immobilizing of atoms

HI dear

I have two groups of atoms (group1 and group2) in my simulation. The atoms of group2 are surrounded by atoms of group1.

I want to immobilize group2, but group2 should interacts with group1.

For immobilizing the group2, I don’t include group2 in time integration.

With this regard, does group2 interact with group1. If not, what should I do?

As long as there are still group1 <> group2 interactions specified by something like pair_style, and you haven't excluded those interactions with something like neigh_modify exclude, then you'll still get the interactions. All that happens is that you don't update the velocities/positions of the group2 atoms.