three point charges for two atom non-rigid molecules

Hi,

This is a question similar to the thread posed a few years ago (https://lammps.sandia.gov/threads/msg34995.html) concerning support for “3 point charges for two atom sites”.

I was wondering if there is a way to introduce third massless atom site at the COM location with out using rigid approximation to propagate the system (e.g., N2). Also any pointers regarding the corner cases one should be aware while implementing it would greatly be helpful.

P.S. Application is motivated towards using such a potential to study isotopic effects of di-atomic molecules (path integral MD) where the molecular interactions via non-bonded and flexible bond potentials would be necessary.

Thanks !
-Abhi