A semiclassical Thomas-Fermi model to tune the metallicity of electrodes in molecular simulations.

Spurred by the increasing needs in electrochemical energy storage devices, the electrode/electrolyte interface has received a lot of interest in recent years. Molecular dynamics simulations play a proeminent role in this field since they provide a microscopic picture of the mechanisms involved. The current state-of-the-art consists in treating the electrode as a perfect conductor, precluding the possibility to analyze the effect of its metallicity on the interfacial properties. Here we show that the Thomas-Fermi model provides a very convenient framework for accounting for the screening of the electric field at the interface and differenciating good metals such as platinum from imperfect conductors such as graphite. The model is validated against analytical results for two simple systems, namely an empty capacitor and a single charge between two electrodes. We then show the impact of Thomas-Fermi screening on the electrochemical double-layer structure and capacitance for a series of electrolytes in contact with a graphite electrode. The proposed model opens the door for a quantitative prediction of the capacitive properties of new materials for energy storage.