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

Abstract

The electronic band structure and optical constants of diamond are calculated using the empirical-pseudopotential method with an additional $\ensuremath{\ell}=1$ nonlocal term ${V}_{\mathrm{NL}}(\stackrel{\ensuremath{\rightarrow}}{r})$ added to account for the strong potential experienced by $p$ electrons in the core region. ${V}_{\mathrm{NL}}(\stackrel{\ensuremath{\rightarrow}}{r})$ strongly affects the $p$-like conduction bands, and the resulting band structure yields a plot of ${\ensuremath{\epsilon}}_{2}(\ensuremath{\omega})$, 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 $\ensuremath{\Lambda}$ direction in the Brillouin zone.