F-type centres and hydrogen anions in MgO: Hartree-Fock ground states

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Abstract
Second-neighbour defect clusters, described in the Hartree-Fock approximation with Kunz-Klein localising potentials out to fourth neighbours, embedded in an infinite shell model lattice are analysed with consistent distortion and polarisation for F+, F (H-)+, and (H2-)0 defects in MgO. Basis sets for the defects are optimised, and are improved by recontraction for the first and second neighbours. Questions of total energy, nearest-neighbour displacements and localisation are addressed for each defect. For the F+ centre, its ground state in relation to the valence band is discussed, as is the localisation of its unrelaxed excited state. For the F+ and (H2-)0 centres, spin densities are evaluated at each step of the calculation, and compared with experiment. Calculations that completely neglect the ion-size effect of all ions except at the defect centre give some qualitatively plausible results. The full-cluster results are used to derive short-range shell model parameters for H-and H2- in MgO. The method and results are critically reviewed.