[gmx-users] how to extend the order of Ryckaert-Bellemans dihedral

[Yuguang Mu]

I encountered this problem when I want to implement charmm force field
into gromacs.
Because the torsion types which have higher order than 5  are not many.
I just define a  normal torsion , just like defining an improper
dihedral angles.

But in doing so, you have to edit the topological file  second time
to add the torsion types which you defined more than 5 order.

So I agree to extend the order of the Ryckaert-Bellemans type may be
the best solution.


> I'm planning MD of a molecule with fluorocarbon chains with united CFn.
> Since the system size and each molecule itself rather large,
> I need united CFn instead of explicit F atoms.
> Complex torsion potential of CF2-CF2-CF2-CF2 needs more higher order than
> the Ryckaert-Bellemans (up to 5th) potential (e.g. up to 7th or even
> 12th see Cui et al. Fluid Phase Equilibria 146 '98 51-61 etc.).
> How can I extend the order of the Ryckaert-Bellemans type dihedral
> function (e.g. which routines in GROMACS source code needs changes?).
>
> Thank you for advance.


Dr. Yuguang Mu
Institute for Physical and Theoretical Chemistry
J.W. Goethe University Frankfurt am Main
Marie Curie Str. 11
60439 Frankfurt/Main, Germany
Tel: +49-(0)69-798-29711