QM(DFT) and MD studies on formation mechanisms of C₆₀fullerenes

Abstract

Abstract. One of the most puzzling aspects of fullerenes is how such complicated symmetric molecules are formed from a gas of atomic carbons, namely, the atomistic or chemical mechanisms. Are the atoms added one by one or as molecules (C 2 , C 3 )? Is there a critical nucleus beyond which formation proceeds at gas kinetic rates? What determines the balance between forming buckyballs, buckytubes, graphite and soot? The answer to these questions is extremely important in manipulating the systems to achieve particular products. A difficulty in current experiments is that the products can only be detected on time scales of microseconds long after many of the important formation steps have been completed. Consequently, it is necessary to use simulations, quantum mechanics and molecular dynamics, to determine these initial states. Experiments serve to provide the boundary conditions that severely limit the possibilities. Using quantum mechanical methods (density functional theory (DFT)) we derived a force field (MSXX FF) to describe one-dimensional (rings) and two-dimensional (fullerene) carbon molecules. Combining DFT with the MSXX FF, we calculated the energetics for the ring fusion spiral zipper (RFSZ) mechanism for formation of C 60 fullerenes. Our results shows that the RFSZ mechanism is consistent with the quantum mechanics (with a slight modification for some of the intermediates).

Self-Passivating Edge Reconstructions of Graphene

“…The energies were converged to ∼ 10 −5 eV/atom and structures were optimized until forces were less than 0.05 eV/Å. Our calculations agree well with previous relevant experimental as well as theoretical energetic and geometric properties [12,21]. The activation barrier was calculated with nudged elastic band method [29,30] by fixing the atoms beyond the first two zigzag-rows with unit cell of length 4.9Å.…”

“…The reconstructions predicted in this work are expected to survive on graphite terraces due to the weak interaction (5.6 meV/atom) between the basal planes [21]. Using appropriate sample preparation it should be thus possible to observe the reconstruction.…”

A Two-Stage Mechanism of Bimetallic Catalyzed Growth of Single-Walled Carbon Nanotubes

“…11 We consider that the metal atoms would bind most strongly to the exposed edge or a growing tube, which is highly active with isolated sp 2 radical sites containing destabilized π bonds (1,2 benzyne type) in the plane. We consider that there are two likely roles of the metal: (a) nucleation, forming from available precursors a structure onto which carbon molecules and atoms can add to form bucky tubes; [12][13] and (b) growth with defect repair (G-DR), building on the nucleated structure by adding carbon atoms and molecules to build the side walls while eliminating any carbon pentagons that would eventually close off the tube to terminate the growth.…”

On the Formation of SWCNTs and MWCNTs by Arc-Discharge in Aqueous Solutions: The Role of Iron Charge and Counter Ions

“…The mechanism of CNTs formation in the presence of metal catalysts is described in literature (36). Based on the catalytic growth mechanism, iron atoms adsorb into the edge of growing tubes, preventing the closure of the CNT tip (37,38). The experimental results showed that in the presence of ferric ions relatively high amount of short tubes were formed (Figure 6e).…”