Intrinsic defects in KMgF₃: theab initioand the extended-ion study

Abstract

The intrinsic defects in KMgF3, such as VK centres and self-trapped excitons (STEs), are studied by the ab initio method and the extended-ion method. In the ab initio method, the Madelung potentials are introduced into the Fock operator terms to perform calculations on clusters modelling ionic solids. It is found that the VK centre moves toward the nearby interstitial site, still keeping C2v symmetry; and the STE is unstable in the on-centre symmetry, undergoing a relaxation consisting of an axial translation superimposed with a rotation. Such a translation plus rotation relaxation of the STE in KMgF3 is quite different from those in alkali halides and in alkali-earth halides. The calculated results for the excitation energy of the VK centre and for the emission energy of the STE are in reasonable agreement with experiments.