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O: Oberflächenphysik

O 28: Methodisches (Exp. und Theorie)

O 28.7: Talk

Saturday, March 5, 2005, 16:30–16:45, TU EB407

Genetic algorithms in surface cluster expansions — •Ole Wieckhorst und Stefan Müller — Universität Erlangen-Nürnberg, Lehrstuhl für Festkörperphysik, Staudtstr. 7, 91058 Erlangen

The cluster expansion treats the binary alloy problem by mapping DFT-based formation enthalpies of a number of selected input structures onto a finite set of pair and multibody interactions corresponding to characteristic figures like triangulars, tetrahedron, etc. The two critical points of this concept are the selection of an appropriate set of figures and input structures used for the construction, especially when the surface comes into play: The lifting of the symmetry due to the surface causes a lifting of the degeneracy of the figures, thus creating a huge repository of figures and structures to choose from. An effective way of treating such a selection problem are genetic algorithms. It will be demonstrated how the implementation of genetic algorithms in surface cluster expansions allows for a much more efficient and accurate determination of both, energetically relevant figures and input structures compared to conventional fitting procedures. As a first example, we apply this concept to construct a cluster expansion for the (100) surface of the B2-CoAl phase. Here, the segregation profile is controlled by so-called antisite atoms, as we have shown recently [1,2]. (supported by DFG)

[1] V. Blum et al., Phys. Rev. Lett. 89, 266102 (2002)

[2] O. Wieckhorst et al., Phys. Rev. Lett. 92, 195503 (2004)