[gmx-users] Turn off the diheral energy

[Mark Abraham]

Myunggi Yi wrote:
> Dear users,
> 
> I have borrowed some atom types from "ffgmx" for my new molecule, and
> I'm getting distorted molecule. (I'm expecting a plane ring shape, but 
> I'm getting chair shape, especially attached hydrogens)
> However, I can't find which one is which one.

Mixing force fields is an intrinsically bad idea. See 
http://wiki.gromacs.org/index.php/Parameterization

> Is it possible to turn off dihedral energy (proper and improper) for a 
> certain molecule?
> If yes, then how can I do this?

Comment out these parts of your topology file.

Mark