Geometries and stabilities of (n + 4)-membered monocyclic CnB4 (n = 2-9) clusters

The DFT(B3LYP)/6-311+G(d) method is used to study the geometries, growth feature, and relative stability of 106 lower-energy isomers of monocyclic CnB4 (n = 2-9). Vibrational frequency analysis is performed to ensure the optimized isomers are stable at the same level. It is interesting to find that the formation of the lowest-energy isomers of monocyclic CnB4 (n = 2-9) is through joining -Cm- (m = 0-2) and -Cn- (n = 0-5) carbon chains by two B-C-B bridges under the constraint of C2v symmetry (or D2h symmetry if m = n). The stability of global minimum isomers is discussed based on their binding energies per atom, the incremental binding energy, second order energy difference, vertical ionization energy, vertical electron affinity, and average polarizability.