect their properties. In the present study, using first-principles, we have calculated the properties of a number of stable and metastable zirconium carbides ZrC1-x (x = 0 and 1/n, n = 2-8) which were predicted by the evolutionary algorithm USPEX. Effects of carbon vacancies on the structures, mechanical properties, and chemical bonding of these zirconium carbides were systematically investigated. The distribution of carbon vacancies has significant influence on mechanical properties, especially Pugh's ratio. Nonadjacent carbon vacancies enhance Pugh's ratio, while grouped carbon vacancies decrease Pugh's ratio. This is explained by the changes in strength of Zr-C and Zr-Zr bonding around differently distributed carbon vacancies. We further explored the mechanical properties of zirconium carbides with impurities (N and O) by inserting N and O atoms into the sites of carbon vacancies. The enhanced mechanical properties of zirconium carbides were found.
Xu-Dong, Zhang; Wei, Jiang
2016-02-01
The effects of high pressure on lattice stability, mechanical and thermodynamic properties of L12 structure Al3Tm and Al3Lu are studied by first-principles calculations within the VASP code. The phonon dispersion curves and density of phonon states are calculated by using the PHONONPY code. Our results agree well with the available experimental and theoretical values. The vibrational properties indicate that Al3Tm and Al3Lu keep their dynamical stabilities in L12 structure up to 100 GPa. The elastic properties and Debye temperatures for Al3Tm and Al3Lu increase with the increase of pressure. The mechanical anisotropic properties are discussed by using anisotropic indices AG, AU, AZ, and the three-dimensional (3D) curved surface of Young’s modulus. The calculated results show that Al3Tm and Al3Lu are both isotropic at 0 GPa and anisotropic under high pressure. In the present work, the sound velocities in different directions for Al3Tm and Al3Lu are also predicted under high pressure. We also calculate the thermodynamic properties and provide the relationships between thermal parameters and temperature/pressure. These results can provide theoretical support for further experimental work and industrial applications. Project supported by the Scientific Technology Plan of the Educational Department of Liaoning Province and Liaoning Innovative Research Team in University, China (Grant No. LT2014004) and the Program for the Young Teacher Cultivation Fund of Shenyang University of Technology, China (Grant No. 005612).
First-principles calculations of lattice dynamics and thermodynamic properties for Yb14MnSb11
Wang, Yi; Hu, Yong-Jie; Firdosy, Samad A.; Star, Kurt E.; Fleurial, Jean-Pierre; Ravi, Vilupanur A.; Chen, Long-Qing; Shang, Shun-Li; Liu, Zi-Kui
2018-01-01
Systematic first-principles calculations were performed to study the lattice dynamics of Yb14MnSb11 and hence to obtain a wide range of its thermodynamic properties at high temperatures. The calculated results were analyzed in terms of the lattice contribution and the electronic contribution, together with a comparison with a collection of experimental thermochemical data. At 0 K, the electronic density of states showed the typical feature of a p-type semiconductor—a small amount of unoccupied electronic states exclusively made of the major spin by a range of ˜0.6 eV above the Fermi energy. It showed that the Mn atom had a ferromagnetic spin moment of ˜4 μB. As a semiconductor, it was found that the electronic contribution to the heat capacity was substantial, with an electronic heat capacity coefficient of ˜0.0006 J/mole-atom/K2.
First-principles study of electronic properties of Si doped FeSe{sub 0.9} alloys
Energy Technology Data Exchange (ETDEWEB)
Kumar, Sandeep, E-mail: sandeep@phy.iitb.ac.in; Singh, Prabhakar P. [Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400076 (India)
2016-05-23
We have performed first-principles study of electronic and superconducting properties of FeSe{sub 0.9-x}Si{sub x} (x = 0.0, 0.05) alloys using Korringa-Kohn-Rostoker Atomic Sphere Approximation within the coherent potential approximation (KKR-ASA-CPA). In our calculations, we used the local density approximation (LDA) for the exchange correlation potential. Our calculations show that these alloys are nonmagnetic in nature. We found that the substitution of Si at Se site into FeSe{sub 0.9} made subtle affects in the electronic structure with respect to the parent FeSe. The results have been analyzed in terms of changes in the density of states (DOS), band structures, Fermi surfaces and the superconducting transition temperature of FeSe{sub 0.9} and FeSe{sub 0.85}Si{sub 0.05} alloys.
Luo, Yanwei; Zhang, Shuai; Chen, Weiguang; Jia, Yu
2018-04-01
By using first-principles calculations, we systemically investigate the electronic properties of phosphorene/h-BN heterostructure with different interlayer distances. Our results show that the electronic states in the vicinity of the Fermi level are completely dominated by phosphorene, and the system exhibits type-I band alignment consequently. Moreover, we also reveal the variation of the band structure of phosphorene/h-BN heterostructure with different interlayer distances. The band gap undergoes a direct to indirect transition as decreasing the interlayer distance. The mechanism of the band gap transition can be attributed to the different energy levels shifts, according to different electronic orbital characters on the band edge. In specific, the energy level of the P_pz bonding state shifts up while that of the P_px,py bonding state falls down, along with the enhancement of the interactions between phosphorene and h-BN.
Lu, Dao-Bang; Song, Yu-Ling
2018-03-01
Based on density functional theory, we perform first-principles investigations to study the optical properties of the O-, F- and H-terminated SiC nanoribbons with armchair edges (ASiCNRs). By irradiating with an external electromagnetic field, we calculate the dielectric function, reflection spectra, energy loss coefficient and the real part of the conductance. It is demonstrated that the optical constants are sensitive to the low-energy range, different terminal atoms do not make much difference in the shape of the curves of the optical constants for the same-width ASiCNR, and the optical constants of wider nanoribbons usually have higher peaks than that of the narrower ones in low energy range. We hope that our study helps in experimental technology of fabricating high-quality SiC-based nanoscale photoelectric device.
Mechanical properties of Li–Sn alloys for Li-ion battery anodes: A first-principles perspective
Directory of Open Access Journals (Sweden)
Panpan Zhang
2016-01-01
Full Text Available Fracture and pulverization induced by large stress during charging and discharging may lead to the loss of electrical contact and capacity fading in Sn anode materials. A good understanding of mechanical properties is necessary for their optimal design under different lithiation states. On the basis of first-principles calculations, we investigate the stress-strain relationships of Li–Sn alloys under tension. The results show that the ideal tensile strengths of Li–Sn alloys vary as a function of Li concentration, and with the increase of Li+ concentration, the lowest tensile strength decreases from 4.51 GPa (Sn to 1.27 GPa (Li7Sn2. This implies that lithiation weakens the fracture resistance of Li–Sn alloys.
Deng, Xiaohui; Wang, Wenwei; Zhang, Dengyu; Lu, Wei; Fan, Bingbing
2010-05-26
The first-principles spin polarization method is used to investigate the magnetic properties of graphite boron nitride (g-BN) sheet induced by Fe doping. We find that a nitrogen or boron atom substituted by Fe can induce a magnetic moment. From standard Mulliken population analysis, we also find that the magnetic moment is mainly dominated by Fe 3d states. Using Heisenberg exchange coupling theory, we study the exchange coupling mechanisms by constructing two-Fe centers in g-BN. The results show the presence of relatively strong exchange coupling for two-Fe substituted two-B atoms and the coupling is ferromagnetic. For the case of two-Fe substituted two-N atoms, the coupling is antiferromagnetic and the exchange coupling is very weak. The paper enriches recent molecular magnetic investigations.
2011-01-01
The magnetic properties of metal-functionalized graphitic carbon nitride nanotubes were investigated based on first-principles calculations. The graphitic carbon nitride nanotube can be either ferromagnetic or antiferromagnetic by functionalizing with different metal atoms. The W- and Ti-functionalized nanotubes are ferromagnetic, which are attributed to carrier-mediated interactions because of the coupling between the spin-polarized d and p electrons and the formation of the impurity bands close to the band edges. However, Cr-, Mn-, Co-, and Ni-functionalized nanotubes are antiferromagnetic because of the anti-alignment of the magnetic moments between neighboring metal atoms. The functionalized nanotubes may be used in spintronics and hydrogen storage. PMID:21711614
Directory of Open Access Journals (Sweden)
Shenoy Vivek
2011-01-01
Full Text Available Abstract The magnetic properties of metal-functionalized graphitic carbon nitride nanotubes were investigated based on first-principles calculations. The graphitic carbon nitride nanotube can be either ferromagnetic or antiferromagnetic by functionalizing with different metal atoms. The W- and Ti-functionalized nanotubes are ferromagnetic, which are attributed to carrier-mediated interactions because of the coupling between the spin-polarized d and p electrons and the formation of the impurity bands close to the band edges. However, Cr-, Mn-, Co-, and Ni-functionalized nanotubes are antiferromagnetic because of the anti-alignment of the magnetic moments between neighboring metal atoms. The functionalized nanotubes may be used in spintronics and hydrogen storage.
Ehteshami, Hossein; Korzhavyi, Pavel A.
2017-12-01
First-principles-based thermodynamic modeling of cubic α and β phases of Mn represent a challenge due to their structural complexity and the necessity of simultaneous treatment of several types of disorder (electronic, magnetic, and vibrational) that have very different characteristic time scales. Here we employ mean-field theoretical models to describe the different types of disorder and then we connect each layer of theory to the others using the adiabatic principle of separating faster and slower degrees of freedom. The slowest (vibrational) degrees of freedom are treated using the Moruzzi, Janak, and Schwarz formalism [Phys. Rev. B 37, 790 (1988), 10.1103/PhysRevB.37.790] of the Debye-Grüneisen model parametrized based on the first-principles calculated equation of state which includes the free-energy contributions due to the fast (electronic and magnetic) degrees of freedom via the Fermi-Dirac distribution function and a mean-field theory of transverse spin fluctuations. The magnetic contribution due to transverse spin fluctuations has been computed self-consistently within the disordered local moment picture of the paramagnetic state. The obtained results for thermodynamic properties such as lattice parameter, linear thermal expansion coefficient, and heat capacity of both phases show a good agreement with available experimental data. We also tested the assumption about the nature (localized versus delocalized) of magnetic moment on site IV in α -Mn and site I in β -Mn on the thermodynamic properties of these two phases. Similar to the findings of experimental studies, we conclude that magnetic moment on site IV in α -Mn is not of a localized character. However, a similar analysis suggests that the magnetic moment of site I in β -Mn should be treated as localized.
Directory of Open Access Journals (Sweden)
Shuli Tang
2018-02-01
Full Text Available In this paper, the electronic, mechanical and thermodynamic properties of AlNi2Ti are studied by first-principles calculations in order to reveal the influence of AlNi2Ti as an interfacial phase on ZTA (zirconia toughened alumina/Fe. The results show that AlNi2Ti has relatively high mechanical properties, which will benefit the impact or wear resistance of the ZTA/Fe composite. The values of bulk, shear and Young’s modulus are 164.2, 63.2 and 168.1 GPa respectively, and the hardness of AlNi2Ti (4.4 GPa is comparable to common ferrous materials. The intrinsic ductile nature and strong metallic bonding character of AlNi2Ti are confirmed by B/G and Poisson’s ratio. AlNi2Ti shows isotropy bulk modulus and anisotropic elasticity in different crystallographic directions. At room temperature, the linear thermal expansion coefficient (LTEC of AlNi2Ti estimated by quasi-harmonic approximation (QHA based on Debye model is 10.6 × 10−6 K−1, close to LTECs of zirconia toughened alumina and iron. Therefore, the thermal matching of ZTA/Fe composite with AlNi2Ti interfacial phase can be improved. Other thermodynamic properties including Debye temperature, sound velocity, thermal conductivity and heat capacity, as well as electronic properties, are also calculated.
Zhang, Haiquan; Tang, Yanan; Ma, Yaqiang; Ma, Dongwei; Zhao, Mingyu; Dai, Xianqi
2018-01-01
The stable geometry, electronic property and chemical reactivity of dopants (Co, Mo and B) incorporated N4 centers in graphene sheets (D-GN4) are investigated using the first-principles calculations. It is found that the GN4 sheet can strongly stabilizes the dopant and makes it more positively charged, which would regulate the adsorption behaviors of gas molecules. Compared with the adsorbed CO molecule, the D-GN4 substrates exhibit high sensitivity toward the O2 molecule. The individual CO (or O2) on the Mo-GN4 have the largest energy difference, while they have moderate adsorption energies on B-GN4 sheet. Besides, the dopants (or adsorbed gases) can effectively regulate the electronic structure and magnetic properties of GN4 (or D-GN4) systems, such as the adsorption of O2 (or CO) can decrease (or increase) the magnetic moment of Mo-GN4 system and the magnetic property of Co-GN4 is enlarged by the adsorbed O2. As a result, we may distinguish the kinds of adsorbed gases by testing the change in magnetic property of the system, which can provide important reference for exploring the surface reactivity of graphene-based materials and designing the novel gas sensors or spintronic devices.
Saha, Ashim Kumar; Yoshiya, Masato
2018-03-01
Stability of native point defect species and optical properties are quantitatively examined through first principles calculations in order to identify possible native point defect species in MoS2 and its influences on electronic structures and resultant optical properties. Possible native point defect species are identified as functions of thermodynamic environment and location of Fermi-level in MoS2. It is found that sulphur vacancies can be introduced more easily than other point defect species which will create impurity levels both in bandgap and in valence band. Additionally, antisite Mo and/or Mo vacancies can be created depending on chemical potential of sulphur, both of which will create impurity levels in bandgap and in valence band. Those impurity levels result in pronounced photon absorption in visible light region, though each of these point defects alone has limited impact on the optical properties unless their concentration remained low. Thus, attention must be paid when intentional impurity doping is made to MoS2 to avoid unwanted modification of optical properties of MoS2. Those impurity may enable further exploitation of photovoltaic energy conversion at longer wavelength.
Structural, elastic and thermodynamic properties of Ti2SC
Indian Academy of Sciences (India)
Administrator
Abstract. The structural parameters, elastic constants and thermodynamic properties of Ti2SC were investi- gated under pressure and temperature by using first-principles plane-wave pseudopotential density functional theory within the generalized gradient approximation. The obtained results are in agreement with the.
Yim, Kanghoon; Lee, Joohee; Lee, Dongheon; Lee, Miso; Cho, Eunae; Lee, Hyo Sug; Nahm, Ho-Hyun; Han, Seungwu
2017-01-01
Throughout the past decades, doped-ZnO has been widely used in various optical, electrical, magnetic, and energy devices. While almost every element in the Periodic Table was doped in ZnO, the systematic computational study is still limited to a small number of dopants, which may hinder a firm understanding of experimental observations. In this report, we systematically calculate the single-element doping property of ZnO using first-principles calculations. We develop an automation code that enables efficient and reliable high-throughput calculations on thousands of possible dopant configurations. As a result, we obtain formation-energy diagrams for total 61 dopants, ranging from Li to Bi. Furthermore, we evaluate each dopant in terms of n-type/p-type behaviors by identifying the major dopant configurations and calculating carrier concentrations at a specific dopant density. The existence of localized magnetic moment is also examined for spintronic applications. The property database obtained here for doped ZnO will serve as a useful reference in engineering the material property of ZnO through doping.
Energy Technology Data Exchange (ETDEWEB)
Hu, Yonghong, E-mail: hchyh2001@tom.com [School of Nuclear Technology and Chemistry & Biology, Hubei University of Science and Technology, Xianning 437100 (China); Wu, Yunyi [Department of Energy Materials and Technology, General Research Institute for Nonferrous Metals, Beijing (China); Zhang, Shengli [Institute of Optoelectronics & Nanomaterials, Herbert Gleiter Institute of Nanoscience, College of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094 (China)
2016-12-15
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.
First-principles calculation of electronic and optical properties of graphene like ZnO (G-ZnO)
Farooq, Rabia; Mahmood, Tariq; Anwar, Abdul Waheed; Abbasi, Ghadah Niaz
2016-02-01
Semiconductor metal oxides are favorable for their exotic properties like wide band gap, transparency, enhanced charge mobility, and strong luminescence at room temperature. These properties have put metal oxides under limelight, especially ZnO has earned a renowned position in emanate industry for transparent electrodes, electronics, super-capacitors, photo-voltaic cells, gas-sensors, and many more. ZnO is not only environmental friendly but also a highly stable and cheap photo catalytic source naturally available in high abundance. First principles calculation is performed to study optoelectronic properties of ZnO. Geometry optimization of graphene like ZnO (G-ZnO) is preformed using generalized gradient approximation along with hybrid functional (GGA-PBE and GGA-PBE + U) to calculate various structural and electronic parameters of G-ZnO. Employing Hubbard (U) parameter improved band gap and c/a ratio calculation as 1.245 eV and 1.613 respectively; also dielectric constant is calculated as 4.58 (U = 15 eV) which is in accordance with the available experimental data.
Directory of Open Access Journals (Sweden)
Yaxuan Cai
2017-06-01
Full Text Available The electronic structure and ferroelectric mechanism of trichloroacetamide were studied using first principles calculations and density functional theory within the generalized gradient approximation. Using both Bader charge and electron deformation density, large molecular spontaneous polarization is found to originate from the charge transfer cause by the strong “push-pull” effect of electron-releasing interacting with electron-withdrawing groups. The intermolecular hydrogen bonds, NH⋯O, produce dipole moments in adjacent molecules to be aligned with each other. They also reduce the potential energy of the molecular chain threaded by hydrogen bonds. Due to the symmetric crystalline properties, however, the polarization of trichloroacetamide is mostly compensated and therefore small. Using the Berry Phase method, the spontaneous polarization of trichloroacetamide was simulated, and good agreement with the experimental values was found. Considering the polarization characteristics of trichloroacetamide, we constructed a one-dimensional ferroelectric Hamiltonian model to calculate the ferroelectric properties of TCAA. Using the Hamiltonian model, the thermal properties and ferroelectricity of trichloroacetamide were studied using the Monte Carlo method, and the Tc value was calculated.
Wang, Z. P.; Fang, Q. H.; Li, J.; Liu, B.
2018-04-01
Structural, mechanical and electronic properties of βTiNb alloy under high pressure have been investigated based on the density functional theory (DFT). The dependences of dimensionless volume ratio, elastic constants, bulk modulus, Young's modulus, shear modulus, ductile/brittle, anisotropy and Poisson's ratio on applied pressure are all calculated successfully. The results reveal that βTiNb alloy is mechanically stable under pressure below 23.45 GPa, and the pressure-induced phase transformation could occur beyond this critical value. Meanwhile, the applied pressure can effectively promote the mechanical properties of βTiNb alloy, including the resistances to volume change, elastic deformation and shear deformation, as well as the material ductility and metallicity. Furthermore, the calculated electronic structures testify that βTiNb alloy performs the metallicity and the higher pressure reduces the structural stability of unit cell.
Arróyave, Raymundo; Liu, Zi-Kui
2006-11-01
A comprehensive analysis of the structural, vibrational, and thermodynamic properties of the intermetallic compounds in the Mg-Ca-Sn system has been performed via first-principles calculations. The enthalpies of formation at 0K for all the known structures in this ternary system are calculated and the results are favorably compared—within ˜5kJ/mol-atom in most cases—to the available experimental data. The vibrational contributions to the thermodynamic properties of fcc Ca, hcp Mg, β-Sn , Mg2Ca , Ca2Sn , CaSn , Ca5Sn3 , CaSn3 , Mg2Sn , and MgCaSn are calculated using the supercell method. In all cases, bond stiffening resulting from compound formation results in upward frequency shifts in the phonon density of states, yielding in turn negative entropies of formation. The effects of volume expansion on the vibrational properties were considered through the quasiharmonic approximation. Thermal electronic contributions were also calculated from the electronic density of states. The electronic degrees of freedom were found to be less important than volume expansion at determining the high temperature thermodynamic properties. The predicted thermodynamic properties of the structures agreed satisfactorily with the experimental data available. The relative importance of these two nonharmonic corrections is reversed when analyzing the formation properties. In all compounds, except for CaSn3 , it was found that the variation of both the formation enthalpies and entropies with temperature is negative. This results in a destabilization of the compounds with respect to their constituent elements as the temperature is increased.
Rush, Larry E., Jr.
This thesis mainly focuses on characterizing and understanding the electronic properties of sodium-ion electrolytes using first-principles calculations. The core of these calculations is built upon a functional understanding of the relationship between quantum mechanics and the crystalline geometries that contribute to unique properties of materials such as diffusion mechanisms of ions within solid-state materials, conductivity, and ground state structures. The goal of this body of work is to understand how this relationship can give us insight into materials that might have use in an emerging field within battery technology. Sodium-ion solid-state batteries are an auspicious technology because nature has provided us with widely distributed precursor materials in such a way that removes geopolitical constraints in its construction and distribution. This is extremely important to individuals (and a collection of individuals) who want to expedite the wide use of clean and renewable energy from a societal perspective. An example is Morocco's initiative to generate 52% of its total energy consumption from clean and renewable energy sources to eliminate dependencies on foreign countries to supply energy resources. Sodium-ion solid-state batteries are an inexpensive option for large-scale grid storage, so this could play a role in providing a cost-effective option for Morocco. The challenging part is to sift through the large chemical space of sodium-ion solid-state electrolytes to find optimal materials for battery technology, and that is what motivates this body of work.
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.
Harb, Moussab
2015-08-26
Using accurate first-principles quantum calculations based on DFT (including the perturbation theory DFPT) with the range-separated hybrid HSE06 exchange-correlation functional, we predict essential fundamental properties (such as bandgap, optical absorption coefficient, dielectric constant, charge carrier effective masses and exciton binding energy) of two stable monoclinic vanadium oxynitride (VON) semiconductor crystals for solar energy conversion applications. In addition to the predicted band gaps in the optimal range for making single-junction solar cells, both polymorphs exhibit relatively high absorption efficiencies in the visible range, high dielectric constants, high charge carrier mobilities and much lower exciton binding energies than the thermal energy at room temperature. Moreover, their optical absorption, dielectric and exciton dissociation properties are found to be better than those obtained for semiconductors frequently utilized in photovoltaic devices like Si, CdTe and GaAs. These novel results offer a great opportunity for this stoichiometric VON material to be properly synthesized and considered as a new good candidate for photovoltaic applications.
First-principles study of the electronic and optical properties of Li(Nb,Os)O3 alloys
Shen, Zhen-Xiong; Ren, Xinguo; He, Lixin
2018-03-01
Ferroelectric materials have some unique properties that are promising for photovoltaic applications. However, traditional ferroelectrics usually have a very large bandgap and therefore extremely low absorption in the visible light range. In this work, we study the electronic and optical properties of LiNb1-xOsxO3 alloys via first-principles calculations. We show that doping Os in LiNbO3 can effectively tune the bandgaps of the material. Specifically, less than 10% Os doping in LiNbO3 can reduce the bandgap from 3.78 eV to around 0.7 eV. The optical absorption of LiNb1-xOsxO3 alloys is improved to about two orders of magnitude than that of pure LiNbO3 in the visible light and infrared range. We further show that the alloys can still maintain their ferroelectricity and therefore have the potential for ferroelectric photovoltaic applications.
Wang, Xinyu; Zhen, Siqi; Min, Yi; Zhou, Pengxia; Huang, Yanyan; Zhong, Chonggui; Dong, Zhengchao; Liu, Junming
2017-11-01
We use first-principles calculations based on the density functional theory to investigate the magnetic properties, optical properties, and electronic structure of perovskite-type multiferroic EuTiO3 (ETO) thin films with biaxial strain. The calculations indicate that, in ETO films, the magnetic moment of Eu ions and the energy of the direct band gap decrease slowly (increase rapidly) with increasing compressive (tensile) strain. A direct band gap tunable from 1.0 to 1.52 eV is expected in ferroelectric and ferromagnetic ETO thin films upon application of 1%-4% tensile strain, and photogenerated carriers with spin-polarization can be induced from Eu 4f to Ti 3d states. This behavior can be confirmed by monitoring the strain-dependent optical absorption coefficient of ETO thin films and is explained by the shift of the strain-tuned electronic structure. These results suggest the potential applications of ETO thin films in multiferroic photovoltaic cells.
Structural stabilities and electronic properties of Mg28-nAln clusters: A first-principles study
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Bao-Juan Lu
2017-09-01
Full Text Available In this paper, we have constructed the alloy configurations of Mg28-nAln by replacing atoms at various possible positions, starting from the stable structures of Mg28 and Al28 clusters. According to the symmetry of the cluster structure, the isomers of these initial structures have been screened with the congruence check, which would reduce computational hours and improve efficiency. Using the first-principles method, the structural evolution, mixing behavior and electronic properties of Mg28-nAln clusters are investigated for all compositions. We conclude that Al atoms prefer to reside in the central positions of Mg−Al clusters and Mg atoms tend to occupy the peripheral location. The negative mixing enthalpies imply the stabilities of these Mg-Al clusters and thus possible applications in catalysis and hydrogen storage materials. Among Mg28-nAln clusters, Mg24Al4, Mg21Al7, Mg14Al14, Mg26Al2 and Mg27Al1 present relatively high thermodynamic stabilities, and the electronic properties of these stable structures are discussed with the charge distributions around the Fermi level.
First principles study of the magnetic properties and charge transfer of Ni-doped BiFeO3
Sun, Yuan; Sun, Zhenghao; Wei, Ren; Huang, Yuxin; Wang, Lili; Leng, Jing; Xiang, Peng; Lan, Min
2018-03-01
We present a first-principles study of electronic structures and magnetic properties in Ni-doped BiFeO3 using the density functional theory + U methods. The BiNixFe1-xO3 (x = 0.125, 0.25, 0.5) multiferroic ceramics represent ferromagnetic properties due to the ferrimagnetic order in Ni-O-Fe, and the magnetic moment rises with increase in Ni doping concentration agreeing well with experimental results. Ni atoms prefer to occupy the diagonal positions in the quasi-plane Ni-O-Fe eight-membered ring. Charge transfer from Bi 6s state to Ni 3d state through O 2p orbital lead to the 2+ oxidation state of Ni, indicating high Néel temperatures of BiNixFe1-xO3, and the electronic state of the system can be described as Bi4+xBi3+1-xNi2+xFe3+1-xO3. The spin polarization of Bi 6s state and O 2p state near the Fermi level contributes to the total magnetic moment. A spin-polarized acceptor level of about 0.4 eV constituted by Bi 6s state and O 2p state is found, which is responsible for the increase in leakage current of Ni-doped BiFeO3.
First-principles study of optical properties of α-CuSe/klockmannite: Bulk and nano-layers
International Nuclear Information System (INIS)
Shojaei, Ali Reza; Vaez, Aminollah; Nourbakhsh, Zahra; Madaniyan, Zeynab Sadat
2014-01-01
The optical properties of α-CuSe bulk and its nano-layers (NLs) have been studied by the first principles theoretical study in the framework of density functional theory. These properties are calculated with regard to dielectric function, refractive index, extinction coefficient, reflection coefficient, absorption coefficient, energy-loss function, and optical conductivity. To create NLs, two different thicknesses through CuSe bulk are chosen in the (0001) direction as the first and second thicknesses. The former thickness is divided into six different NLs with variant alternations. These NLs have the same chemical composition and are structural isomers. Among the NLs, the optical properties of the most stable NL and its double thickness are calculated and compared with the bulk state. The imaginary part of dielectric function has a main peak at low energies because α-CuSe is a conductive compound in the bulk state. The electronic structure of NLs shows that they have remained conductive in x (or y) direction, but they interestingly have a dielectric behavior with an ultra-low electrical conductivity in z direction. The optical curves in the bulk and NLs show the anisotropic feature between x and z directions. In the range of infrared to red light, the bulk refractive index, n z (ω), is very large, about 6, while n x (ω) is about 3. Results show that the NLs have wide absorption curves in the range of solar spectrum from infrared to ultraviolet. - Highlights: • Optical properties of α-CuSe bulk and its nano-layers (NLs) are studied • Our calculations are performed within framework of Density functional theory using full potential method. • The NLs stabilities and thickness effect on their optical properties are discussed. • Bulk and NLs optical curves show anisotropic feature between x (or y) and z directions. • NLs showed conductivity in x (or y) direction but ultra-low conductivity in z direction
Elastic and viscoplastic properties
International Nuclear Information System (INIS)
Lebensohn, R.A.
2015-01-01
In this chapter, we review crystal elasticity and plasticity-based self-consistent theories and apply them to the determination of the effective response of polycrystalline aggregates. These mean-field formulations, which enable the prediction of the mechanical behaviour of polycrystalline aggregates based on the heterogeneous and/or directional properties of their constituent single crystal grains and phases, are ideal tools to establish relationships between microstructure and properties of these materials, ubiquitous among fuels and structural materials for nuclear systems. (author)
Magnetic properties in BiFeO{sub 3} doped with Cu and Zn first-principles investigation
Energy Technology Data Exchange (ETDEWEB)
Rong, Qing-Yan [School of Physics and Electronics, Hunan University, Changsha 410082 (China); Department of Physics and Mathematics, Hunan Institute of Engineering, Xiangtan 411104 (China); Xiao, Wen-Zhi, E-mail: xiaowenzhi@hnu.edu.cn [School of Physics and Electronics, Hunan University, Changsha 410082 (China); Department of Physics and Mathematics, Hunan Institute of Engineering, Xiangtan 411104 (China); Xiao, Gang [School of Physics and Electronics, Hunan University, Changsha 410082 (China); Department of Physics and Mathematics, Hunan Institute of Engineering, Xiangtan 411104 (China); Hu, Ai-Ming [Department of Physics and Mathematics, Hunan Institute of Engineering, Xiangtan 411104 (China); Wang, Ling-Ling, E-mail: llwang@hnu.edu.cn [School of Physics and Electronics, Hunan University, Changsha 410082 (China)
2016-07-25
Based on first-principles spin-polarized density functional theory calculations, the electronic structures, and magnetic properties of Cu and Zn-doped BiFeO{sub 3} are investigated. The calculated formation energies show that Cu prefers to occupy Fe site, while the Zn prefer to occupy Bi site. All the doped BiFeO{sub 3} systems turn out to be favorable for G-type antiferromagnetic arrangement. The substitution of Cu and Zn for Fe produces a magnetic moment of 3.0 and 4.0 μ{sub B} per dopant, respectively. The net magnetic moments are from the broken symmetry of the AFM spin ordering network. For the substitution of Cu and Zn for Bi, the net magnetic moment originates from Cu/Zn itself and hole introduced by Cu/Zn. Two-Cu/Zn-doped cases show various magnetic behaves. If O vacancy is far away from dopants, the O vacancies don't affect the net magnetic moment of the substitution of Cu and Zn for Fe, but have notable effect for Bi site doping. The O vacancies result in metallicity in all doped cases. Our study demonstrates that the nonmagnetic Cu and Zn doping will lead to the diversity and complexity of magnetic properties depending on doping sites, distance between dopants, intrinsic defect, and so on, which could be responsible for the observed various magnetic behaviors in Cu/Zn-doped BiFeO{sub 3} samples. - Highlights: • The Fe site doping produces magnetic moments, due to the breaking of the symmetry. • The Bi site doping produces magnetic moments which originate from unpaired holes. • Different substitutions of Cu/Zn for Fe result in various magnetic properties. • The O vacancies make all the doped samples metallic and affect magnetic properties.
International Nuclear Information System (INIS)
Raji, Abdulrafiu T.; Lombardi, Enrico B.
2015-01-01
We report a first-principles investigation of the structural, electronic and magnetic properties of cobalt–vacancy defect complexes in graphene, within the framework of density-functional theory (DFT), incorporating DFT+U. Specifically, we consider the interactions of cobalt and vacancies in graphene, at varying separations and sub-lattices. We show that it is energetically favorable for substitutional Co in graphene to trap an additional vacancy in graphene, forming a Co–vacancy complex. In all the configurations considered, the most stable configuration is when the Co atom is embedded in a divacancy. The magnetic moment induced on the cobalt atom varies as the vacancy–cobalt separation changes, depending not only on the separation, but also on the sub-lattice of the vacancy relative to cobalt. Furthermore, for each separation and sub-lattice considered, the linear density of states of graphene is modified such that Dirac point is either not discernible or has shifted above the Fermi energy. Since individual vacancies or transition metal (TM) atoms, such as cobalt in graphene, have mostly been studied in isolation up to now, ignoring possible transition metal–vacancy interactions, these results have important implications to the fundamental understanding of TM–vacancy defect interactions in graphene
Directory of Open Access Journals (Sweden)
Ning Yang
2017-11-01
Full Text Available The new three-dimensional structure that the graphene connected with SWCNTs (G-CNTs, Graphene Single-Walled Carbon Nanotubes can solve graphene and CNTs′ problems. A comprehensive study of the mechanical and electrical performance of the junctions was performed by first-principles theory. There were eight types of junctions that were constituted by armchair and zigzag graphene and (3,3, (4,0, (4,4, and (6,0 CNTs. First, the junction strength was investigated. Generally, the binding energy of armchair G-CNTs was stronger than that of zigzag G-CNTs, and it was the biggest in the armchair G-CNTs (6,0. Likewise, the electrical performance of armchair G-CNTs was better than that of zigzag G-CNTs. Charge density distribution of G-CNTs (6,0 was the most homogeneous. Next, the impact factors of the electronic properties of armchair G-CNTs were investigated. We suggest that the band gap is increased with the length of CNTs, and its value should be dependent on the combined effect of both the graphene’s width and the CNTs’ length. Last, the relationship between voltage and current (U/I were studied. The U/I curve of armchair G-CNTs (6,0 possessed a good linearity and symmetry. These discoveries will contribute to the design and production of G-CNT-based devices.
First-principles study of the adsorption properties of atoms and molecules on UN2 (001) surface
Xu, Mengjuan; Liu, Guangdong; Ao, Bingyun; Chen, Piheng; Hu, Wangyu; Deng, Huiqiu
2017-09-01
Uranium nitrides are one kind of accident-tolerant fuels and have been paid more attention recently. With the first-principles Density-Functional Theory (DFT) calculations, the adsorptions properties of some typical atoms, molecules and radical (including O, H, H2, O2, H2O and OH) adsorbed on the UN2 (001) surface have been studied in the present work. The preferred sites and stable configurations for those adsorbates on the UN2 (001) surface have been obtained. It's found that O or H atom prefers to be adsorbed at the bridge site; O2 adsorption will dissociate into two O atoms and occupy the nearest neighbor bridge sites; the interaction between H2 molecule and the UN2 (001) surface is very weak; OH prefers to occupy the bridge site with its O-H bond vertical to the surface; the surface adsorption of H2O is non-dissociated and adsorption energies are dependent on the initial structures and adsorption modes.
First-principles study of electronic properties of FeSe{sub 1-x}S{sub x} alloys
Energy Technology Data Exchange (ETDEWEB)
Kumar, Sandeep, E-mail: sandeep@phy.iitb.ac.in; Singh, Prabhakar P. [Department of Physics, Indian Institute of Technology-Bombay, Mumbai-400076 (India)
2016-05-06
We have studied the electronic and superconducting properties of FeSe{sub 1-x}S{sub x} (x = 0.0, 0.04) alloys by first-principles calculations using the Korringa-Kohn-Rostoker Atomic Sphere Approximation within the coherent potential approximation (KKR-ASA-CPA). The electronic structure calculations show the ground states of S-doped FeSe to be nonmagnetic. We present the results of our unpolarized calculations for these alloys in terms of density of states (DOS), band structures, Fermi surfaces and the superconducting transition temperature of FeSe and FeSe{sub 0.96}S{sub 0.04} alloys. We find that the substitution of S at Se site into FeSe exhibit the subtle changes in the electronic structure with respect to the parent FeSe. We have also estimated bare Sommerfeld constant (γ{sub b}), electron-phonon coupling constant (λ) and the superconducting transition temperature (T{sub c}) for these alloys, which were found to be in good agreement with experiments.
First-principles calculation of the structure and electronic properties of Fe-substituted Bi2Ti2O7
Huang, Jin-Dou; Zhang, Zhenyi; Lin, Feng; Dong, Bin
2017-12-01
We performed first-principles calculations to investigate the formation energy, geometry structure, and electronic property of Fe-doped Bi2Ti2O7 systems with different Fe doping content. The calculated formation energies indicate that the substitutional configurations of Fe-doping Bi2Ti2O7 are easy to obtain under O-rich growth condition, but their thermodynamic stability decreases with the increase of Fe content. The calculated spin-resolved density of states and band structures indicate that the introduction of Fe into Bi2Ti2O7 brings high spin polarization. The spin-down impurity levels in Fe x Bi2-x Ti2O7 and spin-up impurity levels in Fe x Bi2Ti2-x O7 systems locate in the bottom of conduction band and narrow the band gap significantly, thus leading to the absorption of visible light. Interestingly, the impurity states in Fe x Bi2-x Ti2O7 are the efficient separation center of photogenerated electron and hole, and less affected by Fe doping content, in comparison, the levels of impurity band in Fe x Bi2Ti2-x O7 systems are largely effected by the Fe doping content, and high Fe doping content is the key factor to improve the separating rate of photogenerated electron and hole.
First-principles study of the structure properties of Al(111)/6H-SiC(0001) interfaces
Wu, Qingjie; Xie, Jingpei; Wang, Changqing; Li, Liben; Wang, Aiqin; Mao, Aixia
2018-04-01
This paper presents a systematic study on the energetic and electronic structure of the Al(111)/6H-SiC(0001) interfaces by using first-principles calculation with density functional theory (DFT). There are all three situations for no-vacuum layer of Al/SiC superlattics, and two cases of C-terminated and Si-terminated interfaces are compared and analyzed. Through the density of states analysis, the initial information of interface combination is obtained. Then the supercells are stretched vertically along the z-axis, and the fracture of the interface is obtained, and it is pointed out that C-terminated SiC and Al interfaces have a better binding property. And, the fracture positions of C-terminated and Si-terminated interfaces are different in the process of stretching. Then, the distance variation in the process of stretching, the charge density differences, and the distribution of the electrons near the interface are analyzed. Al these work makes the specific reasons for the interface fracture are obtained at last.
Energy Technology Data Exchange (ETDEWEB)
Li, A.Y. [School of Opto-electronic and Communication Engineering, Xiamen University of Technology, Xiamen 361024 (China); Wu, S.Q. [Department of Physics and Institute of Theoretical Physics and Astrophysics, Xiamen University, Xiamen 361005 (China); Yang, Y. [State Key Lab for Physical Chemistry of Solid Surfaces, Xiamen University, Xiamen 361005 (China); Zhu, Z.Z., E-mail: zzhu@xmu.edu.cn [Department of Physics and Institute of Theoretical Physics and Astrophysics, Xiamen University, Xiamen 361005 (China); Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, Xiamen University, Xiamen 361005 (China)
2015-07-15
The transition metal fluorides have been extensively investigated recently as the electrode materials with high working voltage and large capacity. The structural, electronic and magnetic properties of MoF{sub 3} are studied by the first-principles calculations within both the generalized gradient approximation (GGA) and GGA+U frameworks. Our results show that the antiferromagnetic configuration of MoF{sub 3} is more stable than the ferromagnetic one, which is consistent with experimental results. The analysis of the electronic density of states shows that MoF{sub 3} is a Mott–Hubbard insulator with a d–d type band gap, which is similar to the case of FeF{sub 3}. Moreover, small spin polarizations were found on the sites of fluorine ions, which accords with a fluorine-mediated superexchange mechanism for the Mo–Mo magnetic interaction. - Graphical abstract: Deformation charge density and spin-density for MoF{sub 3} in the AF configuration. - Highlights: • The ground state of MoF{sub 3} is shown to be antiferromagnetic, in consistent with experiments. • The electronic states show that MoF{sub 3} is a Mott–Hubbard insulator with a d–d type band gap. • A fluorine-mediated super-exchange mechanism for the Mo–Mo magnetic interaction is shown.
Energy Technology Data Exchange (ETDEWEB)
Mohan, Brij, E-mail: brijmohanhpu@yahoo.com; Kumar, Ashok, E-mail: brijmohanhpu@yahoo.com; Ahluwalia, P. K., E-mail: brijmohanhpu@yahoo.com [Department of Physics, Himachal Pradesh University, Shimla-171005 (India)
2014-04-24
We performed first-principle study of the structural and electronic properties of two-dimensional hydrogenated silicene for two configurations; one is hydrogenation along one side of silicene sheet and second is hydrogenation in both sides of silicene sheet. The one-side hydrogenated silicene is found stable at planar geometry while increased buckling of 0.725 Å is found for both-side hydrogenated silicene. The result shows that the hydrogenation occupy the extended π-bonding network of silicene, and thus it exhibits semi-conducting behaviour with a band gap of 1.77 eV and 2.19 eV for one-side hydrogenated silicene and both-side hydrogenated silicene respectively. However, both-side hydrogenated silicene of binding energy 4.56 eV is more stable than one-side hydrogenated silicene of binding energy 4.30 eV, but experimentally silicene is synthesized on substrates which interacts one side of silicene layer and only other side is available for H-atoms. Therefore, practically one-side hydrogenation is also important.
International Nuclear Information System (INIS)
Mohan, Brij; Kumar, Ashok; Ahluwalia, P. K.
2014-01-01
We performed first-principle study of the structural and electronic properties of two-dimensional hydrogenated silicene for two configurations; one is hydrogenation along one side of silicene sheet and second is hydrogenation in both sides of silicene sheet. The one-side hydrogenated silicene is found stable at planar geometry while increased buckling of 0.725 Å is found for both-side hydrogenated silicene. The result shows that the hydrogenation occupy the extended π-bonding network of silicene, and thus it exhibits semi-conducting behaviour with a band gap of 1.77 eV and 2.19 eV for one-side hydrogenated silicene and both-side hydrogenated silicene respectively. However, both-side hydrogenated silicene of binding energy 4.56 eV is more stable than one-side hydrogenated silicene of binding energy 4.30 eV, but experimentally silicene is synthesized on substrates which interacts one side of silicene layer and only other side is available for H-atoms. Therefore, practically one-side hydrogenation is also important
Energy Technology Data Exchange (ETDEWEB)
Tian Hua; Zhang Chong [Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Dalian University of Technology, Ministry of Education, Dalian 116024 (China); School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); College of Advanced Science and Technology, Dalian University of Technology, Dalian 116024 (China); Zhao Jijun, E-mail: zhaojj@dlut.edu.cn [Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Dalian University of Technology, Ministry of Education, Dalian 116024 (China); College of Advanced Science and Technology, Dalian University of Technology, Dalian 116024 (China); Dong Chuang [Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Dalian University of Technology, Ministry of Education, Dalian 116024 (China); School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Wen Bin [School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Wang Qing [Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Dalian University of Technology, Ministry of Education, Dalian 116024 (China); School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China)
2012-01-15
The structural, electronic, and magnetic properties of amorphous Fe{sub 100-x}B{sub x} alloys (x=9, 17, 25, 27.3, 33.3, 36.3) are investigated using first-principles calculations. In these amorphous alloys, the short-range order is manifested as a series of Fe- or B-centered polyhedra such as tricapped trigonal prism, icosahedron, and bcc-like structural unit. The electron densities of states of the amorphous alloys resemble those of crystalline Fe borides, which further confirm the similarity of the local order in the amorphous and crystalline phases. All B atoms carry small negative moments of about -0.1{mu}{sub B}, while small negative moments are also found on very few Fe sites for the Fe-rich compositions (x=9, 17). The average magnetic moment per Fe atom decreases nonlinearly with increasing B composition, which can be associated with the nonlinear relationship between mass density and composition.
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.
Feng, Caihui; Shan, Jingfeng; Xu, Aoshu; Xu, Yang; Zhang, Meiguang; Lin, Tingting
2017-10-01
Trigonal yttrium hypocarbide (Y2C), crystallizing in a layered hR3 structure, is an intriguing quasi-two-dimensional electride metal with potential application for the next generation of electronics. By using an efficient structure search method in combination with first-principles calculations, we have extensively explored the phase transitions and electronic properties of Y2C in a wide pressure range of 0-200 GPa. Three structural transformations were predicted, as hR3 → oP12 → tI12 → mC12. Calculated pressures of phase transition are 20, 118, and 126 GPa, respectively. The high-pressure oP12 phase exhibits a three-dimensional extended C-Y network built up from face- and edge-sharing CY8 hendecahedrons, whereas both the tI12 and mC12 phases are featured by the presence of C2 units. No anionic electrons confined to interstitial spaces have been found in the three predicted high-pressure phases, indicating that they are not electrides. Moreover, Y2C is dynamically stable and also energetically stable relative to the decomposition into its elemental solids.
International Nuclear Information System (INIS)
Dridi, Z.; Bouhafs, B.; 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 x and TiN 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 x and TiN 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 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 x are compared to a recent full-potential calculation with relaxed 16-atom supercells
International Nuclear Information System (INIS)
Shao, Xiji; Li, Detian; Cai, Jianqiu; Luo, Haijun; Dong, Changkun
2016-01-01
Graphical abstract: - Highlights: • Substitutional nitrogen atom doping in capped (5, 5) SWNT is investigated. • Serious defects appear from breaks of C−N bonds with N contents of above 23.3 at.%. • Work function drops after N doping and may reach 4.1 eV. - Abstract: The structural and electronic properties of the capped (5, 5) single-walled carbon nanotube (SWNT), including the structural stability, the work function, and the charge transfer performance, are investigated for the substitutional nitrogen atom doping under different concentrations by first-principles density functional theory. The geometrical structure keeps almost intact with single or two N atom doping, while C−N bonds may break up with serious defects for N concentrations of 23.3 at.% and above. The SWNT remains metallic and the work function drops after doping due to the upward shift of Fermi level, leading to the increase of the electrical conductivity. N doping enhances the oxygen reduction activity stronger than N adsorption because of higher charge transfers.
Tian, Jinzhong; Zhao, Yuhong; Hou, Hua; Han, Peide
2017-12-01
The crystal structure, phase stability, mechanical and thermodynamic properties of the Al2Cu (θ), Al2Cu (θ‧) and Al2Cu (Ω) phases are studied by the first-principles method. The predicted lattice constants are consistent with the available literature data. θ, θ‧ and Ω phases are thermodynamically stable, and do not undergo any phase transition under pressure. The values of B for Ω are larger than that for θ and θ‧ phases, while the values of G for θ are smaller than that for Ω and θ‧ phases. The studies also reveal that pressure can improve the elastic anisotropy of the θ, θ‧ and Ω phases. The Debye temperature, heat capacity and thermal expansion coefficient for the phases are determined by the quasi-harmonic Debye model. Under identical conditions, the values of ΘD from high to low is in the following order: θ‧>Ω>θ. The heat capacity and thermal expansion coefficient for θ, θ‧ and Ω phases decrease with pressure when the temperature is kept constant. In contrast, thermal expansion coefficient α is more sensitive to any changes in pressure than any temperature change in the temperature range, 300-800 K.
First principles study of structural, electronic and optical properties of Pb doped SrHfO3
International Nuclear Information System (INIS)
Luo Benhua; Wang Xueye; Zhang Yu; Xia Yong
2012-01-01
Highlights: ► Dopant formation energy results show that Pb enters the Sr site in SrHfO 3 . ► The bandgap of Sr 0.875 Pb 0.125 HfO 3 is slightly wider compared with SrHfO 3 . ► Bonding between Hf and O is covalent whereas Sr-HfO 3 and Pb-HfO 3 are ionic. ► O 2p states and Hf 5d states play a major role in optical transitions. - Abstract: The structural, electronic and optical properties of Sr 0.875 Pb 0.125 HfO 3 are investigated using the pseudo-potential plane wave method within the generalized gradient approximation (GGA) by first principles. The lattice constants obtained by minimization of the total energy are in agreement with the available experimental data. Dopant formation energy results show that Pb preferentially enters the Sr site in SrHfO 3 , which is in good agreement with experimental observations. The band structures indicate that both SrHfO 3 and Sr 0.875 Pb 0.125 HfO 3 are insulators. The density of states and charge density map indicate that bonding between Hf and O is mainly covalent, whereas bonding of Sr-HfO 3 and Pb-HfO 3 is ionic. In order to understand the optical properties of Sr 0.875 Pb 0.125 HfO 3 , the dielectric functions, loss function, refractive index, absorption coefficient and reflectivity are calculated for radiation up to 40 eV.
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.
Hui, Liangliang; Xie, Zhongjing; Li, Chunmei; Chen, Zhi-Qian
2018-04-01
The first-principles calculations are implemented to investigate the electronic structures, theoretic hardness and magnetic properties of iron borides and nitrides with four different crystal systems containing hexagonal (FeB2, ε-Fe3N), tetragonal (Fe2B, α″-Fe16N2), orthorhombic (α-FeB, θ-Fe3B, ζ-Fe2N), and cubic (zb-FeN, rs-FeN, γ‧-Fe4N, γ-Fe23B6) phase. The calculated lattice parameters using RPBE meet well with the experimental results. The cohesive energy and formation enthalpy values indicate the Fesbnd X (X = B, N) binary compounds are thermodynamically stable. Meanwhile, the h-FeB2 is most difficult phase for experimental synthesis among these interstitial compounds. Moreover, magnetic properties are discussed and show that the mean magnetic moments of o-Fe3B and c-Fe23B6 with the values of 2.227 μB and 2.256 μB per iron atom are approaching to that of pure iron (2.32 μB) while the c-Fe4N and t-Fe16N2 with the values of 2.51 and 2.48 μB are beyond that of pure α-Fe. The c-FeN phase shows nonmagnetic in zb-style while rs-type shows antiferromagnetic with a value of 2.52 μB. Furthermore, the average bonding length and Mulliken population combined with electronic structures are also analysed in this paper which provide that strong Fesbnd X and Xsbnd X covalent bonds are responsible for high hardness. Finally, the theoretic hardness of Xsbnd X, Fesbnd X and Fesbnd Fe bonds is predicted by semi empirical hardness theory.
Energy Technology Data Exchange (ETDEWEB)
Rafique, Muhammad [School of Energy Science and Engineering, Harbin Institute of Technology, 92 West Dazhi Street, Harbin 150001 (China); M.U.E.T, S.Z.A.B, Campus Khairpur Mir' s, Sindh (Pakistan); Shuai, Yong, E-mail: shuaiyong1978@gmail.com [School of Energy Science and Engineering, Harbin Institute of Technology, 92 West Dazhi Street, Harbin 150001 (China); Tan, He-Ping; Hassan, Muhammad [School of Energy Science and Engineering, Harbin Institute of Technology, 92 West Dazhi Street, Harbin 150001 (China)
2017-03-31
Highlights: • First-principles calculations are performed for TMO{sub 3} cluster-doped and TM atoms adsorbed at three O atoms-doped graphene. • Significant magnetic coupling behavior is observed between TM atoms and neighboring C and O atoms for both cases. • The direction of charge transfer is always from monolayer graphene to TMO{sub 3} clusters incorporated into graphene. • TiO{sub 3} and VO{sub 3} doped structures display dilute magnetic semiconductor behavior. • Five different orbitals (d{sub xy}, d{sub yz}, d{sub z}{sup 2}, d{sub xz} and d{sub x}{sup 2}{sub -y}{sup 2}) of 3d TM atoms give rise to magnetic moments for both cases. - Abstract: 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 TMO{sub 3} halogen clusters. In this paper we used two approaches for 3d metal trioxide clusters (i) TMO{sub 3} 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 TMO{sub 3} doped graphene layer, the bond length between C−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 TiO{sub 3} and VO{sub 3} substitution, system exhibits semiconductor properties. Interestingly, TiO{sub 3}-substituted system shows dilute magnetic semiconductor behavior with 2.00 μ{sub B} magnetic moment. On the other hand, the substitution of CoO{sub 3}, CrO{sub 3}, FeO{sub 3} and MnO{sub 3} induced 1.015 μ{sub B}, 2
First-principles study on the gas sensing property of the Ge, As, and Br doped PtSe2
Zhang, Jing; Yang, Gui; Tian, Junlong; Ma, Dongwei; Wang, Yuanxu
2018-03-01
Based on first-principles calculations, the adsorption behaviors of H2, O2, CO, CO2, NH3, NO, and NO2 molecules on the Ge-, As- and Br-doped PtSe2 monolayers are theoretically investigated. The results indicate that it is viable for the dopant atoms to be filled into the Se vacancies under Pt-rich conditions. Ge and As act as p-type dopants, while Br acts as n-type dopant. For the adsorption of molecules, the geometrical structures, adsorption energies, charge transfers and the electronic and magnetic properties of the most stable configurations are presented and discussed. It is found that the Ge-doped PtSe2 monolayers exhibit greatly enhanced sensitivity toward O2, CO, NH3, NO and NO2 molecules and the As-doped PtSe2 monolayers are more sensitive toward O2, NH3, NO and NO2 molecules than the pristine ones. This is evident from large adsorption energies, charge transfers, and obvious changes of the electronic states due to the molecule adsorption. However, Br doping cannot enhance the sensing sensitivity of the PtSe2 monolayer. The possible reason is that when substituting for the Se atom, the doped Br with more 4p electrons and less empty orbitals are already chemically saturated by the two of the three neighboring Pt atoms, and thus lose the ability of charge exchange with the adsorbed molecules. On the contrary, the Ge and As as p-type dopants have sizable empty 4p orbitals near the Fermi level to exchange the electrons with the adsorbed molecules, and thus form strong bonds with them.
Harb, Moussab
2015-03-05
We investigate essential fundamental properties of monoclinic (Ta1-xNbx)ON (x = 0.0625, 0.125, 0.25, and 0.5) solid solution semiconductor materials for water splitting using first-principles computations on the basis of density functional theory (DFT) and density functional perturbation theory (DFPT) using the PBE and HSE06 functionals. The formation energies, band gaps, UV-vis optical absorption coefficients, dielectric constants, charge carrier effective masses, and band edge energy positions of these compounds are evaluated. Similarly to TaON, our calculations reveal strongly 3D delocalized characters of the band edge electronic states through the crystal lattices, high dielectric constants, small hole effective masses along the [001] direction, and small electron effective masses along the [100] direction. This leads to good exciton dissociation ability into free charge carriers, good hole mobility along the [001] direction, and good electron mobility along the [100] direction. The main difference, however, is related to their band edge positions with respect to water redox potentials. TaON with a calculated band gap energy of 3.0 eV is predicted as a good candidate for water oxidation and O2 evolution while the (Ta1-xNbx)ON materials (for 0.25 ≤ x ≤ 0.5) with calculated band gap energies between 2.8 and 2.9 eV reveal suitable band edge positions for water oxidation and H+ reduction. These results offer a grand opportunity for these compounds to be properly synthesized and tested for solar-driven overall water-splitting reactions.
Structural, electronic, magnetic and optical properties of Zn1-xNixO from first-principles
Liu, Huan; Zhang, Jian-Min
2017-05-01
The spin-polarized first-principles calculation is performed to investigate the structural, electronic, magnetic and optical properties of the Zn1-xNix O systems with x=0.00, 0.25, 0.50, 0.75, 1.00. Except for Zn0.5Ni0.5 O with a tetragonal structure, the other Zn1-xNix O systems are cubic structure. Although pure ZnO is a nonmagnetic semiconductor with a band gap of 1.43 eV, the Zn0.75Ni0.25 O , Zn0.5Ni0.5 O , Zn0.25Ni0.75 O and NiO systems are completely half metal and thus usable in spintronic devices. The tetrahedral crystal field of the surrounding four O anions splits Ni-3d states into triply degenerate t2g(dxy ,dyz ,dzx) states with higher energy and doubly degenerate eg(dz2 ,dx2-y2) states with lower energy. The magnetic moments of the Zn1-xNix O systems are mainly contributed by Ni atom with the small parallel contributions of O and Zn atoms. With increasing Ni concentration, the atomic magnetic moments μbarNi, μbarO, and μbarZn, total magnetic moment μtot, conduction band (CB) and valence band (VB) edge spin splittings ΔEC and ΔEV, spin polarized crystal field splittings ΔE↑ and ΔE↓, spin exchange splitting Δx (d) , static dielectric constant ε1 (0) and refractive index n (0) , new appeared small absorption peak at 0-4 eV increase, while the exchange constants N0 α and N0 β , original huge narrow absorption peak around 45 eV decrease.
Filanovich, A. N.; Povzner, A. A.
2017-12-01
In the framework of density functional theory method, the ground state energy of the PuCoGa5 compound is calculated for different values of the unit cell volume. The obtained data were incorporated into the thermodynamic model, which was utilized to calculate the temperature dependencies of thermal and elastic properties of PuCoGa5. The parameters of the developed model were estimated based on data of ab initio phonon spectrum. The Gruneisen parameters, which characterize degree of anharmonicity of the acoustic and optical phonons, are obtained. Using experimental data, non-lattice contributions to the coefficient of thermal expansion and heat capacity are determined. The nature of observed anomalies of the properties of PuCoGa5 is discussed, in particular, the possibility of a valence phase transition.
Dar, Sajad Ahmad; Srivastava, Vipul; Sakalle, Umesh Kumar; Rashid, Adil; Pagare, Gitanjali
2018-02-01
Theoretical investigation on electronic structural, magnetic, mechanical and thermodynamic properties of SrPuO3 perovskite oxide has been accomplished within density functional theory (DFT). For exchange correlations generalized gradient approximation (GGA), on-site coulomb repulsion (GGA + U) and modified Becke-Johnson (mBJ) have been used. The calculated structural parameters including lattice constant were found in good agreement with the available experimental and theoretical results. The spin polarized electronic band structure and density of states present half-metallic nature for the compound with majority spin (spin up states) as metallic and minority spin (spin down states) as semi-conducting. The large value of magnetic moment equal to 4 μ B was found for the compound. Elastic and mechanical properties have been predicted under ambient conditions. Moreover, thermodynamic parameters like Debye temperature (θ D), specific heat (CV), entropy (S) etc have been calculated using quasi-harmonic Debye model under different temperature and pressure values.
Czech Academy of Sciences Publication Activity Database
Mašín, Martin; Bergqvist, L.; Kudrnovský, Josef; Kotrla, Miroslav; Drchal, Václav
2013-01-01
Roč. 87, č. 7 (2013), "075452-1"-"075452-7" ISSN 1098-0121 R&D Projects: GA ČR GA202/09/0775 Institutional support: RVO:68378271 Keywords : Curie temperature * random overlayer * Heisenberg Hamiltonian * first principles * Monte Carlo simulations * magnon spectra Subject RIV: BE - Theoretical Physics Impact factor: 3.664, year: 2013 http://prb. aps .org/abstract/PRB/v87/i7/e075452
Directory of Open Access Journals (Sweden)
Lili Liu
2017-06-01
Full Text Available The pressure effects on the lattice parameters and elastic constants of the tetragonal RNi 2 B 2 C (R=Y, Lu are investigated by means of the first principles. The predicted lattice constants and elastic constants of YNi 2 B 2 C and LuNi 2 B 2 C at 0 GPa agree well with the available data. By the elastic stability criteria under isotropic pressure, it is predicted that YNi 2 B 2 C and LuNi 2 B 2 C with tetragonal structure are not mechanically stable above 93 GPa and 50 GPa, respectively. Pugh’s modulus ratio, Poisson’s ratio, Vickers hardness, elastic anisotropy and Debye temperature of YNi 2 B 2 C in the pressure range of 0–100 GPa and LuNi 2 B 2 C in the pressure range of 0-60 GPa are further investigated. It is shown that the ductility and Debye temperature of tetragonal RNi 2 B 2 C (R=Y, Lu increase with increasing pressure, and LuNi 2 B 2 C is more ductile and lower Debye temperature than YNi 2 B 2 C under different pressures.
Miao, Yurun; Li, Huayang; Wang, Hongjuan; He, Kaihua; Wang, Qingbo
2018-02-01
First principles and quasi-harmonic Debye model have been used to study the thermodynamic properties, enthalpies, electronic and optical properties of MgO up to the core-mantle boundary (CMB) condition (137 GPa and 3700 K). Thermodynamic properties calculation includes thermal expansion coefficient and capacity, which have been studied up to the CMB pressure (137 GPa) and temperature (3700 K) by the Debye model with generalized gradient approximation (GGA) and local-density approximation (LDA). First principles with hybrid functional method (PBE0) has been used to calculate the electronic and optical properties under pressure up to 137 GPa and 0 K. Our results show the Debye model with LDA and first principles with PBE0 can provide accurate thermodynamic properties, enthalpies, electronic and optical properties. Calculated enthalpies show that MgO keep NaCl (B1) structure up to 137 GPa. And MgO is a direct bandgap insulator with a 7.23 eV calculated bandgap. The bandgap increased with increasing pressure, which will induce a blue shift of optical properties. We also calculated the density of states (DOS) and discussed the relation between DOS and band, optical properties. Equations were used to fit the relations between pressure and bandgaps, absorption coefficient (α(ω)) of MgO. The equations can be used to evaluate pressure after careful calibration. Our calculations can not only be used to identify some geological processes, but also offer a reference to the applications of MgO in the future.
International Nuclear Information System (INIS)
Paiva, R de; Azevedo, S
2006-01-01
We apply a first-principles method based on the density functional theory within the generalized gradient approximation, and the full-potential linear augmented plane-wave method, to calculate the structural and electronic properties of cubic (BN) x C 2(1-x) ordered alloys. We investigate the equilibrium lattice parameters, the bulk moduli, the density of states, the band-gap energies and the effective masses of the conduction and valence bands along the [111],[100] and [110] directions. The obtained results are used to provide effective-mass and Luttinger parameters, and to give an important guideline to the material's design for optoelectronic devices, we link the first-principles band calculations with effective mass theory
Directory of Open Access Journals (Sweden)
Shenyu Dai
2018-03-01
Full Text Available The structural, electrical and mid-infrared optical properties of wurtzite structured ZnSe nanowires with different Chromium impurity distribution are investigated using first-principles calculation based on density-functional theory (DFT. The formation energies have been calculated to study the relative stabilities of different Cr doping positions. It is shown that when the Cr doping position shifted from the center to the edge, the splitting energy between 5T2 and 5E levels of Cr d-orbitals is decreased and a redshift is observed in the calculated infrared absorption spectra. A probable reason for these effects of the impurity distribution is discussed. Keywords: First-principles, Nanowires, Impurity distribution, Cr-doped ZnSe
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.
Teng, Zi-Wei; Liu, Chun-Sheng; Yan, Xiao-Hong
2017-05-04
Group V monolayers, e.g., nitrogene, phosphorene, arsenene, and antimonene have recently emerged as attractive candidates for electronic and optoelectronic applications. However, these pristine monolayers are not able to possess direct band gaps suitable for ultraviolet-blue photoresponse. First-principles calculations show that the Pmma-CO monolayer has a direct band gap of 2.4 eV, and predict that the system has a good stability. Unlike an easy direct-indirect gap transition under small strains in phosphorene, the direct band gap feature of Pmma-CO is maintained under a strain up to 12%. Surprisingly, Pmma-CO shows excellent mechanical stability with an anisotropic in-plane stiffness up to 475.7 N m -1 along the b direction, which is higher than that of graphene. The in-plane hole carrier mobility is predicted to be 746.42 cm 2 V -1 s -1 , similar to that of black phosphorene. When synthesized, the Pmma-CO monolayer may have great potential in the design of new ultraviolet/blue optoelectronic devices.
First-principles molecular dynamics study of glassy GeS2: Atomic structure and bonding properties
Celino, M.; Le Roux, S.; Ori, G.; Coasne, B.; Bouzid, A.; Boero, M.; Massobrio, C.
2013-11-01
The structure of glassy GeS2 is studied in the framework of density functional theory, by using a fully self-consistent first-principles molecular dynamics (FPMD) scheme. A comparative analysis is performed with previous molecular dynamics data obtained within the Harris functional (HFMD) total energy approach. The calculated total neutron structure factor exhibits an unprecedented agreement with the experimental counterpart. In particular, the height of the first sharp diffraction peak (FSDP) improves considerably upon the HFMD results. Both the Ge and the S subnetworks are affected by a consistent number of miscoordinations, coexisting with the main tetrahedral structural motif. Glassy GeS2 features a short-range order quite similar to the one found in glassy GeSe2, a notable exception being the larger number of edge-sharing connections. An electronic structure localization analysis, based on the Wannier functions formalism, provides evidence of a more enhanced ionic character in glassy GeS2 when compared to glassy GeSe2.
Li, Xin; Li, Shuangming; Feng, Songke; Zhong, Hong
2018-02-01
A comprehensive analysis has been made of the n-type Mg2Si1 - x Sn x (0.25 ≤ x ≤ 0.75) compounds by the first principles calculation method. The calculated band structures in n-type Mg2Si1 - x Sn x show the conduction band convergence directly. This convergence in energy at x = 0.625 can enhance the Seebeck coefficient of the solid solution in comparison with other Sn contents. The Seebeck coefficient of Mg2Si0.375Sn0.625 could reach - 246 μV K-1 at the optimal doping density of 3 × 1020 cm-3. The enhancement of the Seebeck coefficient in the Mg2Si0.375Sn0.625 alloy results in a higher power factor of 6.2 mW m-1 K-2 at T = 550 K, and the predicted figure of merit is 1.53 at T = 700 K. Additionally, the ZT values can be maintained larger than 1.4 in a wide temperature range from 550 K to 800 K.
Jezierska-Mazzarello, Aneta; Vuilleumier, Rodolphe; Panek, Jarosław J; Ciccotti, Giovanni
2010-01-14
The structure, proton transfer, and vibrational dynamics under ambient conditions of a selected ortho-hydroxy Schiff base type compound, 2-(N-methyl-alpha-iminoethyl)-4-chlorophenol, containing a very short intramolecular hydrogen bond, were investigated computationally in the gas phase and in the crystal by density functional theory (DFT) based first-principle molecular dynamics (FPMD). It is found that the proton is well localized on the nitrogen side of the O...H...N bridge in the crystal phase, in agreement with X-ray diffraction experiments, while a more labile proton is located most of the time on the oxygen side in a vacuum. Environmental effects on this very strong hydrogen bond thus appear crucial and lead to drastic changes of the infrared (IR) spectrum: The computed gas-phase IR spectrum shows a very broad absorption band that covers frequencies from about 1000 to 3000 cm(-1) assigned to the labile proton. In mere contrast, a much more localized absorption band around 2600-2700 cm(-1) is predicted in the crystal phase. Finally, effects of the quantization of the proton motion on the hydrogen bond structure were estimated in two ways. First, we constructed the one-dimensional (1D) potential energy surface (PES) for the proton along the O...H...N bridge in a vacuum. The 1D Schrodinger equation was then solved. Next, path integral molecular dynamics (PIMD) was performed in the solid state. Inclusion of quantum effects does not affect the observed change of the most probable tautomer, upon going from the gas phase to the crystal.
Dai, Shenyu; Feng, Guoying; Zhang, Yuqin; Deng, Lijuan; Zhang, Hong; Zhou, Shouhuan
2018-03-01
The structural, electrical and mid-infrared optical properties of wurtzite structured ZnSe nanowires with different Chromium impurity distribution are investigated using first-principles calculation based on density-functional theory (DFT). The formation energies have been calculated to study the relative stabilities of different Cr doping positions. It is shown that when the Cr doping position shifted from the center to the edge, the splitting energy between 5T2 and 5E levels of Cr d-orbitals is decreased and a redshift is observed in the calculated infrared absorption spectra. A probable reason for these effects of the impurity distribution is discussed.
First-principles study of the structural, optical and thermal properties of AgGaSe2
International Nuclear Information System (INIS)
Hou, H J; Yang, S X; Kong, F J; Yang, J W; Xie, L H
2014-01-01
We have calculated the structural, optical and thermal properties of an AgGaSe 2 crystal using ultrasoft pseudopotentials and the generalized gradient approximation (GGA). The calculated results are in good agreement with the available experimental data and theoretical values. The optical property calculations are performed for the energy range 0–22.5 eV. The thermal properties of the AgGaSe 2 are calculated using the quasi-harmonic Debye model. The pressure and temperature dependences of the bulk modulus, the heat capacity, the Grüneisen parameter, the Debye temperature and the thermal expansion coefficient, as well as the entropy, are obtained in the ranges of 0–6 GPa and 0–1200 K. We also found in our present work that the effects of pressure and temperature on different thermal properties are significant and very useful for crystal growth. (papers)
Energy Technology Data Exchange (ETDEWEB)
Huang, Y.L.; Fan, W.B. [School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063 (China); Hou, Y.H., E-mail: hyhhyl@163.com [School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063 (China); Guo, K.X. [School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063 (China); Ouyang, Y.F. [Department of Physics, Guangxi University, Nanning 530004 (China); Liu, Z.W. [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China)
2017-05-01
The cobalt ferrite (CoFe{sub 2}O{sub 4}) with spinel structure has achieved a great interest as a very important magnetic material which has covered a wide range of applications. The formation condition and energy of possible intrinsic point defects have been investigated by the first-principles calculations, and the effects of the intrinsic point defects on the electronic and magnetic properties of CoFe{sub 2}O{sub 4} have been analyzed. It is found that the growth conditions have a great effect on the formation energy of intrinsic point defects, and each point defect with its fully ionized state is the most stable for the intrinsic point defects with various charge states. In an oxygen rich environment, the cation vacancies are easy to form shallow acceptors, which is conducive to the strength of the p-type conductivity. While in the metal rich environment, the oxygen vacancies tend to form donors which lead to the n-type conductivity. There exists extra levels in the band gap when point defects are present, resulting in a reduction of the band gap. The net magnetic moment depends highly on the defects. - Highlights: • The intrinsic defects in CoFe{sub 2}O{sub 4} were investigated by first-principles calculation. • The effects of intrinsic defects on the electronic structures and magnetic properties of CoFe{sub 2}O{sub 4} were analyzed.
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.
Effect of magnetism on the vibrational properties of the Ni-Cu alloy: a first-principles study
de La Pena-Seaman, Omar; Bustamante-Romero, Ivan; Heid, Rolf; Bohnen, Klaus-Peter
2013-03-01
We have studied the lattice dynamical properties of the Ni1-xCux magnetic alloy within the framework of density functional perturbation theory, using a mixed-basis pseudopotential method and the virtual crystal approximation for modeling the alloy. The system has been investigated for both non-magnetic (NM) and ferromagnetic (FM) phases. The performance of LDA and GGA exchange-correlation functionals on the properties under study was analyzed. The structural optimization for each magnetic phase, NM and FM, in the full range of concentrations (0 BUAP-PTC-299
Fang, C.M.; Wijs, G.A. de
2004-01-01
The phonon spectrum Of C3N4 with defect zincblende-type structure (deltaC(3)N(4)) was calculated by density functional theory (DFT) techniques. The results permit an assessment of important mechanical and thermodynamical properties such as the bulk modulus, lattice specific heat, vibration energy,
Wang, Yinglong; Chen, Chao; Wu, Zhuanhua; Liang, Weihua; Wang, Xiuli; Ding, Xuecheng; Chu, Lizhi; Deng, Zechao; Chen, Jinzhong; Fu, Guangsheng
To investigate the size dependence of the optical properties of the hydrogen-passivated Si nanoparticles (Hp-SiNPs), the energy bands and optical dielectric functions for two types of nanostructures, that is, the spherical Hp-SiNPs (SHp-SiNPs) with various diameters and the cylindrical Hp-SiNPs
International Nuclear Information System (INIS)
Hou, Y H; Liu, Z W; Yu, H Y; Zhong, X C; Qiu, W Q; Zeng, D C; Wen, L S; Zhao, Y J
2010-01-01
Partially inverse spinel CoFe 2 O 4 , which may be prepared through various heat treatments, differs remarkably from the ideal inverse spinel in many properties. The structure of partially inverse spinel CoFe 2 O 4 as well as its electronic and magnetic properties through a systemic theoretical calculation of (Co 1-x Fe x ) Tet (Co x Fe 2-x ) Oct O 4 (x = 0, 0.25, 0.5, 0.75 and 1.0) have been investigated by the generalized gradient approximation (GGA) + U approach. It is found that the Co and Fe ions prefer their high spin configurations with higher spin moments at octahedral sites in all the studied cases, in line with experimental observations. The Co ions at the octahedral sites favour being far away from each other in the partial inverse spinels, which also show half metallicity at certain inversion degrees.
Structural and optoelectronic properties of BxAl1-xSb ternary alloys: first principles calculations
Benchehima, Miloud; Abid, Hamza; Chaouche, Abdallah Chabane; Resfa, Abbes
2017-03-01
In this paper, the full potential linearized augmented plane wave (FP-LAPW) formalism based on density functional theory (DFT) has been performed. To study the structural properties of BxAl1-xSb at different boron concentrations x (0 ≤ x ≤ 1), we have used the local density approximation (LDA) and the generalized gradient approximation of Wu and Cohen (GGA-WC). The phase stability of AlSb and BSb binary compounds in zinc-blend and rock salt phases has been investigated. The equilibrium lattice constant (a), bulk modulus (B) and pressure derivative of bulk modulus B' have been evaluated in both phases. We observe a small deviation from the linear concentration dependence (LCD) of the lattice constant parameter, while an important deviation of bulk modulus from "LCD" has been remarked. We have compared the results obtained to the available theoretical and experimental data for the binaries. The optoelectronic properties of BxAl1-xSb are studied in the most stable determined phase. In addition to the "GGA-WC", the GGA of Engel and Vosko, and the recent developed Tran-Blaha-modified Becke-Johnson (TB-mBJ) schemes were used to study the electronic properties of BxAl1-xSb ternary alloys. It is found that the band gap of BxAl1-xSb vary non-linearly with the boron concentrations, giving a negative deviation from Vegard's law. In addition, the optical properties such as the dielectric function, complex refractive index, absorption coefficient, optical conductivity and absorption coefficient are discussed in detail.
Atomistic simulation of the mechanical properties of β-SiC based on the first-principles
Energy Technology Data Exchange (ETDEWEB)
Zhang, Renhui, E-mail: zrh_111@126.com [Research Center of Material and Chemical Engineering, School of Material and Chemical Engineering, Tongren University, Tongren 554300 (China); Leng, Senlin, E-mail: 764546880@qq.com [Research Center of Material and Chemical Engineering, School of Material and Chemical Engineering, Tongren University, Tongren 554300 (China); Yang, Yingchang; Shi, Wei [Research Center of Material and Chemical Engineering, School of Material and Chemical Engineering, Tongren University, Tongren 554300 (China); Lu, Zhibin, E-mail: zblu@licp.cas.cn [Lanzhou Institute of Chemical Physics, Lanzhou 730000 (China)
2017-05-01
On the basis of the pseudopotential plane-wave method and the local-density-functional theory, this work studied the energetics and stress-strain relationship of β-SiC, where uniform uniaxial compression and tension were considered along (001), (110) and (111) planes. The calculated results were in consistence with the experimental data. The present work should be conducive to understanding the mechanical property of β-SiC.
Wen, Jun-Qing; Zhang, Jian-Min; Chen, Guo-Xiang; Wu, Hua; Yang, Xu
2018-04-01
The density functional theory calculations using general gradient approximation (GGA) applying Perdew-Burke-Ernzerhof (PBE) as correlation functional have been systematically performed to research the formation energy, the electronic structures, band structures, total and partial DOS, and optical properties of Nd doping ZnO with the content from 6.25% to 12.5%. The formation energies are negative for both models, which show that two structures are energetically stable. Nd doping ZnO crystal is found to be a direct band gap semiconductor and Fermi level shifts upward into conduction band, which show the properties of n-type semiconductor. Band structures are more compact after Nd doping ZnO, implying that Nd doping induces the strong interaction between different atoms. Nd doping ZnO crystal presents occupied states at near Fermi level, which mainly comes from the Nd 4f orbital. The calculated optical properties imply that Nd doping causes a red-shift of absorption peaks, and enhances the absorption of the visible light.
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.
Nguyen, Chuong Van; Hieu, Nguyen Van; Nhan, Le Cong; Phuc, Huynh Vinh; IIyasov, Victor V.; Hieu, Nguyen Ngoc
2018-04-01
In this work, we consider the effect of out-plane strain on the electronic properties of AB-stacked bilayer armchair graphene nanoribbons (BAGNRs) using density functional theory. At equilibrium, the interlayer distance of BAGNRs is d_0=3.326 Å. Our DFT calculations show that while the dependence of the band gap of 11-BAGNR on interlayer distance d is insignificant, especially in the case of the d
Nigam, Sandeep; Majumder, Chiranjib
2012-06-01
We report the structure and electronic properties of AgmPdn bimetallic clusters (m, n = 1-2) in gas phase and deposited on the α-Al2O3(0 0 0 1) surface using plane wave pseudopotential approach. The ground state geometry of the mixed clusters is significantly modified after deposition. For Ag2Pd2 tetramer, the gas phase compact tetrahedron structure reorients to open bent rhombus. The charge distribution analysis shows that small amount of charge is accumulated at the Pd site and depleted at the Ag site. The electronic density of states analysis reveals that after deposition, the bands near the Fermi energy become wider.
Zhang, Haijun; Li, Yafei; Tang, Qing; Liu, Lu; Zhou, Zhen
2012-02-21
The structural and electronic properties of core-shell, eutectic, biaxial and superlattice GaN-AlN nanowires were studied through density functional theory computations. Due to more surface dangling bonds, nanowires with smaller diameters are energetically unfavorable. For the GaN-AlN heterostructure nanowires, their electronic properties highly depend on the GaN content, axial strain, configuration, and size. The valence bands are less affected by the GaN content, while the conduction bands depend on it. Hydrogen-passivated nanowires have much larger band gaps than their counterparts, since the surface states are removed by saturating the dangling bonds with hydrogen atoms. Moreover, due to multiple quantum-well structures, the confined electrons (holes) of superlattice nanowires become more localized and the difference of the mobility between the electron and hole becomes less apparent if the width of the barrier is larger. These findings are of value for better understanding heterostructure nanowires and their potential utilization. This journal is © The Royal Society of Chemistry 2012
Electronic and magnetic properties of SrTiO(3)/LaAlO(3) interfaces from first principles.
Chen, Hanghui; Kolpak, Alexie M; Ismail-Beigi, Sohrab
2010-07-20
A number of intriguing properties emerge upon the formation of the epitaxial interface between the insulating oxides LaAlO(3) and SrTiO(3). These properties, which include a quasi two-dimensional conducting electron gas, low temperature superconductivity, and magnetism, are not present in the bulk materials, generating a great deal of interest in the fundamental physics of their origins. While it is generally accepted that the novel behavior arises as a result of a combination of electronic and atomic reconstructions and growth-induced defects, the complex interplay between these effects remains unclear. In this report, we review the progress that has been made towards unraveling the complete picture of the SrTiO(3)/LaAlO(3) interface, focusing primarily on present ab initio theoretical work and its relation to the experimental data. In the process, we highlight some key unresolved issues and discuss how they might be addressed by future experimental and theoretical studies.
First principles calculations of structural and electronic properties of GaN1−xBix alloys
International Nuclear Information System (INIS)
Mbarki, M.; Rebey, A.
2012-01-01
Highlights: ► The FPLAPW is used to calculate the structural and electronic properties of GaN 1−x Bi x . ► The lattice parameter of GaN 1−x Bi x shows an increase with Bi composition. ► We have studied the variation of the energy gap and the electron effective masses of the ternary compound with respect to the composition x of Bi. - Abstract: In this work we have calculated the structural and electronic properties of GaN 1−x Bi x alloy by using the density functional theory based on the full potential linearized augmented plane wave method (FPLAPW). The calculated lattice parameter of GaN 1−x Bi x alloys shows an increase by increasing the composition x of bismuth (Bi), while a significant deviation from Vegard's law is observed. We have studied the variation of the energy gap and the electron effective masses of the ternary compound with respect to the composition x of Bi.
Energy Technology Data Exchange (ETDEWEB)
Takaki, Hirokazu; Kobayashi, Kazuaki; Shimono, Masato [National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan); Kobayashi, Nobuhiko [Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573 (Japan); Hirose, Kenji [Smart Energy Research Laboratories, NEC Corporation, 34 Miyukigaoka, Tsukuba, Ibaraki 305-8501 (Japan)
2016-01-07
We present the thermoelectric properties of TiN/MgO superlattices employing first-principles calculation techniques. The Seebeck coefficients, the electrical conductances, the thermal conductances, and the figure of merit are investigated employing electrical and thermal transport calculations based on density functional theory combined with the nonequilibrium Green's function and nonequilibrium molecular dynamics simulation methods. The TiN/MgO superlattices with a small lattice mismatch at the interfaces are ideal systems to study the way for an enhancement of thermoelectric properties in artificial nanostructures. We find that the interfacial scattering between the two materials in the metal/insulator superlattices causes the electrical conductance to change rapidly, which enhances the Seebeck coefficient significantly. We show that the figure of merit for the artificial superlattice nanostructures has a much larger value compared with that of the bulk material and changes drastically with the superlattice configurations at the atomistic level.
Directory of Open Access Journals (Sweden)
Jing Bai
2016-12-01
Full Text Available First-principles calculations have been used to investigate the effects of Co addition on the preferred site occupation and magnetic properties of Ni-Fe-Ga-Co ferromagnetic shape memory alloys. The formation energy results indicate that the excess Ni constituent preferentially occupies the Fe sites in the off-stoichiometric Ni-Fe-Ga ternary alloy. The added Co tends to take the normal-Ni sites in the Ni-Fe-Ga-Co quaternary alloy during composition adjustment process. The total magnetic moment increases with Co content of the Ni36-xFe12Ga16Cox (x=0, 1, 2, 3 and 4 alloys. The difference between the up and down electronic density of states at the Fermi level gives rise to the increased magnetic property.
Xue, Yuanbin; Wang, Wenyuan; Guo, Yao
2018-02-01
We investigated the atomic and electronic properties of (1 0 0) stacking fault (SF) in undoped and La-doped BaSnO3 by first-principles calculations. It was found that 1/2[1 1 1] (1 0 0) SF is energetically favorable when Ba atoms occupy the interface while 1/2 (1 0 0) [1 0 1] SF becomes the most stable when the SF interface is occupied by Sn atoms. SF influences the distribution of La dopant and the electric properties of the system. In the presence of SF, electronic states near the Fermi level decrease and the bandgap expands by about 0.6 eV. Our results suggest that SF is one of the possible origins for the performance degradation.
Zhu, Yupeng; Liang, Xiao; Qin, Jun; Deng, Longjiang; Bi, Lei
2018-05-01
In this article, a systematic study on the magnetic properties and strain tunability of 3d transition metal ions (Mn, Fe, Co, Ni) doped MoS2 using first-principles calculations is performed. Antiferromagnetic coupling is observed between Mn, Fe ions and the nearest neighbor Mo ions; whereas ferromagnetic coupling is observed in Co and Ni systems. It is also shown that by applying biaxial tensile strain, a significant change of the magnetic moment is observed in all transition metal doped MoS2 materials with a strain threshold. The changes of total magnetic moment have different mechanisms for different doping systems including an abrupt change of the bond lengths, charge transfer and strain induced structural anisotropy. These results demonstrate applying strain as a promising method for tuning the magnetic properties in transition metal ion doped monolayer MoS2.
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.
Terkhi, Sabria; Bentata, Samir; Aziz, Zoubir; Lantri, Tayeb; Abbar, Boucif
2018-02-01
The structural, electronic and magnetic properties of the cubic GdCrO3 perovskite are investigated by mean the full-potential linearized augmented plane wave method based on the density functional theory. We have used three approximations: the generalized gradient (GGA), the GGA + U, where U is on-site Coulomb interaction correction, and the modified Becke-Johnson (mBJ-GGA). Calculated Lattice parameters are where found to be in a very good agreement with experimental measurements. Our results of spin-polarized band structure and density of states show a metallic character of GdCrO3 when using the GGA scheme, whereas a half-metallic ferromagnetic behavior is observed in both cases of GGA + U and mBJ-GGA approaches with an important total magnetic moment of 10.00 μB. The obtained results show that GdCrO3 is an excellent candidate to spintronic applications.
Energy Technology Data Exchange (ETDEWEB)
Hou, Y.H., E-mail: hyhhyl@163.com [School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang, 330063 (China); Huang, Y.L.; Hou, S.J.; Ma, S.C. [School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang, 330063 (China); Liu, Z.W. [School of Materials Science and Engineering, South China University of Technology, Guangzhou, 510640 (China); Ouyang, Y.F. [School of Physical Science and Technology, Guangxi University, Nanning, 530004 (China)
2017-01-01
RE{sup 3+}(RE=La, Ce, Pr, Nd, Eu, Gd) doped cobalt ferrite (CoFe{sub 2}O{sub 4}) have been studied systematically by the first-principles calculations based on density functional theory within the generalized gradient approximation with Hubbard corrections (GGA+U) . The significant effects of RE{sup 3+}doping on the crystal structure, electronic and magnetic properties of CoFe{sub 2}O{sub 4} have been explored. The calculated results show that the RE ions prefer substituting Fe{sup 3+} located at the octahedral sites. And the lattice constant of CoFe{sub 1.875}RE{sub 0.125}O{sub 4} (RE=La, Ce, Pr, Nd, Eu and Gd) decreases due to the decreasing ionic radius of RE as the atomic number increases. The magnetic properties depend on the unpaired 4f electrons of RE{sup 3+} ions. The net magnetic moment of CoFe{sub 2}O{sub 4} increases by doping with Eu and Gd, the reason is that there are more unpaired 4f electrons for Eu{sup 3+}and Gd{sup 3+}. However, the net magnetic moment of CoFe{sub 2}O{sub 4} decreases by doping with La, Ce, Pr, and Nd, due to the reason that these RE ions prefer their low spin configurations. - Highlights: ●RE{sup 3+} doped cobalt ferrite have been studied by the first-principles calculations. ●The RE{sup 3+} in influencing electronic and magnetic properties was discussed. ●The influence of the 4f electrons of RE{sup 3+} on the magnetic properties was analyzed.
First-principles study on half-metallic ferromagnetic properties of Zn1- x V x Se ternary alloys
Khatta, Swati; Tripathi, S. K.; Prakash, Satya
2017-09-01
The spin-polarised density functional theory along with self-consistent plane-wave pseudopotential is used to investigate the half-metallic ferromagnetic properties of ternary alloys Zn1- x V x Se. The generalized gradient approximation is used for exchange-correlation potential. The equilibrium lattice constants, bulk modulus, and its derivatives are calculated. The calculated spin-polarised energy-band structures reveal that these alloys are half-metallic for x = 0.375 and 0.50 and nearly half-metallic for other values of x. The estimated direct and indirect bandgaps may be useful for the magneto-optical absorption experiments. It is found that there is strong Zn 4s, Se 4p, and V 3d orbital hybridization in the conduction bands of both the spins, while Se 4p and V 3d orbital hybridization predominates in the valence bands of both the spins. The s, p-d, and p-d orbital hybridization reduces the local magnetic moment of V atoms and small local magnetic moments are produced on Zn and Se atoms which get coupled with V atoms in ferromagnetic and antiferromagnetic phases, respectively. The conduction and valence-band-edge splittings and exchange constants predict the ferromagnetism in these alloys. The conduction band-impurity (s and p-d) exchange interaction is more significant for ferromagnetism in these alloys than the valence band-impurity (p-d) exchange interaction.
Smart, Tyler J; Ping, Yuan
2017-10-04
Hematite (α-Fe 2 O 3 ) is a promising candidate as a photoanode material for solar-to-fuel conversion due to its favorable band gap for visible light absorption, its stability in an aqueous environment and its relatively low cost in comparison to other prospective materials. However, the small polaron transport nature in α-Fe 2 O 3 results in low carrier mobility and conductivity, significantly lowering its efficiency from the theoretical limit. Experimentally, it has been found that the incorporation of oxygen vacancies and other dopants, such as Sn, into the material appreciably enhances its photo-to-current efficiency. Yet no quantitative explanation has been provided to understand the role of oxygen vacancy or Sn-doping in hematite. We employed density functional theory to probe the small polaron formation in oxygen deficient hematite, N-doped as well as Sn-doped hematite. We computed the charged defect formation energies, the small polaron formation energy and hopping activation energies to understand the effect of defects on carrier concentration and mobility. This work provides us with a fundamental understanding regarding the role of defects on small polaron formation and transport properties in hematite, offering key insights into the design of new dopants to further improve the efficiency of transition metal oxides for solar-to-fuel conversion.
Hafizi, Roohollah; Hashemifar, S Javad; Alaei, Mojtaba; Jangrouei, MohammadReza; Akbarzadeh, Hadi
2016-12-07
In this paper, we employ an evolutionary algorithm along with the full-potential density functional theory (DFT) computations to perform a comprehensive search for the stable structures of stoichiometric (WS 2 ) n nano-clusters (n = 1 - 9), within three different exchange-correlation functionals. Our results suggest that n = 5 and 8 are possible candidates for the low temperature magic sizes of WS 2 nano-clusters while at temperatures above 500 Kelvin, n = 7 exhibits a comparable relative stability with n = 8. The electronic properties and energy gap of the lowest energy isomers were computed within several schemes, including semilocal Perdew-Burke-Ernzerhof and Becke-Lee-Yang-Parr functionals, hybrid B3LYP functional, many body based DFT+GW approach, ΔSCF method, 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 a real time domain is applied to determine the full absorption spectra and optical gap of the lowest energy isomers of the WS 2 nano-clusters.
Li, Xiaojun
2017-10-05
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 BB and BH 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 3c2e and two delocalized 4c2e σ-bonds, while the pyrromethene fragment corresponds to five delocalized 3c2e 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. Copyright © 2017 Elsevier B.V. All rights reserved.
First-principles study of magnetic, electronic and optical properties of double perovskite Bi2FeMnO6
Ahmed, Towfiq; Yarotski, Dzmitry; Jia, Quanxi; Zhu, Jian-Xin
2015-03-01
We study magnetic, electronic and optical properties of double perovskite Bi2FeMnO6 (BFMO) using density functional theory. In these systems, the exchange interaction between Fe and Mn sites gives rise to a ferrimagnetic ordering, which is captured in our ab initio calculations. Thin film Bi2FeMnO6 (BFMO) are generally grown on substrates such as SrTiO3 and Si. Significant strain has been experimentally observed in BFMO unit cells due to slight lattice mismatch between the thin film and substrate unit cells. In this work, we find that the net magnetic moment in BFMO depends on the ``c/a'' ratio of the unit cell, suggesting the strain dependence of magnetization in such system. We further calculate x-ray magnetic dichroism (XMCD) signals of Fe and Mn ions in BFMO for L2 and L3 edges. By applying the XMCD sum rules, we adopted an alternative approach to estimate the spin and orbital magnetic moment from our DFT calculations. We find qualitative agreement between our calculated values and the experimental measurements based on different techniques.Moreover, we study spin resolved optical conductivity and density of states in BFMO. These calculations give insight into electronic structure near Fermi energy, and dominant electronic excitations in the valence-conduction region of BFMO. This work was supported by U.S. DOE at LANL under Contract No. DE-AC52-06NA25396, the LANL LDRD Program.
Pinto, Mirele B; Soares, Antonio Lenito; Mella Orellana, Andy; Duarte, Hélio A; De Abreu, Heitor A
2017-03-30
Different polymorphs of Nb 2 O 5 can be obtained depending on the pressure and temperature of calcination leading to different catalytic properties. Two polymorphs of niobia, T-Nb 2 O 5 and B-Nb 2 O 5 , have been investigated by means of density functional/plane waves method. The equation of state predicted that B-Nb 2 O 5 phase is more stable than the T-Nb 2 O 5 at low temperature; however at high pressure both phases are stable. These results are in good agreement with the available experimental data. The calculated cohesive energies of 6.63 and 6.59 eV·atom -1 for the B-Nb 2 O 5 and T-Nb 2 O 5 , respectively, also corroborate this conclusion, and it can be compared to the experimental value of 9.56 eV atom -1 estimated for the most thermodynamically stable phase. The topological analyses based on quantum theory of atoms in molecules (QTAIM) and electron localization function (ELF) were applied and reveal bonds with large ionic character for both phases. The B-Nb 2 O 5 presented larger stiffness than T-Nb 2 O 5 , and the oxygen sites in the T-Nb 2 O 5 are more compressible. The density of states comparison for both structures indicates that B-Nb 2 O 5 has lower concentration of acid sites compared to T-Nb 2 O 5 . This result is consistent with the experimental observations that the concentration of Lewis acid sites decreases with the temperature.
First principles centroid molecular dynamics simulation of high pressure ices
Ikeda, Takashi
2018-03-01
The nuclear quantum effects (NQEs) on the structural, elastic, electronic, and vibrational properties of high pressure ices (HPIs) VIII, VII, and X at 270 K were investigated via first principles centroid molecular dynamics (CMD). Our simulations clearly show that even at relatively high temperature of 270 K, the NQEs play a definite role in the pressure-induced proton order (ice VIII)-disorder (ice VII) transition occurring at ˜30 GPa in our H2O ice and the subsequent transition to the symmetric phase ice X suggested to occur at ˜80 GPa. The internal pressure computed at constant NVT conditions shows that the NQEs manifest themselves in the equation of state of HPIs. Our employed approach based on first principles CMD for computing vibrational spectra is proved to be able to reproduce well the overall features of the measured infrared and Raman spectra.
First Principles Study of Flexoelectricity
Hong, Jiawang; Vanderbilt, David
2011-03-01
Flexoelectricity is the linear response of polarization to a strain gradient. Because strain gradients break inversion symmetry, flexoelectricity allows for charge to be extracted from deformations even in materials that are not piezoelectric. The flexoelectric effect is negligible on conventional length scales, but it becomes very strong at the nanoscale where large strain gradients can significantly affect the functional properties of dielectric thin films and superlattices. We present first-principles calculations of flexoelectric effects in nonpiezoelectric materials by introducing the strain gradient artificially in a slab geometry and obtain the flexoelectric coefficients. Furthermore, we model the results in terms of quantities, such as dynamical charges and higher multipole moments that can be computed in the bulk, bringing us closer to a full theory of flexoelectricity. R. Resta, Phys. Rev. Lett. 105, 127601 (2010).
Hendrickx, Marc F A; Clima, S; Chibotaru, L F; Ceulemans, A
2005-10-06
An ab initio multiconfigurational approach has been used to calculate the ligand-field spectrum and magnetic properties of the title cyano-bridged dinuclear molybdenum complex. The rather large magnetic coupling parameter J for a single cyano bridge, as derived experimentally for this complex by susceptibility measurements, is confirmed to a high degree of accuracy by our CASPT2 calculations. Its electronic structure is rationalized in terms of spin-spin coupling between the two constituent hexacyano-monomolybdate complexes. An in-depth analysis on the basis of Anderson's kinetic exchange theory provides a qualitative picture of the calculated CASSCF antiferromagnetic ground-state eigenvector in the Mo dimer. Dynamic electron correlations as incorporated into our first-principles calculations by means of the CASPT2 method are essential to obtain quantitative agreement between theory and experiment.
Honer, C. J.; Prosniewski, M. J.; Putatunda, A.; Singh, David J.
2017-10-01
We report the properties of the antiferromagnetic selenite MnSeO3 and the non-magnetic analogue ZnSeO3, based on first principles calculations. These compounds are rare examples of ABO3 perovskites with a tetravalent A-site and a divalent B-site. The electronic structure is discussed in the context of the bonding and crystal structure. There is cross-gap hybridization between the O p states that form the valence bands of these compounds and the unoccupied p states of Se, reflecting the lone pair physics that leads to the strong off-centering of Se from the perovskite A-site. The G-type antiferromagnetism of MnSeO3 is a local moment in nature arising from high spin Mn2+ with short range interactions. Additionally, there is an interesting spin-dependent hybridization of Mn d and O p states analogous to that in colossal magnetoresistance manganites.
Wang, L; Hua, L; Chen, L F
2009-12-02
We have investigated the structural, magnetic and electronic properties of single-crystal SrRu(1-x)Mn(x)O(3), using first-principles density functional theory within the generalized gradient approximation (GGA)+U schemes. The entire series of SrRu(1-x)Mn(x)O(3) (x = 0, 0.25, 0.5 and 1) is stabilized in the single-crystal perovskite structure which is in agreement with experimental findings. Our spin-polarized calculations give a metallic ground state for the xmagnetic structure for x = 0 is found to be the ferromagnetic state while the magnetic structures for 0magnetic structures for x≥0.5 are found to be the antiferromagnetic states. The substitution of itinerant Ru ions by localized Mn ions enhances the p-d coupling between O and the transition metal. It also strongly drives the system from the ferromagnetic metal to the antiferromagnetic insulator.
Temperature dependence of elastic properties of paratellurite
International Nuclear Information System (INIS)
Silvestrova, I.M.; Pisarevskii, Y.V.; Senyushenkov, P.A.; Krupny, A.I.
1987-01-01
New data are presented on the temperature dependence of the elastic wave velocities, elastic stiffness constants, and thermal expansion of paratellurite. It is shown that the external pressure appreciably influences the elastic properties of TeO 2 , especially the temperature dependence of the elastic modulus connected with the crystal soft mode. (author)
Indian Academy of Sciences (India)
Santosh singh
2017-06-19
Jun 19, 2017 ... behaviour of the optical spectra in the optical region for transparent conducting application. Keywords. Optoelectronic; titanium oxide. PACS Nos 73.61.GA; 78.66. 1. Introduction. Improving the optoelectronic properties of the already existing transparent conducting materials as well as searching for new ...
International Nuclear Information System (INIS)
Ghosh, G.; Walle, A. van de; Asta, M.
2008-01-01
The thermodynamic properties of solid solutions with body-centered cubic (bcc), face-centered cubic (fcc) and hexagonal close-packed (hcp) structures in the Al-TM (TM = Ti, Zr and Hf) systems are calculated from first-principles using cluster expansion (CE), Monte-Carlo simulation and supercell methods. The 32-atom special quasirandom structure (SQS) supercells are employed to compute properties at 25, 50 and 75 at.% TM compositions, and 64-atom supercells have been employed to compute properties of alloys in the dilute concentration limit (one solute and 63 solvent atoms). In general, the energy of mixing (Δ m E) calculated by CE and dilute supercells agree very well. In the concentrated region, the Δ m E values calculated by CE and SQS methods also agree well in many cases; however, noteworthy discrepancies are found in some cases, which we argue originate from inherent elastic and dynamic instabilities of the relevant parent lattice structures. The importance of short-range order on the calculated values of Δ m E for hcp Al-Ti alloys is demonstrated. We also present calculated results for the composition dependence of the atomic volumes in random solid solutions with bcc, fcc and hcp structures. The properties of solid solutions reported here may be integrated within the CALPHAD formalism to develop reliable thermodynamic databases in order to facilitate: (i) calculations of stable and metastable phase diagrams of binary and multicomponent systems, (ii) alloy design, and (iii) processing of Al-TM-based alloys
International Nuclear Information System (INIS)
Palummo, M.; Reining, L.; Ballone, P.
1993-01-01
In this paper we outline the major features of the ''ab-initio'' simulation scheme of Car and Parrinello, focusing on the physical ideas and computational details at the basis of its efficiency and success. We briefly review the main applications of the method. We discuss the limitations of the standard scheme, as well as recent developments proposed in order to extend the reach of the method. Moreover, we consider more in detail two specific subjects. First, we describe a simple improvement (Gradient Corrections) on the basic approximation of the ''ab-initio'' simulation, i.e. the Local Density Approximation. These corrections can be easily and efficiently included in the Car-Parrinello code, bringing computed structural and cohesive properties significantly closer to their experimental values. Finally, we discuss the choice of the pseudopotential, with special attention to the possibilities and limitations of the last generation of soft pseudopotentials. (orig.)
International Nuclear Information System (INIS)
Zhang, J.; Huang, Y.N.; Mao, C.; Peng, P.
2012-01-01
Highlights: ► The co-incorporation of Ti and F into MgH 2 lattice is energetically favorable. ► The incorporated Ti and F in MgH 2 preferably generate TiH 2 and MgF 2 , respectively. ► The synergistic effect of Ti and F is superior to that of pure Ti. ► The weakened interactions of Mg–H explain enhanced dehydrogenation properties. - Abstract: The energetic and electronic properties of MgH 2 co-doped with Ti and F are investigated using first-principles calculations based on density functional theory. The calculation results show that incorporation of Ti combined with F atoms into MgH 2 lattice is energetically favorable relative to single incorporation of Ti atom. After dehydrogenation, the co-doped Ti and F in MgH 2 preferably generate TiH 2 and MgF 2 , respectively. Comparatively, the combined effect of Ti and F in improving the dehydrogenation properties of MgH 2 is superior to that of pure Ti. These results provide a reasonable explanation for experimental observations. Analysis of electronic structures suggests the enhanced dehydrogenation properties of doped MgH 2 can be attributed to the weakened bonding interactions between Mg and H due to foreign species doping.
Fukuichi, Masayuki; Momida, Hiroyoshi; Geshi, Masaaki; Michiuchi, Masato; Sogabe, Koichi; Oguchi, Tamio
2018-04-01
Much is not systematically known about the origin of mechanical properties among 5d transition metal carbides including tungsten carbide. In order to understand the microscopic origin of hardness, the mechanical properties and electronic structures of 5d transition metal monocarbides MC (M = Hf, Ta, W, Re, Os, Ir, and Pt) in five different structures (NaCl, WC, ZnS, CsCl, and NiAs type) are analyzed using first-principles calculations based on the density functional theory. Our results would indicate that WC-type WC and NiAs-type ReC have the highest and second highest hardness among all of the MC, respectively, in terms of the Debye temperature. By examining the Debye temperature in the series, it is found that MC in the range of less and more than half filled 5d shells are brittle and ductile, respectively. Our results would indicate that filling in the bonding and anti-bonding states contributes to brittleness and ductility. The Debye temperature could be a key to understanding hardness in terms of bulk and shear moduli. In addition, we evaluate some other structural properties such as equilibrium volume, formation enthalpy, and elastic constant to investigate structural stability. Based on the theoretical findings, the microscopic mechanisms of hardness and brittleness in the transition metal carbides are discussed.
Lahmer, M. A.
2018-03-01
The effect of oxygen vacancy formation on the stability, structural, electronic, and optical properties of the ZnAl2O4(100) surface was investigated by using the first-principles method. The obtained results show that, in the case of the Free-defect surface, the AlO2-terminated surface is more stable than the Zn-terminated surface. The results of structural relaxation show that, for each surface termination, the interlayer distances near the surface oscillate in a damping style. In addition, the work function values and the optical properties of these two surfaces are quite different. Our results show that the work function of the Zn-terminated surface is at least 2 times smaller than that of the AlO2 surface. On the other hand, ab initio thermodynamic calculations show that the O reduction occurs in the case of the AlO2 surface under all growth conditions, while, there is no evidence for O reduction in the case of the Zn-terminated surface. Our results show also that neutral oxygen vacancies can affect greatly the electronic and optical properties of the ZnAl2O4(100) surface.
International Nuclear Information System (INIS)
Ding Yi; Wang Yanli; Ni Jun; Shi Lin; Shi Siqi; Tang Weihua
2011-01-01
Using first principles calculations, we investigate the structural, vibrational and electronic structures of the monolayer graphene-like transition-metal dichalcogenide (MX 2 ) sheets. We find the lattice parameters and stabilities of the MX 2 sheets are mainly determined by the chalcogen atoms, while the electronic properties depend on the metal atoms. The NbS 2 and TaS 2 sheets have comparable energetic stabilities to the synthesized MoS 2 and WS 2 ones. The molybdenum and tungsten dichalcogenide (MoX 2 and WX 2 ) sheets have similar lattice parameters, vibrational modes, and electronic structures. These analogies also exist between the niobium and tantalum dichalcogenide (NbX 2 and TaX 2 ) sheets. However, the NbX 2 and TaX 2 sheets are metals, while the MoX 2 and WX 2 ones are semiconductors with direct-band gaps. When the Nb and Ta atoms are doped into the MoS 2 and WS 2 sheets, a semiconductor-to-metal transition occurs. Comparing to the bulk compounds, these monolayer sheets have similar structural parameters and properties, but their vibrational and electronic properties are varied and have special characteristics. Our results suggest that the graphene-like MX 2 sheets have potential applications in nano-electronics and nano-devices.
Bhamu, K. C.; Praveen, C. S.
2017-12-01
Here we report the structural, electronic, optical, and thermoelectric properties of delafossite type 2H-CuGaO2 using first principles calculations. The present calculation predict an indirect band gap of 1.20 eV and a direct band gap of 3.48 eV. A detailed analysis of the electronic structure is provided based on atom and orbital projected density of states. Frequency dependent dielectric functions, refractive index, and absorption coefficient as a function of photon energy are discussed. The thermoelectric properties with power factor, and the figure of merit are reported as a function of chemical potential in the region ± 0.195 (μ -EF) eV at constant temperature of 300 and 800 K. The thermoelectric properties shows that 2H-CuGaO2 could be potential candidate for engineering devises operating at high temperature for the chemical potential in the range of ± 0.055 (μ -EF) eV and beyond this range the thermoelectric performance of 2H-CuGaO2 get reduced.
Djaadi, Soumaia; Eddine Aiadi, Kamal; Mahtout, Sofiane
2018-04-01
The structures, relative stability and magnetic properties of pure Ge n +1, neutral cationic and anionic SnGe n (n = 1–17) clusters have been investigated by using the first principles density functional theory implemented in SIESTA packages. We find that with the increasing of cluster size, the Ge n +1 and SnGe n (0, ±1) clusters tend to adopt compact structures. It has been also found that the Sn atom occupied a peripheral position for SnGe n clusters when n 12. The structural and electronic properties such as optimized geometries, fragmentation energy, binding energy per atom, HOMO–LUMO gaps and second-order differences in energy of the pure Ge n +1 and SnGe n clusters in their ground state are calculated and analyzed. All isomers of neutral SnGe n clusters are generally nonmagnetic except for n = 1 and 4, where the total spin magnetic moments is 2μ b. The total (DOS) and partial density of states of these clusters have been calculated to understand the origin of peculiar magnetic properties. The cluster size dependence of vertical ionization potentials, vertical electronic affinities, chemical hardness, adiabatic electron affinities and adiabatic ionization potentials have been calculated and discussed.
Ma, Zhuang; Zheng, Jiayi; Wang, Song; Gao, Lihong
2018-01-01
It is an effective method to protect components from high power laser damage using high reflective materials. The rare earth tantalates RETaO4 with high dielectric constant suggests that they may have very high reflectivity, according to the relationship between dielectric constant and reflectivity. The crystal structures, electronic structures, and optical properties of RETaO4 (RE=Y, La, Sm, Eu, Dy, Er) have been studied by first-principle calculations. With the increasing atomic number of RE (i.e., the number of 4f electrons), a 4f electron shell moves from the bottom of conduction band to the forbidden gap and then to the valence band. The relationship between the electronic structures and optical properties is explored. The electron transitions among O 2p states, RE 4f states, and Ta 5d states have a key effect on optical properties such as dielectric function, absorption coefficient, and reflectivity. For the series of RETaO4, the appearance of the 4f electronic states will obviously promote the improvement of reflectivity. When the 4f states appear at the middle of the forbidden gap, the reflectivity reaches the maximum. The reflectivity of EuTaO4 at 1064 nm is up to 93.47%, indicating that it has potential applications in the antilaser radiation area.
Energy Technology Data Exchange (ETDEWEB)
Sayede, A. [Universite Lille Nord de France, F-59000 Lille (France); Khenata, R. [Laboratoire de Physique Quantique et de Modlisation Mathmatique, Universite de Mascara, Mascara, 29000 (Algeria); Chahed, A.; Benhelal, O. [Condensed Matter and Sustainable Development Laboratory, Djillali Liabes University of Sidi Bel-Abbes, Sidi Bel-Abbes 22000 (Algeria)
2013-05-07
We have studied the structural and electronic properties of Ce{sub 2}Ti{sub 2}O{sub 7} (CeTO) and Pr{sub 2}Ti{sub 2}O{sub 7} (PrTO) by first-principles density functional theory calculations. The computed structural parameters are in fairly good agreement with the available experimental findings. Band structure calculations using the GGA+U approach predict an insulating ground state for the herein studied compounds. The insulating band gaps of 2.00 eV and 2.83 eV are found for CeTO and PrTO, respectively. The analysis of the density of states reveals that the strongly localized RE 4f levels act as charge-trapping sites, predicting a lower photocatalytic activity for CeTO. We have also calculated the optical properties for both CeTO and PrTO. Based on these properties, it is predicted that these titanates are insensitive to ultra-violet radiation, while they are more sensitive to frequencies of the radiation in visible and early UV regions.
International Nuclear Information System (INIS)
Yang Ping; Li Pei; Zhang Li-Qiang; Wang Xiao-Liang; Wang Huan; Song Xi-Fu; Xie Fang-Wei
2012-01-01
The lattice, the band gap and the optical properties of n-type ZnO under uniaxial stress are investigated by first-principles calculations. The results show that the lattice constants change linearly with stress. Band gaps are broadened linearly as the uniaxial compressive stress increases. The change of band gap for n-type ZnO comes mainly from the contribution of stress in the c-axis direction, and the reason for band gap of n-type ZnO changing with stress is also explained. The calculated results of optical properties reveal that the imaginary part of the dielectric function decreases with the increase of uniaxial compressive stress at low energy. However, when the energy is higher than 4.0 eV, the imaginary part of the dielectric function increases with the increase of stress and a blueshift appears. There are two peaks in the absorption spectrum in an energy range of 4.0–13.0 eV. The stress coefficient of the band gap of n-type ZnO is larger than that of pure ZnO, which supplies the theoretical reference value for the modulation of the band gap of doped ZnO. (condensed matter: structural, mechanical, and thermal properties)
Li, Dandan; Du, Juan; Zhang, Qian; Xia, Congxin; Wei, Shuyi
2018-03-01
Through first-principles calculations we study the electronic structures and optical properties of two-dimensional (2D) Sn1-xTi(Zr)xS2 alloys. The results indicate that the band gap value of Sn1-xTi(Zr)xS2 alloys is decreased continuously when Ti(Zr) concentration is increased, which is very beneficial to optoelectronic devices applications. Moreover, the static dielectric constant is increased when the Ti(Zr) concentration is increased in the 2D Sn1-xTi(Zr)xS2 alloys. In addition, we also calculate the imaginary part 𝜀2(ω) dispersion of Sn1-xTi(Zr)xS2 alloys along the plane with different Ti(Zr) concentrations. The threshold energy values decrease with increasing Ti(Zr) concentrations in the Sn1-xTi(Zr)xS2 ternary alloys. Moreover, the calculations of formation energy also indicate that these 2D alloys can be fabricated under some experimental conditions. These results suggest that Ti(Zr) substituting Sn atom is an efficient way to tune the band gap and optical properties of 2D SnS2 nanosheets.
Zhandun, V. S.; Zinenko, V. I.
2017-12-01
Within the first principles approach implemented in the VASP package, a correlation between magnetic, electronic, polarization, and optical properties, on the one hand, and the structural ordering of cations, on the other hand, is investigated in double perovskites LaPbTSbO6 (T = Fe, Co, Ni). Two types of cation ordering are considered: simultaneous layered (LL) and checkerboard (RR) ordering of both cations. These two types of ordering are chosen due to their significance; namely, the ordering RR is one of the most implementable types of cation ordering in double perovskites, and compounds with layered ordering can be considered as a heterostructure consisting of periodically alternating metal-nonmagnetic metal layers, which is of interest for experimental synthesis and investigation. It is found that the type of cation ordering in compounds with T = Fe and Ni radically changes the magnetic and/or electronic properties of the compound. Moreover, it is found that low-symmetry stable phases are polar for both types of cation ordering, and the values of spontaneous polarization are evaluated.
Suzuki, Atsushi; Oku, Takeo
2018-02-01
The electronic structures and magnetic properties of manganese (Mn)-doped formamidinium lead halide perovskite compounds (FAPbI3, where FA = NH2CHNH2 +) were investigated for solar cell application. The effects of Mn doping into FAPbI3 crystals on electronic structures, chemical shifts in nuclear magnetic resonance, and optical absorption spectra were studied by first-principles calculation on the basis of the density functional theory. The electron density distribution of the 6p orbital was delocalized on an iodine atom at the highest occupied molecular orbital, and that of the 3d orbital was localized on a Mn atom at the lowest unoccupied molecular orbital. The absorption properties in the near-infrared region originated from the first excitation process of ligand-metal charge transfer (LMCT). The chemical shifts of I-NMR and the g-tensor of Mn ions were associated with nuclear quadrupole interactions based on an electron field gradient and asymmetry parameters. The combination of LMCT with magnetic interactions is important for developing photovoltaic solar cells with a broad-band optical absorption spectrum in the near-infrared region.
Li, Hongping; Lv, Shuhui; Liu, Xiaojuan; Meng, Jian
2011-05-01
First-principles calculations using the augmented plane wave plus local orbitals method, as implemented in the WIEN2K code, have been carried out to study the A-B intersite charge transfer and the correlated electrical and magnetic properties of the perovskite BiCu(3)Fe(4)O(12), especially as regards the charge transfer. The results indicate that the charge transfer between A-site Cu and B-site Fe is by way of O 2p orbitals, and during this process orbital hybridization plays an important role. More importantly, the charge transfer is of 3d(9) + 4d(5)L(0.75) →3d(9)L + 4d(5) type (here L denotes an oxygen hole or a ligand hole). During this process, the magnetic interaction experiences a transition from Cu-Fe ferrimagnetic coupling to G-type antiferromagnetic coupling within B-site Fe with paramagnetic Cu(3+). As to electrical property, it undergoes a metal to insulator transition. All our calculated results are consistent with the available experimental results. Copyright © 2010 Wiley Periodicals, Inc.
Singh, Vijay; Kosa, Monica; Majhi, Koushik; Major, Dan Thomas; Arie Zaban Collaboration, Prof.
First-principles density functional theory (DFT) and a many-body Green's function method have been employed to elucidate the electronic, magnetic, and photonic properties of a spinel compound, Co3O4. Co3O4 is believed to be a strongly correlated material, where the on-site Coulomb interaction (U) on Co d orbitals is presumably important, although this view has recently been contested. The suggested optical band gap for this material ranges from 0.8 to 2.0 eV, depending on the type of experiments and theoretical treatment. Thus, the correlated nature of the Co d orbitals in Co3O4 and the extent of the band gap are still under debate, raising questions regarding the ability of DFT to correctly treat the electronic structure in this material. To resolve the above controversies, we have employed a range of theoretical methods, including pure DFT, DFT +U, and a range-separated exchange-correlation functional (HSE06) as well as many-body Green's function theory (i.e., the GW method). We compare the electronic structure and band gap of Co3O4 with available photoemission spectroscopy and optical band gap data and confirm a direct band gap of ca. 0.8 eV. Furthermore, we have also studied the optical properties of Co3O4 by calculating the imaginary part of the dielectric function (Im(ɛ)) , facilitating direct comparison with the measured optical absorption spectra.
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.
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.
Feng, Nan
2014-02-05
Using first-principles calculations, we have investigated the electronic structure and magnetic properties of Fe-X 6 clusters (X = S, C, N, O, and F) incorporated in 4 4 monolayer MoS 2, where a Mo atom is substituted by Fe and its nearest S atoms are substituted by C, N, O, and F. Single Fe and Fe-F 6 substituions make the system display half-metallic properties, Fe-C 6 and Fe-N 6 substitutions lead to a spin gapless semiconducting behavior, and Fe-O 6 doped monolayer MoS 2 is semiconducting. Magnetic moments of 1.93, 1.45, 3.18, 2.08, and 2.21...? B are obtained for X = S, C, N, O, and F, respectively. The different electronic and magnetic characters originate from hybridization between the X and Fe/Mo atoms. Our results suggest that cluster doping can be an efficient strategy for exploring two-dimensional diluted magnetic semiconductors.
International Nuclear Information System (INIS)
Rached, H.; Bendaoudia, S.; Rached, D.
2017-01-01
The main goal of the present work is to obtain report on the magnetic phase stability, mechanical, electronic and optical properties of double perovskite oxides Pb 2 FeMO 6 (M = Mo, Re and W) by employing the ab-initio plane-wave method, based on the density functional theory (DFT). The exchange-correlation (XC) energy of electrons was treated using the Perdew–Burke–Ernzerhof parametrization. The ground-state electronic properties for different magnetic configurations were calculated. The formation enthalpies has been evaluated in order to determinate the stability of our compounds. The independent elastic constants and the related mechanical properties are investigated. The electronic structure calculation reveal the half-metallic ferrimagnets (FiM-HM) for all investigated compounds. The optical constants as the dielectric function, refractive index, optical reflectivity and absorption coefficient were calculated and discussed in detail. Therefore, our compounds are identified as potential candidates for spintronic applications and high performance electronic devices. - Highlights: • Based on the DFT calculation, the Pb 2 FeMO 6 (M = Mo, Re and W) compounds have been investigated. • The ground-state properties are predicted. • The mechanical properties reveals that these compounds are stable against any elastic deformations. • The electronic structures reveals the half-metallic ferrimagnets (FiM-HM) for all investigated compounds.
Energy Technology Data Exchange (ETDEWEB)
Rached, H., E-mail: habib_rached@yahoo.fr [Laboratoire des Matériaux Magnétiques, Faculté des Sciences Exactes, Université Djillali Liabès de Sidi Bel-Abbès, Sidi Bel-Abbès, 22000 (Algeria); Département de Physique, Faculté des Sciences Exactes et Informatique, Université Hassiba BenBouali de Chlef, Chlef, 02000 (Algeria); Bendaoudia, S. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences Exactes, Université Djillali Liabès de Sidi Bel-Abbès, Sidi Bel-Abbès, 22000 (Algeria); Rached, D., E-mail: rachdj@yahoo.fr [Laboratoire des Matériaux Magnétiques, Faculté des Sciences Exactes, Université Djillali Liabès de Sidi Bel-Abbès, Sidi Bel-Abbès, 22000 (Algeria)
2017-06-01
The main goal of the present work is to obtain report on the magnetic phase stability, mechanical, electronic and optical properties of double perovskite oxides Pb{sub 2}FeMO{sub 6} (M = Mo, Re and W) by employing the ab-initio plane-wave method, based on the density functional theory (DFT). The exchange-correlation (XC) energy of electrons was treated using the Perdew–Burke–Ernzerhof parametrization. The ground-state electronic properties for different magnetic configurations were calculated. The formation enthalpies has been evaluated in order to determinate the stability of our compounds. The independent elastic constants and the related mechanical properties are investigated. The electronic structure calculation reveal the half-metallic ferrimagnets (FiM-HM) for all investigated compounds. The optical constants as the dielectric function, refractive index, optical reflectivity and absorption coefficient were calculated and discussed in detail. Therefore, our compounds are identified as potential candidates for spintronic applications and high performance electronic devices. - Highlights: • Based on the DFT calculation, the Pb{sub 2}FeMO{sub 6} (M = Mo, Re and W) compounds have been investigated. • The ground-state properties are predicted. • The mechanical properties reveals that these compounds are stable against any elastic deformations. • The electronic structures reveals the half-metallic ferrimagnets (FiM-HM) for all investigated compounds.
Elastic properties of spherically anisotropic piezoelectric composites
International Nuclear Information System (INIS)
En-Bo, Wei; Guo-Qing, Gu; Ying-Ming, Poon
2010-01-01
Effective elastic properties of spherically anisotropic piezoelectric composites, whose spherically anisotropic piezoelectric inclusions are embedded in an infinite non-piezoelectric matrix, are theoretically investigated. Analytical solutions for the elastic displacements and the electric potentials under a uniform external strain are derived exactly. Taking into account of the coupling effects of elasticity, permittivity and piezoelectricity, the formula is derived for estimating the effective elastic properties based on the average field theory in the dilute limit. An elastic response mechanism is revealed, in which the effective elastic properties increase as inclusion piezoelectric properties increase and inclusion dielectric properties decrease. Moreover, a piezoelectric response mechanism, of which the effective piezoelectric response vanishes due to the symmetry of spherically anisotropic composite, is also disclosed. (condensed matter: structure, thermal and mechanical properties)
Ilyasov, Victor V.; Pham, Khang D.; Zhdanova, Tatiana P.; Phuc, Huynh V.; Hieu, Nguyen N.; Nguyen, Chuong V.
2017-12-01
In this paper, we systematically investigate the atomic structure, electronic and thermodynamic properties of adsorbed W atoms on the polar Ti-terminated TixCy (111) surface with different configurations of adsorptions using first principle calculations. The bond length, adsorption energy, and formation energy for different reconstructions of the atomic structure of the W/TixCy (111) systems were established. The effect of the tungsten coverage on the electronic structure and the adsorption mechanism of tungsten atom on the TixCy (111) are also investigated. We also suggest the possible mechanisms of W nucleation on the TixCy (111) surface. The effective charges on W atoms and nearest-neighbor atoms in the examined reconstructions were identified. Additionally, we have established the charge transfer from titanium atom to tungsten and carbon atoms which determine by the reconstruction of the local atomic and electronic structures. Our calculations showed that the charge transfer correlates with the electronegativity of tungsten and nearest-neighbor atoms. We also determined the effective charge per atom of titanium, carbon atoms, and neighboring adsorbed tungsten atom in different binding configurations. We found that, with reduction of the lattice symmetry associated with titanium and carbon vacancies, the adsorption energy increases by 1.2 times in the binding site A of W/TixCy systems.
Energy Technology Data Exchange (ETDEWEB)
Zhang, Yong [School of Mathematics, Physics and Energy Engineering, Hunan Institute of Technology, Hengyang 421002 (China); Xie, Zhong-Xiang, E-mail: xiezxhu@163.com [School of Mathematics, Physics and Energy Engineering, Hunan Institute of Technology, Hengyang 421002 (China); Yu, Xia; Wang, Hai-Bin; Deng, Yuan-Xiang [School of Mathematics, Physics and Energy Engineering, Hunan Institute of Technology, Hengyang 421002 (China); Ning, Feng, E-mail: fning@gxtc.edu.cn [College of Physics and Electronic Engineering, Guangxi Teachers Education University, Nanning 530001 (China)
2016-08-06
Using first-principle calculations with density functional theory, we investigated the modification of electronic properties in zinc-blende (ZB) and wurtzite (WZ) InSb nanowires (NWs) grown along the [111] and [0001] directions for different size, different surface coverage and different mechanical strain. The results show that before the surface passivation, ZBNWs and WZNWs exhibit the metallic character and the semiconductor character, respectively. WZNWs show a crossover from a direct to an indirect as diameter decreases. After the surface passivation, both ZBNWs and WZNWs are found to be direct-gap character. The electronic band structure shows a significant response to changes in surface passivation with pseudo hydrogen and halogen. The band structure with mechanical strain is strongly dependent on the crystal orientation and the NW diameter. In ZBNWs, compressive strain induces the indirect band gap character, whereas tensile strain can not form it. WZNWs have various strain dependence in that both compressive and tensile strain make InSb show a direct band gap character. A brief analysis of these results is given. - Highlights: • InSb nanowires with different surfaces can show the different band structures. • Band gap magnitude of InSb nanowires depends on the suppression of surface states. • Different types of mechanical strains show the different effect on the band structure of the InSb nanowires.
Berber, Mohamed; Doumi, Bendouma; Mokaddem, Allel; Mogulkoc, Yesim; Sayede, Adlane; Tadjer, Abdelkader
2018-01-01
We have used first-principle methods of density functional theory within the full potential linearized augmented plane wave scheme to investigate the electronic and magnetic properties of cubic rock-salt, SrO, doped with vanadium (V) impurity as Sr1- x V x O at various concentrations, x = 0.25, 0.5, and 0.75. We have found that the ferromagnetic state arrangement of Sr1- x V x O is more stable compared to the anti-ferromagnetic state configuration. The electronic structures have a half-metallic (HM) ferromagnetic (F) behavior for Sr0.75V0.25O and Sr0.5V0.5O. This feature results from the metallic and semiconducting natures of majority-spin and minority-spin bands, respectively. The HMF gap decreases with the increasing concentration of vanadium atoms due to the broadening of 3 d (V) levels in the gap, and hence the Sr0.25V0.75O becomes metallic ferromagnetic. The Sr0.75V0.25O revealed a large HM gap with spin polarization of 100%. The Sr1- x V x O compound at low concentrations seems a better candidate to explore the half-metallicity for practical spintronics applications.
International Nuclear Information System (INIS)
Kwon, Choah; Kang, Joonhee; Kang, Woojong; Kwak, Dohyun; Han, Byungchan
2016-01-01
Using first principles density functional theory (DFT) calculations we obtain thermodynamic and kinetic properties of U in an electrorefining process for spent nuclear fuels using a LiCl-KCl eutectic molten salt and Mo as a cathode. The thermodynamic stability of electrodeposited U from the molten salt onto the Mo(110) surface electrode is evaluated by activity coefficients as function of surface coverages of U and Cl. Additionally, ab-initio molecular dynamic simulations combined with the Stokes-Einstein-Sutherland relation enables us to calculate the viscosity of the LiCl-KCl eutectic molten salt. Our results well agree with previously reported experimental data endorsing the credibility. Based on our atomic-level mechanical understanding we propose that an accurate computational model system incorporating the electrochemical conditions of the electrorefining process essential for the purpose of establishing thermodynamic and kinetic database of U, otherwise critical deviations are inevitable. More interestingly, the effect of coadsorption of Cl with U on the Mo(110) surface plays a key role in stabilizing electrodeposited U on the cathode. Our approach can be useful for validating published experimental database and for identifying key factors guiding a rational design of highly efficient electrorefining system for spent nuclear fuels, and thus reducing high-level radioactive nuclear wastes.
International Nuclear Information System (INIS)
Zhang, Z.L.; Xiao, H.Y.; Zu, Xiaotao T.; Gao, Fei; Weber, William J.
2009-01-01
A first-principles method has been employed to investigate the structural and energetic properties for A2Ti2O7 (A = Lu, Er, Y, Gd, Sm, Nd, La), including the formation energies of the cation antisite-pair, the anion Frenkel pair that defines anion-disorder, and the coupled cation antisite-pair/anion-Frenkel. It is proposed that the interaction may have more significant influence on the radiation resistance behavior of titanate pyrochlores, although the interactions are relatively much stronger than the interactions. It is found that the defect formation energies are not simple functions of the A-site cation radii. The formation energy of the cation antisite-pair increases continuously as the A-site cation varies from Lu to Gd, and then decreases continuously with the variation of the A-site cation from Gd to La, in excellent agreement with the radiation-resistance trend of the titanate pyrochlores. The band gaps in these pyrochlores were also measured, and the band gap widths changed continuously with cation radius.
Akamatsu, Hirofumi; Fujita, Koji; Hayashi, Hiroyuki; Kawamoto, Takahiro; Kumagai, Yu; Zong, Yanhua; Iwata, Koji; Oba, Fumiyasu; Tanaka, Isao; Tanaka, Katsuhisa
2012-04-16
A comparative study of the crystal and electronic structure and magnetism of divalent europium perovskite oxides EuMO(3) (M = Ti, Zr, and Hf) has been performed on the basis of both experimental and theoretical approaches playing complementary roles. The compounds were synthesized via solid-state reactions. EuZrO(3) and EuHfO(3) have an orthorhombic structure with a space group Pbnm at room temperature contrary to EuTiO(3), which is cubic at room temperature. The optical band gaps of EuZrO(3) and EuHfO(3) are found to be about 2.4 and 2.7 eV, respectively, much larger than that of EuTiO(3) (0.8 eV). On the other hand, the present compounds exhibit similar magnetic properties characterized by paramagnetic-antiferromagnetic transitions at around 5 K, spin flop at moderate magnetic fields lower than 1 T, and the antiferromagnetic nearest-neighbor and ferromagnetic next-nearest-neighbor exchange interactions. First-principles calculations based on a hybrid Hartree-Fock density functional approach yield lattice constants, band gaps, and magnetic interactions in good agreement with those obtained experimentally. The band gap excitations are assigned to electronic transitions from the Eu 4f to Mnd states for EuMO(3) (M = Ti, Zr, and Hf and n = 3, 4, and 5, respectively). © 2012 American Chemical Society
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.
Shi, Li-Bin; Li, Ming-Biao; Xiu, Xiao-Ming; Liu, Xu-Yang; Zhang, Kai-Cheng; Liu, Yu-Hui; Li, Chun-Ran; Dong, Hai-Kuan
2017-05-01
An amorphous Al2O3 (a-Al2O3)/MoS2 interface has attracted much attention because of its unique properties. In this study, the interface behaviors under non-strain and biaxial strain are investigated by first principles calculations based on the density functional theory. First of all, the generation process of the a-Al2O3 sample is described by molecular dynamics. The calculated bandgap of a-Al2O3 is 3.66 eV for generalized gradient approximation-Perdew, Burke, and Ernzerhof and 5.26 eV for Heyd-Scuseria-Ernzerhof functional. Then, we give a detailed description of the band alignment for the a-Al2O3/MoS2 interface. The valence band offset and conduction band offset change with the number of MoS2 layers. It is noted that the valence band maximum (VBM) of MoS2 moves upward as the number of MoS2 layers is increased. The leakage current for metal/a-Al2O3/MoS2 MOS is also illustrated. At last, the band structure of monolayer MoS2 under biaxial strain ranging from -6% to 6% is discussed, and the impact of the biaxial strain on the band offset is investigated. The VBM of monolayer MoS2 moves downward as the strain changes from compressive to tensile.
International Nuclear Information System (INIS)
Bezi Javan, M.; Tajabor, N.
2012-01-01
We studied the structural, electronic and magnetic properties of small Fe n clusters (n=2-7) endohedrally doped in icosahedral C 60 and C 80 fullerenes using first principles calculations based on the density functional theory. It is found that the encapsulated Fe n clusters inside icosahedral C 80 are energetically favorable while Fe n -C 60 metallofullerene nano-cages are not. The binding energies of the Fe n encapsulated in C 60 are positive and increase with the number of iron atoms (n) while those of the Fe n -C 80 are negative and their absolute values increase up to n=6. The encapsulation does not significantly change the enclosed cluster structure, but the total magnetic moment of the larger clusters reduces due to a stronger Fe-C hybridization. - Highlights: → Encapsulated Fe n clusters inside C 80 cage are energetically favorable while Fe n -C 60 nano-cages are not. → Encapsulation does not significantly change the enclosed cluster structure. → Total magnetic moment of the larger clusters reduces due to a stronger Fe-C hybridization.
He, Wangqiang; Huang, Houbing; Liu, Zhuhong; Ma, Xingqiao
2018-01-01
Not Available Project supported by the National Natural Science Foundation of China (Grant Nos. 11174030 and 11504020) and the Fundamental Research Funds for the Central Universities of China (Grant No. FRF-TP-16-064A1, 06500031).
International Nuclear Information System (INIS)
Shi, Li Bin; Wang, Yong Ping; Dong, Hai Kuan
2015-01-01
Graphical abstract: - Highlights: • Cr, Mn and Fe doped graphene is more active to adsorb HCN molecule than pristine graphene. • The conductivity of Fe and Mn doped graphene hardly changes after adsorption HCN molecule. • The conductivity of Cr doped graphene can be affected significantly due to HCN adsorption. • The Cr, Mn and Fe may destroy the long range order in graphene. • Phonon density of states suggests that Cr doped graphene is stable. - Abstract: The adsorption energy, electronic structure, lattice vibration and magnetic properties of Cr, Mn and Fe doped graphene with and without HCN adsorption are investigated by the first principles based on density functional theory. The physisorption and chemisorption have been identified. In the paper, Cr-NG, Mn-NG and Fe-NG denote HCN adsorption on Cr, Mn and Fe doped graphene with N atom toward the adsorption site. It is found that the adsorption energy is −1.36 eV for Fe-NG, −0.60 eV for Mn-NG and −0.86 eV for Cr-NG. The Cr-NG will convert from half-metallic behavior to semiconductor after adsorbing HCN molecule, which indicates that the conductivity changes significantly. Phonon density of states (PDOS) shows that the long range order in graphene can be destroyed by doping Fe, Mn and Cr. The imaginary frequency mode in PDOS suggests that Fe and Mn doped graphene is unstable, while Cr doped graphene is stable. The electronic properties are sensitive toward adsorbing HCN, indicating that Cr doped graphene is a promising sensor for detecting HCN molecule. This study provides a useful basis for understanding of a wide variety of physical properties on graphene
Bakhshayeshi, A.; Sarmazdeh, M. Majidiyan; Mendi, R. Taghavi; Boochani, A.
2017-04-01
Electronic, magnetic, and optical properties of Co2MnAs full-Heusler compound have been calculated using a first-principles approach with the full-potential linearized augmented plane-wave (FP-LAPW) method and generalized gradient approximation plus U (GGA + U). The results are compared with various properties of Co2Mn Z ( Z = Si, Ge, Al, Ga, Sn) full-Heusler compounds. The results of our calculations show that Co2MnAs is a half-metallic ferromagnetic compound with 100% spin polarization at the Fermi level. The total magnetic moment and half-metallic gap of Co2MnAs compound are found to be 6.00 μ B and 0.43 eV, respectively. It is also predicted that the spin-wave stiffness constant and Curie temperature of Co2MnAs compound are about 3.99 meV nm2 and 1109 K, respectively. The optical results show that the dominant behavior, at energy below 2 eV, is due to interactions of free electrons in the system. Interband optical transitions have been calculated based on the imaginary part of the dielectric function and analysis of critical points in the second energy derivative of the dielectric function. The results show that there is more than one plasmon energy for Co2MnAs compound, with the highest occurring at 25 eV. Also, the refractive index variations and optical reflectivity for radiation at normal incidence are calculated for Co2MnAs. Because of its high magnetic moment, high Curie temperature, and 100% spin polarization at the Fermi level as well as its optical properties, Co2MnAs is a good candidate for use in spintronic components and magnetooptical devices.
International Nuclear Information System (INIS)
Wang, Mingliang
2014-01-01
This work studied the dependences of the mechanical and electronic properties of TiB 2 on pressures using the first-principles method, based on the density functional theory. The results showed that pressure has a profound impact on the structural, mechanical and electronic properties of TiB 2 . The calculated structural and mechanical parameters (i.e. bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, and Debye temperature) were in good agreement with both the available experimental and theoretical results at zero pressure. In addition, the mechanical parameters presented linearly increasing dependences on external pressure. Through the analysis of the density of states and Mulliken charges, the interlayer bonding in TiB 2 should be formed in a complex manner. There were three origins for the interlayer interactions between the B and Ti atomic layers: (a) planar Bsp 2 covalent bonding of moderate hybridizing with the Ti3d state −9.94 eV of the bonding state; (b) strong B2p and Ti3d hybridization of covalent bonding at −3.13 eV of the bonding state; (c) ionic bonding between Ti and B atoms. These interactions between the B and Ti interlayers determined the high hardness and high melting point of TiB 2 . As the pressures elevated, the charge transfer between Ti and B atoms increased, and the B–B and Ti–B bond lengths all decreased in accordingly. Thus, it was concluded that the ionic and covalent bonds can be strengthened. This could be responsible for causing the enhanced mechanical properties in TiB 2 . As for the metallicity, the quantity of charges of free-electron transfer from Tis to Ti3p and Ti3d states remained level, leading to no change of electric conductivity in TiB 2 under high pressures. (paper)
Wang, Mingliang
2014-11-01
This work studied the dependences of the mechanical and electronic properties of TiB2 on pressures using the first-principles method, based on the density functional theory. The results showed that pressure has a profound impact on the structural, mechanical and electronic properties of TiB2. The calculated structural and mechanical parameters (i.e. bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, and Debye temperature) were in good agreement with both the available experimental and theoretical results at zero pressure. In addition, the mechanical parameters presented linearly increasing dependences on external pressure. Through the analysis of the density of states and Mulliken charges, the interlayer bonding in TiB2 should be formed in a complex manner. There were three origins for the interlayer interactions between the B and Ti atomic layers: (a) planar Bsp2 covalent bonding of moderate hybridizing with the Ti3d state -9.94 eV of the bonding state; (b) strong B2p and Ti3d hybridization of covalent bonding at -3.13 eV of the bonding state; (c) ionic bonding between Ti and B atoms. These interactions between the B and Ti interlayers determined the high hardness and high melting point of TiB2. As the pressures elevated, the charge transfer between Ti and B atoms increased, and the B-B and Ti-B bond lengths all decreased in accordingly. Thus, it was concluded that the ionic and covalent bonds can be strengthened. This could be responsible for causing the enhanced mechanical properties in TiB2. As for the metallicity, the quantity of charges of free-electron transfer from Tis to Ti3p and Ti3d states remained level, leading to no change of electric conductivity in TiB2 under high pressures.
Jaiganesh, G.; Kalpana, G.
2013-01-01
The first-principles study of the electronic structure and ferromagnetism of AeX (Ae=Be, Mg, Sr and Ba; X=Si, Ge and Sn) compounds have been performed in the ground-state CrB-type and hypothetical NaCl- and zinc blende-type structures by spin-polarization and non-spin-polarization calculations. The TBLMTO-ASA program was used for the purpose. In the CrB-type structure, all these compounds exhibit non-magnetic and metallic behavior. The calculations show that in the NaCl- and ZB-type structures BeSi, BeGe, BeSn, MgSi, MgGe and MgSn compounds are non-magnets whereas SrSi, SrGe, SrSn, BaSi, BaGe and BaSn compounds are ferromagnetic and metallic. Apart from this the ZB-type SrSi, SrGe, BaSi and BaGe compounds exhibit half-metallicity at their equilibrium volume with a magnetic moment of 2.0 μB per formula unit. However, ZB-type SrSn and BaSn compounds are found to exhibit half-metallic property under expansion of volume. The magnetism arises mainly from the anion p-like states and partial involvement of cation d-like states. The ground state properties like equilibrium lattice parameters, bulk modulus, cohesive energy, magnetic moment, spin-flip-gap and majority spin band gap are calculated and compared with available results. The band structure and density of states are also presented. These materials will be useful for the study of p-electron magnetism and in spintronic devices.
Akhtar, Shaheen; Alay-e-Abbas, Syed Muhammad; Abbas, Syed Muhammad Ghulam; Arshad, Muhammad Imran; Batool, Javaria; Amin, Nasir
2018-04-01
In this paper, we report first-principles spin-polarized density functional theory calculations for exploring the effect of aliovalent Mo and C dopants on the electronic properties and photocatalysis potential of doped modifications of wide-bandgap cubic perovskite oxide BaHfO3 for water splitting. The structural and thermodynamic properties are computed by using the generalized gradient approximation, whereas the modified Becke-Johnson local density approximation is used to calculate the electronic structures of pristine, cation (Mo), and anion (C) monodoped and cation-anion (Mo, C) codoped BaHfO3. The spin-polarized calculations reveal that substitutional dopants CO and MoHf in the BaHfO3 lattice are thermodynamically stable. The incorporation of C in the O site reduces the bandgap of BaHfO3 and acts as a double-acceptor system, whereas a metallic character is obtained when Mo is doped into the Hf site giving rise to a double-donor system. We show that the acceptor and donor states of the C- and Mo-monodoped BaHfO3 can be passivated by (Mo, C) codoping at nearest-neighbor Hf and O sites of the BaHfO3 lattice, respectively. Analysis of the calculated electronic structure and optical absorption of (Mo, C) codoped BaHfO3 with reference to the H2O oxidation and reduction potentials reveals that this system is a suitable candidate for efficient splitting of water through photocatalysis in the visible region of the electromagnetic spectrum.
Tack, Liew Weng; Azam, Mohd Asyadi; Seman, Raja Noor Amalina Raja
2017-04-06
Single-walled carbon nanotubes (SWCNTs) and metal oxides (MOs), such as manganese(IV) oxide (MnO 2 ), cobalt(II, III) oxide (Co 3 O 4 ), and nickel(II) oxide (NiO) hybrid structures, have received great attention because of their promising application in lithium-ion batteries (LIBs). As electrode materials for LIBs, the structure of SWCNT/MOs provides high power density, good electrical conductivity, and excellent cyclic stability. In this work, first-principles calculations were used to investigate the structural and electronic properties of MOs attached to (5, 5) SWCNT and Li-ion adsorption to SWCNT/metal oxide composites as electrode materials in LIBs. Emphasis was placed on the synergistic effects of the composite on the electrochemical performance of LIBs in terms of adsorption capabilities and charge transfer of Li-ions attached to (5, 5) SWCNT and metal oxides. Also, Li adsorption energy on SWCNTs and three different metal oxides (NiO, MnO 2 , and Co 3 O 4 ) and the accompanying changes in the electronic properties, such as band structure, density of states and charge distribution as a function of Li adsorption were calculated. On the basis of the calculation results, the top C atom was found to be the most stable position for the NiO and MnO 2 attachment to SWCNT, while the Co 3 O 4 molecule, the Co 2+ , was found to be the most stable attachment on SWCNT. The obtained results show that the addition of MOs to the SWCNT electrode enables an increase in specific surface area and improves the electronic conductivity and charge transfer of an LIB.
Elastic properties of Gum Metal
International Nuclear Information System (INIS)
Kuramoto, Shigeru; Furuta, Tadahiko; Hwang, Junghwan; Nishino, Kazuaki; Saito, Takashi
2006-01-01
In situ X-ray diffraction measurements under tensile loading and dynamic mechanical analysis were performed to investigate the mechanisms of elastic deformation in Gum Metal. Tensile stress-strain curves for Gum Metal indicate that cold working substantially decreases the elastic modulus while increasing the yield strength, thereby confirming nonlinearity in the elastic range. The gradient of each curve decreased continuously to about one-third its original value near the elastic limit. As a result of this decrease in elastic modulus and nonlinearity, elastic deformability reaches 2.5% after cold working. Superelasticity is attributed to stress-induced martensitic transformations, although the large elastic deformation in Gum Metal is not accompanied by a phase transformation
Elastic properties of graphite and interstitial defects
International Nuclear Information System (INIS)
Ayasse, J.-B.
1977-01-01
The graphite elastic constants C 33 and C 44 , reflecting the interaction of the graphitic planes, were experimentally measured as a function of irradiation and temperature. A model of non-central strength atomic interaction was established to explain the experimental results obtained. This model is valid at zero temperature. The temperature dependence of the elastic properties was analyzed. The influence of the elastic property variations on the specific heat of the lattice at very low temperature was investigated [fr
Stability, elastic properties, and electronic structure of germanane nanoribbons
International Nuclear Information System (INIS)
Dong, Shan; Chen, Chang-Qing
2015-01-01
The stability, elastic properties, and electronic structure of germanane nanoribbons (GeNRs) are studied from first-principles calculations. When using atomic H as the hydrogen source, a germanane monolayer spontaneously breaks into ribbons. GeNRs can be easily stretched due to their small in-plane stiffness, suggesting that it is feasible to modulate their properties by strain. All GeNRs show direct band gaps at the Γ point when external strain is zero, with the gap value decreasing with increasing ribbon width. When axial tensile strain is applied, the band gap decreases, and a direct-to-indirect gap transition occurs. The transition can be attributed to different deformation potentials of different states in the valence band. These results suggest potential applications of GeNRs in the fields of pressure sensors and tunable optical electronics. (paper)
Wang, Xiaotian; Zhao, Weiqi; Cheng, Zhenxiang; Dai, Xuefang; Khenata, R.
2018-01-01
In this paper, we have investigated the electronic, magnetic, half-metallic and mechanical properties of a new Zr-based equiatomic quaternary Heusler (EQH) compound ZrRhTiTl by means of the first-principles calculations. With the help of the generalized gradient approximation (GGA) in the scheme of Perdew-Burke-Enzerhof (PBE), we reveal that the ZrRhTiTl is an excellent half-metallic material (HMM) at its equilibrium lattice constant 6.70 Å. In the minority-spin direction, a quite large band gap (Ebg) of 0.584 eV and a half-metallic band-gap (EHM) of 0.137 eV can be observed. For ZrRhTiTl, the formation energy of -1.18 eV and the cohesive energy of 19.35 eV suggest that it is a thermo-stabilized material in theory. The formation mechanism of EHM in the minority-spin direction has also been discussed by considering of the possible d-d hybridization between Zr, Ti and Rh elements. The total magnetic moment of ZrRhTiTl is 2 μB and it satisfies the famous Slater-Pauling rule Mt = Zt-18. Two types of strain, i.e., uniform strain and tetragonal deformation, have been taken into account to examine the magneto-electronic and half-metallic behaviors of ZrRhTiTl EQH compound. Finally, we show that ZrRhTiTl is mechanically stable, ductile and anisotropic.
Xiao, Gang; Wang, Ling-Ling; Rong, Qing-Yan; Xu, Hai-Qing; Xiao, Wen-Zhi
2017-11-01
First-principles calculations are performed to comparatively study the structural, electronic structures and magnetic properties of Mo doped AlN, GaN and InN monolayers (MLs). After Mo atom doping, the semiconducting GaN and InN MLs transform to metal, while the AlN ML keeps semiconducting with a reduced gap. Total magnetic moments of 1.0 and 0.54 μB, which mainly arising from the localized Mo 4d states, are induced by doping in AlN and InN MLs, respectively, while the doped GaN ML is still nonmagnetic. Nevertheless, the excessive localization and strongly ionic character of the Mo-4d states in AlN ML directly impedes the magnetic coupling, leading to a paramagnetic ground states. A similar case is observed in Mo atoms doped InN ML. The firm N-Mo interaction prevent the impurity states permeating out the range of N-Mo pair, resulting in a quick vanishing of ferromagnetic coupling as the distance between two Mo atoms increasing. All configurations of Mo atoms doped GaN ML in this paper are room temperature ferromagnetic. Spin polarized itinerant electrons mediate the magnetic interaction between two Mo atoms. Increasing the Mo concentration may stabilize the FM state and produce a higher Curie temperature. Our calculations show that GaN nanosheets with Mo atoms doped may be a nice candidate for future spintronic devices. And we conclude that a appropriate magnitude of localization (or delocalization) is what the key point to produce room temperature ferromagnetism from this comparative study.
Energy Technology Data Exchange (ETDEWEB)
Yin, Zhu-Hua [College of Physics and Information Technology, Shaanxi Normal University, Xian, 710119, Shaanxi (China); Zhang, Jian-Min, E-mail: jmzhang@snnu.edu.cn [College of Physics and Information Technology, Shaanxi Normal University, Xian, 710119, Shaanxi (China); Xu, Ke-Wei [State Key Laboratory for Mechanical Behavior of Materials, Xian Jiaotong University, Xian, 710049, Shaanxi (China)
2016-11-01
The spin-polarized first-principles calculations are performed to study the structural, electronic and magnetic properties of a single and two identical transition metal (TM) atoms X (X = V, Cr, Mn, Fe, Co and Ni) doped ZnS dilute magnetic semiconductors (DMS). The single V-, Cr-, Fe- and Ni-doped ZnS systems exhibit the magnetic half-metallic (HM) characters, while Mn- and Co-doped ZnS systems display magnetic semiconducting characters. For two identical TM atoms doped ZnS systems, the two identical V, Cr and Ni atoms are in a ferromagnetic (FM) coupling under the double-exchange (DE) mechanism, leading V-, Cr- and Ni-doped ZnS systems to be HM with FM coupling. While two identical Mn- and Co-doped ZnS systems are semiconductors with antiferromagnetic (AFM) coupling consisting with the superexchange (SE) mechanism. Specifically, two identical Fe atoms display a competition between the SE and DE mechanisms. The Zn{sub 70}Fe{sub 2}S{sub 72} system is metal with AFM coupling at the nearest separation of two Fe atoms while HM with FM coupling at the farther separations of two Fe atoms. - Graphical abstract: The 3 × 2 × 3 supercell containing 72 formula units of zincblende ZnS. Red (Green) balls represent the S (Zn) atoms. One TM atom or two identical TM atoms X (X = V, Cr, Mn, Fe, Co or Ni) to substitute for one Zn atom at position 0 or two Zn atoms at positions 0 and i (i = 1, 2, 3 or 4). - Highlights: • A single V, Cr, Fe or Ni (Mn or Co) atoms doped ZnS are magnetic HM (magnetic semiconductor). • Two V, Cr or Ni (two Mn or Co) atoms doped ZnS are FM HM (AFM semiconductor). • Two Fe atoms doped ZnS are AFM metal (FM HM) at the nearest (farther) separations.
First principles phonon calculations in materials science
Togo, Atsushi; Tanaka, Isao
2015-01-01
Phonon plays essential roles in dynamical behaviors and thermal properties, which are central topics in fundamental issues of materials science. The importance of first principles phonon calculations cannot be overly emphasized. Phonopy is an open source code for such calculations launched by the present authors, which has been world-widely used. Here we demonstrate phonon properties with fundamental equations and show examples how the phonon calculations are applied in materials science.
Yan, X.; Chen, Xing-Qiu; Michor, H.; Wolf, W.; Witusiewicz, V. T.; Bauer, E.; Podloucky, R.; Rogl, P.
2018-03-01
By combining theoretical density functional theory (DFT) and experimental studies, structural and magnetic phase stabilities and electronic structural, elastic, and vibrational properties of the Laves-phase compound NbMn2 have been investigated for the C14, C15, and C36 crystal structures. At low temperatures C14 is the ground-state structure, with ferromagnetic and antiferromagnetic orderings being degenerate in energy. The degenerate spin configurations result in a rather large electronic density of states at Fermi energy for all magnetic cases, even for the spin-polarized DFT calculations. Based on the DFT-derived phonon dispersions and densities of states, temperature-dependent free energies were derived for the ferromagnetic and antiferromagnetic C14 phase, demonstrating that the spin-configuration degeneracy possibly exists up to finite temperatures. The heat of formation Δ298H0=-45.05 ±3.64 kJ (molf .u .NbMn2) -1 was extracted from drop isoperibolic calorimetry in a Ni bath. The DFT-derived enthalpy of formation of NbMn2 is in good agreement with the calorimetric measurements. Second-order elastic constants for NbMn2 as well as for related compounds were calculated.
Energy Technology Data Exchange (ETDEWEB)
Jaiganesh, G. [Department of Physics, Anna University, Chennai 600 025, Tamil Nadu (India); Kalpana, G., E-mail: g_kalpa@yahoo.com [Department of Physics, Anna University, Chennai 600 025, Tamil Nadu (India)
2013-01-15
The first-principles study of the electronic structure and ferromagnetism of AeX (Ae=Be, Mg, Sr and Ba; X=Si, Ge and Sn) compounds have been performed in the ground-state CrB-type and hypothetical NaCl- and zinc blende-type structures by spin-polarization and non-spin-polarization calculations. The TBLMTO-ASA program was used for the purpose. In the CrB-type structure, all these compounds exhibit non-magnetic and metallic behavior. The calculations show that in the NaCl- and ZB-type structures BeSi, BeGe, BeSn, MgSi, MgGe and MgSn compounds are non-magnets whereas SrSi, SrGe, SrSn, BaSi, BaGe and BaSn compounds are ferromagnetic and metallic. Apart from this the ZB-type SrSi, SrGe, BaSi and BaGe compounds exhibit half-metallicity at their equilibrium volume with a magnetic moment of 2.0 {mu}{sub B} per formula unit. However, ZB-type SrSn and BaSn compounds are found to exhibit half-metallic property under expansion of volume. The magnetism arises mainly from the anion p-like states and partial involvement of cation d-like states. The ground state properties like equilibrium lattice parameters, bulk modulus, cohesive energy, magnetic moment, spin-flip-gap and majority spin band gap are calculated and compared with available results. The band structure and density of states are also presented. These materials will be useful for the study of p-electron magnetism and in spintronic devices. - Highlights: Black-Right-Pointing-Pointer Electronic Structure and ferromagnetism in AeX (Ae=Be, Mg, Sr, Ba; X=Si, Ge and Sn) compounds. Black-Right-Pointing-Pointer AeX (Ae=Sr, Ba; X=Si, Ge and Sn) compounds in the NaCl- and ZB- structure are ferromagnetic metals. Black-Right-Pointing-Pointer ZB-type SrSi, SrGe, BaSi and BaGe show half-metallicity with a magnetic moment of 2.00 {mu}{sub B}. Black-Right-Pointing-Pointer Magnetism arises from anion p-like states and cation d-like states (p-electron magnetism). Black-Right-Pointing-Pointer These compounds may be useful spintronic
International Nuclear Information System (INIS)
Huang Yuhong; Jie Wanqi; Zha Gangqiang
2012-01-01
Highlights: ► E f and E c of ZnCrM decrease as anionic atomic radius and electronegativity increase. ► ZnCrM is half-metallic with band gaps of 1.06, 0.65 and 0.83 eV, respectively. ► The conventional gaps decrease with the increase of anion radius successively. ► The effective potential is more attractive for minority spin than for the majority. ► The s-d interaction is repulsive, while p-d interaction is attractive. - Abstract: Using the first-principle method, the structural, electronic and magnetic properties of Zn 0.75 Cr 0.25 M (M = S, Se, Te) have been investigated. The calculated formation energy and cohesive energy of Zn 0.75 Cr 0.25 M are negative and the absolute values of them decrease with the increase of atomic radius as well as the electronegativity of the anions. Zn 0.75 Cr 0.25 M display half-metallic characteristics with energy band gaps of 1.06, 0.65 and 0.83 eV, respectively. The conventional gaps for minority spin are 2.91, 2.16 and 1.75 eV for Zn 0.75 Cr 0.25 S, Zn 0.75 Cr 0.25 Se and Zn 0.75 Cr 0.25 Te respectively, which decrease with the increase of anion radius successively, similar to that observed in the binary compounds of ZnM. For all the three materials, exchange splitting energies Δ x (pd) due to the effect of Cr 3d state are negative, implying that the effective potential is more attractive for minority spin than that for majority spin, and the absolute value of Δ x (pd) decreases with the increase of atomic radius of anions. The calculated positive values of N 0 α suggest interactions between Zn-s and Cr-3d states are repulsive, while the negative values of N 0 β show that p–d interactions at the valence band are more attractive. All these conclusions demonstrate that Zn 0.75 Cr 0.25 M are promising candidates for practical applications in spintronics.
Harb, Moussab
2014-01-01
Finding an ideal photocatalyst for achieving efficient overall water splitting still remains a great challenge. By applying accurate first-principles quantum calculations based on DFT with the screened non-local hybrid HSE06 functional, we bring rational insights at the atomic level into the influence of non-stoichiometric compositions on essential properties of tantalum (oxy)nitride compounds as visible-light-responsive photocatalysts for water splitting. Indeed, recent experiments show that such non-stoichiometry is inherent to the nitridation methods of tantalum oxide with unavoidable oxygen impurities. We considered here O-enriched Ta3N5 and N-enriched TaON materials. Although their structural parameters are found to be very similar to those of pure compounds and in good agreement with available experimental studies, their photocatalytic features for visible-light-driven overall water splitting reactions show different behaviors. Further partial nitration of TaON leads to a narrowed band gap, but partially oxidizing Ta3N5 causes only subtle changes in the gap. The main influence, however, is on the band edge positions relative to water redox potentials. The pure Ta3N5 is predicted to be a good candidate only for H+ reduction and H2 evolution, while the pure TaON is predicted to be a good candidate for water oxidation and O2 evolution. Non-stoichiometry has here a positive influence, since partially oxidized tantalum nitride, Ta(3-x)N(5-5x)O5x (for x ≥ 0.16) i.e. with a composition in between TaON and Ta3N5, reveals suitable band edge positions that correctly bracket the water redox potentials for visible-light-driven overall water splitting reactions. Among the various explored Ta(3-x)N(5-5x)O5x structures, a strong stabilization is obtained for the configuration displaying a strong interaction between the O-impurities and the created Ta-vacancies. In the lowest-energy structure, each created Ta-vacancy is surrounded by five O-impurity species substituting
A first principle study of hydrogenated graphdiyne
Qiu, Huanhuan; Sheng, Xianlei
2018-03-01
Based on recently synthesized two-dimensional graphdiyne, we have constructed several hydrogenated graphdiyne structures and studied their electronic structures and magnetic properties by first-principles calculations. Both direct and indirect band gap semiconductors are found in the nomagnetic hydrogenated configurations. Moreover, half semiconductors are found in the magnetic ground states of some hydrogenated graphdiyne structures we considered, although there is no transition metal element in the materials.
Analytic representation for first-principles pseudopotentials
International Nuclear Information System (INIS)
Lam, P.K.; Cohen, M.L.; Zunger, A.
1980-01-01
The first-principles pseudopotentials developed by Zunger and Cohen are fit with a simple analytic form chosen to model the main physical properties of the potentials. The fitting parameters for the first three rows of the Periodic Table are presented, and the quality of the fit is discussed. The parameters reflect chemical trends of the elements. We find that a minimum of three parameters is required to reproduce the regularities of the Periodic Table. Application of these analytic potentials is also discussed
Fadila, Belkharroubi; Ameri, Mohammed; Bensaid, Djillali; Noureddine, Moulay; Ameri, Ibrahim; Mesbah, Smain; Al-Douri, Y.
2018-02-01
The structural, magnetic, electronic, elastic and mechanical properties of full-Heusler compounds Co2YAl (Y = Fe, Ti), in L21 type structure are determined using the density functional theory based full potential linearized augmented plane waves (FP-LAPW) method. We have used four approaches to evaluate the structural stability for the two compounds, Co2FeAl and Co2TiAl, the Local Spin Density approximation (LSDA), the LSDA + USIC, the Spin-Perdew-Burke-Ernzerhof generalized gradient approximation GGA and PBE-GGA + USIC. The results show that the equilibrium lattice constants using the general gradient approximation method are in good agreement with experimental values. The electronic and magnetic properties of 3d transition metal based full Heusler compounds Co2YAl (Y = Fe, Ti) within the framework of Perdew-Burke-Ernzerhof generalized gradient approximation GGA, GGA + USIC besides new modified Becke and Johnson GGA (mBJ-GGA) have been calculated by exchange-correlation potentials. The calculated density of states (DOS) and band structure for Co2YAl show the existence of energy band gap in their minority-spin channel and half-metallic character, while their total magnetic moment following the Slater-Pauling rule Mt = Zt - 24. The mechanical properties of bulk modulus, shear modulus, Young's modulus E, anisotropic ratio, Poisson's ratio ν and B/G ratio are also investigated to explore the ductile and brittle nature of these compounds. To collect more information on the mechanical stability, we have calculated Lame's coefficients, Cauchy pressure, Kleinman parameter, sound velocities and Debye temperature θD Our calculated values are in agreement with experimental and theoretical data.
First-principles study of the phase stability and the mechanical properties of W-Ta and W-Re alloys
Directory of Open Access Journals (Sweden)
Ning Wei
2014-05-01
Full Text Available The phase stability and mechanical properties of binary W1−xTax and W1−xRex alloys were investigated using the full-potential augmented plane-wave method. The special quasirandom structures(SQSs of these alloys are mechanically stable due to all of the positive elastic constants and negative binding energies. The binding energies of both the W1−xTax and W1−xRex alloys also exhibit energy favorable asymmetry toward the W-rich side. In addition, the bulk modulus of the W1−xTax alloys decrease gradually with the increase of the Ta concentration, while those of the W1−xRex alloys increase gradually with the increase of the Re concentration. Consequently, the bulk modulus of W metal can be improved by doping with Re, implying that the resistance to deformation is enhanced. Based on the mechanical characteristic G/B and Poisson's ratio ν, both the W1−xTax and W1−xRex alloys are regarded as being ductile materials, the ductility of which improves with the increase of Ta or Re.
Electron-phonon interactions from first principles
Giustino, Feliciano
2017-01-01
This article reviews the theory of electron-phonon interactions in solids from the point of view of ab initio calculations. While the electron-phonon interaction has been studied for almost a century, predictive nonempirical calculations have become feasible only during the past two decades. Today it is possible to calculate from first principles many materials properties related to the electron-phonon interaction, including the critical temperature of conventional superconductors, the carrier mobility in semiconductors, the temperature dependence of optical spectra in direct and indirect-gap semiconductors, the relaxation rates of photoexcited carriers, the electron mass renormalization in angle-resolved photoelectron spectra, and the nonadiabatic corrections to phonon dispersion relations. In this article a review of the theoretical and computational framework underlying modern electron-phonon calculations from first principles as well as landmark investigations of the electron-phonon interaction in real materials is given. The first part of the article summarizes the elementary theory of electron-phonon interactions and their calculations based on density-functional theory. The second part discusses a general field-theoretic formulation of the electron-phonon problem and establishes the connection with practical first-principles calculations. The third part reviews a number of recent investigations of electron-phonon interactions in the areas of vibrational spectroscopy, photoelectron spectroscopy, optical spectroscopy, transport, and superconductivity.
Energy Technology Data Exchange (ETDEWEB)
Moreira, E. [Departamento de Fisica Teorica e Experimental, Universidade Federal do Rio Grande do Norte, 59072-970 Natal-RN (Brazil); Henriques, J.M. [Centro de Educacao e Saude, Universidade Federal de Campina Grande, Campus Cuite, 58175-000 Cuite-PB (Brazil); Azevedo, D.L. [Departamento de Fisica, Universidade Federal do Maranhao, Centro de Ciencias Exatas e Tecnologia, 65085-580 Sao Luis-MA (Brazil); Caetano, E.W.S., E-mail: ewcaetano@gmail.com [Instituto Federal de Educacao, Ciencia e Tecnologia do Ceara, 60040-531 Fortaleza-CE (Brazil); Freire, V.N. [Departamento de Fisica, Universidade Federal do Ceara, Centro de Ciencias, Caixa Postal 6030, Campus do Pici, 60455-760 Fortaleza-CE (Brazil); Albuquerque, E.L. [Departamento de Biofisica e Farmacologia, Universidade Federal do Rio Grande do Norte, 59072-970 Natal-RN (Brazil)
2012-03-15
Neutron diffraction data for Sr{sub x}Ba{sub 1-x}SnO{sub 3} (x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) solid solutions were used as inputs to obtain optimized geometries and electronic properties using the density functional theory (DFT) formalism considering both the local density and generalized gradient approximations, LDA and GGA, respectively. The crystal structures and SnO{sub 6} octahedra tilting angles found after total energy minimization agree well with experiment, specially for the GGA data. Elastic constants were also obtained and compared with theoretical and experimental results for cubic BaSnO{sub 3}. While the alloys with cubic unit cell have an indirect band gap, tetragonal and orthorhombic alloys exhibit direct band gaps (exception made to x=1.0). The Kohn-Sham minimum electronic band gap oscillates from 1.52 eV (cubic x=0.0, LDA) to 2.61 eV (orthorhombic x=1.0, LDA), and from 0.74 eV (cubic BaSnO{sub 3}, GGA) to 1.97 eV (orthorhombic SrSnO{sub 3}, GGA). Parabolic interpolation of bands has allowed us to estimate the effective masses for charge carriers, which are shown to be anisotropic and larger for holes. - Graphical Abstract: Highlights: Black-Right-Pointing-Pointer DFT calculations were performed on Sr{sub x}Ba{sub 1-x}SnO{sub 3} solid solutions. Black-Right-Pointing-Pointer Calculated crystal structures agree well with experiment. Black-Right-Pointing-Pointer Alloys have direct or indirect gaps depending on the Sr molar fraction. Black-Right-Pointing-Pointer The Kohn-Sham gap variation from x=0.0 to x=1.0 is close to the experimental value. Black-Right-Pointing-Pointer Carrier effective masses are very anisotropic, specially for holes.
Guo, R. K.; Liu, G. D.; Lin, T. T.; Wang, W.; Wang, L. Y.; Dai, X. F.
2018-02-01
It is predicted that the ZrCrCoZ(Z=B, Al, Ga, In) compounds with LiMnPbSn-type structure are half-metallic ferrimagnets with a large half-metallic gap by the first-principles calculations. The half-metallicity of the ZrCrCoZ(Z=B, Al, Ga, In) compounds are quite robust to the axial and uniaxial strain. The total magnetic moments in per unit cell are 4 μB for the ZrCrCoZ(Z=B, Al, Ga, In) compounds and follow the Slater-Pauling rule, which can be attributed to the great spin-splitting. The calculated formation energies are negative for all the ZrCrCoZ(Z=B, Al, Ga, In) compounds, which indicates that those compounds are in the thermodynamic stability and the possibility of synthesis in experiment.
Bhattacharjee, Satadeep; Eriksson, Olle; Sanyal, Biplab
2012-07-25
First principles electronic structure calculations have been performed for the double perovskite Bi(2)CoMnO(6) in its non-centrosymmetric polar state using the generalized gradient approximation plus the Hubbard U approach. We find that the ferromagnetic state is more favored compared to the ferrimagnetic state with both Co and Mn in high spin states. The calculated dynamical charge tensors are anisotropic reflecting a low-symmetry structure of the compound. The magnetic structure dependent phonon frequencies indicate the presence of a weak spin-phonon coupling. Using the Berry phase method, we obtain a spontaneous ferroelectric polarization of 5.88 μC cm(-2), which is close to the experimental value observed for a similar compound, Bi(2)NiMnO(6).
Alternative First Principle Approach for Determination of Elements of ...
African Journals Online (AJOL)
Stiffness coefficients which in essence are elements of stiffness matrix of a uniform beam element are derived in this work from first principles using elastic curve equation and initial value method. The obtained initial value solution enables exact values of stiffness coefficients, fixed end moments and shears as well as ...
Mary, J. Arul; Vijaya, J. Judith; Bououdina, M.; Kennedy, L. John; Dai, J. H.; Song, Y.
2015-02-01
Ce, Cu co-doped ZnO (Zn1-2xCexCuxO: x=0.00, 0.01, 0.02, 0.03, 0.04 and 0.05) nanocrystals were synthesized by a microwave combustion method. These nanocrystals were investigated by using X-ray diffraction (XRD), UV-visible diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). The stability and magnetic properties of Ce and Cu co-doped ZnO were probed by first principle calculations. XRD results revealed that all the compositions are single crystalline. hexagonal wurtzite structure. The optical band gap of pure ZnO was found to be 3.22 eV, and it decreased from 3.15 to 3.10 eV with an increase in the concentration of Cu and Ce content. The morphologies of Ce and Cu co-doped ZnO samples confirmed the formation of nanocrystals with an average grain size ranging from 70 to 150 nm. The magnetization measurement results affirmed the antiferro and ferromagnetic state for Ce and Cu co-doped ZnO samples and this is in agreement with the first principles theoretical calculations.
First principles study of AlBi
International Nuclear Information System (INIS)
Amrani, B.; Achour, H.; Louhibi, S.; Tebboune, A.; Sekkal, N.
2008-05-01
Using the first principles method of the full potential linear augmented plane waves (FPLAPW), the structural and the electronic properties of AlBi are investigated. It is found that this compound has a small and direct semiconducting gap at Γ. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of the volume, the bulk modulus, the variation of the thermal expansion α, as well as the Debye temperature θ D and the heat capacity C v are successfully obtained in the whole range from 0 to 30 GPa and temperature range from 0 to 1200 K. (author)
Phase stability and elastic properties of Cr-V alloys
Gao, M. C.; Suzuki, Y.; Schweiger, H.; Doǧan, Ö. N.; Hawk, J.; Widom, M.
2013-02-01
V is the only element in the periodic table that forms a complete solid solution with Cr and thus is particularly important in alloying strategy to ductilize Cr. This study combines first-principles density functional theory calculations and experiments to investigate the phase stability and elastic properties of Cr-V binary alloys. The cluster expansion study reveals the formation of various ordered compounds at low temperatures that were not previously known. These compounds become unstable due to the configurational entropy of bcc solid solution as the temperature is increased. The elastic constants of ordered and disordered compounds are calculated at both T = 0 K and finite temperatures. The overall trends in elastic properties are in agreement with measurements using the resonant ultrasound spectroscopy method. The calculations predict that addition of V to Cr decreases both the bulk modulus and the shear modulus, and enhances the Poisson’s ratio, in agreement with experiments. Decrease in the bulk modulus is correlated to decrease in the valence electron density and increase in the lattice constant. An enhanced Poisson’s ratio for bcc Cr-V alloys (compared to pure Cr) is associated with an increased density of states at the Fermi level. Furthermore, the difference charge density in the bonding region in the (110) slip plane is highest for pure Cr and decreases gradually as V is added. The present calculation also predicts a negative Cauchy pressure for pure Cr, and it becomes positive upon alloying with V. The intrinsic ductilizing effect from V may contribute, at least partially, to the experimentally observed ductilizing phenomenon in the literature.
Phase stability and elastic properties of Cr-V alloys
Energy Technology Data Exchange (ETDEWEB)
Gao, M C; Suzuki, Y; Schweiger, H; Doğan, Ö N; Hawk, J; Widom, M
2013-01-23
V is the only element in the periodic table that forms a complete solid solution with Cr and thus is particularly important in alloying strategy to ductilize Cr. This study combines first-principles density functional theory calculations and experiments to investigate the phase stability and elastic properties of Cr–V binary alloys. The cluster expansion study reveals the formation of various ordered compounds at low temperatures that were not previously known. These compounds become unstable due to the configurational entropy of bcc solid solution as the temperature is increased. The elastic constants of ordered and disordered compounds are calculated at both T = 0 K and finite temperatures. The overall trends in elastic properties are in agreement with measurements using the resonant ultrasound spectroscopy method. The calculations predict that addition of V to Cr decreases both the bulk modulus and the shear modulus, and enhances the Poisson’s ratio, in agreement with experiments. Decrease in the bulk modulus is correlated to decrease in the valence electron density and increase in the lattice constant. An enhanced Poisson’s ratio for bcc Cr–V alloys (compared to pure Cr) is associated with an increased density of states at the Fermi level. Furthermore, the difference charge density in the bonding region in the (110) slip plane is highest for pure Cr and decreases gradually as V is added. The present calculation also predicts a negative Cauchy pressure for pure Cr, and it becomes positive upon alloying with V. The intrinsic ductilizing effect from V may contribute, at least partially, to the experimentally observed ductilizing phenomenon in the literature.
Credibility is the first principle
International Nuclear Information System (INIS)
Beecher, William
2002-01-01
The first principle of an effective public affairs program on nuclear energy is credibility. If credibility is lacking, no matter how artful the message, it will not be persuasive. There has long been a problem in the United States. For years much of the industry followed the practice, when there was an event at a nuclear power plant that resulted in an unplanned release of radioactivity, to tell the public there was 'no release' if in fact the release was below the technical specifications of what the NRC mandates as being safe. The NRC is a safety regulator. It can tell nuclear power plant operators what to do, or not do, when it comes to safety, but doesn't have the right to tell them what to say to the public. The example of an emergency exercise and the NRC press release on that occasion showed the direction how companies could be influenced to behave in order to prevent such avoidably negative news coverage, i.e. attaining credibility when public anxiety is concerned
Prediction of electronic, structural and elastic properties of the hardest oxide: TiO{sub 2}
Energy Technology Data Exchange (ETDEWEB)
Caravaca, M.A.; Mino, J.C. [Departamento de Fisico-Quimica, Facultad de Ingenieria, UNNE, Resistencia (Argentina); Casali, R.A. [Departamento de Fisica, Facultad de Ciencias Exactas, Naturales y Agrimensura, UNNE, Corrientes (Argentina)
2009-03-15
This work combines the theory of elasticity with first principles quantum mechanic calculations to predict the electronic, structural and elastic properties: elastic constants, bulk moduli of the TiO{sub 2} (Titania) in the Pnma phase. Band-structure shows a direct gap in {gamma} which increases its value under hydrostatic pressure. It has two regimes: in the range 0-50 GPa the band-gap has a negative second pressure derivative and changes its sign in the range 50-100 GPa. The band gap becomes indirect at pressures above 150 GPa. This phase improves its mechanical stability and insulator properties under extreme conditions of hydrostatic pressures. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
International Nuclear Information System (INIS)
Sun, Ting; Wu, Xiaozhi; Wang, Rui; Li, Weiguo
2015-01-01
The adhesion and ductility of (100) and (110) Al/TiC interfaces alloyed by Mg, Zn, Cu, Fe, and Ti have been investigated using first-principles methods. Fe and Ti can enhance the adhesion of (100) and (110) interfaces. Mg and Zn have the opposite effect. Interfacial electronic structures have been created to analyze the changes of the work of adhesion. It is found that more charge is accumulated at interfaces alloyed by Fe and Ti compared with pure Al/TiC. There is also an obvious downward shift in the Fermi energy of Fe, Ti at the interface. Furthermore, the unstable stacking fault energies of the interfaces are calculated; the results demonstrate that the preferred slip direction is the 〈110〉 direction for (100) and (110) Al/TiC. Based on the Rice criterion of ductility, the results predict that Mg, Fe, and Ti are promising candidates for improving the ductility of Al/TiC interfaces. (paper)
First-principles calculations of flexoelectric coefficients
Hong, Jiawang; Vanderbilt, David
2013-03-01
Flexoelectricity, which is the linear response of polarization to a strain gradient, can have a significant effect on the functional properties of dielectric thin films, superlattices and nanostructures. Despite growing experimental interest, there have been relatively few theoretical studies of flexoelectricity, especially in the context of first-principles calculations. In this talk, we present a complete theory of both the electronic (or ``frozen-ion'')[1] and lattice contributions to flexoelectricity, and demonstrate a supercell method for calculating the flexoelectric coefficients using first-principles density-functional methods. Results are presented for cubic materials including CsCl and SrTiO3. In order to obtain all the elements of the flexoelectric tensor, transverse as well as longitudinal, we carry out calculations on supercells extended along different orientations (e.g., [110] as well as [100]), taking special care to carry out conversions between objects calculated under fixed E or fixed D electric boundary conditions in different parts of the procedure. In this way, all the elements of both the electronic and lattice contributions to the flexoelectric tensor are determined.
First-principles theory of flexoelectricity
Vanderbilt, David
2013-03-01
Flexoelectricity is the linear response of polarization to a strain gradient. Because strain gradients break inversion symmetry, flexoelectricity occurs in all insulating crystals. The flexoelectric effect is negligible on conventional length scales, but it can become very strong at the nanoscale where large strain gradients can significantly affect the functional properties of dielectric thin films and superlattices. Previous theories have tended to focus either on the lattice or the electronic (i.e., frozen-ion) contribution, and have involved some approximations or limitations. Here we develop a general first-principles theory of the flexoelectric tensor, formulated in such a way that the tensor elements can be computed directly in the context of density-functional calculations. Special attention will be paid to several subtleties, including surface contributions, pseudopotential dependence, the calculation of transverse components, fixed E vs. fixed D boundary conditions, and a degree of non-uniqueness that is present for some strain gradients. We introduce several practical supercell-based methods for calculating the flexoelectric coefficients from first principles, and demonstrate them by computing the coefficients for a variety of insulating materials.(Work done in collaboration with Jiawang Hong. Supported by ONR N00014-12-1-1035.)
Theoretical study of structural, elastic and thermodynamic properties of CZTX (X = S and Se) alloys
Energy Technology Data Exchange (ETDEWEB)
Bensalem, S., E-mail: bensalemse@gmail.com [Centre de Développement des Energies Renouvelables, CDER, BP 62 Route de l’Observatoire Bouzaréah, 16340 Algiers (Algeria); Département de Physique, Faculté des Sciences, Université de Sétif 1, 19000 Sétif (Algeria); Chegaar, M. [Département de Physique, Faculté des Sciences, Université de Sétif 1, 19000 Sétif (Algeria); Laboratoire d’Optoélectronique et Composants, Université de Sétif 1, 19000 Sétif (Algeria); Maouche, D.; Bouhemadou, A. [Laboratoire de Développement de Nouveaux Matériaux et leurs Caractérisations, Université de Sétif 1, 19000 Sétif (Algeria)
2014-03-15
Highlights: • CZTX (X = S, Se) alloys are relatively new absorbers for solar cells applications. • Elastic and thermodynamic properties of these alloys are not well understood. • The considered types “kesterite and stannite” can coexist in experimental samples. • Elastic and thermodynamic properties of both types have been investigated. • Coexistence of both types does not influence the behavior of CZTX-based devices. -- Abstract: By means of first-principles calculation approach, structural parameters, elastic and thermodynamic properties of Copper–Zinc–Tin–(Sulphide, Selenide) or Cu{sub 2}ZnSnX{sub 4} (X = S and Se) alloys for the kesterite (KS) and stannite (ST) types have been investigated. The calculated lattice parameters are in good agreement with experimental reported data. The elastic constants are calculated for both types of both compounds using the static finite strain scheme; the pressure dependence of elastic constants is predicted. The bulk modulus, anisotropy factor, shear modulus, Young’s modulus, Lame’s coefficient and Poisson’s ratio have been estimated from the calculated single crystalline elastic constants. The analysis of B/G ratio shows that Cu{sub 2}ZnSnX{sub 4} or CZTX compounds behave as ductile. Through quasi-harmonic approximation, the temperature dependence of some thermodynamic functions and lattice heat capacity of both compounds for both types have been performed.
Elastic Properties of the Solid Electrolyte Li7La3Zr2O12 (LLZO)
DEFF Research Database (Denmark)
Yu, Seungho; Schmidt, Robert D.; Garcia-Mendez, Regina
2016-01-01
The oxide known as LLZO, with nominal composition Li7La3Zr2O12, is a promising solid electrolyte for Li-based batteries due to its high Li ion conductivity and chemical stability with respect to lithium. Solid electrolytes may also enable the use of metallic Li anodes by serving as a physical...... is predicted to be enhanced as the electrolyte’s shear modulus increases. In the present study a combination of first-principles calculations, acoustic impulse excitation measurements, and nanoindentation experiments are used to determine the elastic constants and moduli for high-conductivity LLZO compositions...... barrier that suppresses dendrite initiation and propagation during cycling. Prior linear elasticity models of the Li electrode/solid electrolyte interface suggest that the stability of this interface is highly dependent on the elastic properties of the solid separator. For example, dendritic suppression...
The temperature behaviour of the elastic and thermodynamic properties of fcc thorium
Energy Technology Data Exchange (ETDEWEB)
Jaroszewicz, S., E-mail: jaroszew@tandar.cnea.gov.ar [Gerencia de Investigacion y Aplicaciones, Comision Nacional de Energia Atomica, Av. Gral. Paz 1499, San Martin (Argentina); Instituto de Tecnologia Jorge A. Sabato, UNSAM-CNEA (Argentina); Mosca, H.O. [Gerencia de Investigacion y Aplicaciones, Comision Nacional de Energia Atomica, Av. Gral. Paz 1499, San Martin (Argentina); Instituto de Tecnologia Jorge A. Sabato, UNSAM-CNEA (Argentina); Garces, J.E. [DAEE, Centro Atomico Bariloche, Comisin Nacional de Energia Atomica, Av. Bustillo 9500, Bariloche, Rio Negro (Argentina)
2012-10-15
The temperature behaviour of the structural, elastical and thermal properties of fcc thorium have been calculated from a free-parameter Helmholtz free energy developed by computing the cohesive energy from first principles calculations coupled to the Chen-Moebius lattice inversion method and the Debye-Grueneisen quasiharmonic model. The elastic constants, shear modulus, Young modulus, Poisson's ratio and thermodynamic properties of fcc Th as the entropy, the harmonic specific heat, the (P, V, T) equation of state and the thermal lattice expansion are found to be in a very good agreement with experiments and ab initio phonon calculations. The results of this work show the potentiality of the Chen-Moebius method coupled to ab initio calculation of the cohesive energy to develop a free-parameter pair potential capable of giving an overall description of fcc Th properties at T = 0 K with an error similar to ab initio calculations.
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
Yuan, Xiao-Li; Xue, Mi-An; Chen, Wen; An, Tian-Qing
2016-11-01
We employed density-functional theory (DFT) within the generalized gradient approximation (GGA) to investigate the ZrTi2 alloy, and obtained its structural phase transition, mechanical behavior, Gibbs free energy as a function of pressure, P-V equation of state, electronic and Mulliken population analysis results. The lattice parameters and P-V EOS for α, β and ω phases revealed by our calculations are consistent with other experimental and computational values. The elastic constants obtained suggest that ω-ZrTi2 and α-ZrTi2 are mechanically stable, and that β-ZrTi2 is mechanically unstable at 0 GPa, but becomes more stable with increasing pressure. Our calculated results indicate a phase transition sequence of α → ω → β for ZrTi2. Both the bulk modulus B and shear modulus G increase linearly with increasing pressure for three phases. The G/B values illustrated good ductility of ZrTi2 alloy for three phases, with ωJournal web page at http://dx.doi.org/10.1140/epjb/e2016-70218-0
Elastic, mechanical, and thermodynamic properties of Bi-Sb binaries: Effect of spin-orbit coupling
Singh, Sobhit; Valencia-Jaime, Irais; Pavlic, Olivia; Romero, Aldo H.
2018-02-01
Using first-principles calculations, we systematically study the elastic stiffness constants, mechanical properties, elastic wave velocities, Debye temperature, melting temperature, and specific heat of several thermodynamically stable crystal structures of BixSb1 -x (0
Optical potential from first principles
Rotureau, J.; Danielewicz, P.; Hagen, G.; Nunes, F. M.; Papenbrock, T.
2017-02-01
We develop a method to construct a microscopic optical potential from chiral interactions for nucleon-nucleus scattering. The optical potential is constructed by combining the Green's function approach with the coupled-cluster method. To deal with the poles of the Green's function along the real energy axis we employ a Berggren basis in the complex energy plane combined with the Lanczos method. Using this approach, we perform a proof-of-principle calculation of the optical potential for the elastic neutron scattering on 16O. For the computation of the ground state of 16O, we use the coupled-cluster method in the singles-and-doubles approximation, while for the A ±1 nuclei we use particle-attached/removed equation-of-motion method truncated at two-particle-one-hole and one-particle-two-hole excitations, respectively. We verify the convergence of the optical potential and scattering phase shifts with respect to the model-space size and the number of discretized complex continuum states. We also investigate the absorptive component of the optical potential (which reflects the opening of inelastic channels) by computing its imaginary volume integral and find an almost negligible absorptive component at low energies. To shed light on this result, we computed excited states of 16O using the equation-of-motion coupled-cluster method with singles-and-doubles excitations and we found no low-lying excited states below 10 MeV. Furthermore, most excited states have a dominant two-particle-two-hole component, making higher-order particle-hole excitations necessary to achieve a precise description of these core-excited states. We conclude that the reduced absorption at low energies can be attributed to the lack of correlations coming from the low-order cluster truncation in the employed coupled-cluster method.
Predicted boron-carbide compounds: a first-principles study.
Wang, De Yu; Yan, Qian; Wang, Bing; Wang, Yuan Xu; Yang, Jueming; Yang, Gui
2014-06-14
By using developed particle swarm optimization algorithm on crystal structural prediction, we have explored the possible crystal structures of B-C system. Their structures, stability, elastic properties, electronic structure, and chemical bonding have been investigated by first-principles calculations with density functional theory. The results show that all the predicted structures are mechanically and dynamically stable. An analysis of calculated enthalpy with pressure indicates that increasing of boron content will increase the stability of boron carbides under low pressure. Moreover, the boron carbides with rich carbon content become more stable under high pressure. The negative formation energy of predicted B5C indicates its high stability. The density of states of B5C show that it is p-type semiconducting. The calculated theoretical Vickers hardnesses of B-C exceed 40 GPa except B4C, BC, and BC4, indicating they are potential superhard materials. An analysis of Debye temperature and electronic localization function provides further understanding chemical and physical properties of boron carbide.
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.
Energy Technology Data Exchange (ETDEWEB)
Hadjab, Moufdi [Applied Materials Laboratory, Research Center, University Djillali Liabes, 22000, Sidi Bel Abbes (Algeria); Thin Films Development and Applications Unit UDCMA, Setif – Research Center in Industrial Technologies CRTI, P. O. Box 64, Cheraga, 16014, Algiers (Algeria); Berrah, Smail [Mastery Renewable Energies Laboratory (LMER), University of A. Mira, Bejaia (Algeria); Abid, Hamza; Ziane, Mohamed Issam; Bennacer, Hamza [Applied Materials Laboratory, Research Center, University Djillali Liabes, 22000, Sidi Bel Abbes (Algeria); Reshak, Ali H., E-mail: maalidph@yahoo.co.uk [New Technologies – Research Center, University of West Bohemia, Univerzitni 8, 30614, Pilsen (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007, Kangar, Perlis (Malaysia)
2016-10-01
In this paper, we have presented a theoretical study of the optical properties for the cubic Mg{sub x}Zn{sub 1−x}O (x = 0.0, 0.125, 0.375, 0.625, 0.875 and 1.0) alloys using the full-potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT). The local density approximation (LDA) was applied to calculate the structural properties. In order to explore the desired properties, the Mg{sub x}Zn{sub 1−x}O alloys were modeled at various x compositions from 0.0 to 1.0 by step of 0.125. The recently modified semi-local Becke-Johnson potential with LDA correlation in the form of mBJ-LDA was used to predict the energy band gap, optical dielectric function, refractive index, absorption coefficient, reflectivity, optical conductivity and the electron energy loss of Mg{sub x}Zn{sub 1−x}O alloys. The obtained results show good agreement with the experimental data, which indicate that the investigated ternary alloys are among promising material for the fabrication of electronic, optoelectronic devices and their applications. - Highlights: • Theoretical study of optical properties of the cubic alloy Mg{sub x}Zn{sub 1−x}O. • The lattice constants, the bulk modulus B and it’s pressure derivative B′ were obtained. • The calculated energy gaps within mBJ show good agreement with the experimental data. • The optical properties were calculated and discussed in details.
Mesoscale elastic properties of marine sponge spicules.
Zhang, Yaqi; Reed, Bryan W; Chung, Frank R; Koski, Kristie J
2016-01-01
Marine sponge spicules are silicate fibers with an unusual combination of fracture toughness and optical light propagation properties due to their micro- and nano-scale hierarchical structure. We present optical measurements of the elastic properties of Tethya aurantia and Euplectella aspergillum marine sponge spicules using non-invasive Brillouin and Raman laser light scattering, thus probing the hierarchical structure on two very different scales. On the scale of single bonds, as probed by Raman scattering, the spicules resemble a combination of pure silica and mixed organic content. On the mesoscopic scale probed by Brillouin scattering, we show that while some properties (Young's moduli, shear moduli, one of the anisotropic Poisson ratios and refractive index) are nearly the same as those of artificial optical fiber, other properties (uniaxial moduli, bulk modulus and a distinctive anisotropic Poisson ratio) are significantly smaller. Thus this natural composite of largely isotropic materials yields anisotropic elastic properties on the mesoscale. We show that the spicules' optical waveguide properties lead to pronounced spontaneous Brillouin backscattering, a process related to the stimulated Brillouin backscattering process well known in artificial glass fibers. These measurements provide a clearer picture of the interplay of flexibility, strength, and material microstructure for future functional biomimicry. Copyright © 2015 Elsevier Inc. All rights reserved.
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.
Ghosh, Anima; Thangavel, R.
2017-11-01
In present work, the electronic structure and optical properties of the FeX2 (X = S, Se, Te) compounds have been evaluated by the density functional theory based on the scalar-relativistic full potential linear augmented plane wave method via Wien2K. From the total energy calculations, it has been found that all the compounds have direct band nature, which determined by iron 3 d states at valance band edge and anion p dominated at conduction band at Γ-point and the fundamental band gap between the valence band and conduction band are estimated 1.40, 1.02 and 0.88 eV respectively with scissor correction for FeS2, FeSe2 and FeTe2 which are close to the experimental values. The optical properties such as dielectric tensor components and the absorption coefficient of these materials are determined in order to investigate their usefulness in photovoltaic applications.
Phuc, Huynh V.; Hieu, Nguyen N.; Hoi, Bui D.; Hieu, Nguyen V.; Thu, Tran V.; Hung, Nguyen M.; Ilyasov, Victor V.; Poklonski, Nikolai A.; Nguyen, Chuong V.
2018-01-01
In this paper, we studied the electronic properties, effective masses, and carrier mobility of monolayer MoS_2 using density functional theory calculations. The carrier mobility was considered by means of ab initio calculations using the Boltzmann transport equation coupled with deformation potential theory. The effects of mechanical biaxial strain on the electronic properties, effective mass, and carrier mobility of monolayer MoS_2 were also investigated. It is demonstrated that the electronic properties, such as band structure and density of state, of monolayer MoS_2 are very sensitive to biaxial strain, leading to a direct-indirect transition in semiconductor monolayer MoS_2. Moreover, we found that the carrier mobility and effective mass can be enhanced significantly by biaxial strain and by lowering temperature. The electron mobility increases over 12 times with a biaxial strain of 10%, while the carrier mobility gradually decreases with increasing temperature. These results are very useful for the future nanotechnology, and they make monolayer MoS_2 a promising candidate for application in nanoelectronic and optoelectronic devices.
Lawal, Abdullahi; Shaari, A.; Ahmed, R.; Jarkoni, Norshila
2017-09-01
Bismuth telluride (Bi2Te3), a layered compound with narrow band gap has been potentially reported for thermoelectric. However, strong light interaction of Bi2Te3 is an exciting feature to emerge it as a promising candidate for optoelectronic applications within broadband wavelengths. In this study, we investigate structural, electronic and optical properties of Bi2Te3 topological insulator using combination of density functional theory (DFT) and many-body perturbation theory (MBPT) approach. With the inclusion of van der Waals (vdW) correction in addition to PBE, the lattice parameters and interlayer distance are in good agreement with experimental results. Furthermore, for the precise prediction of fundamental band gap, we go beyond DFT and calculated band structure using one-shot GW approach. Interestingly, our calculated quasiparticle (QP) band gap, Eg of 0.169 eV, is in good agreement with experimental measurements. Taken into account the effects of electron-hole interaction by solving Bethe-Salpeter equation, the calculated optical properties, namely, imaginary and real parts of complex dielectric function, absorption coefficient, refractive index, reflectivity, extinction coefficient, electron energy loss function and optical conductivity all are in better agreement with available experimental results. Consistencies of our findings with experimental data validate the effectiveness of electron-hole interaction for theoretical investigation of optical properties.
Energy Technology Data Exchange (ETDEWEB)
Sakhraoui, T., E-mail: tsakhrawi@yahoo.com [Laboratoire de la Matière Condensée et des Nanosciences, Département de Physique, Faculté des Sciences de Monastir, 5019 Monastir (Tunisia); Université de Strasbourg, CNRS, IPCMS, UMR 7504, F-67000 Strasbourg (France); Said, M. [Laboratoire de la Matière Condensée et des Nanosciences, Département de Physique, Faculté des Sciences de Monastir, 5019 Monastir (Tunisia); Alouani, M. [Université de Strasbourg, CNRS, IPCMS, UMR 7504, F-67000 Strasbourg (France)
2017-06-15
Highlights: • Density functional theory is used to study the interface between the FeRh alloy and MgO. • We focus on the effect of the oxidation on the electronic structure and magnetic properties of the FeRh/MgO (0 0 1) interface. • We show the change on the structure of the Fe-d states. • We examine the charge transfer and the local spin density modification after interface oxidation. - Abstract: The effect of interfacial oxidation on electronic structure and magnetic properties at the FeRh/MgO (0 0 1) interface is studied by ab initio methods. The results show the formation of an interfacial FeO-like layer between the FeRh and the MgO barrier, which has a direct impact on Fe e{sub g} states at the interface. It is shown that these e{sub g} states are more affected than that the t{sub 2g} states at the Fermi level due to the strong hybridization of these states with the p-states of oxygen. Thus, the oxidation modifies crucially the electronic structure and the magnetic properties as compared to those of an ideal interface. In particular, it was found that spin polarization of the ferromagnetic state is substantially enhanced. A simple two-current Julliere model shows that the TMR increases with oxidation.
GPU based acceleration of first principles calculation
International Nuclear Information System (INIS)
Tomono, H; Tsumuraya, K; Aoki, M; Iitaka, T
2010-01-01
We present a Graphics Processing Unit (GPU) accelerated simulations of first principles electronic structure calculations. The FFT, which is the most time-consuming part, is about 10 times accelerated. As the result, the total computation time of a first principles calculation is reduced to 15 percent of that of the CPU.
Dong, Zhihua; Schönecker, Stephan; Chen, Dengfu; Li, Wei; Long, Mujun; Vitos, Levente
2017-11-01
We propose a first-principles framework for longitudinal spin fluctuations (LSFs) in disordered paramagnetic (PM) multicomponent alloy systems and apply it to investigate the influence of LSFs on the temperature dependence of two elastic constants of PM austenitic stainless steel Fe15Cr15Ni. The magnetic model considers individual fluctuating moments in a static PM medium with first-principles-derived LSF energetics in conjunction with describing chemical disorder and randomness of the transverse magnetic component in the single-site alloy formalism and disordered local moment (DLM) picture. A temperature-sensitive mean magnetic moment is adopted to accurately represent the LSF state in the elastic-constant calculations. We make evident that magnetic interactions between an LSF impurity and the PM medium are weak in the present steel alloy. This allows gaining accurate LSF energetics and mean magnetic moments already through a perturbation from the static DLM moments instead of a tedious self-consistent procedure. We find that LSFs systematically lower the cubic shear elastic constants c' and c44 by ˜6 GPa in the temperature interval 300-1600 K, whereas the predominant mechanism for the softening of both elastic constants with temperature is the magneto-volume coupling due to thermal lattice expansion. We find that non-negligible local magnetic moments of Cr and Ni are thermally induced by LSFs, but they exert only a small influence on the elastic properties. The proposed framework exhibits high flexibility in accurately accounting for finite-temperature magnetism and its impact on the mechanical properties of PM multicomponent alloys.
Benlamari, S.; Boukhtouta, M.; Taïri, L.; Meradji, H.; Amirouche, L.; Ghemid, S.
2018-03-01
Structural, electronic, optical, and thermal properties of ternary II-IV-V2 (BeSiSb2 and MgSiSb2) chalcopyrite semiconductors have been calculated using the full-potential linearized augmented plane wave scheme␣in the generalized gradient approximation. The optimized equilibrium structural parameters ( a, c, and u) are in good agreement with theoretical results obtained using other methods. The band structure and density of states reveal that BeSiSb2 has an indirect (Γ-Z) bandgap of about 0.61 eV, whereas MgSiSb2 has a direct (Γ-Γ) bandgap of 0.80 eV. The dielectric function, refractive index, and extinction coefficient were calculated to investigate the optical properties, revealing that BeSiSb2 and MgSiSb2 present very weak birefringence. The temperature dependence of the volume, bulk modulus, Debye temperature, and heat capacities ( C v and C p) was predicted using the quasiharmonic Debye model at different pressures. Significant differences in properties are observed at high pressure and high temperature. We predict that, at 300 K and 0 GPa, the heat capacity at constant volume C v, heat capacity at constant pressure C P, Debye temperature θ D, and Grüneisen parameter γ will be about 94.91 J/mol K, 98.52 J/mol K, 301.30 K, and 2.11 for BeSiSb2 and about 96.08 J/mol K, 100.47 J/mol K, 261.38 K, and 2.20 for MgSiSb2, respectively.
Bahari, Ali; jalalinejad, Amir; Bagheri, Mosahhar; Amiri, Masoud
2017-11-01
In this paper, structural and electronic properties and stability of (10, 0) born nitride nanotube (BNNT) are considered within density functional theory by doping group IV elements of the periodic table. The HOMO-LUMO gap has been strongly modified and treated a dual manner by choosing B or N sites for dopant atoms. Formation energy calculation shows that B site doping is more stable than N site doping. Results also show that all dopants turn the pristine BNNT into a p-type semiconductor except for carbon-doped BNNT at B site.
Ahmed, Nisar; Nisar, Jawad; Kouser, R.; Nabi, Azeem G.; Mukhtar, S.; Saeed, Yasir; Nasim, M. H.
2017-06-01
Wide band gap magnetic semiconductors made of lanthanide compounds have a wide range of applications in opto-magneto-electronic industry and electro (photo) luminescence devices. We have carried out a systematic study of electronic, magnetic and optical properties of rare earth potassium sulfides KMS2 (M = Nd, Ho, Er, and Lu) using density functional theory (DFT) with full potential linearized augmented plane wave method (FP-LAPW). Different exchange and correlation approximations are employed such as generalized gradient approximation (GGA), GGA + U and TB-mBJ. It is inferred that the GGA + U approach correctly predicts the localized behavior of 4f electrons in lanthanide atoms for the calculation of band gaps, electronic, magnetic and optical properties. All compounds are stable in ferromagnetic phase except KLuS2, while KLuS2 is a non-magnetic semiconductor because there is no unpaired f-electron. Band gaps of KMS2 are estimated and these materials are found to be wide band gap semiconductors. These materials absorb mainly ultraviolet (UV) radiations, which make them good photoluminescent materials with a strong dependence on the direction of the polarization of incident photons.
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).
Zhao, Ting; Wang, Yu-An; Zhao, Zong-Yan; Liu, Qiang; Liu, Qing-Ju
2018-01-01
In order to explore the similarity, difference, and tendency of binary copper-based chalcogenides, the crystal structure, electronic structure, and optical properties of eight compounds of Cu2Q and CuQ (Q = O, S, Se, and Te) have been calculated by density functional theory with HSE06 method. According to the calculated results, the electronic structure and optical properties of Cu2Q and CuQ present certain similarities and tendencies, with the increase of atomic number of Q elements: the interactions between Cu-Q, Cu-Cu, and Q-Q are gradually enhancing; the value of band gap is gradually decreasing, due to the down-shifting of Cu-4p states; the covalent feature of Cu atoms is gradually strengthening, while their ionic feature is gradually weakening; the absorption coefficient in the visible-light region is also increasing. On the other hand, some differences can be found, owing to the different crystal structure and component, for example: CuO presents the characteristics of multi-band gap, which is very favorable to absorb infrared-light; the electron transfer in CuQ is stronger than that in Cu2Q; the absorption peaks and intensity are very strong in the ultraviolet-light region and infrared-light region. The findings in the present work will help to understand the underlying physical mechanism of binary copper-based chalcogenides, and available to design novel copper-based chalcogenides photo-electronics materials and devices.
Directory of Open Access Journals (Sweden)
D. H. Galván
2015-01-01
Full Text Available Fully relativistic full-potential density functional calculations with an all-electron linearized augmented plane waves plus local orbitals method were carried out to perform a comparative study on the structural and electronic properties of the cubic oxide δ-Bi2O3 phase, which is considered as one of the most promising materials in a variety of applications including fuel cells, sensors, and catalysts. Three different density functionals were used in our calculations, LDA, the GGA scheme in the parametrization of Perdew, Burke, and Ernzerhof (PBE96, and the hybrid scheme of Perdew-Wang B3PW91. The examined properties include lattice parameter, band structure and density of states, and charge density profiles. For this modification the three functionals reveal the characteristics of a metal and the existence of minigaps at high symmetry points of the band structure when spin-orbit coupling is taken into account. Density of states exhibits hybridization of Bi 6s and O 2p orbitals and the calculated charge density profiles exhibit the ionic character in the chemical bonding of this compound. The B3PW91 hybrid functional provided a better agreement with the experimental result for the lattice parameter, revealing the importance of Hartree-Fock exchange in this compound.
Energy Technology Data Exchange (ETDEWEB)
Rached, H. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences exactes, Université Djillali Liabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Rached, D., E-mail: rachdj@yahoo.fr [Laboratoire des Matériaux Magnétiques, Faculté des Sciences exactes, 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); Abidri, B.; Rabah, M.; Benkhettou, N. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences exactes, Université Djillali Liabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Omran, S. Bin [Department of Physics and Astronomy, College of Science, King Saud University, P.O.Box 2455, Riyadh 11451 (Saudi Arabia)
2015-04-01
The structural stabilities, electronic and magnetic properties of Co{sub 2−x}Cr{sub x}MnAl alloys with (x=0,1 and 2) were investigated using the full-potential linear muffin-tin orbital (FP-LMTO) method, in the framework of the density functional theory (DFT) within the generalized gradient approximation (GGA) for the exchange correlation functional. The ground state properties including lattice parameter, bulk modulus for the two considered crystal structures Hg{sub 2}CuTi-Type (X-Type) and Cu{sub 2}MnAl-Type (L2{sub 1}-Type) are calculated. The half-metallicity within ferromagnetic ground state starts to appear in CoCrMnAl and Cr2MnAl. In the objective for the proposition of the new HM-FM in the Full-Heusler alloys, our results classified CoCrMnAl as new HM-FM material with high spin polarization. - Highlights: • Based on DFT calculations, Co2-xCrxMnAl Heusler alloys have been investigated. • The magnetic phase stability was determined from the total energy calculations. • The LMTO calculations have classified CoCrMnAl as new HM-FM material with high spin polarization.
Ahuja, Babu Lal; Sharma, Sonu; Heda, Narayan Lal; Tiwari, Shailja; Kumar, Kishor; Meena, Bhoor Singh; Bhatt, Samir
2016-05-01
We present the first-ever experimental Compton profiles (CPs) of Sc2O3 and Y2O3 using 740 GBq 137Cs Compton spectrometer. The experimental momentum densities have been compared with the theoretical CPs computed using linear combination of atomic orbitals (LCAO) within density functional theory (DFT). Further, the energy bands, density of states (DOS) and Mulliken's population (MP) data have been calculated using LCAO method with different exchange and correlation approximations. In addition, the energy bands, DOS, valence charge density (VCD), dielectric function, absorption coefficient and refractive index have also been computed using full potential linearized augmented plane wave (FP-LAPW) method with revised functional of Perdew-Becke-Ernzerhof for solids (PBEsol) and modified Becke Johnson (mBJ) approximations. Both the ab-initio calculations predict wide band gaps in Sc2O3 and Y2O3. The band gaps deduced from FP-LAPW (with mBJ) are found to be close to available experimental data. The VCD and MP data show more ionic character of Sc2O3 than Y2O3. The ceramic properties of both the sesquioxides are explained in terms of their electronic and optical properties.
Energy Technology Data Exchange (ETDEWEB)
Lamouri, R.; Tadout, M. [Materials and Nanomaterials Center, MAScIR Foundation, Rabat Design Center, Rue Mohamed Al Jazouli – Madinat Al Irfane, Rabat 10 100 (Morocco); LaMCScI (ex LMPHE), B.P. 1014, Faculty of Science-Mohammed V University, Rabat (Morocco); Hamedoun, M. [Materials and Nanomaterials Center, MAScIR Foundation, Rabat Design Center, Rue Mohamed Al Jazouli – Madinat Al Irfane, Rabat 10 100 (Morocco); Benyoussef, A. [Materials and Nanomaterials Center, MAScIR Foundation, Rabat Design Center, Rue Mohamed Al Jazouli – Madinat Al Irfane, Rabat 10 100 (Morocco); LaMCScI (ex LMPHE), B.P. 1014, Faculty of Science-Mohammed V University, Rabat (Morocco); Hassan II Academy of Science and Technology, Rabat (Morocco); Ez-zahraouy, H.; Benaissa, M. [LaMCScI (ex LMPHE), B.P. 1014, Faculty of Science-Mohammed V University, Rabat (Morocco); Mounkachi, O., E-mail: o.mounkachi@mascir.com [Materials and Nanomaterials Center, MAScIR Foundation, Rabat Design Center, Rue Mohamed Al Jazouli – Madinat Al Irfane, Rabat 10 100 (Morocco)
2017-08-15
Highlights: • SnFe{sub 2}O{sub 4} a new half-metal spinel oxides for spintronic application. • The most stable normal spinel structures are identified for SnFe{sub 2}O{sub 4}. • Spin-polarized calculations give a half-metallic character for SnFe{sub 2}O{sub 4}. - Abstract: In this work, a study of the electronic and magnetic properties of SnFe{sub 2}O{sub 4} spinel ferrite for different case of octahedral and tetrahedral distribution was carried out by using the Full Potential Linearized Plane Wave (FP-LAPW) method in density functional theory (DFT) implemented in the WIEN2K package, with the generalized gradient (GGA) and Tran-Blaha modified Becke-Johnson approximations for the exchange and correlation functional. Our spin-polarized calculations based on mBJ correction show a half metallic behavior for SnFe{sub 2}O{sub 4} which confirm the usefulness of SnFe{sub 2}O{sub 4} in spintronic application. From the magnetic properties calculations, it is found that the magnetic moment per formula unit is 8.0327 µ{sub β}, 0.000015 µ{sub β} and 3.99µ{sub β} in SnFe{sub 2}O{sub 4} 100% normal, 100% inverse and 50% inverse, respectively.
Datta, Soumendu; Raychaudhuri, A. K.; Saha-Dasgupta, Tanusri
2017-04-01
Using spin polarized density functional theory based calculations, combined with ab initio molecular dynamics simulation, we carry out a systematic investigation of the bimetallic Ni13-nAgn nano-clusters, for all compositions. This includes prediction of the geometry, mixing behavior, and electronic properties. Our study reveals a tendency towards the formation of a core-shell like structure, following the rule of putting Ni in a high coordination site and Ag in a low coordination site. Our calculations predict negative mixing energies for the entire composition range, indicating mixing to be favored for the bimetallic small sized Ni-Ag clusters, irrespective of the compositions. The magic composition with the highest stability is found for the NiAg12 alloy cluster. We investigate the microscopic origin of a core-shell like structure with negative mixing energy, in which the Ni-Ag inter-facial interaction is found to play a role. We also study the magnetic properties of the Ni-Ag alloy clusters. The Ni dominated magnetism consists of parallel alignment of Ni moments while the tiny moments on Ag align in anti-parallel to Ni moments. The hybridization with the Ag environment causes reduction of Ni moment.
Xue, Dong; Myles, Charles
2015-03-01
We have performed first-principles calculations of the vibrational and thermal properties of the semiconductor clathrates RbxGaxSn136-x and CsxGaxSn136-x for x = 8, 16, and 24. Our calculations used the VASP code to obtain the equilibrium geometries and the PHONOPY code to obtain the harmonic phonon modes. For x = 24, the phonon dispersion relations predict an upshift of the low-lying optical modes (<30cm-1) in the presence of the light guest (``rattler'') Rb. We also find large isotropic atomic displacement parameters (Uiso) when the Rb occupies the large cages (Sn28) . The modes associated with these guests should contribute strongly to lowering the lattice thermal conductivity (kL) . This is reinforced by our evaluation of the guest-associated effective potential energy curves E(x). Our calculated effective harmonic spring constants K for these guests show that a simple harmonic oscillator model is in good agreement with the first principles lattice dynamical calculations. The similarity between ωos = (K/M)1/2 and our computed guest phonon frequencies implies that anharmonic contributions to the guest vibrational modes are not significant. Our calculations of the vibrational contribution to the specific heat and our estimation of kLare also presented and discussed.
Shulenburger, Luke
2015-11-01
MgO is a major constituent of Earth's mantle, the rocky cores of gas giants and is a likely component of the interiors of many exoplanets. The high pressure - high temperature behavior of MgO directly affects equation of state models for planetary structure and formation. In this work, we examine MgO under extreme conditions using experimental and theoretical methods to determine the phase diagram and transport properties. Using plate impact experiments on Sandia's Z facility a low entropy solid-solid phase transition from B1 to B2 is clearly determined. The melting transition, on the other hand, is subtle, involving little to no signal in us-up space. Theoretical work utilizing density functional theory (DFT) provides a complementary picture of the phase diagram. The solid-solid phase transition is identified through a series of quasi-harmonic phonon calculations and thermodynamic integration, while the melt boundary is found using phase coexistence calculations. The calculation of reflectivity along the Hugoniot and the influence of the ionic structure on the transport properties requires particular care because of the underestimation of the band gap and attendant overestimation of transport properties due to the use of semi-local density functional theory. We will explore the impact of this theoretical challenge and its potential solutions in this talk. Finally, understanding the behavior of MgO as the pressure releases from the Hugoniot state is a key ingredient to modeling giant impact events. We explore this regime both through additional DFT calculations and by observing the release state of the MgO into lower impedance materials. The integrated use of DFT simulations and high-accuracy shock experiments together provide a comprehensive understanding of MgO under extreme conditions. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U
Temperature-dependent elastic properties of Ti1−xAlxN alloys
International Nuclear Information System (INIS)
Shulumba, Nina; Hellman, Olle; Rogström, Lina; Raza, Zamaan; Tasnádi, Ferenc; Odén, Magnus; Abrikosov, Igor A.
2015-01-01
Ti 1−x Al x N is a technologically important alloy that undergoes a process of high temperature age-hardening that is strongly influenced by its elastic properties. We have performed first principles calculations of the elastic constants and anisotropy using the symmetry imposed force constant temperature dependent effective potential method, which include lattice vibrations and therefore the effects of temperature, including thermal expansion and intrinsic anharmonicity. These are compared with in situ high temperature x-ray diffraction measurements of the lattice parameter. We show that anharmonic effects are crucial to the recovery of finite temperature elasticity. The effects of thermal expansion and intrinsic anharmonicity on the elastic constants are of the same order, and cannot be considered separately. Furthermore, the effect of thermal expansion on elastic constants is such that the volume change induced by zero point motion has a significant effect. For TiAlN, the elastic constants soften non-uniformly with temperature: C 11 decreases substantially when the temperature increases for all compositions, resulting in an increased anisotropy. These findings suggest that an increased Al content and annealing at higher temperatures will result in a harder alloy
International Nuclear Information System (INIS)
Araujo, Rafael B.; Almeida, J. S. de; Ferreira da Silva, A.
2013-01-01
In this work, we use density functional theory to investigate the influence of semilocal exchange and correlation effects on the electronic properties of III-nitride semiconductors considering zinc-blende and wurtzite crystal structures. We find that the inclusion of such effects through the use of the Tran-Blaha modified Becke-Johnson potential yields an excellent description of the electronic structures of these materials giving energy band gaps which are systematically larger than the ones obtained with standard functionals such as the generalized gradient approximation. The discrepancy between the experimental and theoretical band gaps is then significantly reduced with semilocal exchange and correlation effects. However, the effective masses are overestimated in the zinc-blende nitrides, but no systematic trend is found in the wurtzite compounds. New results for energy band gaps and effective masses of zinc-blende and wurtzite indium nitrides are presented
International Nuclear Information System (INIS)
Bouchani, A.; Arabi, H.; Abolhasani, M. R.
2007-01-01
The electronic and structural properties of both zinc-blende and wurtzite phases of In N were investigated by using full potential augmented plane wave method within density functional theory. For exchange correlation potential, local density approximation, generalized gradient approximation and an alternative form of generalized gradient approximation proposed by Engel and Vosko (EV-generalized gradient approximation ) have been used. Results obtained for band structure of these compounds have been compared with experimental results as well as other theoretical work and closer to experimental data. The lattice constants, bulk modulus are calculated for each of both phases. We have also investigated the structural transitions of In N and have calculated the transition pressure between zinc-blende and rock salt phases.
Elastic and transport properties of topological semimetal ZrTe
Guo, San-Dong; Wang, Yue-Hua; Lu, Wan-Li
2017-11-01
Topological semimetals may have substantial applications in electronics, spintronics, and quantum computation. Recently, ZrTe was predicted as a new type of topological semimetal due to the coexistence of Weyl fermions and massless triply degenerate nodal points. In this work, the elastic and transport properties of ZrTe are investigated by combining the first-principles calculations and semiclassical Boltzmann transport theory. Calculated elastic constants prove the mechanical stability of ZrTe, and the bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio also are calculated. It is found that spin-orbit coupling (SOC) has slightly enhanced effects on the Seebeck coefficient, which along the a(b) and c directions for pristine ZrTe at 300 K is 46.26 μVK-1 and 80.20 μVK-1, respectively. By comparing the experimental electrical conductivity of ZrTe (300 K) with the calculated value, the scattering time is determined as 1.59 × 10-14 s. The predicted room-temperature electronic thermal conductivity along the a(b) and c directions is 2.37 {{Wm}}-1{{{K}}}-1 and 2.90 {{Wm}}-1{{{K}}}-1, respectively. The room-temperature lattice thermal conductivity is predicted as 17.56 {{Wm}}-1{{{K}}}-1 and 43.08 {{Wm}}-1{{{K}}}-1 along the a(b) and c directions, showing very strong anisotropy. Calculated results show that isotope scattering produces an observable effect on lattice thermal conductivity. To observably reduce lattice thermal conductivity by nanostructures, the characteristic length should be smaller than 70 nm, based on cumulative lattice thermal conductivity with respect to the phonon mean free path (MFP) at 300 K. It is noted that the average room-temperature lattice thermal conductivity of ZrTe is slightly higher than that of isostructural MoP, which is due to larger phonon lifetimes and smaller Grüneisen parameters. Finally, the total thermal conductivity as a function of temperature is predicted for pristine ZrTe. Our works provide valuable
Yurtsever, Ayhan; Fernández-Torre, Delia; Onoda, Jo; Abe, Masayuki; Morita, Seizo; Sugimoto, Yoshiaki; Pérez, Rubén
2017-05-11
Noble metal nanostructures dispersed on metal oxide surfaces have applications in diverse areas such as catalysis, chemical sensing, and energy harvesting. Their reactivity, chemical selectivity, stability, and light absorption properties are controlled by the interactions at the metal/oxide interface. Single-atom metal adsorbates on the rutile TiO 2 (110)-(1 × 1) surface have become a paradigmatic model to characterize those interactions and to understand the unique electronic properties of these supported nanostructures. We combine Kelvin probe force microscopy (KPFM) experiments and density functional theory (DFT) calculations to investigate the atomic-scale variations in the contact potential difference of individual Pt atoms adsorbed on a hydroxylated (h) TiO 2 (110)-(1 × 1) surface. Our experiments show a significant drop in the local contact potential difference (LCPD) over Pt atoms with respect to the TiO 2 surface, supporting the presence of an electron transfer from the Pt adsorbates to the substrate. We have identified two characteristic regimes by LCPD spectroscopy. At far tip-sample distances, LCPD values show a weak distance dependence and can be attributed to the intrinsic charge transfer from Pt to the oxide support. Beyond the onset of short-range chemical interactions, LCPD values exhibit a strong distance dependence that we ascribe to the local structural and charge rearrangements induced by the tip-sample interaction. These findings also apply to other electropositive adsorbates such as potassium and the hydrogen atoms forming the OH groups that are present on the h-TiO 2 (110) surface, promoting KPFM as a suitable tool for the understanding of electron transfer in catalytically active materials.
Energy Technology Data Exchange (ETDEWEB)
Song, Ting [State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals, Lanzhou University of Technology, Lanzhou 730050 (China); School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); Ma, Qin, E-mail: maqin_lut@yeah.net [State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals, Lanzhou University of Technology, Lanzhou 730050 (China); Sun, Xiao-Wei [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); Liu, Zi-Jiang [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); Department of Physics, Lanzhou City University, Lanzhou 730070 (China); Wei, Xiao-Ping [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); Tian, Jun-Hong [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China)
2017-02-15
First-principles calculations based on density functional theory and quasi-harmonic Debye model are used to investigate the high-pressure and high-temperature physical properties, including the lattice constant, magnetic moment, density of states, pressure-volume-temperature relationship, bulk modulus, thermal expansivity, heat capacity, and Grüneisen parameter for the new Mn-based full-Heusler alloy Mn{sub 2}RuSi in CuHg{sub 2}Ti-type structure. The optimized equilibrium lattice constant is consistent with experimental and other theoretical results. The calculated total spin magnetic moment remains an integral value of 2.0 μ{sub B} in the lattice constant range of 5.454–5.758 Å, and then decreases very slowly with the decrease of lattice constant to 5.333 Å. By the spin resolved density of states calculations, we have shown that Mn{sub 2}RuSi compound presents half-metallic ferrimagnetic properties under the equilibrium lattice constant. The effects of temperature and pressure on bulk modulus, thermal expansivity, heat capacity, and Grüneisen parameter are opposite, which are consistent with a compression rate of volume. Furthermore, the results show that the effect of temperature is larger than pressure for heat capacity and the effect of high temperature and pressure on thermal expansion coefficient is small. All the properties of Mn{sub 2}RuSi alloy are summarized in the pressure range of 0–100 GPa and the temperature up to 1200 K. - Highlights: • High-pressure and high-temperature physical properties of Mn2RuSi were investigated. • Ferrimagnetic ground state has been confirmed in Mn2RuSi alloy. • The first-principle calculations and quasi-harmonic Debye model were used. • The pressure up to 100 GPa and the temperature up to 1200 K.
First-principles-based Landau energy functionals for perovskite ferroelectrics
Pitike, Krishna Chaitanya; Gadigi, Neha; Mangeri, John; Cooper, Valentino; Nakhmanson, Serge
ABO3 perovskite-oxide ferroelectrics are well known for their useful functional properties. These materials, as well as their solid solutions, exhibit rich phase diagrams that can be exploited, e.g., to obtain large piezoelectric and dielectric responses. Mesoscale-level investigations of their behavior usually utilize Landau phenomenological theory, where the system energy functional is represented by a polynomial expansion in powers of polarization and strain that is parameterized from experimental data. In this project, we present an approach for fitting the Landau functionals for perovskite ferroelectrics directly from first principles simulations with the help of statistical and machine learning tools. Initial data sets are created by computing the energies for a wide range of possible structural configurations involving polar and elastic distortions with standard density-functional theory (DFT) codes. A small fraction of this data is then processed by supervised machine learning algorithms to train a Landau-style polynomial model that can predict the system energies to within 20 meV of the DFT results. KCP and SMN are thankful to the NSF (DMR 1309114) for partial funding. KCP also acknowledges the support from the ASTRO program at ORNL. VRC was supported by the U.S. DOE, MSED and the Office of Science Early Career Research Program.
Exciton multiplication from first principles.
Jaeger, Heather M; Hyeon-Deuk, Kim; Prezhdo, Oleg V
2013-06-18
-phonon energy relaxation. Multiple excitons are generated through impact ionization within picoseconds. The basis of exciton multiplication in quantum dots is the collective result of photoexcitation, dephasing, and nonadiabatic evolution. Each process is characterized by a distinct time-scale, and the overall multiple exciton generation dynamics is complete by about 10 ps. Without relying on semiempirical parameters, we computed quantum mechanical probabilities of multiple excitons for small model systems. Because exciton correlations and coherences are microscopic, quantum properties, results for small model systems can be extrapolated to larger, realistic quantum dots.
Phuc, Huynh V.; Hieu, Nguyen N.; Hoi, Bui D.; Phuong, Le T. T.; Nguyen, Chuong V.
2018-02-01
In the present work, electronic properties and Schottky contact of graphene adsorbed on the MoS2 monolayer under applied out-plane strain are studied using density functional theory calculations. Our calculations show that weak van derpp Waals interactions between graphene and monolayer MoS2 are dominated at the interlayer distance of 3.34 Å and the binding energy per C atom of - 25.1 meV. A narrow band gap of 3.6 meV has opened in G/MoS2 heterointerface, and it can be modulated by the out-plane strain. Furthermore, the Schottky barrier and Schottky contact types in the G/MoS2 heterointerface can be controlled by the out-plane strain. At the equilibrium state (d = 3.34 Å), the intrinsic electronic structure of G/MoS2 heterointerface is well preserved and forms an n-type Schottky barrier of 0.49 eV. When the interlayer distance decreases, the transition from n-type to p-type Schottky contact occurs at d = 2.74 Å. Our studies promote the application of ultrathin G/MoS2 heterointerface in the next-generation nanoelectronic and photonic devices such as van-der-Waals-based field effect transistors.
Energy Technology Data Exchange (ETDEWEB)
Khatta, Swati; Tripathi, S.K.; Prakash, Satya [Panjab University, Central of Advanced Study in Physics, Department of Physics, Chandigarh (India)
2017-09-15
The spin-polarised density functional theory along with self-consistent plane-wave pseudopotential is used to investigate the half-metallic ferromagnetic properties of ternary alloys Zn{sub 1-x}V{sub x}Se. The generalized gradient approximation is used for exchange-correlation potential. The equilibrium lattice constants, bulk modulus, and its derivatives are calculated. The calculated spin-polarised energy-band structures reveal that these alloys are half-metallic for x = 0.375 and 0.50 and nearly half-metallic for other values of x. The estimated direct and indirect bandgaps may be useful for the magneto-optical absorption experiments. It is found that there is strong Zn 4s, Se 4p, and V 3d orbital hybridization in the conduction bands of both the spins, while Se 4p and V 3d orbital hybridization predominates in the valence bands of both the spins. The s, p-d, and p-d orbital hybridization reduces the local magnetic moment of V atoms and small local magnetic moments are produced on Zn and Se atoms which get coupled with V atoms in ferromagnetic and antiferromagnetic phases, respectively. The conduction and valence-band-edge splittings and exchange constants predict the ferromagnetism in these alloys. The conduction band-impurity (s and p-d) exchange interaction is more significant for ferromagnetism in these alloys than the valence band-impurity (p-d) exchange interaction. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Deluque Toro, C.E., E-mail: deluquetoro@gmail.com [Grupo de Nuevos Materiales, Universidad Popular del Cesar, Valledupar (Colombia); Rodríguez M, Jairo Arbey [Grupo de Estudios de Materiales—GEMA, Departamento de Física, Universidad Nacional de Colombia, AA 5997 Bogotá DC (Colombia); Landínez Téllez, D.A. [Grupo de Física de Nuevos Materiales, Departamento de Física, Universidad Nacional de Colombia, AA 5997 Bogotá DC (Colombia); Moreno Salazar, N.O. [Departamento de Física, Universidade Federal de Sergipe (Brazil); Roa-Rojas, J. [Grupo de Física de Nuevos Materiales, Departamento de Física, Universidad Nacional de Colombia, AA 5997 Bogotá DC (Colombia)
2014-12-15
The Ba{sub 2}YTaO{sub 6} double perovskite presents a transition from cubic (Fm−3m) to tetragonal structure (I4/m) at high temperature. In this work, we present a detailed study of the structural and electronic properties of the double perovskite Ba{sub 2}YTaO{sub 6} in space group Fm−3m and I4/m. Calculations were made with the Full-Potential Linear Augmented Plane Wave method (FP-LAPW) within the framework of the Density Functional Theory (DFT) with exchange and correlation effects in the Generalized Gradient (GGA) and Local Density (LDA) approximations. From the minimization of energy as a function of volume and the fitting of the Murnaghan equation some structural characteristics were determined as, for example, total energy, lattice parameter (a=8.50 Å in cubic phase and a=5.985 Å and c=8.576 Å in tetragonal), bulk modulus (135.6 GPa in cubic phase and 134.1 GPa in tetragonal phase) and its derivative. The study of the electronic characteristics was performed from the analysis of the electronic density of states (DOS). We find a non-metallic behavior for this with a direct band gap of approximately 3.5 eV and we found that the Ba{sub 2}YTaO{sub 6} (I4/m) phase is the most stable one. {sup ©} 2013 Elsevier Science. All rights reserved.
Harb, Moussab
2013-08-29
Density functional theory (DFT) and density functional perturbation theory (DFPT) were applied to study the structural, electronic, and optical properties of a (Na2-xCux)Ta4O11 solid solution to accurately calculate the band gap and to predict the optical transitions in these materials using the screened coulomb hybrid (HSE06) exchange-correlation formalism. The calculated density of states showed excellent agreement with UV-vis diffuse reflectance spectra predicting a significant red-shift of the band gap from 4.58 eV (calculated 4.94 eV) to 2.76 eV (calculated 2.60 eV) as copper content increased from 0 to 83.3%. The band gap narrowing in these materials, compared to Na2Ta4O11, results from the incorporation of new occupied electronic states, which are strongly localized on the Cu 3d orbitals, and is located within 2.16-2.34 eV just above the valence band of Na2Ta4O11. These new occupied states, however, possess an electronic character localized on Cu, which makes hole mobility limited in the semiconductor. © 2013 American Chemical Society.
Aimouch, D. E.; Meskine, S.; Boukortt, A.; Zaoui, A.
2018-04-01
In this study, structural, electronic and magnetic properties of Mn doped (ZnO:Mn) and (Mn,Cr) co-doped zinc oxide (ZnO:(Mn,Cr)) have been calculated with the FP-LAPW method by using the LSDA and LSDA+U approximations. Going through three configurations of Mn,Cr co-doped ZnO corresponding to three different distances between manganese and chromium, we have analyzed that ZnO:(Mn,Cr) system is more stable in its preferred configuration2. The lattice constant of undoped ZnO that has been calculated in this study is in a good agreement with the experimental and theoretical values. It was found to be increased by doping with Mn or (Mn,Cr) impurities. The band structure calculations showed the metallic character of Mn doped and Mn,Cr co-doped ZnO. As results, by using LSDA+U (U = 6eV), we show the half-metallic character of ZnO:Mn and ZnO:Mn,Cr. We present the calculated exchange couplings d-d of Mn doped ZnO which is in a good agreement with the former FPLO calculation data and the magnetization step measurement of the experimental work. The magnetic coupling between neighboring Mn impurities in ZnO is found to be antiferromagnetic. In the case of (Mn,Cr) co-doped ZnO, the magnetic coupling between Mn and Cr impurities is found to be antiferromagnetic for configuration1 and 3, and ferromagnetic for configuration2. Thus, the ferromagnetic coupling is weak in ZnO:Mn. Chromium co-doping greatly enhance the ferromagnetism, especially when using configuration2. At last, we present the 2D and 3D spin-density distribution of ZnO:Mn and ZnO:(Mn,Cr) where the ferromagnetic state in ZnO:(Mn,Cr) comes from the strong p-d and d-d interactions between 2p-O, 3d-Mn and 3d-Cr electrons. The results of our calculations suggest that the co-doping ZnO(Mn, Cr) can be among DMS behavior for spintronic applications.
Methods for First-Principles Alloy Thermodynamics
van de Walle, Axel
2013-11-01
Traditional first-principles calculations excel at providing formation energies at absolute zero, but obtaining thermodynamic information at nonzero temperatures requires suitable sampling of all the excited states visited in thermodynamic equilibrium, which would be computationally prohibitive via brute-force quantum mechanical calculations alone. In the context of solid-state alloys, this issue can be addressed via the coarse-graining concept and the cluster expansion formalism. This process generates simple, effective Hamiltonians that accurately reproduce quantum mechanical calculation results and that can be used to efficiently sample configurational, vibrational, and electronic excitations and enable the prediction of thermodynamic properties at nonzero temperatures. Vibrational and electronic degrees of freedom are formally eliminated from the problem by writing the system's partition function in a nested form in which the inner sums can be readily evaluated to yield an effective Hamiltonian. The remaining outermost sum corresponds to atomic configurations and can be handled via Monte Carlo sampling driven by the resulting effective Hamiltonian, thereby delivering thermodynamic properties at nonzero temperatures. This article describes these techniques and their implementation in the alloy theoretic automated toolkit, an open-source software package. The methods are illustrated by applications to various alloy systems.
Electronic, elastic, optical properties of rutile TiO2 under pressure: A DFT study
International Nuclear Information System (INIS)
Mahmood, Tariq; Cao, Chuanbao; Khan, Waheed S.; Usman, Zahid; Butt, Faheem K.; Hussain, Sajad
2012-01-01
The electronic, elastic constants and optical properties of rutile TiO 2 have been investigated using first principle pseudopotential method within generalized gradient approximation (GGA) proposed by Perdew-Burke-Ernzerhof (PBE). The calculated volume, bulk modulus and pressure derivative of bulk modulus are in good agreement with previous experimental and computational results. An underestimated band gap (1.970 eV) along with the higher density of states and expanded energy bands around the fermi level is obtained. Calculated elastic constants satisfying the Born stability criteria suggest that rutile TiO 2 is mechanically stable under higher hydrostatic pressure. The acoustic wave speeds in [1 0 0], [0 1 0], [0 0 1], [1 1 0] and [45° to [1 0 0] and [0 0 1
Theoretical study of elastic, mechanical and thermodynamic properties of MgRh intermetallic compound
Directory of Open Access Journals (Sweden)
S. Boucetta
2014-03-01
Full Text Available In the last years, Magnesium alloys are known to be of great technological importance and high scientific interest. In this work, density functional theory plane-wave pseudo potential method, with local density approximation (LDA and generalized gradient approximation (GGA are used to perform first-principles quantum mechanics calculations in order to investigate the structural, elastic and mechanical properties of the intermetallic compound MgRh with a CsCl-type structure. Comparison of the calculated equilibrium lattice constant and experimental data shows good agreement. The elastic constants were determined from a linear fit of the calculated stress–strain function according to Hooke's law. From the elastic constants, the bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio σ, anisotropy factor A and the ratio B/G for MgRh compound are obtained. The sound velocities and Debye temperature are also predicted from elastic constants. Finally, the linear response method has been used to calculate the thermodynamic properties. The temperature dependence of the enthalpy H, free energy F, entropy S, and heat capacity at constant volume Cv of MgRh crystal in a quasi-harmonic approximation have been obtained from phonon density of states and discussed for the first report. This is the first quantitative theoretical prediction of these properties.
Elastic and mechanical properties of lanthanide monoxides
Energy Technology Data Exchange (ETDEWEB)
Shafiq, M. [Center for Computational Materials Science, University of Malakand, Chakdara (Pakistan); Department of Physics, University of Malakand, Chakdara (Pakistan); Arif, Suneela [Department of Physics, Hazara University, Mansehra (Pakistan); Ahmad, Iftikhar, E-mail: ahma5532@gmail.com [Center for Computational Materials Science, University of Malakand, Chakdara (Pakistan); Department of Physics, University of Malakand, Chakdara (Pakistan); Asadabadi, S. Jalali [Department of Physics, Faculty of Science, University of Isfahan, Hezar Gerib Avenue, Isfahan 81744 (Iran, Islamic Republic of); Maqbool, M. [Department of Physics and Astronomy, Ball State University, Muncie, IN 47306 (United States); Rahnamaye Aliabad, H.A. [Department of Physics, Hakim Sabzevari University, Sabzevar (Iran, Islamic Republic of)
2015-01-05
Highlights: • Elastic, mechanical and thermal properties of rare-earth lanthanide monoxide are theoretically investigated. • Higher values of Young’s modulus indicate that these compounds are stiffer. • These compounds show anisotropic character and also show resistance against deforming force due to compressible character. • These mechanically stable materials can be effectively used for practical applications. - Abstract: In this article we communicate theoretical results of the mechanical properties of lanthanide monoxide LnO (Ln = La, Ce, Pr, Nd, Sm, Eu, Tb, Ho, Er and Yb) i.e., bulk modulus, shear modulus, Young’s modulus, anisotropic ratio, Kleinman parameters, Poisson’s ratio, Lame’s coefficients, sound velocities for shear and longitudinal waves, and Debye temperature. Cauchy pressure and B/G ratio are also investigated to explore the ductile and brittle nature of these compounds. The calculations are performed with the density functional theory based full potential linearized augmented plane waves (FP-LAPW) method. The calculated results reveal that lanthanide based monoxides are mechanically stable and possess good resistive power against elastic deformations. Therefore, these mechanically stable materials can effectively be used for practical applications. The computed DOSs shows the metallic character of these compounds. Contour plots of the electron charge densities are also computed to reveal the nature of bonding in these compounds.
First-principles calculations of mobility
Krishnaswamy, Karthik
First-principles calculations can be a powerful predictive tool for studying, modeling and understanding the fundamental scattering mechanisms impacting carrier transport in materials. In the past, calculations have provided important qualitative insights, but numerical accuracy has been limited due to computational challenges. In this talk, we will discuss some of the challenges involved in calculating electron-phonon scattering and carrier mobility, and outline approaches to overcome them. Topics will include the limitations of models for electron-phonon interaction, the importance of grid sampling, and the use of Gaussian smearing to replace energy-conserving delta functions. Using prototypical examples of oxides that are of technological importance-SrTiO3, BaSnO3, Ga2O3, and WO3-we will demonstrate computational approaches to overcome these challenges and improve the accuracy. One approach that leads to a distinct improvement in the accuracy is the use of analytic functions for the band dispersion, which allows for an exact solution of the energy-conserving delta function. For select cases, we also discuss direct quantitative comparisons with experimental results. The computational approaches and methodologies discussed in the talk are general and applicable to other materials, and greatly improve the numerical accuracy of the calculated transport properties, such as carrier mobility, conductivity and Seebeck coefficient. This work was performed in collaboration with B. Himmetoglu, Y. Kang, W. Wang, A. Janotti and C. G. Van de Walle, and supported by the LEAST Center, the ONR EXEDE MURI, and NSF.
Urban growth simulation from ``first principles''
Andersson, Claes; Lindgren, Kristian; Rasmussen, Steen; White, Roger
2002-08-01
General and mathematically transparent models of urban growth have so far suffered from a lack in microscopic realism. Physical models that have been used for this purpose, i.e., diffusion-limited aggregation, dielectric breakdown models, and correlated percolation all have microscopic dynamics for which analogies with urban growth appear stretched. Based on a Markov random field formulation we have developed a model that is capable of reproducing a variety of important characteristic urban morphologies and that has realistic microscopic dynamics. The results presented in this paper are particularly important in relation to ``urban sprawl,'' an important aspect of which is aggressively spreading low-density land uses. This type of growth is increasingly causing environmental, social, and economical problems around the world. The microdynamics of our model, or its ``first principles,'' can be mapped to human decisions and motivations and thus potentially also to policies and regulations. We measure statistical properties of macrostates generated by the urban growth mechanism that we propose, and we compare these to empirical measurements as well as to results from other models. To showcase the open-endedness of the model and to thereby relate our work to applied urban planning we have also included a simulated city consisting of a large number of land use classes in which also topographical data have been used.
Energy Technology Data Exchange (ETDEWEB)
Gao, Ning; Quan, Chuye [Key Laboratory for Organic Electronics & Information Displays (KLOEID), Synergetic Innovation Center for Organic Electronics and Information Displays (SICOEID), Institute of Advanced Materials - IAM, School of Materials Science and Engineering - SMSE, Nanjing University of Posts and Telecommunications - NUPT, Nanjing 210023 (China); Ma, Yuhui [Key Laboratory for Organic Electronics & Information Displays (KLOEID), Synergetic Innovation Center for Organic Electronics and Information Displays (SICOEID), Institute of Advanced Materials - IAM, School of Materials Science and Engineering - SMSE, Nanjing University of Posts and Telecommunications - NUPT, Nanjing 210023 (China); School of Science, Nanjing University of Posts and Telecommunications (NUPT), Nanjing 210023 (China); Key Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials (IAM), National Synergistic Innovation Center for Advanced Materials - SICAM, Nanjing Tech University - Nanjing Tech, 30 South Puzhu Road, Nanjing 211816 (China); Han, Yumin; Wu, Zhenli [Key Laboratory for Organic Electronics & Information Displays (KLOEID), Synergetic Innovation Center for Organic Electronics and Information Displays (SICOEID), Institute of Advanced Materials - IAM, School of Materials Science and Engineering - SMSE, Nanjing University of Posts and Telecommunications - NUPT, Nanjing 210023 (China); Mao, Weiwei [Key Laboratory for Organic Electronics & Information Displays - KLOEID, Synergetic Innovation Center for Organic Electronics and Information Displays (SICOEID), Institute of Advanced Materials (IAM), School of Materials Science and Engineering - SMSE, Nanjing University of Posts and Telecommunications - NUPT, Nanjing 210023 (China); School of Science, Nanjing University of Posts and Telecommunications (NUPT), Nanjing 210023 (China); and others
2016-01-15
We propose first-principles methods to study the structure, electronic, optical and magnetic properties of BiFeO{sub 3} (BFO) and Bi{sub 0.9}Ca{sub 0.1}FeO{sub 3} (BCFO). The morphology, optical band gap as well as magnetic hysteresis also have been investigated using experimental methods. X-ray diffraction data shows that Bi-site doping with Ca could result in a transition of crystal structure (from single phase rhombohedral (R3c) to two phase coexistence). Changing of Fermi level and decreasing of band gap indicating that the Ca-doped BFO exhibit a typical half-metallic nature. The optical absorption properties are related to the electronic structure and play the key role in determining their band gaps, also we have analyzed the inter-band contribution to the theory of optical properties such as absorption spectra, dielectric constant, energy-loss spectrum, absorption coefficient, optical reflectivity, and refractive index of BCFO. Enhancement of magnetic properties after doping is proved by both experimental and calculated result, which can be explained by size effect and structural distortion.
First-principle calculations of the structural, electronic ...
Indian Academy of Sciences (India)
Abstract. 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 ...
First principles calculations of structural, electronic and thermal ...
Indian Academy of Sciences (India)
Home; Journals; Bulletin of Materials Science; Volume 37; Issue 5. First principles calculations of structural, electronic and thermal properties of lead chalcogenides PbS, PbSe and PbTe compounds. N Boukhris H Meradji S Amara Korba S Drablia S Ghemid F El Haj Hassan. Volume 37 Issue 5 August 2014 pp 1159-1166 ...
First-principle calculations of the structural, electronic ...
Indian Academy of Sciences (India)
First-principle calculations were performed to study the structural, electronic, thermodynamic and thermal properties of 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 ...
Magneto-elastic effects and thermodynamic properties of ferromagnetic hcp Co
International Nuclear Information System (INIS)
Kuang, Fang-Guang; Kuang, Xiao-Yu; Kang, Shu-Ying; Mao, Ai-Jie
2014-01-01
Using first principles projector augmented wave (PAW) potential method, the magneto-elastic effects and thermodynamic properties of ferromagnetic hcp Cobalt at high pressure and temperature are investigated. The calculated elastic constants from PBE+U method demonstrate a noticeable improvement with regard to experimental data. Various physical quantities under high pressure also present significant improvements, such as the bulk modulus, shear modulus, Young's modulus, Debye temperature, various sound velocities and the normalized acoustic velocities in the meridian plane. That is due to the fact that Cobalt system possesses large correlation effects. Meanwhile, the phonon dispersion curves are in excellent agreement with experimental data. It is not observed any anomaly or instability under compression. However, according to the E 2g -phonon frequencies, the obtained pressure variation of C 44 elastic modulus also suggests that the system has miraculous magneto-elastic effects. Moreover, the pressure and temperature dependence of thermodynamic properties are derived within the quasi-harmonic approximation for the first time. The obtained Grüneisen ratio, Anderon–Grüneisen parameter and the volume dependence of Grüneisen ratio display manifestly temperature and pressure dependences.
Ma, Xiaoyang; Li, Dechun; Zhao, Shengzhi; Li, Guiqiu; Yang, Kejian
2014-01-01
First-principles calculations based on density functional theory have been performed for the quaternary GaAs1-x-y N x Bi y alloy lattice-matched to GaAs. Using the state-of-the-art computational method with the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, electronic, and optical properties were obtained, including band structures, density of states (DOSs), dielectric function, absorption coefficient, refractive index, energy loss function, and reflectivity. It is found that the lattice constant of GaAs1-x-y N x Bi y alloy with y/x =1.718 can match to GaAs. With the incorporation of N and Bi into GaAs, the band gap of GaAs1-x-y N x Bi y becomes small and remains direct. The calculated optical properties indicate that GaAs1-x-y N x Bi y has higher optical efficiency as it has less energy loss than GaAs. In addition, it is also found that the electronic and optical properties of GaAs1-x-y N x Bi y alloy can be further controlled by tuning the N and Bi compositions in this alloy. These results suggest promising applications of GaAs1-x-y N x Bi y quaternary alloys in optoelectronic devices.
Bijoy, T K; Murugan, P; Kumar, Vijay
2018-03-05
We study the structural stability and electronic properties of new classes of DNA-like inorganic double helices of the type A 2 B 2 XY (A = Si-Pb, B = Cl-I, and XY = PN and SiS) by employing first principles density functional theory (DFT) calculations including van der Waals interactions. In these quaternary double helices PN or SiS forms the inner helix while the AB helix wraps around the inner helix and the two are interconnected. We find that the bromides and iodides of Ge, Sn, and Pb as well as Pb 2 Cl 2 PN form structurally stable double helices while Ge 2 I 2 SiS as well as bromides and iodides of Sn and Pb have stable double helices. The atomic structures of different double helices have been analyzed in detail to understand the stability of these systems as there is up to about 80% difference in the interatomic distances in the two helices which is remarkable. Also in these new classes of double helices there is polar covalent bonding in the inner helix due to heteroatoms. We have calculated the DDEC6 partial atomic charges and bond orders which suggest strong covalent bonding in the inner helix. The electronic structure reveals that these double helices are semiconducting and in many cases the band gap is direct. Furthermore, we have studied the effects of doping and found that hole doping is the most appropriate way to tuning their electronic properties.
Xu, Xin-Yu; Wang, Hui-Yuan; Zha, Min; Wang, Cheng; Yang, Zhi-Zheng; Jiang, Qi-Chuan
2018-04-01
In this study, the structural stability and electronic properties of Al(111)/4H-SiC(0001) interface, as well as the effects of Ti, Si, Mg and Cu additions on the interfacial adhesive strength are investigated via the first-principles method. Surface energy calculations show that 4H-SiC(0001) with C-termination is more active than Si-termination. Moreover, polar covalent bonds are formed across Al/4H-SiC interface. The results of separation energies suggest that the introduction of Ti and Si can improve the adhesive strength of C-terminated Al(111)/4H-SiC(0001) interface, whereas Mg and Cu have the opposite effect. According to the analysis of interfacial electronic structure, the covalent bonds across Al/4H-SiC interface are further enhanced with the addition of Ti and Si atoms, contributing to the improved adhesive strength in this case. However, the interactions between interfacial atoms are weakened with Mg and Cu doped in C-terminated interface, which results in the decrease of interfacial adhesion strength. Our calculations provide a guide to experiments on the design of 4H-SiC reinforced Al-matrix composites with tailored properties.
Quasigluon lifetime and confinement from first principles
Siringo, Fabio
2017-12-01
The mass and the lifetime of a gluon are evaluated from first principles at a finite temperature across the deconfinement transition of pure SU(3) Yang-Mills theory, by a direct calculation of the pole of the propagator in the complex plane, using the finite temperature extension of a massive expansion in the Landau gauge. Even at T =0 , the quasigluon lifetime is finite, and the gluon is canceled from the asymptotic states, yielding a microscopic proof of confinement from first principles. Above the transition, the damping rate is a linear increasing function of temperature as predicted by standard perturbation theory.
Huang, Shuo; Vida, Ádám; Heczel, Anita; Holmström, Erik; Vitos, Levente
2018-02-01
This article was originally published Online First without open access. After publication in volume 69, issue 11, page 2107-2112 the author decided to opt for Open Choice and to make the article an open access publication.
Elastic and microplastic properties of titanium in different structural states
Kardashev, B. K.; Betekhtin, V. I.; Kadomtsev, A. G.; Narykova, M. V.; Kolobov, Yu. R.
2017-09-01
The behavior of elastic (Young's modulus) and microplastic properties of titanium depending on the initial structure and subsequent severe plastic deformation that transforms the material (concerning the grain size) into the submicrocrystalline structural state has been studied. It has been shown that, to a great extent, different initial structures of the metal predetermine its elastic properties after deformation.
Boron nitride elastic and thermal properties. Irradiation effects
International Nuclear Information System (INIS)
Jager, Bernard.
1977-01-01
The anisotropy of boron nitride (BN) and especially thermal and elastic properties were studied. Specific heat and thermal conductivity between 1.2 and 300K, thermal conductivity between 4 and 350K and elastic constants C 33 and C 44 were measured. BN was irradiated with electrons at 77K and with neutrons at 27K to determine properties after irradiation [fr
Elastic properties of superconducting bulk metallic glasses
International Nuclear Information System (INIS)
Hempel, Marius
2015-01-01
Within the framework of this thesis the elastic properties of a superconducting bulk metallic glass between 10 mK and 300 K were first investigated. In order to measure the entire temperature range, in particular the low temperature part, new experimental techniques were developed. Using an inductive readout scheme for a double paddle oscillator it was possible to determine the internal friction and the relative change of sound velocity of bulk metallic glasses with high precision. This allowed for a detailed comparison of the data with different models. The analysis focuses on the low temperature regime where the properties of glassy materials are governed by atomic tunneling systems as described by the tunneling model. The influence of conduction electrons in the normal conducting state and quasiparticles in the superconducting state of the glass were accounted for in the theoretical description, resulting in a good agreement over a large temperature range between measured data and prediction of the tunneling model. This allowed for a direct determination of the coupling constant between electrons and tunneling systems. In the vicinity of the transition temperature Tc the data can only be described if a modified distribution function of the tunneling parameters is applied.
Surface elastic properties in silicon nanoparticles
Melis, Claudio; Giordano, Stefano; Colombo, Luciano
2017-09-01
The elastic behavior of the external surface of a solid body plays a key role in nanomechanical phenomena. While bulk elasticity enjoys the benefits of a robust theoretical understanding, many surface elasticity features remain unexplored: some of them are here addressed by blending together continuum elasticity and atomistic simulations. A suitable readdressing of the surface elasticity theory allows to write the balance equations in arbitrary curvilinear coordinates and to investigate the dependence of the surface elastic parameters on the mean and Gaussian curvatures of the surface. In particular, we predict the radial strain induced by surface effects in spherical and cylindrical silicon nanoparticles and provide evidence that the surface parameters are nearly independent of curvatures and, therefore, of the surface conformation.
Sifi, C; Meradji, H; Slimani, M; Labidi, S; Ghemid, S; Hanneche, E B; El Haj Hassan, F
2009-05-13
Using first principles total energy calculations within the full potential linearized augmented plane wave (FP-LAPW) method, we have investigated the structural, electronic, thermodynamic and optical properties of Pb(1-x)Ca(x)S, Pb(1-x)Ca(x)Se and Pb(1-x)Ca(x)Te ternary alloys. The effect of composition on lattice parameter, bulk modulus, band gap, refractive index and dielectric function was investigated. Deviations of the lattice constants from Vegard's law and the bulk modulus from linear concentration dependence were observed for the three alloys. Using the approach of Zunger and co-workers, the microscopic origins of band gap bowing have been detailed and explained. The disorder parameter (gap bowing) was found to be mainly caused by the chemical charge transfer effect. On the other hand, the thermodynamic stability of these alloys was investigated by calculating the excess enthalpy of mixing, ΔH(m), as well as the phase diagram. It was shown that all of these alloys are stable at low temperature. The calculated refractive indices and optical dielectric constants were found to vary nonlinearly with Ca composition.
Energy Technology Data Exchange (ETDEWEB)
Shen, Lanxian [Education Ministry Key Laboratory of Renewable Energy Advanced Materials and Manufacturing Technology, Yunnan Provincial Renewable Energy Engineering Key Lab, Solar Energy Research Institution, Yunnan Normal University, Kunming 650500 (China); Li, Decong [College of Optoelectronic Engineering, Yunnan Open University, Kunming 650500 (China); Liu, Hongxia; Liu, Zuming [Education Ministry Key Laboratory of Renewable Energy Advanced Materials and Manufacturing Technology, Yunnan Provincial Renewable Energy Engineering Key Lab, Solar Energy Research Institution, Yunnan Normal University, Kunming 650500 (China); Deng, Shukang, E-mail: skdeng@126.com [Education Ministry Key Laboratory of Renewable Energy Advanced Materials and Manufacturing Technology, Yunnan Provincial Renewable Energy Engineering Key Lab, Solar Energy Research Institution, Yunnan Normal University, Kunming 650500 (China)
2016-12-01
In this study, the structural and electronic structural properties of Ba{sub 8}Ga{sub 16}Sn{sub 30−x}Ge{sub x} (0≤x≤30) are determined by the first-principle method on the basis of density functional theory. Consistent with experimental findings, calculated results reveal that Ge atoms preferentially occupy the 2a and 24g sites in these compounds. As the content of Ge in Ge-substituted clathrate is increased, the lattice parameter is decreased, and the structural stability is enhanced. The bandgaps of the compound at 1≤x≤10 are smaller than those of Ba{sub 8}Ga{sub 16}Sn{sub 30}. By contrast, the bandgaps of the compound at x>10 are larger than those of Ba{sub 8}Ga{sub 16}Sn{sub 30}. The substitution of Ge for Sn affects p-type conductivity but not n-type conductivity. As Ge content increases, the whole conduction band moves to the direction of high energy, and the density of states of valence-band top decreases. The calculated potential energy versus displacement of Ba indicates that the vibration energy of this atom increases as cage size decreases. Because Ge substitution also affects clathrate structural symmetry, the distance of Ba atom deviation from the center of the cage initially increases and subsequently decreases as the Ge content increases.
Luo, Jiaolian; Chen, Ruxue; Zhang, Xiaoming
2017-12-01
The Zn3V2O8 and (Zn1-xEux)3V2O8 have been production by Solid phase method. The crystal structure, the crystal morphology and the luminescence property of Zn3V2O8 and (Zn1-xEux)3V2O8 have been studied. Based on the first-principles planar wave super-soft pseudopotential method of density functional theory (DFT), the α-Zn3V2O8 crystal model was used to calculate the electronic structure and optical properties of the model. The results show that the crystal structure of Zn3V2O8 and (Zn1-xEux)3V2O8 were the same, and the particle uniformity of (Zn1-xEux)3V2O8 was better than Zn3V2O8. The emission band Zn3V2O8 and (Zn1-xEux)3V2O8 were present at the wave length of 420-690 nm and 300-400nm, the luminescence property of (Zn1-xEux)3V2O8 was enhance by Eu-doped. α-Zn3V2O8 is an indirect band gap, α-Zn3V2O has a band gap of 2.715eV, pure α-Zn3V2O8 has a peak, appeared at 3.91eV that is caused by the optical transition between V 3d and O 2p states.
First-principle calculations of structural, electronic, optical, elastic ...
Indian Academy of Sciences (India)
Laboratoire de Physique des Rayonnements, Département de Physique, Faculté des Sciences, Université Badji Mokhtar, Annaba, Algeria; Laboratoire de Physique et d'électronique (LPE), Faculté des Sciences I, Université Libanaise, El Hadath, Beirut, Lebanon; Laboratoire des Matériaux Semi-Conducteurs et Métalliques ...
Modelling the elastic properties of cellulose nanopaper
DEFF Research Database (Denmark)
Mao, Rui; Goutianos, Stergios; Tu, Wei
2017-01-01
The elastic modulus of cellulose nanopaper was predicted using a two-dimensional (2D) micromechanical fibrous network model. The elastic modulus predicted by the network model was 12 GPa, which is well within the range of experimental data for cellulose nanopapers. The stress state in the network...
Hamaguchi, Motoyuki; Momida, Hiroyoshi; Oguchi, Tamio
2018-04-01
We study the cathode properties of Li2MTiO4 (M = V, Cr, Mn, Fe, Co, and Ni) for Li-ion batteries by performing first-principles calculations. Formation energies and voltages for Li2-xMTiO4 (0 ≤ x ≤ 2) models with rock-salt-based structures considering several Li concentrations (2 - x) are calculated. Two dominant charge/discharge reaction mechanisms associated with redox reactions of M and O are found mainly in the ranges of lower and higher x, respectively. In the higher-x region, the O redox reactions can destabilize atomic structures, because the electron removal from O-p states produces high peaks at the fermi level in the density of states. The structural stability of O using the models with O deficiency is calculated, and the result shows that O can dissociate much more easily than Li in the higher-x region. The critical Li concentration at which the vacancy formation energy of O becomes lower than that of Li is estimated, and the critical x value decreases with increasing number of 3d electrons as M changes from V to Ni. The calculated voltages of Li2MTiO4 with O deficiency are lower than those without O deficiency, showing that the O dissociation degrades battery performances. Our systematic study for the series of M predicts that Li2CrTiO4 may be the best cathode material considering its cathode properties of high voltage and stability against O dissociation.
Energy Technology Data Exchange (ETDEWEB)
Munir, Junaid; Mat Isa, Ahmad Radzi [Physics Department, Faculty of Science, Universiti Teknologi Malaysia, Skudai 81310, Johor (Malaysia); Yousaf, Masood [IBS Center for Multidimensional Carbon Materials, Ulsan National Institute of Science and Technology, Ulsan 689-798 (Korea, Republic of); Aliabad, H.A. Rahnamaye [Department of Physics, Hakim Sabzevari University (Iran, Islamic Republic of); Ain, Qurat-ul [Key Laboratory for Laser Plasamas (MOE) & Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Saeed, M.A., E-mail: saeed@utm.my [Physics Department, Faculty of Science, Universiti Teknologi Malaysia, Skudai 81310, Johor (Malaysia)
2016-10-15
This article reports the electronic, structure, magnetic and optical properties of reduced hybrid layered complex Ni(pyz)V{sub 4}O{sub 10} (pyz=C{sub 4}H{sub 4}N{sub 2}) studied by employing density functional theory with local density approximation (LDA), generalized gradient approximation (GGA) of Perdew–Burke–Ernzerhof-96 (PBE) and modified Becke–Johnson (mBJ) exchange-correlation potential and energy. The band structure and density of states of these compounds are also presented. The total density of states (DOS) for up and down spin states clearly split, which means that the exchange interaction causes the ordered spin arrangement. PBE-mBJ calculation reveals a wider band gap in spin down state, which shows a half-metallic electronic character at the equilibrium state. The spin-polarized calculations indicate metallic nature in orthorhombic crystalline phase. It is also noted that the optical conductivity for PBE-mBJ is larger than that of LDA and PBE-GGA. Furthermore, the results show a half-metallic ferromagnetic ground state for Ni(pyz)V{sub 4}O{sub 10} in PBE-mBJ potential. The present results suggest Ni(pyz)V{sub 4}O{sub 10} compound as a potential candidate for the future optoelectronic and spintronic applications. - Highlights: • First study of the electronic, structure, magnetic and optical properties of reduced hybrid layered complex Ni(pyz)V{sub 4}O{sub 10} (pyz=C{sub 4}H{sub 4}N{sub 2}) by first principles. • PBE-mBJ calculation reveals a wider band gap in spin down state indicating its half-metallic electronic character. • The large spin magnetic moment on Ni and V cations indicates the ferromagnetic interaction which makes this compound suitable candidate for spintronics applications. • An optical band gap reveals that this compound is also useful for the application in optoelectronics.
Elastic properties of fly ash-stabilized mixes
Directory of Open Access Journals (Sweden)
Sanja Dimter
2015-12-01
Full Text Available Stabilized mixes are used in the construction of bearing layers in asphalt and concrete pavement structures. Two nondestructive methods: resonant frequency method and ultrasonic pulse velocity method, were used for estimation of elastic properties of fly ash–stabilized mixes. Stabilized mixes were designed containing sand from the river Drava and binder composed of different share of cement and fly ash. The aim of the research was to analyze the relationship between the dynamic modulus of elasticity determined by different nondestructive methods. Data showed that average value of elasticity modulus obtained by the ultrasound velocity method is lower than the values of elasticity modulus obtained by resonant frequency method. For further analysis and enhanced discussion of elastic properties of fly ash stabilized mixes, see Dimter et al. [1].
Boron Fullerenes: A First-Principles Study
Directory of Open Access Journals (Sweden)
Gonzalez Szwacki Nevill
2007-01-01
Full Text Available AbstractA family of unusually stable boron cages was identified and examined using first-principles local-density functional method. The structure of the fullerenes is similar to that of the B12icosahedron and consists of six crossing double-rings. The energetically most stable fullerene is made up of 180 boron atoms. A connection between the fullerene family and its precursors, boron sheets, is made. We show that the most stable boron sheets are not necessarily precursors of very stable boron cages. Our finding is a step forward in the understanding of the structure of the recently produced boron nanotubes.
First-principles molecular dynamics for metals
International Nuclear Information System (INIS)
Fernando, G.W.; Qian, G.; Weinert, M.; Davenport, J.W.
1989-01-01
A Car-Parrinello-type first-principles molecular-dynamics approach capable of treating the partial occupancy of electronic states that occurs at the Fermi level in a metal is presented. The algorithms used to study metals are both simple and computationally efficient. We also discuss the connection between ordinary electronic-structure calculations and molecular-dynamics simulations as well as the role of Brillouin-zone sampling. This extension should be useful not only for metallic solids but also for solids that become metals in their liquid and/or amorphous phases
First-Principles Study of Substitution of Au for Ni in Ni3Sn4
Tian, Yali; Wu, Ping
2018-02-01
First-principles calculations were performed to investigate the effects of substitution of Au for Ni on the structural, elastic, thermodynamic and electronic properties of Ni3Sn4. The calculated lattice constants for the pure phase are consistent with the reported values. Substitution of Au for Ni results in a stable thermodynamic structure. The bulk modulus, shear modulus, Young's modulus, hardness and thermal conductivity are decreased and the relative brittleness is improved after substitution. A three-dimensional graphic representation of the anisotropy of Young's modulus indicates that substitution of Au for Ni increases the anisotropy. All of the compound compositions examined are metallic and nonmagnetic. The electronic density of states manifests a conjoined peak between - 6 eV and - 4 eV hybridized by Au-d electrons and Sn-p electrons when the fraction of Au atom is above 14.29 at.% in Ni3Sn4.
First-principles study of complex material systems
He, Lixin
This thesis covers several topics concerning the study of complex materials systems by first-principles methods. It contains four chapters. A brief, introductory motivation of this work will be given in Chapter 1. In Chapter 2, I will give a short overview of the first-principles methods, including density-functional theory (DFT), planewave pseudopotential methods, and the Berry-phase theory of polarization in crystallines insulators. I then discuss in detail the locality and exponential decay properties of Wannier functions and of related quantities such as the density matrix, and their application in linear-scaling algorithms. In Chapter 3, I investigate the interaction of oxygen vacancies and 180° domain walls in tetragonal PbTiO3 using first-principles methods. Our calculations indicate that the oxygen vacancies have a lower formation energy in the domain wall than in the bulk, thereby confirming the tendency of these defects to migrate to, and pin, the domain walls. The pinning energies are reported for each of the three possible orientations of the original Ti--O--Ti bonds, and attempts to model the results with simple continuum models are discussed. CaCu3Ti4O12 (CCTO) has attracted a lot of attention recently because it was found to have an enormous dielectric response over a very wide temperature range. In Chapter 4, I study the electronic and lattice structure, and the lattice dynamical properties, of this system. Our first-principles calculations together with experimental results point towards an extrinsic mechanism as the origin of the unusual dielectric response.
Temperature-dependent elastic properties of Ti{sub 1−x}Al{sub x}N alloys
Energy Technology Data Exchange (ETDEWEB)
Shulumba, Nina [Department of Physics, Chemistry, and Biology (IFM), Linköping University, SE-581 83 Linköping (Sweden); Functional Materials, Saarland University, D-66123 Saarbrücken (Germany); Hellman, Olle [Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California 91125 (United States); Department of Physics, Chemistry, and Biology (IFM), Linköping University, SE-581 83 Linköping (Sweden); Rogström, Lina; Raza, Zamaan; Tasnádi, Ferenc; Odén, Magnus [Department of Physics, Chemistry, and Biology (IFM), Linköping University, SE-581 83 Linköping (Sweden); Abrikosov, Igor A. [Department of Physics, Chemistry, and Biology (IFM), Linköping University, SE-581 83 Linköping (Sweden); Materials Modeling and Development Laboratory, NUST “MISIS,” 119049 Moscow (Russian Federation); LACOMAS Laboratory, Tomsk State University, 634050 Tomsk (Russian Federation)
2015-12-07
Ti{sub 1−x}Al{sub x}N is a technologically important alloy that undergoes a process of high temperature age-hardening that is strongly influenced by its elastic properties. We have performed first principles calculations of the elastic constants and anisotropy using the symmetry imposed force constant temperature dependent effective potential method, which include lattice vibrations and therefore the effects of temperature, including thermal expansion and intrinsic anharmonicity. These are compared with in situ high temperature x-ray diffraction measurements of the lattice parameter. We show that anharmonic effects are crucial to the recovery of finite temperature elasticity. The effects of thermal expansion and intrinsic anharmonicity on the elastic constants are of the same order, and cannot be considered separately. Furthermore, the effect of thermal expansion on elastic constants is such that the volume change induced by zero point motion has a significant effect. For TiAlN, the elastic constants soften non-uniformly with temperature: C{sub 11} decreases substantially when the temperature increases for all compositions, resulting in an increased anisotropy. These findings suggest that an increased Al content and annealing at higher temperatures will result in a harder alloy.
Bahlakeh, Ghasem; Ramezanzadeh, Bahram; Saeb, Mohammad Reza; Terryn, Herman; Ghaffari, Mehdi
2017-10-01
The effect of cerium oxide treatment on the corrosion protection properties and interfacial interaction of steel/epoxy was studied by electrochemical impedance spectroscopy, (EIS) classical molecular dynamics (MD) and first principle quantum mechanics (QM) simulation methods X-ray photoelectron spectroscopy (XPS) was used to verify the chemical composition of the Ce film deposited on the steel. To probe the role of the curing agent in epoxy adsorption, computations were compared for an epoxy, aminoamide and aminoamide modified epoxy. Moreover, to study the influence of water on interfacial interactions the MD simulations were executed for poly (aminoamide)-cured epoxy resin in contact with the different crystallographic cerium dioxide (ceria, CeO2) surfaces including (100), (110), and (111) in the presence of water molecules. It was found that aminoamide-cured epoxy material was strongly adhered to all types of CeO2 substrates, so that binding to ceria surfaces followed the decreasing order CeO2 (111) > CeO2 (100) > CeO2 (110) in both dry and wet environments. Calculation of interaction energies noticed an enhanced adhesion to metal surface due to aminoamide curing of epoxy resin; where facets (100) and (111) revealed electrostatic and Lewis acid-base interactions, while an additional hydrogen bonding interaction was identified for CeO2 (110). Overall, MD simulations suggested decrement of adhesion to CeO2 in wet environment compared to dry conditions. Additionally, contact angle, pull-off test, cathodic delamination and salt spray analyses were used to confirm the simulation results. The experimental results in line with modeling results revealed that Ce layer deposited on steel enhanced substrate surface free energy, work of adhesion, and interfacial adhesion strength of the epoxy coating. Furthermore, decrement of adhesion of epoxy to CeO2 in presence of water was affirmed by experimental results. EIS results revealed remarkable enhancement of the corrosion
A metallic superhard boron carbide: first-principles calculations.
Ma, Mengdong; Yang, Bingchao; Li, Zihe; Hu, Meng; Wang, Qianqian; Cui, Lin; Yu, Dongli; He, Julong
2015-04-21
A monoclinic BC3 phase (denoted M-BC3) has been predicted using first principles calculations. The M-BC3 structure is formed by alternately stacking sequences of metallic BC-layers and insulating C atom layers, thus, the structure exhibits two-dimensional conductivity. Its stability has been confirmed by our calculations of the total energy, elastic constants, and phonon frequencies. The pressure of phase transition from graphite-like BC3 to M-BC3 is calculated to be 9.3 GPa, and the theoretical Vickers hardness of M-BC3 is 43.8 GPa, this value indicates that the compound is a potentially superhard material. By comparing Raman spectral calculations of M-BC3 and previously proposed structures with the experimental data, we speculate that the experimentally synthesized BC3 crystal may simultaneously contain M-BC3 and Pmma-b phases.
Determination of viral capsid elastic properties from equilibrium thermal fluctuations.
May, Eric R; Brooks, Charles L
2011-05-06
We apply two-dimensional elasticity theory to viral capsids to develop a framework for calculating elastic properties of viruses from equilibrium thermal fluctuations of the capsid surface in molecular dynamics and elastic network model trajectories. We show that the magnitudes of the long wavelength modes of motion available in a simulation with all atomic degrees of freedom are recapitulated by an elastic network model. For the mode spectra to match, the elastic network model must be scaled appropriately by a factor which can be determined from an icosahedrally constrained all-atom simulation. With this method we calculate the two-dimensional Young's modulus Y, bending modulus κ, and Föppl-von Kármán number γ, for the T=1 mutant of the Sesbania mosaic virus. The values determined are in the range of previous theoretical estimates.
Theory-Guided Materials Design of Multi-Phase Ti-Nb Alloys with Bone-Matching Elastic Properties
Directory of Open Access Journals (Sweden)
Jörg Neugebauer
2012-10-01
Full Text Available We present a scale-bridging approach for modeling the integral elasticresponse of polycrystalline composite that is based on a multi-disciplinary combination of(i parameter-free first-principles calculations of thermodynamic phase stability andsingle-crystal elastic stiffness; and (ii homogenization schemes developed forpolycrystalline aggregates and composites. The modeling is used as a theory-guidedbottom-up materials design strategy and applied to Ti-Nb alloys as promising candidatesfor biomedical implant applications. The theoretical results (i show an excellent agreementwith experimental data and (ii reveal a decisive influence of the multi-phase character ofthe polycrystalline composites on their integral elastic properties. The study shows thatthe results based on the density functional theory calculations at the atomistic level canbe directly used for predictions at the macroscopic scale, effectively scale-jumping severalorders of magnitude without using any empirical parameters.
Correlations between elastic moduli and properties in bulk metallic glasses
International Nuclear Information System (INIS)
Wang Weihua
2006-01-01
A survey of the elastic, mechanical, fragility, and thermodynamic properties of bulk metallic glasses (BMGs) and glass-forming liquids is presented. It is found that the elastic moduli of BMGs have correlations with the glass transition temperature, melting temperature, mechanical properties, and even liquid fragility. On the other hand, the elastic constants of available BMGs show a rough correlation with a weighted average of the elastic constants for the constituent elements. Although the theoretical and physical reasons for the correlations are to be clarified, these correlations could assist in understanding the long-standing issues of glass formation and the nature of glass and simulate the work of theorists. Based on the correlation, we show that the elastic moduli can assist in selecting alloying components for controlling the elastic properties and glass-forming ability of the BMGs and thus can guide BMG design. As case study, we report the formation of the families of rare-earth-based BMGs with controllable properties
Some properties of the Boltzmann elastic collision operator
International Nuclear Information System (INIS)
Delcroix, J. L.; Salmon, J.
1959-01-01
The authors point out some properties (an important one is a variational property) of the Boltzmann elastic collision operator, valid in a more general framework than that of the Lorentz gas. Reprint of a paper published in 'Le journal de physique et le radium', tome 20, Jun 1959, p. 594-596 [fr
Elastic properties of RCC under flexural loading-experimental and ...
Indian Academy of Sciences (India)
In structural analysis,especially in indeterminate structures, it becomes essential to know material and geometrical properties of members. The codal provisions recommend elastic properties of concrete and steel and these are fairly accurate enough. The stress–strain curve for concrete cylinder or a cube specimen is ...
Elastic and Thermodynamic Properties of Zirconium and Hafnium ...
Indian Academy of Sciences (India)
65
Key words: Electronic band structure, Elastic properties, Mechanical properties, Ductility, Debye. Temperature. PACS: 61,62,64,71,72,73. 1. Introduction. Refractory materials in the form of intermetallics are used in all major industries, such as electronics, aerospace, automotive, chemicals, mining, nuclear technology, metal.
Structural, Electronic and Elastic Properties of Ternary Alloy CoxNi1-xSi2
Ouchene, S.; Kadri, M. T.; Baaouague, K.; Belkhir, H.
2013-09-01
First-principles calculations, by means of the full-potential linearized augmented plane wave (FP-LAPW) method using the generalized gradient approximation (GGA), were carried out for the structural, electronic and elastic properties of transition metals disilicides alloy CoxNi1-xSi2 in the fluorite structure. The composition effect on lattice constants and bulk modulus has been analyzed. The deviations of the lattice constants from Vegard's law and the bulk modulus from linear concentration dependence (LCD) were observed for CoxNi1-xSi2. We also calculated the densities of states for the distorted CoxNi1-xSi2 alloys as well as for the ordered phases CoSi2 and NiSi2. Theoretical values of Young's modulus, shear modulus, Poisson's ratio and Debye temperature are estimated from the computed elastic constants. The analysis of the ratio of shear modulus to bulk modulus shows that the alloy is more brittle than the binary compounds. The calculated results are compared with other reported values.
Crystal structure of Earth's inner core: A first-principles study
Moustafa, S. G.; Schultz, A. J.; Zurek, E.; Kofke, D. A.
2017-12-01
Since the detection of the Earth's solid inner core (IC) by Lehmann in 1936, its composition and crystal structure (which are essential to understand Earth's evolution) have been controversial. While seismological measurements (e.g. PREM) can give a robust estimation of the density, pressure, and elasticity of the IC, they cannot be directly used to determine its composition and/or crystal structure. Experimentally, reaching the extreme IC conditions ( 330 GPa and 6000 K) and getting reliable measurements is very challenging. First-principles calculations provide a viable alternative that can work as a powerful investigative tool. Although several attempts have been made to assess phase stability at IC conditions computationally, they often use a low level of theory for electronic structure (e.g., classical force-field), adopt approximate methods (e.g., quasiharmonic approximation, fixed hcp-c/a), or do not consider finite-size effects. The study of phase stability using accurate first-principles methods is hampered in part by the difficulty of computing the free energy (FE), the central thermodynamic quantity that determines stability, while including anharmonic and finite-size effects. Additional difficulty related to the IC in particular is introduced by the dynamical instability of one of the IC candidate structures (bcc) at low temperature. Recently [1-3], we introduced a novel method (denoted as "harmonically mapped averaging", or HMA) to efficiently measure anharmonic properties (e.g. FE, pressure, elastic modulus) by molecular simulation, yielding orders of magnitude CPU speedup compared to conventional methods. We have applied this method to the hcp candidate phase of iron at the IC conditions, obtaining first-principles anharmonic FE values with unprecedented accuracy and precision [4]. We have now completed and report HMA calculations to assess the phase stability of all IC candidate phases (fcc/hcp/bcc). This knowledge is the prerequisite for
First-principles calculations of two cubic fluoropervskite compounds: RbFeF3 and RbNiF3
International Nuclear Information System (INIS)
Mubarak, A.A.; Al-Omari, Saleh
2015-01-01
We present first-principles calculations of the structural, elastic, electronic, magnetic and optical properties for RbFeF 3 and RbNiF 3 . The full-potential linear augmented plan wave (FP-LAPW) method within the density functional theory was utilized to perform the present calculations. We employed the generalized gradient approximation as exchange-correlation potential. It was found that the calculated analytical lattice parameters agree with previous studies. The analysis of elastic constants showed that the present compounds are elastically stable and anisotropic. Moreover, both compounds are classified as a ductile compound. The calculations of the band structure and density functional theory revealed that the RbFeF 3 compound has a half-metallic behavior while the RbNiF 3 compound has a semiconductor behavior with indirect (M–Γ) band gap. The ferromagnetic behavior was studied for both compounds. The optical properties were calculated for the radiation of up to 40 eV. A beneficial optics technology is predicted as revealed from the optical spectra. - Highlights: • RbFeF 3 and RbNiCl 3 compounds are elastically stable. • RbFeF 3 and RbNiCl 3 compounds are classified as a ductile compound. • The RbFeF 3 compound has a half-metallic behavior while the RbNiF 3 compound has a semiconductor behavior. • The optical properties were calculated for the radiation of up to 40 eV
Safeguards First Principle Initiative (SFPI) Cost Model
International Nuclear Information System (INIS)
Price, Mary Alice
2010-01-01
The Nevada Test Site (NTS) began operating Material Control and Accountability (MC and A) under the Safeguards First Principle Initiative (SFPI), a risk-based and cost-effective program, in December 2006. The NTS SFPI Comprehensive Assessment of Safeguards Systems (COMPASS) Model is made up of specific elements (MC and A plan, graded safeguards, accounting systems, measurements, containment, surveillance, physical inventories, shipper/receiver differences, assessments/performance tests) and various sub-elements, which are each assigned effectiveness and contribution factors that when weighted and rated reflect the health of the MC and A program. The MC and A Cost Model, using an Excel workbook, calculates budget and/or actual costs using these same elements/sub-elements resulting in total costs and effectiveness costs per element/sub-element. These calculations allow management to identify how costs are distributed for each element/sub-element. The Cost Model, as part of the SFPI program review process, enables management to determine if spending is appropriate for each element/sub-element.
Safeguards First Principle Initiative (SFPI) Cost Model
Energy Technology Data Exchange (ETDEWEB)
Mary Alice Price
2010-07-11
The Nevada Test Site (NTS) began operating Material Control and Accountability (MC&A) under the Safeguards First Principle Initiative (SFPI), a risk-based and cost-effective program, in December 2006. The NTS SFPI Comprehensive Assessment of Safeguards Systems (COMPASS) Model is made up of specific elements (MC&A plan, graded safeguards, accounting systems, measurements, containment, surveillance, physical inventories, shipper/receiver differences, assessments/performance tests) and various sub-elements, which are each assigned effectiveness and contribution factors that when weighted and rated reflect the health of the MC&A program. The MC&A Cost Model, using an Excel workbook, calculates budget and/or actual costs using these same elements/sub-elements resulting in total costs and effectiveness costs per element/sub-element. These calculations allow management to identify how costs are distributed for each element/sub-element. The Cost Model, as part of the SFPI program review process, enables management to determine if spending is appropriate for each element/sub-element.
THERMODYNAMIC MODELING AND FIRST-PRINCIPLES CALCULATIONS
Energy Technology Data Exchange (ETDEWEB)
Turchi, P; Abrikosov, I; Burton, B; Fries, S; Grimvall, G; Kaufman, L; Korzhavyi, P; Manga, R; Ohno, M; Pisch, A; Scott, A; Zhang, W
2005-12-15
The increased application of quantum mechanical-based methodologies to the study of alloy stability has required a re-assessment of the field. The focus is mainly on inorganic materials in the solid state. In a first part, after a brief overview of the so-called ab initio methods with their approximations, constraints, and limitations, recommendations are made for a good usage of first-principles codes with a set of qualifiers. Examples are given to illustrate the power and the limitations of ab initio codes. However, despite the ''success'' of these methodologies, thermodynamics of complex multi-component alloys, as used in engineering applications, requires a more versatile approach presently afforded within CALPHAD. Hence, in a second part, the links that presently exist between ab initio methodologies, experiments, and CALPHAD approach are examined with illustrations. Finally, the issues of dynamical instability and of the role of lattice vibrations that still constitute the subject of ample discussions within the CALPHAD community are revisited in the light of the current knowledge with a set of recommendations.
Effective elastic properties of sintered materials with branched cracks
Fedelinski, Piotr
2018-01-01
The aim of work is analysis of sintered materials with branched cracks growing from the voids situated at corners of fibers. The material is modelled as a two-dimensional linear-elastic structure using the boundary element method (BEM). The materials without voids and with voids having different shapes are considered. The influence of lengths of cracks and shapes of voids on stress intensity factors (SIF) and effective elastic properties (the Young modulus and the Poisson ratio) are studied. The overall properties of the sintered materials are determined by considering the representative volume element (RVE) with large number of branched cracks. The sensitivity of effective elastic properties on boundary conditions imposed on the RVE is studied.
First-principle investigations on the structural dynamics of Ti2GaN
International Nuclear Information System (INIS)
Yang, Z.J.; Li, J.; Linghu, R.F.; Cheng, X.L.; Yang, X.D.
2013-01-01
Highlights: •Our calculated lattice parameter of Ti 2 GaN shows that c axis is always stiffer than a axis. •The elastic constants investigations demonstrated that the Ti 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 2 GaN. Our calculated lattice parameter shows that c axis is always stiffer than a axis. The elastic constants investigations demonstrated that Ti 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
Torsional Elastic Property Measurements of Selected Orthodontic Archwires.
1987-01-01
properties of denture base acrylics . 26 In this experiment, an inverted pendulum was hung by a fine, fixed wire. The amplitude and frequency of...of Polymers. Polymer Engineering and Science 19:664-675. 26. Braden M, Stafford GD: Viscoelastic Properties of Some Denture Base Materials. J Dent...D-AiB5 669 TORSIONAL ELASTIC PROPERTY MEASUREMENTSO SLECE ORTHODONTIC ARCHWlIRES(U) AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH B E LARSON 1987
Elastic properties of synthetic materials for soft tissue modeling
International Nuclear Information System (INIS)
Mansy, H A; Grahe, J R; Sandler, R H
2008-01-01
Mechanical models of soft tissue are useful for studying vibro-acoustic phenomena. They may be used for validating mathematical models and for testing new equipment and techniques. The objective of this study was to measure density and visco-elastic properties of synthetic materials that can be used to build such models. Samples of nine different materials were tested under dynamic (0.5 Hz) compressive loading conditions. The modulus of elasticity of the materials was varied, whenever possible, by adding a softener during manufacturing. The modulus was measured over a nine month period to quantify the effect of ageing and softener loss on material properties. Results showed that a wide range of the compression elasticity modulus (10 to 1400 kPa) and phase (3.5 0 -16.7 0 ) between stress and strain were possible. Some materials tended to exude softener over time, resulting in a weight loss and elastic properties change. While the weight loss under normal conditions was minimal in all materials (<3% over nine months), loss under accelerated weight-loss conditions can reach 59%. In the latter case an elasticity modulus increase of up to 500% was measured. Key advantages and limitations of candidate materials were identified and discussed
Dynamic visco-elastic properties of dental composite resins.
Mesquita, Renata V; Axmann, Detlef; Geis-Gerstorfer, Jürgen
2006-03-01
This study aimed to examine the visco-elastic properties of dental composites by dynamic mechanical analysis under the influence of clinically relevant temperatures and variable frequencies, after being stored in air or distilled water for up to 3 months. Two direct (Diamond Lite and Grandio) and two indirect (Artglass and Vita Zeta LC) composites were used. Samples were immediately tested (baseline) or stored at 37 degrees C, either in air or distilled water for 1 day, 7 or 90 days before testing. During dynamic testing, elastic modulus, viscous modulus and loss tangent were determined over a frequency range from 0.1 to 10 Hz at constant temperatures between 5 and 55 degrees C. Results were analyzed by one-way ANOVA and Turkey's-test. Elastic and viscous moduli were higher for direct than for indirect composites. No such evidence was found for loss tangent. Only the elastic modulus showed statistically relevant differences in the direct and indirect materials groups: Grandio showed higher modulus than Diamond Lite, while Artglass had higher modulus than Vita Zeta LC. The elastic modulus reduced with increasing temperature and decreasing frequency, while the loss tangent showed the opposite trend. The influence of temperature and frequency on viscous modulus was not conclusive. The elastic modulus was more sensitive to moisture than viscous modulus and loss tangent but all three properties showed no overall consistent trend in the results following the storage periods. Dynamic mechanical analysis was a valuable tool to characterize the visco-elastic properties of dental composites, thus giving us a greater insight into material behavior.
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 Modelling of Shape Memory Alloys Molecular Dynamics Simulations
Kastner, Oliver
2012-01-01
Materials sciences relate the macroscopic properties of materials to their microscopic structure and postulate the need for holistic multiscale research. The investigation of shape memory alloys is a prime example in this regard. This particular class of materials exhibits strong coupling of temperature, strain and stress, determined by solid state phase transformations of their metallic lattices. The present book presents a collection of simulation studies of this behaviour. Employing conceptually simple but comprehensive models, the fundamental material properties of shape memory alloys are qualitatively explained from first principles. Using contemporary methods of molecular dynamics simulation experiments, it is shown how microscale dynamics may produce characteristic macroscopic material properties. The work is rooted in the materials sciences of shape memory alloys and covers thermodynamical, micro-mechanical and crystallographical aspects. It addresses scientists in these research fields and thei...
High pressure elasticity and thermal properties of depleted uranium
International Nuclear Information System (INIS)
Jacobsen, M. K.; Velisavljevic, N.
2016-01-01
Studies of the phase diagram of uranium have revealed a wealth of high pressure and temperature phases. Under ambient conditions the crystal structure is well defined up to 100 gigapascals (GPa), but very little information on thermal conduction or elasticity is available over this same range. This work has applied ultrasonic interferometry to determine the elasticity, mechanical, and thermal properties of depleted uranium to 4.5 GPa. Results show general strengthening with applied load, including an overall increase in acoustic thermal conductivity. Further implications are discussed within. This work presents the first high pressure studies of the elasticity and thermal properties of depleted uranium metal and the first real-world application of a previously developed containment system for making such measurements.
Atomistic calculations of interface elastic properties in noncoherent metallic bilayers
International Nuclear Information System (INIS)
Mi Changwen; Jun, Sukky; Kouris, Demitris A.; Kim, Sung Youb
2008-01-01
The paper describes theoretical and computational studies associated with the interface elastic properties of noncoherent metallic bicrystals. Analytical forms of interface energy, interface stresses, and interface elastic constants are derived in terms of interatomic potential functions. Embedded-atom method potentials are then incorporated into the model to compute these excess thermodynamics variables, using energy minimization in a parallel computing environment. The proposed model is validated by calculating surface thermodynamic variables and comparing them with preexisting data. Next, the interface elastic properties of several fcc-fcc bicrystals are computed. The excess energies and stresses of interfaces are smaller than those on free surfaces of the same crystal orientations. In addition, no negative values of interface stresses are observed. Current results can be applied to various heterogeneous materials where interfaces assume a prominent role in the systems' mechanical behavior
First principles studies of semiconductor epitaxial growth
Tsai, Bao-Liang
This thesis conducts investigations mainly on the structures, energetics, and recations of semiconductor as well as oxide surfaces using first principles cluster model approach. The first part of the research work addresses the issues in the epitaxial growth of Hgsb{1-x}Cdsb{x}Te (MCT) materials. Hg divalent compounds were studied thoroughly using a variety of quantum chemical methods in order to understand the energetics of Hg precursors for growth. The (001) growth surfaces were then examined in detail using cluster model calculations. Based on these results, a novel metal-organic molecular beam epitaxial (MOMBE) growth strategy with favorable energetics for growing MCT using Hsb2C=CH-CHsb2-Hg-Cequiv C-CHsb3 is proposed. It is hoped that with this new growth strategy, the Hg vacancy and p-doping problems that currently exist in growth can be avoided. The second part of the thesis discusses the molecular beam epitaxial (MBE) growth of cubic GaN on the (001) surface using various N sources. Surface reconstructions and the interactions of gas-phase atomic and molecular nitrogens with the surface were elucidated using cluster models. Using these results an energy phase diagram for the growth of GaN has been constructed. It suggests that excited state molecular Nsb2\\ (sp3Sigmasbsp{u}{+}) is the most favorable of all N species for growth of high quality GaN because it can undergo a dissociative chemisorption process. Ground state atomic N\\ (sp4S) is also good for growth. The doublet excited states N\\ (sp2D and sp2P) might cause surface N abstraction, leading to N vacancies in the material. Finally, a Fe(OH)sb3(Hsb2O)sb3 GVB cluster model of crystalline alpha-Fesb2Osb3 was developed. This simple model can describe the local geometry and bonding of Fe in the bulk oxide. Using quantum mechanical calculations, the orientation of the oleic imidazoline (OI) molecule bonding to the oxide surface has been determined. OI class of molecules are used extensively for corrosion
Elastic properties of magnetostrictive rare-earth-iron alloys
International Nuclear Information System (INIS)
Cullen, J.R.; Blessing, G.; Rinaldi, S.
1978-01-01
The elastic properties of certain magnetostrictive rare-earth-iron alloys, namely polycrystalline Tbsub(0.3)Dysub(0.7)Fesub(2), Smsub(0.88)Dysub(0.12)Fesub(2)and amorphous TbFesub(2), were investigated ultrasonically. In all cases two shear waves were observed propagating simultaneously when a magnetic field was applied perpendicular to the direction of propagation. A model to explain this behaviour, based on magnetic-elastic coupling within local regions of these disordered materials, is developed and discussed in two limiting cases: (i) strongly coupled regions for which an effective isotropic magneto-elastic coupling is appropriate, and (ii) materials for which the elastic properties of the conglomerate are determined by averaging over those of independent regions. Experimental results up to fields of 25 kOe on the alloys mentioned above are exhibited and compared with the limiting cases (i) and (ii). In the case of polycrystalline Tbsub(0.3)Dysub(0.7)Fesub(2) further comparison is made between the determination of the magneto-elastic coupling constants using this model and the determination by using the results of a previous single-crystal study. (author)
Elastic and thermodynamic properties of zirconium- and hafnium ...
Indian Academy of Sciences (India)
2018-02-02
Feb 2, 2018 ... https://doi.org/10.1007/s12034-017-1537-3. Elastic and thermodynamic properties of zirconium- and hafnium-doped Rh3V intermetallic compounds: potential aerospace material. M MANJULA, M SUNDARESWARI. ∗ and E VISWANATHAN. Department of Physics, Sathyabama University, Chennai 600119, ...
Structural, elastic, electronic and optical properties of bi-alkali ...
Indian Academy of Sciences (India)
and efficient method for the calculation of the ground-state properties of materials [22 ... Murnaghan equation of state [28]. The optimization curves for the compounds are shown in figure 2. In the ground state, a (Å), B (GPa) and Bo are evaluated. The calculated ... the cubic structure only three elastic constants are required.
Anisotropy in elastic properties of lithium sodium sulphate ...
Indian Academy of Sciences (India)
Anisotropy in elastic properties of lithium sodium sulphate hexahydrate single crystal—An ultrasonic study. GEORGE VARUGHESE. ,∗. , A S KUMAR†, J PHILIP†† and GODFREY LOUIS#. Department of Physics, Catholicate College, Pathanamthitta 689 648, India. †SPAP, M.G. University, Kottayam 686 560, India. ††STIC ...
Erratum to: Elastic and piezoelectric properties, sound velocity and ...
Indian Academy of Sciences (India)
Erratum to: Elastic and piezoelectric properties, sound velocity and Debye temperature of (B3) BBi compound under pressure. S DAOUD1,∗, N BIOUD2 and N LEBGAA2. 1Faculté des Sciences et de la Technologie, Université de Bordj Bou Arreridj, 34000, Algeria. 2Laboratoire d'Optoélectronique & Composants, Université ...
Elastic properties of RCC under flexural loading-experimental and ...
Indian Academy of Sciences (India)
The experimental results are verified by using 3D finite element techniques. This study refers to the effect of variation of percentage of main longitudinal rein- forcement and concrete grade. Effect of confinement is not considered and it appears in a separate study. Keywords. Indeterminate structures; elastic properties; ...
SIMULATION OF THERMO-ELASTICS PROPERTIES OF THERMAL ...
African Journals Online (AJOL)
30 juin 2011 ... SIMULATION OF THERMO-ELASTICS PROPERTIES OF THERMAL. BARRIER COATINGS. A. M. Ferouani*, H. I. Faraoun and H. Aourag*. Laboratoire d'Étude et Prédiction des Matériaux, Unité de Recherche Matériaux et. Energies Renouvelables, Faculté des sciences, Département de physique, ...
Elastic and thermodynamic properties of zirconium-and hafnium ...
Indian Academy of Sciences (India)
... Live Streaming. Home; Journals; Bulletin of Materials Science; Volume 41; Issue 1. Elastic and thermodynamic properties of zirconium- and hafnium-doped Rh 3 V intermetallic compounds: potential aerospace material. M MANJULA M SUNDARESWARI E VISWANATHAN. Volume 41 Issue 1 February 2018 Article ID 19 ...
Energy Technology Data Exchange (ETDEWEB)
Jain, Ekta, E-mail: jainekta05@gmail.com [Department of Physics, Government M. L. B. Girls P. G. Autonomous College, Bhopal-462002 (India); Pagare, Gitanjali, E-mail: gita-pagare@yahoo.co.in [Department of Physics, Sarojini Naidu Government Girls P. G. Autonomous College, Bhopal-462016 (India); Sanyal, S. P., E-mail: sps.physicsbu@gmail.com [Department of Physics, Barkatullah University, Bhopal-462026 (India)
2016-05-06
The structural, electronic, elastic, mechanical and thermal properties of AlFe intermetallic compound in B{sub 2}-type (CsCl) structure have been investigated using first-principles calculations. The exchange-correlation term was treated within generalized gradient approximation. Ground state properties i.e. lattice constants (a{sub 0}), bulk modulus (B) and first-order pressure derivative of bulk modulus (B’) are presented. The density of states are derived which show the metallic character of present compound. Our results for C{sub 11}, C{sub 12} and C{sub 44} agree well with previous theoretical data. Using Pugh’s criteria (B/G{sub H} < 1.75), brittle character of AlFe is satisfied. In addition shear modulus (G{sub H}), Young’s modulus (E), sound wave velocities and Debye temperature (θ{sub D}) have also been estimated.
First-principles modeling of magnetic misfit interfaces
Grytsiuk, Sergii
2013-08-16
We investigate the structural and magnetic properties of interfaces with large lattice mismatch, choosing Pt/Co and Au/Co as prototypes. For our first-principles calculations, we reduce the lattice mismatch to 0.2% by constructing Moiré supercells. Our results show that the roughness and atomic density, and thus the magnetic properties, depend strongly on the substrate and thickness of the Co slab. An increasing thickness leads to the formation of a Co transition layer at the interface, especially for Pt/Co due to strong Pt-Co interaction. A Moiré supercell with a transition layer is found to reproduce the main experimental findings and thus turns out to be the appropriate model for simulating magnetic misfit interfaces.
First principles modeling of panchromatic dyes for solar cells applications.
di Felice, Rosa; Calzolari, Arrigo; Dong, Rui; Buongiorno Nardelli, Marco
2013-03-01
The state-of-the-art dye in Grätzel solar cells, N719, exhibits a total solar-to-electric conversion efficiency of 11.2%. However, it severely lacks absorption in the red and the near infrared regions of the electromagnetic spectrum, which represent more than 70% of the solar radiation spectrum. Using calculations from first principles in the time-dependent domain, we have studied the electronic and optical response of a novel class of panchromatic sensitizers that can harvest solar energy efficiently across the visible and near infrared regions, which have been recently synthesized [A. El-Shafei, M. Hussain, A. Atiq, A. Islam, and L. Han, J. Mater. Chem. 22, 24048 (2012)]. Our calculations show that, by tuning the properties of antenna groups, one can achieve a substantial improvement of the optical properties.
First principles study of α and δ-Pu
International Nuclear Information System (INIS)
Chattaraj, Debabrata; Dash, Smruti
2017-01-01
The structural and electronic properties of α-and δ-Pu has been investigated using state of the art first principles method. All the calculations have been performed using a plane wave based pseudopotential method under the framework of spin polarized density functional theory. The effect of relativistic spin-orbit interactions on these properties has been investigated. The calculated lattice parameters are found to be within ±1% of the experimental data. The cohesive energy of α-and δ-Pu are calculated to be -3.125 and -3.126 eV/atom. The nature of chemical bonding present in those phases of Pu is depicted by calculated density of states spectra. (author)
Structural, elastic, optoelectronic and magnetic properties of ...
Indian Academy of Sciences (India)
2017-09-22
Sep 22, 2017 ... In recent times, ternary compounds with chemical formula. CdRE2X4 (RE = rare earth, X = S, Se) .... equation of state (EOS) to obtain the ground state properties of the title compound, such as the lattice ... cubic CdHo2S4 are C11 = 134.76 GPa, C12 = 29.48 GPa and C44 = 23.41 GPa. To the best of our ...
Structural, elastic, electronic and optical properties of bi-alkali ...
Indian Academy of Sciences (India)
The structural parameters, elastic constants, electronic and optical properties of the bi-alkali antimonides (Na2KSb, Na2RbSb, Na2CsSb, K2RbSb, K2CsSb and Rb2CsSb) were calculated using state-of-the-art density functional theory. Different exchange-correlation potentials were adopted to predict the physical properties.
Elastic properties and electron transport in InAs nanowires
Energy Technology Data Exchange (ETDEWEB)
Migunov, Vadim
2013-02-22
The electron transport and elastic properties of InAs nanowires grown by chemical vapor deposition on InAs (001) substrate were studied experimentally, in-situ in a transmission electron microscope (TEM). A TEM holder allowing the measurement of a nanoforce while simultaneous imaging nanowire bending was used. Diffraction images from local areas of the wire were recorded to correlate elastic properties with the atomic structure of the nanowires. Another TEM holder allowing the application of electrical bias between the nanowire and an apex of a metallic needle while simultaneous imaging the nanowire in TEM or performing electron holography was used to detect mechanical vibrations in mechanical study or holographical observation of the nanowire inner potential in the electron transport studies. The combination of the scanning probe methods with TEM allows to correlate the measured electric and elastic properties of the nanowires with direct identification of their atomic structure. It was found that the nanowires have different atomic structures and different stacking fault defect densities that impacts critically on the elastic properties and electric transport. The unique methods, that were applied in this work, allowed to obtain dependencies of resistivity and Young's modulus of left angle 111 right angle -oriented InAs nanowires on defect density and diameter. It was found that the higher is the defect density the higher are the resistivity and the Young's modulus. Regarding the resistivity, it was deduced that the stacking faults increase the scattering of the electrons in the nanowire. These findings are consistent with the literature, however, the effect described by the other groups is not so pronounced. This difference can be attributed to the significant incompleteness of the physical models used for the data analysis. Regarding the elastic modulus, there are several mechanisms affecting the elasticity of the nanowires discussed in the thesis. It
Orlikowski, Daniel; Söderlind, Per; Moriarty, John A.
2006-08-01
The thermoelastic properties of tantalum have been investigated over its theoretical high-pressure bcc solid phase (up to 26000K at 10Mbar ) using an advanced first-principles approach that accurately accounts for cold, electron-thermal, and ion-thermal contributions in materials where anharmonic effects are small. Specifically, we have combined ab initio full-potential linear-muffin-tin-orbital electronic-structure calculations for the cold and electron-thermal contributions to the elastic moduli with phonon contributions for the ion-thermal part calculated using model generalized pseudopotential theory. For the latter, a summation of terms over the Brillouin zone is performed within the quasiharmonic approximation, where each term is composed of a strain derivative of the phonon frequency at a particular k point. At ambient pressure, the resulting temperature dependence of the Ta elastic moduli is in excellent agreement with ultrasonic measurements. The experimentally observed anomalous behavior of C44 at low temperatures is shown to originate from the electron-thermal contribution. At higher temperatures, the main contribution to the temperature dependence of the elastic moduli comes from thermal expansion, but inclusion of the electron- and ion-thermal contributions is essential to obtain quantitative agreement with experiment. In addition, the pressure dependence of the moduli at ambient temperature compares well with recent diamond-anvil-cell measurements to 1.05Mbar . Moreover, the calculated longitudinal and bulk sound velocities in polycrystalline Ta at higher pressure and temperature in the vicinity of shock melting (˜3Mbar) agree well with data obtained from shock experiments. However, at high temperatures along the melt curve above 1Mbar , the B' shear modulus becomes negative, indicating the onset of unexpectedly strong anharmonic effects. Finally, the assumed temperature dependence of the Steinberg-Guinan strength model obtained from scaling with the
Linear elastic properties derivation from microstructures representative of transport parameters.
Hoang, Minh Tan; Bonnet, Guy; Tuan Luu, Hoang; Perrot, Camille
2014-06-01
It is shown that three-dimensional periodic unit cells (3D PUC) representative of transport parameters involved in the description of long wavelength acoustic wave propagation and dissipation through real foam samples may also be used as a standpoint to estimate their macroscopic linear elastic properties. Application of the model yields quantitative agreement between numerical homogenization results, available literature data, and experiments. Key contributions of this work include recognizing the importance of membranes and properties of the base material for the physics of elasticity. The results of this paper demonstrate that a 3D PUC may be used to understand and predict not only the sound absorbing properties of porous materials but also their transmission loss, which is critical for sound insulation problems.
Elastic properties of ultrathin diamond/AlN membranes
Energy Technology Data Exchange (ETDEWEB)
Zuerbig, V., E-mail: verena.zuerbig@iaf-extern.fraunhofer.de [Fraunhofer Institute for Applied Solid State Physics IAF, Tullastr. 72, 79108 Freiburg (Germany); IMTEK, University of Freiburg, Georges-Köhler-Allee 103, 79110 Freiburg (Germany); Hees, J.; Pletschen, W.; Sah, R.E.; Wolfer, M.; Kirste, L.; Heidrich, N.; Nebel, C.E. [Fraunhofer Institute for Applied Solid State Physics IAF, Tullastr. 72, 79108 Freiburg (Germany); Ambacher, O. [Fraunhofer Institute for Applied Solid State Physics IAF, Tullastr. 72, 79108 Freiburg (Germany); IMTEK, University of Freiburg, Georges-Köhler-Allee 103, 79110 Freiburg (Germany); Lebedev, V. [Fraunhofer Institute for Applied Solid State Physics IAF, Tullastr. 72, 79108 Freiburg (Germany)
2014-05-02
Nanocrystalline diamond- (NCD) and AlN-based ultrathin single layer and bilayer membranes are investigated towards their mechanical properties. It is shown that chemo-mechanical polishing and heavy boron doping of NCD thin films do not impact the elastic properties of NCD layers as revealed by negligible variations of the NCD Young's modulus (E). In addition, it is demonstrated that the combination of NCD elastic layer and AlN piezo-actuator is highly suitable for the fabrication of mechanically stable ultrathin membranes in comparison to AlN single layer membranes. The elastic parameters of NCD/AlN heterostructures are mainly determined by the outstanding high Young's modulus of NCD (E = 1019 ± 19 GPa). Such ultrathin unimorph membranes allow for fabrication of piezo-actuated AlN/NCD microlenses with tunable focus length. - Highlights: • Mechanical properties of nanocrystalline diamond (NCD) and AlN circular membranes • No influence of polishing of NCD thin films on the mechanical properties of NCD • No influence of heavy boron-doping on the mechanical properties of NCD • Demonstration of mechanically stable piezo-actuated NCD/AlN membranes • Reported performance of AlN/NCD microlenses with adjustable focus length.
YaJuan, Guo; JianFeng, Jia; XiaoHua, Wang; Ying, Ren; HaiShun, Wu
2013-02-01
This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy).This article has been retracted at the request of the Editor-in-Chief.The Authors have plagiarized part of a paper that had already appeared in: V. Ozolins, E. H. Majzoub and C. Wolverton, First-Principles Prediction of Thermodynamically Reversible Hydrogen Storage Reactions in the Li-Mg-Ca-B-H System, J. Am. Chem. Soc. 131 (2009) 230-237; DOI:http://dx.doi.org/10.1021/ja8066429.One of the conditions of submission of a paper for publication is that authors declare explicitly that their work is original and has not appeared in a publication elsewhere. Re-use of any data should be appropriately cited. As such this article represents a severe abuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.
A micromechanics model of the elastic properties of human dentine
Energy Technology Data Exchange (ETDEWEB)
Kinney, J. H. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Balooch, M. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Marshall, G. W. [Univ. of California, San Francisco, CA (United States). Dept. of Restorative Dentistry; Marshall, S. J. [Univ. of California, San Francisco, CA (United States). Dept. of Restorative Dentistry
1999-10-01
A generalized self-consistent model of cylindrical inclusions in a homogeneous and isotropic matrix phase was used to study the effects of tubule orientation on the elastic properties of dentin. Closed form expressions for the five independent elastic constants of dentin were derived in terms of tubule concentration, and the Young's moduli and Poisson ratios of peri- and intertubular dentin. An atomic force microscope (AFM) indentation technique determined the Young's moduli of the peri- and intertubular dentin as approximately 30 GPa and 15 GPa, respectively. Over the natural variation in tubule density found in dentin, there was only a slight variation in the axial and transverse shear moduli with position in the tooth, and there was no measurable effect of tubule orientation. We conclude that tubule orientation has no appreciable effect on the elastic behavior of normal dentin, and that the elastic properties of healthy dentin can be modeled as an isotropic continuum with a Young's modulus of approximately 16 GPa and a shear modulus of 6.2 GPa.
First principles calculations of structural, electronic and thermal ...
Indian Academy of Sciences (India)
Administrator
2013-07-28
Jul 28, 2013 ... ambient conditions in the cubic NaCl structure. The lead salts exhibit properties which are ... The fitting of the Murnaghan (1944) equation of state to the total energies vs unit cell volumes, yields to the ... as interatomic bonding, equations of state and phonon spectra. Most importantly, knowledge of elastic ...
Structural phase transition and elastic properties of mercury chalcogenides
Energy Technology Data Exchange (ETDEWEB)
Varshney, Dinesh, E-mail: vdinesh33@rediffmail.com [School of Physics, Vigyan Bhavan, Devi Ahilya University, Khandwa Road Campus, Indore 452001 (India); Shriya, S. [School of Physics, Vigyan Bhavan, Devi Ahilya University, Khandwa Road Campus, Indore 452001 (India); Khenata, R. [Laboratoire de Physique Quantique et de Modelisation Mathematique (LPQ3M), Departement de Technologie, Universite de Mascara, 29000 Mascara (Algeria)
2012-08-15
Pressure induced structural transition and elastic properties of ZnS-type (B3) to NaCl-type (B1) structure in mercury chalcogenides (HgX; X = S, Se and Te) are presented. An effective interionic interaction potential (EIOP) with long-range Coulomb, as well charge transfer interactions, Hafemeister and Flygare type short-range overlap repulsion extended up to the second neighbor ions and van der Waals interactions are considered. Emphasis is on the evaluation of the pressure dependent Poisson's ratio {nu}, the ratio R{sub BT/G} of B (bulk modulus) over G (shear modulus), anisotropy parameter, Shear and Young's modulus, Lame constant, Kleinman parameter, elastic wave velocity and thermodynamical property as Debye temperature. The Poisson's ratio behavior infers that Mercury chalcogenides are brittle in nature. To our knowledge this is the first quantitative theoretical prediction of the pressure dependence of elastic and thermodynamical properties explicitly the ductile (brittle) nature of HgX and still awaits experimental confirmations. Highlights: Black-Right-Pointing-Pointer Vast volume discontinuity in phase diagram infers transition from ZnS to NaCl structure. Black-Right-Pointing-Pointer The shear elastic constant C{sub 44} is nonzero confirms the mechanical stability. Black-Right-Pointing-Pointer Pressure dependence of {theta}{sub D} infers the softening of lattice with increasing pressure. Black-Right-Pointing-Pointer Estimated bulk, shear and tetragonal moduli satisfied elastic stability criteria. Black-Right-Pointing-Pointer In both B3 and B1 phases, C{sub 11} and C{sub 12} increase linearly with pressure.
The first principle calculation of two-dimensional Dirac materials
Lu, Jin
2017-12-01
As the size of integrated device becoming increasingly small, from the last century, semiconductor industry is facing the enormous challenge to break the Moore’s law. The development of calculation, communication and automatic control have emergent expectation of new materials at the aspect of semiconductor industrial technology and science. In spite of silicon device, searching the alternative material with outstanding electronic properties has always been a research point. As the discovery of graphene, the research of two-dimensional Dirac material starts to express new vitality. This essay studied the development calculation of 2D material’s mobility and introduce some detailed information of some approximation method of the first principle calculation.
First principles investigation of nitrogenated holey graphene
Xu, Cui-Yan; Dong, Hai-Kuan; Shi, Li-Bin
2018-04-01
The zero band gap problem limits the application of graphene in the field of electronic devices. Opening the band gap of graphene has become a research issue. Nitrogenated holey graphene (NHG) has attracted much attention because of its semiconducting properties. However, the stacking orders and defect properties have not been investigated. In this letter, the structural and stacking properties of NHG are first investigated. We obtain the most stable stacking structure. Then, the band structures for bulk and multilayer NHG are studied. Impact of the strain on the band gaps and bond characteristics is discussed. In addition, we investigate formation mechanism of native defects of carbon vacancy (VC), carbon interstitial (Ci), nitrogen vacancy (VN), and nitrogen interstitial (Ni) in bulk NHG. Formation energies and transition levels of these native defects are assessed.
Energy Technology Data Exchange (ETDEWEB)
Ivashchenko, V.I., E-mail: ivash@ipms.kiev.ua [Institute of Problems of Material Science, National Academy of Science of Ukraine, Krzhyzhanosky Str. 3, 03142 Kyiv (Ukraine); Veprek, S., E-mail: stan.veprek@lrz.tum.de [Department of Chemistry, Technical University Munich, Lichtenbergstrasse 4, D-85747 Garching (Germany); Argon, A.S. [Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Turchi, P.E.A. [Lawrence Livermore National Laboratory (L-352), P.O. Box 808, Livermore, CA 94551 (United States); Gorb, L. [Badger Technical Services, LLC, Vicksburg, MS 39180 (United States); U.S. Army ERDC, Vicksburg, MS 39180 (United States); Hill, F. [U.S. Army ERDC, Vicksburg, MS 39180 (United States); Leszczynski, J. [Department of Chemistry and Biochemistry, Interdisciplinary Center for Nanotoxicity, Jackson State University, Jackson, MS 39217 (United States)
2015-03-02
TiN/SiN{sub x} heterostructures with one monolayer of the interfacial SiN{sub x} have been investigated in the framework of first-principles molecular dynamics calculations in the temperature range of 0 to 1400 K with subsequent static relaxation. The atomic configurations, thermal stability and stress–strain relations have been calculated. Among the heterostructures studied, only the TiN(111)/SiN/TiN(111) and TiN(111)/Si{sub 2}N{sub 3}/TiN(111) ones are thermally stable. Upon tensile load, decohesion occurs between the Ti−N bonds adjacent to the SiN{sub x} interfacial layer for TiN(001)/SiN/TiN(001) and TiN(111)/Si{sub 2}N{sub 3}/TiN(111) heterostructures, and inside the TiN slab for TiN(001)/Si{sub 3}N{sub 4}/TiN(001) and TiN(110)/SiN/TiN(110) ones. Upon shear, failure occurs in TiN near the interfaces in all the heterostructures, except for the TiN(001)/Si{sub 3}N{sub 4}/TiN(001) one, for which the plastic flow occurs inside the TiN slab. Based on these results we estimate the maximum achievable hardness of nc-TiN/Si{sub 3}N{sub 4} nanocomposites free of impurities to be about 170 GPa. - Highlights: • Interface stability in TiN/SiN{sub x} heterostructures at T ≤ 1400 K is studied by quantum molecular dynamics. • Ideal decohesion and shear strengths of the heterostructures have been calculated. • Achievable hardness of nc-TiN/Si{sub 3}N{sub 4}-like nanocomposites of about 170 GPa is calculated. • Experimentally achieved lower hardness is limited by flaws, such as oxygen impurities.
International Nuclear Information System (INIS)
Ivashchenko, V.I.; Veprek, S.; Argon, A.S.; Turchi, P.E.A.; Gorb, L.; Hill, F.; Leszczynski, J.
2015-01-01
TiN/SiN x heterostructures with one monolayer of the interfacial SiN x have been investigated in the framework of first-principles molecular dynamics calculations in the temperature range of 0 to 1400 K with subsequent static relaxation. The atomic configurations, thermal stability and stress–strain relations have been calculated. Among the heterostructures studied, only the TiN(111)/SiN/TiN(111) and TiN(111)/Si 2 N 3 /TiN(111) ones are thermally stable. Upon tensile load, decohesion occurs between the Ti−N bonds adjacent to the SiN x interfacial layer for TiN(001)/SiN/TiN(001) and TiN(111)/Si 2 N 3 /TiN(111) heterostructures, and inside the TiN slab for TiN(001)/Si 3 N 4 /TiN(001) and TiN(110)/SiN/TiN(110) ones. Upon shear, failure occurs in TiN near the interfaces in all the heterostructures, except for the TiN(001)/Si 3 N 4 /TiN(001) one, for which the plastic flow occurs inside the TiN slab. Based on these results we estimate the maximum achievable hardness of nc-TiN/Si 3 N 4 nanocomposites free of impurities to be about 170 GPa. - Highlights: • Interface stability in TiN/SiN x heterostructures at T ≤ 1400 K is studied by quantum molecular dynamics. • Ideal decohesion and shear strengths of the heterostructures have been calculated. • Achievable hardness of nc-TiN/Si 3 N 4 -like nanocomposites of about 170 GPa is calculated. • Experimentally achieved lower hardness is limited by flaws, such as oxygen impurities
First-principles calculations of two cubic fluoropervskite compounds: RbFeF3 and RbNiF3
Mubarak, A. A.; Al-Omari, Saleh
2015-05-01
We present first-principles calculations of the structural, elastic, electronic, magnetic and optical properties for RbFeF3 and RbNiF3. The full-potential linear augmented plan wave (FP-LAPW) method within the density functional theory was utilized to perform the present calculations. We employed the generalized gradient approximation as exchange-correlation potential. It was found that the calculated analytical lattice parameters agree with previous studies. The analysis of elastic constants showed that the present compounds are elastically stable and anisotropic. Moreover, both compounds are classified as a ductile compound. The calculations of the band structure and density functional theory revealed that the RbFeF3 compound has a half-metallic behavior while the RbNiF3 compound has a semiconductor behavior with indirect (M-Γ) band gap. The ferromagnetic behavior was studied for both compounds. The optical properties were calculated for the radiation of up to 40 eV. A beneficial optics technology is predicted as revealed from the optical spectra.
Structural, elastic, electronic and optical properties of bi-alkali ...
Indian Academy of Sciences (India)
The structural parameters, elastic constants, electronic and optical properties of the bi-alkali antimonides (Na 2 KSb, Na 2 RbSb, Na 2 CsSb, K 2 RbSb, K 2 CsSb and Rb 2 CsSb) were calculated using state-of-the-art density functional theory. Different exchange-correlation potentials were adopted to predict the physical ...
Structural, elastic, electronic and optical properties of bi-alkali
Indian Academy of Sciences (India)
The structural parameters, elastic constants, electronic and optical properties of the bi-alkali antimonides (Na 2 KSb, Na 2 RbSb, Na 2 CsSb, K 2 RbSb, K 2 CsSb and Rb 2 CsSb) were calculated using state-of-the-art density functional theory. Different exchange-correlation potentials were adopted to predict the physical ...
A first-principles study of the SnO2 monolayer with hexagonal structure
Xiao, Wen-Zhi; Xiao, Gang; Wang, Ling-Ling
2016-11-01
We report the structural, electronic, magnetic, and elastic properties of a two-dimensional (2D) honeycomb stannic oxide (SnO2) monolayer based on comprehensive first-principles calculations. The free-standing and well-ordered 2D centered honeycomb SnO2 (T-SnO2) monolayer with D3d point-group symmetry has good dynamical stability, as well as thermal stability at 500 K. The T-SnO2 monolayer is a nonmagnetic wide-bandgap semiconductor with an indirect bandgap of 2.55/4.13 eV obtained by the generalized gradient approximation with the Perdew-Burke-Ernzerhof/Heyd-Scuseria-Ernzerhof hybrid functional, but it acquires a net magnetic moment upon creation of a Sn vacancy defect. The elastic constants obtained from the relaxed ion model show that the T-SnO2 monolayer is much softer than MoS2. The bandgap monotonically decreases with increasing strain from -8% to 15%. An indirect-to-direct bandgap transition occurs upon applying biaxial strain below -8%. Synthesis of the T-SnO2 monolayer is proposed. We identify the Zr(0001) surface as being suitable to grow and stabilize the T-SnO2 monolayer. The unique structure and electronic properties mean that the T-SnO2 monolayer has promising applications in nanoelectronics. We hope that the present study on the stable free-standing SnO2 monolayer will inspire researchers to further explore its importance both experimentally and theoretically.
Seismic Velocity and Elastic Properties of Plate Boundary Faults
Jeppson, Tamara N.
The elastic properties of fault zone rock at depth play a key role in rupture nucleation, propagation, and the magnitude of fault slip. Materials that lie within major plate boundary fault zones often have very different material properties than standard crustal rock values. In order to understand the mechanics of faulting at plate boundaries, we need to both measure these properties and understand how they govern the behavior of different types of faults. Mature fault zones tend to be identified in large-scale geophysical field studies as zones with low seismic velocity and/or electrical resistivity. These anomalous properties are related to two important mechanisms: (1) mechanical or diagenetic alteration of the rock materials and/or (2) pore fluid pressure and stress effects. However, in remotely-sensed and large-length-scale data it is difficult to determine which of these mechanisms are affecting the measured properties. The objective of this dissertation research is to characterize the seismic velocity and elastic properties of fault zone rocks at a range of scales, with a focus on understanding why the fault zone properties are different from those of the surrounding rock and the potential effects on earthquake rupture and fault slip. To do this I performed ultrasonic velocity experiments under elevated pressure conditions on drill core and outcrops samples from three plate boundary fault zones: the San Andreas Fault, California, USA; the Alpine Fault, South Island, New Zealand; and the Japan Trench megathrust, Japan. Additionally, I compared laboratory measurements to sonic log and large-scale seismic data to examine the scale-dependence of the measured properties. The results of this study provide the most comprehensive characterization of the seismic velocities and elastic properties of fault zone rocks currently available. My work shows that fault zone rocks at mature plate boundary faults tend to be significantly more compliant than surrounding crustal
Chern-Simons theory from first principles
International Nuclear Information System (INIS)
Marino, E.C.
1994-01-01
A review is made of the main properties of the Chern-Simons field theory. These include the dynamical mass generation to the photon without a Higgs field, the statistical transmutation of charged particles coupled to it and the natural appearance of a transverse conductivity. A review of standard theories proposed for the Quantum Hall Effect which use the Chern-Simons term is also made, emphasizing the fact that this terms is put in an artificial manner. A physical origin for the Chern-Simons term is proposed, starting from QED in 3+1 D with the topological term and imposing that the motion of charged matter is restricted to an infinite plane. (author). 12 refs
Spectroscopy of organic semiconductors from first principles
Sharifzadeh, Sahar; Biller, Ariel; Kronik, Leeor; Neaton, Jeffery
2011-03-01
Advances in organic optoelectronic materials rely on an accurate understanding their spectroscopy, motivating the development of predictive theoretical methods that accurately describe the excited states of organic semiconductors. In this work, we use density functional theory and many-body perturbation theory (GW/BSE) to compute the electronic and optical properties of two well-studied organic semiconductors, pentacene and PTCDA. We carefully compare our calculations of the bulk density of states with available photoemission spectra, accounting for the role of finite temperature and surface effects in experiment, and examining the influence of our main approximations -- e.g. the GW starting point and the application of the generalized plasmon-pole model -- on the predicted electronic structure. Moreover, our predictions for the nature of the exciton and its binding energy are discussed and compared against optical absorption data. We acknowledge DOE, NSF, and BASF for financial support and NERSC for computational resources.
First-Principles Investigations on Europium Monoxide
Wang, Hao
2011-05-01
Europium monoxide is both an insulator and a Heisenberg ferromagnet (Tc=69 K). In the present thesis, the author has investigated the electronic structure of different types of EuO by density functional theory. The on-site Coulomb interaction of the localized Eu 4f and 5d electrons, which is wrongly treated in the standard generalized gradient approximation method, is found to be crucial to obtain the correct insulating ground state as observed in experiments. Our results show that the ferromagnetism is stable under pressure, both hydrostatic and uniaxial. For both types of pressure an insulator-metal transition is demonstrated. Moreover, the experimentally observed insulator-metal transition in oxygen deficient and gadolinium-doped EuO is reproduced in our calculations for impurity concentrations of 6.25% and 25%. Furthermore, a 10- layer EuO thin film is theoretically predicted to be an insulator with a narrow band gap of around 0.08 eV, while the Si/EuO interface shows metallic properties with the Si and O 2p as well as Eu 5d bands crossing the Fermi level.
Magnetic and elastic properties of the antiferromagnet uranium mononitride
International Nuclear Information System (INIS)
Van Doorn, C.F.
1976-10-01
The magnetic and elastic properties of antiferromagnetic uranium mononitride single crystals are studied in the thesis from the measurements of the temperature dependences of the magnetic susceptibility, electrical resistivity and elastic constants. The elastic constants C 11 , C 12 and C 44 were determined in the temperature interval 4 to 300 K by ultrasonic measurements of the five possible wave velocities in the [100] and [110] directions. A test for internal consistency was also made. A dip of about 9 percent occurs in C 11 at a temperature of 5 to 6 K lower than the Neel temperature T(N) (equals about 53 K). Starting at T(N), a renormalization in C 44 is proportional to the square of the sublattice magnetization also occurs. Both these results agree with model calculations which include spin-phonon interactions. The investigation of this anomaly was extended by measuring the electrical resistivity of a sample cut from the same crystal as that on which the elasticity was measured. No anomalous behavior was observed at the temperature where C 11 displays its anomaly. However, a discontinuity in the temperature derivative of the resistance was found at T(N). The possible effect of a magnetic field on the resistivity, as well as on the elasticity, was investigated without any measurable effect. The magnetic susceptibility was measured with a Foner magnetometer between 4 and 1 000 K. It was found that above the Neel temperature the paramagnetic susceptibility followed a revised Curie-Weiss law. In an attempt to ascertain the ionic state of the 5f-uranium ion in UN, use was made of the experimentally determined Weiss constant, spin disorder resistivity and Knight shift. A calculation was made that gave a good representation of the ratio of the experimental susceptibilities along the [100] and [110] directions in the ordered region [af
Designing a prosthesis to simulate the elastic properties of skin.
Bellamy, K E; Waters, M G J
2005-01-01
The materials which are currently used to make maxillofacial prostheses are far from ideal and require considerable improvement with respect to their ability to mimic the properties of skin. To this aim, a novel three-layered maxillofacial prosthesis has been designed consisting of a silicone rubber base layer, an inner gel layer and an outer polymeric coating (to simulate the elastic properties of skin). The aim of the work in this study was to develop the inner silicone gel layer which displays similar properties to facial skin. Through the use of unique linear extensometry testing, in vivo measurements for the Area under the Curve (AUC), Hysteresis (viscoelastic behaviour), Fmax (maximum force), F30 and F60 (force after 30 and 60 seconds) were obtained from the facial skin of 15 volunteers. The results were used as a basis for developing silicone gel formulations for the inner layer, to closely resemble those of facial skin. Gels were made by the addition of both low and high molecular weight unreactive silicone fluids and were further tested for compression, water absorption and dehydration. Testing showed that a gel has been produced that closely simulates the elastic properties of skin when bonded to a base silicone rubber layer. Further testing will need to deduce whether these properties will be affected by the addition of the outer polymeric layer.
First Principles Design of Non-Centrosymmetric Metal Oxides
Young, Joshua Aaron
The lack of an inversion center in a material's crystal structure can result in many useful material properties, such as ferroelectricity, piezoelectricity and non-linear optical behavior. Recently, the desire for low power, high efficiency electronic devices has spurred increased interest in these phenomena, especially ferroelectricity, as well as their coupling to other material properties. By studying and understanding the fundamental structure-property relationships present in non-centrosymmetric materials, it is possible to purposefully engineer new compounds with the desired "acentric" qualities through crystal engineering. The families of ABO3 perovskite and ABO2.5 perovskite-derived brownmillerite oxides are ideal for such studies due to their wide range of possible chemistries, as well as ground states that are highly tunable owing to strong electron-lattice coupling. Furthermore, control over the B-O-B bond angles through epitaxial strain or chemical substitution allows for the rapid development of new emergent properties. In this dissertation, I formulate the crystal-chemistry criteria necessary to design functional non-centrosymmetric oxides using first-principles density functional theory calculations. Recently, chemically ordered (AA')B2O 6 oxides have been shown to display a new form of rotation-induced ferroelectric polarizations. I now extend this property-design methodology to alternative compositions and crystal classes and show it is possible to induce a host of new phenomena. This dissertation will address: 1) the formulation of predictive models allowing for a priori design of polar oxides, 2) the optimization of properties exhibited by these materials through chemical substitution and cation ordering, and 3) the use of strain to control the stability of new phases. Completion of this work has led to a deeper understanding of how atomic structural features determine the physical properties of oxides, as well as the successful elucidation of
Carbyne from first principles: chain of C atoms, a nanorod or a nanorope.
Liu, Mingjie; Artyukhov, Vasilii I; Lee, Hoonkyung; Xu, Fangbo; Yakobson, Boris I
2013-11-26
We report an extensive study of the properties of carbyne using first-principles calculations. We investigate carbyne's mechanical response to tension, bending, and torsion deformations. Under tension, carbyne is about twice as stiff as the stiffest known materials and has an unrivaled specific strength of up to 7.5 × 10(7) N·m/kg, requiring a force of ∼10 nN to break a single atomic chain. Carbyne has a fairly large room-temperature persistence length of about 14 nm. Surprisingly, the torsional stiffness of carbyne can be zero but can be "switched on" by appropriate functional groups at the ends. Further, under appropriate termination, carbyne can be switched into a magnetic semiconductor state by mechanical twisting. We reconstruct the equivalent continuum elasticity representation, providing the full set of elastic moduli for carbyne, showing its extreme mechanical performance (e.g., a nominal Young's modulus of 32.7 TPa with an effective mechanical thickness of 0.772 Å). We also find an interesting coupling between strain and band gap of carbyne, which is strongly increased under tension, from 2.6 to 4.7 eV under a 10% strain. Finally, we study the performance of carbyne as a nanoscale electrical cable and estimate its chemical stability against self-aggregation, finding an activation barrier of 0.6 eV for the carbyne-carbyne cross-linking reaction and an equilibrium cross-link density for two parallel carbyne chains of 1 cross-link per 17 C atoms (2.2 nm).