Ordered phases of Na adsorbed on Pt(111): Experiment and theory

Using low-energy electron diffraction structural analysis and first-principles calculations based on the generalized gradient approximation we have investigated the (√3×√3)R30°−Na and (2×2)−Na overlayers on Pt(111). In both phases the Na adatoms occupy hcp hollow sites. The measured and calculated adsorption geometries agree quantitatively. We have also studied the possibility of substitutional adsorption at the coverage Θ=1/4. The results are compared with other alkali adsorption systems, in particular K on Pt(111)