Ab initio calculation of the effect of metal ions on the vibrational spectrum of water

A number of small water clusters were calculated and their predicted infrared and Raman (both polarized and depolarized) spectra compared with bulk water and with recent cluster results in the gas phase. The frequencies of hexaaquametal ions (both with and without a second hydration sphere) were compared with each other and with water trimer, and trends were examined and rationalized. An investigation of aquamagnesium(II) was carried out using some new features (analytic second derivatives with effective core potentials, ONIOM calculations), as implemented in Gaussian 98.