Basis set effects on the calculated bonding energies of neutral benzene dimers: importance of diffuse polarization functions

The bonding energies of the parallel and T-shape benzene dimers were calculated using several basis sets including multiple polarization functions. The diffuse polarization functions were important to evaluate the attractive interaction. Small basis sets considerably underestimated the bonding energies. The bonding energies of five orientations of dimers were calculated at the MP2/6-311G(2df, 2p) level. The calculated bonding energy of the displaced parallel dimer was considerably larger than the recently reported value calculated with small basis sets.