Densities of States in Cu-Rich Ni-Cu Alloys by the Coherent-Potential Approximation: Comparisons with Rigid-Band and Virtual-Crystal Approximation

It is shown that the coherent-potential approximation is capable of explaining the densities of states of Cu-rich Ni-Cu alloys as obtained from recent photoemission experiments. The coherent-potential approximation predicts the formation of a separate Ni $d$ band for these alloys, this being consistent with the qualitative picture of Friedel-Anderson virtual bound states. This picture cannot be obtained from either the rigid-band model or the virtual-crystal approximation.