[gmx-users] torsion potential with 7 parameters

Ángel Piñeiro fangel at usc.es
Wed Jan 30 12:45:07 CET 2008

If the transformation can not be analytical, I could fit (numerically)
the parameters of the Ryckaert-Belleman potential to the function that
results from the original one... Although this is not probably the best
way of using the force field as originally proposed, the difference
should be negligible.

Another alternative is to edit the code to introduce the new function,
but I guess this is not trivial, any tip on this?

Angel Pineiro.

On Wed, 2008-01-30 at 22:26 +1100, Mark Abraham wrote:
> > Ángel Piñeiro wrote:
> >> Dear David
> >> I have taken a look to the manual (version 3.3) and I haven't found
> >> information about how to tabulate bonded potential functions (it seems
> >> that Ran is right). On the other hand, what do you mean exactly with
> >> adding two dihedrals?
> > It could well be that you'll have to wait for 4.0 for the tabulated
> > dihedrals.
> >
> > You can however specify two torsion potentials around the same bond.
> > This is how it is done routinely in CHARMM, where there are even more
> > than two for some torsions.
> Yep, although with sufficiently cunning trigonometry, you can reduce any
> combination of those to one Ryckaert-Belleman dihedral. This doesn't help
> for n >= 6, however.
> Mark
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