An Extension of the Coherent-Potential Approximation. I: Total and Partial Densities-of-States

Abstract

The coherent-potential approximation (CPA) is extended within the single-site approximation for general type of disorder in a substitionally disordered system. The present formalism can be applied to a disordered Hamiltonian if it can be transformed by an appropriate renormalization into a renormalized one whose disordered part is a sum of contributions from individual sites, where each contribution depends on the configuration of the corresponding site only but is not necessarily localized on the site. The ranges of applicability of CPA and its various extensions including the present formalism are exactly given and interrelationship among these formalisms is discussed in detail. In addition, accuracy of the present formalism when it is applied to systems with various types of disorder is examined.