Higher Dimensional Distribution Functions (Beyond RDF)

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

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.

​a 4d-distribution is tricky to visualize, you'd have to render multiple
(nested?, transparent?) isosurfaces and possibly run a clipping plane
through it. or do projections.

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?

​i don't think so.

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

​nope.

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).

​it is not clear to me, what exactly you are after, thus i am hesitant to
give specific advice.

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?

​if you are not under pressure to produce results, i would continue looking
around in the published literature to review examples of what other people
have done under similar circumstances. perhaps there is a more accessible
approach.​

​axel.​