**Large scale molecular dynamics simulations of homogeneous nucleation**

J Diemand and R Angelil and KK Tanaka and H Tanaka, JOURNAL OF CHEMICAL PHYSICS, 139, 074309 (2013).

DOI: 10.1063/1.4818639

We present results from large-scale molecular dynamics (MD) simulations
of homogeneous vapor-to-liquid nucleation. The simulations contain
between 1 x 10(9) and 8 x 10(9) Lennard-Jones (LJ) atoms, covering up to
1.2 mu s (56 x 10(6) time-steps). They cover a wide range of
supersaturation ratios, S similar or equal to 1.55-10(4), and
temperatures from kT = 0.3 to 1.0 epsilon (where epsilon is the depth of
the LJ potential, and k is the Boltzmann constant). We have resolved
nucleation rates as low as 10(17) cm(-3) s(-1) (in the argon system),
and critical cluster sizes as large as 100 atoms. Recent argon
nucleation experiments probe nucleation rates in an overlapping range,
making the first direct comparison between laboratory experiments and
molecular dynamics simulations possible: We find very good agreement
within the uncertainties, which are mainly due to the extrapolations of
argon and LJ saturation curves to very low temperatures. The self-
consistent, modified classical nucleation model of Girshick and Chiu **J.
Chem. Phys. 93, 1273 (1990)** underestimates the nucleation rates by up
to 9 orders of magnitudes at low temperatures, and at kT = 1.0 epsilon
it overestimates them by up to 10(5). The predictions from a semi-
phenomenological model by Laaksonen et al. **Phys. Rev. E 49, 5517
(1994)** are much closer to our MD results, but still differ by factors
of up to 104 in some cases. At low temperatures, the classical theory
predicts critical clusters sizes, which match the simulation results
(using the first nucleation theorem) quite well, while the semi-
phenomenological model slightly underestimates them. At kT = 1.0
epsilon, the critical sizes from both models are clearly too small. In
our simulations the growth rates per encounter, which are often taken to
be unity in nucleation models, lie in a range from 0.05 to 0.24. We
devise a new, empirical nucleation model based on free energy functions
derived from subcritical cluster abundances, and find that it performs
well in estimating nucleation rates. (C) 2013 AIP Publishing LLC.

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