First-principles GW calculations for fullerenes, porphyrins, phtalocyanine, and other molecules of interest for organic photovoltaic applications

TL;DR

This paper assesses the accuracy of ab initio GW calculations for ionization energies and HOMO-LUMO gaps in molecules relevant to organic photovoltaics, demonstrating improved results with Hartree-Fock starting points.

Contribution

It introduces an efficient Gaussian-basis GW implementation and shows that starting from Hartree-Fock eigenvalues yields highly accurate quasiparticle energies.

Findings

G0W0 improves ionization energies over DFT but underestimates gaps.

Hartree-Fock starting points yield 2-4% accuracy compared to experiments.

Efficient Gaussian-basis GW with contour deformation is effective for molecular systems.

Abstract

We evaluate the performances of ab initio GW calculations for the ionization energies and HOMO-LUMO gaps of thirteen gas phase molecules of interest for organic electronic and photovoltaic applications, including the C60 fullerene, pentacene, free-base porphyrins and phtalocyanine, PTCDA, and standard monomers such as thiophene, fluorene, benzothiazole or thiadiazole. Standard G0W0 calculations, that is starting from eigenstates obtained with local or semilocal functionals, significantly improve the ionization energy and band gap as compared to density functional theory Kohn-Sham results, but the calculated quasiparticle values remain too small as a result of overscreening. Starting from Hartree-Fock-like eigenvalues provides much better results and is equivalent to performing self-consistency on the eigenvalues, with a resulting accuracy of 2~4% as compared to experiment. Our calculations are based on an efficient gaussian-basis implementation of GW with explicit treatment of the dynamical screening through contour deformation techniques.