First-order Coulomb interaction energies for atoms and diatomic molecules

Abstract

Abstract Gaussian multipoles (differentiated Gaussian functions) are used to describe molecular charge densities. Their use simplifies considerably the calculation of the first-order Coulomb interaction energy between pairs of molecules, which is an important part of the intermolecular potential. Methods are developed for expressing the charge densities of linear molecules economically and accurately using Gaussian multipoles. Partial-wave expansions are calculated for the first-order Coulomb interaction energies of H2-He, N2-He, CO-He, H2-H2, N2-N2 and CO-H2, and their convergence is discussed as a function of molecular anisotropy and intermolecular separation. It is confirmed that the multipole approximation is very inaccurate for physically important dimer separations.