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Structure and Dynamics of Aluminum Clusters

Published online by Cambridge University Press:  28 February 2011

J. Bernholc
Affiliation:
Department of Physics, North Carolina State University, Raleigh, NC 27695–8202.
Jae-Yel Yi
Affiliation:
Department of Physics, North Carolina State University, Raleigh, NC 27695–8202.
Dirk J. Oh
Affiliation:
P. O. Box 7, Dae-Duk Dan-Ji, Korea Advanced Energy Research Institute, Chung-Nam, Korea.
D. J. Sullivan
Affiliation:
Department of Physics, North Carolina State University, Raleigh, NC 27695–8202.
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Abstract

The energetics and structures of metallic clusters containing up to 55 atoms are studied by the Car-Parrinello (quantum-molecular dynamics) method with Al chosen as a paradigm. It is found that the structural energy differences between small cluster (icosahedral) and bulk (fee) structures are surprisingly small, indicating that the icosahedron-fee structural transition can occur very early in Al clusters. Simulated annealing studies for 13- and 55-atom clusters, where both perfectly symmetric icosahedral and cuboctahedral (fee) structures exist, show that the distortions from the ideal structures are substantial. For the 55-atom cluster several inequivalent but energetically nearly degenerate structures are found, which is likely to lead to floppiness at finite temperatures as well as a low melting point. Although the structure factors for the annealed structures are nearly identical, they are very different from those of either of the ideal structures. The computed IPs and EAs differ by less than 0.1 eV for weakly annealed cuboctahedral and icosahedral clusters, making the structural identification on the basis of IP and EA measurements very difficult. The quantum-mechanical results are also used to develop a classical potential for long-time molecular dynamics simulations of large clusters.

Type
Research Article
Copyright
Copyright © Materials Research Society 1991

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