Effect of interatomic potential on the energetics of hydrogen and helium-vacancy complexes in bulk, or near surfaces of tungsten

Hydrogen (H) trapping by helium-vacancy (HeV) complexes in bulk and the near surface region of tungsten (W) have been investigated by molecular statics calculations that evaluate two different WH interatomic potentials, which use the same WHe, HeHe and HeH potentials. One of the WH potentials is a bond-order potential (BOP) developed by Juslin et al., while the other is an embedding atom method (EAM) potential developed by Wang et al.. Both potentials overestimate the H binding energies to He clusters in bulk W, as compared to DFT calculations, but properly predict the functional form of the H binding energies to He clusters with increasing number of He and H. The BOP simulations reveal that H binding energies to HexV complexes generally increase with increasing number of He. However, the EAM results indicate that the H binding energy as a function of number of He depends on the number of H, and the H binding energies change slightly at high He content. Compared with available DFT data, both BOP and EAM underestimate the H binding energies to HexV2Hm complexes. The BOP reproduces the He formation energy below a W surface, while the EAM potential better reproduces the H formation energy and the interactions between H and HeV complexes. Based on these comparisons, we determine that the EAM potential is more accurate than BOP for large-scale molecular dynamics simulations of WHeH interactions. The EAM potential predicts that the difference in the average binding energies of H to stable HeV complexes near the W surface is less than 0.2 eV and the difference decreases with increasing He content. Thus, the EAM potential indicates that the effect of surfaces on H binding energies to large HeV complexes below the W surfaces can be ignored.