Towards a systematically improvable many-body description of antiferromagnetic iron oxide

TL;DR

This study uses quantum Monte Carlo methods to analyze the properties of antiferromagnetic iron oxide, revealing the importance of wave function choice and highlighting the need for systematically improvable many-body wave functions.

Contribution

It systematically investigates how different wave function generation techniques affect QMC predictions for FeO, emphasizing the importance of wave function choice for accurate property estimation.

Findings

Lattice distortion prediction depends on single particle orbitals.

Magnetic moment is insensitive to wave function construction.

Charge transfer plays a significant role in FeO's electronic structure.

Abstract

We report variational and fixed-node diffusion quantum Monte Carlo (QMC) calculations of anti-ferromagnetic iron oxide (FeO) in the ground state B1 crystal structure. The goal of this study was a systematic investigation of the sensitivity of several ground state properties to a variety of QMC wave function generation techniques including advanced wave functions such as multi-determinant expansions and backflow transformations. We found that the predicted lattice distortion was largely controlled by the choice of single particle orbitals used to construct the wave function, rather than by subsequent wave function optimization techniques within QMC. However, the absolute magnetic moment was remarkably insensitive to the method of wave function construction. QMC estimates of total spin density indicate that in addition to strong electronic correlation of the Fe $3d$ states, charge transfer may be an important but challenging piece of physics to accurately capture within existing QMC methods. Finally, we highlight the need for advanced and systematically improvable many-body wave functions suitable for accurately describing challenging real systems.