  We study the salt-dependent conformations of dilute flexible polyelectrolytes
in solution via computer simulations. Low concentrations of multivalent salt
induce the known conformational collapse of individual polyelectrolyte chains,
but as the salt concentration is increased further this is followed by a
reexpansion. We explicitly demonstrate that multivalent counterions can
overcompensate the bare charge of the chain in the reexpansion regime. Both the
degree of reexpansion and the occurrence of overcharging sensitively depend on
ion size. Our findings are relevant for a wide range of salt-induced
complexation phenomena.
