Electronic Spectrum of Trigonal Selenium

Abstract

From empirical form factors for cubic ZnSe, a pseudopotential is derived for elemental selenium. With some minor adjustment to obtain the direct experimental gap, this pseudopotential is used to calculate energy bands along all symmetry axes of the Brillouin zone. Based on a coarse regular point mesh and quadratic interpolation, the imaginary part of the dielectric function is calculated in the random-phase approximation. Fairly good agreement is obtained with the measured optical spectrum, and some of the observed peaks are identified. It is found that the spectrum is determined not only by the joint density of states but also very strongly by variations in $k$ space of the oscillator strengths. The real part of the dielectric function and the reflectivity spectrum have also been calculated for polarizations parallel and perpendicular to the trigonal axis.