Some tests of basic assumptions in transition state theory for hydrogen diffusion in FCC-metals

Transition state theory is frequently used to describe interstitial diffusion in solids. A basic assumption in this theory is that equilibrium statistical mechanics can be used to characterize the different configurations in the transition state, the region in configuration space which acts as a bottleneck for the motion of the interstitial. The authors have performed a detailed test of this assumption for hydrogen diffusion in palladium by combining the molecular dynamics and the Monte Carlo techniques. The study clearly confirms that equilibrium statistical mechanics can be used to characterize the different transition state configurations even though the presence of the hydrogen atom in the transition state strongly influences the fluctuations in the system and despite the fact that the time-scales for the motion of the H atom and the Pd atoms differ considerably.