Chemisorption of hydrogen on titanium: Embedding theory and comparisons with small clusters

Abstract

The chemisorption of H 2 on Ti(0001) is treated using an ab initio CI theory for the surface region. Dissociation of H 2 occurs above the surface but more stable 3-fold coordination sites lie closer to the surface at ∼ 1.3 Å. Adsorption in adjacent 3-fold sites is less stable than in separated sites sharing only one surface atom. The calculated adsorption energy of 45 kcal/mol H 2 compares favorably with experiment. Bonding involves mainly the 4s electrons of the metal leading to hydridic hydrogens and a polarized lattice electron distribution, but d bonding and correlation effects significantly increase the binding energy. Calculations on small metal clusters also show dissociative adsorption but much larger hydrogen binding energies are obtained.