  The microscopic behavior of water under different conditions and in different
environments remains the subject of intense debate. A great number of the
controversies arise due to the contradictory predictions obtained within
different theoretical models. Relative to conclusions derived from force fields
or density functional theory, there is comparably less room to dispute
highly-correlated electronic structure calculations. Unfortunately, such ab
initio calculations are severely limited by system size. In this study, a
detailed analysis of the two- and three-body water interactions evaluated at
the CCSD(T) level is carried out to quantitatively assess the accuracy of
several force fields, density functional theory, and ab initio-based
interaction potentials that are commonly used in molecular simulations. Based
on this analysis, a new model, HBB2-pol, is introduced which is capable of
accurately mapping CCSD(T) results for water dimers and trimers into an
efficient analytical function. The accuracy of HBB2-pol is further established
through comparison with the experimentally determined second and third virial
coefficients.
