A density functional study for the isomers of anionic sulfur clusters S_n^- ( n=3-20 )

The signals of anionic sulfur clusters are intense in the mass spectrum of sulfur clusters generated in direct laser vaporization. We have acquired numerous isomers of sulfur clusters by means of the B3LYP DFT method. According to total energies, the most stable S_n^- (n=3-13) isomers are predicted. The helical S_n (n=14-20) structures are also calculated. Most of the anionic clusters are with chain configurations; the ring clusters with threefold atom(s) are higher in total energy. The most stable forms of isomers, from S₉^- to S₁₃^-, show helical configurations that are completely different from those of the corresponding neutral and cationic clusters.