Path integral Monte Carlo study of the hydrated electron

The structure of an excess electron in water at room temperature is investigated using the Feynman path integral technique. The interaction potential between the electron and water is modeled by an effective potential, made up of three terms: a static potential, a repulsive potential, and a polarization potential. The polarization part is treated in two different ways: approximated as pairwise additive, and exactly with the many body polarization effects treated self-consistently. It is shown that the excess electron forms a cavity with the radius of the electron being 2.24 Å for pairwise additive polarization and 2.11 Å for the self-consistent treatment of the polarization. There is no sharp geometrical coordination number of water molecules around the electron. The water molecules within a distance of about 3.5 Å from the center of the electronic change distribution point their OH bonds towards the electron, and form only three hydrogen bonds. It is also found that the pair correlation function of the solvent molecules close to the electron are considerably different from the corresponding quantities calculated in the bulk. The electron, therefore, is shown to modify the local density to a large extent. There are important structural differences between the many body polarization model and the two body polarization model. It is concluded that for a quantitative description of the structure of the hydrated electron, the self-consistent treatment of the long range (many body) polarization effects are important.