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In terms of first-principles investigation of H-tungsten (W) interaction, we reveal a generic optimal electron density mechanism for H on W(110) surface and at a vacancy in W. Both the surface and vacancy internal surface can provide a quantitative optimal electron density of ∼0.10 electron/Å 3 for H binding to make H stability. We believe that such a mechanism is also applicable to other surfaces such as W(100) surface because of the (100) surface also providing an optimal electron density for H binding, and further likely actions on other metals.

The diffusion behaviours of hydrogen (H), deuterium (D), and tritium (T) from W(110) surface into bulk and in bulk W are investigated using first-principles calculations combined with simplified models. The diffusion energy barrier is shown to be 1.87 eV from W(110) surface to the subsurface, along with a much reduced barrier of 0.06 eV for the reverse diffusion process. After H enters into the bulk, its diffusion energy barrier with quantum correction is 0.19 eV. In terms of the diffusion theory presented by Wert and Zener, the diffusion pre-exponential factor of H is calculated to be 1.57×10−7 m2·s−1, and it is quantitatively in agreement with the experimental value of 4.1×10−7 m2·s−1. Subsequently, according to mass dependence () of H isotope effect, the diffusion pre-exponential factors of D and T are estimated to be 1.11×10−7 m2·s−1 and 0.91×10−7 m2·s−1, respectively.

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