Divacancy binding energies in face-centered cubic Al and hexagonal close-packed Mg were examined by using ab initio calculations which were based upon density-functional theory. Dense k-point meshes and large super-cells were used to obtained convergent values. In Al, the first-nearest-neighbor divacancy was unstable; with a negative binding energy. However, the second-nearest neighbor divacancy was stable; with a positive binding energy. In Mg, both the first-nearest-neighbor and second-nearest neighbor divacancies, corresponding to the first-nearest-neighbor divacancy in face-centered cubic structures, were stable; with positive binding energies that were in accord with the conventional view. The difference in the stability of divacancies in Al and Mg was analyzed by making calculations of divacancies in hexagonal close-packed Al and face-centered cubic Mg. The tendency to form local directional bonds, with covalency at defects, was considered to be the electronic cause of the peculiar nature of divacancies in Al.

Ab initio Study on Divacancy Binding Energies in Aluminum and Magnesium. T.Uesugi, M.Kohyama, K.Higashi: Physical Review B, 2003, 68[18], 184103 (5pp)