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 α -phase and the high-pressure β -phase of SiS 2 . 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 α -phase of SiS 2 was determined to be an indirect-gap semiconductor with the band gap E gi = 2.44 eV ( T 1 → X 8 transition), while the β -phase was shown to be direct gap with E gd = 2.95 eV ( Г 3 → Г 2 transition). The calculated energy distribution of the total density of states in the valence band of α -SiS 2 qualitatively and quantitatively correlates with the main experimental features of the X-ray photoelectron spectrum.