Setting no interaction between certain pairs of atoms

My MD system consists of several LARGE particles and a number of SMALL particles.
(say, 10 Large + 100000 Small particles)
I use LJ potentials for Large-Large and Large-Small pairs, but I like to impose no interactions between Small-Small pairs.

I could do the simulation by using “pair_style lj/cut” and setting epsilon=0 for Small-Small pairs.
But it is very inefficient because LAMMPS should calculate all Small-Small pairs for nothing.

If you know any way to set no interaction between certain pairs, could you please let me know?
Thank you very much.

Check out the neigh_modify exclude command which can
exclude certain type-type interactions. You probably also
want to check out the neighbor "multi" option which is
designed to build neighbor list efficiently when you have 2
or more length scales.