AB-INITIO CALCULATION OF VIBRATIONAL-MODES IN SEMICONDUCTORS

We calculate vibrational modes in semiconductors using density-functio nal theory in the local density approximation and norm-conserving Trou llier-Martins pseudopotentials. We obtain the vibration frequencies fr om a direct calculation of the dynamical matrix by using the supercell method with plane wave expansion. In order to show the feasibility of the method we here present the results for the phonon-dispersion curv es of GaAs, ZnSe and cubic GaN crystals, which are in very good agreem ent with neutron-scattering experiments and second-order Raman spectro scopy.