The influence of microscopic or local fields on the full frequency- and wavevector-dependent dielectric loss function of Si has been calculated, based on accurate empirical pseudopotential calculations of the electronic structure. It is shown that local-field effects, dramatically significant at optical (q ~ 0) wavevectors, diminish with increasing magnitude of q to negligible proportions as q approaches the Brillouin zone boundary. In addition it is shown that the calculated volume-plasmon dispersion relation is improved in comparison with experimental results by the inclusion of local-field effects.
Local-field Effects in the High-q-vector Dielectric Response of Si