Local MP2 Study of Naphthalene, Indole, and 2,3-Benzofuran Dimers

Abstract

The ground-state structures of the van der Waals dimers of naphthalene, indole, and 2,3-benzofuran have been optimized at the local MP2/6-31G* level of theory without any symmetry restrictions. The binding energies of complexes were evaluated at the local MP2 approximation using 6-31G*, 6-311G**, cc-pvtz(-f), and aug-pvtz(-f) basis sets. The binding energies are strongly dependent on the basis set size and not completely converged even for the largest basis set tested. The relative stability of studied complexes is, however, similar for the two largest basis sets used in this study. It was found that in all cases the major contribution to the binding energy is the correlation energy representing from 90 to 100% of all stabilization energy. Among two types of studied complexes, parallel and T-shaped, the parallel complexes are the most stable ones due to better correlation stabilization, with one of the naphthalene parallel dimers being the most stable out of all studied complexes showing the stabilization energy of −8.02 kcal/mol. All indole and T-shape 2,3-benzofuran dimers evidence N−H and C−H−π hydrogen bonds as follows from the geometry changes and the charge transfer from one molecule to another. The Kitaura−Morokuma analysis of SCF binding energy shows that T-shape complexes are better stabilized by electrostatic interactions and less destabilized by exchange repulsion compared to parallel ones.