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

Pedro Alexandre de Araújo Gomes Lapido Loureiro palaplou at
Tue Aug 24 16:50:41 CEST 2010

It is probably due to the fact that z-dimensions are different in your two
Check "Surface tension coupling" in the manual.



2010/8/24 Ozge Engin <ozge.engin at>

> 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
> not.
> Am I missing something that is straightforward?
> Regards
> --
> Ozge Engin
>  ★☆
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