For starters I would consider carefully reading Tersoff’s papers to see how a bond-order potential works. Then Brenner’s REBO papers, then read Stuart’s AIREBO paper to see how it is different from both Tersoff and Brenner. In Lammps, the potentials are separate and do not share their respective bond-orders. Since bond order is THE key to calculating the correct interaction energies and forces and they are not shared in LAMMPS between the potentials. you are SOL if you want to mix the two potentials. But then again, as Axel mentions, its almost impossible to tell what you are even trying to do, and why you are trying to do it, so maybe mixing the two potentials isn’t really what you are trying to do at all. I am guessing you want long range interactions for C-C. With more info we might be able point you in a better direction.