ANALYTIC PROPERTIES AND ACCURACY OF THE GENERALIZED BLACKMAN-ESTERLING-BERK COHERENT-POTENTIAL APPROXIMATION

The Blackman-Esterling-Berk (BEB) theory, generalized to nonorthogonal basis sets and complicated elementary cells [K. Koepernik, B. Velicky , R Hayn, and H. Eschrig, Phys. Rev. B 55, 5717 (1997)], is inspected in great detail with respect to its analytic properties and numerical accuracy. We give a proof of the single impurity limit fulfilled by BE B theory, thus clarifying some critical points in the derivation of th e theory. We undertake extensive numerical tests for the BEB coherent- potential approximation (CPA) to check the range of applicability of t he included single-site approximation. The BEB CPA turns out to give g ood results in a wide range of energy parameters.