Abstract
The Axilrod-Teller-Muto non-additive triple-dipole dispersion energy term is modified to model the available non-expanded triple-dipole ab initio perturbation results of O'Shea and Meath for the lowest quartet state of H3 and hence accounts for the charge-overlap effects at small interatomic separations. It is suggested that the new energy term can be used for trimers of other spherically symmetric systems (for example inert gas trimers) by means of a reduced coordinate approach.