# Dresden 2006 – wissenschaftliches Programm

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# MM: Metall- und Materialphysik

## MM 33: Symposium Materials Modelling II

### MM 33.2: Vortrag

### Donnerstag, 30. März 2006, 15:15–15:30, IFW A

**Efficient tools for the surface cluster expansion of binary alloy surfaces** — •Ole Wieckhorst and Stefan Müller — Universität Erlangen-Nürnberg, Lehrstuhl für Festkörperphysik, Staudtstr. 7, D-91058 Erlangen, Germany

The combination of density functional theory (DFT) with concepts from statistical physics is applied to the segregation at binary alloy surfaces. The binary alloy problem is solved in the cluster expansion 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 triangles, tetrahedrons, etc. One critical point of this concept is the selection of an appropriate set of figures, especially when the surface comes into play, which can be solved by treating this selection problem with a genetic algorithm. The number of figures, that has to be selected can be reduced dramatically by properly choosing a reference energy, which can be viewed as an approximation to the surface formation energies. It will be shown how the mixed space cluster expansion can be used to incorporate additional relaxation effects at the surface into this reference energy, thus reducing the need for a large number of manybody figures to compensate for large relaxation energies. As an example, we studied antisite segregation [1,2]in the B2-CoAl(100) surface. (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).