Local Monte Carlo for electrostatics in anisotropic and nonperiodic geometries

We present an implementation of a local Monte Carlo algorithm for simulating charged particles in anisotropic and nonperiodic geometries. Specifically, we consider a quasi-two-dimensional periodic slab geometry with an either infinite or finite third dimension. For the infinite case, we show that the method generates accurate electrostatics equivalent to standard two-dimensional Ewald formulas. We then implement constant charge or constant potential (Dirichlet) boundary conditions, which frequently occur in experimental studies of charged complex fluids or polyelectrolytes. As a demonstration of the versatility of the approach, we compute ion density profiles in front of oppositely charged surfaces (the electric double layer) and find excellent agreement with theory in known analytic limits.