ON THE TRIPLE-DIPOLE DISPERSION ENERGY FOR NONSPHERICAL MOLECULES WITH AN APPLICATION TO THE O-2-O-2-O-2 INTERACTION

The symbolic computation language MAPLE is used to verify an exact exp ression for the triple-dipole dispersion energy (DDD), derived previou sly, for interactions involving up to three linear (C-state) molecules . The derivation of the original expression, which is complicated, was carried out manually and involved many tedious algebraic steps. Recen t results for the anisotropic triple-dipole dispersion energy coeffici ents for the O-2-O-2-O-2 interaction, together with the exact expressi on for the DDD itself, are used to illustrate the importance of the an isotropic dispersion energy, relative to the isotropic triple-dipole e nergy, and to help investigate the validity of a frequently used avera ge energy approximation for the anisotropic DDD. The discussion includ es comments concerning the importance of the DDD energy in the context of the contribution of non-additive energies to the properties of mat ter. (C) 1997 Elsevier Science B.V.