Calculating properties with the polymorphous coherent-potential approximation

The formulas for calculating properties of an alloy such as the density of states, the charge density, and the Bloch spectral density function are derived from multiple-scattering theory for the polymorphous coherent-potential approximation (PCPA). The chemical shifts obtained for three alloy systems using the PCPA, the Korringa-Kohn-Rostoker CPA, and the locally self-consistent multiple-scattering method are compared with experiment. A significant improvement in the treatment of Coulomb effects is achieved using the PCPA with only a little more computational effort than for the older isomorphous CPA's.