Ionic bonds in molecular mechanics

Dears Sirs,

I'd liketo simulate interaction between nanoclusters from metal oixde (for example, Al2O3). As i understand from tutorials for Discover and Forsite, I need to type atoms, to remove bonds between them and

select No from both the Calculate  forcefield types in Automation tab. This thing should be done only for Compass forcefield or for any other forcefileds (I'm going to use Universal forcefiled)?

Thank you for help in advance,

Ekaterina