Electronic energy bands in the fluorite structure: CaF2and CdF2

The electronic band structures of calcium and cadmium fluoride are calculated by a combined tight-binding and pseudopotential method. The overall shape of the valence bands is found to be the same in these two compounds and agrees quite well with a "universal valence-band structure" calculated for the fluorite structure. Yet it is found that the excited cationic $d$ states lie too high in the conduction band. It is then shown that with a simple semiempirical modification of the cationic pseudopotential model a coherent interpretation of the optical spectra of the two crystals can be proposed.