Ab initio calculation of structural phase transitions in AlN crystal

Density functional theory and the quasiharmonic approximation have been used to study the phase diagram of aluminum nitride. AlN was exposed to pressures ranging from -20 to 20 GPa. The phonon dispersion relations and phonon density of states have been calculated for the wurtzite, zinc blende, and rocksalt phases of AlN. The pressure-temperature phase diagram of AlN was constructed and compared with the available experimental data. It shows that at ambient temperature and pressure the most stable phase of AlN is the hexagonal wurtzite structure, while at high pressures and temperatures the rocksalt phase becomes more stable.