C24: Ring or fullerene?

The energy difference between the ring and fullerene forms of C24have been calculated by means of ab initio methods, and compared to density functional methods. The calculations strongly suggest that the fullerene form is favored by ∼80 kcal/mol over a monocyclic ring structure, which is at variance with experimental findings. Density functional results vary considerably, although functionals including exact exchange (B3LYP and B3PW91) give reasonable results when basis sets of at least triple zeta quality are employed. © 1998 American Institute of Physics.