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JavaScript animated nobel gas

Background

The JavaScript-animation shows a two-dimensional molecular dynamics
simulation with a Lennard-Jones-potential force.
The Lennard-Jones potential energy is U(r) = ε ·
(r_{0}/r)^{12} - 2ε ·
(r_{0}/r)^{6}.
r_{0} is the equilibrium
distance between the atomic nuclei (no net force)
and ε is the depth of the potential.
The force is F(r) =
-dU/dr (Van der Waals for longer distances).
The depth ε is proportional to a temperature T_{0} =
ε/k, where k is the Boltzmann-constant.
The mean kinetic energy of a free particle is
1/2·mv_{x}^{2} =
1/2·mv_{y}^{2} = 1/2·kT.
For Argon we have T_{0} = 124 K and r_{0} =
384 pm.
The argon atom has an empirical radius of 71 pm
(https://www.periodensystem.info/elemente/argon/).
The most common isotope (Ar-40) has a mass of 39.962 u.
The movement is restricted to two dimensions.
The Euler-Cromer method is used for numerical integration.
The time-step is chosen such that the particles move about 0.1 pixel
per frame.