Water/vacuum system

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Dear Gromacs Users,

I want to run a water/vacuum system to calculate surface tension of water. I have hydrated DMPC bilayer system from which I have removed the DMPC molecules and all water molecules present in the upper leaflet. Then I translated the lower leaflet water molecules and energy minimized the structure.
Kindly see the attached snapshot of the

energy minimized structure.

Kindly let me know whether the approach which I am employing is correct or not.

Thanks in advance,
Abhinav Srivastava