Regensburg 2010 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 65: Density functional theory and beyond for real materials III
O 65.4: Vortrag
Donnerstag, 25. März 2010, 11:15–11:30, H34
Benzene on Cu(111): Adsorption and Assembly by Lateral van der Waals and Surface-State-Mediated Interactions — Kristian Berland1, •Theodore L. Einstein2, and Per Hyldgaard1 — 1Chalmers U. Tech., Sweden — 2U. Maryland, USA
Combining a van der Waals density functional (vdW-DF) [PRL 92 (2004) 246401] and estimation of lateral vdW and indirect electronic interactions, we study the adsorption, surface diffusion, and lateral assembly of benzene on Cu(111) [KB,TLE,PH, PRB 80 (2009) 155431]. The vdW-DF inclusion of nonlocal correlations changes the relative stability of 8 high-symmetry binding positions and increases the adsorption energy over tenfold. We find that benzene can move almost freely along a honeycomb web of “corridors” linking fcc and hcp sites via bridge sites, consistent with the low diffusion barrier in experiment.
We further present an extended vdW-DF scheme which accounts well for the structural phases of benzene on Cu(111). Experiments show that benzene condenses into two different structural phases: a compact and a sparse phase, both of approximately hexagonal symmetry. The vdW-DF calculations demonstrate that the denser benzene-overlayer phase, with lattice constant 6.74 Å, is due to direct benzene-benzene vdW attraction. The structure of the second, sparser phase, with lattice spacing 10.24 Å, is attributed to the indirect electronic interactions mediated by the well-known metallic surface state on Cu(111). To support this claim, we use a formal Harris-functional approach to evaluate nonperturbatively the asymptotic form of this indirect interaction.
Supported by 1Vetenskapsrådet 621-2008-4346 & 2NSF CHE07-50334