Quantifying Molecular Properties of Hexagonal Water Clusters

Density functional theory and polarizable continuum model (DFT/M06-2X/PCM) calculations, which make use of Gaussian basis sets, have been carried out to study the molecular properties of large hexagonal water clusters as a model for ice Ih. The series of (H₂O)_n (n = 96-332) clusters has been designed to reduce dangling hydrogen bonds on the surface and to preserve hexagonal crystallinity as much as possible. Large cluster structures are very stable, and computed electronic energy and entropy show asymptotic behavior with data astonishingly close to experimental thermodynamics. An excellent computation/experimental comparison has also been obtained for the neutron and X-ray diffraction structural data, as well as for infrared, Raman, inelastic neutron, and hyper-Raman fundamental vibrational frequencies. The overall results suggest that the use of large-size clusters, together with reliable and standard quantum chemical methods, is a highly promising and safe methodology to investigate experimentally challenging phenomena in water science.