First-principles calculations of the electronic structure of open-shell condensed matter systems

TL;DR

This paper introduces a Green's function approach within the GW approximation to accurately compute quasiparticle excitations in open-shell systems, emphasizing the importance of self-energy poles for multiplet structures.

Contribution

It presents a novel method for calculating self-energy with high precision using mean-field theories on a fine frequency grid for open-shell systems.

Findings

Accurate multiplet structures depend on precise self-energy poles.

Method successfully applied to molecules and nitrogen-vacancy centers in diamond.

Results agree well with experimental data and high-level theories.

Abstract

We develop a Green's function approach to quasiparticle excitations of open-shell systems within the GW approximation. It is shown that accurate calculations of the characteristic multiplet structure require a precise knowledge of the self energy and, in particular, its poles. We achieve this by constructing the self energy from appropriately chosen mean-field theories on a fine frequency grid. We apply our method to a two-site Hubbard model, several molecules and the negatively charged nitrogen-vacancy defect in diamond, and obtain good agreement with experiment and other high-level theories.