Thanks!
So how do I get gmx rdf to calculate the centre of mass of the whole system. Would dyn_mol_com do the job? (I have tried looking through the gromacs manual but the documentation is minimal and difficult to understand for me)
I can’t choose one O and calculate rdf from that because I am calculating rdf over a trajectory, so I can’t choose one O because it won’t stay at the centre after a few frames.
Also do I need the -seltype option? I don’t understand what it does.