Improved coarse-grained model for molecular-dynamics simulations of water nucleation

Condensation of a liquid droplet from a supersaturated vapour phase is initiated by a prototypical nucleation event. As such it is challenging to compute its rate from atomistic molecular dynamics simulations. In fact at realistic supersaturation conditions condensation occurs on time scales that far exceed what can be reached with conventional molecular dynamics methods. Another known problem in this context is the distortion of the free energy profile associated to nucleation due to the small, finite size of typical simulation boxes. In this work the problem of time scale is addressed with a recently developed enhanced sampling method while contextually correcting for finite size effects. We demonstrate our approach by studying the condensation of argon, and showing that characteristic nucleation times of the order of magnitude of hours can be reliably calculated, approaching realistic supersaturation conditions, thus bridging the gap between what standard molecular dynamics simulations can do and real physical systems.

Section: Nucleation Ratesmentioning

confidence: 86%

Overcoming time scale and finite size limitations to compute nucleation rates from small scale well tempered metadynamics simulations

Salvalaglio

Tiwary

Maggioni

et al. 2016

“…47 We also put the experimental data for water nucleation. 6,20,22,23,26,27 For the experimental results and Zipoli et al, 57 T c is set to be 647 K. 20 From Fig. 5, J seems to be scaled by ln S/(T c /T − 1) 1.5 , but is not proportional to it.…”

Section: B Nucleation Ratementioning

confidence: 99%

“…The nucleation rates by SP model (solid 47 and Zipoli et al, 57 respectively. In Zipoli et al, 57 we use the nucleation rates at 350 K. The nucleation rates by SP model (solid curve) are also plotted.…”

Section: A a Typical Casementioning

confidence: 99%

“…3. For the MD simulations using SPC/E water model, we set T c = 630 K. 47 We also put the experimental data for nucleation of water by Miller et al, 6 Wölk and Strey, 20 Khan et al, 22 Kim et al, 23 Brus et al, 26 and Manka et al 27 For the experimental results and Zipoli et al, 57 T c is set to be 647 K. 20 energy of a cluster better than the MCNT, but the gradient of the CNT data is different to the numerical results.…”

Section: Formation Free Energymentioning

confidence: 99%

See 1 more Smart Citation

Molecular dynamics simulations of the nucleation of water: Determining the sticking probability and formation energy of a cluster

Tanaka

Kawano

Tanaka

2014

We performed molecular dynamics simulations of the nucleation of water vapor in order to test nucleation theories. Simulations were performed for a wide range of supersaturation ratios (S = 3-25) and water temperatures (T w = 300-390 K). We obtained the nucleation rates and the formation free energies of a subcritical cluster from the cluster size distribution. The classical nucleation theory and the modified classical nucleation theory (MCNT) overestimate the nucleation rates in all cases. The semi-phenomenological model, which corrects the MCNT prediction using the second virial coefficient of a vapor, reproduces the formation free energy of a cluster with the size 20 to within 10% and the nucleation rate and cluster size distributions to within one order of magnitude. The sticking probability of the vapor molecules to the clusters was also determined from the growth rates of the clusters. The sticking probability rapidly increases with the supersaturation ratio S, which is similar to the Lennard-Jones system. © 2014 AIP Publishing LLC. [http://dx

“…MD nucleation simulations of mW water have been carried out, yet only on small systems with relatively high nucleation rates [44,45]. The monoatomic water model proposed by Zipoli et al (2013) [46] offers similar advantages. However, we found that short-range potentials require extremely long equilibration times to form the correct equilibrium abundance of small clusters (dimers, trimers, etc.)…”

Section: Introductionmentioning

confidence: 99%

Homogeneous SPC/E water nucleation in large molecular dynamics simulations

Angélil

Diemand

Tanaka

et al. 2015

We perform direct large molecular dynamics simulations of homogeneous SPC/E water nucleation, using up to˜4 ṡ106 molecules. Our large system sizes allow us to measure extremely low and accurate nucleation rates, down to˜1019 cm-3 s-1, helping close the gap between experimentally measured rates˜1017 cm-3 s-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 180 K in the temperature range. Homogeneous SPC/E water nucleation in large molecular dynamics simulations We perform direct large molecular dynamics simulations of homogeneous SPC/E water nucleation, using up to ∼4 · 10 6 molecules. Our large system sizes allow us to measure extremely low and accurate nucleation rates, down to ∼10 19 cm −3 s −1 , helping close the gap between experimentally measured rates ∼10 17 cm −3 s −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 180 K in the temperature range. C 2015 AIP Publishing LLC. [http://dx