Fully selfconsistent GW calculations for molecules

TL;DR

This study compares various computational methods for calculating molecular ionization potentials, demonstrating that fully selfconsistent GW provides highly accurate results, especially when based on Hartree-Fock starting points.

Contribution

It introduces a comprehensive selfconsistent GW approach for molecules, including full frequency dependence and off-diagonal elements, improving ionization potential accuracy over previous methods.

Findings

Selfconsistent GW reduces ionization potential errors by up to 50% compared to Hartree-Fock.

One-shot G0W0 based on Hartree-Fock yields the most accurate IPs among tested methods.

Including core-valence exchange significantly impacts excitation energy calculations.

Abstract

We calculate single-particle excitation energies for a series of 33 molecules using fully selfconsistent GW, one-shot G$_0$W$_0$, Hartree-Fock (HF), and hybrid density functional theory (DFT). All calculations are performed within the projector augmented wave (PAW) method using a basis set of Wannier functions augmented by numerical atomic orbitals. The GW self-energy is calculated on the real frequency axis including its full frequency dependence and off-diagonal matrix elements. The mean absolute error of the ionization potential (IP) with respect to experiment is found to be 4.4, 2.6, 0.8, 0.4, and 0.5 eV for DFT-PBE, DFT-PBE0, HF, G$_0$W$_0$[HF], and selfconsistent GW, respectively. This shows that although electronic screening is weak in molecular systems its inclusion at the GW level reduces the error in the IP by up to 50% relative to unscreened HF. In general GW overscreens the HF energies leading to underestimation of the IPs. The best IPs are obtained from one-shot G$_0$W$_0$ calculations based on HF since this reduces the overscreening. Finally, we find that the inclusion of core-valence exchange is important and can affect the excitation energies by as much as 1 eV.