Ab initio SCF and limited CI calculations on the d-d transitions in NiO

Abstract

SCF and limited CI calculations on d-d transitions in NiO are presented. The calculations were performed on NiO₆ ^10-, stabilized by an electrostatic field. Closed Ni d-orbitals turned out delocalized from the calculations, but this was found to be an artifact of the calculation. The CI calculation showed that the d-electrons are in fact well localized on the metal, and that this localization may be obtained after pairwise rotations between the appropriate delocalized orbitals. The configuration interaction results are thus insensitive to the choice of reference state, provided that excitations describing the pairwise rotation are included in the CI expansion; only minor effects were obtained when excited-state orbitals instead of ground state orbitals were used in the calculations. A crystal-field treatment, based on SCF wave functions, yielded excitation energies in good agreement with the CI results. The computed results are satisfactory and the order ³ A _2g , ³ T _2g , ³ T _1g and ¹ E_g is proposed for the ground and first three excited states.