By using a first-principles method employing the local density approximation plus Hubbard parameter approach, a study was made of point defects, and of the interactions between them. The defect states associated with Ni or O vacancies were identified within the energy gap. It was found that Ni vacancies introduced shallow levels into the density of states for the spin direction opposite to that of the removed Ni atom, while the O vacancy created more localized in-gap states. The interaction profiles between vacancies indicated that specific defect arrangements were strongly favored for both Ni and O vacancies. In the case of Ni vacancies, defect ordering in a simple-cubic style was found to be most stable, leading to a half-metallic behavior. The ionized O vacancies also show a tendency toward clustering, more strongly than neutral pairs. The microscopic origin of vacancy clustering was understood based on overlap integrals between defect states.

Interaction and Ordering of Vacancy Defects in NiO. S.Park, H.S.Ahn, C.K.Lee, H.Kim, H.Jin, H.S.Lee, S.Seo, J.Yu, S.Han: Physical Review B, 2008, 77[13], 134103 (7pp)