The static-exchange electron-water pseudopotential, in conjunction with a polarizable water model: A new Hamiltonian for hydrated-electron simulations

Abstract

Previously, Turi and Borgis [J. Chem. Phys. 117, 6186 (2002)] parametrized an electron-water interaction potential, intended for use in simulations of hydrated electrons, by considering H(2)O(-) in the "static exchange" (essentially, frozen-core Hartree-Fock) approximation, then applying an approximate Phillips-Kleinman procedure to construct a one-electron pseudopotential representing the electron-water interaction. To date, this pseudopotential has been used exclusively in conjunction with a simple point charge water model that is parametrized for bulk water and yields poor results for small, neutral water clusters. Here, we extend upon the work of Turi and Borgis by reparametrizing the electron-water pseudopotential for use with the AMOEBA water model, which performs well for neutral clusters. The result is a one-electron model Hamiltonian for (H(2)O)(n)(-), in which the one-electron wave function polarizes the water molecules, and vice versa, in a fully self-consistent fashion. The new model is fully variational and analytic energy gradients are available. We have implemented the new model using a modified Davidson algorithm to compute eigenstates, with the unpaired electron represented on a real-space grid. Comparison to ab initio electronic structure calculations for (H(2)O)(n)(-) cluster isomers ranging from n=2 to n=35 reveals that the new model is significantly more accurate than the Turi-Borgis model, for both relative isomer energies and for vertical electron detachment energies. Electron-water polarization interactions are found to be much more significant for cavity states of the unpaired electron than for surface states.

Charge transfer to solvent dynamics in iodide aqueous solution studied at ionization threshold

“…This is called the cavity model of the hydrated electron. Theoretically, this cavity can be described by pseudopotentials [21,19,22]. Corresponding simulations agree reasonably well with experiments.…”

A new electron-methanol molecule pseudopotential and its application for the solvated electron in methanol

“…65,66 Another recent study pointed out the role of polarizable water models, which may also be potentially important for all cluster sizes. 67 The electron-water molecule model has nonetheless become successful. Ab initio test calculations indicated that the small cluster behavior is still reasonable, showing a reasonably linear correlation between the ab initio stabilization energies and those calculated with the pseudopotential.…”

Does the Hydrated Electron Occupy a Cavity?

“…Although the presence of the latter two features has been noted in work examining water-cluster anions (3,19), these features have not been incorporated into the pseudopotentials in previous bulk e − aq simulations (1, 2), so their importance to the behavior of the bulk hydrated electron has not been explored. Thus, to account for the presence of these features, we have fitted our potential to a sum of hydrogen-and oxygencentered terms, plus a sum of terms centered midway between the two hydrogen atoms; the fit is shown in the right panels of Fig.…”

“…The effect that the hydrated electron has on the structure of the nearby water molecules is summarized in Fig. 2D, which shows water-water RDFs for water molecules inside the electron (within 3.25 Å of the electron's COM, middle curves) and those in pure water at both normal (1.00 g/cm 3 , lower curves) and higher (1.23 g/cm 3 , upper curves) densities. Clearly, the water molecules inside the electron are packed together more like water at high density than like water at normal density.…”