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Ab initio calculations of Xe monolayers adsorbed on Cu(111) surfaces

LEED, He atom scattering and SEXAFS measurements reveal that xenon monolayers adsorbed on Cu(111) and Pt(111) surfaces form commensurate (sqrt(3)xsqrt(3))R30 structures. Adsorption energies, interatomic distances and phonon frequencies characteristic of Xe monolayers have also been measured with high precision. We have carried out ab initio density functional calculations and determined the structure and force constants for these systems. We find that inclusion of intra- and inter-layer Van der Waals interactions is essential for a quantitative agreement with the experimental data. We have explicitly incorporated the Van der Waals interaction into the density functional calculations with the GGA functional. The chemisorptive bonding plays an important role in determining the adsorption sites, equilibrium distances and force constants, but contributes comparatively little to the binding energy of XeXe, XeCu and XePt bonds. The crucial step in implementing the Van der Waals interaction is a careful evaluation of the position of the image plane and of the dynamic polarizability of the metal surface. We have found a preference for the on-top site adsorption as observed experimentally. The adsorption distances, energies and phonon frequencies are also in good agreement with experiment.

van der Waals interactions; Xe adsorption; Cu surface

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