[gmx-users] Ryckaert-Bellemans type dihedral

[Mark Abraham]

Suman Chakrabarty wrote:
> Hi,
> 
> I need to write my own topology file for a system using
> Ryckaert-Bellemans type dihedral potential. Since I should remove the
> 1-4 non-bonded interaction in this case, I wanted to know whether it is
> enough not to keep any [ pairs ] entry in the topology file (manual page
> 113), or I should explicitly put nrexcl as 4 in the [ moleculetype ]
> section. What is the full-proof method of using RB potential?

It depends whether you want other 1,4 interactions when using other 
dihedral potentials elsewhere, and whether the forcefield defines 
pairtypes. Generate a small test case, invoke grompp, and then look at 
the gmxdump output to confirm your expectations.

Mark