You can use pair_hybrid overlay to superpose potentials. I don't know
what a Sutherland potential is - the list of LAMMPS pair potentials
is on the doc page. You can figure out whether LAMMPS has something
similar easier than I can.
Re: ion interactions, I still don't know what you're asking. Several
LAMMPS potentials have Coulomb options. If the pairwise interaction
is something other than Coulomb's law, then you'll need to say what