Dispersion Interactions between Rare Gas Atoms: Testing the London Equation Using ab Initio Methods

Abstract

A computational chemistry experiment is described in which students can use advanced ab initio quantum mechanical methods to test the ability of the London equation to account quantitatively for the attractive (dispersion) interactions between rare gas atoms. Using readily available electronic structure applications, students can calculate the interaction energies of the four rare gas dimers (He2, Ne2, Ar2, and Kr2) and the six heterodimers at internuclear distances large enough to warrant neglecting repulsive interactions. The London C6 coefficients, obtained from experimental polarizability volumes and ionization energies, are used with the calculated interaction energies to test the London equation. The role of the higher-order C8 term in accounting for dispersion interactions in the dimers is examined. In addition, students calculate a portion of the argon dimer interaction potential at large internuclear separations and compare this potential with that predicted by the London equation.