[gmx-users] What is the meaning of negative surface tension?

[gozde ergin]

Also when I check the pressure in X,Y and Z axis,
Pzz = -0.34 bar
Pyy = -1275 bar
Pxx = 32 bar.
Pyy and Pxx should be equal to each other. So basically system is not under equilibrium conditions.
How should I solve this problem? Any idea?

> On 23 Sep 2016, at 09:27, gozde ergin <gozdeeergin at gmail.com> wrote:
> 
> Dear all,
> 
> I am simulating organic covered salty water system in order to estimate the surface tension. Force field is Charmm36 and water model in TIP3P.
> Surface tension is -127 mN/m after 5 ns run. What is the meaning of negative surface tension?
> I was expecting +30 ~ +40 mN/m but not negative. 
> Maybe my system was not under equilibrium conditions. 
> Will longer running solve the problem? Any help would be appreciated.
> 
> Thanks in advance.