Dielectric Matrix Calculations in Helical Chain Semiconductors

Abstract

In the last decade there have been many attempts to compute the dielectric function in semiconductors within microscopic approaches based on the knowledge of the electronic band structure, Very recently also Se and Te were studied from this point of view. Dielectric function calculations have been performed both in the pseudopotential scheme [l,2] and by describing the chemical bond through localized atomic orbitals [3,4]. The most questioned point has concerned the magnitude of the so-called local-field effects in these semiconductors. The problem was raised by a reflectivity measurement in Se [5] which was formerly interpreted, within a molecular model, in terms of large local-field corrections. On the contrary the pseudopotential calculations [1,2] explained the large pressure dependence of the reflectivity without invoking local-field effects. However these calculations did not face explicitly the problem of evaluating the microscopic fields.