Mirroring their role in electrical and optical physics, two-dimensional
crystals are emerging as novel platforms for fluid separations and water
desalination, which are hydrodynamic processes that occur in nanoscale
environments. For numerical simulation to play a predictive and descriptive
role, one must have theoretically sound methods that span orders of magnitude
in physical scales, from the atomistic motions of particles inside the channels
to the large-scale hydrodynamic gradients that drive transport. Here, we use
constraint dynamics to derive a nonequilibrium molecular dynamics method for
simulating steady-state mass flow of a fluid moving through the nanoscopic
spaces of a porous solid. After validating our method on a model system, we use
it to study the hydrophobic effect of water moving through pores of
electrically doped single-layer graphene. The trend in permeability that we
calculate does not follow the hydrophobicity of the membrane, but is instead
governed by a crossover between two competing molecular transport mechanisms.Comment: 6 pages, 3 figure