Is the hydrogen bond in water dimer and ice covalent?

The changes in charge and momentum distributions upon forming a hydrogen bond in the water dimer are examined. The computed Compton profile anisotropies show the same oscillations as were observed for solid ice. These oscillations are already found when the unperturbed orbitals of the water monomers are used to construct a Slater determinant for the dimer, Hence we conclude that the oscillations an irrelevant to the discussion of the covalent character of the bond. Rather they just reflect the result of antisymmetrizing the product of monomer wave functions. In fact, at the oxygen-oxygen distance in ice, the calculations indicate a net antibonding contribution to energy from overlap effects.