Role of explicit solvation and level of theory in predicting the aqueous reduction potential of carbonate radical anion by DFT

Abstract

Chemical oxidation reactions, a key class of electron transfer processes, have broad applications, including the treatment of persistent and mobile pollutants. Marcus theory, paired with density functional theory (DFT) simulations, enables quantification of thermodynamic properties in these reactions. However, accurately modeling species with complex solvent interactions, especially radicals, requires careful selection of computational methods. Reduction potentials provide critical benchmarks for evaluating solvent models and functional choices by comparing simulated values to literature data. In this study, we used the carbonate radical, known for its strong intermolecular interactions, as a model to assess solvation models and computational functionals. Implicit solvation methods significantly underperformed, predicting only one-third of the measured reduction potential. Accurate results were obtained using explicit solvation with 18 water molecules for ωB97xD/6-311++G(2d,2p) and 9 water molecules for M06-2X/6-311++G(2d,2p). B3LYP/6-311++G(2d,2p) showed improvement with additional explicit solvation but failed to match literature benchmarks. Functional performance differences, analyzed through natural bond orbital (NBO) and charge transfer calculations, emphasized the critical role of dispersion corrections. Testing various dispersion correction methods revealed consistent improvements in reduction potential accuracy. These findings highlight the necessity of explicit solvation for modeling electron transfer reactions with extensive solvent interactions and underscore the importance of selecting appropriate functionals and dispersion corrections for reliable predictions.