Dielectrons in water clusters

Abstract

The energetics, structure, and stability of a dielectron solvated in an internal cavity in water clusters, (H2O)−2n, at 300 K are investigated using coupled quantum-classical molecular-dynamics simulations. In these calculations the ground state of the dielectron is calculated concurrently with the atomic configurations using the local-spin-density functional method, and the nuclear degrees of freedom evolve classically on the Born–Oppenheimer potential-energy surface. For n=64 and 128 the internal single-cavity dielectron state is unstable, while for n=256 (as well as in bulk water) it is energetically stable, fluctuating between a compact spherical configuration (e2c) and an elongated ellipsoidal dumbbell-shaped one (e2d). Transitions between these two states of the dielectron are accompanied by structural and orientational transformations of the surrounding water molecules. The induced molecular orientational order is enhanced and is of longer range in (H2O)−2256 than is the case for a solvated single excess electron. By extrapolating our results to the bulk limit we conclude that a spin-paired dielectron state in bulk water, at 300 K, is a stable species relative to two single separated hydrated electrons.