Atom Id s,

​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.
Thanks again,

Minimization and Verlet (dynamics) are not any different
in how they handle reverse comm.