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

Self-consistent calculations based on density-functional theory with gradie nt corrections are used to compare the electronic and chemisorptive propert ies 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 surf ace Pd atoms are negatively charged by an electron transfer from the Mn ato ms and that the "giant" magnetic moments existing on Mn atoms in the bulk a rt: 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 stab le than the bridge and the hollow ones while the binding energies are sligh tly weaker. In the case of Pd,Mn(100) (B), the stability order is totally d ifferent, 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 t han on a nonmagnetic one, in relation with an adsorption-induced diminution of the magnetic moment. The results are interpreted in terms of orbital in teractions. [S0163-1829(99)03308-1].