Electrolytes confined between polarizable surfaces in slit pores with anisotropic permittivity tensor.

We present a method that enables efficient simulations of coarse-grained electrolyte solutions inside a narrow slit pore with an anisotropic dielectric permittivity tensor. The electrostatic equations for polarizable surfaces are solved using a 2D periodic Green's function method combined with a slab-corrected anisotropic 3D Ewald summation. We apply this approach in Monte Carlo simulations to study 1:1 electrolytes confined between both polarizable dielectric and metallic surfaces. Our results show that dielectric anisotropy strongly reshapes the double-layer structure. While the individual ion-image interactions depend strictly on the bulk-like parallel permittivity, the suppression of the perpendicular permittivity dramatically amplifies direct in-plane ion-ion correlations. Under strong anisotropy, these lateral correlations dominate the thermodynamics completely, rendering the structural profiles of mutually opposing dielectric and metallic boundaries practically identical by forcing the smaller cations directly into the contact plane of the larger anions.