Ab Initio Calculation of the Ultraviolet-Visible (UV-vis) Absorption Spectrum, Electron-Loss Function, and Reflectivity of Solids

The field frequency has recently been taken into account in the coupled-perturbed Hartree−Fock or Kohn−Sham method implemented in the CRYSTAL code for calculating the high-frequency dielectric constant of semiconductors up to the first electronic transitions. In this work, we document how the code has been generalized and improved in order to compute the full ultraviolet−visible (UVvis) absorption spectrum, the electron loss function, and the reflectivity from the real and imaginary parts of the electric response property. We show how spectra are modified when the crystalline orbital relaxation due to the dynamic electric field is taken into account, and how this modification increases with the percentage of Hartree−Fock exchange in the unperturbed hybrid Hamiltonian