Practical Considerations for Continuum Models Applied to Surface Electrochemistry

Modelling the electrolyte at the electrochemical interface remains a major challenge in ab initio simulations of charge transfer processes at surfaces. Recently, the development of hybrid polarizable continuum models/ab initio models have allowed for the treatment of solvation and electrolyte charge in a computationally efficient way. However, challenges remain in its application. Recent literature has reported that large cell heights are required to reach convergence, which presents a serious computational cost. Furthermore, calculations of reaction energetics require costly iterations to tune the surface charge to the desired potential. In this work, we present a simple capacitor model of the interface that illuminates how to circumvent both of these challenges. We derive a correction to the energy for finite cell heights to obtain the large cell energies at no additional computational expense. We furthermore demonstrate that the reaction energetics determined at constant charge are easily mapped to those at constant potential, which eliminates the need to apply iterative schemes to tune the system to a constant potential. These developments together represent more than an order of magnitude reduction of the computational overhead required for the application of polarizable continuum models to surface electrochemistry. Charge density isosurface illustrating the strong dipole moment exhibited by CO2 on Pt (111). The yellow surface corresponds to electron density equal to 0.01 eÅ−3, whereas the blue corresponds to negative electron density of the same magnitude. The strong dipole moment gives a potential dependence of CO2 adsorption, despite no formal proton/electron transfer process occurring. These potential dependencies can be seen with continuum solvation techniques, which we explore in this work.