ELECTRONIC AND OPTICAL-PROPERTIES OF RED HGI2

Within the local-density approximation we have used the linear muffin- tin orbital method, without geometrical approximations, to calculate t he electronic structure of red HgI2. Using the self-consistent potenti al we have calculated the energy bands and from these derived the anis otropic frequency-dependent dielectric function and the reflectivity s pectrum. The calculated dielectric function is in good agreement with the experimental data in contrast to previous theoretical work. The ef fect bf the spin-orbit coupling on the optical properties has also bee n studied and found to be significant. In this work we predict a rathe r large anisotropy in the dielectric function resulting from the low-s ymmetry crystal structure.