Ab initio study of the π–π interaction in the pyridine dimer: Effects of bond functions

Abstract

A systematic ab initio study was carried out to investigate the π–π intermolecular interaction in the pyridine dimer. Potential energy curves were calculated for eight major configurations at second-order Møller–Plesset approximation (MP2) using various large basis sets augmented with bond functions. The basis set superposition error (BSSE) was considered by the counterpoise method. The study shows that bond functions can effectively give accurate description of π–π interactions. The intermolecular energies at the MP2 potential minima of the eight configurations were recalculated using the coupled-cluster method including single, double, and perturbative triple configurations, CCSD(T), with the aug-cc-pVDZ basis set augmented with the bond functions {6s6p4d2f}. Two most stable geometries were found to be antiparallel-displaced, with the CCSD(T) interaction energies of −3.05 and −2.95kcal/mol, respectively. The CCSD(T) interaction energies of other configurations were found to be −1.05, −2.30, −1.42, −2.29, −1.79, and −1.83kcal/mol, respectively. Dispersion is largely responsible for attraction in the pyridine dimer and, as a result, electron correlation beyond MP2 is necessary as in the case of heteroaromatic molecules.