Shedding Light on the Accuracy of Optimally Tuned Range-Separated Approximations for Evaluating Oxidation Potentials

There is a surge in the literature on the development of exchange-correlation density functionals for a wide variety of physical and chemical properties. As a recent endeavor toward the systematic and nonempirical design of density functional approximations, optimally tuned range-separated hybrid (OT-RSH) models have been introduced. In this work, we propose novel OT-RSH density functionals for predicting the oxidation potentials of organic compounds from different categories. In this regard, detailed analysis of the role of nonempirical optimization of the range separation parameter and importance of short- and long-range exact-like exchange in OT-RSH calculations of the oxidation potential has also been done. It is shown that the newly developed OT-RSH approximations not only perform better than other standard long-range corrected functionals but also in many cases outperform other conventional hybrid functionals with a fixed amount of exact-like exchange. Plus, we find that the proposed functionals describe well the oxidation potentials of compounds for which the tuning of the range separation parameter was not performed. From a different perspective, accountability of the computed frontier orbital energies from the OT-RSH density functionals for estimation of oxidation potentials has also been evaluated. Our results reveal that the negative highest occupied molecular orbital energies of molecules and the negative lowest unoccupied molecular orbital energies of their cations correlate remarkably with the observed oxidation potentials. Admittedly, with more efforts along this line, modern OT-RSH functionals with broader applicability can be released for computational electrochemistry.