Localized electron behaviour within band theory a Hartree-Fock description of MxMg1-xO(M=Mn, Ni)

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Abstract
Results are presented of ab initio periodic unrestricted Hartree-Fock calculations which show the density of states for MxMg1-xO(M=Mn, Ni) to be essentially independent of dopant (M) concentration x. The small variations of the projected densities of states with dopant concentration are of the same magnitude as those resulting from changes in 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 systems. It is thus argued that the unrestricted Hartree-Fock approach correctly reproduces the qualitative features of the ground state of magnetic insulators such as MnO and NiO which result from strong on-site Coulomb interactions between essentially localized electrons.