Quantitative Molecular Orbital Energies within a $G_0W_0$ Approximation

TL;DR

This study demonstrates that a one-shot $G_0W_0$ approach can accurately compute ionization potentials and electron affinities for small organic molecules, with results closely matching experimental data when properly converged.

Contribution

It introduces an effective completion strategy for unoccupied states and emphasizes the importance of dielectric function cutoff for accurate $G_0W_0$ calculations.

Findings

Computed IPs and EAs agree within 0.2 eV with experiments

Convergence depends on unoccupied states and dielectric cutoff

A sufficient dielectric cutoff is crucial for larger systems

Abstract

Using many-body perturbation theory within the $G_0W_0$ approximation, we explore routes for computing the ionization potential (IP), electron affinity (EA), and fundamental gap of three gas-phase molecules -- benzene, thiophene, and (1,4) diamino-benzene -- and compare with experiments. We examine the dependence of the IP on the number of unoccupied states used to build the dielectric function and the self energy, as well as the dielectric function plane-wave cutoff. We find that with an effective completion strategy for approximating the unoccupied subspace, and a converged dielectric function kinetic energy cutoff, the computed IPs and EAs are in excellent quantitative agreement with available experiment (within 0.2 eV), indicating that a one-shot $G_0W_0$ approach can be very accurate for calculating addition/removal energies of small organic molecules. Our results indicate that a sufficient dielectric function kinetic energy cutoff may be the limiting step for a wide application of $G_0W_0$ to larger organic systems.