Study of the heterometallic bond nature in PdCu(111) surfaces

In this paper a theoretical study of the bonding mechanism between heteroatoms of PdCu alloys using cluster models and several ab initio methods is reported. Models of the Pd8Cu92(111) and Pd40Cu60(111) surfaces have been analyzed. For these Cu-rich alloys, we find that surface Pd centers are negatively charged. The Pd net charge increases with the Cu/Pd atomic ratio of the alloy in parallel with a decrease of the Pd 4d electronic population. The influence of the bimetallic bond on the electronic structure of core, valence, and Fermi levels is discussed, and the apparent contradiction between the net negative charge predicted for Pd and the positive binding energy shift computed and experimentally observed in these alloys for Pd core and Pd-like valence levels is interpreted.