  In this study, we examined the thickness of the electrical double layer (EDL)
in ionic liquids using density functional theory (DFT) calculations and
molecular dynamics (MD) simulations. We focused on the BF4- anion adsorption
from 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) ionic liquid on
the Au(111) surface. At both DFT and MD levels, we evaluated the
capacitance-potential dependence for the Helmholtz model of the interface.
Using MD simulations, we also explored a more realistic, multilayer EDL model
accounting for the ion layering. Concurrent analysis of the DFT and MD results
provides a ground for thinking whether the electrical double layer in ionic
liquids is one- or multi-ionic-layer thick.
