Search

Abstract: The plane-wave pseudo-potential method within the framework of first-principles is used to investigate the structural and elastic properties of Mg2Si in its low pressure phase (Fm-3m) and intermediate pressure phase (Pnma). The high-pressure lattice constants, the elastic constants, the elastic moduli and the anisotropy factors of the anti-cotunnite Mg2Si are presented and discussed. The results show that our system is mechanically stable. The reversible phase transition from anti-fluorite to anti-cotunnite structure is successfully reproduced through the quasi-harmonic Debye model. The phase boundary can be described as P=4.06826−6.95×10−3 T+5.08838×10−5 T 2−4.24073×10−8 T 3. To complete the fundamental characteristics of these compounds we have analysed the thermodynamic properties such as thermal expansion, bulk modulus, isochoric heat capacity and Debye temperature in a pressure range 0–21GPa and a temperature range 0–1200K. The obtained results tend to support the experimental data when available. Therefore, the present results indicate that the combination of first-principles and quasi-harmonic approximations is an efficient scheme to simulate the high-temperature behaviours of semiconductors like Mg2Si. [Copyright &y& Elsevier]

Abstract: First-principles calculations of the crystal structures (wurtzite (WZ) and rocksalt (RS)) and phase transition of AlN have been carried out with the plane-wave pseudopotential density functional theory (DFT) method. The calculated values (for crystal structures) are in agreement with available experimental value and other calculated data. Through the quasi-harmonic Debye model combined with the first-principles theory, the thermodynamic properties of different phases under high temperature and high pressure are investigated. The phase transition from WZ structure to RS structure occurs at the pressure of 15.0GPa, which agrees well with experimental value. The evaluated equilibrium volume using this model agrees with the values obtained from ab intio and from experiment. The temperature and pressure dependence of quantities such as the equation of state (EOS), the isothermal bulk modulus, the heat capacity, and the thermal expansion are successfully obtained. [Copyright &y& Elsevier]

Abstract: 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 18.2GPa, 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 CV on the pressure P, together with the heat capacity CV on the temperature T are also successfully obtained. [Copyright &y& Elsevier]

Abstract: The equations of state (EOS) and other thermodynamic properties of TiB2 are investigated using ab initio plane-wave pseudopotential density functional theory method. The obtained results are in good agreement with the experimental measured data and other theoretical calculated ones. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of relative volume V/V 0 on pressure P, cell volume V on temperature T, and Debye temperature Θ and specific heat C V on pressure P are successfully obtained. [Copyright &y& Elsevier]