Parity alternation in the linear ground-state beryllium-doped carbon clusters BeC_n^- (n = 1-8)

Making use of molecular graphics software, we designed numerous models of BeC_n^- (n = 1-8). Geometry optimization and calculation on vibration frequency were carried out by the B3LYP density functional method. After comparison of structure stability, we found that the ground-state isomers of BeC_n^- (n = 1-8) are linear with the beryllium atom located at one end of the C_n chain, except that the linear BeC₅^- isomer is slightly higher in energy than the planar cyclic BeC₅^- isomer. When n is even, the C_n chain of BeC_n^- (n = 1-8) is polyacetylene-like whereas when at odd n, the carbon chain is cumulene-like. The BeC_n^- (n = 1-8) with even n are found to be more stable than those with odd n, and the result is in good accord with the relative intensities of BeC_n^- (n = 1-8) observed in mass spectrometric studies. In this paper, we provide satisfactory explanation for such trend of even/odd alternation based on concepts of bonding nature, electronic configuration, electron affinity, incremental binding energy, and dissociation channels.