Convergence of quasiparticle self-consistent GW calculations of transition metal monoxides

TL;DR

This paper investigates the convergence behavior of fully self-consistent GW calculations for transition metal monoxides, showing that convergence is slow but results are robust and align well with experimental data.

Contribution

It provides a detailed analysis of the convergence process in quasiparticle self-consistent GW calculations for transition metal oxides, highlighting the importance of iterative approaches.

Findings

Convergence of QPscGW is slow and path-dependent.

Results are weakly dependent on initial wavefunctions.

Converged properties agree well with experimental data.

Abstract

Finding an accurate ab initio approach for calculating the electronic properties of transition metal oxides has been a problem for several decades. In this paper, we investigate the electronic structure of the transition metal monoxides MnO, CoO, and NiO in their undistorted rock-salt structure within a fully iterated quasiparticle self-consistent GW (QPscGW) scheme. We study the convergence of the QPscGW method, i.e., how the quasiparticle energy eigenvalues and wavefunctions converge as a function of the QPscGW iterations, and we compare the converged outputs obtained from different starting wavefunctions. We find that the convergence is slow and that a one-shot G$_0$W$_0$ calculation does not significantly improve the initial eigenvalues and states. It is important to notice that in some cases the "path" to convergence may go through energy band reordering which cannot be captured by the simple initial unperturbed Hamiltonian. When we reach a fully iterated solution, the converged density of states, band-gaps and magnetic moments of these oxides are found to be only weakly dependent on the choice of the starting wavefunctions and in reasonably good agreement with the experiment. Finally, this approach provides a clear picture of the interplay between the various orbitals near the Fermi level of these simple transition metal monoxides. The results of these accurate {\it ab initio} calculations can provide input for models aiming at describing the low energy physics in these materials.