Hi,

I’m trying to use LAMMPS machinery to implement 5-centre pairwise model (5CPM) for molecular nitrogen (N2).

My current attempt is based on fix/rigid/small with N2 molecule being defined in the following way:

X_1 - N - X_2 - X_3 - X_2 - N - X_1

where N is nitrogen atom and X_i are 5-centre sites where potential is evaluated.

X_i masses are set to something negligible.

The pair_style python is used to compute energy and forces between different sites.

The intra-molecular interactions are excluded.

For each N2-N2 interaction all 25 distances between X_i sites must be used.

The problem with this approach, I think, is that in the case when the distance between some sites is greater than cutoff distance not all 25 interaction are computed.

Is is possible to alter this approach such that energy/forces are only computed if all X_i sites are within the cutoff distance (or possibly based on centre of mass distance)?

If not, is there a different way to tackle this problem?

Cheers