[gmx-users] OPLS force field issue

[Justin Lemkul]

On 4/30/15 4:46 AM, Mary wrote:
> Dear gmx users,
>
> I also try to use the OPLS force field for my simulations. After defining
> suitable atomtypes:
>
> opls_110 (type C2)
> opls_071 (type C2)
>
> I would like to add the suitable bondtypes, angletypes and so on. But where
> do I get those parameters for the angles and k?
>

If they're not in the force field, you have to derive them.

> I thought, that the values have to be in the ffbonded.itp.
>

Not necessarily.  What leads you to believe that these particular atom types 
should be bonded?  You can't necessarily just combine any two types.  If the 
parameters are missing, that probably means the types are not what you want for 
whatever it is you're trying to do.

-Justin

> If I am interested in opls_182 for example, which has the bond type CT (I
> got this information from the atomtypes.atp) I found several informations
> about CT in the ffbonded:
>
> [ bondtypes ]
> ; i    j  func       b0          kb
> CT    CT      1    0.15290   224262.4   ; CHARMM 22 parameter file
>
> [ angletypes ]
> ;  i    j    k  func       th0       cth
> CT     CT     CT      1   112.700    488.273   ; CHARMM 22 parameter file
>
> But there are no parameters listet for C2.
> I know that I could also "ignore" the parameters and include the oplsaa.ff
> in my topology file but is there also a way to get those parameters directly?
>
> I suppose there is a way, as I found various posts including this
> parameters as for example in this post.
>
> (".....>   C2    C3       1    0.16020   292880.0   ;..... )"
>
> Many thanks in advance!
>
> Mary
>
>
>

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

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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