Water: From Clusters to the Bulk.

Water is of fundamental importance for human life and plays an important role in many biological and chemical systems. Although water is the most abundant compound on earth, it is definitely not a simple liquid. It possesses strongly polar hydrogen bonds which are responsible for a striking set of anomalous physical and chemical properties. For more than a century the combined importance and peculiarity of water inspired scientists to construct conceptual models, which in themselves reproduce the observed behavior of the liquid. The exploration of structural and binding properties of small water complexes provides a key for understanding bulk water in its liquid and solid phase and for understanding solvation phenomena. Modern ab initio quantum chemistry methods and high-resolution spectroscopy methods have been extremely successful in describing such structures. Cluster models for liquid water try to mimic the transition from these clusters to bulk water. The important question is: What cluster properties are required to describe liquid-phase behavior?