First-principles atomistic molecular-dynamics simulation in the microcanonical and canonical ensembles was used to study the diffusion of interstitial hydrogen in α-iron. Hydrogen to iron ratios between 1.16 and 1.2 were considered by locating interstitial hydrogen atoms at random positions in a 2x2x2 super-cell. It was found that the average optimum absorption site and the barrier for diffusion depended upon the concentration of interstitials. The iron Debye temperature decreased monotonically for increasing concentration of interstitial hydrogen, proving that iron-iron interatomic potential was significantly weakened in the presence of a large number of diffusing hydrogen atoms.

Ab initio Molecular Dynamics Simulation of Hydrogen Diffusion in α-Iron. Sanchez, J., Fullea, J., Andrade, M.C., De Andres, P.L.: Physical Review B, 2010, 81[13], 132102