Modelling of C2 addition route to the formation of C60

TL;DR

This study models the minimal energy pathways of C2 addition leading to C60 fullerene formation, identifying dominant growth routes and stability transitions during synthesis.

Contribution

It introduces a semi-empirical quantum mechanics model to elucidate the most probable growth routes of fullerenes, highlighting the energetic favorability of the fullerene road over the pentagon road.

Findings

Ring structures dominate growth at n=10.

C60 formation proceeds via the fullerene road.

Fullerene road is energetically favored over the pentagon road.

Abstract

To understand the phenomenon of fullerene growth during its synthesis, an attempt is made to model a minimum energy growth route using a semi-empirical quantum mechanics code. C2 addition leading to C60 was modelled and three main routes, i.e. cyclic ring growth, pentagon and fullerene road, were studied. The growth starts with linear chains and, at n = 10, ring structures begins to dominate. The rings continue to grow and, at some point n > 30, they transform into close-cage fullerenes and the growth is shown to progress by the fullerene road until C60 is formed. The computer simulations predict a transition from a C38 ring to fullerene. Other growth mechanisms could also occur in the energetic environment commonly encountered in fullerene synthesis, but our purpose was to identify a minimal energy route which is the most probable structure. Our results also indicate that, at n = 20, the corannulene structure is energetically more stable than the corresponding fullerene and graphene sheet, however a ring structure has lower energy among all the structures up to n 6 40. Additionally, we have also proved that the fullerene road is energetically more favored than the pentagon road. The overall growth leading to cage closure for n = 60 may not occur by a single route but by a combination of more than one route.