Your answer was very helpful, and I'm on the right track, thank you!

I have a question on your suggestion:
As I'm interested in performing a repeated set of calculations (e.g. varying some of the
parameters of the problem), everything works if I replace '_Z2' by '_Z4' and then '_Z6', etc.
Would it be possible to devise a more automated procedure of doing this without manually
changing this '_Zn'?

Thanks a lot!