[gmx-users] average pressure using g_energy

[Mark Abraham]

On 12/26/2011 10:43 PM, Efrat Exlrod wrote:
>
> Hi,
>
> We have run an NPT equilibration on a protein embedded in a membrane 
> and calculated the average pressure using g_energy. We then imported 
> the resulting xvg file into excel and recalculated the average. The 2 
> numbers differed. Specifically, the gromacs average pressure 
> was 0.942858 while that calculated by excel was -0.726106. 
> Are g_energy calculations performed on a different set of numbers than 
> the one printed by g_energy to the xvg file? If not, can anyone 
> comment on a potential source for this difference?
>
>

See g_energy -h for why the values differ and 
http://www.gromacs.org/Documentation/Terminology/Pressure#Fluctuation 
for why they (can) vary so much.

Mark

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