Water cage clusters (H2O)n from n=6 to 12:: Do they model liquid water?

The optimal structures, the interaction energies, the HOH stretch and HOH bending frequencies of water cage clusters (H2O)(n), n = 6-12 have been investigated by ab initio method (MP2/DZ level). The clusters correspond to the relatively regular cage structures characterized by distinct groups of O...O bond lengths and HOH angles. As a result, the HOH stretch spectrum contains well separated DAA and DDA bands red-shifted by hundreds of cm(-1) with respect to water monomer and a third band for the dangling OH at the "crystal like" clusters. The "amorphous like" clusters yield numerous hydrogen bonded bands in a broad spectral range. The new spectral feature in the gap between DDA and DAA bands at the OH stretch region is the presence of the new lines due to four-coordinated DDAA water molecules for (H2O)(12) cluster. In contrast to the OH stretch, the vibrational bending frequencies are blue-shifted by 40-170 cm(-1) with respect to H2O(g). Features due to different structural elements were identified.