Structure, stability and diffusion of hydrogen in tungsten: A first-principles study

Using a first-principles method, we have investigated structure, stability and diffusion of hydrogen (H) in tungsten (W). We found that single H atom prefers to occupy the tetrahedral interstitial site with the formation energy of ∼-2.45 eV. Two H in the tetrahedral interstitial sites form a pairing cluster along the <1 1 0> directions with the H-H distance of ∼2.22 Å, while the corresponding binding energy is only 0.02 eV, indicating a very weak attractive interaction. This suggests that H itself is not capable of trapping other H atoms to form a H₂ molecule. The kinetics of H in intrinsic W is discussed, and the diffusion barrier of H that jumps between the tetrahedral interstitials is calculated to be 0.20 eV.