[gmx-users] Two different force field use in one simulation?

[Justin Lemkul]

On 10/26/16 8:49 AM, Mijiddorj Batsaikhan wrote:
> Dear Justin,
>
> Thank you very much. Can I use 2 different force fields in same simulation?
> It means charmm27 for the DOPI and charmm36 for other groups.
>

No, nor should you try.  CHARMM27 lipid parameters are demonstrably worse than 
CHARMM36.  Just read the references for the CHARMM36 lipid parameters and you 
will see why.  Creating a CHARMM36 topology for DOPI from POPI or some other 
related species is a trivial modification of adding two carbons.  There's no 
need to try to use any complex topology builder that uses outdated parameters to 
try to get a topology for it.

In a more general sense, "mixing" force fields is never correct.  A force field 
is a balanced, self-consistent entity.  Without proper balance between terms, 
you're not doing a useful simulation.  You're running a very expensive random 
number generator.

-Justin

>
> Best regards,
>
> Mijiddorj
>
>
>
>> Dear gmx users,
>>
>> I would like to simulate a system that consists of 2 different membranes
>> and protein molecule. DOPI membrane model could not find from Charmm-gui
>> ,embrane builder's models. I built the system DMPI membrane instead of
>> DOPI. Then I modified DMPIs to DOPIs, and got charmm27 force field
>> parameters using swissparam. Charmm-gui give me charmm36 parameters. I
> want
>> to use charmm27 for only DOPI. I have some questions.
>>
>> (1) Is these type of modification possible to the simulations?
>>
>> (2)  How can I convert charmm27 to charmm36 parameter?
>>
>
> You can't just convert one force field to another.  CHARMM36 is superior to
> the
> outdated CHARMM27 for lipids, so it is a much better force field model for
> doing
> current simulations.
>
> -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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