The water molecules trapped by the excess electron

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The water cluster anions and the complexes of a group 1 metal atom with water clusters are studied with the ab initio MO calculations. They commonly have a structural unit of the excess electron cloud surrounded by a few HO bonds. The unit is called the OH {e} HO structure. The HO bonds interacting with the electron cloud {e} have harmonic frequencies shifted to downward and their bond lengths are lengthened, similar to the HO bond in the hydrogen bond. Thus, the bond {e} HO can be called electron-hydrogen bond.The photoionization spectra of water cluster anions are studied with L2 integral basis set. The isomerand size-dependence of the spectra are examined. The photoabsorption spectra of the complexes of a group 1 metal atom with water clusters are also studied, and the dramatic size dependence is demonstrated. A series of Rydberg type transitions are found for the clusters.It has been known that the Basis Set Superposition Error (BSSE) has serious effects in evaluating the binding energy of weak molecular and atomic complexes. The method to remove the BSSE has been a long research subject in quantum chemistry. We have developed the locally projected scf MO (LP SCFMO) for molecular interaction, which can be applicable to clusters having any number of molecular units. The new method is presented with projection operators, and the formula are transparent and their meanings are clear. The LP SCFMO was applied to water clusters, and the size dependence and basis set dependence were systematically examined. The results demonstrate that the SCF level of approximation of LP MO theory substantially underestimates the binding energy. It is because the LP SCF does not contain the electron delocalization over the molecular units. To improve the method, the perturbation expansion is required with the non-orthogonal molecular orbitals. The computational procedure is under development.