Correlated band structure of NiO, CoO and MnO by variational cluster approximation

TL;DR

This paper applies the variational cluster approximation to transition metal oxides NiO, CoO, and MnO, successfully calculating their spectral functions with results aligning well with experiments.

Contribution

It introduces a method using trial self-energies from exact diagonalization of a TMO6-cluster to accurately compute spectral functions of transition metal oxides.

Findings

Spectral functions agree with experimental data

Self-energy contains irrelevant degrees of freedom

Method effectively bridges cluster and lattice systems

Abstract

The variational cluster approximation proposed by Potthoff is applied to the calculation of the single-particle spectral function of the transition metal oxides MnO, CoO and NiO. Trial self-energies and the numerical value of the Luttinger-Ward functional are obtained by exact diagonalization of a TMO6-cluster. The single-particle parameters of this cluster serve as variational parameters to construct a stationary point of the grand potential of the lattice system. The stationary point is found by a crossover procedure which allows to go continuously from an array of disconnected clusters to the lattice system. The self-energy is found to contain irrelevant degrees of freedom which have marginal impact on the grand potential and which need to be excluded to obtain meaningful results. The obtained spectral functions are in good agreement with experimental data.