title: Activation energies for quantum diffusion of hydrogen in metals and on metal surfaces using delocalized nuclei within the density-functional theory.
abstract: Hydrogen diffusion on the Cu(001) surface and in bulk Nb and Ta is studied in the quantum regime using first-principles electronic-structure calculations. We present, for the first time, a direct density-functional calculation of the activation energy required to establish the quantum-mechanically delocalized hydrogen coincidence configuration and of the corresponding tunneling matrix element. For the two bulk systems a direct comparison can be made with nuclear magnetic resonance data, and we find excellent agreement for both the coincidence energy and the tunneling matrix element.
authors.affiliation: Department of Applied Physics, Chalmers University of Technology and Göteborg University, SE-412 96 Göteborg, Sweden. sundell@fy.chalmers.se
authors.forename: Per G
authors.initials: PG
authors.lastname: Sundell
authors.forename: Göran
authors.initials: G
authors.lastname: Wahnström