Dynamical excitonic effects in metals and semiconductors

The dynamics of an electron-hole pair induced by the time-dependent screened Coulomb interaction is discussed. In contrast to the case where the static electron-hole interaction is considered we demonstrate the occurrence of important dynamical excitonic effects in the solution of the Bethe-Salpeter equation. This is illustrated in the calculated absorption spectra of noble metals (copper and silver) and silicon. Dynamical corrections strongly affect the spectra, partially canceling dynamical self-energy effects and leading to good agreement with experiment.