[gmx-users] on force fields

[Mark Abraham]

On 16/02/2011 3:41 PM, Mr Bernard Ramos wrote:
> Hi everyone!
> I need to update the gromos force field 53A6 with the new force field 
> 53ACARBO (JCC 10 NOV 2010).
> 1. I will have to change the parameter values in the file 
> ff_bonded.itp and ff_nonbonded.itp in the gromos53a6.ff. Are these the 
> only files that I need to update if I need to switch to a new force field?
>

You should make a copy of the whole force field directory into your 
working directory, rename the new directory suitably, make a suitable 
change to forcefield.doc, and then edit .itp files suitably. This means 
you're leaving your reference version untouched and can edit locally to 
your heart's content, and can be sure you're selecting the right force 
field with pdb2gmx and/or in your .top file.

> 2. The new force field 53ACARBO has a new gromos functional form 
> for select torsional potentials. How to I go over implementing this in 
> gromos?
>

Preferably as a sum of existing functional forms. Or use tabulated 
bonded interactions (see manual and wiki).

Mark
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