Disordered alloys with short-range order: A Korringa-Kohn-Rostoker formulation within the cluster coherent-potential approximation

Abstract

We present a generalization of the Korringa-Kohn-Rostoker cluster coherent-potential approximation for systems with short-range order (SRO). For this purpose we have used the generalized augmentedspace formalism of Gray and Kaplan, in which one can deal with independent (corresponding to purely random systems) as well as dependent (corresponding to systems with SRO) random variables. The expression for the configuration-averaged Green s function in this case is essentially an expansion about the Green s function for a purely random system, and contains an infinite number of terms. For simplicity, we truncate the series after the second-order correction term. Using this approximation, we have calculated the density of states {DOS) for a one-dimensional muffin-tin alloy with Markovian-type SRO and find that the introduction of SRO can produce large changes in the DOS. We also find that the approximation yields non-negative DOS at all energies for a reasonably wide range of SRO parameter.

Short-range correlations in disordered systems: nonlocal coherent-potential approximation

“…Unfortunately, the formalism could only be implemented for model systems and also became intractable beyond a two-site cluster. Generalization to include SRO based on the generalized ASF by Gray and Kaplan [129] also proved problematic [128]; however, Mookerjee and Prasad [130] extended the generalized ASF and implemented the cluster-CPA with SRO in the TB-LMTO [131] framework, although implementation was again possible only for model systems. Finally, application to realistic systems was achieved when Saha et al combined the generalized ASF with the recursion technique of Haydock [132,133] and developed the TB-LMTO-ASR method [134,135].…”