Evaluating theGWApproximation with CCSD(T) for Charged Excitations Across the Oligoacenes

Abstract

Charged excitations of the oligoacene family of molecules, relevant for astrophysics and technological applications, are widely studied and therefore provide an excellent system for benchmarking theoretical methods. In this work, we evaluate the performance of many-body perturbation theory (MPBT) within the GW approximation, relative to new high-quality CCSD(T) reference data, for charged excitations of the acenes. We compare GW calculations with a number of hybrid density functional theory starting points and with eigenvalue selfconsistency. Special focus is given to elucidating the trend of GW -predicted excitations with molecule length, from benzene to hexacene. We find that GW calculations with starting points based on an optimally-tuned range separated hybrid (OTRSH) density functional and eigenvalue self-consistency can yield quantitative ionization potentials for the acenes. However, for the larger acenes, the predicted electron affinities can deviate considerably from reference values. Our work paves the way for predictive and cost-effective GW calculations of chargedexcitations of molecules and identifies certain limitations of current GW methods used in practice for larger molecules.

The GW approximation: content, successes and limitations

“…Of course, results depend on this starting point, and the choice of an optimal starting point is crucial. In Ref , GW calculations were performed for acenes for various lengths of the chains, ranging from benzene to hexacene. Different hybrid functionals were used as starting points, and eigenvalues (not eigenfunctions) were calculated self‐consistently.…”

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

“…[22][23][24][25][26] The GW formalism achieved a very accurate description of quasiparticle energies and gap in isolated molecules, as demonstrated by extensive benchmarks against gas-phase experiments 22,[27][28][29][30][31][32][33] and high-level quantum chemistry calculations. [34][35][36][37][38][39] Thanks to efficient algorithms and parallel implementations, GW calculations enabled accurate calculations on systems exceeding hundred atoms. 23,[40][41][42][43][44] Yet, charged excitations in extended systems are largely governed by long-range electrostatic interactions that are not amenable to a full QM treatment.…”

Stochastic Vertex Corrections: Linear Scaling Methods for Accurate Quasiparticle Energies

“…27,32,33 The typical strategy is thus to use G 0 W 0 on top of the "best" possible DFT starting point. [34][35][36][37][38] Recent benchmark for acenes, however, revealed that GW suffers from substantial errors for QP energies of unoccupied states. 38 Beyond GW techniques include approximate vertex functions (Γ), which are closely related to the electron-hole interaction kernel in the Bethe-Salpeter equation (BSE).…”