First-principles investigation on vacancy trapping behaviors of hydrogen in vanadium

We have investigated the structure and stability of hydrogen (H), as well as H-vacancy (vac) interaction in a vanadium (V) single crystal employing a first-principles method including consideration of zero-point energy correction. A single H atom is shown to be energetically favorable in the tetrahedral interstitial site (T-site) in V. Two H atoms tend to pair up at two neighboring T-sites along the 〈1 1 0〉 directions with a binding energy of 0.04 eV and the equilibrium distance of 2.11 Å. H easily bonds to the vacancy, and the most stable site for a single H is ∼1.26 Å from the vacancy center close to an octahedral interstitial site. When more H atoms are added, vacancy-nH complexes are easily formed. A monovacancy is shown to be capable of trapping as many as 12 H or six H atoms via the "simultaneous insertion of all H atoms" or the "sequential insertion of individual H atoms", respectively. These results will provide a useful reference for V as a candidate structural material in a fusion Tokamak.