  We present ab initio absorption spectra of six three-dimensional
semiconductors and insulators calculated using Gaussian-based periodic
equation-of-motion coupled-cluster theory with single and double excitations
(EOM-CCSD). The spectra are calculated efficiently by solving a system of
linear equations at each frequency, giving access to an energy range of tens of
eV without explicit enumeration of excited states. We assess the impact of
Brillouin zone sampling, for which it is hard to achieve convergence due to the
cost of EOM-CCSD. Although our most converged spectra exhibit lineshapes that
are in good agreement with experiment, they are uniformly shifted to higher
energies by about 1 eV. We tentatively attribute this discrepancy to a
combination of vibrational effects and the remaining electron correlation,
i.e., triple excitations and above.
