COMP 52 |
| Molecular dynamics simulations using potential energy surfaces obtained with the density functional tight binding (DFTB) quantum chemical method (QM/MD) have recently shown that fullerene formation is a dynamic self-assembly process far from thermodynamic equilibrium, with fullerene cages emerging as dissipative structures during the cooling of hot carbon vapor.[1] In an extension of these fullerene formation studies we present quantum chemical molecular dynamics simulations of synthesis of carbon nanotubes from carbon-containing feedstock gases in the presence of transition metal (Fe/Co/Ni) catalysts,[2] using DFTB parameters developed in the Morokuma group.[3] These simulations suggest that growth of the sidewalls is likely made possible by the presence of polyyne chains attached to the ends of the nucleated cap, similar as in the case of “octopus on the rock” structures during fullerene formation, but with slower pace due to the presence of the metal catalyst particles, and lower temperatures. We observe noticeable differences in catalyst melting and SWNT nucleation regarding Fen/Con/Nin particles with n ranging from 38 to about 200. We also report important differences when CVD gases such as acetylene are used instead of laser evaporation/carbon arc-simulating C2 vapor. [1] S. Irle, G. Zheng, Z. Wang, K. Morokuma, J. Phys. Chem. B 110, 21135 (2006), highlighted in: Nature materials, Nanozone, August 10, 2006. [2] S. Irle, G. Zheng, Y. Okamoto, and K. Morokuma, J. Comput. Theor. Nanosci., submitted [3] G. Zheng, H. Witek, P. Bobadova-Parvanova, S. Irle, D. G. Musaev, R. Prabhakar, K. Morokuma, M. Elstner, C. Köhler, and T. Frauenheim, J. Chem. Theory Comput., submitted. |
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Quantum Chemistry
1:30 PM-4:15 PM, Sunday, August 19, 2007 BCEC -- 162A, Oral
Division of Computers in Chemistry |