Broken-symmetry self-consistent GW approach: degree of spin contamination and evaluation of effective exchange couplings in solid antiferromagnets

TL;DR

This paper develops a self-consistent GW method with a broken-symmetry approach to accurately evaluate magnetic exchange couplings in solid antiferromagnets, showing good agreement with multireference calculations.

Contribution

It introduces a robust computational procedure for calculating magnetic couplings using self-consistent GW with broken symmetry, preserving spin states and reducing contamination.

Findings

The method accurately estimates exchange constants in nickel and manganese oxides.

Broken-symmetry GW preserves the spin contamination levels similar to Hartree-Fock.

Results align well with multireference wave-function calculations.

Abstract

We adopt a broken-symmetry strategy for evaluating effective magnetic constants $J$ within the fully self-consistent GW method. To understand the degree of spin contamination present in broken-symmetry periodic solutions, we propose several size-extensive quantities that demonstrate that the unrestricted self-consistent GW preserves well the broken-symmetry character of the unrestricted Hartree--Fock solutions. The extracted $J$ are close to the ones obtained from multireference wave-function calculations. In this paper, we establish a robust computational procedure for finding magnetic coupling constants from self-consistent GW calculations and apply it to solid antiferromagnetic nickel and manganese oxides.