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.     

First-principles studies of structural,mechanical, electronic,optical properties and pressure-induced phase transition of CuInO2 polymorph

Using the first-principles density-functional theory within the generalized gradient approximation (GGA), we have investigated the structural, elastic, mechanical, electronic, and optical properties and phase transition of CuInO₂. Structural parameters including lattice constants and internal parameter, pressure effects and phase transition pressure were calculated. We have obtained the elastic coefficients, bulk modulus, shear modulus, Young's modulus and Poisson's ratio. We find that two phases of CuInO₂ are indirect band gap semiconductors (F–Γ and H–Γ for 3R and 2H, respectively). Optical properties, including the dielectric function, refractive index, extinction coefficient, reflectivity, absorption coefficient, loss function and optical conductivity have been obtained for radiations of up to 30 eV.     

Theoretical studies of elastic and thermodynamic properties of cubic B20 CoSi

The full potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory as implemented in the WIEN2k package is applied successfully to the study of the equilibrium lattice parameter and the elastic constants of the cubic B20 structural CoSi. The quasi-harmonic Debye model, in which the phononic effects are considered, is used to investigate the thermodynamic properties of B20 CoSi. Young's modulus and Poisson ratio are obtained from the calculated elastic constants and compared with the available data. The pressure and temperature dependence of the volume, the bulk modulus, the thermal expansion coefficient, the heat capacity and the Debye temperature are successfully obtained in the whole pressure range from 0 to 40 GPa and temperature range from 0 to 1400 K .     

Theoretical investigations on structural, elastic and electronic properties of thallium halides

Theoretical investigations on structural, elastic and electronic properties, viz. ground state lattice parameter, elastic moduli and density of states, of thallium halides (viz. TlCl and TlBr) have been made using the full potential linearized augmented plane wave method within the generalized gradient approximation (GGA). The ground state lattice parameter and bulk modulus and its pressure derivative have been obtained using optimization method. Young's modulus, shear modulus, Poisson ratio, sound velocities for longitudinal and shear waves, Debye average velocity, Debye temperature and Grüneisen parameter have also been calculated for these compounds. Calculated structural, elastic and other parameters are in good agreement with the available data.     

Structural,elastic and mechanical properties of orthorhombic SrHfO3 under pressure from first-principles calculations

Structural, elastic and mechanical properties of orthorhombic SrHfO₃ under pressure have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density functional theory. The calculated equilibrium lattice parameters and elastic constants of orthorhombic SrHfO₃ at zero pressure are in good agreement with the available experimental and calculational values. The lattice parameters, total enthalpy, elastic constants and mechanical stability of orthorhombic SrHfO₃ as a function of pressure were studied. With the increasing pressure, the lattice parameters and volume of orthorhombic SrHfO₃ decrease whereas the total enthalpy increases. Orthorhombic SrHfO₃ is mechanically stable with low pressure (<52.9 GPa) whereas that is mechanically instable with high pressure (>52.9 GPa). The bulk modulus, shear modulus, Young's modulus and mechanical anisotropy of orthorhombic SrHfO₃ as a function of pressure were analyzed. It is found that orthorhombic SrHfO₃ under pressure has larger bulk modulus, better ductility and less mechanical anisotropy than orthorhombic SrHfO₃ at 0 GPa.     

Structural,elastic, electronic and thermal properties of M2SbP (M = Ti,Zr and Hf)

The structural, elastic, electronic and thermal properties of M₂SbP (M = Ti, Zr and Hf) were studied by means of a pseudo-potential plane-wave method based on the density functional theory within both the local density approximation and the generalised gradient approximation. The optimised zero-pressure geometrical parameters, i.e. the two unit cell lengths (a, c) and the internal coordinate (z), were in good agreement with available experimental and theoretical data. The effect of high pressure, up to 20 GPa, on the lattice constants shows that the contractions along the a-axis were higher than along c-axis. The anisotropic independent elastic constants were calculated using the static finite strain technique. Numerical estimations of the bulk modulus, shear modulus, Young's modulus, Poisson's ratio, average sound velocity and Debye temperature for ideal polycrystalline M₂SbP aggregates were performed in the framework of the Voigt–Reuss–Hill approximation. The calculated band structures show that all studied materials are electrical conductors. Analysis of the atomic site projected densities showed that the bonding is of covalent–ionic nature with the presence of metallic character. The density of states at the Fermi level is dictated by the transition metal d–d bands; the Sb element has little effect. Thermal effects on some macroscopic properties of M₂SbP were predicted using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. The variations of the volume expansion coefficient, heat capacity and Debye temperature with pressure and temperature in the ranges 0–50 GPa and 0–2000 K were obtained successfully.     

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.     

A first-principle study of the structural, elastic, lattice dynamical and thermodynamic properties of PrX (X=P, As)

The structural, phase transition, elastic, lattice dynamic and thermodynamic properties of rare-earth compounds PrP and PrAs with NaCl (B1), CsCl (B2), ZB (B3), WC (B_h) and CuAu (L1₀) structures are investigated using the first principles calculations within the generalized gradient approximation (GGA). For the total-energy calculation, we have used the projected augmented plane-wave (PAW) implementation of the Vienna Ab-initio Simulation Package (VASP). Specifically, some basic physical parameters, e.g. lattice constants, bulk modulus, elastic constants, shear modulus, Young's modulus and Poison's ratio, are predicted. The obtained equilibrium structure parameters are in excellent agreement with the experimental and theoretical data. The temperature and pressure variations of the volume, bulk modulus, thermal expansion coefficient, heat capacity and Debye temperature are calculated in wide pressure and temperature ranges. The phonon dispersion curves and corresponding one-phonon density of states (DOS) for both compounds are also computed in the NaCl (B1) structure.     

Structural,mechanical and thermal properties of some Holmium Pnictides under pressure: A theoretical approach

The high pressure structural, elastic and thermal properties of holmium pnictides HoX (X=N, P, As and Bi) were investigated theoretically by using an inter-ionic potential theory with modified ionic charge parameter. We have predicted a structural phase transition from NaCl (B₁) to CsCl (B₂)-type structure at pressure of 139 GPa for HoN, 52 GPa for HoP, 44 GPa for HoAs and 26 GPa for HoBi. Other properties, such as lattice constant, bulk modulus, cohesive energy, second and third-order elastic constants were calculated and compared with the available experimental and theoretical data. In order to gain further information the brittle behaviour of these compounds was observed. Some other properties like Shear modulus (G), Young's modulus (E), Poisson's ratio (ν), anisotropy factor (A), sound velocities, Debye temperature (θ_D) were calculated. The variation of elastic constants (C₁₁ and C₄₄) and Debye temperature (θ_D) with pressure was also presented.     

Structural parameters, electronic structures, elastic stiffness and thermal properties of M2PC (M=V, Nb, Ta)

Using pseudo-potential plane-wave method based on the density functional theory in conjunction with the generalized gradient approximation, structural parameters, electronic structures, elastic stiffness and thermal properties of M₂PC, with M=V, Nb, Ta, were studied. The optimized zero pressure geometrical parameters are in good agreement with the available results. Pressure effect, up to 20 GPa, on the lattice parameters was investigated. Electronic properties are studied throughout the calculation of densities of states and band structures. The elastic constants and their pressure dependence were predicted using the static finite strain technique. We performed numerical estimations of the bulk modulus, shear modulus, Young's modulus, Poisson's ratio and average sound velocity for ideal polycrystalline M₂PC aggregates in framework of the Voigt-Reuss-Hill approximation. We estimated the Debye temperature and the theoretical minimum thermal conductivity of M₂PC.     

The structural, elastic and thermodynamic properties of intermetallic compound CeGa2

The structural, elastic and thermodynamic characteristics of CeGa₂ compound in the AlB₂ (space group: P6/mmm) and the omega trigonal (space group: P-3m1) type structures are investigated using the methods of density functional theory within the generalized gradient approximation (GGA). The thermodynamic properties of the considered structures are obtained through the quasi-harmonic Debye model. The results on the basic physical parameters, such as the lattice constant, the bulk modulus, the pressure derivative of bulk modulus, the phase-transition pressure (P _t ) from P6/mmm to P-3m1 structure, the second-order elastic constants, Zener anisotropy factor, Poisson’s ratio, Young’s modulus, and the isotropic shear modulus are presented. In order to gain further information, the pressure and temperature-dependent behavior of the volume, the bulk modulus, the thermal expansion coefficient, the heat capacity, the entropy, Debye temperature and Grüneisen parameter are also evaluated over a pressure range of 0–6 GPa and a wide temperature range of 0–1800 K. The obtained results are in agreement with the available experimental and the other theoretical values.     

The structural, elastic and thermodynamical properties of zinc-blend structure InN from first principles

A theoretical study of the structural, elastic and thermodynamic properties of the cubic zinc-blende (ZB) structure InN are presented in this paper by performing first principles calculations within local density approximation. The values of lattice constant, bulk modulus and its pressure derivatives and elastic constants are in excellent agreement with the available experimental data and other theoretical results. It is found that the ZB structure InN should be unstable above 20 GPa mechanically. The pressure and temperature dependencies of the bulk modulus, the heat capacity and the thermal expansion coefficient and the entropy S, as well as the Grüneisen parameter are obtained by the quasi-harmonic Debye model in the ranges of 0-1500 K and 0-25 GPa.     

First-principles investigations on structural,elastic, electronic properties and Debye temperature of orthorhombic Ni3Ta under pressure

The structural, elastic, electronic properties and Debye temperature of Ni₃Ta under different pressures are investigated using the first-principles method based on density functional theory. Our calculated equilibrium lattice parameters at 0 GPa well agree with the experimental and previous theoretical results. The calculated negative formation enthalpies and elastic constants both indicate that Ni₃Ta is stable under different pressures. The bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio ν are calculated by the Voigt–Reuss–Hill method. The bigger ratio of B/G indicates Ni₃Ta is ductile and the pressure can improve the ductility of Ni₃Ta. In addition, the results of density of states and the charge density difference show that the stability of Ni₃Ta is improved by the increasing pressure. The Debye temperature Θ _D calculated from elastic modulus increases along with the pressure.     

Elastic and thermodynamic properties of CaB6 under pressure from first principles

The elastic and thermodynamic properties of CsCl-type structure CaB₆ under high pressure are investigated by first-principles calculations based on plane-wave pseudopotential density functional theory method within the generalized gradient approximation (GGA). The calculated lattice parameters of CaB₆ under zero pressure and zero temperature are in good agreement with the existing experimental data and other theoretical data. The pressure dependences of the elastic constants, bulk modulus B (GPa), and its pressure derivative B′, shear modulus G, Young's modulus E, elastic Debye temperature Θ_B, Zener's anisotropy parameter A, Poisson ratios σ, and Kleinmann parameter ζ are also presented. An analysis for the calculated elastic constants has been made to reveal the mechanical stability of CaB₆ up to 100 GPa. The thermodynamic properties of the CsCl-type structure CaB₆ are predicted using the quasi-harmonic Debye model. The pressure-volume-temperature (P-V-T) relationship, the variations of the heat capacity C_V, Debye temperature Θ_D, and the thermal expansion α with pressure P and temperature T, as well as the Grüneisen parameters γ are obtained systematically in the ranges of 0-100 GPa and 0-2000 K.     

High pressure effect on structural and mechanical properties of some LnO (Ln=Sm, Eu, Yb) compounds

The structural and mechanical properties of LnO (Ln=Sm, Eu, Yb) compounds have been investigated using a modified interionic potential theory, which includes the effect of Coulomb screening. We predicted a structural phase transition from NaCl (B₁)- to CsCl (B₂)-type structure and elastic properties in LnO compounds at very high pressure. The anomalous properties of these compounds have been correlated in terms of the hybridisation of f-electrons of the rare earth ion with conduction band and strong mixing of f-states of lanthanides with the p-orbital of neighbouring chalcogen ion. For EuO, the calculated transition pressure, bulk modulus and lattice parameter are close to the experimental data. The nature of bonds between the ions is predicted by simulating the ion-ion (Ln-Ln and Ln-O) distances at high pressure. The second order elastic constants along with shear modulus and Young's modulus, elastic anisotropy and Poisson's ratio are also presented for these oxides.     

Phase transition,structural, mechanical and thermal properties of erbium pnictides under pressure

In this article, we have investigated the high-pressure structural phase transition of erbium pnictides (ErX; X?=?N, P and As). An extended interaction potential model has been developed (including the zero-point energy effect in three-body interaction potential model). Phase transition pressures are associated with a sudden collapse in volume. The phase transition pressures and associated volume collapses have been predicted successfully. The elastic constants, their combinations and pressure derivatives are also reported. The pressure behaviour of elastic constants, bulk modulus and shear modulus have been presented and discussed. Moreover, the thermophysical properties such as molecular force constant (f), infrared absorption frequency (υ ₀), Debye temperature (θ _D) and Grunneisen parameter (γ) have also been predicted.     

First-principles study of elastic and electronic properties of layered ternary nitride SrZrN2 under pressure

The structural, elastic, and electronic properties of SrZrN₂ under pressure up to 100?GPa have been carried out with first-principles calculations based on density functional theory. The calculated lattice parameters at 0?GPa and 0?K by using the GGA-PW91-ultrasoft method are in good agreement with the available experimental data and other previous theoretical calculations. The pressure dependence of the elastic constants and the elastic-dependent properties of SrZrN₂, such as bulk modulus B, shear modulus G, Young's modulus E, Debye temperature Θ, shear and longitudinal wave velocity V_S and V_L, are also successfully obtained. It is found that all elastic constants increase monotonically with pressure. When the pressure increases up to 140?GPa, the obtained elastic constants do not satisfy the mechanical stability criteria and a phase transition might has occurred. Moreover, the anisotropy of the directional-dependent Young's modulus and the linear compressibility under different pressures are analysed for the first time. Finally, the pressure dependence of the total and partial densities of states and the bonding property of SrZrN₂ are also investigated.     

Electronic structure,elastic and thermodynamic properties of α-phase Na3N under pressure from first principles

The structural, electronic, elastic and thermodynamic properties of α-phase Na₃N under pressure are investigated by performing first principles calculations within generalized gradient approximation. The elastic constants, bulk modulus, shear modulus, Young's modulus, and Poisson's ratio dependencies on pressure are also calculated. The thermodynamic properties of the α-phase Na₃N are calculated using the quasi-harmonic Debye model. The dependencies of the heat capacity and the thermal expansion coefficient, as well as the Grüneisen parameter on pressure and temperature are investigated systematically in the ranges of 0–1 GPa and 0–100 K.     

Thermodynamic properties of cubic ZrC under high pressure from first-principles calculations

The elastic and thermodynamic properties of Zirconium carbide (ZrC) are investigated by ab initio plane-wave pseudopotential density function theory method. The obtained lattice constant, elastic constant and bulk modulus B are consistent with the experimental and theoretical data. Through the quasi-harmonic Debye model, the dependences of the normalized volume V/V ₀ and the bulk modulus B on pressure P, as well as the specific heat C _V on the temperature T are obtained successfully. The relationships of the thermal expansion α with temperature and pressure are also investigated, which indicate the temperature hardly has any effect on the thermal expansion α at high pressure. Supported by the National Natural Science Foundation of China (Grant No. 10776022)     

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.