Highly Accurate Coupled Cluster Potential Energy Curves for the Benzene Dimer: Sandwich, T-Shaped, and Parallel-Displaced Configurations

State-of-the-art electronic structure theory has been applied to generate potential energy curves for the sandwich,
T-shaped, and parallel-displaced configurations of the simplest prototype of aromatic π−π interactions, the
benzene dimer. Results were obtained using second-order Møller−Plesset perturbation theory (MP2) and
coupled-cluster with singles, doubles, and perturbative triples [CCSD(T)] with different augmented, correlation-consistent basis sets. At the MP2 level, the smallest basis set used (a modified aug-cc-pVDZ basis)
underestimates the binding by ∼0.5 kcal mol-1 at equilibrium and by ∼1 kcal mol-1 at smaller intermonomer
distances compared to results with a modified aug-cc-pVQZ basis (denoted aug-cc-pVQZ*). The best MP2
binding energies differ from the more accurate CCSD(T) values by up to 2.0 kcal mol-1 at equilibrium and
by more than 2.5 kcal mol-1 at smaller intermonomer distances, highlighting the importance of going beyond
MP2 to achieve higher accuracy in binding energies. Symmetry adapted perturbation theory is used to analyze
interaction energies in terms of electrostatic, dispersion, induction, and exchange-repulsion contributions.
The high-quality estimates of the CCSD(T)/aug-cc-pVQZ* potential energy curves for the benzene dimer
presented here provide a better understanding of how the strength of π−π interactions varies with distance
and orientation of the rings and will assist in the development of approximate methods capable of modeling
weakly bound π−π systems.