Calculation of the dispersion-dipole coefficients for interactions between H, He, and H2

Abstract

Collisions between atoms and molecules create an induced dipole moment which, at long range separations, stems, in part, from the van der Waals interactions between the colliding species. This contribution is known as the dispersion dipole moment and is of the order R−7, where R is the separation between particles. Although there have been several approximate calculations of the dispersion-dipole coefficients which govern this contribution, and are the counterparts to the van der Waals dispersion-energy coefficients, there have been few ab initio calculations. In this article we present highly accurate results, based on explicitly electron-correlated wave functions, for the dispersion-dipole coefficients pertaining to interactions between pairs chosen from H, He, and H2. We also obtain values with some of the currently used approximate formulas. A comparison shows that these values differ, in general, by a significant amount (∼20–∼40 %) from the accurate ones. We also tabulate values of the dipole–dipole-quadrupole polarizability tensor (B) for imaginary frequency (iω) for a range of frequencies appropriate to a 64-point Gauss–Legendre quadrature for H, He, and H2. These values were used in certain numerical integrations we made to verify our original results which had been obtained by analytic integration—they may, however, be useful in other contexts. For H–H2 and H2–H2, these are the only ab initio calculations of the dispersion-dipole coefficients of which we are aware.