  Implicit solvation is an effective, highly coarse-grained approach in
atomic-scale simulations to account for a surrounding liquid electrolyte on the
level of a continuous polarizable medium. Originating in molecular chemistry
with finite solutes, implicit solvation techniques are now increasingly used in
the context of first-principles modeling of electrochemistry and
electrocatalysis at extended (often metallic) electrodes. The prevalent ansatz
to model the latter electrodes and the reactive surface chemistry at them
through slabs in periodic boundary condition supercells brings its specific
challenges. Foremost this concerns the diffculty to describe the entire double
layer forming at the electrified solid-liquid interface (SLI) within supercell
sizes tractable by commonly employed density-functional theory (DFT). We review
liquid solvation methodology from this specific application angle, highlighting
in particular its use in the widespread {\em ab initio} thermodynamics approach
to surface catalysis. Notably, implicit solvation can be employed to mimic a
polarization of the electrode's electronic density under the applied potential
and the concomitant capacitive charging of the entire double layer beyond the
limitations of the employed DFT supercell. Most critical for continuing
advances of this effective methodology for the SLI context is the lack of
pertinent (experimental or high-level theoretical) reference data needed for
parametrization.

Chemical Physics;Computational Physics