Accurate description of charged excitations in molecular solids from embedded many-body perturbation theory

TL;DR

This paper introduces a hybrid quantum/classical approach using many-body Green's function $GW$ formalism to accurately compute charged excitations in molecular solids, accounting for environmental effects and achieving close agreement with experimental measurements.

Contribution

The authors develop a novel QM/MM method combining $GW$ calculations with classical polarizable models to better describe charged excitations in molecular crystals.

Findings

Accurately predicts ionization potentials and electron affinities within 0.2 eV of experimental data.

Distinguishes between polarization and crystal field effects on energy levels.

Demonstrates the method's effectiveness on pentacene and perfluoropentacene crystals.

Abstract

We present a novel hybrid quantum/classical (QM/MM) approach to the calculation of charged excitations in molecular solids based on the many-body Green's function $GW$ formalism. Molecules described at the $GW$ level are embedded into the crystalline environment modeled with an accurate classical polarizable scheme. This allows the calculation of electron addition and removal energies in the bulk and at crystal surfaces where charged excitations are probed in photoelectron experiments. By considering the paradigmatic case of pentacene and perfluoropentacene crystals, we discuss the different contributions from intermolecular interactions to electronic energy levels, distinguishing between polarization, which is accounted for combining quantum and classical polarizabilities, and crystal field effects, that can impact energy levels by up to $\pm0.6$ eV. After introducing band dispersion, we achieve quantitative agreement (within 0.2 eV) on the ionization potential and electron affinity measured at pentacene and perfluoropentacene crystal surfaces characterized by standing molecules.