Theoretical investigation of the electronic structure of NiO by ab initio molecular-orbital calculations

Abstract

The electronic structure of NiO near the Fermi level was investigated by ab initio molecular-orbital calculations using the unrestricted Hartree-Fock (UHF) method with basis sets appropriate for nickel and oxygen atoms in order to explain why NiO behaves as an insulator. In the present analysis, we used a cluster composed of finite unit cells of NiO containing the (Ni-O6)10- cluster. We obtained the result that NiO was an insulator, with a band structure where the upper Ni 3d band was above the Fermi level, and the upper O 2p, the lower O 2p and the lower Ni 3d bands were below the Fermi level. These results were in good agreement with the experimental results obtained by photoelectron spectroscopy (PES) and bremsstrahlung isochromat spectroscopy (BIS), and with the electronic structures derived from the charge-transfer model proposed by Sawatzky and Allen (1984). The main peak observed in PES corresponds to the d8L state, i.e. O 2p band, and the satellite peaks correspond mainly to the mixed state produced by the correlation between the 2p state of O atoms and the d8 state of Ni atoms.