You don't care about the radii for electrostatics, so you just ignore it
when you pick your maximum search distance. The radius has nothing to do
with energy evaluations, just with searches for nearby pairs.
Of course - but the radius attribute is used for both purposes. It seems
weird to require the user to specify a dummy radius attribute for
electrostatics (which, as you say, isn't needed for the actual energy
evaluation) just to make the nonbonded list work. Plus, I imagine the
nonbonded list can be made more efficient if it knows that all "spheres"
are the same (e.g. have zero radius). So either we keep both sphere and
non-sphere nonbonded lists, or the implementation can be asked to ignore
the radii (not sure what your earlier email meant, but perhaps taking a
FloatKey* and having NULL mean "ignore radius").