Ab initio model-potential embedded-cluster study of Jahn-Teller parameters and electronic transition energies of Cr2+ in oxide and fluoride octahedral 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 potential-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 the complete-active-space self-consistent-field [Chem. Phys. 48, 157 (1980)] and the averaged coupled-fair functional (ACPF) [J. Chem. Phys. 82, 890 (1985)] methods. Impurity-ligand equilibrium distances, vibrational frequencies, Jahn-Teller energies, and energy barriers between compressed and elongated D-4h structures of the (CrO6)(10-) and (CrF6)(4-) clusters are calculated using an embedding method that has been shown to be able to describe the differential effects brought about on a given cluster by the different host lattices. Vertical transition energies (both absorption and emission) between the two states at the optimized cluster geometries are also calculated, correlating two different sets of electrons through ACPF calculations. As in an earlier calculation of 3d(9) and 4d(9) transition-metal ions, the Jahn-Teller coupling is shown to be stronger in going from MgO to SrO, within the oxide family of lattices, being dynamic in all the lattices.