Synergetic effect of H and He with vacancy in vanadium solid from first-principles simulations

Abstract Using first-principles calculations, we investigate the stability and energetics of H–He–vacancy complexes and He–He/He–H/H–H interactions in bulk vanadium to explore the synergetic effect of H and He impurities with vacancy. Inside vacancy space, He prefers to occupy octahedral site rather than vacancy center, different from of the cases of bcc Fe and W. Equilibrium He–H (2.33 A) and H–H (2.45 A) distances in the vacancy are longer than He–He distance (1.75 A) and they exhibit a weak attraction. One He–vacancy complex can trap up to five H atoms and the stable configurations with different amount of trapped H atoms are discussed in details. If a He atom occupies vacancy center, formation of H 2 molecule in the He–vacancy complex is almost impossible. Moreover, formation energy of a new vacancy around the H–He–vacancy complex does not remarkably reduce with increasing number of H atoms. We thus suggest that creation of a new vacancy around the He-complex via H aggregation is thermodynamically difficult.