Abstract
We report a numerical simulation of the rate of crystal nucleation
of sodium chloride from its melt at moderate supercooling. In this
regime nucleation is too slow to be studied with "brute force" molecular-dynamics
simulations. The melting temperature of ("Tosi Fumi") NaCl is approximately
1060 K. We studied crystal nucleation at T = 800 and 825 K. We observe
that the critical nucleus formed during the nucleation process has
the crystal structure of bulk NaCl. Interestingly, the critical nucleus
is clearly faceted, the nuclei have a cubical shape. We have computed
the crystal-nucleation rate using two completely different approaches,
one based on an estimate of the rate of diffusive crossing of the
nucleation barrier, the other based on the forward flux sampling
and transition interface sampling methods. We find that the two methods
yield the same result within an order of magnitude. However, when
we compare the extrapolated simulation data with the only available
experimental results for NaCl nucleation, we observe a discrepancy
of nearly five orders of magnitude. We discuss the possible causes
for this discrepancy.
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