  Ab initio modeling of electrochemical systems is becoming a key tool for
understanding and predicting electrochemical behavior. Development and careful
benchmarking of computational electrochemical methods are essential to ensure
their accuracy. Here, using charging curves for an electrode in the presence of
an inert aqueous electrolyte, we demonstrate that most continuum models, which
are parameterized and benchmarked for molecules, anions, and cations in
solution, undersolvate metal surfaces, and underestimate the surface charge as
a function of applied potential. We examine features of the electrolyte and
interface that are captured by these models, and identify improvements
necessary for realistic electrochemical calculations of metal surfaces.
Finally, we reparameterize popular solvation models using the surface charge of
Ag(100) as a function of voltage to find improved accuracy for metal surfaces
without significant change in utility for molecular and ionic solvation.
