  Employing recent advances in nonequilibrium response theory and
nonequilibrium ensemble reweighting, we study the dynamic and static
correlations that give rise to an electric field dependent ionic conductivity
in electrolyte solutions. We consider solutions modeled with both implicit and
explicit solvents, with different dielectric properties, and at multiple
concentrations. Implicit solvent models at low concentration and small
dielectric constant exhibit strongly field-dependent conductivities. We
compared these results to the Onsager-Wilson theory of the Wien effect, which
provides a qualitatively consistent prediction at low concentrations and high
static dielectric constants, but is inconsistent away from these regimes. The
origin of the discrepancy is found to be increased ion correlations under these
conditions. Explicit solvent effects act to suppress nonlinear responses,
yielding a weakly field-dependent conductivity over the range of physically
realizable field strengths. By decomposing the relevant time correlation
functions, we find that the insensitivity of the conductivity to the field
results from the persistent frictional forces on the ions from the solvent. Our
findings illustrate the utility of nonequilibrium response theory in
rationalizing nonlinear transport behavior.
