[gmx-users] Conversion of charmm36 parameters from namd to gromacs

Justin Lemkul jalemkul at vt.edu
Mon Dec 4 19:53:16 CET 2017

On 12/4/17 12:21 PM, Daniel Bauer wrote:
> Hello,
> I finally found my error in the conversion. As always, the devil is in
> the detail. I was under the assumption that parameters listed in the
> original forcefield files (toppar) are also sigma and epsilon values.
> However, as you know, the original files list Rmin values (and not sigma).
> With the correct conversion term:
> eps = Rmin/(10*2^(1/6))
> I can now reproduce the conversion of the numbers from the charmm
> implementation to gromacs (and thus know how to apply my NBFIX for this
> value).

I don't know what NBFIX you might have, but FYI there is a value that 
will become official in the next release of the force field. We've 
validated it against proteins and nucleic acids. See the SI of 



Justin A. Lemkul, Ph.D.
Assistant Professor
Virginia Tech Department of Biochemistry

303 Engel Hall
340 West Campus Dr.
Blacksburg, VA 24061

jalemkul at vt.edu | (540) 231-3129


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