LOCALIZED ELECTRON BEHAVIOR WITHIN BAND THEORY - A HARTREE-FOCK DESCRIPTION OF M(X)MG(1-X)O (M=MN, NI)

Results are presented of nb initio periodic unrestricted Hartree-Fock calculations which show the density of states for M(x)Mg(1-x)O (M = Mn , Ni) to be essentially independent of dopant (M) concentration x. The small variations of the projected densities of states with dopant con centration are of the same magnitude as those resulting from changes i n magnetic order. This is consistent with the marked similarity of the low-energy optical spectra of NiO, NixMg1-xO and aqueous solutions of Ni(II) salts, which suggests 'independent ion' behaviour in these sys tems. It is thus argued that the unrestricted Hartree-Fock approach co rrectly reproduces the qualitative features of the ground state of mag netic insulators such as MnO and NiO which result from strong on-site Coulomb interactions between essentially localized electrons.