Is the Bethe–Salpeter Formalism Accurate for Excitation Energies? Comparisons with TD-DFT, CASPT2, and EOM-CCSD ?

Denis Jacquemin (1) , Ivan Duchemin (2) , Xavier Blase (3)

1 CEISAM - Chimie Et Interdisciplinarité : Synthèse, Analyse, Modélisation
2 LSIM - Laboratory of Atomistic Simulation
3 NEEL - TMC - Théorie de la Matière Condensée

Developing ab initio approaches able to provide accurate excited-state energies at a reasonable computational cost is one of the biggest challenges in theoretical chemistry. In that framework, the Bethe–Salpeter equation approach, combined with the GW exchange-correlation self-energy, which maintains the same scaling with system size as TD-DFT, has recently been the focus of a rapidly increasing number of applications in molecular chemistry. Using a recently proposed set encompassing excitation energies of many kinds [J. Phys. Chem. Lett. 2016, 7, 586–591], we investigate here the performances of BSE/GW. We compare these results to CASPT2, EOM-CCSD, and TD-DFT data and show that BSE/GW provides an accuracy comparable to the two wave function methods. It is particularly remarkable that the BSE/GW is equally efficient for valence, Rydberg, and charge-transfer excitations. In contrast, it provides a poor description of triplet excited states, for which EOM-CCSD and CASPT2 clearly outperform BSE/GW. This contribution therefore supports the use of the Bethe–Salpeter approach for spin-conserving transitions.

Domaines: Chimie

Denis Jacquemin, Ivan Duchemin, Xavier Blase. Is the Bethe–Salpeter Formalism Accurate for Excitation Energies? Comparisons with TD-DFT, CASPT2, and EOM-CCSD ?. Journal of Physical Chemistry Letters, 2017, 8 (7), pp.1524. ⟨10.1021/acs.jpclett.7b00381⟩. ⟨hal-01550200⟩