AB-INITIO LATTICE-DYNAMICS OF DIAMOND

We present a first principles calculation of lattice dynamical propert ies of diamond. Our calculations have been performed using density-fun ctional perturbation theory together with plane-wave expansion and non local pseudopotentials. As a first step we have evaluated the equilibr ium structure of diamond via the minimization of the total energy. The n, harmonic phonon dispersion curves and phonon eigenvectors have been evaluated within the linear-response framework. As a by-product of th e calculation we have also obtained the internal-strain parameter. Fur thermore, we have also tested the validity of the ab initio calculatio n for describing properties beyond the harmonic approximation. Using t he quasiharmonic approximation we have calculated the thermal expansio n coefficient and the mode Gruneisen parameter dispersion curves. Wher e experimental data are available, good agreement is found with our th eoretical predictions.