Computational evaluation of Henry's constants and isosteric heats of sorption for Lennard-Jones sorbates in Na-Y zeolite

Henry's constants and isosteric heats of sorption at infinite dilution are calculated for Lennard-Jones sorbates, including the rare gases Ar, Kr and Xe, in Na-Y zeolite. Isosteric heats of sorption are calculated as a function of sorbate size by molecular dynamics (MD) as well as from the temperature dependence of Henry's constants. The MD approach samples the low potential energy regions which form part of the dynamically connected pore space. In contrast, the Henry's constants are evaluated from the infinite dilution limit of the Widom particle insertion method and therefore can, in principle, sample all available, low potential energy pore regions regardless of dynamical connectivity. We show that the difference in the results obtained by the two approaches depends significantly on sorbate size. For a certain range in the sorbate size parameter, the extent of consistency between the two approaches will be sensitive to both temperature and the MD run lengths, providing an interesting illustration of the distinction between available and dynamically connected pore volumes.