First-principles calculations of pressure-induced phase transformation in AlN and GaN

Ab initio total energy calculations have been carried out to study pressure-induced wurtzite and zinc-blende to rocksalt phase transformation in AlN and GaN. The effects of d electrons on the phase transition pressure and pressure coefficients of band gap have been studied. It is shown that the presence of Ga 3d electrons do have a certain effect on the transition pressure, while other factors such as the variation of charge distribution with pressure should also be considered to explain the higher phase transition pressure for GaN than AlN. Our calculations also show that Ga 3d electrons affect the pressure coefficients of band gap slightly.