[gmx-users] Average simulation time for correct surface tension

[gozde ergin]

Dear users,

I am trying to estimate the surface tension of cis-pinonic covered water surfaces.
Li. et al 2010 did the same thing and his simulation time was 2 ns.
On the other hand there are some other studies mentioned that simulation time should be long around 200 ns because surface tension is difficult to estimate accurately, since fluctuations are large and convergence is slow (Engin et. al 2010).

I would like to give a an example below. I simulated the system for 20 ns. First 6 ns is for equilibration and last 14 ns sampling.

For first 6 ns :

Energy                      Average   Err.Est.       RMSD  Tot-Drift
-------------------------------------------------------------------------------
#Surf*SurfTen               1181.02         22    2327.09    32.8309  (bar nm)

For last 14 ns: 

Energy                      Average   Err.Est.       RMSD  Tot-Drift
-------------------------------------------------------------------------------
#Surf*SurfTen               1244.15         10    2339.36    -63.287  (bar nm)

RMSD is larger than Average value so i am confused how long should I run?

Thanks