The quantitative description of redox potentials of chemical systems remains a challenge for modern computational chemistry. It requires proper quantum-chemical treatment of open-shell molecular systems as well as an accurate description of solvent-solute interactions. The latter can be subdivided into reliable sampling of configurational space and quantifying long-range electrostatic interactions. Here we combine linear response approximation (LRA) with molecular mechanics (MM) molecular dynamics (MD) for configurational sampling, and QM/MM methods that account for self-consistent solvent-solute polarization, to yield accurate estimates of redox potentials in homogeneous solutions. Our studies show that, although accurate numerical results can be obtained when long-range electrostatic interactions are properly accounted for (using either the Born Solvation Model or extrapolation schemes), the latter should be done with care due to artifacts likely originating from MM forcefields. Specifically, we have found that configurations obtained from MD trajectories for solutes in water solvent described by TIP3P MM models tend to over stabilize charged species. Here we explore the effects of various MM water forcefields on computed vertical ionization energies, vertical electron affinities, oxidation and reduction free energies, and redox potentials.  In addition to the results for small molecules in aqueous solution, we also present computed redox potentials for several representative molecules in acetonitrile.<br/>

Simulating redox potentials in aqueous solutions with explicit solvent models: The role of MM forcefields

256th National Meeting (2018)

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