An optimally tuned range-separated hybrid starting point for ab initio GW plus Bethe-Salpeter equation calculations of molecules

International audienceThe ab initio GW plus Bethe-Salpeter equation (GW-BSE, where G is the one particle Green's function and W is the screened Coulombinteraction) approach has emerged as a leading method for predicting excitations in both solids and molecules with a predictive powercontingent upon several factors. Among these factors are the (1) generalized Kohn-Sham eigensystem used to construct the GW self-energyand to solve the BSE and (2) the efficacy and suitability of the Tamm-Dancoff approximation. Here, we present a detailed benchmark studyof low-lying singlet excitations from a generalized Kohn-Sham (gKS) starting point based on an optimally tuned range-separated hybrid(OTRSH) functional. We show that the use of this gKS starting point with one-shot G0 W0 and G0 W0 -BSE leads to the lowest mean absoluteerrors (MAEs) and mean signed errors (MSEs), with respect to high-accuracy reference values, demonstrated in the literature thus far forthe ionization potentials of the GW100 benchmark set and for low-lying neutral excitations of Thiel's set molecules in the gas phase, withoutthe need for self-consistency. The MSEs and MAEs of one-shot G0 W0 -BSE@OTRSH excitation energies are comparable to or lower thanthose obtained with other functional starting points after self-consistency. Additionally, we compare these results with linear-response time-dependent density functional theory (TDDFT) calculations and find GW-BSE to be superior to TDDFT when calculations are based on thesame exchange-correlation functional. This work demonstrates tuned range-separated hybrids used in combination with GW and GW-BSEcan greatly suppress starting point dependence for molecules, leading to accuracy similar to that for higher-order wavefunction-based theoriesfor molecules without the need for costlier iterations to self-consistency