The phase transition and the elastic and thermodynamic properties of AlN: First principles

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 15.0 GPa, 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.