Theoretical studies of the chemisorption of hydrogen on copper

The chemisorption of H2 on Cu(100) is treated using a many-electron embedding theory in which the copper lattice is modeled as a 38-atom cluster. Ab initio valence (4s) CI calculations carried out on a local electronic subspace permit an accurate description of bonding at the surface. Dissociated hydrogen is found to bind exotherimically to the (100) surface at several stable adsorption sites in fourfold, bridge, and atop atom H positions. Calculated H2 binding energies are in the range 13–22 kcal/mol. However, high energy barriers to dissociation of 35–40 kcal/mol exist due to the repulsion of molecular H2 by the surface and the difficulty of stretching H2 significantly above the surface. A characteristic of stretched or dissociated H2 is the occurrence of H levels well up into the Cu 4s band from 5.5 to 7.8 eV below EF.