Limiting pair interaction between different molecules

LAMMPS LAMMPS Development
1

Hi,

I would like to modify a pair style such that if two different molecules have more than one pair of atoms that interact, only a single pair has their interaction “counted” (meaning, if the force and energy due to their interaction is non-zero, it is kept that way, and every other pair set to 0). For example, if I have two linear trimers made of spheres, and the trimers are positioned such that two pairs of spheres between the trimers are close enough to interact (assume here the pair style only turns on for overlap of the spheres), only one of the pairs of spheres has its interaction counted. Which pair may not matter, and I think choosing either arbitrarily is ok.
It seems that this is a tough thing to do, as when running in parallel I’m unsure of how to track whether a pair between two molecules has already been “counted”, and to make sure that every other pair is ignored.

2

I don’t think that a mode,l where a single, arbitrarily chosen atom out of a group of atoms interacts, is going to result in meaningful (and publishable!) results.

It would be far simpler and more consistent to just specify a single site, identified by a specific atom type, that would represent the intra-molecule interactions. That kind of model would not need any modification to existing pair styles.