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

L Yang and ZJ Bergstrom and BD Wirth, JOURNAL OF NUCLEAR MATERIALS, 512, 357-370 (2018).

DOI: 10.1016/j.jnucmat.2018.10.032

Hydrogen (H) trapping by helium-vacancy (He-V) complexes in bulk and the near surface region of tungsten (W) have been investigated by molecular statics calculations that evaluate two different W-H interatomic potentials, which use the same W-He, He-He and He-H potentials. One of the W-H 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 He x V 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 He-V complexes. Based on these comparisons, we determine that the EAM potential is more accurate than BOP for large-scale molecular dynamics simulations of W-He-H interactions. The EAM potential predicts that the difference in the average binding energies of H to stable He-V 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 He-V complexes below the W surfaces can be ignored. (C) 2018 Elsevier B.V. All rights reserved.

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