Thank you Steve,
I was modifying fix orient/fcc for my purpose actually. from your answer I understand now that the reverse communication is probably done within verlet in their case (because they do not have a reverse_comm()within the fix) . In my case I have changed fix orient/fcc to work with minimization , I think that’s perhaps why I would need to add the reverse comm to my code. I’ll have to see whether just adding this routine would take care of the issue.