Charge-transfer model for carbonaceous electrodes in polar environments

A realistic treatment of metallic and semimetallic systems in polar environments requires an explicit treatment of charges induced into the metallic surface. In classical electrostatics, a metallic surface is properly described if the electric field perpendicular to the surface vanishes. For nanoscale materials, however, charge screening is imperfect because the nanoscale object's surface density of states is finite. Here, we demonstrate that from quantum considerations a classical mean-field charge-transfer model can be extracted, which is demonstrated for graphene and metallic single-wall carbon nanotubes. The model is easily parametrized and gives an approximate description of the binding of point charges on these structures. Potential applications include the modeling of charged or fully biased nanoscale systems in a polar environment, which we demonstrate by simulating a water droplet in a biased graphene nanocapacitor at a fraction of the computational cost of a fully quantum-mechanical treatment.