First-principles calculations for an antiferromagnetic structure containing 4 types of point defect, U vacancy, O vacancy, U interstitial and O interstitial, were performed using the projector augmented wave method with generalized gradient approximation; combined with the Hubbard U correction. The defect formation energies were estimated, under lattice relaxation, for super-cells containing 1, 2 or 8 unit cells of UO2. The electronic structure, the atomic displacement and the stability of defected systems were obtained, and the effects of cell-size upon these properties were considered. The results constituted a self-consistent dataset, of formation energies and atomic distance variations of various point defects in UO2, having relatively high precision. It was shown that a super-cell with 8 unit cells or more was required in order to investigate defect behavior with reliable precision, since point defects had a wide-ranging effect; not only upon the first-nearest neighbor atoms of the defect, but also upon the second-nearest neighbors and even more distant atoms.

First-Principles Calculation of Point Defects in Uranium Dioxide. M.Iwasawa, Y.Chen, Y.Kaneta, T.Ohnuma, H.Y.Geng, M.Kinoshita: Materials Transactions, 2006, 47[11], 2651-7