title: Benchmark of Bethe-Salpeter for Triplet Excited-States.
abstract: We have evaluated the accuracy of the Bethe-Salpeter singlet-triplet transition energies as well as singlet-triplet and triplet-triplet splittings for 20 organic molecules, using as reference the CC3 values determined by Thiel and co-workers with both the TZVP and aug-cc-pVTZ atomic basis sets. Our excitation energies are obtained on the basis of GW quasiparticle energy levels that are self-consistently converged with respect to the starting DFT eigenvalues. In its current form, BSE/GW is often unable to provide a balanced description of both singlet and triplet excited-states. While the singlet-singlet and triplet-triplet energy separations are obtained accurately, triplets are located too close in energy from the ground-state, by typically -0.55 eV when using standard functionals to generate the starting eigenstates. Applying the Tamm-Dancoff approximation upshifts the BSE triplet energies and allows reducing this error to ca. -0.40 eV, while using M06-HF eigenstates allows a further increase and hence a reduction of the error for triplet states, but at the cost of larger errors for the singlet excited-states. At this stage, the most accurate TD-DFT estimates therefore remain competitive for computing singlet-triplet transition energies. Indeed, with M06-2X, irrespective of the application or not of the Tamm-Dancoff approximation and of the selected atomic basis set, the deviations obtained with TD-DFT are rather small.
authors.affiliation: Laboratoire CEISAM - UMR CNR 6230, Université de Nantes , 2 Rue de la Houssinière, BP 92208, 44322 Nantes Cedex 3, France.|Institut Universitaire de France , 103 bd St. Michel, 75005 Paris Cedex 5, France.
authors.forename: Denis
authors.identifier: http://orcid.org/0000-0002-4217-0708
authors.initials: D
authors.lastname: Jacquemin
authors.affiliation: INAC, SP2M/L_Sim, CEA/UJF Cedex 09, 38054 Grenoble, France.|Institut NEEL, Université Grenoble Alpes , F-38042 Grenoble, France.
authors.forename: Ivan
authors.identifier: http://orcid.org/0000-0003-4713-1174
authors.initials: I
authors.lastname: Duchemin
authors.affiliation: Laboratoire CEISAM - UMR CNR 6230, Université de Nantes , 2 Rue de la Houssinière, BP 92208, 44322 Nantes Cedex 3, France.
authors.forename: Aymeric
authors.initials: A
authors.lastname: Blondel
authors.affiliation: Institut NEEL, Université Grenoble Alpes , F-38042 Grenoble, France.|CNRS, Institut NEEL, F-38042 Grenoble, France.
authors.forename: Xavier
authors.initials: X
authors.lastname: Blase