A relation between kinetic-energy density and the band gap in alkali and alkaline-earth oxides

Alkali and alkaline-earth oxides are analysed by means of Bader's atom-in-molecule theory and density functional theory. Particular attention is devoted to the analysis of properties of the bond critical points. A linear relation is found between the kinetic-energy density at the bond critical point between cation and anion and the electronic band gap. This result might shed new light on the relationship between ground-state density, the nature of the bonds and insulating behaviour. Its generality is discussed.