In this paper the elastic and thermodynamic properties of the cubic zinc-blende structure BeS at different pressures and temperatures are investigated by using ab initio plane-wave pseudopotential density functional theory method within the generalized gradient approximation (GGA).The calculated results are in excellent agreement with the available experimental data and other theoretical results.It is found that the zinc-blende structure BeS should be unstable above 60GPa.The thermodynamic properties of the zinc-blende structure BeS are predicted by using the quasi-harmonic Debye model.The pressure-volume-temperature (P V T) relationship,the variations of the thermal expansion coefficient α and the heat capacity C V with pressure P and temperature T,as well as the Gru¨neisen parameter-pressure-temperature (γ P T) relationship are obtained systematically in the ranges of 0-90GPa and 0-2000K.
The phase transition of SrS from NaCl structure (B1) to CsCl structure (B2) is investigated by means of ab initio plane-wave pseudopotential density functional theory,and the thermodynamic properties of the B1 and the B2 structures are obtained through the quasi-harmonic Debye model.It is found that the transition phase from the B1 to the B2 structures occurs at 17.9 GPa,which is in good agreement with experimental data and other calculated results.Moreover,the thermodynamic properties (including specific heat capacity,the Debye temperature,thermal expansion and Gru¨neisen parameter) have also been obtained successfully.
This paper studies the equilibrium structure parameters and the dependences of the elastic properties on pressure for rutile TiO2 by using the Cambridge Serial Total Energy Package (CASTEP) program in the frame of density functional theory. The obtained equilibrium structure parameters, bulk modulus B0 and its pressure derivative B0 are in good agreement with experiments and the theoretical results. The six independent elastic constants of rutile TiO2 under pressure are theoretically investigated for the first time. It is found that, as pressure increases, the elastic constants C11 ,C33 , C66 , C12 and C13 increase, the variation of elastic constant C 44 is not obvious and the anisotropy will weaken.
