Atomistic behavior of helium-vacancy clusters in aluminum

We have performed a molecular dynamics (MD) technique to calculate the formation energies of small He nV m clusters in Al using the embedded atom method (EAM), the Baskes-Melius potential and the Lennard-Jones potential for describing the interactions of Al-Al, Al-He and He-He, respectively. The binding energies of an interstitial He atom, an isolated vacancy and a self-interstitial Al atom to a He nV m cluster are also obtained from the calculated formation energies of the clusters. All the binding energies mainly depend on the He-vacancy ratio (n/m) of clusters rather than the clusters size. The binding energies of a He atom and an Al atom to a He nV m cluster decrease with the ratio, but the binding energy of a vacancy to a He nV m cluster increases with the ratio. The results indeed show that He atoms can increase the binding energy of a vacancy to a He nV m cluster, and decrease the binding energies of a He atom and an Al atom to the cluster, namely, He atom acts as a catalyst for the formation of He nV m clusters