Electronic structure of low-pressure and high-pressure phases of silicon disulfide

Self-consistent density functional theory calculations of band spectra, densities of states as well as the spatial distribution of valence electron charge density were carried out for the low-pressure alpha-phase and the high-pressure beta-phase of SiS2. Group-theoretical analysis performed for both phases enabled the symmetry of wave functions in a number of high-symmetry points of the Brillouin zone as well as the structure of valence band representations to be found. Based on the calculations of the band structure, the orthorhombic alpha-phase of SiS2 was determined to be an indirect-gap semiconductor with the band gap E (gi) = 2.44 eV (T (1) -> X (8) transition), while the beta-phase was shown to be direct gap with E (gd) = 2.95 eV (D" (3) -> D" (2) transition). The calculated energy distribution of the total density of states in the valence band of alpha-SiS2 qualitatively and quantitatively correlates with the main experimental features of the X-ray photoelectron spectrum.