Electronic structure calculations on the Ar-C6H12 interaction: Application to the microsolvation of the chair conformer

We report a theoretical study of the intermolecular potential for Ar-C6H12, with the cyclohexane fixed in both chair and twisted-boat conformers; the geometry of these conformers has been optimized at different levels of theory and the results compared with available data in the literature. For constructing the intermolecular potential, we applied the MP2 methodology with two basis from the augmented correlation-consistent basis set family: aug-cc-pVNZ (N = D and T). The accuracy of the MP2 calculations has been checked at the minima geometries obtained with the MP2/aug-cc-pVTZ level of theory, for all lines of approach of argon to cyclohexane considered here, by performing single-point CCSD(T)/aug-cc-pVDZ and MP2/aug-cc-pVQZ calculations. In turn, the best MP2 results (using the aug-cc-pVTZ) for the interaction energy have been fitted to a pairwise analytic potential for Ar-C6H12. Then, this potential function was employed in a global geometry optimization of the clusters Arn C6H12 (n = 1-20), with the cyclohexane fixed in the chair conformer.