Ab initio calculations of polyhedra liquid water

Ab initio calculations have been performed using the 6-31G* basis set for different structures of water clusters (H2O)n, n=1–10, 15. When increasing the number of water molecules, it appears that for n > 5, we observe a transition from planar to three-dimensional structures. All the different clusters present many stable geometries that are all very close in energy. To be sure that a minimum of the energy potential surface has been reached, vibrational frequencies for both (H2O)n and (D2O)n were calculated. When n increases, the O–O distance is always decreasing. From this study, we deduced that in the temperature range −10 to 100 °C, the most abundant clusters in liquid water at density 1 g/ml contain more than five water molecules.