Low energy excitations in NiO based on a direct Δ-SCF approach

Abstract

This paper reports calculated energies and electronic structures of nineteen excited states in NiO based on a Δ-SCF approach reported previously for the d →d transitions in NiO and Sr2CuO2Cl2. They are the spin-flip: → eight d → d : (one electron)3A2g →3T2g, (two electron)3A2g → 3T1g, 3A2g → a1Eg, 3A2g → 1T2g, 3A2g → 1T1g, 3A2g → b1Eg, 3A2g → b1T2g; two O(2p) → Ni(3d); seven Ni(3d) → O(2p) (including two spin-flip) and the O(2s) → Ni(3d) charge transfer excitations, which span an energy range from 0.25 eV to 17.53 eV, and include the fundamental band gap associated with an excitonic O(2p) → Ni(3d) transition at 4.23 eV. These are compared to absorption and emission spectra, and previous calculations. In the case of the O(2p) → Ni(3d) excitations, comparisons are given for gap and Γ-point energies derived from HF, PBE0, HSE06, B3LYP, B1WC, GGA and LDA one-electron approximations. Finally, the directly calculated Stokes shifts and associated luminescence energies for the two O(2p) → Ni(3d) transitions are reported, where the excitonic value is found to be in good agreement with the recently reported experimental value.