Electronic structure of the Pt(001) surface with and without an adsorbed gold monolayer

Results of all-electron self-consistent semirelativistic local-density-functional linearized-augmented-plane-wave (LAPW) investigations of the clean and Au-covered Pt(001) surface are presented. The charge density within the fourfold hollow sites at the surface was found to be very similar on both surfaces, as expected. The work function of the Au/Pt surface was reduced by 0.43 eV compared to the clean Pt surface. The interface atom ${4f}_{7.2}$ core-state level on the Au/Pt surface is shifted by 0.3 eV to reduced binding energy. On the clean Pt surface, the density of states (DOS) on the surface atomic layer shows a large peak at about -1.0 eV due to surface states. This peak persists at -1.0 eV after Au coverage on the Au/Pt surface and is due to a band of interface states localized on the interface Pt atomic layer. Significantly, however, there are no states on the Au/Pt surface which are localized both on the Au and interface-Pt layers. Furthermore, the $d$-band DOS on the adsorbed Au layer is fully occupied. These results are used to discuss the experimentally observed enhanced reactivity of the Au/Pt surface and lead to the conclusion that the morphology of the experimentally observed surface may be quite different from that previously thought and modeled here.