Defect motion at finite temperature on a hydrogen-bonded chain

We have previously considered the energetics and dynamics of ionic and orie ntational defects in the proton displacement pattern on a hydrogen-bonded c hain at zero temperature. Here we examine thermal effects on ionic defect m otion in such a chain. The chain is represented by a classical lattice hami ltonian and a modified tight-binding electronic hamiltonian. Temperature is incorporated using the Nose-Hoover method. We find that the threshold fiel d for defect motion is reduced somewhat by temperature, as would be expecte d. The degree of reduction depends on whether the heavy-ion sublattice is t aken 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 th e dielectric screening. Mobilities are on the order of 0.005 cm(2)/V s, wel l below the values initially observed by Eigen and de Maeyer, but consisten t with more recent observations. (C) 1999 Elsevier Science B.V. All rights reserved.