[lammps-users] Questions?

Dear Lammps:

1)When I want to calculate the radial distribution function of the polymer melts,but because the RDF is not computed for distances longer than the force cutoff,then if I want an RDF for larger distance,what measures in detail I should take?

2)The code “fix msd command” is to computer the mean-squared displacement of the group of atoms every N steps,then when I want to study the mean-squared displacement of the polymer density melt (averaging over all the chains rather than all the atoms),what should I do? Can you give me some advice?(The code "fix gyration command"has the same problem.)

Thank you very much!

If you want to compute somthing further away than the cutoff, LAMMPS
doesn't have the info to compute it. At least in parallel. So you're better
off computing it as a post-processing step. I.e. write your own code
to do it, reading a dump file.

Re msd: you could modify fix msd to do what you want or add your
own command. See the Section modify doc pages.