Intrinsic defects, such as VK centers and self-trapped excitons, were studied by using the ab initio method and the extended-ion method. In the former method, the Madelung potentials were introduced into the Fock operator terms in order to perform calculations on clusters which modelled ionic solids. It was found that the VK center moved towards the nearby interstitial site, while maintaining keeping C2v symmetry, and that the self-trapped exciton was unstable in the on-center symmetry; undergoing a relaxation which consisted of an axial translation superposed on a rotation. Such a translation-plus-rotation relaxation of the self-trapped exciton was quite different to those found in alkali halides and in alkali-earth halides. It was noted that the calculated results for the excitation energy of the VK center, and for the emission energy of the self-trapped exciton, were in reasonable agreement with experiment.

Intrinsic Defects in KMgF3 - the ab initio and the Extended-Ion Study. G.Q.Huang, L.F.Chen, M.Liu, D.Y.Xing: Journal of Physics - Condensed Matter, 2003, 15[26], 4567-76