State-of-the-art electronic structure methods have been applied to the
simplest prototype of aromatic pi-pi interactions, the benzene
dimer. By comparing to results with a large aug-cc-pVTZ basis set, we
demonstrate that more modest basis sets such as aug-cc-pVDZ are
sufficient for geometry optimizations of intermolecular parameters at
the second-order Moller-Plesset perturbation theory (MP2) level.
However, basis sets even larger than aug-cc-pVTZ are important for
accurate binding energies. The complete basis set MP2 binding
energies, estimated by explicitly correlated MP2-R12/A techniques, are
significantly larger in magnitude than previous estimates. When
corrected for higher-order correlation effects via coupled-cluster
with singles, doubles, and perturbative triples [CCSD(T)], the binding
energies D_{e} (D_{0}) for the sandwich, T-shaped, and
parallel-displaced configurations are found to be 1.8 (2.0), 2.7 (2.4),
and 2.8 (2.7) kcal mol^{-1}, respectively.