Molecular dynamics study of the diffusion properties of H in Fe with point defects

Molecular dynamics (MD) simulations have been performed to investigate the diffusion properties of hydrogen (H) atoms in body-center-cubic (bcc) iron (Fe) with point defects, i.e., vacancies (Vs) and self-interstitial atoms (SIAs). Firstly, the binding energies of a H atom to a H/SIA-H cluster have been calculated by molecular statics simulations. The results show that single-H diffusion should be the major diffusion mechanism in perfect bcc Fe and bcc Fe with SIAs, but for bcc Fe with Vs, results from literatures show that multi-H diffusion should be taken into account. Further, the mean squared displacements method has been employed to determine the diffusivities and diffusion energy barriers of single-H at different temperatures in perfect bcc Fe. The diffusion energy barrier varies with the temperature. Furthermore, the H diffusion properties with different point defect concentrations have also been demonstrated, which showed that diffusivities reduce as the point defect concentration increases and the influence of point defects reduces as the temperature increases. Especially, SIAs exhibit negligible effect when the temperature is higher than 600 K.