Ferroelectricity and isotope effects in hydrogen-bonded KDP crystals
  Based on an accurate first principles description of the energetics in H-bonded KDP, we conduct a first study of nuclear quantum effects and of the changes brought about by deuteration. Cluster tunneling involving also heavy ions is allowed, the main effect of deuteration being a depletion of the proton probability density at the O-H-O bridge center, which in turn weakens its proton-mediated covalent bonding. The ensuing lattice expansion couples selfconsistently with the proton off-centering, thus explaining both the giant isotope effect, and its close connection with geometrical effects. 
S. Koval (1,2), J. Kohanoff (3), R. L. Migoni (1,2) and E. Tosatti   (1,4) ((1) Universidad Nacional de Rosario, Argentina; ...