The genesis of energy bands formed by sublattice states in alkaline-earth metal oxides and sulfides

The self-consistent electron energy band spectra of crystals and charged sublattices of alkaline-earth metal oxides and sulfides are calculated in the framework of the density functional theory within the pseudopotential approximation in the basis set of localized orbitals. The charge states of sublattices (such as neutral sublattices, empty metal sublattices, and doubly charged anion sublattices) are analyzed with due regard for the electrical neutrality of the crystal. It is demonstrated that the valence bands of the studied crystals are very similar to the valence bands of the doubly charged anion sublattices. The distributions of the valence electron densities of the crystals are virtually identical to those of the anion sublattices. The lower conduction bands of the crystals and doubly charged anion sublattices also almost coincide with each other for MgO and MgS but differ substantially for CaO and CaS. This is associated with the difference between the contributions from the anions and cations to the conduction band of the crystals. It is found that these contributions depend on the relative energy positions of p and d unoccupied states.