Properties of helium defects in bcc and fcc metals investigated with density functional theory

The relative stability of single He defects in bcc and fcc metals is investigated using ab initio calculations based on density functional theory. The results indicate that the tetrahedral position is energetically more favorable for a He interstitial than the octahedral site in bcc metals, but the relative stability of He defects in fcc metals varies, depending on local environments. The He formation energies in bcc Fe and fcc Ni at the tetrahedral and octahedral positions with and without spin polarization are investigated. It is of interest to find that the magnetism of host atoms does not directly affect the relative stabilities of He in interstitial sites in bcc Fe and fcc Ni.