CALCULATION OF THE SURFACE FLOW OF A DILUTE GAS IN MODEL PORES FROM 1ST PRINCIPLES .1. CALCULATION OF FREE-MOLECULE FLOW IN AN ADSORBENT FORCE-FIELD BY 2 METHODS

An ab initio calculation of the flow of a dilute (i.e., collisionless) gas, through a channel in which a force field due to the walls acts on the flowing molecules, can be carried out either by a molecular path tracing (MPT) method or by a Monte Carlo (MC) method. The latter yields diffusion coefficients both from transmission probabilities and also by a direct application of random walk theory. The two methods are described here as applied to a two-dimensional slit in which the adsorbate-adsorbent potential is represented by a triangular well. Although highly simplified, this model retains the essential features of a more realistic system. It is shown that discrepancies between the MPT method as usually applied and the MC method can be attributed to end-effects" and a previously described procedure which corrects for these in MPT calculations is verified here by the MC results. The significance of end-effects in the wider context of model porous materials is briefly discussed. © 1979."