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

[Erik Lindahl]

On Wednesday, Mar 5, 2003, at 23:56 US/Pacific, Yuguang Mu wrote:

> 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.
>

It is actually close to trivial to implement it in the code, the only 
problematic part is that we might need to extend the format in the 
forcefield and run input file.

You can of course always add multiple dihedrals with arbitrary 
multiplicity, but that will be slightly slower (the angle is 
recalculated) if you have a _lot_ of them.

If we were to implement a special type for it, are there any practical 
limits to the number of terms, and is the format the same as 
ryckaert-bellemans, or?

Cheers,

Erik