Abstract
We investigated the energetics and configurations of two interstitial He atoms in bcc Fe crystal using first-principle method. Two interstitial He atoms will bind together as helium pair if the initial He-He distance is less than 2.82 Å. From a formation energy decomposing analysis we found that, pairing of two He atoms would reduce the interface between He and Fe matrix which mitigates the perturbation of He-1s and Fe-3d orbitals. As a dominant part of the fomation energy, the electron variation energy caused by two close He atoms is less than that of two far He atoms, which accounts for the reason of binding between two close He atoms. Besides, the migration of helium pair along direction [1 0 0] was investigated by a He-He formation energy hypersurface. Through the comparison with Nudged Elastic Band calculation, it’s found that this special energy hypersurface was effective in revealing the migration of helium pair in metals.
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