Carbon clusters near the crossover to fullerene stability

The energetic stability of structural isomers of C-24, C-26, C-28, and C-32 clusters, including fullerenes, is studied using diffusion quantum Monte Carlo methods. We predict that a C-24 isomer is the smallest stable graphitic fragment and that the smallest stable fullerenes are the C-26 and C-28 clusters with C-2v and T-d symmetry, respectively. Given suitable experimental conditions these small fullerenes should therefore be producible in abundance, facilitating production of fullerene-based solids.