What is the CHARMM version? One possible solution might be an upgrade; the latest release is c44b2.

We have seen some issues that are dependent on the mpi implementation (openmpi, mvapich2, intel mpi) and the version number. Trying an alternative mpi library may be useful.

I have limited experience with Drude simulations, and do not have much insight on this issue.

Rick Venable
computational chemist