Site selectivity in chemisorption of C on Pd(211)

Results of ab initio electronic structure calculations of C on Pd(211), a vicinal of Pd(111), show a hierarchy of adsorption sites with adsorption energy ranging from -8.210.5em0exto0.5em0ex-5.460.3em0exeV (0.33 ML coverage) and scaling almost linearly with the effective coordination at the site. In the most preferred site, C atoms sit almost under the Pd step atoms and influence drastically multilayer relaxations and surface registry of Pd(211). The adsorption energy at this site is -9.100.3em0exeV for 0.17 ML coverage. The local densities of electronic states indicate strong hybridization between C p states and neighboring Pd d states leading to the formation of strong covalent CPd bonds. The depletion of the electronic density of states of the Pd surface atoms at the Fermi level suggests a poisoning effect of C which is found to be coverage dependent. We compare the changes in the electronic structure of Pd(211) on C adsorption with those on S adsorption.