Different potentials

I’m trying to calculate silicon oxide. Is it possible to use different potentials during the procedures: melting-quench (BKS potential), relaxation (ReaxFF potential), MSD (ReaxFF potential)? Or should I use only one potential during 3 calculations?

In this paper I have used a Buckingham potential to create amorphous silica by quenching the melt SiO2 and anneal the surface. Then the solid silica surface was described with the Coulomb and LJ potentials in a subsequent simulation with an organic interface.
Whether or not this is a good choice for you, depends on the physical phenomenon you want to describe. In the case I cited, the protocol was to create a realistic silica surface with an appropriate potential, and then switch to a different one to simulate the interaction between the solid surface and the interface of a liquid crystal.

Don’t use ReaxFF unless you want to model chemical reactions. ReaxFF potentials are not very transferable and primarily trained for reactions not bulk properties.