Dielectric response in insulators: A wave-vector- and frequency-dependent model.

Abstract

We have calculated a random-phase-approximation-type expression for the dielectric response function of several large-band-gap insulators using a development of the model suggested by Fry. This model should be good for systems with well-localized valence-electron functions and flat valence-electron bands. We show that in this model it is a minor approximation to use spherically symmetric bands in the integration over reciprocal space. This allows simple and fast evaluations of our expressions, thus avoiding Brillouin-zone integrations and summations over band indices. The results of our calculations are compared with ab initio data on static dielectric matrices from Baldereschi, with model calculations on the static dielectric function from Rezvani and Friauf and with electron-energy-loss spectra for LiF from Fields et al., using only one fit parameter. In addition, the Johnson f-sum rule is tested for this model. We also verify that our approximation gives the correct singular behavior of the (0,K) matrix elements.