A question about Compute RDF

LAMMPS
,
1

Dear all

I use LAMMPS 15Dec2018. Using compute RDF, I need to find O-O and O-H RDFs in a system that includes water. For some cases, the calculated RDF is normalized, but for others. I am wondering if I have to normalize the latter manually. In this case, how can I ensure the calculated coordination number?
In the following, you can see one of the samples of the second case:
I would appreciate it if I had your advice.
Thanks
Best
NKh
OH_RDF
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1.530713636

2

We strongly advise against using such an old version of LAMMPS. In the 5 1/2 years since that release a lot of bugs have been found and fixed and a lot of improvements made to LAMMPS.

Furthermore, if you would come across a bug, nobody would be willing to spend time on locating and fixing a bug in an older version that is not confirmed to exist in the current version.

The definition of the radial distribution function g(r) assumes a homogeneous atomic bulk system. Any time a system deviates from that, you may get results that deviate from what is expected for a homogeneous bulk system. In essence the g(r) is the ratio between the particle distribution of an ideal gas and the histogram from the actual system. If your system, for example, forms clusters, then it is more likely to find atoms at close distance than at longer distance, so the g(r) will reflect that by having larger values than a homogeneous system at shorter distance and lower values at longer distance.

To learn more about this, you have to study some text books on the subject. My favorite is “Theory of Simple Liquids” by Hansen and McDonald (https://shop.elsevier.com/books/theory-of-simple-liquids/hansen/978-0-12-387032-2).