[gmx-users] opls Ryckaert-Bellemans parameters

Frederic Leroy frederic.leroy at urv.net
Thu Jun 23 00:27:25 CEST 2005

zjim wrote:

> dear all:
> I wanted to change the opls torsion parameters into Ryckaert-Bellemans
> parameters in order to apply them also in gromacs. According to the
> manu, it can be done as follow:
> C0 = V0 + V2 + 1/2 (V1 + V3)
> C1 = 1/2(3V3 - V1)
> C2 = -V2
> C3 = -2V3
> C4 = 0
> C5 = 0
> yet, the reference i get doesn't have the value of coefficient V0, so
> it was unable to achieve the change.So, my question how can i get the
> value of V0 ? Is it a determinate value or not.does somebody know
> this, please give some advice.
Hi Zjim,

if you didn't find any value for V0, there is a high probability that it
should be put to 0. For instance, in the OPLS AA force field, V0 is 0.
I would like to advise you to simply plot your torsional potential
function respect to the torsion angle as it is done un the manual and
check the shape of the curve. You should find minima and maxima at the
relevant conformations of your torsional angle system. Then you will be
sure that V0 is really 0.
I hope this will help.

Frederic, Tarragona Univ, Spain.

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