Lowest-energy structure of (C-60)(n) clusters and thermal effects

The lowest-energy structures of fullerene clusters (C-60)(n)(n less than or equal to 57) described by the Pacheco and Ramalho potential are systematic ally optimized by a global optimization procedure which combines the geneti c algorithm and database conjugate-gradient method. The structures of neutr al fullerene clusters show that for small-size clusters icosahedra are the lowest-energy structures, and for n greater than or equal to 17 decahedral and close-packed structures are lower in energy than icosahedral ones. Howe ver, taking account of the thermal effect, the icosahedral structure instea d of decahedral and close-packed ones is the most stable structure when the cluster is cooled from a high-temperature state.