Incorporation of a dispersion energy term to Fraga's atom–atom pair intermolecular potential. Application to benzene, s-tetrazine, and their mixed dimers

Abstract

Two ways of incorporating dispersion energy by adding a new r^–6 term to an atom–atom pair potential proposed by Fraga have been tested, as well as Fraga's potential itself, with respect to both minimal basis set and SCF plus dispersion energy calculations of benzene–benzene, benzene–s-tetrazine, and s-tetrazine–s-tetrazine dimers taken from the literature. Fraga's potential has the form of an expansion in powers of 1/r. In spite of the crude approach to intermolecular potential it represents, this potential, with the addition of an estimate of the dispersion contribution, predicts energies and conformations in good agreement with previous calculated and experimental data for the benzene–benzene dimers and allows for an extensive exploration of the interaction surface in the other dimers. In this way, new insight into the reliability and limitations of this pair potential is obtained.