Assessing a First-Principles Model of an Electrochemical Interface by Comparison with Experiment

Electrified interfaces are central for electrocatalysis, batteries, and molecular electronics. Experimental characterization of these complex interfaces with atomic resolution is highly challenging. First-principles modeling could provide a link between the measurable quantities and an atomic scale understanding. However, such simulations are far from straightforward. Although approaches that include the effect of the potential and the electrolyte have been proposed, detailed validation has been scarce and indirect since atomically resolved experimental studies of systems that can be convincingly simulated are scarce. We introduce here the adsorption of pyridine on Au(111) as a convenient and relevant model: the adsorption mode of pyridine switches as a function of the electrochemical potential. We demonstrate that the primitive surface charging model gives qualitatively correct results at a low complexity. For quantitative agreement, however, the model needs to include a more realistic description of the electrical double layer. Approximating the latter through the linearized Poisson-Boltzmann equation leads to a quantitative improvement, lowering the error in the transition potential from 1 V to an acceptable 0.3 V. Hence, we demonstrate the qualitative usefulness of the surface charging method and the excellent agreement that can be obtained by slightly more sophisticated electrolyte models.