Impact of charging in constant potential electrochemistry modeling

A huge issue in computational electrochemistry is that different modeling approaches, used to study electron transfer reactions, give different results and cannot easily be reconciled with each other. One discrepancy is their handling of interface charging. I study charging of electrolyte-Cu(111) interfaces with electrons and cations (or positive continuum charge) and observe that the charging energy depends strongly on the electrolyte model. When the electrolyte is a film containing water and KOH ions, there is a close to one-to-one stabilization (1 eV/V) of the energy with more negative potential, which fits with an ideal charging behavior, where the inserted electron-cation pairs do not repel each other. This is in strong contrast to the charging of an interface with implicit solvent, where the lack of electric-field screening result in large repulsion, which could give the erroneous impression that charging can be ignored in electrochemistry modeling. I further consider constant potential CO2 adsorption to highlight the importance of charging and using an electrolyte model with water and ions, and show that other modeling approaches gives significantly different and less stable CO2 adsorption energies.