Quantum symmetrization of hydrogen bonds in ice

The structure of hydrogen bonds in ice is considered theoretically taking into account the quantum tunneling of protons along the bonds and the Coulomb interaction of protons of different bonds. It is shown that the width and height of the potential barrier become very small at sufficiently small hydrogen-bond lengths and the tunneling of protons along the bonds leads to the formation of quantum symmetric hydrogen bonds. When selecting the variational wavefunction of protons, local correlations given by the ice rules are taken into account. This leads to an increase in the contribution of quantum tunneling and to the possibility of experimental observation of the symmetrization effect at a lower pressure than the usual self-consistent field approximation used earlier. Quantum symmetrization of hydrogen bonds occurs at longer hydrogen-bond lengths, i.e., at a lower pressure than the classical symmetrization of bonds because of the transformation of the proton potential to a form with one well.