Communication: A hybrid Bethe-Salpeter/time-dependent density-functional-theory approach for excitation energies.

A hybrid Bethe-Salpeter/time-dependent density-functional-theory method is described that aims at improving the performance of the GW/Bethe-Salpeter-equation (GW/BSE) method in general and for excited triplet states in particular. The static screened exchange W used in the BSE is combined with the correlation kernel of the underlying density functional in a manner that retains a proven feature of the BSE, that is, the correct description of charge-transfer excitations. The performance of the new method, labeled cBSE, is assessed using G0W0 or evGW quasiparticle energies, and an improved performance is observed. The cBSE approach shows nearly equal performance for excited singlet and triplet states, rivaling coupled-cluster theory (in the CC2 approximation) in accuracy at a computational cost that is at least one order of magnitude smaller.