[gmx-users] Surface tension readings in NVT vs NPT simulations

[aldi asmadi]

David,

I have a question that is still related to your reply.  If the bulk
liquid NPT and the interfacial liquid-vapor NVT simulations are
performed using dispersion corrections to the pressure and energy,
while the intefacial liquid-liquid NPAT simulation don't use any
correction, can we say that all results are valid since we don't give
the same treatment for all systems?

In the NPT and NVT calculations, we apply corrections in order to
reduce the discrepancy between the calculated and experimental
properties (say density and surface tension) as small as possible.
Here we have more confidence that our molecules in systems behave
accordingly judging from the macroscopic values we obtain.  Meanwhile,
in the NPAT calculation, we don't use such correction meaning that the
property (say interfacial tension) is expected to deviate more from
the experimental value? This indicates that the system behaves
differently in comparison to the same simulation conducted with
correction?

Many thanks,
Aldi


On Sat, Mar 12, 2011 at 11:44 AM, David van der Spoel
<spoel at xray.bmc.uu.se> wrote:
> On 2011-03-12 06.09, Denny Frost wrote:
>>
>> I am running MD simulations on Liquid/Liquid interfaces and measuring
>> the interfacial tension between them.  I have found that the readings in
>> NVT simulations are close to experimental values, but have a lot of
>> variation.  I run NPT simulations on the exact same system and find the
>> results show very little variation, but the values are far from
>> experimental results.  Does anyone know why this happens?
>>
> Please be more specific. How do you do NPT simulations? This may influence
> the result. To get good result I would suggest to do pressure coupling only
> in the normal direction and to turn off dispersion corrections to the
> pressure.
>
> --
> David van der Spoel, Ph.D., Professor of Biology
> Dept. of Cell & Molec. Biol., Uppsala University.
> Box 596, 75124 Uppsala, Sweden. Phone:  +46184714205.
> spoel at xray.bmc.uu.se    http://folding.bmc.uu.se
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