  We used molecular dynamics simulations and the path sampling technique known
as forward flux sampling to study homogeneous nucleation of NaCl crystals from
supersaturated aqueous solutions at 298 K and 1 bar. Nucleation rates were
obtained for a range of salt concentrations for the Joung-Cheatham NaCl force
field combined with the SPC/E water model. The calculated nucleation rates are
significantly lower than available experimental measurements. The estimates for
the nucleation rates in this work do not rely on classical nucleation theory,
but the pathways observed in the simulations suggest that the nucleation
process is better described by classical nucleation theory than an alternative
interpretation based on Ostwald's step rule, in contrast to some prior
simulations of related models. In addition to the size of NaCl nucleus, we find
that the crystallinity of a nascent cluster plays an important role in the
nucleation process. Nuclei with high crystallinity were found to have higher
growth probability and longer lifetimes, possibly because they are less exposed
to hydration water.
