Carbon clusters near the crossover to fullerene stability

The energetic stability of structural isomers of C₂₄, C₂₆, C₂₈, and C₃₂ clusters, including fullerenes, is studied using diffusion quantum Monte Carlo methods. We predict that a C₂₄ isomer is the smallest stable graphitic fragment and that the smallest stable fullerenes are the C₂₆ and C₂₈ 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.