Accurate Calculation of Weak Intermolecular Interactions

Abstract

A variety of weak intermolecular interactions is investigated using both high-accuracy and approximate methods. A high accuracy potential energy curve for the interaction of two krypton atoms was produced as a prerequisite for the computation of the most important thermophysical properties of the krypton gas. To obtain the desired spectroscopic accuracy around the potential miminum, corrections to the “gold standard” CCSD(T) were calculated, including higher-orders of coupled-cluster theory and the inclusion of relativistic effects. As an additional requirement for the computation of the second dielectric virial coefficient, similar steps were taken to produce an accurate analytic form for the interaction-induced isotropic pair polarizability for the krypton dimer. The resulting potential and polarizability functions were among the most accurate in the literature at time of publishing and the thermophysical properties were in marked agreement with experimental data. The interactions of CO2 and models of metal-organic frameworks were explored using a variety of wavefunction and density functional methods as a way to evaluate the adequacy of these methods, and the potential multireference character of such models was considered. The interaction energy is decomposed using symmetry-adapted perturbation theory (SAPT) to provide insight into the character of the interactions. Lastly, recent work in the advancement and expansion of SAPT is detailed. This work includes the implementation of the second-order SAPT complete exchange terms using generalized Coulomb and exchange matrices and density-fitting, as well as the extension of the recent first-order spin-flip SAPT exchange energy beyond the single-exchange approximation.