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Abstract
Homogeneous nucleation of the crystal phase in n-octane melts was studied by molecular
simulation with a realistic, united-atom model for n-octane. The structure of the
crystal phase and the melting point of n-octane were determined through molecular
dynamics simulation and found to agree with experimental results. Molecular dynamics
simulations were performed to observe the nucleation events at constant pressure and
constant temperature corresponding to about 20% supercooling. Umbrella sampling Monte
Carlo simulations were used to calculate the nucleation free energy for three temperatures,
ranging from 8% to 20% supercooling, and to reveal details of the critical nucleus
for the first time. The cylindrical nucleus model was found to provide a better quantitative
description of the critical nucleus than the spherical nucleus model. The interfacial
free energies of the cylinder model were calculated from the simulation data. As the
temperature increased, the interfacial free energy of the side surface remained relatively
unchanged, at 7-8 mJ/m(2), whereas the interfacial free energy of the end surface
decreased significantly from 5.4 mJ/m(2) to about 3 mJ/m(2). These results, and the
methods employed, provide valuable and quantitative information regarding the rate-limiting
step during the solidification of chain molecules, with ramifications for both short
alkanes and polymers.