SELF-CONSISTENT MODEL OF HYDROGEN CHEMISORPTION

The chemisorption of a hydrogen atom on a transition-metal surface is treated theoretically on the basis of the Anderson Hamiltonian in Hartree-Fock approximation, which includes the interelectronic interaction within the 1s orbital. One-electron theory is shown to be inadequate for this problem. The localized states which may occur are discussed. A simple expression for the chemisorption energy ΔE is obtained, and a variational method is given for obtaining its self-consistent value. The metal eigenfunctions enter ΔE only through a function Δ(ε), and the foregoing results are exemplified and applied when this function is semielliptical. When the band is half-filled, a single analytic formula for the one-electron part of ΔE is obtained, in accord with the Kohn-Majumdar theorem. With some further assumptions, ΔE and the charge on the atom are calculated for adsorption on Ti, Cr, Ni, and Cu. The values of the hopping integral between the 1s orbital and a neighboring metal d orbital required to fit the experimental ΔE are found to be similar and are reasonable. The correct prediction that |ΔE|Ni>|ΔE|Cu is believed to be significant. A suggestive correlation is found between observations of catalytic ortho-para hydrogen interconversion on Pd-Au alloys and a rigidband calculation of ΔE. © 1969 The American Physical Society.