Cluster calculations of CO chemisorbed on the bridge site of Pd(100)

The interaction of CO chemisorbed on the bridge site of the Pd(100) surface has been investigated by means of ab initio relativistic and nonrelativistic Hartree-Fock and MCSCF calculations. Pd2 and Pd8 clusters were used to determine the Pd/CO chemisorption properties. The interaction energy has been decomposed into different contributions arising from intraunit polarization and interunit effects including charge transfer and covalent bonding. Besides the classical π back bonding found for other transition metal surfaces, the CO σ donation to the partially occupied 4dσ-5sp metal hybrid orbitals significantly contributes to the chemisorption energy. By increasing the cluster size from Pd2 to Pd8, the average Pd atomic configuration becomes more d9s1 -like, with consequent increase of the órepulsion between the metal 5sp and the CO 5σ charge distributions. However, this increased repulsion is largely compensated by the increased metal polarization resulting in a strong surface bond. © 1990 American Institute of Physics.