  We report a new Quantum Mechanical/Molecular Dynamics (QM/MD) simulation loop
to model the coupling between the electron and atom dynamics in solid/liquid
interfacial systems. The method can describe simultaneously both the quantum
mechanical surface polarizability emerging from the proximity to the
electrolyte, and the electrolyte structure and dynamics. In the current set up
Density Functional Tight Binding calculations for the electronic structure
calculations of the surface are coupled with classical molecular dynamics to
simulate the electrolyte solution. The reduced computational cost of the QM
part makes the coupling with a classical simulation engine computationally
feasible and allows simulation of large systems for hundreds of nanoseconds. We
tested the method by simulating both a non-charged graphene flake and a
non-charged and charged infinite graphene sheet immersed in an NaCl electrolyte
solution. We found that, when no bias is applied, ions preferentially remained
in solution and only cations are mildly attracted to the surface of the
graphene. This preferential adsorption of cations vs anions seems to persist
also when the surface is moderately charged and rules out any substantial
ions/surface charge transfer.
