First-principles investigations of the energetics of He-defect cluster in FCC nickel

We have done comprehensive first-principles calculations of He-vacancy-interstitial clusters in FCC nickel. The calculated total binding energy of V (n) (Ni vacancy cluster), I (n) (Ni interstitial cluster), He (n) (helium interstitial cluster), He V-n (helium interstitials in one vacancy), and He nV (2) (helium interstitials in one divacancy) cluster is reported. The total binding energy of a two Ni interstitial cluster is relatively large (1.07 eV), and the binding energy between a monovacancy and a vacancy cluster containing < 20 vacancies is relatively small ( < 0.8 eV). The dissociation/emission energy barrier of a Ni interstitial from a He (3) interstitial cluster (three helium interstitial clusters) and a He V-8 cluster (eight helium interstitials in one vacancy) is <= 1.06 and <= 1.32 eV, respectively. The diffusion activation energy of helium is 1.36 eV via a dissociative mechanism. Comparisons with reported experimental results of helium diffusion and helium desorption have been done to verify the calculation results. The relative stability of stacking fault tetrahedron and void has been investigated further based on quasi-harmonic phonon calculations directly to consider the temperature effects. The reported binding energy results can be used to build molecular simulation potentials or provide input parameters for the cluster dynamics or lattice Monte Carlo simulations of helium-defect cluster evolution.