Self-consistent-field studies of core-level shifts in ionic crystals. II. MgO and BeO

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Abstract
We have performed restricted Hartree-Fock self-consistent-field calculations on BeO and MgO clusters embedded in a point-charge field (chosen to represent the Madelung field in BeO and MgO crystals) in order to understand better the role of the many contributory shifts to the ionization potentials which occur for atoms in polar crystals. We find that core levels on the anion shift less than would be expected by Madelung-potential arguments alone. The reasons for this are discussed. Furthermore, the O(1s)–valence-band energy separation is found to be extremely similar in BeO and MgO (as is found experimentally) and this allows an explanation of the experimental observation that the O(1s) binding energy is approximately constant in many oxides. We also calculate relaxation energies, effective orbital sizes, and shakeup probabilities.