LAUSR

Abstract We investigate interstitial C interactions with H/He, stability of C n -vacancy/H n -C-vacancy/He n -C-vacancy complexes ( n  = 1–5) and trapping of H/He in C-vacancy/C 2 -vacancy/H-He-C-vacancy in bcc vanadium using first-principles calculations. Interstitial C-H/C-He interactions are very weak and H/He preferential site keeps unchanged. A vacancy can accumulate two C atoms and the C 2 -vacancy cluster is more stable than the C-vacancy cluster. The electron localization function analysis shows that the C atoms form strong C-C bonds in vacancy and weaken the C-vanadium bonds. The stable configurations of H n /He n -C-vacancy clusters are partially different and the dissolution of H/He from H n -C-vacancy/He n -C-vacancy complexes is easier than H n -vacancy/He n -vacancy complexes with n  ≥ 2. The synergetic interactions of H and He in C-vacancy complex are also investigated and H/He trapping strength decreases in H-He-C-vacancy complex. The presence of C weakens vacancy trapping for more H/He atoms due to large distance of C-H/C-He.