Abstract
The 'surface molecule' treatment of the chemisorption problem relies for its validity on the presence of an orbital, localized on the surface atoms of the substrate, with which the adatom can bind. In this letter, exact calculations have been performed for the one-electron tight-binding s- and d-band substrates to examine this localization. In a few cases the surface molecule picture is valid, and a simple criterion has been devised to explain the results. Some consequences are discussed.