Molecular Dynamics Study of sp-Defect Migration in Odd Fullerene: Possible Role in Synthesis of Abundant Isomers of Fullerenes

TL;DR

This study uses molecular dynamics simulations to investigate how sp-defects migrate and interact in odd fullerenes, revealing mechanisms that could explain the formation of abundant fullerene isomers.

Contribution

It introduces a detailed atomistic mechanism for fullerene isomer formation involving sp-defect migration and annealing, supported by MD and DFT calculations.

Findings

Sp-defect migration occurs via stochastic exchange mechanisms.

sp$^2$-structure can be rearranged through sp-assisted ring changes.

Sp defect pairs can annihilate, influencing fullerene isomer diversity.

Abstract

To explain 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 sp$^2$ atoms. The first type is sto-chastic sp-defect migration analogous to exchange mechanism of adatom migration on a surface. The second type cor-responds to changes in the ring configuration of the sp$^2$-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 performed density functional theory calculations of the barriers of sp-defect migration events, is sufficient to deliver the sp atom to defects of sp$^2$ structure during the fullerene formation time. Based on 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 sp$^2$-structure defects, 3) sp$^2$-defect annealing assisted by the sp atom and 4) subsequent annihilation of pairs of sp defects.