Excess electrons in polar molecular clusters

Electron attachment and localization to water and ammonia clusters, (NH3)−n and (H2O)−n (n=16–256), is studied using path-integral molecular dynamics simulations, employing an electron–molecule pseudopotential which includes Coulomb, polarization, exclusion, and exchange contributions. Due to the nature of the interactions the ammonia clusters do not form stable well-bound surface states for any size, in contrast to the case of medium size water clusters. The onset of bound excess electron states in ammonia clusters occurs for size n≥32, via an internal localization mode, in agreement with experimental data.