Weighted two-particle Green's functions in the coherent-potential approximation.

Abstract

We extend the two-particle theory of disordered systems within the coherent-potential approximation to obtain weighted contributions to averaged two-particle resolvents which arise from separate alloy components. Starting from first principles in a model of diagonal disorder and the single-site approximation for a binary substitutional alloy ${\mathit{A}}_{\mathit{cB}1\mathrm{\ensuremath{-}}\mathit{c}}$ we extend the approach of a fundamental paper by Velick\'y to evaluate various weighted forms of a general class of two-particle Green's functions. Applications in a wide range of linear response theory are discussed in detail as well as the behavior of the weighted functions in a strong disorder limit. To exemplify our analytic calculations the optical absorption in a disordered model alloy is studied numerically. \textcopyright{} 1996 The American Physical Society.