[gmx-users] Moments of inertia calculation using g_gyrate

[George Abadir]

Hi,
     I did a caluclation for the moment of inertia of amino acid 
molecules using g_gyrate with the options -p and -moi for calculating 
the moments of inertia with respect to the principal axes. I noticed 
that in the output matrix there are 5 columns: one is for time and then 
one is labeled "Itot" and then three for the moments of inertia around 
the principal axes. My quesstion is what does "Itot" mean? It should 
mean "total moment of inertia" but about which axis? Is it an axis that 
passes through the centre of mass of the molecule? If so, what is its 
orientation? I could not find a clear answer in the documentation so any 
help will be much appreciated. Thanks alot,
Regards,
George