  Multivalent ions in solutions with polyelectrolytes (PE) induce electrostatic
correlations that can drastically change ion distributions around the PEs and
their mutual interactions. Using coarse-grained molecular dynamics simulations,
we show how in addition to valency, ion shape and concentration can be
harnessed as tools to control like-charged PE-PE interactions. We demonstrate a
correlation between the orientational ordering of aspherical ions and how they
mediate the effective PE-PE attraction induced by multivalency. The interaction
type, strength, and range can thus be externally controlled in ionic solutions.
Our results can be used as generic guidelines to tune the self-assembly of
like-charged polyelectrolytes by variation of the characteristics of the ions.
