QM/MM electrostatic coupling and number of replicas

[Frank Uhlig]

Dear CP2k'lers,

I am curious about the QM/MM capabilities of CP2K and would appreciate
some more detailed explanation on the treatment of the coupling
between periodic images.
As I understood, the keyword REPLICA in section

CP2K_INPUT / FORCE_EVAL / QMMM / PERIODIC

will set the number of replicas included in the real-space part of the
evaluation of the QM/MM interaction and all other periodic replicas of
the MM part (i.e. long-range contribution) will be handled in
reciprocal space. From a technical point of view, what will happen if
one sets REPLICA to 0? Will there be no contribution in the real-space
sum or only the contribution from the original system (i.e. the
non-replicated MM part).

Does, and if so how, this keyword (REPLICA) influence the calculation
of the electrostatic interaction amongst the QM periodic images?

Best regards and thanks in advance,

Frank