Image charge effects under metal and dielectric boundary conditions.

Image charge effect is a fundamental problem in electrostatics. However, a proper treatment at the continuum level

for many-ion systems, such as electrolyte solutions or ionic liquids, remains an open theoretical question. Here we

demonstrate and systematically compare the image charge effects under metal and dielectric boundary conditions (BCs),

based on a renormalized Gaussian fluctuation theory. Our calculations for a simple 1:1 symmetric electrolyte in the

point charge approximation show that the double layer structure, capacitance and interaction forces between like-

charged plates, depend strongly on the type of boundaries, even in the weak-coupling regime. Like-charge attraction is

predicted for both metal and dielectric BCs. We provide these results to serve as a baseline for comparison with more

realistic molecular dynamics simulations and experiments