[gmx-users] Spherical constraint (spherical force)

[Mikhail Stukan]

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.

Thank you very much in advance.
Mikhail


=============================================
Dr Mikhail Stukan
Schlumberger Dhahran Carbonate Research Center,
Dhahran Techno Valley  - KFUPM,
P.O. Box 39011, Dammam / Doha Camp  31942,
Kingdom of Saudi Arabia
Tel: +966 3 331 6182
Fax:+966 3 330 0845
mstukan at slb.com<mailto:mstukan at slb.com>

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