Ojwang', J. G. O. and van Santen, Rutger and Kramer, Gert Jan and van Duin, Adri C. T. and Goddard, William A. (2008) Predictions of melting, crystallization, and local atomic arrangements of aluminum clusters using a reactive force field. Journal of Chemical Physics, 129 (24). Art. No. 244506. ISSN 0021-9606 http://resolver.caltech.edu/CaltechAUTHORS:OJWjcp08b
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A parametrized reactive force field model for aluminum ReaxFFAl has been developed based on density functional theory (DFT) data. A comparison has been made between DFT and ReaxFFAl outputs to ascertain whether ReaxFFAl is properly parametrized and to check if the output of the latter has correlation with DFT results. Further checks include comparing the equations of state of condensed phases of Al as calculated from DFT and ReaxFFAl. There is a good match between the two results, again showing that ReaxFFAl is correctly parametrized as per the DFT input. Simulated annealing has been performed on aluminum clusters Aln using ReaxFFAl to find the stable isomers of the clusters. A plot of stability function versus cluster size shows the existence of highly stable clusters (magic clusters). Quantum mechanically these magic clusters arise due to the complete filling of the orbital shells. However, since force fields do not care about electrons but work on the assumption of validity of Born–Oppenheimer approximation, the magic clusters are therefore correlated with high structural symmetry. There is a rapid decline in surface energy contribution due to the triangulated nature of the surface atoms leading to higher coordination number. The bulk binding energy is computed to be 76.8 kcal/mol. This gives confidence in the suitability of ReaxFF for studying and understanding the underlying dynamics in aluminum clusters. In the quantification of the growth of cluster it is seen that as the size of the clusters increase there is preference for the coexistence of fcc/hcp orders at the expense of simple icosahedral ordering, although there is some contribution from distorted icosahedral ordering. It is found that even for aluminum clusters with 512 atoms distorted icosahedral ordering exists. For clusters with N≥256 atoms fcc ordering dominates, which implies that at this point we are already on the threshold of bulklike bonding.
|Additional Information:||© 2008 American Institute of Physics. Received 5 September 2008; accepted 25 November 2008; published 30 December 2008. This work is part of the research programs of Advanced Chemical Technologies for Sustainability (ACTS), which is funded by Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO). J.G.O.O. would like to thank Saman Alavi for help with the Lindemann index script.|
|Subject Keywords:||aluminum, binding energy, crystallization, density functional theory, equations of state, isomerism, melting, metal clusters, simulated annealing, surface energy|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Archive Administrator|
|Deposited On:||07 Jan 2009 20:15|
|Last Modified:||26 Dec 2012 10:41|
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