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
it is.
Steve