COMPENSATION OF DYNAMICAL QUASI-PARTICLE AND VERTEX CORRECTIONS IN OPTICAL-SPECTRA

The inclusion of dynamical quasiparticle effects lifts the underestima tion of band gaps in semiconductors and insulators derived within dens ity-functional theory. Simultaneously, they give rise to a remarkable reduction of the strengths of the quasiparticle peaks that is not obse rved in optical spectra. We show that dynamical contributions to the v ertex corrections widely compensate the peak renormalization due to th e dynamics in the quasiparticle formation. The slight reduction of the absorption spectrum yields an improvement of the computed f-sum rule.