Lattice vibration spectrum of GaN from first-principle calculations

We report first-principle calculations in the framework of the density functional perturbation theory of the lattice vibration properties of GaN in the wurtzite and rocksalt phases at zero and under pressures ranging from 0 to 40 GPa. The calculations predict the full phonon spectrum throughout the Brillouin zone and phonon density of states. Generally, the calculated zone-center modes for the wurtzite structure are found to be in good agreement with previous theoretical and experimental results. For the phonons of rocksalt GaN in the presence of hydrostatic pressure, these are the first results to our knowledge. The pressure dependence of the zone-center optical frequencies is examined and discussed which allowed the calculation of the pressure coefficients and mode Gruneisen parameters.