We carry out molecular dynamics (MD) and Monte Carlo (MC) simulations tocharacterize nucleation in liquid clusters of 600 Lennard-Jones particles overa broad range of temperatures. We use the formalism of mean first-passage timesto determine the rate and find that Classical Nucleation Theory (CNT) predictsthe rate quite well, even when employing simple modelling of crystallite shape,chemical potential, surface tension and particle attachment rate, down to thetemperature where the droplet loses metastability and crystallization proceedsthrough growth-limited nucleation in an unequilibrated liquid. Below thiscrossover temperature, the nucleation rate is still predicted when MCsimulations are used to directly calculate quantities required by CNT.Discrepancy in critical embryo sizes obtained from MD and MC arises whentwinned structures with five-fold symmetry provide a competing free energypathway out of the critical region. We find that crystallization begins withhcp-fcc stacked precritical nuclei and differentiation to various endstructures occurs when these embryos become critical. We confirm that using thelargest embryo in the system as a reaction coordinate is useful in determiningthe onset of growth-limited nucleation and show that it gives the same freeenergy barriers as the full cluster size distribution once the proper referencestate is identified. We find that the bulk melting temperature controls therate, even though the solid-liquid coexistence temperature for the droplet issignificantly lower. The value of surface tension that renders close agreementbetween CNT and direct rate determination is significantly lower than what isexpected for the bulk system.
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