Ab initio modelling of defects in oxides

Two materials, magnesium oxide and magnesium aluminate spinel, have been studied using the ab initio methodology, density functional theory. In the case of MgO, energetics of a variety of point defects were considered. These defects were isolated Schottky and Frenkel defects and interstitial pairs, along with a number of Schottky defects and di-interstitials. Comparisons were made between the density functional theory results and results obtained from empirical potential simulations and these generally showed good agreement. Both methodologies predicted the first nearest neighbour Schottky defects to be the most energetically favourable of the considered Schottky defects and that the first, second, and fifth nearest neighbour di-interstitials were of similar energy and were favoured over the other di-interstitial configurations. Relaxed structures of the defects were analysed, which showed that empirical potential simulations were accurately predicting the displacements of atoms surrounding di-interstitials, but overestimated O atom displacement for Schottky defects. [Continues.]