[gmx-users] viscosity

Dommert Florian dommert at icp.uni-stuttgart.de
Thu Jun 2 12:51:06 CEST 2011


On Wed, 2011-06-01 at 23:37 +0200, Thomas Koller wrote: 
> Hello,
>  
> I calculate the viscosity with g_energy using option -vis (Gromacs
> 4.0.7):
>  
> g_energy -f file.trr -s file.tpr -vis visc.xvg
>  
> Why do I get viscosity values only until the half of the simulation
> time?

This results from the method an autocorrelation function is averaged.
For an average that is unbiased you need the same number of samples for
every time step. You achieve this by shifting the choice of the value
for t=0 through the trajectory. The maximal length of the average you
can achieve with this is exactly half the simulation time.

/Flo
   
>  
> Thomas
>  
>  
> -- 
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-- 
Florian Dommert
Dipl. - Phys.

Institute for Computational Physics
University Stuttgart

Pfaffenwaldring 27
70569 Stuttgart

EMail: dommert at icp.uni-stuttgart.de
Homepage: http://www.icp.uni-stuttgart.de/~icp/Florian_Dommert

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