From: Brian Radak (
Date: Sun Mar 18 2018 - 15:27:05 CDT

I don't believe that you can automatically mix arithmetic and geometric
mixing rules (or at least I don't know of any mechanism that NAMD has with
which to do this). My guess would be that you would have to create a
specialized prm file that implements appropriate NBFixes for either the
CHARMM or OPLS types.

I have never heard of mixing these two force fields before - is there a
specific reason you are not using CGenFF for the ligand? Presumably that is
the most "literature friendly" approach.


On Fri, Mar 16, 2018 at 3:14 PM, Srijita Paul <> wrote:

> Hi,
> I am trying to run a simulation where I want to use charm general force
> field for protein and opls-aa force field for the ligand. I have saved the
> opls-aa parameter in charm format in .prm file. But after running the
> simulation I am getting such type of error for all the atoms of the ligand
> and simulation failed.
> 0:463(1165) atom 648 found 0 exclusions but expected 5
> In my configuration file I also tried the command "vdwGeometricSigma
> yes" and got the same error.
> Can I use charm and opls-aa force field together in a same simulation. If
> yes why this error is comming and what should I do for it?

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