Calculation of the Band Structure and Optical Constants of Diamond Using the Nonlocal-Pseudopotential Method

The electronic band structure and optical constants of diamond are calculated using the empirical-pseudopotential method with an additional =1 nonlocal term VNL(→r) added to account for the strong potential experienced by p electrons in the core region. VNL(→r) strongly affects the p-like conduction bands, and the resulting band structure yields a plot of ε₂(ω), the imaginary part of the dielectric function, which is in satisfactory agreement with experiment. In addition, the temperature-dependent peak at 7.8 eV in the optical spectrum, whose origin has been somewhat of a mystery, is identified with optical transitions beginning at L and extending out along the Λ direction in the Brillouin zone.