Structural and electronic properties of Pt/Fe nanoclusters from EHT calculations

Extended Huckel theory (EHT) calculations are presented for pure Pt and mix ed Pt/Fe nanoclusters, with a number of atoms in the range N-at = 13-309. I cosahedral and single-crystal (cuboctahedral, truncated octahedral) geometr ies are considered, optimized through a many-body potential approach for pu re Pt clusters. In the mixed Pt/Fe clusters, the Fe atoms simply replace Pt atoms in an otherwise unrelaxed structure. It is found that single-crystal configurations are generally preferred over icosahedral ones and that - up to an Fe content of similar to 30% - the Fe atoms segregate in the interio r of the cluster and the mixing reaction is exothermic. The electronic prop erties of the clusters are analyzed and are found to rapidly converge to a quasi-metallic behaviour for a number of atoms larger than similar to 150. The theoretical results are compared with the known experimental data on th ese systems. (C) 1999 Elsevier Science B.V. All rights reserved.