Theory of diffusion and aggregation of radiation-induced defects in MgO and α-Al₂O₃ crystals

This paper describes three separate-but related-investigations of defects in the technologically important ceramics MgO and α-Al₂O₃. We used several different but complementary theoretical techniques. Pair-potential methods are well-suited to the calculation of defect energies of formation, aggregation and migration when no charge re-distribution occurs. CNDO or INDO semi-empirical methods must be used for very large clusters or unit cells containing hundreds of atoms. First-principles methods like Hartree-Fock and density-functional theory schemes are appropriate for small unit cells containing up to 16 or 32 atoms. Here the use of these methods for isolated defects and clusters in MgO and corundum, and for oxygen atom interstitials in MgO is discussed.