Ab initio studies of phonons in MgO by the direct method including LO mode Original Research Article

The ab initio method within the local-density approximation is applied to calculate the Hellmann–Feynman forces for the cubic and elongated supercells of the polar MgO crystal. From these forces, using the direct method, the phonon dispersion relations and the phonon density of states are derived. The LO/TO splitting was extracted from phonon frequencies found within the elongated supercell.