Ab initio intermolecular potential of the ethylene dimer

Abstract

The intermolecular potential of the ethylene dimer in the ground state has been computed nonempirically with the exchange perturbation theory. The principal terms of interaction energy considered are the Coulombic and exchange energies as the first order ones, then the dispersion energy as the second order one, and other higher terms are neglected. Computations were made exactly without multipole expansion approximation, to the order of the square of intermolecular overlap integrals. Nine orientations of molecules are considered. Three kinds of basis set, i.e., STO-3G, 4-31G, and 4-31G* were employed, and the results were compared to each other and also with those by other authors. The potential minimun was obtained for all orientations against results of other authors, and the most stable one has the slightly shifted parallel structure near to that found in the ethylene crystal.