Compensation of Dynamical Quasiparticle and Vertex Corrections in Optical Spectra

The inclusion of dynamical quasiparticle effects lifts the underestimation of band gaps in semiconductors and insulators derived within density-functional theory. Simultaneously, they give rise to a remarkable reduction of the strengths of the quasiparticle peaks that is not observed in optical spectra. We show that dynamical contributions to the vertex corrections widely compensate the peak renormalization due to the dynamics in the quasiparticle formation. The slight reduction of the absorption spectrum yields an improvement of the computed $f$-sum rule.