[gmx-users] Different hexane/water surface tensions for different ensembles (NVT and NAɣT)

Ozge Engin ozge.engin at gmail.com
Tue Aug 24 16:05:20 CEST 2010

Hi all,

I am trying to calculate the surface tension of hexane/water interface. I
used two different ensembles: constant particle, volume, temperature (NVT),
and constant area but let the box fluctuate on the z axis (NAɣT). Everything
except the ensemble is the same for two simulation set-up s: number of
molecules, temperature, temperature coupling, electrostatic and VDW
interaction schemes, cut-off etc.

I found a value close to the experimental one (52 dyn/cm) by using the NVT
ensemble. In order to check whether it is dependent on the system size, I
tried different sized systems, but it does not change. The results were the
same within the error bars, which is good. However, when I attempt to change
the ensemble to NAɣT I found different result. It is around 48 (1) dyn/cm.
Actually, I expected to have the same values with the two ensembles, but

Am I missing something that is straightforward?


Ozge Engin
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