The diffusion mechanism of an excess proton in imidazole molecule chains: first results of an ab initio molecular dynamics study

The diffusion mechanism of an excess proton in imidazole molecule chains is studied by Car-Parrinello-type ab initio molecular dynamics simulations. T he diffusion process is described by a Grotthuss mechanism (structure diffu sion) involving proton transfer and local rather than long-range cooperativ e reorientation of the imidazole chain. At T = 390 K, the proton transfer s tep is found to be fast with a time scale of 0.3 ps. The reorientation step is found to be rate-determining. According to our model, the time scale fo r the reorientation step is estimated to be approximately 30 ps in this tem perature range. (C) 2001 Elsevier Science B.V. All rights reserved.