An empirical potential to simulate helium and hydrogen in irradiated tungsten, applied to a mechanistic model for the energetics of gas-filled voids

Materials used in commercial D-T fusion reactors will be exposed to irradiation and a mixture of helium and hydrogen plasma. Modeling the microstructural evolution of such materials requires the use of large-scale molecular dynamics simulations. The focus of this study is to develop a fast embedded atom method potential for the interactions among the three elements (W, H, and He), fitted to accurately reproduce both the<i>ab initio</i>formation energies and relaxation volumes of small defect clusters containing light gases within tungsten. The potential enables the study of tungsten under irradiation and in the presence of light gases. To demonstrate the utility of the potential, we construct a thermodynamically motivated model for predicting the energetics of light-gas-filled voids. The W-He-H system energy is represented by analytical expressions that describe the energetics of hydrogen occupying distinct configurations. The model is validated using molecular dynamics simulations with the new interatomic potential and results in a simple expression that quantifies the difference in hydrogen trapping between a mono-vacancy and a large void.