Direct and indirect H-H interactions in the hydrogenated (2 x 1)-H/Pd(311) and Pd(111) surfaces have been investigated using density functional theory (DFT). The report shows that significant H-H interactions exist both along the atomic Pd(311) rows as well as between adjacent rows, through the Pd atom 'barrier'. Higher H coverage studies on both Pd(311) and Pd(111) 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. (C) 2013 Elsevier B.V. All rights reserved.