Multipolar contributions to electron self-energies: extreme tight binding model

Discrete dipole models provide a means of calculating optical properties of semiconductor surfaces rapidly and quite accurately, but they are generall y regarded as being purely phenomenological. A connection between such mode ls and a quantum mechanical extreme tight binding (ETB) model is establishe d here. The dielectric function obtained from an extreme tight binding mode l is shown to be of similar form to that of a model in which a solid is tre ated as a lattice of polarizable, pointlike entities, the discrete dipole m odel. The dielectric matrix is expressed in terms of its eigenvectors and e igenvalues, which are dipole waves and plasmon energies. The ETB dielectric matrix is used to derive the self-energy of valence and conduction band st ates in fee argon. This results in a simple physical picture where intra- a nd inter-band scattering events result in virtual monopoles and dipoles on a lattice which couple to plasmon modes. The self-energies of electron and hole states of fee argon are analysed in terms of multipolar contributions.