INCLUSION OF CHARGE CORRELATIONS IN CALCULATIONS OF THE ENERGETICS AND ELECTRONIC-STRUCTURE FOR RANDOM SUBSTITUTIONAL ALLOYS

Currently, the coherent-potential approximation (CPA) implemented via the multiple-scattering theory of Korringa, Kohn, and Rostoker (KKR) g ives the best first-principles description of the electronic structure for random substitutional alloys. However, the total energy has an im portant component of electrostatic energy missing, namely, that arisin g from the correlation of charges with varying atomic environments. We develop a ''charge-correlated'' CPA method (cc-CPA) which includes (s ome) local environmental charge correlations within the KKR-CPA method . We investigate the cc-CPA energetics for several alloys and show tha t the formation energies are in better agreement with experimental res ults. These calculations show that the excess charge on a species is a lmost completely screened by the first-neighbor shell. We then derive a simplified scheme to include the vast majority of the omitted electr ostatic 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.