Defect motion at finite temperature on a hydrogen-bonded chain

Abstract

We have previously considered the energetics and dynamics of ionic and orientational defects in the proton displacement pattern on a hydrogen-bonded chain at zero temperature. Here we examine thermal effects on ionic defect motion in such a chain. The chain is represented by a classical lattice hamiltonian and a modified tight-binding electronic hamiltonian. Temperature is incorporated using the Nose-Hoover method. We find that the threshold field for defect motion is reduced somewhat by temperature, as would be expected. The degree of reduction depends on whether the heavy-ion sublattice is taken to be stationary or mobile, but in either case the threshold fields at 200 K are still comparable to breakdown fields for reasonable values of the dielectric screening. Mobilities are on the order of 0.005 cm 2/V s, well below the values initially observed by Eigen and de Maeyer, but consistent with more recent observations.