AB-INITIO MODEL-POTENTIAL EMBEDDED-CLUSTER STUDY OF JAHN-TELLER PARAMETERS AND ELECTRONIC-TRANSITION ENERGIES OF CR2+ IN OXIDE AND FLUORIDEOCTAHEDRAL COORDINATION

In this paper we present the results of an ab initio model potential [ J. Chem. Phys. 89, 5739 (1988)] embedded-cluster calculation of the po tential-energy surface parameters of the two lowest electronic states ((5)E(g), and T-5(2g)) of Cr2+-doped MgO, CaO, SrO, and KMgF3 using th e complete-active-space self-consistent-field [Chem. Phys. 48, 157 (19 80)] and the averaged coupled-fair functional (ACPF) [J. Chem. Phys. 8 2, 890 (1985)] methods. Impurity-ligand equilibrium distances, vibrati onal frequencies, Jahn-Teller energies, and energy barriers between co mpressed and elongated D-4h structures of the (CrO6)(10-) and (CrF6)(4 -) clusters are calculated using an embedding method that has been sho wn to be able to describe the differential effects brought about on a given cluster by the different host lattices. Vertical transition ener gies (both absorption and emission) between the two states at the opti mized cluster geometries are also calculated, correlating two differen t sets of electrons through ACPF calculations. As in an earlier calcul ation of 3d(9) and 4d(9) transition-metal ions, the Jahn-Teller coupli ng is shown to be stronger in going from MgO to SrO, within the oxide family of lattices, being dynamic in all the lattices.