The properties of charged clusters and surfaces are of fundamental interest in cluster and surface science, atmospheric chemistry and astrophysics. The presence of excess electrons at surfaces changes their catalytic activity for radical or other reactions. Aqueous systems are of special interest due to water's unique role in biological or chemical processes. Thus, in the past numerous experimental and theoretical studies focused on characterizing solvated electron states in water clusters. Depending on cluster size and preparation conditions, possible electron localization sites were found both at the surface and in the interior of small water clusters. In recent years, the dynamics of solvated electrons in thin ice films on metal substrates has been studied experimentally.
We investigated the localization of an excess electron at the ice Ih(0001) surface using first-principles calculations. We performed gradient-corrected density functional theory calculations (DFT-GGA) employing a plane wave basis set and a periodically repeated ice surface cell of 2x2 surface periodicity. Electron-ion interaction was modeled using ultrasoft pseudopotentials. To account for spurios self-interaction effects that artificially delocalize the excess electron, the DFT wavefunctions were used as input for a partial self-interaction-correction scheme. There, the excess electron's potential was corrected for self-interaction, whereas the remaining electrons were treated on usual DFT basis.
In a previous study we investigated the neutral ice Ih(0001) surface, and found water adsorption primarily on several non-crystallographic surface sites. Starting from these geometries we find localization of the excess electron at surface adsorbed water molecules that is more pronounced than on the ideally terminated ice basal plane. Results are compared to localization at other surface defects such as vacancies and to ideal or defect bulk ice sites. |