Calculating adsorption isotherms using Lennard Jones particle density distributions.

The computation of particle density distributions in pore channels is a fundamental post process practice in molecular adsorption simulations. The distributions, although not appropriate for direct experimental interrogation, when expressed in variable temperature, may be used to evaluate thermodynamic properties. As with molecular simulations, we can spotlight any frame or region of interest inside the computational cell, the distributions and subsequently the thermodynamic evaluations can be pore or site specific. This allows us to establish correlations for the adsorption capacity, on different pore partitions and surface textures and compare strengths of explicit interactions. We confirm this assumption using adsorption simulations of Lennard Jones particles such as argon in the dual cylindrical cavity of ZIF-69. We initiate the computations from the density distribution functions and reproduce full curves of adsorption isotherms which correlate well with the direct simulations. The computations are fast and implemented using linear van' t Hoff plots for the surface coverage at a sequence of pressures.