First-principles study on the mechanics, optical, and phonon properties of carbon chains

Abstract

Besides graphite, diamond, graphene, carbon nanotubes, and fullerenes etc., there is another allotrope of carbon: carbyne, existing in the form of a onedimensional chain of carbon atoms. It has been theoretically predicted that carbyne would be stronger, stiffer and more exotic than other materials that have been synthesized before. In this article, the two kinds of carbyne, i.e., cumulene and polyyne, are investigated by the first principles, where the mechanical properties, electronic structure, optical and phonon properties of the two carbynes are calculated.The results on the crystal binding energy and the formation energy show that polyyne is more stable and harder than cumulene, and both are difficult to be synthesized from diamond or graphite. The tensile stiffness, bond stiffness and Young's modulus of cumulene are 94.669 eV/Å, 90.334GPa and 60.62GPa, respectively; while the corresponding values of polyyne are 94.939eV/Å, 101.42GPa and 60.06GPa, respectively. The supercell calculation shows that carbyne is the most stable at N=5, where N is the supercell number. It indicates that the carbon chain with 10 atoms is the most stable. The calculation on the electronic band structure shows that cumulene is conductor, while polyyne is semiconductor with a band gap as 0.37eV. The dielectric function of carbynes varies in different direction, consistent with the one dimensional nature of the carbon chains. In the phonon dispersion of cumulene there are imaginary frequencies with the lowest value down to -3.817THz, which indicates that cumulene could be unstable at room temperature and normal pressure.

Structural Deformation and Metal-Semiconductor Transition in Coupled Carbon Chains

“…Experimentally, long polyyne chains have been synthesised [24,25,26] with interesting optical [25] and mechanical properties [27]. The single polyyne chain is semiconducting [28,29,30] and bandgap tuning has been observed under strain [31,17]. Also (semi-conducting) polyyne to (metallic) cumulene transition has been demonstrated experimentally under application of strain [32].…”

A review of arc-discharge method towards large-scale preparation of long linear carbon chains

“…[6,7] However, most first-principle calculations agree with that cumulenes are unstable and will transform to polyynes through Peierls distortion, generating bond alternative length (BLA). [8][9][10][11] Very recently, Romanin et al reported the theoretical study considering quantum-anharmonicity and revealed the transition between the two structures only occurs at extremely high and unphysical temperatures, explaining why experimental results only detect polyyne rather than cumulene. [12] Besides, finite LCCs and infinite LCCs are also distinguished, because the former is considered as a group of finite molecules usually containing other elements, whose properties are affected by length and end group, for instance polyynes terminated by hydrogen (C 2n H 2 , n < 10).…”

Extraordinary mechanical performance in charged carbyne

“…In addition to the well-known two-dimensional (2D) graphene [1,2] and three-dimensional (3D) diamond, [3,4] onedimensional (1D) carbon chains, carbyne, has also attracted increasing attention, [5,6] since carbyne with an extreme structure has been predicted to have extreme properties. [7][8][9][10][11] However, carbyne has a higher energy than graphite carbon because of sp 1 hybridization, making the fabrication of such material challenging. [12][13][14] Fortunately, carbyne formed at high temperatures and pressures was indicated in interstellar dust and meteorites, [15][16][17][18] and experimentalists have developed several methods for fabricating carbyne chains or segments, such as bulk production of long carbyne chains inside doublewalled carbon nanotubes, [19] deriving carbyne segments from graphene, [20] synthesis of confined carbyne, [21] and synthesis of carbyne on metal surface or within evaporating liquid carbon.…”