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Microscopic Screening and Phonon Frequencies in Si

In the dielectric screening theory of covalent semiconductors the phonon dispersion relations are derived from the electron density response matrix. This matrix is obtained from the polarizability using the electron energies and wavefunctions. The crystal psuedopotential is calculated starting from a local electron-ion potential with up to 150 plane waves. Exchange and correlation effects in the dielectric response are included via the local density functional formalism. The procedure ensures consistency between Hamiltonian and dielectric matrices. The dimension of the dielectric matrix is 137. Phonon frequencies of Si in the gamma and X-points are calculated using different approaches and the results are compared with experiment.