AB-INITIO LATTICE-DYNAMICS OF DIAMOND

We present a first principles calculation of lattice dynamical properties of diamond. Our calculations have been performed using density-functional perturbation theory together with plane-wave expansion and nonlocal pseudopotentials. As a first step we have evaluated the equilibrium structure of diamond via the minimization of the total energy. Then, harmonic phonon dispersion curves and phonon eigenvectors have been evaluated within the linear-response framework. As a by-product of the calculation we have also obtained the internal-strain parameter. Furthermore, we have also tested the validity of the ab initio calculation for describing properties beyond the harmonic approximation. Using the quasiharmonic approximation we have calculated the thermal expansion coefficient and the mode Gruneisen parameter dispersion curves. Where experimental data are available, good agreement is found with our theoretical predictions.