高压下固态Kr弹性性质、电子结构和光学性质的第一性原理计算

采用密度泛函理论中平面波基矢,模守恒赝势结合局域密度近似以及广义梯度近似对固态Kr在高压下的结构以及弹性性质进行了研究, 通过计算发现弹性常数,Debye温度以及声速都随压力的增大而增大,所计算的弹性常数与实验和其他的理论符合的很好. 利用Debye模型得到了固态Kr的热力学性质, 熵随压力的增大而减小,随温度升高而升高;而定容热容C_v,定压热容C_p则随温度升高而升高,而且C_v在达到一定温度时趋于定值,所得的热力学性质和实验值是相符的．最后还预测了固态Kr在高压下的电子结构和光学性质, 计算结果表明随压力的增加固态Kr的前沿能带变窄,光吸收系数增大,吸收峰增宽,电子更容易发生跃迁,固态Kr有可能转化为半导体． 关键词： Kr 第一性原理 弹性常数 光学性质     

Prediction study of the structural,elastic, electronic and optical properties of the antiperovskite BiNBa3

We use an ab initio full-potential linear muffin-tin orbital method within the local density approximation (LDA) to study the structural, elastic, electronic and optical properties of the antiperovskite BiNBa₃. The calculated lattice parameter is in good agreement with previous calculations. The elastic constants and their pressure dependence are calculated; we found a linear dependence of elastic stiffness on the pressure. We estimated the Debye temperature of this compound from the average sound velocity. We also present results of the effective masses for the electrons in the conduction band (CB) and the holes in the valence band (VB). To complete the fundamental characteristics of this compound we have analyzed the optical properties.     

Structural, electronic, elastic and optical properties of fluoro-perovskite KZnF3

We determine the structural, electronic, elastic and optical properties of fluoro-perovskite KZnF₃ using the full potential linear augmented plane wave approach (FP-LAPW) based on the density functional theory (DFT). The exchange-correlation potential is treated by the local density approximation (LDA) and the generalized gradient approximation (GGA). The calculated structural parameters are in good agreement with the available data. We have obtained an indirect band gap. The effect of the pressure on the band gaps is investigated. We evaluate the elastic constants (C_ij), elastic moduli and the Debye temperature. The imaginary and the real parts of the dielectric function ε(ω) and some optical constants are also calculated.     

Ab initio calculations of the elastic, electronic, optical, and vibrational properties of PdGa compound under pressure

The structural, elastic, electronic, optical, and vibrational properties of cubic PdGa compound are investigated using the norm-conserving pseudopotentials within the local density approximation (LDA) in the framework of the density functional theory. The calculated lattice constant has been compared with the experimental value and has been found to be in good agreement with experimental data. The obtained electronic band structures show that PdGa compound has no band gap. The second-order elastic constants have been calculated, and the other related quantities such as the Young’s modulus, shear modulus, Poisson’s ratio, anisotropy factor, sound velocities, and Debye temperature have also been estimated. Our calculated results of elastic constants show that this compound is mechanically stable. Furthermore, the real and imaginary parts of the dielectric function and the optical constants such as the electron energy-loss function, the optical dielectric constant and the effective number of electrons per unit cell are calculated and presented in the study. The phonon dispersion curves are also derived using the direct method.     

Band parameters of α-LiBeN semiconductor from density functional calculations

The structural, elastic, electronic, optical and thermal properties of α phase in LiBeN semiconductor have been studied using pseudo-potential plane wave method based on the density functional theory. The computed lattice parameter agrees well with previous theoretical work. The elastic constants and their pressure dependence are predicted using the static finite strain technique. A set of isotropic elastic parameters and related properties, namely bulk and shear moduli, Young’s modulus, Poisson’s ratio, average sound velocity and Debye temperature are numerically estimated in the frame work of the Voigt–Reuss–Hill approximation for α-LiBeN polycrystalline aggregate. The assignments of the structures in the optical spectra and band structure transitions have been examined and discussed. The thermal effect on heat capacities is investigated by the quasi-harmonic Debye model. To the best of our knowledge, most of the studied properties of the material of interest are reported for the first time.     

Band structure,Fermi surface,elastic,thermodynamic,and optical properties of AlZr_3,AlCu_3,and AlCu_2Zr:First-principles study

The electronic properties(Fermi surface,band structure,and density of states(DOS)) of Al-based alloys AlM_3(M=Zr and Cu) and AlCu_2Zr are investigated using the first-principles pseudopotential plane wave method within the generalized gradient approximation(GGA).The structural parameters and elastic constants are evaluated and compared with other available data.Also,the pressure dependences of mechanical properties of the compounds are studied.The temperature dependence of adiabatic bulk modulus,Debye temperature,specific heat,thermal expansion coefficient,entropy,and internal energy are all obtained for the first time through quasi-harmonic Debye model with phononic effects for T = 0 K-100 K.The parameters of optical properties(dielectric functions,refractive index,extinction coefficient,absorption spectrum,conductivity,energy-loss spectrum,and reflectivity) of the compounds are calculated and discussed for the first time.The reflectivities of the materials are quite high in the IR-visible-UV region up to ~ 15 eV,showing that they promise to be good coating materials to avoid solar heating.Some of the properties are also compared with those of the Al-based Ni_3 Al compound.     

FP-LMTO calculations of the structural,elastic, thermodynamic,and electronic properties of the ideal-cubic perovskite BiGaO3

Using the first-principles full-potential linear muffin-tin orbital method within the local density approximation, we have studied the structural, elastic, thermodynamic, and electronic properties of the ideal-cubic perovskite BiGaO₃. It is found that this compound has an indirect band gap. The valence band maximum (VBM) is located at Γ-point, whereas the conduction band minimum (CBM) is located at X-point. The pressure and volume dependences of the energy band gaps have been calculated. The elastic constants at equilibrium are also determined. We derived the bulk and shear moduli, Young’s modulus, and Poisson’s ratio. The thermodynamic properties are predicted through the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. The variation of the bulk modulus, heat capacities, and Debye temperature with pressure and temperature are successfully obtained.     

Elastic,electronic and thermodynamic properties of fluoro-perovskite KZnF3 via first-principles calculations

The elastic, electronic and thermodynamic properties of fluoro-perovskite KZnF₃ have been calculated using the full-potential linearized augmented plane wave (FP-LAPW) method. The exchange-correlation potential is treated with the generalized gradient approximation of Perdew-Burke-Ernzerhof (GGA-PBE). Also, we have used the Engel and Vosko GGA formalism (GGA-EV) to improve the electronic band structure calculations. The calculated structural properties are in good agreement with available experimental and theoretical data. The elastic constants C _ij are calculated using the total energy variation with strain technique. The shear modulus, Young’s modulus, Poisson’s ratio and the Lamé coefficients for polycrystalline KZnF₃ aggregates are estimated in the framework of the Voigt-Reuss-Hill approximations. The ductility behavior of this compound is interpreted via the calculated elastic constants C _ij . Electronic and bonding properties are discussed from the calculations of band structure, density of states and electron charge density. The thermodynamic properties are predicted through the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. The variation of bulk modulus, lattice constant, heat capacities and the Debye temperature with pressure and temperature are successfully obtained.     

Mechanical,electronic and thermodynamic properties of TE-C36 under high pressure

The structural parameters, mechanical, electronic and thermodynamic properties of TE-C36 under high pressure were calculated via the density functional theory in combination with the quasi-harmonic Debye model. The results show that the pressure has significant effects on the equilibrium structure parameters, mechanical, electronic and thermodynamic properties of TE-C36. The obtained ground state structural parameters are in good agreement with previous theoretical results. The mechanically and dynamically stable under pressure were confirmed by the calculated elastic constants and phonon dispersion spectra. The elastic constants, elastic modulus, B/G ratio, Poisson’s ratio and Vicker’s hardness were determined in the pressure range of 0–100?GPa. The elastic anisotropy of TE-C36 under pressure are also determined in detail. The electronic structure calculations reveal that TE-C36 remains a direct band gap semiconductor when the pressure changes from 0 to 100?GPa, and the band gap decreases with increasing pressure. Furthermore, the pressure and temperature dependence of thermal expansion coefficient, heat capacity and Debye temperature are predicted in a wide pressure (0–90?GPa) and temperature (0–2500?K) ranges. The obtained results are expected to provide helpful guidance for the future synthesis and application of TE-C36.     

Structural,elastic, electronic,optical and thermal properties of c-SiGe<Subscript>2</Subscript>N<Subscript>4</Subscript>

We have investigated the structural, elastic, electronic, optical and thermal properties of c-SiGe₂N₄ by using the ultrasoft pseudopotential density functional method within the generalized gradient approximation. The calculated structural parameters, including the lattice constant, the internal free parameter, the bulk modulus and its pressure derivative are in agreement with the available data. The independent elastic constants and their pressure dependence, calculated using the static finite strain technique, satisfy the requirement of mechanical stability, indicating that c-SiGe₂N₄ compound could be stable. We derive the shear modulus, Young’s modulus, Poisson’s ratio and Lamé’s coefficients for ideal polycrystalline c-SiGe₂N₄ aggregate in the framework of the Voigt-Reuss-Hill approximation. We estimate the Debye temperature of this compound from the average sound velocity. Band structure, density of states, Mulliken charge populations and pressure coefficients of energy band gaps are investigated. Furthermore, in order to understand the optical properties of c-SiGe₂N₄, the dielectric function, refractive index, extinction coefficient, optical reflectivity and electron energy loss are calculated for radiation up to 40 eV. Thermal effects on some macroscopic properties of c-SiGe₂N₄ are predicted using the quasi-harmonic Debye model in which the lattice vibrations are taken into account. We have obtained successfully the variations of the primitive cell volume, volume expansion coefficient, heat capacities and Debye temperature with pressure and temperature in the ranges of 0–40 GPa and 0–2000 K. For the first time, the numerical estimates of the elastic constants and related parameters, and the thermal properties are performed for c-SiGe₂N₄.     

Ab initio studies of the structural,elastic, electronic and thermal properties of NiTi2 intermetallic

First principles calculations were performed in the framework of the density functional theory (DFT) using the Full Potential–Linear Augment Plane Wave method (FP–LAPW) within the generalized gradient approximation (GGA) to predict the structural, electronic, elastic and thermal properties of NiTi₂ intermetallic compound. By using the Wien2k all-electron code, calculations of the ground state and electronic properties such as lattice constants, bulk modulus, presure derivative of bulk modulus, total energies and density of states were also included. The elastic constants and mechanical properties such as Poisson’s ratio, Young’s modulus and shear modulus are estimated from the calculated elastic constants of the single crystal. Through the quasi-harmonic Debye model, the preasure and temperature dependences of the linear expansion coefficient, bulk modulus and heat capacity have been investigated. Finally, the Debye temperature has been estimated from the average sound velocity according to the predicted polycrystal bulk properties and from the single crystal elastic constants.     

DFT - based study of electronic structures and mechanical properties of LiTaO3: ferroelectric and paraelectric phases

Abstract

By applying ab initio calculation within density functional theory (DFT), we study the structure parameters, electronic band structure, elastic coefficients, polycrystalline elastic properties, anisotropy factors and Debye temperature of ferroelectric and paraelectric phases of LiTaO₃ within the generalised gradient approximation at ambient pressure. The atomic structure in both phases is fully relaxed and the lattice constant, angle and atomic positions are well consistent with experimental values. The computed single-crystal elastic coefficients indicate that mechanical stability of LiTaO₃ in both phases is confirmed using the generalised Born criteria. The shear, bulk and Young’s modulus, Poisson’s ratio, and Vickers hardness were computed according to theoretical elastic constants by Voight–Reuss–Hill method. Several anisotropy factors and indexes are computed to illustrate mechanical anisotropy. Both phases are shown to be weakly anisotropic. The Debye temperature is estimated using the longitude and transverse elastic wave velocity of the ideal polycrystalline LiTaO₃ aggregates. We have found that LiTaO₃ in both phases has an indirect energy band gap. The differences in the electronic structure and density of states for both phases are quite small. Our results indicate that the mechanical and bonding properties of both phases are very similar. The obtained results were compared with the available experimental and theoretical values.     

Ab initio investigation of the structural,elastic and electronic properties of the anti-perovskite TlNCa3

We have investigated the structural, elastic and electronic properties of the anti-perovskite TlNCa₃ using ab initio calculations within the generalized gradient approximation and the local density approximation for the exchange–correlation potential. The lattice constant, bulk modulus, elastic constants and their pressure dependence, energy band structures, density of states and charge density distribution are calculated and analyzed in comparison with the available experimental and theoretical data. The bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, Lamé’s coefficients, average sound velocity and Debye temperature are numerically estimated for ideal polycrystalline TlNCa₃ aggregates in the framework of the Voigt–Reuss–Hill approximation. This is the first theoretical prediction of the elastic constants and their related properties for TlNCa₃ that requires experimental confirmation.     

The stabilities, electronic structures and elastic properties of Rb-As systems

The structural, electronic and elastic properties of Rb–As systems (RbAs in NaP, LiAs and AuCu structures, RbAs2 in the MgCu2 structure, Rb3 As in Na3As, Cu3 P and Li3Bi structures, and Rb5 As4 in the A5B4 structure) are investigated with the generalized gradient approximation in the frame of density functional theory. The lattice parameters, cohesive energies, formation energies, bulk moduli and the first derivatives of the bulk moduli (to fit Murnaghan’s equation of state) of the considered structures are calculated and reasonable agreement is obtained. In addition, the phase transition pressures are also predicted. The electronic band structures, the partial densities of states corresponding to the band structures and the charge density distributions are presented and analysed. The second-order elastic constants based on the stress-strain method and other related quantities such as Young’s modulus, the shear modulus, Poisson’s ratio, sound velocities, the Debye temperature and shear anisotropy factors are also estimated.     

Electronic structure and elastic properties of scandium carbide and yttrium carbide: A first principles study

We have studied the electronic, structural, and elastic properties of scandium carbide and yttrium carbide by means of accurate first principles total energy calculations using the full-potential linearized plane wave method (FP-LAPW). We have used the generalized gradient approximation (GGA) for the exchange and correlation potential. Volume optimization, energy band structure, and density of states (DOS) of the systems are presented. The second order elastic constants have been calculated and other related quantities such as the Zener anisotropy factor, Poisson's ratio, Young's modulus, Kleinman parameter, Debye temperature, and sound velocities have been determined. The band gap calculation shows that YC is relatively more ionic than ScC.     

Structural,elastic and thermodynamic properties of the tetragonal structure of germanium carbonitride

The structural, mechanical, electronic and thermodynamic properties of the tetragonal structure germanium carbonitride (t-GeCN) were first investigated using the density function theory with the ultrasoft psedopotential scheme in the frame of the generalized gradient approximation and the local density approximation. The elastic constants have confirmed that the t-GeCN is mechanically stable and phonon spectra have confirmed that the t-GeCN is dynamically stable. The anisotropy studies show that t-GeCN exhibits a larger anisotropy in its Poisson's ratio, Young's modulus, shear modulus, sound velocities and universal elastic anisotropy index. Electronic structure study shows that t-GeCN is an indirect semiconductor with band gap of 0.628 eV. The thermodynamic properties of t-GeCN, including Debye temperature, heat capacity, Grüneisen parameter and thermal expansion coefficient are investigated utilizing the quasi-harmonic Debye model.     

Structural,electronic, optical and thermodynamic investigations of NaXF3 (X = Ca and Sr): First-principles calculations

The structural, electronic and optical properties for fluoro-perovskite NaXF₃ (X?=?Ca and Sr) compounds have calculated by WIEN2k code based on full potential linearized augmented plane wave (FP-LAPW) approach within density functional theory (DFT). To perform the total energy calculations, exchange-correlation energy/potential functional has been utilized into generalized gradient approximation (GGA) and local density approximation (LDA). Our evaluated results like equilibrium lattice constants, bulk moduli, and their pressure derivatives are in agreement with the available data. The electronic band structure calculation has revealed an indirect band-gap nature of NaCaF₃, while NaSrF₃ has direct band gap. Total and partial densities of states confirm the degree of localized electrons in different bands. The optical transitions in NaCaF₃ and NaSrF₃ compounds were identified by assigning corresponding peaks obtained from the dispersion relation for the imaginary part of the dielectric function. The thermodynamic properties were calculated using quasi-harmonic Debye model to account lattice vibrations. In addition, the influence of temperature and pressure effects was analyzed on bulk modulus, lattice constant, heat capacities and Debye temperature.     

高温高压下碳化钨晶体的结构、力学、电子、光学以及热力学性能的第一性原理计算

本文利用密度泛函理论中的广义梯度近似对碳化钨晶体的三种结构(碳化钨相、闪锌矿相以及纤锌矿相)进行了优化,得到能量最低的稳定构型,并在此基础上计算了它的力学、电子、光学和高温高压下的热力学性质.研究表明:在0～300 GPa压力范围内,碳化钨相具有最高的稳定性.同时,高压下碳化钨相的弹性常数满足Born-Huang准则,且0 GPa和300 GPa下的声子色散没有虚频,证明了高压下碳化钨相的静力学稳定性和动力学稳定性.电子性质表明了碳化钨的金属性.光学性质表明碳化钨在高能区很难吸收光.热力学性质的研究表明:体积比V/V_0对压强的变化更敏感;高温时C_V曲线近似一条直线;给定压强下热膨胀系数α在600 K温度以上增长非常缓慢;压强对德拜温度Θ_D的影响较大;在低压下格林艾森系数γ的变化较大.     

First-principles study of the structural, elastic, electronic, optical, and vibrational properties of intermetallic Pd2Ga

The structural,elastic,electronic,optical,and vibrational properties of the orthorhombic Pd2Ga compound are investigated using the norm-conserving pseudopotentials within the local density approximation in the frame of density functional theory.The calculated lattice parameters have been compared with the experimental values and found to be in good agreement with these results.The second-order elastic constants and the other relevant quantities,such as the Young’s modulus,shear modulus,Poisson’s ratio,anisotropy factor,sound velocity,and Debye temperature,have been calculated.It is shown that this compound is mechanically stable after analysing the calculated elastic constants.Furthermore,the real and imaginary parts of the dielectric function and the optical constants,such as the optical dielectric constant and the effective number of electrons per unit cell,are calculated and presented.The phonon dispersion curves are derived using the direct method.The present results demonstrate that this compound is dynamically stable.     

First-principles study of the structural, elastic, electronic, optical, and vibrational properties of intermetallic Pd2Ga

The structural, elastic, electronic, optical, and vibrational properties of the orthorhombic Pd₂Ga compound are investigated using the norm-conserving pseudopotentials within the local density approximation in the frame of density functional theory. The calculated lattice parameters have been compared with the experimental values and found to be in good agreement with these results. The second-order elastic constants and the other relevant quantities, such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocity, and Debye temperature, have been calculated. It is shown that this compound is mechanically stable after analysing the calculated elastic constants. Furthermore, the real and imaginary parts of the dielectric function and the optical constants, such as the optical dielectric constant and the effective number of electrons per unit cell, are calculated and presented. The phonon dispersion curves are derived using the direct method. The present results demonstrate that this compound is dynamically stable.