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