Electronic structure of NiO: Antiferromagnetic transition and photoelectron spectra in the ordered phase

Abstract

The thermodynamics of the antiferromagnetic ordering transition in NiO and the photoelectron spectra in the antiferromagnetic phase are studied by the variational cluster approximation. Using realistic Racah parameters to describe the Coulomb interaction in the Ni $3d$ shell and a Slater-Koster parameter $(pd\ensuremath{\sigma})$ which is slightly ($10%$) increased over the band-structure estimate, the calculated N\'eel temperature is 481 K (experimental value: 523 K). The magnetic susceptibility above ${T}_{N}$ has Curie-Weiss form. A significant contribution to the stabilization of the antiferromagnetic phase comes from electron hopping between oxygen which would be missed in theories that consider superexchange along a single bond only. The single-particle spectral function in the ordered phase is in good agreement with experiment, in particular, a number of dispersionless bands which are not reproduced by most calculations are obtained correctly. These flat bands are shown to be direct experimental evidence for a dispersionless electronic self-energy with several poles in the energy range of the valence band which originate from the multiplets of the ${\mathrm{Ni}}^{3+}$ ion. Small but possibly experimentally detectable changes of the photoelectron spectra with temperature are discussed, in particular, a widening of the insulating gap in the paramagnetic phase by approximately $10%$ is predicted.