[gmx-users] about CHARMM force field in GROMACS

[Justin Lemkul]

On 9/22/16 1:56 PM, jing liang wrote:
> Hi,
>
> in GROMACS web site there is a recommendation when using CHARMM27 set of
> parameters:
>
> constraints = h-bonds
> cutoff-scheme = Verlet
> vdwtype = cutoff
> vdw-modifier = force-switch
> rlist = 1.2
> rvdw = 1.2
> rvdw-switch = 1.0
> coulombtype = PME
> rcoulomb = 1.2
> DispCorr = no
>
> Is there some issue with the simulations if one uses different values for
> cutoff distances?
>

Cutoffs are part of the force field.  If you start adjusting them, you can throw 
things into imbalance and turn the simulation into garbage.  With PME, the value 
of rcoulomb becomes somewhat irrelevant, though.  Verlet will adjust rlist as 
needed to buffer the neighbor list, in a manner comparable to what we do in 
CHARMM with an explicit vdW cutoff and neighbor list cutoff.

-Justin

-- 
==================================================

Justin A. Lemkul, Ph.D.
Ruth L. Kirschstein NRSA Postdoctoral Fellow

Department of Pharmaceutical Sciences
School of Pharmacy
Health Sciences Facility II, Room 629
University of Maryland, Baltimore
20 Penn St.
Baltimore, MD 21201

jalemkul at outerbanks.umaryland.edu | (410) 706-7441
http://mackerell.umaryland.edu/~jalemkul

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