Ab initio calculation of intermolecular dispersion energy and induction energy of nitramide dimer

The dispersion energies, induction energies and their exchange counterparts (exchange-dispersion and exchange-induction energies) between two interacting nitramide molecules at several separations are derived based upon symmetry-adapted perturbation theory (SAPT). The results show that (1) the effect of intramonomer electron correlation on dispersion energies and induction energies for nitramide dimer system is remarkable especially in the region near the van der Waals minimum distance (0.42 nm). (2) At smaller separations the dispersion energies and the induction energies are largely quenched by their exchange counterparts, and this case in induction interaction is much more remarkable than in dispersion interaction. (3) Since at shorter distances there exists the strong short-range interaction due to electron transfer which quickly decays and even disappears at larger separations, the two different R-dependency formulae of induction energies were found: one is cu. R^−12.7 at short distances, and the other cu R^−7.0 at large separations. The latter R-dependency is similar to that (ca. R^−7.2) of dispersion. (4) In the case of strong polar interaction existing in nitramide dimer, the “true” induction correlation terms of higher order than ¹E_ind⁽²²⁾ may be important.