Optical spectra of nickelates and charge-transfer transitions

Specific features of the charge-transfer (CT) states and O 2p→Ni3d CT transitions in the octahedral (NiO6)10-(NiO6)10- complex are considered in the cluster approach. The reduced matrix elements (RMEs) of the electric-dipole transition operator are calculated on many-electron wave functions of the complex corresponding to the initial and final states of a CT transition.Modelling the optical spectrum of nickelates has yielded a complicated CT band. The model spectrum is in satisfactory agreement with experimental data which demonstrates the limited validity of the generally accepted concept of a simple structure of CT spectra.