The kinetics of crystal growth and dissolution from the melt in Lennard-Jones systems

Abstract

The growth and dissolution of implanted fcc nanocrystallites in a subcooled liquid have been studied using nonequilibrium Molecular Dynamics simulation techniques. The initial sizes of the 70 implanted crystals were each close to the critical cluster size of 120 atoms predicted by classical nucleation theory. The simulated system consisted of approximately 13 500 atoms interacting with a Lennard-Jones potential. The time evolution of the crystal sizes was followed in order to obtain statistics from which the kinetics and the probabilities of growth and dissolution were extracted using a Markovian technique. The growing crystallites showed facets that correspond to hexagonally packed layers. Very small crystals adopted an octahedral shape, but this shape was lost as the crystals grew. Although the implanted crystals had an fcc structure originally, the crystals grew in a mixture of hcp and fcc geometries with a larger proportion of the latter. Our analysis showed the critical cluster size for the implants to be 170 atoms, somewhat larger than the value predicted by a Gibbsian nucleation theory. The rate of growth showed minima, suggesting the existence of ‘‘magic numbers’’ in crystal growth from the melt. Homogeneous nucleation was also simulated. The free energies of the subcritical crystallites is smaller than predicted by classical nucleation theory using the properties of the bulk liquid and solid phases. The rate of nucleation is compared with theoretical predictions.