[lammps-users] ch2lmp multiple forcefield files

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1

Dear LAMMPS users,

I wish to simulate a protein in a sugar solution, modeled by CHARMM all22_prot and all36_carb respectively. I have succeeded in building the system for CHARMM (with appropriate pdb and psf files). When I simulate with NAMD2, I list both prot and carb parameter files in the input script. But when I attempt to convert the pdb and psf files to a LAMMPS data file, the ch2lmp tool supports only one set of CHARMM parameter and topology files. If I attempt to use ch2lmp with only one of the pairs of par/top files, an unusable LAMMPS data file results.

Essentially, this is a simple problem. I can simulate both protein and sugar with lammps. Is there an easy way to combine the two sets of forcefield files into one set so I can use ch2lmp on the combined psf/pdb? Alternatively, is there a simple way to combine separate data files for the protein and sugar?

Thanks,

Harold

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I imagine you can cut/pate the 2 ff files together by hand if you
understand the format. If you mean how to combine 2 LAMMPS input
data files, then you can also do this by hand if the atom types
are non-overlapping. You can also use the Pizza.py data tool to
read multiple data files. If you know a bit of Python it's not hard to
merge them and write out a combined data file.

Steve

3

Dear Steve and LAMMPS users,

Cut/paste of the forcefield files did the trick. I apologize for asking
such a simple question, which was a CHARMM question more than a LAMMPS one.
I imagine the python tools provide an equally elegant solution.

Harold