Electron localization in water clusters. II. Surface and internal states

Electron attachment and localization in small water clusters (H ₂O)_n (n=8-128) is studied using path-integral molecular dynamics simulations. The electron-water molecule interaction is described via a pseudopotential which includes Coulomb, polarization, exclusion and exchange contributions. Different electron localization modes are found depending on cluster size. For small and intermediate size clusters (n=8-32), the energetically favored localization mode involves a surface state and the calculated excess electron binding energies are in agreement with experimentally measured values. In larger clusters, n=64, 128, internal localization (solvation) is energetically favored. In both cases the localization of the excess electron is accompanied by large cluster molecular reorganization. The cluster size dependence of the localization mode, the energetics, structure, and excess electron distributions in the negative molecular anions (H ₂O)_n^-, and the dependence on temperature are explored.