Comment on 'An electron-water pseudopotential for condensed phase simulation' [J. Chem. Phys. 86, 3462 (1987)]

Some time ago, Schnitker and Rossky derived a pseudopotential describing the interaction of an excess electron with water and used it to study the properties of the hydrated electron with molecular dynamics simulation. The derivation was based on ideas from electron-molecule scattering theory, with the wave function of the water-plus-electron system treated at the single-determinant Hartree–Fock level. Schnitker and Rossky’s application of this approach to water used the assumption that the pseudo-orbital associated with the pseudopotential is constant across each occupied molecular orbital of the water molecule, and this assumption leads to a particularly simple analytic form for the pseudopotential, which is given by Eq. 3 , below. Many properties of the hydrated electron have been understood in the context provided by the Schnitker and Rossky SR pseudopotential, although similar results have been seen with other pseudopotentials. With the published SR pseudopotential, the hydrated electron occupies a nearly spherical cavity and has a radius of gyration of 2.1 A. There are six water molecules in the first solvation shell, arranged quasioctahedrally in the so-called Kevan structure, with one hydrogen atom on each first-shell water pointing directly toward the hydrated electron’s center of mass see, e.g., Fig. 2 b . Recently, however, we discovered an error in the electron-water pseudopotential published by SR that dramatically changes the predicted properties of the hydrated electron. Thus, we believe it is worthwhile to comment on the nature of the error and to describe how the properties of the hydrated electron change when this error is corrected. Briefly, the error in the original paper is as follows: with the approximations made by SR, the part of the pseudopotential that accounts for the repulsion of the excess electron by the electrons in the occupied water molecular orbitals takes the form