On the T-shaped structures of the benzene dimer

We report the geometries of two distorted T-shaped benzene dimer structures optimized at the RI-MP2/aug-cc-pVTZ level of theory. At the extrapolated RI-MP2/aug-cc-pV(TQ)Z level, the Cs over atom and Cs over bond configurations were found to be lower in energy than the conventionally accepted C2v T-shaped structure by 0.146 and 0.163 kcal/mol, respectively. When ΔCCSD(T)/6-311+G(2df,p) corrections were included, these structures remained lower in energy than the C2v reference by 0.127 and 0.132 kcal/mol, respectively, with Cs over bond as the minimum energy T-shaped structure. While not the focus of this Letter, we also report that the C2v T-shaped configuration is stabilized by 0.31 kcal/mol over the C2h parallel-displaced configuration at the ΔCCSD(T)/aug-cc-pVTZ approximation to the CCSD(T)/CBS limit.