Recent developments in modeling the electric double layer with density functional theory

Improving our fundamental understanding of charge transfer processes at the electrified double layer currently relies heavily on density functional theory (DFT) simulations, as many in situ and operando spectroscopic methods are hindered by the aqueous electrolyte. However, modeling charged states with semi-local DFT faces serious challenges, and several bifurcating strategies have been developed in an attempt to address them. In this Mini Review, we present a highly abridged overview of some of the challenges faced when modeling charge transfer processes across the electric double layer with DFT. Focusing primarily on charge transfer kinetics, we highlight polarizable continuum models (PCMs) and their use in evaluating energetics in the adiabatic limit of electron transfer, i.e. treating electrons grand canonically during a coupled proton-electron transfer (CPET) reaction. We highlight their use in understanding electrocatalytic processes, in particular the ability to localize transition states at constant potential. Finally, we present our outlook on opportunities for improvement in this critical research area, and nascent methods being developed to test the validity of PCMs and evaluating energetics in the grand canonical ensemble.