The effect of impurities upon the motion of a kink pair was considered. It was found that, in the case of a repulsion-type impurity, there was a critical velocity for the incident kink pair. If the velocity of the incident kink pair was equal to the critical velocity, its trajectory in phase space was expected to branch. When the velocity was lower than the critical value, forbidden regions and allowable regions for its motion existed and separated each other. In the presence of an external force and damping, the pinned position of the kink pair was not only dependent upon the external force but was also related to the distribution of neighboring impurities.

Interaction between Kink-Pairs and Impurities in an Inhomogeneous Hydrogen-Bonded Chain. J.Z.Xu: Solid State Communications, 1995, 95[8], 563-8