Electronic and high pressure elastic properties of RECd and REHg (RE=Sc,La and Yb) intermetallic compounds

Structural, electronic, elastic and mechanical properties of Cd and Hg based rare earth intermetallics (RECd and REHg; RE=Sc, La and Yb) have been investigated using the full-potential linearized augmented plane-wave (FP-LAPW) method within the density-functional theory (DFT). The ground state properties such as lattice constant (a₀), bulk modulus (B) and its pressure derivative (B′) have been obtained using optimization method and are found in good agreement with the available experimental results. The calculated enthalpy of formation shows that LaHg has the strongest alloying ability and structural stability. The electronic band structures and density of states reveal the metallic character of these compounds. The structural stability mechanism is also explained through the electronic structures of these compounds. The chemical bonding between rare earth atoms and Cd, Hg is interpreted by the charge density plots along (1 1 0) direction. The elastic constants are predicted from which all the related mechanical properties like Poisson’s ratio (σ), Young’s modulus (E), shear modulus (G_H) and anisotropy factor (A) are calculated. The ductility/brittleness of these intermetallics is predicted. Chen’s method has been used to predict the Vicker’s hardness of RECd and REHg compounds. The pressure variation of the elastic constants is also reported in their B₂ phase.     

Structural,elastic, thermodynamic and electronic properties of LuX (X = N,Bi and Sb) compounds: first principles calculations

ABSTRACT

The structural, electronic, elastic and thermodynamic properties of LuX (X = N, Bi and Sb) based on rare earth into phases, Rocksalt (B1) and CsCl (B2) have been investigated using full-potential linearized muffin-tin orbital method (FP-LMTO) within density functional theory. Local density approximation (LDA) for exchange-correlation potential and local spin density approximation (LSDA) are employed. The structural parameters as lattice parameters a₀, bulk modulus B, its pressure derivate B’ and cut-off energy (E_c) within LDA and LSDA are presented. The elastic constants were derived from the stress–strain relation at 0 K. The thermodynamic properties for LuX using the quasi-harmonic Debye model are studied. The temperature and pressure variation of volume, bulk modulus, thermal expansion coefficient, heat capacities, Debye temperature and Gibbs free energy at different pressures (0–50 GPa) and temperatures (0–1600 K) are predicted. The calculated results are in accordance with other data.     

Electronic and thermal properties of B2-type AlRE intermetallic compounds: A first principles study

The ground state electronic structure and thermal properties of B₂-type intermetallic compounds AlRE (RE: Pm, Sm, Eu, Tb, Gd and Dy) have been studied using a self-consistent tight-binding linear muffin-tin orbital (TB-LMTO) method at ambient as well as at high pressure. These compounds show metallic behavior under ambient condition. The band structure, total energy, density of states and ground state properties like lattice parameter, bulk modulus are calculated in the present work. The Debye-Grüneisen model is used to calculate the Debye temperature and the Grüneisen constant. The calculated results are in good agreement with the reported experimental and other theoretical results. The variation in the Debye temperature with pressure has also been reported. We present a detailed analysis of the role of f electrons of RE in the AlRE system.     

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.     

Structural and Thermodynamic Properties of TiAl intermetallics under High Pressure

The structural and thermodynamic properties of TiAl intermetallics under high pressure have been investigated by ab initio plane-wave pseudopotential density functional theory method.It is found that the ratio of lattice parameter c to a keeps almost constant with a value of 1.02 under the pressure from 0 to 20 GPa,which agrees well with the experimental results.With the pressure increasing from 20 to 45 GPa the values of c/a decrease almost linearly from 1.02 to 0.99.These calculated results indicate under low pressure the variation rate for a-axis is almost the same to that for c-axis,but under higher pressure the variation for a-axis is smaller than along c-axis.Through the quasi-harmonic Debye model,the equation of state(EOS) of TiAl intermetallics,as well as the thermal expansion and heat capacity at various pressures and temperatures are also studied.     

Pressure effect on structural,electronic and thermodynamic investigations of europium filled skutterudite EuFe4Sb12: LDA and LSDA approximations

Numerical calculations based on the full potential muffin-tin orbitals method (FP-LMTO) within the local density approximation (LDA) and the local spin-density approximation (LSDA) to investigate the structural, electronic and thermodynamic properties of filled skutterudite EuFe₄Sb₁₂ are presented. The electronic band structure and density of states profiles prove that this material is a conductor. The present investigation is also extended to the elastic constants, such as the bulk modulus B, anisotropy factor A, shear modulus G, young's modulus E, Poisson's ratio ν, and the B/G ratio with pressure in the range of 0–40 GPa. The sound velocities and Debye temperatures are also predicted from the above constants. The variations of the primitive cell volume, expansion coefficient α, bulk modulus B, heat capacity (C_p and C_v), Debye temperature θ_D, Helmholtz free energy A, Gibbs free energy G, entropy S, and internal energy U with pressure and temperature in the range 0–3000 K are calculated successfully.     

Investigations of structural,electronic, mechanical and lattice dynamic properties of TiRu3 and TiOs3 compounds

Ab initio calculations of structural, electronic, elastic, and phonon properties of TiRu₃ and TiOs₃ compounds have been studied using the density functional theory (DFT) within the generalized gradient approximation (GGA). The basic structural properties such as lattice constants, bulk modulus and pressure derivative of bulk modulus of these compounds were studied and compared with the previous theoretical data. Electronic band structures and partial densities of states for TiRu₃ and TiOs₃ compounds were computed and analyzed. The electronic band calculations showed that the TiRu₃ and TiOs₃ compounds have metallic nature. Phonon spectra, their total and projected densities of states for these compounds were computed by using a linear-response method in the framework of the density functional perturbation theory. The specific heat capacities at a constant volume C_V and Debye temperature of TiCr₃ and TiOs₃ compounds were also calculated and discussed.     

First-principles investigation of the structural,optoelectronic and thermodynamic properties of InAsxP1-x ternary alloys under hydrostatic pressure effect

The main objective of our work is the study of structural, optoelectronic and thermodynamic properties of InAs_xP_1-x alloys in the zinc-blende structure using the full potential linearized augmented plane wave method (FP-LAPW) based on density functional theory (DFT). Different exchange correlation potentials were used, as well as the local density approximation (LDA) and the generalized gradient approximation (GGA) parameterized by Perdew–Burke–Ernzerhof (PBE-GGA) and PBE sol-GGA of Perdew, to estimate structural properties such as lattice parameters, the bulk modulus and its first pressure derivative. For electronic properties, the Tran-Blaha modified Becke–Johnson potential (TB-mBJ) was used for density of states (DOS) and band structure calculations. The results show that the compounds of interest are semiconductors with direct band gaps for the full range of x compositions and that the optical band gap decreases from 1.58 to 0.41 eV with increasing As concentrations. The obtained results show a good agreement with experimental and theoretical data found in the literature. In addition, we have investigated the dielectric function as well as the refractive index and the reflectivity. The electronic and optical properties were studied under hydrostatic pressure (P = 0, 5, 10, 15, 20, and 25 GPa), and it was found that the band gaps of the binary compounds change from a direct to an indirect harmonic Debye model was used, which takes into account the effect of pressure P and temperature T on the lattice parameter, to explore the heat capacity, the Debye temperature and the entropy under pressures ranging from 0 to 20 GPa and temperatures ranging from 0 to 1200 K.     

高压下TiC的弹性、电子结构及热力学性质的第一性原理计算

利用基于密度泛函理论的第一性原理平面波赝势方法 并结合准谐徳拜模型研究了NaCl结构的TiC在高压下的弹性性质、电子结构和热力学性质. 计算所得零温零压下的晶格常数、体弹模量及弹性常数与实验值符合得很好. 零温下弹性常数和弹性模量随压强增大而增大. 通过态密度和电荷密度的分析, Ti-C键随压强增大而增强. 运用准谐德拜模型, 成功计算了TiC在高温高压下的体弹模量、熵、热膨胀系数、徳拜温度、 Grüneisen参数和比热容. 结果表明压强对体弹模量、热膨胀系数和徳拜温度的影响大于温度对其的影响. 热容随着压强升高而减小, 在高温高压下, 热容接近Dulong-Petit极限.     

Structural, electronic, elastic and thermal properties of Mg2Si

First-principles calculations of the lattice parameter, electron density maps, density of states and elastic constants of Mg₂Si are reported. The lattice parameter is found to differ by less than 0.8% from the experimental data. Calculations of density of states and electron density maps are also performed to describe the orbital mixing and the nature of chemical bonding. Our results indicate that the bonding interactions in the Mg₂Si crystal are more covalent than ionic. The quasi-harmonic Debye model, by means of total energy versus volume calculations obtained with the plane-wave pseudopotential method, is applied to study the elastic, thermal and vibrational effects. The variations of bulk modulus, Grüneisen parameter, Debye temperature, heat capacity C_v, C_p and entropy with pressure P up to 7 GPa in the temperature interval 0-1300 K have been systemically investigated. Significant differences in properties are observed at high pressure and high temperature. When T<1300 K, the calculated entropy and heat capacity agree reasonably with available experimental data. Therefore, the present results indicate that the combination of first-principles and quasi-harmonic Debye model is an efficient approach to simulate the behavior of Mg₂Si.     

Electronic and thermodynamic properties of B2-FeSi from first principles

The electronic and thermodynamic properties of B2-FeSi have been investigated using the first-principles method based on the plane-wave basis set. The calculated equilibrium lattice constant is in good agreement with available experimental and theoretical data. Our results have shown that B2-FeSi was a narrow gap semiconductor of above 0.055 eV and exhibited metallic characteristics. The density of states (DOS) can also describe orbital mixing. Using the quasi-harmonic Debye model, the thermodynamic properties of B2-FeSi have been analyzed. Variations of the Debye temperature Θ_D, thermal expansion α, heat capacity C_v, entropy S and the Grüneisen parameter γ on temperature T and pressure P were obtained successfully in the ranges of 0-2400 K and 0-140 GPa.     

Theoretical study of the structural, elastic, electronic and thermal properties of the MAX phase Nb2SiC

Structural, elastic, electronic and thermal properties of the MAX phase Nb₂SiC are studied by means of a pseudo-potential plane-wave method based on the density functional theory. The optimized zero pressure geometrical parameters are in good agreement with the available theoretical data. The effect of high pressure, up to 40 GPa, on the lattice constants shows that the contractions along the c-axis were higher than those along the a-axis. The elastic constants C_ij and elastic wave velocities are calculated for monocrystal Nb₂SiC. Numerical estimations of the bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, average sound velocity and Debye temperature for ideal polycrystalline Nb₂SiC aggregates are performed in the framework of the Voigt-Reuss-Hill approximation. The band structure shows that Nb₂SiC is an electrical conductor. The analysis of the atomic site projected densities and the charge density distribution shows that the bonding is of covalent-ionic nature with the presence of metallic character. The density of states at Fermi level is dictated by the niobium d states; Si element has a little effect. Thermal effects on some macroscopic properties of Nb₂SiC are predicted using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. The variations of the primitive cell volume, volume expansion coefficient, bulk modulus, heat capacity and Debye temperature with pressure and temperature in the ranges of 0-40 GPa and 0-2000 K are obtained successfully.     

First-principles calculations on structural, elastic, electronic, optical and thermal properties of CsPbCl3 perovskite

The structural, elastic, electronic, optical and thermal properties of the semiconductor perovskite CsPbCl₃ were investigated using the pseudo-potential plane wave (PP-PW) scheme in the frame of generalized gradient approximation (GGA) and local density approximation (LDA). The computed lattice constant agrees reasonably with experimental and theoretical ones. The CsPbCl₃ crystal behaves as ductile material. The valence bands are separated from the conduction bands by a direct band gap R-R. We distinguished hybridization between Pb-p states and Cl-p states in the valence bonding region. Under compression at P=30 GPa, this material will have a metallic character. The thermal effect on the lattice constant, bulk modulus, Debye temperature and heat capacity C_V was predicted using the quasi-harmonic Debye model. To the author's knowledge, most of the studied properties are reported for the first time.     

Electronic structure, optical and thermodynamic properties of orthorhombic UCoGe under pressure

The electronic structures, optical and thermodynamic properties of orthorhombic UCoGe are investigated using the generalized gradient approximation (GGA) formalism in the framework of the density functional theory (DFT). The obtained lattice parameters, bulk modulus B and its pressure derivative B′ of UCoGe are in agreement with the available experimental data. From the analysis of band structure and density of states coming out from our calculations, we can see that UCoGe in the ground state belongs to a typical metallic alloy. Various optical properties, including the dielectric function and absorption coefficient as functions of the photon energy are calculated. The thermodynamic properties of UCoGe are predicted using the quasi-harmonic Debye model for the first time. The Debye temperature, the Grüneisen parameter, the heat capacity and the thermal expansion coefficient are obtained at high pressures and temperatures.     

Charge density wave instability in the quasi two-dimensional metal γ-Mo4011

Transport and specific heat properties have been studied on the orthorhombic molybdenum oxide γ-Mo₄0₁₁. The anisotropy of the electrical resistivity establishes that this compound is a quasi two-dimensional metal, as expected from crystal structure data. Both the resistivity and the thermopower show that an electronic transition, probably due to a charge density wave instability takes place at T_c = 100 K. Low temperature specific heat data provide an estimation of the Debye temperature and of the electronic density of states in the low temperature metallic phase.     

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.     

First-principles calculations of elastic and thermo-physical properties of Al, Mg and rare earth lanthanide elements

The elastic constants of the Al, Mg and rare earth (RE) lanthanide elements have been calculated at T=0 K by using the projector augmented-wave (PAW) method within the generalized gradient approximation (GGA). The bulk moduli, shear moduli, Young's moduli and Poisson's ratio of poly-crystalline solid are estimated from the calculated elastic constants of single crystal. Based on the quasi-harmonic Debye model, the Debye temperature, heat capacity, Grüneisen parameter and linear thermal expansion coefficient are also estimated. The present calculated results are in reasonable agreement with the available experimental data and other theoretical results. The present calculation of elastic constants for Ce also indicates that the PAW potential (named “Ce_3”), for which one f electron is kept frozen in the core and hence fix the valency of Ce to three (Ce_3) does not yield good results for the elastic constants.     

Elastic properties,Debye temperature,density of states and electron–phonon coupling of ZrB12 under pressure

The structural parameters, elastic constants and the electronic density of states of ZrB₁₂ under pressure are determined using first-principles calculations with plane-wave pseudopotential density functional theory, within the generalized gradient approximation. From the elastic constants the elastic parameters and Debye temperature were calculated. They increase as the pressure is increased. The density of states at the Fermi level decreases as pressure is increased, changing from 0.576 to 0.515. Using the Debye temperature and the McMillan equation, the electron–phonon coupling constant was obtained as a function of pressure. It is found that the electron–phonon coupling constant is proportional to the logarithm of the ratio between the value of the Debye temperature and the value of the superconducting critical temperature.     

高压下TiAl3结构及热动力学性质的第一性原理研究

采用平面波赝势密度泛函理论研究了钛铝系金属间化合物TiAl₃的结构性质, 计算值与实验值及其他理论值相符合. 通过准谐德拜模型研究了TiAl₃的热动力学性质, 计算得到了相对体积(V/V₀)与压强和温度的关系, 以及不同温度和压强下的热膨胀系数和热容. 与TiAl的计算结果进行对比, 发现随着温度的升高, TiAl的热膨胀系数增大的速度高于TiAl₃, 且随着压强的增大温度效应减弱; TiAl₃的热容值近似为TiAl的热容值的2倍. 关键词： 结构性质 热动力学性质 第一性原理 高压     

Ab initio study of PrAg intermetallic compound

In this work, a first-principles study on PrAg compound using the density functional theory implemented in the projector-augmented wave (PAW) method in the CsCl (B2) crystal structure has been performed. Based on the optimized structural parameter, which is in good agreement with experimental data, the electronic structure, elastic, thermodynamics and vibrational properties have been investigated. The temperature and pressure variations of volume, bulk modulus, thermal expansion coefficient, heat capacities, and Debye temperatures in wide pressure (0-30 GPa) and temperature ranges have also been predicted.