Two-electron defect systems in ionic crystals: application to F' centres in alkali halides

Abstract

The extended-ion method for the study of excited states in ionic crystals is modified for such two-electron defect systems as the F' centre and positronium in alkali halides. Exclusive use of 1s floating Gaussian functions as the basis is the main feature of the method. Some degree of electron correlation is built-in in this method. Applied to F' centres, it is found that in NaI the spin-singlet ground state is deeply bound, and there is also a bound triplet state. Comparison with experimental data regarding the optical and thermal dissociation energies in several alkali halides gives reasonable agreement.

Two-dimensional angular correlation study of delocalized positronium in alkali halides

“…Recently, the relative intensities of the central and some satellite peaks for NaF, NaCl, and KCl were calculated by Zhang and Song [11,12] using the extended-ion method to account for this interesting effect. Their calculations show that the odd-index satellite peaks are practically reduced to zero.…”