Inclusion of charge correlations in calculations of the energetics and electronic structure for random substitutional alloys

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Abstract
Currently, the coherent-potential approximation (CPA) implemented via the multiple-scattering theory of Korringa, Kohn, and Rostoker (KKR) gives the best first-principles description of the electronic structure for random substitutional alloys. However, the total energy has an important component of electrostatic energy missing, namely, that arising from the correlation of charges with varying atomic environments. We develop a ‘‘charge-correlated’’ CPA method (cc-CPA) which includes (some) local environmental charge correlations within the KKR-CPA method. We investigate the cc-CPA energetics for several alloys and show that the formation energies are in better agreement with experimental results. These calculations show that the excess charge on a species is almost completely screened by the first-neighbor shell. We then derive a simplified scheme to include the vast majority of the omitted electrostatic energy from charge correlations which requires only a species-dependent shift of the potentials within the original KKR-CPA method. We also discuss the ramifications on the electronic structure.