[gmx-users] Dihedral multiplicity

[Anton Feenstra]

David van der Spoel wrote:
> 
> On Tue, 30 Apr 2002, Xavier Periole wrote:
> 
> >
> >Hi all,
> >
> >I wanted to modify the multiplicity of a proper dihedral angle
> >in the topol.top file. I rapidly figured out that is not possible
> 
> It is quite trivial, just add new parameters for the particular dihedral.
> You will have to add all parameters, and if you change the multiplicity
> you have to  add the params twice. This is because grompp interprets a
> difference between the parameters you give and those in the database as
> input for free energy perturbation, and while you can change the force
> constant and phase angle you can not change the multiplicity.

If you really need to perturb the multiplicity, you can let the 
'original' vanish (i.e. perturb to zero force) and let the 'new' one
grow (i.e. perturb from zero force), although that might not give
you the kind of intermediate states that you might need...

-- 
Groetjes,

Anton
 ________ ___________________________________________________________
|        | Anton Feenstra                                            |
| .      | Dept. of Pharmacochemistry - Free University Amsterdam    |
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