Homogeneous SPC/E water nucleation in large molecular dynamics simulations

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We perform direct large molecular dynamics simulations of homogeneous SPC/E water nucleation, using up to 4· 10⁶ molecules. Our large system sizes allow us to measure extremely low and accurate nucleation rates, down to 10¹⁹cm⁻³s⁻¹, helping close the gap between experimentally measured rates 10¹⁷cm⁻³s⁻¹. We are also able to precisely measure size distributions, sticking efficiencies, cluster temperatures, and cluster internal densities. We introduce a new functional form to implement the Yasuoka-Matsumoto nucleation rate measurement technique (threshold method). Comparison to nucleation models shows that classical nucleation theory over-estimates nucleation rates by a few orders of magnitude. The semi-phenomenological nucleation model does better, under-predicting rates by at worst, a factor of 24. Unlike what has been observed in Lennard-Jones simulations, post-critical clusters have temperatures consistent with the run average temperature. Also, we observe that post-critical clusters have densities very slightly higher, 5%, than bulk liquid. We re-calibrate a Hale-type J vs. S scaling relation using both experimental and simulation data, finding remarkable consistency in over 30 orders of magnitude in the nucleation rate range, and 180K in the temperature range.