Accurate Potentials for Argon−Water and Methane−Water Interactions via ab Initio Methods and Their Application to Clathrate Hydrates

Abstract

High level ab initio quantum mechanical calculations were used to determine the intermolecular potential energy surface between argon and water, corrected for many-body interactions, to predict monovariant and invariant phase equilibria for the argon hydrate and mixed methane−argon hydrate systems. A consistent set of reference parameters for the van der Waals and Platteeuw model, = 1077 ± 5 kcal/mol and = 1294 ± 11 kcal/mol, were developed for Structure II hydrates and are not dependent on any fitted parameters. Our previous methane−water ab initio energy surface has been recast onto a site−site potential model that predicts guest occupancy experiments with improved accuracy compared to previous studies. This methane−water potential is verified via ab initio many-body calculations and thus should be generally applicable to dense methane−water systems. New reference parameters, = 1203 ± 3 kcal/mol and = 1170 ± 19 kcal/mol, for structure I hydrates using the van der Waals and Platteeuw model were also dete...