High photon energy spectroscopy of NiO: experiment and theory

TL;DR

This study combines experimental hard x-ray photoemission spectroscopy with advanced theoretical methods to accurately describe the electronic structure of NiO, emphasizing the need for a hybrid GW and DMFT approach.

Contribution

The paper demonstrates that a combination of GW and DMFT methods is essential for accurately modeling the electronic structure of NiO, highlighting the limitations of each method alone.

Findings

GW corrections improve energy positioning of O and Ni states.

LDA+DMFT alone cannot fully explain HAXPES spectra.

Photoionization cross section inclusion is crucial for interpretation.

Abstract

We have revisited the valence band electronic structure of NiO by means of hard x-ray photoemission spectroscopy (HAXPES) together with theoretical calculations using both the GW method and the local density approximation + dynamical mean-field theory (LDA+DMFT) approaches. The effective impurity problem in DMFT is solved through the exact diagonalization (ED) method. We show that the LDA+DMFT method alone cannot explain all the observed structures in the HAXPES spectra. GW corrections are required for the O bands and Ni-s and p derived states to properly position their binding energies. Our results establish that a combination of the GW and DMFT methods is necessary for correctly describing the electronic structure of NiO in a proper ab-initio framework. We also demonstrate that the inclusion of photoionization cross section is crucial to interpret the HAXPES spectra of NiO.We argue that our conclusions are general and that the here suggested approach is appropriate for any complex transition metal oxide.