Dielectric Function of a Model Insulator

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Abstract
A wave-number- and frequency-dependent dielectric function has been calculated for a model insulator using the random-phase approximation. The model insulator consists of a free-electron conduction band represented by a single orthogonalized plane wave (OPW) and a valence band represented by linear combinations of ionic wave functions. All energy bands are assumed parabolic and isotropic. Numerical results are obtained for Ar, KCl, CsCl, MnS, and Si, in reasonable agreement with previous calculations. Screened exchange potentials have been obtained by using an interpolation formula, and evaluated for the chlorine ion in CsCl.