  A better understanding of interfacial mechanisms is needed to improve the
performances of electrochemical devices. Yet, simulating an electrode surface
at fixed electrolyte composition remains a challenge. Here we apply a finite
electric field to a single electrode held at constant potential and in contact
with an aqueous ionic solution, using classical molecular dynamics. The
polarization yields two electrochemical interfaces on opposite sides of the
same metal slab. While the net charge on one electrode surface is the opposite
of the net charge on the other, maintaining overall charge neutrality of the
metal. The electrode surface charges fluctuations are compensated by the
adsorption of ions from the electrolyte, forming a pair of electric double
layers with aligned dipoles. This opens the way towards the efficient
simulation of electrochemical interfaces using any flavor of molecular
dynamics, from classical to first principles-based methods.
