How to skip certain pairwise computations

​Suppose I have particles tagged type-1 and type-2, and for pairwise computations, I want the code to only execute 1–1, 1–2 computations, but skip 2–2, and retain all type-2’s locations unchanged. I am not sure if LAMMPS supports the way that I described here.

The reason is that, I want to avoid using the strategy as to first have all pairs computed, and then fix the force as zero for type-2 particles. This is because the type-2 particles may account for 80% ~ 90% of all (tens of millions of) particles, and the post-fix strategy might be still very expensive.

Thanks in advance for sharing any experience here.

Best regard,

You can use neigh_modify exclude to exclude 2-2 interactions. Please see neigh_modify doc page for details.