[MMTK] 2D simulations?
khinsen at cea.fr
khinsen at cea.fr
Thu Apr 7 19:19:29 CEST 2005
On 07.04.2005, at 16:46, mmtk-bounces at python.net wrote:
> A newbie question: is it possible to do strictly 2D simulations in
> MMTK? I
> modified the argon.py example script with the intention of making it
> work
> in 2D (to simulate a L-J gas in the plane) by setting the z dimension
> of
> the OrthorhombicPeriodicUniverse to zero. No luck - I get a
> segfault/NaNs.
MMTK doesn't like zero-volume universes. I guess it shouldn't crash,
but this is certainly not supposed to work.
There are a couple of approaches of different complexity and
flexibility. It all depends on what you need. A first approach would be
to place your atoms on a plane (z=0 for example) in a periodic universe
of finite z-extension, and make sure that their initial velocities are
in the plane as well. With only pairwise potentials, the atoms should
then always stay in the plane. The question is, however, if such an
arrangement is numerically stable. If there are only slight deviations,
you could get away with perdiodically resetting the z component of all
positions and velocities to zero.
If that doens't work, and assuming you need only a straightforward
Verlet-type integrator, you could write your own integrator in Python
code that uses only the x and y coordinates. You would lose a bit of
speed, but not that much, as a plain Verlet integrator can be expressed
in terms of efficient array operations. If you need a thermostat, this
approach might not be realistic any more. You would then have to write
your 2D integrator in C, using the Langevin integrator in the Examples
directory as a model.
Konrad.
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--
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Konrad Hinsen
Laboratoire Leon Brillouin, CEA Saclay,
91191 Gif-sur-Yvette Cedex, France
Tel.: +33-1 69 08 79 25
Fax: +33-1 69 08 82 61
E-Mail: khinsen at cea.fr
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