A comparative study of modern and robust computational methods applied to -complexes of moderate size: The case of the ethene/benzenium ion complex

Quantum-chemical calculations of energy difference between ethene/benzenium ion complex and its fragments are reported. We pursue the greatest accuracy by tackling first a focal-point analysis to robustly estimate the fleetingness of the molecule. Previous calculations showed how MP2 failed to locate the complex on the energy surface due to basis sets superposition error, and thus predicting ethylbenzenium ion as the energetically favoured system. However, MP2-based balanced treatment of intra- and inter-pair correlation effects (SCS-MP2) greatly improves the results. DFT studies with dispersion corrections, including double-hybrid functionals, are presented and further assessed. Finally, IR signatures of involved species are also compared.