Molecular Dynamics Study of sp-Defect Migration in Odd Fullerene: Possible Role in Synthesis of Abundant Isomers of Fullerenes
Alexander S. Sinitsa, Irina V. Lebedeva, Yulia G. Polynskaya, А. М. Попов, Andrey A. Knizhnik
Abstract
To explain a recent experiment showing the role of odd fullerenes in formation of abundant fullerene isomers a reactive molecular dynamics (MD) study has been performed. Three types of bond rearrangement reactions are found by MD simulations at 3000 K in odd fullerenes which contain an extra sp atom among all other sp2 atoms. The first type is stochastic sp-defect migration analogous to the exchange mechanism of adatom migration on a surface. The second type corresponds to changes in the ring configuration of the sp2 structure assisted by the sp atom which can lead to annealing of seven-membered rings or separation of five-membered rings. The third type is formation of short-living one-coordinated atoms or two additional sp atoms. Annihilation of a pair of sp defects has been also observed in the MD simulations. It is shown that the frequency of sp-defect migration at a lower temperature, as estimated from the performed density functional theory calculations of the barriers of sp-defect migration events, is sufficient to deliver the sp atom to defects of the sp2 structure during the fullerene formation time. On the basis of these results, we propose to supplement the self-organization paradigm of fullerene formation by the following four-stage atomistic mechanism of formation of abundant isomers of fullerenes: (1) attachment of single carbon atoms, (2) sp-defect migration to sp2-structure defects, (3) sp2-defect annealing assisted by the sp atom, and (4) subsequent annihilation of pairs of sp defects.