Nonsite diagonal properties from the Korringa-Kohn-Rostocker nonlocal coherent-potential approximation

We present a formalism for the Bloch spectral function within the framework of the recently devised Korringa-Kohn-Rostocker nonlocal coherent potential approximation (KKR-NLCPA). This is applicable to the study of the effects of short-range order (SRO) on the electronic structure of disordered systems. We show how a coarse-grained average of the spectral function over regions in reciprocal space results directly from the KKR-NLCPA. By considering fluctuations about the NLCPA effective medium we find an expression for the spectral function itself. The results of explicit calculations on the bcc Cu50Zn50 and the fcc Cu77Ni23 solid solutions are presented in order to examine the effects of SRO upon their electronic structure and to illustrate the validity of our formalism.