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[lammps-users] Higher Dimensional Distribution Functions (Beyond RDF)
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[lammps-users] Higher Dimensional Distribution Functions (Beyond RDF)


From: James Mansell <jmmansel@...1442...>
Date: Fri, 11 May 2018 13:17:19 -0400

Hello LAMMPS users,

I would like to calculate the two-particle (pair) distribution function in small systems with external potentials having continuous "infinitely long" cylindrical symmetry.  [Forgive my abuse of terminology.]  Due to the external potential, RDF is no longer a sufficient descriptor.  I need four dimensions to describe this distribution.

After searching the documentation and mailing list archives, I have not found any discussions of such a requirement, but I figure it is worth a shot to ask the following:

1. Does LAMMPS have any standard compute or other capability that might be helpful for doing this that I have overlooked?

2. Has anyone out there done something like this, or know of anyone who has done it, that could be helpful?

3. Is this a somewhat reasonable thing to try to implement (in LAMMPS)?  I am considering writing a compute, which I have not done before.  I would rather know in advance if more experienced users think this is a bad idea (not that I would not try it anyway).

Incidentally, my systems are quite small and simple ( < 2,500 LJ particles, < 2,000 nm^-3), and by taking advantage of symmetries and other information, I believe a suitable "mesh" could be produced with fewer than 1E9 bins, perhaps significantly fewer.  So, it seems like the curse of dimensionality should be manageable IF I am careful.

I guess I could also consider a spatial decomposition other than discrete bins.  Or some other method entirely?

Any help is much appreciated.

Kind regards,

Matt