Periodic spin-polarized density functional theory predictions were made of H adsorption, absorption, dissolution and diffusion energetics on, and in, ferromagnetic body-centered cubic material. It was found that H preferred to remain on the surface instead of in the sub-surface or in the bulk. The dissolution of H in bulk Fe was predicted to be endothermic; with H occupying tetrahedral sites over a wide range of concentrations. This was consistent with the known low solubility of H in pure Fe. In the initial absorption step, it was predicted that H occupied the deep sub-surface tetrahedral-site, for Fe(110), and the shallow sub-surface tetrahedral-site for Fe(100). The diffusion of H into Fe sub-surfaces was predicted to have a much lower barrier for Fe(100) than for Fe(110). In the case of H diffusion in bulk Fe, it was found that H did not diffuse through body-centered cubic Fe in a straight-line trajectory, but instead hopped from one tetrahedral-site to a neighboring tetrahedral-site via a curved path. A previously suggested path, via the octahedral site, was excluded due to its higher barrier and the rank of the saddle-point.

Diffusion of Interstitial Hydrogen into and Through BCC Fe from First Principles. D.E.Jiang, E.A.Carter: Physical Review B, 2004, 70[6], 064102 (9pp)