ORDERED PHASES OF POTASSIUM ON PT(111) - EXPERIMENT AND THEORY

Using low-energy electron diffraction structural analysis and first-pr inciples calculations based on the local-density approximation we have investigated the (root 3x root 3)R30 degrees K and (2X2) K overlayers on Pt{111}. The measured and calculated adsorption geometries agree q uantitatively. In both phases the K adatoms occupy threefold symmetric hcp hollow sites, the preference for the hcp site over the fee site b eing a consequence of the polarization of the surface Pt d electrons. We have not found any indication of K incorporation into the Pt{111} s urface, as has been recently suggested. [S0163-1829(98)06412-1].