Cosine law for the atomically rough nanopore: Modeling lattice vibrations with a modified Lowe-Andersen thermostat

This work proposes a simulation technique that can be used to compute the thermal interaction between a rarefied gas and an atomically rough nanopore. A standard pore geometry, the slit pore, is used to derive the correct version of the cosine law in case the wall consists out of individual atoms. Having the correct cosine law drastically reduces the computational cost of calculating the gas-wall pair interaction in the rarefied gas regime since it is no longer necessary to consider a fully flexible crystal lattice. By considering only a small modification of the Lowe-Andersen thermostat, a well-known simulation technique that uses diffusive gas-heatbath collisions, we show how it can be used to incorporate lattice flexibility even if the wall is modeled as a rigid lattice.