Interactions of alkali ions with the Au(100) surface in the DFT cluster model approach

The problem of adsorption of alkali ions on gold is studied from the theore tical point of view. The interactions of five ions, Li+, Na+, K+, Rb+ and C s+ with the Au atom and the AU(12) cluster modelling the Au(100) surface, w ere calculated using one of the density functional techniques, namely the B 3LYP method. For the 12-atom cluster, an interaction energy and a charge on the ion at its optimal distance from the Au(100) crystallographic plane we re computed at three main positions of the ion on the metal surface: hollow , bridge and top. The adsorption energy was found to increase in the order Cs+ < Rb+ < K+ < Na+ < Li+ This same trend is observed in the electron tran sfer from the metal to the ions. A less clear tendency is found in the adso rption energies of the same ion at the different sites on the surface. For the two smaller ions the hollow site is found to be preferred for adsorptio n, while for the three larger cations the top position is favoured. For all ions the energy difference between the most and the least stable site on t he surface is relatively small (< 10 kJ mol(-1)). The importance of the inn er charge distribution inside the metal cluster is also discussed. The arti ficial interactions between the ions and charges located on atoms in the Au ,, cluster were estimated using a simplified model. They are shown to const itute a relatively large contribution to the energy values obtained from th e cluster model calculations. A strong dependence of some results on the ba sis set used for the Au atom is documented. (C) 2000 Elsevier Science S.A, All rights reserved.