Ab initio calculation of the contribution from anion dipole polarization and dynamic correlation to 4f-5d excitations of Ce3+ in ionic compounds -: art. no. 045129

In this study basic effects are investigated of ion-host interactions on 4f-5d excitations of Ce3+ ions in wideband ionic host compounds. Particularly the shift of the average 4f-5d transition energy compared to that of the free ion, the centroid shift, is of interest. The self-induced dipole effect where the 4f or 5d electron dynamically polarizes the neighboring ions is analyzed in detail. Taking into account the overlap of the 5d orbital of Ce3+ with the neighbor anions, the standard classical expression was modified, and the result is that this not only drastically reduces the value of the polarization contribution to the centroid shift but also the steep dependence on the distance to the anions almost vanishes. This polarization effect and the additional contributions such as covalency and dynamic correlation should be included in a configuration interaction (CI) calculation applied on a cluster of ions around the Ce3+ ion. Calculations with Hartree-Fock Moller-Plesset perturbation theory corrected to second order for perturbation effects and coupled-cluster theory with single, double, and triple excitations were conducted with various basis sets and cluster sizes and it turned out that the results do not include the polarization effect and so this contribution had to be calculated separately and was added to the CI results. Good agreement at the 0.15 eV level is obtained between theory and experiment for Ce3+ in BaF2, LaAlO3, and LaCl3.