The energetics and electronic structure of defective and irregular surfaces on MgO

Ab initio calculations based on the density-functional pseudopotential approach have been used to study the fully relaxed structure, the electron distribution and the electronic density of states of (001) terraces, steps, corners and reverse corners, and of F-centers at these surface features on MgO. The calculations confirm earlier predictions of the relaxed structures of surface irregularities based on simple interaction models. A substantial narrowing of the band-gap is found at the surface, which for terraces and steps is due to surface states at the bottom of the conduction band, but for the corner and reverse corner is also due to surface states at the top of the valence band. The F-center formation energy decreases steadily as the coordination of the oxygen site is reduced. The energy of the F-center level shows a tendency to approach the top of the valence band as the coordination of its site decreases.