Using ab initio molecular dynamics to determine the mobility of single, di and tri self-interstitial configurations in hcp Zr

Atomic configurations and activation energies for diffusion of point defects and point defects clusters are important elements to consider when predicting the microstructural evolution of zirconium-based materials under irradiation. Using Density Functional Theory (DFT) we performed molecular dynamics (MD) calculations to determine the diffusion coefficient of self-interstitials (SIA) clusters containing up to three atoms in the hexagonal close packed (hcp) structure of zirconium. The calculated values of the activation energy for single SIA diffusion are in line with previous DFT studies performed with accurate constrained minimization techniques, which validates the adopted methodology. Diffusion in the basal plane is similar for mono-, di- and tri-SIAs but diffusion along the $\overrightarrow{c}$ axis is significantly slowed down by the addition of SIA. Quantitative differences with existing empirical potential results highlight the usefulness of the ab initio MD calculations reported in this work.