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O: Oberflächenphysik

O 24: Adsorption III

O 24.2: Vortrag

Dienstag, 28. März 2006, 16:00–16:15, TRE Phys

The ordering behavior of oxygen at Pd(100) studied with a first-principles lattice-gas Hamiltonian approach — •Yongsheng Zhang, Jutta Rogal, and Karsten Reuter — Fritz-Haber-Institut, Faradayweg 4-6, D-14195 Berlin, Germany

We study the mesoscopic ordering behavior of oxygen on Pd(100) from first-principles by parametrizing a lattice-gas Hamiltonian (LGH) with density-functional theory data. Using this LGH we carry out mesoscopic Monte Carlo simulations in order to obtain the surface phase diagram for sub-monolayer coverages or as a function of the oxygen pressure. The calculated lateral interactions between oxygen atoms adsorbed in fourfold hollow sites are dominated by a first-nearest neighbor repulsion. Together with a smaller second nearest-neighbor repulsion and a third nearest-neighbor attraction, this stabilizes both experimentally known ordered structures, namely a p(2 × 2) and a c(2 × 2) phase. The critical temperatures for the order-disorder transition are found to be in good agreement with experimental values from low-energy electron diffraction measurements [1]. The population of bridge sites at higher coverages is critically discussed.

[1] S.-L. Chang and P.A. Thiel, J. Chem. Phys. 88, 2071 (1988).