Determination of long-range intermolecular interaction energies using RPA/moment function methods. Application to H 2O, H 2O 2 and H 2O/H 2O 2 mixtures

Abstract

The fully expanded expression for the Boltzmann-averaged pairwise intermolecular interaction energy of two molecules of arbitrary symmetry in the long-range (interaction < kT) limit has recently been determined explicitly as a series in r − n ( r is the intermolecular separation) for n < 11. The resultant expression contains only multipolar products (point moment functions: PMFs) and energy terms which are characteristic of the ground state and excitation properties of the isolated molecules. These quantities are determined for H 2O and H 2O 2 using the single particle-hole RPA method, and the interaction energy contributions determined by direct state summation. Static electric dipole polarizabilities are determined as a by-product of the procedure, and are shown to agree closely with finite field results using a comparable basis. For the chiral H 2O 2/H 2O 2 system, the r −6 and r −9 discrimination energies are also calculated, suggesting that the r −9 contributions could well exceed the r −6 discriminatory terms for separations less than 20 au.