Parity alternation of linear ground-state C_nS^2- (n = 6-18) clusters

Making use of the software of molecular graphics, we designed many patterns of C_nS^2- (n = 6-18) models. We carried out geometry optimization and calculation on vibrational frequency by means of the B3LYP density functional method. The most probable ground-state isomers of C_nS^2- (n = 6-18) are linear with the sulfur atom located at one end of the C_n chain. When n is even, the isomer is polyacetylene-like. The C_nS^2- (n = 6-18) with even number of carbon atoms are more stable than those with odd number, matching the peak pattern observed in studies of mass spectrometry. The trend of odd/even alternation is also detected in certain bond length, atomic charge, electronic configuration, the highest vibrational frequency, energy difference, electron detachment energy, and incremental binding energy of the most probable ground-state isomers.