Dealing with Coulumbic interactions in the Core-shell model

I don’t want all of the type1-type2 coulumbic interactions to be disabled, just between certain particles. In this diagram, Ac-As, Bc-Bs, Cc-Cs would be disabled. Since Ac and Cs are the same type-pair as Ac-As they would have their interaction type-pair disabled, I don’t want that.

Alternatively, I could make a new coulumbic interaction that would not diverge as r->0

-mike w.