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O: Oberflächenphysik

O 33: Nanostrukturen II

O 33.8: Talk

Thursday, March 27, 2003, 16:45–17:00, FOE/ORG

The cluster-expansion technique: An efficient computational tool to investigate adatom configurations on plane crystal surfaces — •Reinhard Singer, Ralf Drautz, and Manfred Fähnle — Max–Planck–Institut für Metallforschung, Heisenbergstr. 3, 70569 Stuttgart

The energetics of adatom configurations on plane crystal surfaces has been described in many papers within the framework of a generalized Ising model involving pair interactions and sometimes higher-distance interactions like triplets etc. which have been added in an ad-hoc manner. In analogy to the cluster-expansion technique used in the literature [1] for compounds and alloys it is shown that under certain circumstances the energetics of adatom configurations may be completely represented by an infinite sum of contributions of all possible cluster figures on the two-dimensional lattice of adatom sites. In a practical calculation the sum has to be terminated at a maximum cluster, but the property of completeness makes it possible to converge the series systematically. The cluster interaction parameters occurring in the truncated series are determined by fitting the cluster expansion to the energies of selected reference configurations calculated by the ab-initio electron theory. The power of the method is demonstrated for the case of Li adatoms on Mo(112). The method is now being applied to figure out under which circumstances stable monatomic magnetic adatom chains are formed on plane crystal surfaces.

[1] J. M. Sanchez, F. Ducastelle and D. Gratias, Physica A 128, 334 (1984)