Benchmarking Cation-π Interactions: Assessment of Density Functional Theory and Möller-Plesset Second-Order Perturbation Theory Calculations with Optimized Basis Sets (mp2) for Complexes of Benzene, Phenol, and Catechol with Na, K, Rb, and Cs.

The reliability of several density functional theory (DFT) functionals and of the Möller-Plesset second-order perturbation theory calculations with modified basis sets (mp2) approach in describing cation-π interactions is systematically investigated by benchmarking their performances with respect to high quality reference CCSD(T) calculations of the binding energies between alkaline cations of varying radius (Na, K, Rb, and Cs) and three aromatic species (benzene, phenol, and catechol). For this class of noncovalent interaction, mp2 delivers, on average, results in very good agreement with the reference CCSD(T) data, yet at a very small computational cost, exploiting the reduced dimensions of the modified basis set. Conversely, the tested DFT functionals show a more erratic behavior, with different performances depending on both the investigated system and the combination of the employed functional and basis set. The mp2 computational convenience is further exploited to extensively sample two-dimensional interaction energy surfaces of all investigated cation-π systems, which allow for a deeper insight on the effect of the increasing number of hydroxyl substituents, revealing the insurgence, upon substitution, of alternative minima, evident in particular for the smaller cations. The present results strongly support for further applications of the mp2 method to study a larger variety of aromatic/metal cation species, relevant both in biological processes and in technological applications.