Ordered phases of potassium on Pt{111}: Experiment and theory

Using low-energy electron diffraction structural analysis and first-principles calculations based on the local-density approximation we have investigated the (√3×√3)R30^∘ K and (2×2) K overlayers on Pt{111}. The measured and calculated adsorption geometries agree quantitatively. In both phases the K adatoms occupy threefold symmetric hcp hollow sites, the preference for the hcp site over the fcc site being a consequence of the polarization of the surface Pt d electrons. We have not found any indication of K incorporation into the Pt{111} surface, as has been recently suggested.