Density functional study of the adsorption of Na and K on Rh(111)

Ab initio total energy calculations using density functional theory with the generalized gradient approximation have been performed for the adsorption of Na and K adsorbed in (root3 x root3)R30degrees and (2 x 2) patterns on the Rh(111) surfaces. All the optimized geometry parameters are in excellent agreement with the available experimental results. For Na and K adsorption at 0.25 and 0.33 ML the hcp hollow sites were found to be preferred, which agree well with available experiments. The differences in binding energies between the on-top and hcp-hollow sites were found to become smaller with increasing size of alkali metal. Our calculations revealed that partial charge has transferred from AM adsorbate to Rh substrate, which is slightly larger for the lower coverage. It was also found that charge transfer from AM to substrate changes only a little as the AM size increases. In addition, the substrate rumpling and lateral displacements of Rh atoms in the topmost substrate layer were demonstrated to play minor roles for AM adsorption. (C) 2004 Published by Elsevier B.V.