Regensburg 2007 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 7: Metal Substrates: Adsorption I

O 7.1: Vortrag

Montag, 26. März 2007, 11:15–11:30, H39

Ground state search via cluster-expansion for a multi-site adsorption scenario: H in the Ir(100)-5×1-H phase — •Daniel Lerch, Ole Wieckhorst, Andreas Klein, Lutz Hammer, Stefan Müller, and Klaus Heinz — Festkörperphysik, Universität Erlangen-Nürnberg, Staudtstr. 7, D- 91058 Erlangen

Upon H adsorption the (quasi-)hexagonal 5×1-reconstruction of Ir(100) is lifted and a recently discovered hydrogen induced Ir(100)-5×1-H surface is formed [1]. Thereby, our density functional theory calculations have shown that there is a clear preference for H to adsorb on bridge sites. Within the 5×1 unit cell of the surface, six bridge sites can be found which are energetically relevant. Obviously this constitutes a very large configuration space when trying to determine the ground state configuration for the adsorption of more than one adsorbate per 5×1 unit-cell, or configurations with larger periodicities than the unit-cell. A sensible approach for the treatment of large configuration spaces is the cluster-expansion (CE). Its application to multisite adsorption systems has now been implemented successfully within our CE code UNCLE and used to determine the ground states for the adsorption of up to 1.2 ML H on Ir(100)-5×1-H. This is the first case where the CE formalism has been applied successfully to a problem with multiple adsorbate sites. The results from both DFT and CE will be presented along with experimental findings.

[1] L. Hammer et al. PRL 91 (2003) 156101