[gmx-users] adding walls? to EDL simulation?

[Andreas]

hello users,

I have been building a small system with a graphene layer on each side 
(Z-offset water and ions in between). i know which atoms in the top file 
belongs two which layer and can easily add a charge. As i have pbc 
conditions i would have in my current system both graphene layers 
directly next to each other. should i simply make the box bigger, after 
having added the solvent  (how to decide how big?) and create a sort of 
empty space (does a big empty space effect the simulation negatively?)  
or can/should an pbc=xy be used with two walls, if so how to setup those 
walls?

best regards

Andreas