The valence band structures of BeO, MgO, and CaO

We have performed direct measurements of the valence band structures of the light alkaline earth oxides BeO, MgO, and CaO using electron momentum spec troscopy (EMS). From these measurements, we have determined the band disper sions, valence bandwidths, and O(2s)-O(2p) intervalence bandgaps at the Gam ma point. For comparison we have also performed Hartree-Fock (HF) and densi ty-functional (DFT) calculations in the linear combination of atomic orbita ls (LCAO) approximation. Intervalence bandgaps compare reasonably well with the DFT calculations and previous experimental and theoretical studies. Ou r measured bandwidths, however, are significantly smaller. In particular, w e find that contrary to conventional wisdom, the local density approximatio n of DFT overestimates the valence bandwidths of these ionic solids. (C) 20 00 American Institute of Physics. [S0021-9606(00)70642-8].