Density functional periodic study of CO adsorption on the Pd3Mn(100) alloy surface:: Comparison with Pd(100)

Self-consistent calculations based on density-functional theory with gradient corrections are used to compare the electronic and chemisorptive properties of Pd(100) and Pd3Mn(100). There are two types of Pd3Mn(100) surfaces, one with only Pd atoms (A) and one with Pd and Mn atoms alternately ordered (B). The study of five-layer slabs shows that, for both surfaces, the surface Pd atoms are negatively charged by an electron transfer from the Mn atoms and that the "giant" magnetic moments existing on Mn atoms in the bulk art: retained. For CO adsorption on Pd,Mn(100) (A), the adsorption sites are in the same stability order as for Pd(100), with the on-top site less stable than the bridge and the hollow ones while the binding energies are slightly weaker. In the case of Pd,Mn(100) (B), the stability order is totally different, with the on-top site on Pd far more stable than the other sites. It is pointed out that CO adsorption on a magnetic atom is less favorable than on a nonmagnetic one, in relation with an adsorption-induced diminution of the magnetic moment. The results are interpreted in terms of orbital interactions. [S0163-1829(99)03308-1].