LOCAL-FIELD EFFECTS IN THE HIGH-Q-VECTOR DIELECTRIC RESPONSE OF SI

The influence of microscopic or local fields on the full frequency- an d wavevector-dependent dielectric loss function of Si has been calcula ted, based on accurate empirical pseudopotential calculations of the e lectronic structure. It is shown that local-field effects, dramaticall y significant at optical (q almost-equal-to 0) wavevectors, diminish w ith increasing magnitude of q to negligible proportions as q approache s the Brillouin zone boundary. In addition it is shown that the calcul ated volume-plasmon dispersion relation is improved in comparison with experimental results by the inclusion of local-field effects.