A Refined Intermolecular Interaction Potential for Methane: Spectral Analysis and Molecular Dynamics Simulations

Abstract

Abstract The previously constructed methane interaction potential energy surface calculated at the second‐order Møller‐Plesset (MP2) perturbation theory has been significantly improved in two aspects. First, all ab initio potential energy data are calculated by the supermolecule counterpoise corrected coupled cluster with single and double and perturbative triple excitations [CCSD(T)] method with Dunning’s correlation‐consistent aug‐cc‐pVXZ, X=D, T, Q, 5, basis sets and extrapolated to the complete basis set (CBS) limits with a convergence precision of 0.01 kcal/mol. Second, instead of the simple 4‐site model proposed in the previous study, a 5‐site model has been used to represent the ab initio potential data. The simulated infrared spectrum using the potential energy surface seems to be broadly in line with the spectral features observed in experiments. Molecular dynamics simulations using the ab initio force field show quantitative agreements with experiments. The properties examined in this paper include the atom‐to‐atom radial distribution functions in liquid and supercritical phases and the self‐diffusion coefficients over a wide range of thermodynamic conditions. It is shown that the refined ab initio force field can be applied to study fluid properties in different phases.