Elucidation of the indirect H–H interaction in (2 × 1)-H/Pd(3 1 1) and on Pd(1 1 1)

Direct and indirect H–H interactions in the hydrogenated (2 × 1)-H/Pd(3 1 1) and Pd(1 1 1) surfaces have been investigated using density functional theory (DFT). The report shows that significant H–H interactions exist both along the atomic Pd(3 1 1) rows as well as between adjacent rows, through the Pd atom ‘barrier’. Higher H coverage studies on both Pd(3 1 1) and Pd(1 1 1) have shown that the H–H indirect interaction is remarkably similar for both surfaces despite their significant geometrical differences; the interaction is mainly dependent on only the inter-nuclear H–H distance. The mechanism of the interaction is shown to be mediated by surface state electrons.