Chaos and dynamical coexistence in Lennard-Jones clusters

The chaotic dynamics in Lennard-Jones microclusters is revisited for sizes ranging from 3 to 147 monomers. We calculate the largest Liapunov exponent lambda in classical molecular dynamics simulations at several total energies, carefully looking at the convergence of lambda. Contrary to previous results, no evidence for any distinct signature of the solid-liquid phase transition is found in the variations of lambda versus E for clusters smaller than 38 atoms (except LJ(3)). Larger clusters with 38, 55 and 147 atoms undergo a clear but continuous increase of lambda above the freezing energy. This increase occurs simultaneously with a drop in the kinetic temperature between the freezing and melting energies. Hence dynamical coexistence appears to smooth the strong variations of lambda near melting. (C) 1998 American Institute of Physics.