Fig. 1: Imaginary part of the dielectric function ε2 of liquid water.

The calculations are performed at various levels of theory: Bethe-Salpeter equation (BSE) on top of quasiparticle self-consistent GW (qsGW) (solid, blue), BSE on top of qsGW with Bootstrap vertex corrections (qs\(G\tilde{W}\)) (solid, orange), and their respective results in the random phase approximation (RPA) (dotted). Experimental spectra from Hayashi and Hiraoka17 (purple) and Heller et al.8 (green) are shown for comparison.