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The three low-energy isomers of C20. (From the left) The monocyclic ring, corannulene-like bowl structure, and the fullerene cage.
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The C 20 molecule exists as three low-energy isomers: the monocyclic ring, a corannulene-like bowl structure, and the cage-the smallest possible fullerene. The curious structures of these isomers, along with the valuable properties and possible applications of fullerenes more generally, mean that C 20 has attracted interest both experimentally and...
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Fullerenes are used extensively in organic electronics as electron acceptors among other uses; however, there are still several key mysteries regarding their formation such as the importance of graphitic intermediates and the thermokinetics of initial cage formation. To this end, we have conducted density functional tight binding molecular dynamics...
Citations
... As a successful instance, experimental synthesis and observation of cyclic C 20 has been reported very recently, [99] however, energy of bowl-shaped C 20 is significantly lower than it. [100] N 18 can undergo combustion reaction, that is N 18 (gas) + 18O 2 (gas)!18NO 2 (gas), the standard reaction enthalpy calculated using the aforementioned level is À 426.6 kcal/mol. Such a significant heat release implies that if a relatively stable N 18 solid can be prepared under a proper condition, it has potential to be employed as a combustible material and can, in principle, be infinitely regenerated, since nitrogen molecule is the most abundant component in the atmosphere. ...
The cyclic molecule cyclo[18]carbon composed of 18 carbon atoms has been observed in condensed phase experiment in recent years and has attracted great attention. Through state‐of‐art quantum chemistry calculation, this study found that 18 nitrogen atoms can also form a macrocyclic system, cyclo[18]nitrogen (N18), though its lifetime is very short at room temperature and can only exist for a relatively long time at very low temperatures. We comprehensively theoretically studied properties of N18, including geometric configurations, thermal decomposition mechanism and rate, molecular dynamics behavior, energetic properties, vibrational and electronic spectra. We also discussed in depth the electronic structure of N18, including nature of the N−N bonds, lone‐pairs, charge distribution characteristics, electronic delocalization, and aromaticity. This work is not only the first exploration of the macrocyclic N18 molecule, but also the first time to systematically examine a very long‐chain substance fully composed of nitrogen atoms in isolated state.
... One remarkable feature of the C 20 molecule/cluster is its occurrence in various geometrical configurations, which endows this molecule with several distinct isomers, for example cage, bowl, and monocyclic ring. The C 20 isomers possess significantly different structural as well as electronic structure properties [28,30]. Electron correlations play a key role in the C 20 isomers [30], hence, electron colliding with each isomer would allow these intrinsic features in the underlying scattering processes to show up. ...
... The C 20 isomers possess significantly different structural as well as electronic structure properties [28,30]. Electron correlations play a key role in the C 20 isomers [30], hence, electron colliding with each isomer would allow these intrinsic features in the underlying scattering processes to show up. The cage, bowl, and ring isomers of C 20 are selected as targets in the present article to search for isomer effects in electron scattering processes. ...
Low energy electron scattering processes with cage, bowl, and ring isomers of C20 are investigated employing the Dirac partial wave analysis. Rather than using a model potential to simulate the electron interaction with such isomers, we evaluate a more realistic interaction—the electrostatic potential (ESP) within a DFT framework using the B3LYP functional. A detailed collision picture is further modelled by considering several projectile–target interactions. Prominent isomer effects are observed in all the scattering observables for both the resonant as well as non-resonant scattering processes. Counter-intuitively, the ring isomer offers the maximum resonant and non-resonant collision contribution, despite having the simplest structure and the lowest electron density distribution. Different partial waves are involved in the formation of scattering resonances in the C20 isomers. Abiding to the marked differences in the cross sections, the temporal picture of the collision carries over such isomer effects distinctly. Diffraction of elastic electrons over the surfaces of cage, bowl, and ring isomers of C20 is an intriguing feature. Considerable amount of incoming flux is directed into inelastic channels at relatively lower energies leading to significant absorption effects, holding distinctively the isomer effects in such processes simultaneously.
Structural prediction of low-energy isomers of carbon twelve-atom clusters is carried out using the recently developed machine-learning potential GAP-20. The GAP-20 agrees with density-functional theory calculations regarding geometric structures and average C-C bond lengths for most isomers. However, the GAP-20 substantially lowers the energies of cage-like structures, resulting in a wrong ground state. A comparison of the cohesive energies with the density-functional theory points out that the GAP-20 only gives good results for monocyclic rings. Two multicyclic rings appear as new low-energy isomers, which have yet to be discovered in previous research.
Computational modeling is a rapidly growing approach investigating the geometric structure, electronic properties, and applications of both organic and inorganic materials beyond the limits of the experimental techniques and complementing experimental results by providing insights at the atomic level. In this chapter, the fundamental computational approaches, including ab initio methods, density functional theory, molecular dynamics, and Monte Carlo methods employed to describe dimensional organic materials, including zero-dimensional (clusters, fullerenes, cages), one-dimensional (carbon nanotubes), two-dimensional (graphene, its derivatives, and layered covalent organic frameworks (COFs)) and three-dimensional COFs are discussed. The aim of this contribution is to provide a brief understanding and motivation to researchers who may benefit from computational modeling techniques and subsequently apply similar strategies in order to study the fundamental properties of such organic materials at the atomistic scale, especially for those interested in the design of new hypothetical organic materials and exploration of their novel properties.
The structural and energetic features of small cationic carbon clusters with up to ten atoms are investigated using the Hartree–Fock, density functional theory, and fixed-node diffusion Monte Carlo simulations. The results show that the cationic carbon clusters present significant structural changes with relevant Jahn-Teller distortion compared to the neutral ones. A satisfactory agreement with available experimental results is observed for ionization potential, relative binding energy, and atomic dissociation energy. Our calculations present quantitative investigations on the electron correlation effects in the cationic carbon clusters and show the important roles of the electron correlation in the stability of these clusters.
We describe a novel variant of the driven molecular dynamics (DMD) method derived for probing Raman active vibrations. The method is an extension of the conventional μ-DMD formulation for simulating IR activity by means of coupling an oscillating electric field to the molecule’s dipole moment, μ, and inducing absorption of energy via tuning the field to a resonant frequency. Presently, we modify the above prescription to invoke Raman activity by coupling two electric fields, i.e. a ‘Pump’ photon of frequency ωP and a Stokes photon of frequency ωS to the molecule’s polarizability tensor, α, with the difference in the frequencies ω = ωP – ωS corresponding to the Stokes Raman shift. If ω is close to a Raman active vibrational frequency, energy absorption ensues. Varying ω allows identifying and assigning all Raman active vibrational modes, including anharmonic corrections, by means of trajectory analysis. We show that only one element of the full polarizability tensor, and its nuclear derivative, is needed for an α-DMD trajectory, making this method well suited for ab initio dynamics implementation. Numerical results using first-principles calculations are presented and discussed for the vibrational fundamentals, combination bands, overtones of H2O, CH4, and the C20 fullerene.
The cyclocarbons constitute a family of molecular carbon allotropes consisting of rings of two-coordinate atoms. Their high reactivities make them difficult to study, but there has been much progress towards understanding their structures and properties. Here we provide a short account of theoretical and experimental work on these carbon rings, and highlight opportunities for future research in this field.
Computational electronic-structure calculations of nanoscale systems are powerful tools which provide fundamental insight, help interpret experiment results, and ultimately aid the development of new materials. Density functional theory (DFT) dominates this field, and has had an enormously beneficial impact on nanoscience. However, there are still many situations in which present DFT fails to provide accurate quantitative predictions. The development of methods which provide more reliable predictive power is a growing field, and these approaches are becoming practical alternatives to DFT for nanoscience applications. In this article, we review four promising alternatives: Diffusion Monte Carlo, domain-based local pair natural orbital coupled cluster, the time-dependent formulation of DFT, and the GW method. We provide descriptive overviews of each method, accompanied by examples of where they have been applied to problems relevant to nanoscience, and discuss the major challenges they currently face as well as the outlook for the future. Between them these methods comprise a flexible toolkit whose continued development will be a big step towards the reliable computational design of new materials.
