Growth of Nanophase Clusters and Potential Energy Minima: Hysteresis, Oscillations, and Phase Transitions

The structures of small Lennard-Jones clusters (local and global minima) in the range n = 30 - 55 atoms are investigated during growth by random atom deposition using Monte Carlo simulations. The cohesive energy, average coordination number, and bond angles are calculated at different temperatures and deposition rates. Deposition conditions which favor thermodynamically stable (global minima) and metastable (local minima) are determined. We have found that the transition from polyicosahedral to quasicrystalline structures during cluster growth exhibits hysteresis at low temperatures. A minimum critical size is required for the evolution of the quasicrystalline family, which is larger than the one predicted by thermodynamics and depends on the temperature and the deposition rate. Oscillations between polyicosahedral and quasicrystalline structures occur at high temperatures in a certain size regime. Implications for the applicability of global optimization techniques to cluster structure determination are also discussed.