The rapidly advancing ability to study quantum mechanical behavior in condensed phase systems via molecular-level simulation is discussed and illustrated in the context of the hydrated electron system. The recently developed models and techniques are outlined, and applications to equilibrium structure, steady-state optical spectroscopy, and aspects of electronic relaxation dynamics are described. The a priori simulation approach reveals not only an average structure consistent with earlier inferences from experiment but also significant fluctuations which are demonstrated to play a critical role in determining the energetic distribution of electronic states and the characteristic, featureless absorption spectrum. Studies of the transient electronic relaxation of initially created excess electrons in water via electronically adiabatic dynamics are presented which permit direct contact with ultrafast time-resolved, optical spectra. The results indicate that the dynamics of electron solvation per se does not dominate the experimentally observed rate of appearance of the equilibrium hydrated species.

The optical-absorption spectrum of an excess electron solvated in a molecular sample of liquid water at 300 K has been calculated with use of solvent configurations generated via path-integral simulation and subsequent solution of the excess-electronic eigenvalue problem. Electronic transitions from an slike ground state to three bound, localized, p-like excited states dominate the broad asymmetric spectrum with excitations into an apparent continuum following at higher energy. Asymmetric distortions and radial fluctuations of the solvent cavities contribute comparably to the spectral broadening.

A new algorithm for the quantum dynamical simulation of a mixed classical-quantum system that rigorously includes nonadiabatic quantum transitions is applied to the problem of the solvation dynamics of an initially energetic excess electron in liquid water. Computed results reveal a major channel associated with the appearance of a relatively long-lived solvated excited state postulated earlier; this state is identified as a distorted form of the equilibrium first excited state. The transient spectra evaluated directly from the simulation compare well with experimental data.

A simple electron–molecule pseudopotential is obtained that describes the interaction between an excess electron and a rigid water molecule in the electronic ground state. The potential is completely local and involves only spherically symmetric terms with respect to the three molecular nuclei (interaction site model). The potential is thus suitable for large-scale computer simulations, as well as more analytical theories. A description is given of the contributions included in this potential, as well as the ramifications of alternative choices.

An excess electron in a sample of classical water molecules at room temperature has been simulated using path integral techniques. The electron–water interaction is modeled by a pseudopotential with effective core repulsion and further terms for the Coulomb interaction and polarization effects. Various discretizations of the electron path, up to 1000 points, are examined. The charge distribution of the electron is found to be compact and to occupy a cavity in the water, in agreement with the conventional picture. The solvation shell structure is similar to that of relatively large solvated atomic anions, but the radial electron-solvent correlations are largely smeared out due to fluctuations of the electronic density distribution. In parts of the simulation the structure of the first solvation shell corresponds on the average to the structure proposed for hydrated electrons by Kevan. The computed solvation energy and the estimated energy of the first optical excitation agree reasonably well with experimental data.