Optical Absorption of Insulators and the Electron-Hole Interaction: An<i>Ab Initio</i>Calculation

We present a computationally efficient scheme to calculate the optical absorption of insulators from first principles, including the electron-hole interaction. Excited states of the solid are chosen to consist of single electron-hole pairs. The electron-hole interaction is statically screened using a model dielectric function. Only two pieces of input are required, the crystal structure of the material and the macroscopic dielectric constant. We apply this scheme to two wide-gap insulators, LiF and MgO, and obtain excellent agreement with experimental measurements of their UV reflectance spectra.