Overlap-model and ab initio cluster calculations of ion properties in distorted environments

Electronic structure calculations on eight alkali fluorides and chlorides a re performed in which the first shell of cations about a central anion is d istorted and induced anion dipole and quadrupole moments are obtained. The charge-density overlap model used is validated against previous full-cluste r calculations of distortion-induced moments and overall gives the same phy sical account of these properties for small anions and cations. Its use all ows the calculations to be extended to RbF and RbCl. The overlap model mimi cs the full-cluster description of short-range damping of the multipole mom ents, and the induced moments are used to fit a simple model of the short-r ange interactions. Fitted parameter sets are shown to transfer between syst ems in a physically transparent manner. (C) 2001 Elsevier Science B.V. All rights reserved.