A first-principles study on hydrogen behavior in helium-implanted tungsten and molybdenum

Abstract We perform first-principles calculations to investigate the interaction of H with He in W and Mo. One vacancy with one He atom located at the vacancy center (Vac-He 1 ) could trap up to 12 H atoms, forming a Vac-He 1 –H 12 complex in W and Mo. There is no H 2 molecule formed in the Vac-He 1 –H n ( n ranges from 1 to 12) complex. The calculations of the formation energy of Vac-He 1 –H n complexes indicate that Vac-He 1 –H 4 is the most energetically favorable. The formation energy of Vac-He 1 –H n is larger than that of Vac-H n by up to 0.6 eV in both W and Mo. Vac-He m ( m > 1) complex could also trap H atom, and the binding energy of Vac-He m with one closest H atom does not increase with the He atom number m . On the basis of the obtained energetics of Vac-He m complexes, a cascade mechanism is shown that once a Vac-He 1 complex traps enough H atoms, neighboring W or Mo atoms will become weakly bound thus easily removed.