The energy spectrum of single-hole states in transition metal oxides

The p-d hybridised single-hole states of the transition-met al-oxygen tetra hedron (TMO4) are collectivised due to the direct p-p hopping between oxyge ns of different clusters. The lowest-lying energy band is always narrow and fully occupied. The first excited band gets occupied as an effect of valen ce-uncompensated doping, so it can be almost localised. The possible hole e xcitations to the two higher energy bands, which are wider, may imply the M ott-like hopping form of charge transport in these systems.