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The structural, mechanical, electronic, and bonding properties and phase transition of NaZnSb are explored using the generalized gradient approximation based on ab initio plane-wave pseudopotential density functional theory.With the help of the quasi-harmonic Debye model, we probe the Gruneisen parameter, thermal expansivity, heat capacity, Debye temperature, and entropy of NaZnSb in the tetragonal phase. The results indicate that the lattice constants and the bulk modulus and its first pressure derivative agree well with the available theoretical and experimental data. NaZnSb in its ground state structure exhibits a distinct energy gap of about 0.41 eV, which increases with increasing pressure. Our conclusions are consistent with the theoretical predictions obtained by the ABINIT package, but are different from those obtained through the tight-binding linear muffin-tin orbital method. As a result, further experimental and theoretical researches need to be carried out. For the purpose of providing a comparative and complementary study for future research, we first investigate the thermodynamic properties of NaZnSb.

We investigate the elastic and thermodynamic properties of nanolaminate V2AlC by using the ab initio pseudopotential total energy method. The axial compressibility shows that the c axis is always stiffer than a axis. The elastic constants revealed the structural instability at about 500 and 732 GPa. Furthermore, elastic constants C44 reached its maximum at about 550 GPa, differing with the other four C11, C12, C13 and C33 constants. The Poisson’s ratio investigations demonstrated that a higher ionic or weaker covalent contribution in intra-atomic bonding and the degree of ionicity increases with pressure. The G/B and B/C44 investigations revealed that V2AlC is brittle and the brittleness decreases with pressure. Also, we found that V2AlC is elastic anisotropic materials and the degree of anisotropy rapidly rises with pressure. Study on Debye temperature and Gruneisen parameter observed weak temperature and strong pressure responses, whereas the sensitive dependence in the thermal expansion coefficient and Helmholtz free energy are clearly seen.

In this study, first-principles calculations of the crystal structure and the elastic properties of osmium have been carried out using 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 pressure dependence of the elastic constants, the aggregate elastic moduli (B, G, E), the Poisson's ratio, the Lame constant, the compressibility, the longitudinal wave and transverse wave velocities, the Debye temperature and the elastic anisotropy have been investigated. Moreover, the temperature and pressure dependence of the thermal expansion coefficient is estimated from the Debye approximation.

First-principles calculations of the crystal structure and the elastic properties of α-Ta4AlC3 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 pressure dependence of the elastic constants cij, the aggregate elastic moduli (B, G, E), the Poisson's ratio, and the elastic anisotropy has been investigated. Using the quasi-harmonic Debye model considering the phonon effects, the temperature and pressure dependencies of isothermal bulk modulus, and the thermal expansions, and Gruneisen parameters, as well as Debye temperatures are investigated systematically in the ranges of 0–60 GPa and 0–1500 K as well as compared to available data.

First-principles calculations of the crystal structure and the elastic properties of OsN2 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 dependence of the elastic constants c i j , the aggregate elastic moduli ( B , G , E ) , Poisson’s ratio, and the elastic anisotropy on pressure has been investigated. Moreover, the variation of the Debye temperature and the compressional and shear elastic wave velocities with pressure P up to 60 GPa at 0 K have been investigated for the first time.

First-principles calculations of the crystal structures, and elastic properties of wurtzite-type indium nitride (w-InN) have been carried out with the plane-wave pseudopotential density functional theory method. The calculated values (for crystal structures) are in very good agreement with experimental data as well as with some of the existing model calculations. The dependence of the elastic constants cij, the aggregate elastic modulus (B, G, E), and the elastic anisotropy on pressure have been investigated. Moreover, the variation of the Poisson ratio, Debye temperature, and the compressional and shear elastic wave velocities with pressure P up to 10 GPa at 0 K have been investigated for the first time.

First-principles calculations of the crystal structures of rhenium diboride (ReB2) 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 quasi-harmonic Debye model, using a set of total energy versus molar volume obtained with the first-principles calculations, is applied to the study of the thermal and vibrational effects. The structural parameters, thermal expansions, heat capacities, Gruneisen parameters and Debye temperatures dependence on the temperature and pressure are obtained in the whole pressure range from 0 to 70 GPa and temperature range from 0 to 2000 K as well as compared with available data.

First-principles calculations of the crystal structures, and phase transition, and elastic properties of cadmium oxide (CdO) have been carried out with the plane-wave pseudopotential density functional theory method. The calculated values (for crystal structures) are in good agreement with experimental data as well as with some of the existing model calculations. The dependence of the elastic constants c i j , the aggregate elastic modulus ( B , G , E ), and the elastic anisotropy on pressure have been investigated. Moreover, the variation of the Poisson ratio, Debye temperature, and the compressional and shear elastic wave velocities with pressure P up to 119 GPa at 0 K have been investigated for the first time. We also find that NaCl-type CdO should be unstable at pressures higher than 119.07 GPa.

The phase transition of SiC from the zinc blende (ZB) structure to the rocksalt (RS) structure under pressure is investigated by the first principles plane-wave pseudopotential density functional theory method. The results obtained are in good agreement with the experimentally measured data and other theoretically calculated results. It is found that the pressures of transition of SiC from the ZB structure to the RS structure are 74.6 GPa from total energy–volume data and 75.4 GPa from the enthalpy calculations. Moreover, through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of relative volume V/V0 on pressure P at T=0, 1400 K are successfully obtained. The calculated volume reduction at the transition is 18%. In particular, from the high-pressure elastic constants obtained, the ZB structure SiC is found unstable when the applied pressure is larger than 126.6 GPa. This value is in excellent agreement with the experimental data and the molecular dynamics (MD) simulation results.

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 / V 0 on the pressure P , the Debye temperature Θ and heat capacity C V on the pressure P , together with the heat capacity C V on the temperature T are also successfully obtained.

The elastic constants of cubic boron nitride (c–BN) are calculated by the first-principles method at ambient condition. The dependence of the elastic constants, the bulk modulus B, and the shear modulus G on the applied pressure are presented. The calculated results are in good agreement with the comparable experimental and theoretical values. The deviation from the Cauchy relation and the elastic anisotropy are investigated. The normalized elastic constants c ij ′ are introduced to investigate elasticity of c–BN in more detail. Moreover, the thermodynamic properties (Debye temperature, melting temperature) and sound velocity have been investigated under high pressure for the first time.

The transition phase of PtC from zincblende (ZB) structure to rocksalt (RS) structure is investigated by ab initio plane-wave pseudopotential density functional theory; 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 ZB structure to RS structure occurs at the pressure of 51.7 GPa, which agrees well with other calculated values. Moreover, the dependences of the relative volume V / V 0 on the pressure P , the Debye temperature Θ and heat capacity C V on the pressure P , together with the heat capacity C V on the temperature T are also successfully obtained.

The equations of state (EOS) and other thermodynamic properties of cubic boron nitride (C-BN) have been studied by the first-principles method under high pressure. Under ambient conditions, our results are consistent with the available experimental data and those calculated by others. At the same time, the dependences of Young’s modulus and the shear modulus of C-BN on pressure P are successfully obtained. Moreover, the variation of the Poisson ratio, Debye temperature, specific heat, and thermal expansion coefficient with pressure P up to 200 GPa at 300 K have been investigated for the first time by means of a quasi-harmonic Debye model, in which phononic effects are considered.

The elastic constants of superconducting MgB2 are calculated using a molecular dynamics method (MD) with shell model. The lattice parameters, live independent elastic constants, equations of state (EOS), Debye temperature, and bulk modulus of MgB2,are obtained. Meanwhile, the dependence of the bulk modulus B, the lattice parameters a and c, and the unit cell volume V on the applied pressure are presented. It is demonstrated that the method introduced here can well reproduce the experimental results with a reasonable accuracy.

Using Vanderbilt-type plane-wave ultrasoft pseudopotentials within the generalized gradient approximation (GGA) in the frame of density functional theory (DFT), we have investigated the crystal structures, elastic, and thermodynamic properties for Ti2SC under high temperature and high pressure. The calculated pressure dependence of the lattice volume is in excellent agreement with the experimental results. The calculated structural parameter of the Ti atom experienced a subtle increase with applied pressures and the increase suspended under higher pressures. The elastic constants calculations demonstrated that the crystal lattice is still stable up to 200 GPa. Investigations on the elastic properties show that the c axis is stiffer than the a axis, which is consistent with the larger longitudinal elastic constants (C33, C11) relative to transverse ones (C44, C12, C13). Study on Poisson's ratio confirmed that the higher ionic or weaker covalent contribution in intra-atomic bonding for Ti2SC should be assumed and the nature of ionic increased with pressure. The ratio (B/G) of bulk (B) and shear (G) moduli as well as B/C44 demonstrated the brittleness of Ti2SC at ambient conditions and the brittleness decreased with pressure. Moreover, the isothermal and adiabatic bulk moduli displayed opposite temperature dependence under different pressures. Again, we observed that the Debye temperature and Gruneisen parameter show weak temperature dependence relative to the thermal expansion coefficient, entropy, and heat capacity, from which the pressure effects are clearly seen.

We investigate the elastic and the thermodynamic properties of nanolaminate V2GeC by using the ab initio pseudopotential total energy method. The axial compressibility shows that the c axis is always stiffer than the a axis. The elastic constant calculations demonstrate that the structural stability is within 0–800 GPa. The calculations of Young's and shear moduli reveal the softening behaviour at about 300 GPa. The Possion ratio makes a higher ionic or a weaker covalent contribution to intra-atomic bonding and the degree of ionicity increases with pressure. The relationship between brittleness and ductility shows that V2GeC is brittle in ambient conditions and the brittleness decreases and ductility increases with pressure. Moveover, we find that V2GeC is largely isotropic in compression and in shear, and the degree of isotropy decreases with pressure. The Gruneisen parameter, the Debye temperature and the thermal expansion coefficient are also successfully obtained for the first time.