First-principles study of H on the reconstructed W(100) surface

The first-principles calculations were used to study the hydrogen energetics on the (100) tungsten (root 2 x root 2)R45 degrees surface. Two equilibrium sites for H at the surface are identified, with a low migration barrier from the energetically clearly higher long bridge site to the short bridge site. At low coverages, the majority of H surface diffusion events take place via the short bridge sites. The energetics for H penetration from the surface to the solute site in the bulk was defined, showing that the bulk H diffusion via neighboring tetrahedral sites takes place at depths beyond the second subsurface layer.