Molecular dynamics simulations of electrical double layer capacitance and polarizability.

Electrical double layers, which form in response to surface charge on a conductor in contact with electrolyte solution, influence the thermodynamics and kinetics of electrochemical processes. Here we use atomistic molecular dynamics simulations to investigate the electrode-electrolyte interface, in which we control the total excess charge on the electrode, and dynamically distribute charges to individual electrode atoms to screen electric fields inside the metal. We measure the local dielectric constant in the electrolyte using a novel AC electric field method, which is substantially more efficient compared to traditional dipole fluctuation or static response methods. The dielectric response in the double layer is markedly anisotropic, enhanced in the in-plane direction (ε≈110) and suppressed in the out-of-plane direction (ε≈3). Finally, we measure the double layer differential capacitance, which we use together with the measured dielectric constants, to assess classical double layer theories (Gouy-Chapman and Stern models).