Compton scattering and the character of the hydrogen bond in ice I-h

Compton scattering is an experimental technique which probes the electron momentum density. Here we present a method which allows the calculation of the Compton profile using the formalism of the maximally localized Wannier functions. We applied this method to analyze recent experimental measurements of the anisotropy component of the Compton profile which have been interpreted as the signature of the partial covalent character of the hydrogen bond in ice I-h. We are able to reproduce well the experimental results, however we do not find evidence of a covalent nature of the hydrogen bond. In fact our analysis shows that, although the wave functions in ice I-h have a quantum-mechanical, multicenter character, this gives rise to an antibonding, repulsive interaction between neighboring water molecules. Application to our technique to other, nonhydrogen bonded systems, and analysis of the corresponding Compton scattering profile anisotropy, gives further support to our interpretation.