[DFTB-Plus-User] Electric field in periodic calculations

[sn]

Dear DFTB users,

I am currently trying to use the external electric field for periodic 
calculations.
My system is a slab normal to z direction, with a big vacuum to avoid 
interactions.
I would like to apply an external electric field along z direction, and 
I have some questions:

1- Do I have to set the vacuum layer to be quite infinite to be sure the 
field to be constant 20 A° around the supercell's center?
2- My supercell is monoclinic. Each time I try to launch a calculation I 
have the following message: "Interaction between atoms .. and .. crosses 
the saw-tooth discontinuity in the electric field." whatever the 
position of the supercell origin... What do I do wrong? Or is it just an 
uncompatibility with monoclinic cells?

Thank you...

Sébastien Nénon