  Applying the novel exact-exchange (EXX) Kohn-Sham method within
time-dependent density-functional theory, we obtained the optical absorption
spectrum of bulk silicon in good agreement with experiments including excitonic
features. Analysis of the EXX kernel shows that inclusion of the Coulomb
coupling of electron-hole pairs and the correct long-wavelength behavior in the
kernel is crucial for the proper description of excitonic effects in
semiconductors.
