Structural, thermodynamic and electronic properties of zinc-blende AIN under pressure are investigated by first- principles calculations based on the plane-wave basis set. Through the analysis of enthalpy variation of AIN in the zinc-blende （ZB） and the rock-salt （RS） structures with pressure, we find the phase transition of A1N from ZB to RS structure occurs at 6.7GPa. By using the quasi-harmonic Debye model, we obtain the heat capacity Cv, Debye temperature θD, Gruneisen parameter γ and thermal expansion coefficient α. The electronic properties including fundamental energy gaps and hydrostatic deformation potentials are investigated and the dependence of energy gaps on pressure is analysed.
We investigate the structural and thermodynamic properties of OsN2 by a plane-wave pseudopotential density functional theory method. The obtained lattice constant, bulk modulus and cell volume per unit formula are consistent with the available theoretical data. Moreover, the pressure-induced phase transition of OsN2 from pyrite structure to fluorite structure has been obtained. It is found that the transition pressure of OsN2 at zero temperature is 67.2 GPa. The bulk modulus B as well as other thermodynamic quantities of fluorite OsN2 （including the Griineisen constant γ and thermal expansion α） on temperatures and pressures have also been obtained.
The electronic and optical properties of the cubic zinc-blende （ZB） structured filled tetrahedral semiconductor α-LiZnN under pressure are investigated by using ab initio plane wave pseudopotential density functional theory method within the generalized gradient approximation （GGA）.The electronic band structure and the density of state under pressure are systematically described.The basic optical constants,including the reflection and absorption spectra,the energy-loss function,the complex refractive index and the dielectric function,are calculated and analysed at different external pressures.Our results suggested that the ZB α-LiZnN is transparent in the partially ultra-violet to the visible light region,and it seems that the transparency is hardly affected by the pressure.
The structural, elastic constants and anisotropy of RuB2 under pressure are investigated by first-principles calculations based on the plane wave pseudopotential density functional theory method within the local density approximation （LDA） as well as the generalized gradient approximation （GGA） for exchange and correlation. The results accord well with the available experimental and other theoretical data. The elastic constants, elastic anisotropy, and Debye temperature ／varTheta as a function of pressure are presented. It is concluded that RuB2 is brittle in nature at low pressure, whereas it becomes ductile at higher pressures. An analysis for the calculated elastic constant has been made to reveal the mechanical stability of RuB2 up to 100~GPa.
The pressure induced phase transitions of TiO2 from anatase to columbite structure and from rutile to columbite structure and the temperature induced phase transition from anatase to rutile structure and from columbite to rutile structure are investigated by ab initio plane-wave pseudopotential density functional theory method （DFT）, together with quasi-harmonic Debye model. It is found that the zero-temperature transition pressures from anatase to columbite and from rutile to columbite are 4.55 GPa and 19.92 GPa, respectively. The zero-pressure transition temperatures from anatase to rutile and from columbite to rutile are 950 K and 1500 K, respectively. Our results are consistent with the available experimental data and other theoretical results. Moreover, the dependence of the normalized primitive cell volume V/Vo on pressure and the dependences of thermal expansion coefficient α on temperature and pressure are also obtained successfully.
