The SPME algorithm in DL_POLY_2 does not work for aperiodic (IMCON=0) or slab (IMCON=6) boundary conditions.
Action:
If the system must have aperiodic or slab boundaries, nothing can be
done. In the latter case however, it may be acceptable to represent
the same system with slabs replicated in the z direction, thus
permitting a periodic simulation.