Multipolar contributions to electron self-energies: extreme tightbinding model

Abstract

Discrete dipole models provide a means of calculating optical properties ofsemiconductor surfaces rapidly and quite accurately, but they are generallyregarded as being purely phenomenological. A connection between such modelsand a quantum mechanical extreme tight binding (ETB) model is establishedhere. The dielectric function obtained from an extreme tight binding model isshown to be of similar form to that of a model in which a solid is treated asa lattice of polarizable, pointlike entities, the discrete dipole model. Thedielectric matrix is expressed in terms of its eigenvectors and eigenvalues,which are dipole waves and plasmon energies. The ETB dielectric matrix is usedto derive the self-energy of valence and conduction band states in fcc argon.This results in a simple physical picture where intra- and inter-bandscattering events result in virtual monopoles and dipoles on a lattice whichcouple to plasmon modes. The self-energies of electron and hole states of fccargon are analysed in terms of multipolar contributions.