Reference Energies for Intramolecular Charge-Transfer Excitations

TL;DR

This paper provides highly accurate reference energies for intramolecular charge-transfer excitations in organic compounds, benchmarking various computational methods against these references.

Contribution

It introduces a composite protocol for calculating reference energies and benchmarks multiple wave function, Green's function, and TD-DFT methods for charge-transfer excitations.

Findings

Reference energies for 30 transitions in 17 compounds.

Benchmarking results for various computational methods.

Identification of the most accurate approaches for charge-transfer excitations.

Abstract

In the aim of completing our previous efforts devoted to local and Rydberg transitions in organic compounds, we provide a series of highly-accurate vertical transition energies for intramolecular charge-transfer transitions occurring in ($\pi$-conjugated) molecular compounds. To this end we apply a composite protocol consisting of linear-response CCSDT excitation energies determined with Dunning's double-$\zeta$ basis set corrected by CC3/CCSDT-3 energies obtained with the corresponding triple-$\zeta$ basis. Further basis set corrections (up to \emph{aug}-cc-pVQZ) are obtained at the CCSD and CC2 level. We report 30 transitions obtained in 17 compounds. These reference values are then used to benchmark a series of wave function (CIS(D), SOPPA, RPA(D), EOM-MP2, CC2, CCSD, CCSD(T)(a)*, CCSDR(3), CCSDT-3, CC3, ADC(2), ADC(3), and ADC(2.5)), the Green's function-based Bethe-Salpeter equation (BSE) formalism performed on top of the partially self-consistent ev$GW$ scheme considering two different starting points (BSE/ev$GW$@HF and BSE/ev$GW$@PBE0), and TD-DFT combined with several exchange-correlation functionals (B3LYP, PBE0, M06-2X, CAM-B3LYP, LC-$\omega$HPBE, $\omega$B97X, $\omega$B97X-D, and M11).