(321ba) Melting Transition in Repulsive Lennard Jones Crystals

In this paper we present a detailed study of crystallization transitions in a repulsive Lennard Jones (rLJ)system. The equilibrium characteristics of the transition have been studied using Expanded ensemble density of states (ExEDOS) simulations in bond order parameter space. A systematic analysis of precritical and critical nuclei as a function of supercooling reveals a gradual change from a bcc to an fcc structure inside the crystalline nucleus as it grows (at large degrees of supercooling). The dynamics of the transition has been studied using an improved transition path sampling technique which uses a biased selection of shooting frames to optimize shooting moves. The dynamics from transition path sampling along with equilibrium free energy profiles using ExEDOS provide a comprehensive, and hitherto unavailable picture of melting transitions in rLJ crystals. We have now elucidated transition structures and pathways which had not been seen before. Furthermore, by comparing the results of rLJ systems to those a full Lennard-Jones fluid, we have arrived at a much more complete understanding of the role of attractive interactions in crystallization.