Using a first-principles method, the structure, stability and diffusion of hydrogen in tungsten were investigated. It was found that single H atom preferred to occupy the tetrahedral interstitial site, with a formation energy of about −2.45eV. Two H in the tetrahedral interstitial sites form a pairing cluster along the <110> directions with the H–H distance of about 2.22Å, while the corresponding binding energy was only 0.02 eV, indicating a very weak attractive interaction. This suggests that H itself was not capable of trapping other H atoms to form a H2 molecule. The kinetics of H in intrinsic W was discussed, and the diffusion barrier of H that jumps between the tetrahedral interstitials was calculated to be 0.20 eV.

Structure, Stability and Diffusion of Hydrogen in Tungsten - a First-Principles Study. Y.L.Liu, Y.Zhang, G.N.Luo, G.H.Lu: Journal of Nuclear Materials, 2009, 390-391, 1032-4