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1.
We have investigated structural and elastic properties of PtN2 under high pressures using norm-conserving pseudopotentials within the local density approximation (LDA) in the frame of density-functional theory. Calculated results of PtN2 are in agreement with experimental and available theoretical values. The a/a0, V/V0, ductility/brittleness, elastic constants Cij, shear modulus C′, bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio σ and anisotropy factor A as a function of applied pressure are presented. Through the quasi-harmonic Debye model, we also study thermodynamic properties of PtN2. The thermal expansion versus temperature and pressure, thermodynamic parameters X (X=Debye temperature or specific heat) with varying pressure P, and heat capacity of PtN2 at various pressures and temperatures are estimated.  相似文献   

2.
First-principles calculations of the crystal structure and the elastic properties of RuB2 have been carried out with the plane-wave pseudopotential density functional theory method. The calculated values are in very good agreement with experimental data as well as with some of the existing model calculations. The elastic constants cij, the aggregate elastic moduli (B, G, E), Poisson's ratio, and the elastic anisotropy with pressure have been investigated. Through the quasi-harmonic Debye model considering the phonon effects, the isothermal bulk modulus, the thermal expansions, Grüneisen parameters, and Debye temperatures depending on the temperature and pressure are obtained in the whole pressure range from 0 to 60 GPa and temperature range from 0 to 1100 K as well as compared to available data.  相似文献   

3.
Structural, electronic, elastic and thermal properties of Mg2Si   总被引:1,自引:0,他引:1  
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 Cv, Cp 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.  相似文献   

4.
The effect of hydrostatic pressure on the structures of HfN at 0 K was investigated by using the projector augmented wave (PAW) within the Perdew–Burke–Ernzerhof (PBE) form of the generalized gradient approximation (GGA). The transition pressure between NaCl (B1) and CsCl (B2) structures is predicted to be 277.3 GPa. This value is consistent with that reported by Kroll, while in contrast to the results obtained by Ojha et al. and Meenaatci et al. Moreover, the elastic properties of B1-HfN and B2-HfN under high pressures are successfully obtained. It is found that the elastic constants, bulk modulus B, shear modulus G, compressional and shear wave velocities increase monotonically with increasing pressure. The Debye temperature Θ calculated from the elastic constants of HfN is in good agreement with the experimental values. The anisotropies of B1-HfN and B2-HfN at zero pressure have also been discussed.  相似文献   

5.
A detailed theoretical study of the isothermal and adiabatic bulk moduli of MgF2 with a fluorite structure under high pressure and temperature has been carried out by means of first-principles density functional theory calculations combined with the quasi-harmonic Debye model in which the phononic effects are considered. Particular attention is paid to the prediction of the isothermal bulk modulus and its first and second pressure derivatives for the first time. The calculated ground state properties agree well with other theoretical values. At extended pressure and temperature ranges, the variation of the bulk modulus which plays a central role in the formulation of approximate equations of state has also been predicted. The properties of MgF2 with a fluorite structure are summarized in the pressure range of 0–135 GPa and the temperature up to melting temperature 1500 K.  相似文献   

6.
The elastic constants and thermodynamic properties of Li2O for high temperatures and pressures are calculated by the ab initio unrestricted Hartree-Fock (HF) linear combination of atomic orbital (LCAO) periodic approach. The lattice constant, elastic constants, Debye temperature, and thermal expansion coefficient obtained are in good agreement with the available experimental data and other theoretical results. It is found that at zero pressure the elastic constants C11, C12 and C44, bulk modulus B and Debye temperature ΘD decrease monotonically over the wide range of temperatures from 0 to 1100 K. When the temperature , C12 approaches zero, consistently with the transition temperature 1200 K. However, with increasing pressure, they all increase monotonically and the anisotropy will weaken.  相似文献   

7.
The elastic properties, electronic structure and thermodynamic behavior of the TaB have been investigated for the first time in this work. Using first-principles plane-wave ultrasoft-pseudopotential density functional theory (DFT), the ground state properties and equation of state of TaB have been obtained. The average zero-pressure bulk modulus of TaB is 302 GPa. By analyzing the elastically anisotropic behavior and the relative structure parameters of TaB, we found that the crystal cell along the b-axis was more compressible than along the a and c axes. The calculated ratio of bulk modulus and shear modulus (B/G) for TaB is 1.58, demonstrating that TaB is rather brittle. From the elastic stiffness constants, we found that TaB in the Cmcm phase is mechanically stable. The calculated hardness of TaB is 28.6 GPa which is close to the previous data. Moreover, using the Gibbs 2 model, the thermodynamic properties such as the thermal expansion and Debye temperature of TaB have been obtained firstly. At the ambient temperature, the Debye temperatures of TaB are 792 K and 845 K from GGA calculation and LDA calculation, respectively.  相似文献   

8.
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 ΘB, 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 CV, Debye temperature ΘD, 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.  相似文献   

9.
The structural, elastic and thermal properties of three heavy monoantimonides of holmium, erbium and thulium (LnSb, Ln=Ho, Er and Tm) have been investigated theoretically by using an interionic potential theory consisting of long-range Coulomb, short-range repulsive and van der Waal’s (vdW) interactions. These compounds exhibit first-order crystallographic phase transition from their initial NaCl-type structure to CsCl-type structure at pressures 27, 33.2 and 29.8 GPa for HoSb, ErSb and TmSb, respectively. The values of elastic constants and Debye temperatures as a function of pressure are also reported. The elastic properties such as Young modulus (E), Shear modulus (G), Poisson ratio (υ) and anisotropic ratio (A) in an NaCl-type structure are also predicted.  相似文献   

10.
The transition phase of PtN from zincblende (ZB) structure to rocksalt (RS) structure is investigated by ab initio plane-wave pseudopotential density functional theory method, and the thermodynamic properties of the ZB and RS structures under high pressure and temperature are obtained through the quasi-harmonic Debye model. The transition phase from the ZB structure to the RS structure occurs at the pressure of 18.2 GPa, which agrees well with other calculated values. Moreover, the dependences of the relative volume V/V0 on the pressure P, the Debye temperature Θ and heat capacity CV on the pressure P, together with the heat capacity CV on the temperature T are also successfully obtained.  相似文献   

11.
The structural, elastic and thermal properties of four transition metal monocarbides ScC, YC (group III), VC and NbC (group V) have been investigated using full potential linearized augmented plane wave (FP-LAPW) method within generalized gradient approximation (GGA) both at ambient and high pressure. We predict a B1 to B2 structural phase transition at 127.8 and 80.4 GPa for ScC and YC along with the volume collapse percentage of 7.6 and 8.4%, respectively. No phase transition is observed in case of VC and NbC up to pressure 400 and 360 GPa, respectively. The ground state properties such as equilibrium lattice constant (a0), bulk modulus (B) and its pressure derivative (B′) are determined and compared with available data. We have computed the elastic moduli and Debye temperature and report their variation as a function of pressure.  相似文献   

12.
The transition phase of GaN from zincblende (ZB) structure to rocksalt structure (RS) is investigated by ab initio plane-wave pseudopotential density functional theory method, and the thermodynamic properties of the ZB and RS structures are obtained through the quasi-harmonic Debye model. We find that the transition phase from the ZB structure to the RS structure occurs at the pressure of 42.2 GPa, which is in good agreement with other calculated values. Moreover, the dependences of the relative volume V/V0 on the pressure P, the Debye temperature Θ and heat capacity CV on the pressure P, as well as the heat capacity CV on the temperature T are also successfully obtained.  相似文献   

13.
The equilibrium lattice constants, bulk modulus, shear modulus, elastic constants and Debye temperature of LaNi4.75 Sn0.25 under pressure are calculated using the full-potential linearized augmented plane wave (FP-LAPW) method as well as the quasi-harmonic Debye model. The results at zero pressure are in excellent agreement with the experimental data. The Sn atom is found to occupy the equivalent 3g site (0.5a, 0.75b, 0.5c) in the quadruple cell. The Debye temperature of LaNi4.75Sn0.25 is lower than that of LaNi5. The dependences of bulk modulus on finite temperature and on finite pressure are also investigated. The results show that the bulk modulus B increases monotonously as pressure increases.  相似文献   

14.
We investigate the structural and elastic properties of LaTiO3 by the plane-wave pseudopotential density functional theory method. The lattice constants, bulk modulus and its pressure derivative are obtained. These properties in the equilibrium phase are well consistent with the available experimental data. The pressure dependence of the elastic constants, ductility, mechanical stabilities, sound velocity and Debye temperatures are investigated for the first time. From the ratio G/B, we conclude that LaTiO3 is ductile at 0 GPa and becomes more ductile at high pressure. In addition, the anisotropy factors for every symmetry plane and axis as well as linear bulk modulus at diverse pressures have been obtained.  相似文献   

15.
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 Cij 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.  相似文献   

16.
The density functional theory (DFT) calculations of structural, elastic, electronic and optical properties of the cubic antiperovskite AsNMg3 has been reported using the pseudo-potential plane wave method (PP-PW) within the generalized gradient approximation (GGA). The equilibrium lattice, bulk modulus and its pressure derivative have been determined. The elastic constants and their pressure dependence are calculated using the static finite strain technique. We derived the bulk and shear moduli, Young's modulus and Poisson's ratio for ideal polycrystalline AsNMg3 aggregate. We estimated the Debye temperature of AsNMg3 from the average sound velocity. This is the first quantitative theoretical prediction of the elastic properties of AsNMg3 compound, and it still awaits experimental confirmation. Band structure, density of states and pressure coefficients of energy gaps are also given. The fundamental band gap (Γ-Γ) initially increases up to 4 GPa and then decreases as a function of pressure. Furthermore, the dielectric function, optical reflectivity, refractive index, extinction coefficient, and electron energy loss are calculated for radiation up to 30 eV. The all results are compared with the available theoretical and experimental data.  相似文献   

17.
18.
The structural, elastic and thermodynamic properties of thorium tetraboride (ThB4) have been investigated by using first-principles plane-wave pseudopotential density functional theory with generalized gradient approximation. The behaviors of structural parameters under 0-70 GPa hydrostatic pressure are studied by means of Broyden, Fletcher, Goldfarb, and Shanno (BFGS) geometry optimization scheme. By using the stress-strain method, single crystal elastic constants are calculated to test the mechanical stability of the crystal structure and to determine mechanical properties such as bulk modulus at each pressure. However, in order to study the thermodynamic properties of ThB4, the quasi-harmonic Debye model is used. Then, the dependencies of bulk modulus, heat capacities, thermal expansions, Grüneisen parameters and Debye temperatures on the temperature and pressure are obtained in the whole pressure range 0-70 GPa and temperature range 0-1500 K.  相似文献   

19.
We present the results of our calculations on Boron antimony (BSb) compound in zinc-blende (ZB) and rock-salt (RS) structures by performing ab initio calculations within the local density approximation (LDA). Some basic physical properties, such as lattice constant, bulk modulus, cohesive energy, phase transition pressure, second-order elastic constants (Cij), phonon frequencies, and some band structural parameters are calculated and compared with those obtained with other recent theoretical works. In order to further understand the behaviour of BSb compound, we have also predicted, the pressure-dependent behaviours of the band gap, second-order elastic constants (Cij), Young's modulus, poison ratios (ν), Anizotropy factor (A), sound velocities, and Debye temperature for this hypothetical compound.  相似文献   

20.
The structural phase transition, elastic, thermodynamics properties of BeSe in zinc-blende were investigated by performing first-principles calculations within generalized gradient approximation. The phase transition pressure Pt between the B3 phase and the B8 phase of BeSe was determined. The pressure dependencies of elastic constants, shear modulus, Young's modulus, and Poisson's ratio of BeSe are calculated. The thermodynamic properties of the zinc-blende structure BeSe are calculated by using the quasi-harmonic Debye model. The pressure and temperature dependencies of the heat capacity and the thermal expansion coefficient, as well as the Grüneisen parameter are investigated systematically in the ranges of 0–50 GPa and 0–1200 K.  相似文献   

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