# Structure and Properties of Chained Carbon: Recent Ab Initio Studies

^{*}

## Abstract

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## 1. Introduction

^{1}-hybridized bonds, thus representing the tiniest nanorope or nanowire [1]. Carbyne-based materials are prospective for multiple applications including miniature electronic circuits, friction-resistant coatings, biocompatible layers or chemical absorbers, to name a few. The design of a functional chained structure requires a profound understanding of its atomic arrangement and its physical and chemical properties at different temperatures and operating environments.

_{n}), with alternate single and triple bonds, or β-phase (cumulene (=C=C)

_{n}), with double bonds only. The atomic structure and mechanical characteristics of short carbon chains, up to 21 atoms, were studied numerically by ab initio techniques [2]. However, the precise synthesis conditions, phase-transition pathways, and defect formation remain mostly unexplored [3]. The disadvantage of carbyne is its instability in many environments, which prevents its large-scale synthesis and may negatively affect potential applications [4].

^{1}-chains, ordered in a hexagonal array with 5 Å distance between 2D–ordered linear-chained carbon (LCC) [12]. Being synthesized from carbon ions and their clusters in the plasma beam, they nevertheless present a material macroscopic in two dimensions. Although it is being already applied; peculiar regimes of the deposition process are yet to be understood theoretically. An additional issue of LCC is the lack of a straightforward characterization method that quickly assesses its structure.

## 2. Mechanical Properties

^{7}N∙m/kg, with a force of ~10 nN required to break the chain. Amazingly, its torsional stiffness is zero but may be increased by choosing functional groups at the ends. Carbyne self-aggregation was shown to have an activation barrier of 0.6 eV, while the cross-link density for two parallel atomic chains was estimated as 1 cross-link per 17 C atoms [15].

^{-1}Å

^{2}to 46 kcal mol

^{-1}Å

^{2}[17].

_{2}O molecules improves the bond stability, resulting in higher values of mechanical strength. In general, it was observed that the basic environment cuts the chain strength, while the stability is moderately raised in acidic solution [19].

## 3. Thermal Conductivity

^{−5}K

^{−1}at 300 K. The heat capacity anomaly initiates around 3800 K, indicating the phase transition across melting point.

^{n}-hybridized variants of carbon. As it was established by molecular dynamics studies, κ grows from ∼200 W/mK to 680 W/mK when the chain length extends from 20 to 40 nm. However, a little 3% strain may decrease these values by 70%. The thermal conductivity of carbyne shows a positive temperature dependence at a low temperature range and becomes negative at higher temperatures. At the same time, the α- and β-phases have very dissimilar thermal conduction characteristics. Unlike cumulene, which demonstrates a high phonon-related conductivity, the polyyne shows a much lesser thermal transport [3].

^{1}carbon by thermal destruction of graphene heated by a hot discharge plasma, using the tight-binding MD. Though no Van-der-Waals interactions were accounted for, this model gives eligible results at a few thousand Kelvin. The authors have found that the carbyne depletion between its generation in the hot part of the plasma and the final deposition can happen at a rate, which depends on the plasma pressure and flux. Quantitative studies are necessary to give precise predictions for an experimental procedure [24].

## 4. Electronic Properties, Raman Response, and Superconductivity

_{c}of 115 K [37].

## 5. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 1.**Carbon chains are mostly cumulenic or polyynic, depending on terminating molecules: (

**a**–

**d**) Carbon-atom wires with different terminations: Hydrogen-capped (

**a**), phenyl-capped (

**b**), vinylidene-capped (

**c**), and uncapped (

**d**). (

**e**) The bond length as a function of the number of carbon atoms comprising the wire. Reproduced with permission from [7].

**Figure 2.**Structure model of 12 atom-long carbon chains inside a (6,6) carbon nanotube. Reproduced with permission from [11].

**Figure 3.**Scheme of the atomic arrangement in LCC crystal, given in two normal projections. Reproduced with permission from [13].

**Figure 4.**The dependence of the strength F

_{c}, fragility e

_{c}, and hardness k

_{Y}on the number of atoms in carbyne. Reproduced with permission from [2].

**Figure 5.**A visual of nanocomposite composed of carbyne sandwiched by graphene, which is itself embedded in a Ni matrix. Reproduced with permission from [4].

**Figure 6.**Length dependence effect on thermal conductivity. Reproduced with permission from [10].

**Figure 7.**The band gap of finite carbon chains in dependence on the inverse number of atoms by first principle calculations ([9]: orange crosses), predicted [26] for carbyne (green cross), measured in gas phase (solid circles) [27] or for chains dissolved in a solvent (solid triangles and solid stars represent LCCs terminated by different chemical ending groups) [28,29] by absorption spectroscopy, and LCCs inside single (open squares [30,31])/double wall nanotubes ([9]: the light blue shaded area) by resonance Raman spectroscopy. Reproduced with permission from [9].

**Figure 8.**Eigenvectors for the low-frequency Raman modes for a carbyne (black) on the copper surface. Reproduced with permission from [33].

**Figure 9.**The journey of designing a 115 K superconductor. The different carbon structures are shown with increasing T

_{C}. Reproduced with permission from [37].

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**MDPI and ACS Style**

Buntov, E.; Zatsepin, A.; Kitayeva, T.; Vagapov, A.
Structure and Properties of Chained Carbon: Recent Ab Initio Studies. *C* **2019**, *5*, 56.
https://doi.org/10.3390/c5030056

**AMA Style**

Buntov E, Zatsepin A, Kitayeva T, Vagapov A.
Structure and Properties of Chained Carbon: Recent Ab Initio Studies. *C*. 2019; 5(3):56.
https://doi.org/10.3390/c5030056

**Chicago/Turabian Style**

Buntov, Evgeny, Anatoly Zatsepin, Tatiana Kitayeva, and Alexander Vagapov.
2019. "Structure and Properties of Chained Carbon: Recent Ab Initio Studies" *C* 5, no. 3: 56.
https://doi.org/10.3390/c5030056