[gmx-users] dihedral restraints

Chris Spronk C.Spronk at cmbi.kun.nl
Fri Sep 27 13:53:22 CEST 2002

David van der Spoel wrote:

> What should be the exact potential form for dihedral restraints?
> If we define phi_ref as the reference angle and 2*dphi as the allowed
> angular space we define 
> phi' = (phi-phi_ref) MOD 360
> then we have 
> V = k/2 (phi' - dphi) ^2 (phi' > dphi)
> V = k/2 (phi' - dphi) ^2 (phi' < dphi)
> V = 0 (elsewhere)
> Does that look right?

Hi David,

The definition of the potential looks perfect!!
Thinking about this, it probably would be a good idea to have the force 
constant defined in the mdp file, just like disre_fc and orire_fc, and 
use a scaling factor for each individual restraint in the include file 
that contains the definition of the restraints.
Also, if it is easy to implement, it would be nice to have an optional 
time-averaging for the dihedral restraints as well. It is not routinely 
used in NMR, but might become important in the near future.




Chris Spronk
Centre for Molecular and Biomolecular Informatics
University of Nijmegen
Toernooiveld 1
NL-6500 GL Nijmegen
The Netherlands
fax  :	+31/+24/3652977
e-mail: C.Spronk at cmbi.kun.nl

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