FIRST-PRINCIPLES CALCULATIONS OF THE PHONON-SPECTRUM IN SEMICONDUCTORS

Abstract

We present the results of first-principles pseudopotential calculations for the phonon spectrum of Si and GaAs within the local-density functional approximation. From a limited set of planar force constants obtained from the supercell approach, the dynamical matrix is constructed and used to determine the phonon dispersion and the phonon density of states. For GaAs, due to the well-known long range interaction, we only calculate the phonon spectrum along the Gamma --> X and Gamma --> L axis. The calculated phonon frequencies are in good agreement with experimental data. We also calculate the phonon density of states for amorphous Si from first-principles molecular dynamics simulations, which are considered to be more appropriate for nonperiodic systems, and find fairly good agreement with experiments and other calculations.