[gmx-users] Surface tension

[André Farias de Moura]

Hi Ganesh,

as any other pressure-related property, surface tension values over narrow
timescales are really noisy for systems in the range of nanometers
(increasing area should reduce the fluctuation).

If simulations last  long enough, average values should be OK (please mind
that average values may be different from experimental values, unless your
force field has been parametrized to reproduce surface tension itself,
which is not the case for most force fields).

I hope it helps

Andre

On Tue, May 10, 2016 at 3:14 PM, Ganesh Shahane <ganesh7shahane at gmail.com>
wrote:

> Dear Gromacs Users,
>
> I have been trying to calculate the surface tension of pure water in a
> cubic box, in which a layer of water molecules (along the XY plane) is
> surrounded by vacuum on either sides of the Z-direction. Towards this, I
> did an NVT simulation and computed the surface tension using gmx energy
> (Gromacs 5.1) and got the following results:-
>
>  1000.000000  891.987000
>  1005.000000  -1404.097290
>  1010.000000  946.841919
>  1015.000000  2523.864014
>  1020.000000  317.747986
>  1025.000000  422.096313
>  1030.000000  -1233.948364
>  1035.000000  2187.071777
>  1040.000000  -88.564178
>  1045.000000  -981.897888
>  1050.000000  -429.718262
>  1055.000000  121.672829
> .
> .
> .
> .
>
> My question is are the figures obtained as above normal/correct? My concern
> is mainly because of the wide fluctuations in these readings. Also, when
> you report the value of surface tension, do you average the numbers across
> all the frames?
>
> Any help would be appreciated.
>
> Thank you!
>
> --
> Cheers!
> Ganesh Shahane
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-- 
_____________

Prof. Dr. André Farias de Moura
Department of Chemistry
Federal University of São Carlos
São Carlos - Brazil
phone: +55-16-3351-8090