Regensburg 2007 – scientific programme

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O: Fachverband Oberflächenphysik

O 70: Methods: Atomic and Electronic Structure III

O 70.5: Talk

Friday, March 30, 2007, 11:15–11:30, H42

Efficient treatment of segregation phenomena at alloy surfaces: The UNCLE code — •Ole Wieckhorst and Stefan Müller — Universität Erlangen-Nürnberg, Lehrstuhl für Festkörperphysik, Staudtstr. 7, D-91058 Erlangen

The success of the Cluster Expansion (CE) method in alloy surface problems depends heavily on the number of Density Functional calculations (DFT) necessary to stabilize the CE Hamiltonian. That is, a ``good choice'' of input structures, as well as pair- and multibody figures, plays a crucial role for the efficiency of the method. In strongly ordering and symmetry-lowering systems, (surfaces, e.g.), it may even happen that other modern CE's fail to predict the system's properties. We show that our new UNCLE code efficiently selects and reduces the number of relevant layer-dependent pair and multibody interactions. Consequently, the necessary number of DFT calculations is greatly decreased. This is accomplished by use of a mixed-space representation for the bulk and a separate treatment of relaxation energies in the CE Hamiltonian. We will demonstrate that, even with these smaller input sets, the code quantitatively predicts segregation phenomena at alloy surfaces.