Flexible boundary layer using exchange for embedding theories. II. QM/MM dynamics of the hydrated electron

The FlexiBLE embedding method introduced in the preceding companion paper [Z. Shen and W. J. Glover, J. Chem. Phys. X, X (2021)] is applied to explore the structure and dynamics of the aqueous solvated electron at an all-electron density functional theory QM/MM level. Compared to a one-electron mixed quantum/classical description, we find the dynamics of the many-electron model of the hydrated electron exhibits enhanced coupling to water OH stretch modes. Natural Bond Orbital analysis reveals this coupling is due to significant population of water OH σ* orbitals, reaching 20%. Based on this, we develop a minimal frontier orbital picture of the hydrated electron involving a cavity orbital and important coupling to 4-5 coordinating OH σ* orbitals. Implications for the interpretation of the spectroscopy of this interesting species are discussed.