Rearrangements of 55-atom Lennard-Jones and (C60)55 clusters

Roughly 3000 rearrangement pathways have been calculated for each of two clusters bound by simple empirical potentials. The first system is the 55-atom complex described by a pairwise Lennard-Jones potential. The second consists of 55 C60 molecules with an intermolecular potential obtained by spherically averaging atom–atom Lennard-Jones terms, as previously employed in bulk simulations. Various properties of the pathways are calculated, such as a cooperativity index and the integrated path length, and the probability distributions are subjected to statistical analysis. Systematic differences between the atomic Lennard-Jones clusters and the C60 molecular clusters are explained in terms of the effective pair potential; e.g., rearrangements of (C60)55 are generally localized because the potential is relatively short ranged. A pseudo-third-derivative correction is developed to improve the convergence of the eigenvector-following method employed to optimize the geometries and follow the pathways.