Ab initio calculation of the thermodynamic properties and phase diagram of gallium nitride

The thermodynamic properties of gallium nitride (GaN) with wurtzite (WZ) and rocksalt (RS) phases have been investigated by carrying out the first principles-calculations, in which the density-functional theory (DFT) and density-functional perturbation theory (DFPT) have been employed. The quasiharmonic approximation (QHA) has been utilized to estimate the free energies. The phonon dispersion, thermal expansion coefficients, bulk modulus, and heat capacities are presented and provided good agreement with the previous calculation and experimental data. Furthermore, the pressure–temperature (P–T) diagram of WZ–RS phase transition of GaN is predicted and the values of transition pressure range from 32.2 GPa at 0 K to about 21 GPa at 2480 K.