First-principles electronic structure calculations were performed for S2 and S2- molecules in vacuum. It was found that the calculated equilibrium bond lengths and vibrational spectroscopic constants were in good agreement with experiment as well as with previous calculations. Based upon this conformation, the calculations were extended to the substitutional S2- molecule in alkali halides. It was found that an S2- center aligned in the [110] direction was generally favored over one with an [100] or [111] orientation; in agreement with experiment. It was also found that the vibrational frequencies of the S2- anion in the alkali halides shifted to higher energies with decreasing lattice parameter. The results suggested that the change in the bond length of the S2- anion, in the matrix, depended upon the type of halogen atom, while the frequencies were influenced by the type of alkali atom.

First-Principles Study of the Energetics and Vibrational Properties of the S2- Impurity in Alkali-Halide Crystals. K.Nishidate, M.Baba, Sarjono, M.Hasegawa, K.Nishikawa, I.Sokolska, W.Ryba-Romanowski: Physical Review B, 2003, 68[22], 224307 (6pp)