Optical Dielectric Function of the Lithium-Fluoride Crystal

The method of tight binding has been applied in a calculation of the imaginary part of the dielectric function, ${\epsilon }_2$, for a LiF crystal. The large variations of the transition matrix elements over portions of the Brillouin zone are found to have very pronounced effects on ${\epsilon }_2$. Our results suggest a possible reinterpretation of the experimental 13- and 62-eV optical structure as band-to-band, instead of excitonic, transitions.