It was proposed that charge transport in H-bonded crystals, such as ice, occurred via a process that involved 2 types of defect (orientational and ionic) in the proton sub-lattice. An investigation was made of the formation and dynamics of the orientational defects by using 2 approaches. One of these was a quantum-chemical study of the barrier to rotation in finite chains of H2O molecules. The other approach involved an extended tight-binding model for the formation and motion of these defects. It was found, from the first part of this study, that the barrier to rotation could be almost an order of magnitude lower than the barrier to proton hopping along the chain. Construction of a modified tight-binding model permitted the simulation of motion in the uniform electric field of a pair of charged orientational defects. The calculated mobilities of the more mobile positively charged defect ranged from 0.39 to 0.46cm2/Vs for a dielectric screening constant of 50. This result was in agreement with available experimental data.

R.Mittal, I.A.Howard: Physical Review B, 1996, 53[21], 14171-8