Two or More Impurities; Disordered Systems

Abstract

In this chapter we examine first a system consisting of two “impurities” embedded in a periodic tight-binding model (TBM). This prepares the way for the approximate treatment of a disordered system containing a nonzero concentration of impurities. We examine in particular the average DOS, which depends on the average Green’s function, 〈G〉. For the calculation of the latter, various approximation methods are employed; prominent among them is the so-called coherent potential approximation (CPA).