Large Scale Molecular Dynamics Simulations of the Nucleation Process in Supersaturated Vapor -The first direct comparison between laboratory experiments and molecular dynamics simulations-

Research Press Release | September 24, 2013

  • Fig.1) An example of the molecular dynamics simulation of the nucleation process.  A small number of nano-sized critical nuclei are formed in the gas of 10^9  atoms and the growth of these nuclei promotes condensation. The rate at  which critical nuclei are generated thus determines the rate at which condensation  proceeds. By performing large-scale simulations of the nucleation process under a  wide range of parameters, this study measured the formation energy of a critical  nucleus and the sticking probability at which molecules adhere to the nuclei as  well as the nucleation rate, and comprehensively investigated the nucleation  process.
    Fig.1) An example of the molecular dynamics simulation of the nucleation process. A small number of nano-sized critical nuclei are formed in the gas of 10^9 atoms and the growth of these nuclei promotes condensation. The rate at which critical nuclei are generated thus determines the rate at which condensation proceeds. By performing large-scale simulations of the nucleation process under a wide range of parameters, this study measured the formation energy of a critical nucleus and the sticking probability at which molecules adhere to the nuclei as well as the nucleation rate, and comprehensively investigated the nucleation process.
  • Fig.2) A comparison of the nucleation rates obtained from a molecular dynamics  simulation with an argon nucleation laboratory experiment. Large-scale  simulations using a super parallel computer made it possible to simulate  nucleation rates in the same low supersaturation range as the laboratory  experiment, and to successfully reproduce the experiment results.
    Fig.2) A comparison of the nucleation rates obtained from a molecular dynamics simulation with an argon nucleation laboratory experiment. Large-scale simulations using a super parallel computer made it possible to simulate nucleation rates in the same low supersaturation range as the laboratory experiment, and to successfully reproduce the experiment results.
  • Fig. 3) The growth rates α obtained from molecular dynamics simulations and the sticking probabilities β where molecules adhere to the condensation nuclei. The sticking probability depends greatly upon the supersaturation ratio as well as  the temperature.
    Fig. 3) The growth rates α obtained from molecular dynamics simulations and the sticking probabilities β where molecules adhere to the condensation nuclei. The sticking probability depends greatly upon the supersaturation ratio as well as the temperature.
Press Release
Key Points – Used large scale molecular dynamics simulations to make a direct comparison with nucleation laboratory experiments and successfully reproduced the experimental values for the nucleation rate.

– Successfully measured the formation energy of a critical nucleus and sticking probabilities that determine the nucleation process.

– The data acquired at various temperatures and supersaturation ratios are essential for the construction of a high-precision, universal nucleation model.

Overview The nucleation in supersaturated vapor is an essential process in a wide range of scientific and technological fields, but a quantitatively reliable theoretical model does not yet exist. This study used super-parallel computers to perform large-scale simulations involving up to 8×10^9 atoms of the condensation process from a vapor. As a result, the study was successful in quantitatively reproducing argon nucleation for the same supersaturation as the laboratory experiment conditions. Measurement via molecular dynamics simulations of the nano-sized critical nucleus formation energy that determines the nucleation process clearly demonstrated that the formation energy of a critical nucleus is far less than in conventional macroscopic models, which makes it possible to explain the high nucleation rate obtained in laboratory experiments. It was also confirmed that the probability that a monomer sticks to a nucleus depends greatly upon the supersaturation ratio as well as the temperature. The data acquired at various temperatures and supersaturations are expected to be of use in the construction of a high-precision, universal nucleation model.
Inquiries

Hidekazu Tanaka, Associate Professor, Institute of Low Temperature Science, Hokkaido University

TEL:+81-11-706-5472

FAX: +81-11-706-7142

e-mail:hide@lowtem.hokudai.ac.jp


Kyoko Tanaka, Research Fellow, Japan Society for the Promotion of Science (JSPS)

TEL:+81-11-706-5486

FAX: +81-11-706-7142

e-mail:kktanaka@lowtem.hokudai.ac.jp

Japanese Link http://www.hokudai.ac.jp/news/130905_pr_lowtem.pdf
Publications Journal of Chemical Physics (8.21.2013)

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