Accurate correlated calculation of the intermolecular potential surface in the coronene dimer

The binding energy of the coronene dimer was determined by high level ab initio calculations. In the first step a potential energy surface was determined for the stacked dimer at the SCS-MP2/aTZ level. The energy of the stacked parallel dimer was scanned with respect to the lateral displacement of the two molecules at various interplane distances, and the minima and saddle points were determined. These results were refined by high level quadratic CI (QCISD(T)/aDZ) calculations. The aTZ and aDZ basis sets employed are derived from the aug-cc-pVDZ and aug-cc-pVTZ basis sets but diffuse functions are placed only at every second carbon atom, alleviating the severe numerical difficulties of the full augmented basis sets while retaining all important contributions. To estimate the QCISD(T) energies for larger basis set, we employed commonly used procedure of adding basis set correction values obtained at the MP2 level. This hybrid scheme was used to obtain the final optimised geometries and binding energies; these are believed to be close approximations to the basis set limit QCISD(T) values. A few calculations were also performed to the T-shaped conformer, although this is less important in the coronene dimer than in the benzene dimer. The high-level results were used as a benchmark to assess the performance of simpler and less expensive ab initio methods for these large rings with small HOMO-LUMO gaps, for instance the SCS-MP2 method, and modern DFT versions that are optimised for dispersion dominated systems.