We investigate the physical properties of carbyne using first principles calculations. Under tension, carbyne displays an extreme stiffness, beating all known materials in specific stiffness and strength. With respect to bending, despite its one-atom thickness, carbyne behaves as a stiff rod at length scales below its persistence length ~ 14 nm (room temperature). The cylindrical symmetry of carbyne makes it a challenge to define a torsional deformation but can be broken via attachment of "handles" at the chain ends, whereupon the chemical nature of these handles determines whether they will rotate freely or if the system will behave as a beam with a finite tensile stiffness. Based on these three fundamental deformations we produce a comprehensive equivalent continuum-mechanics representation for carbyne [1]. Mechanical deformations also have a profound effect on the electronic properties of carbyne [2]. Under tension, the Peierls dimerization of carbyne (responsible for the symmetry-breaking transition from metallic cumulene phase to dielectric polyyne) quickly increases, and so does the band gap. We explain this unusual phenomenon using a simple yet general analytical model, applicable to all Peierls systems. We also find that stretching strongly affects the transport properties of carbyne, decreasing the mobility as the electron–phonon coupling gets enhanced—however, due to an unusually low effective mass, the mobility remains high compared to conventional materials. By further adding the quantum zero-point motion of atoms into the picture, we show how the Peierls ground state gets destabilized in free carbyne, restoring the metallic cumulene structure, yet a moderate stretching reverses the balance, causing a tension-driven metal–dielectric transition. In another mode of deformation, twisting a carbyne chain with sp² handles by 90 degrees causes a singlet–triplet spin transition. This combination of carbyne′s unique electro/opto-mechanical properties entails many interesting applications in nanoscale mechanical, electronic, and spintronic components, which however rely on the chemical stability of carbyne. To investigate this aspect, we analyze the carbyne–carbyne cross-linking reaction [1,3] to estimate the possible lifetime of this material.

1. M. Liu, V.I. Artyukhov, H. Lee, F. Xu, and B.I. Yakobson, ACS Nano 7, 10075 (2013).
2. V.I. Artyukhov, M. Liu, and B.I. Yakobson, arXiv:1302.7250
3. G. Casillas, A. Mayoral, M. Liu, A. Ponce, V.I. Artyukhov, B.I. Yakobson, and M. Yacaman, Carbon 66, 436 (2014).