[gmx-users] How to use g_rdf with -com?

[C. D. Poon]

In the Gromacs tutorial, the  radial distribution function of 216 water 
molecules in a box can easily be calculated by g_rdf around the oxygen 
atom of the water molecule.  It is straight forward to use the index 
file with one group (OW) in it for the calculation.

I have a box of benzene.  As you can imagine, I must use the center of 
mass of benzene to calculate the radial distribution function.  However, 
I do not seem to understand how to use the -com option in the g_rdf 
command.  Can anyone share your experience in using g_rdf with -com option?

Thanks in advance,

CD Poon.