Hydrogen diffusion in a nickel crystal was examined. Firstly the diffusion coefficients of hydrogen at several temperatures were evaluated. The diffusion coefficients obtained by using mean square displacements agreed well with those obtained by the jump diffusion theory. Considering the correlation factors of hydrogen diffusion, the diffusion coefficients obtained by the jump diffusion theory were closer to that obtained by using mean square displacements. Secondly, the elementary process of hydrogen diffusion was considered. The activation energy of hydrogen diffusion obtained by using mean square displacements and that obtained by nudged elastic band method were different, since the jump of a hydrogen atom to the next stable site was finished before the nickel atoms constructed a stable structure with a transition site including hydrogen. Considering the energy landscape between the stable site and transition site including hydrogen, the activation energy obtained by nudged elastic band method was modified to be close to that obtained by mean square displacements.

Analysis of Hydrogen Diffusion Process and Elementary Process in Nickel Crystal by Molecular Dynamics Simulation. Masaie, T., Doi, Y., Nakatani, A.: Journal of the Society of Materials Science, Japan, 2008, 57[8], 774-9