[gmx-users] question about modified LJ combination rule

[Justin Lemkul]

On 7/7/14, 8:36 AM, sujithkakkat . wrote:
> Dear all,
>
>      I am studying a water-methane system with tip4p-Ice for water and
> oplsaa for methane.
>
> What I want to try is modify the intermolecular non-bonded interaction
> between methane and water. I just want to multiply the combination rule
> (geometric mean) used to obtain the  mean well depth (epsilon) component by
> a scaling factor, without changing any of the non bonding function types.
>
>   I am aware that user defined non-bonding functions are possible. However,
> here I don't want to change the function type, but only slightly modify the
> combination rule 3 , by multiplying the epsilon part  with a scaling factor.
>
> Also, I find that there is no nonbond_params section in OPLSAA where I
> think it would have been possible to edit cross LJ terms .
>
> So, is there an easy way I can do it rather than going for user defined
> non-bonded functions .
>
> Is it ok to  define "nonbond_params" in topology file with oplsaa
> forcefield?
>

Yes, that would be the easiest way to override the normal combination rules.

-Justin

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

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

Department of Pharmaceutical Sciences
School of Pharmacy
Health Sciences Facility II, Room 601
University of Maryland, Baltimore
20 Penn St.
Baltimore, MD 21201

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

==================================================