[gmx-users] Re:Mixing Force Fields

Dr. Vitaly V. Chaban vvchaban at gmail.com
Fri Oct 14 18:05:38 CEST 2011

If the [ defaults ] sections are identical, you have just to add the
items from [atoms], [bonds], etc sections of the new force field to
the appropriate sections of the old force field.

The compatibility of these force fields is a sort of magic that is up to you.

- Vitaly

> I have a general question about mixing force fields.  I want to try to
> use CGenFF to model the drug and I wanted to use CHARMM for the
> solvent.  I see the general advice given online is to always use only
> one forcefield but I know CGenFF was developed off CHARMM but
> specifically for drugs.  If anything, I would like to try it to see
> how different results are from just using CGenFF.  How would one go
> about using two forcefields on your topology? For example below, would
> one simply add the non-default FF to the default FF?
> ;       File 'topol.top' was generated
> ;       By user: Administrator (500)
> ;       On host: fabian-3bef2d6a
> ;       At date: Fri April 1st 02:59 PM 2011
> ;
> ;       This is your topology file
> ;       DRUG SOLUTION w/ Ethanol
> ; Include forcefield parameters
> #include "Charmm.ff"
> #include "Cgenff.ff"
> **Thanks for everyones help.
> --
> Best regards,
> Fabian F. Casteblanco
> Rutgers University --
> Chemical Engineering PhD Student
> C: +908 917 0723
> E:  fabian.casteblanco at gmail.com

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