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From Small Carbon Fragments to Self-Assembled Fullerenes in Quantum Chemical Molecular Dynamics Simulations S. Irle, G. Zheng, M. Elstner, and K. Morokuma Emory University Cherry L. Emerson Center for Scientific Computation 1515 Dickey Drive Atlanta, GA 30033 USA sirle@emory.eduWe present an analysis of our fully quantum chemical molecular dynamics simulations for the formation of fullerene molecules from ensembles of C2 and C6 molecules without assuming a designed reaction pathway. The importance of electronic structure and non-equilibrium dynamics of these systems is discussed by analyzing trajectories at 2000 and 3000 K, in which periodically further batches of randomly oriented small carbon fragments are added. In several trajectories self-assembly of fullerene molecules is observed within less than 100 ps, their size and formation time being dependent on initial carbon density. Three distinct stages can be identified: nucleation of polycyclic structures by entangled linear carbon chains, growth by ring condensation of attached chains, and cage closure (see Figure 1). Giant fullerenes are obtained in this “size-up” approach, and a “size-down” roadmap is discussed based on prolonged heating of these large carbon cages. In “size-down” simulations! of giant fullerenes, C2 elimination at a rate of approximately 1/2 C2/ps is observed, leading eventually to more rigid and kinetically more stable smaller fullerene cages like Buckminsterfullerene C60. Simulated annealing leads to the formation of its famous, perfectly Ih-symmetric soccerball structure.
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Presented at the International Congress
of Nanotechnology, November 7-10, 2004 San Francisco, USA
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