THEORETICAL-ANALYSIS OF THE LIGAND-FIELD SPECTRUM OF K3COF6

We present a detailed ab initio study of the ligand field spectrum of the CoF63- cluster in the K3CoF6 crystal. The crystal environment arou nd the octahedral CoF63- cluster is accounted for by a Madelung potent ial. The ground and ligand field excited states of K3CoF6 have been st udied with the inclusion of correlation effects. Each state was first optimized separately in a complete active space self-consistent field (CASSCF) calculation, including ten active electrons occupying the bon ding e(g) and anti-bonding e(g) and t(2g)* shells. Further correlatio n was incorporated by using the averaged coupled pair functional appro ach (ACPF) with the CASSCF configuration space as reference space and where the maximum number of correlated electrons was up to twenty. The one quintet-quintet transition is already described well at the CASSC F level while the spin-forbidden quintet-triplet transitions require t he inclusion of dynamical correlation.