Global minima of transition metal clusters described by Finnis–Sinclair potentials: A comparison with semi-empirical molecular orbital theory

Abstract

We present putative global minimum energy structures for nanoscopic transition metal clusters, with sizes ranging from N = 3 to 100 atoms, described by the original embedded atom potential of Finnis and Sinclair (FS), using their parameter sets for molybdenum and iron, and compare selected results with predictions from semi-empirical molecular orbital (SE-MO) theory via further optimization using the AM1* and PM6 Hamiltonians. We find that, for Fe clusters, the global minima found for the FS potential consist mainly of polyicosahedral structures with magic numbers N = 13, 19, 23, 26, 29, 39, 60 and 78, whereas, for Mo clusters with sizes N > 30, they are more likely to be bcc terminated by {110} and {100}-type surface facets. We find that the global minimum energy structures obtained for the FS potential are, in general, very good starting points for further SE-MO optimization, although the relative ordering of the resulting structures by energy compared to those obtained from global minima of other potentials used to model metal clusters does not, in general, agree.

Keywords:

• Finnis–Sinclair potential
• transition metal
• nanosized clusters
• numerical simulation
• global optimization
• basin-hopping
• semi-empirical molecular orbital theory
• AM1*
• PM6

Acknowledgements

JAE is grateful to the Japan Society for the Promotion of Science (JSPS) for the funding of a Long Term Invitation Fellowship (No. L08536), held at the University of Tokyo, and both authors would like to thank Fitzwilliam College, Cambridge for supporting a visiting Fellowship for YS. Part of this research was supported by the Grant-in-Aid for Young Scientists (a) (Nos. 18686017 and 21686021) from MEXT, Japan. The authors wish to acknowledge helpful discussions with Prof. Eiji Abe of the University of Tokyo.