[gmx-users] Spherical constraint (spherical force)

Mark Abraham Mark.Abraham at anu.edu.au
Mon Oct 17 15:07:14 CEST 2011

On 17/10/2011 11:41 PM, Mikhail Stukan wrote:
> Dear gmx-user,
> I would like to simulate an isolated  drop of water (without PBC). To  
> prevent water molecules form evaporation I would like to create a 
> spherical constraint around the system. In recent article in PNAS 
> (Caleman, Hub, van Maaren, van der Spoel,  v. 108, 6838 (2011)) where 
> the authors considered similar system it is mentioned that:
> "To avoid such evaporation, we applied a spherical flat-bottom 
> quadratic potential acting on the water. That potential was 
> implemented as an additional force F pointing toward the COM of the 
> droplet..."
> Could anybody give a hint how this approach can be realized in 
> GROMACS? I looked through the manual, but did  not find clear answer 
> how to implement such a force.

I think the only way to do something like this in GROMACS is with a COM 
virtual site and such a distance restraint from each water molecule to 
that virtual site.

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