Vibrational dynamics of glassy SiS2 on the basis of molecular orbital calculations

Ab initio molecular orbital calculations at the Hartree–Fock/3-21G(*) level have been performed on several clusters modeling SiS2 glass. The clusters consist of edge-sharing and/or corner-sharing structural units that can be found in actual glassy SiS2. The experimental Raman spectrum of SiS2 glass was interpreted in terms of vibrational frequencies calculated for these model clusters. The observed Raman bands at 427 and 415 cm−1 were assigned to the breathing motions of S atoms localized in two (or more) and one edge-sharing units, respectively. We also propose that two peaks at 367 and 381 cm−1 occur as a result of an accidental degeneracy or a resonance between the vibrations of the corner- and edge-sharing S atoms. The corner-sharing structure which is isolated from or connected with one edge-sharing also contributes to these peaks around 370 cm−1.