Atomistic Mechanism of Carbon Nanostructure Self-Assembly as Predicted by Nonequilibrium QM/MD Simulations

Abstract

We review our quantum chemical molecular dynamics (QM/MD)-based studies of carbon nanostructure formation under nonequilibrium conditions that were conducted over the past 10C years. Fullerene, carbon nanotube, and graphene formation were simulated on the nanosecond time scale, considering experimental conditions as closely as possible. An approximate density functional method was employed to compute energies and gradients on the fly in direct MD simulations, while the simulated systems were pushed away from equilibrium via carbon concentration or temperature gradients. We find that carbon nanostructure formation from feedstock particles involves a phase transition of sp to sp 2 carbon phases, which begins with the formation of Y-junctions, followed by a nucleus consisting of pentagons, hexagons, and heptagons. The dominance of hexagons in the synthesized

Quantum chemical simulations reveal acetylene-based growth mechanisms in the chemical vapor deposition synthesis of carbon nanotubes

“…It also possesses a hierarchy of different approximations to electron-electron interactions, ranging from zero order (complete neglect) [62] over a spin-unpolarized self-consistent-charge DFTB (SCC-DFTB) second-order approximation [63] to the spin-polarized self-consistent-charge (SDFTB) second-order approximation [65]. The DFTB and SCC-DFTB methods have therefore been employed by us in the study of carbon nanostructure formation before [66][67][68][69].…”

Formation Mechanism of C60under Nonequilibrium and Irreversible Conditions — An Annotation

“…C 60 @C 240 @ C 540 @ C 960 @····C 60n 2···· VI (2) An interesting issue here is the mechanism of nano-onion formation. We have previously proposed a spiral growth mechanism, but 3D spirals involve discontinuous points, making them unsuitable in real systems (17).…”

“…The mechanism of C 60 (I) formation has remained elusive for 25 years, ever since its serendipitous discovery, but recently Irle/Morokuma theoretical group almost solved the problem (1)(2)(3)(4). Their QM/MD simulation of carbon vapor condensation process under irreversible and non-equilibrium conditions generated a highly plausible route wherein vapor of C 2 self-assembled into a series of dissipative structures, eventually overshooting to form giant fullerenes as distinct intermediates ( Figure 1).…”

Density Functional Based Tight Binding (DFTB) Study on the Thermal Evolution of Amorphous Carbon

“…These clusters with fibers acted as carbon source and were able to heal up defects on a graphene sheet [11]. DFTB method has successfully been used to model and predict properties of carbon allotropes [12]- [14]. DFTB is based on Density Functional Theory but uses empirical approximations to reduce computational time [15].…”

“…DFTB is based on Density Functional Theory but uses empirical approximations to reduce computational time [15]. Formalism of DFTB can be found in [12] [15] [16]. In this work, we performed molecular simulation using DFTB method on a-C cluster to further understand the transformation dynamics of sp 3 to sp 2 , as well as the origin and processes by which the carbonous fibers emerged.…”