Solution of the Bethe-Salpeter equation without empty electronic states: Application to the absorption spectra of bulk systems

An approach recently developed to solve the Bethe-Salpeter equation within densitymatrix perturbation theory is extended to the calculation of optical spectra of periodic systems. This generalization requires numerical integrations within the first Brillouin zone that are efficiently performed by exploiting point group symmetries. The technique is applied to the calculation of the optical spectra of bulk Si, diamond C, and cubic SiC. Numerical convergence and the accuracy of the Tamm-Dancoff approximation are discussed in detail.