ICAMS / Interdisciplinary Centre for Advanced Materials Simulation
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Modelling the melting of small metal clusters

Date: 21.08.2008
Place: ICAMS, Raum 1103

Michael Ford, Department of Materials, University of Oxford, Oxford, United Kingdom

Small metal clusters have been shown experimentally to have a complex melting behaviour caused by finite-size effects, yet classical thermodynamic models have been unable to reproduce the observed relationship between melting point depression and cluster size, because they ignore the atomic structure. A correct atomistic computational description of finite materials requires a statistical mechanical treatment, which should allow the prediction of experimentally observed behaviours. My work has used Molecular Dynamics simulations with an Embedded Atom Method interatomic potential developed for tungsten by Ackland & Thetford to study cluster phase changes. Reductions in melting temperatures with respect to the bulk melting temperature were observed, with the results differing from those predicted by the standard thermodynamic models. The initial structure of the clusters was found to be important in determining the phase change behaviour observable over the course of a simulation. Techniques using various possible thermodynamic and atomistic order parameters have also been compared, including caloric curves, heat capacities, Lindemann parameters and velocity autocorrelation functions. Furthermore, progress has been made towards a local description of melting phenomena inside the clusters.

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