Beyond Quasi-Particle Self-Consistent GW for Molecules with Vertex Corrections

We introduce the ΣBSE@LBSE self-energy in the quasi-particle self-consistent GW (qsGW) framework (qsΣBSE@LBSE). Here, L is the two-particle response function, which we calculate by solving the Bethe–Salpeter equation with the static, first-order GW kernel. The same kernel is added to Σ directly. For a set of medium organic molecules, we show that including the vertex both in L and Σ is crucial. This approach retains the good performance of qsGW for predicting first ionization potentials and fundamental gaps, while it greatly improves the description of electron affinities. Its good performance places qsΣBSE@LBSE among the best-performing electron propagator methods for charged excitations. Adding the vertex in L only, as commonly done in the solid-state community, leads to devastating results for electron affinities and fundamental gaps. We also test the performance of BSE@qsGW and qsΣBSE@LBSE for neutral charge-transfer excitation and find both methods to perform similar. We conclude that ΣBSE@LBSE is a promising approximation to the electronic self-energy beyond GW. We hope that future research on dynamical vertex effects, second-order vertex corrections, and full self-consistency will improve the accuracy of this method, both for charged and neutral excitation energies.