Cluster melting computer simulation

The evidence from the analytical model described above that there may be unequal melting and freezing temperatures for finite clusters, has led to a renewed interest in examining in detail the melting portion of the caloric curves of small clusters. In this section we review the early computer simulation work on phase changes in small clusters. We proceed to discuss recent detailed constant energy simulations and their relation to the conclusions of the analytical model proposed for the transition. 

Figure 5.3 Computer simulations performed by Greenfield and Theodorou [141 for free volume clusters before and after 10 Monte Carlo steps within (a) glassy polymer and (b) rubbery polymer. Reprinted with permission from Macromolecules, Geometric analysis of diffusion pathways in glassy and melt atactic polypropylene by M. L Greenfield and D. N. Theodorou, 26, 5461-5472. Copyright (1993) American Chemical Society...

Recently, the results of our computer simulations led us to the conclusion that the Curie, Tc,j, and the melting, temperature of Niw clusters consisting of N atoms are linearly... 

Small particles are also observed to melt in computer simulations at temperatures well below bulk melting. Rare gas clusters as small as 13 particles show apparent phase transitions, although of course at small sizes these are rounded rather than sharp transitions and resemble conformational equilibria more than collective many-body processes. A simulation of gold particles revealed a three-step process for the melting of the larger particles onset of surface diffusion, formation of liquid patches at the surface, and abrupt melting of the whole cluster. The 477-atom cluster melted at 800 K and the 219-atom cluster below 600 K. 

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