[gmx-users] Surface tension

[Ganesh Shahane]

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