Electronic effects in the d-d spectrum of NiO

The different contributions to the 10Dq electronic transition have been analyzed by using different kind of ab initio cluster model wavefunctions. In particular, the orbital sets used provided a guide to the physical mechanisms involved. The analysis of the results shows that orbital relaxation effects accompanying the 10Dq electronic transition are much smaller than had been suggested in previous studies. The apparent large relaxation noted previously is shown to arise from an arbitrary orbital mixing in the canonical Hartree-Fock orbitals. The influence on 10Dq of the chemical effects on both the ground and excited states, the presence of the ligand anions, and the role of electronic correlation have been studied in detail. While these effects lead to contributions of ≈ 0.25 eV, which cannot be neglected, our results show that a model that takes into account the finite size of the ions, as opposed to their representation as point charges, gives a reasonable value for 10Dq in NiO.