Prediction of the Chemical Trends of Oxygen Vacancy Levels in Binary Metal Oxides

We propose simple principles to predict qualitatively the chemical trends of oxygen vacancy levels in binary metal oxides by analyzing the atomic wavefunction characters of the conduction-band minimum (CBM). We show that if the CBM is a metal-oxygen antibonding state due to either s-s coupling, p-p coupling, or p-d coupling, then, in general, the oxygen vacancy level is deep. The stronger coupling leads to deeper levels. If the CBM is a non-bonding d state, then the oxygen vacancy level could be shallow. These principles are confirmed by the calculated trends of oxygen vacancy levels in representative binary metal oxides using hybrid density-functional method.