This is similar to a question that was asked a few days ago, but is
there a way to freeze an atom (setforce group 0.0 0.0 0.0) and be able
to output the force _before_ the setforce fix clears it to zero? For
doing atomistic mechanical testing, this would be necessary for
determining how much force is needed to hold a molecule in place as it
is moved through a system over time. (run x every 1000
displace_atoms ...) Any ideas on how to accomplish this?