[gmx-users] Add gromacs forcefield w/ virtual site

[Marcelo Silva]

I am trying to simulate oxygen using gromacs but there seems to be no 
forcefield parameters for this molecule.

So I would like to add a forcefield to gromacs which is a 3 site model: 
The two oxygens are lennard jones particles and there's a point charge 
at the center of mass.

The reference article is: "New force fields for nitrous oxide and oxygen 
and their application to phase equilibria simulations", Niels Hansen et al

I was wondering if there's anyone more proficient with gromacs that 
could indicate me how to do this (files to modify, how to represent the 
center of mass particle, etc)

Thank you