Title: Hydrogen bonding characterization in water and small molecules,
Abstract: The prototypical Hydrogen bond in water dimer and Hydrogen bonds in the
protonated water dimer, in other small molecules, in water cyclic clusters, and
in ice, covering a wide range of bond strengths, are theoretically investigated
by first-principles calculations based on the Density Functional Theory,
considering a standard Generalized Gradient Approximation functional but also,
for the water dimer, hybrid and van-der-Waals corrected functionals. We compute
structural, energetic, and electrostatic (induced molecular dipole moments)
properties. In particular, Hydrogen bonds are characterized in terms of
differential electron densities distributions and profiles, and of the shifts
of the centres of Maximally localized Wannier Functions. The information from
the latter quantities can be conveyed into a single geometric bonding parameter
that appears to be correlated to the Mayer bond order parameter and can be
taken as an estimate of the covalent contribution to the Hydrogen bond. By
considering the cyclic water hexamer and the hexagonal phase of ice we also
elucidate the importance of cooperative/anticooperative effects in
Hydrogen-bonding formation.