Honors College Thesis

 

Monte Carlo Simulations of Structure and Melting Transition of Small Ag Clusters Public

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  • The behavior of small atomics cluster largely depends on their geometry, due to the high ratio of surface atoms to interior atoms. One interesting aspect to study clusters centers around characterizing the transition behavior between nite and bulk materials, where the ratio of surface atoms to interior atoms is very small. Metropolis Monte-Carlo methods were used to simulate the melting of small silver clusters (3 to 56 atoms) using the Gupta potential. Each cluster was simulated from 200-1200 K in 40 K increments, allowing the cluster to transition from a liquid-like state to a solid state. The speci c heat was calculated at each temperature value. A separate simulation calculated the binding energy per atom of each cooled cluster. For each cluster, the speci c heat vs. temperature showed a slight peak at the phase transition from solid to liquid, corresponding to the latent heat required for the phase change. However, several cluster sizes had much higher peaks than their neighbors, identifying these sizes as clusters with a particularly stable geometry. The icosahedral 'magic number' clusters were 13 and 55 atoms, and showed full 5-fold symmetry in their final cooled state. Additional semi-magic number clusters, 19 and 25 atoms, were also identi ed using the binding energy per atom. These had partial 5-fold symmetry and were not as stable as the icosahedral magic number clusters.
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