Density functional periodic study of CO adsorption on thePd3Mn(100)alloy surface: Comparison with Pd(100)

Abstract

Self-consistent calculations based on density-functional theory with gradient corrections are used to compare the electronic and chemisorptive properties of Pd(100) and ${\mathrm{Pd}}_{3}\mathrm{Mn}(100).$ There are two types of ${\mathrm{Pd}}_{3}\mathrm{Mn}(100)$ 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 are retained. For CO adsorption on ${\mathrm{Pd}}_{3}\mathrm{Mn}(100)$ (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 ${\mathrm{Pd}}_{3}\mathrm{Mn}(100)$ (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.