Carbyne from first principles: Chain of C atoms, a nanorod or a nanorope?

TL;DR

This study provides a comprehensive first-principles analysis of carbyne, revealing its exceptional mechanical strength, tunable electronic properties, and potential as a nanoscale electrical cable, with insights into its stability and functionalization.

Contribution

The paper offers the first detailed elastic, mechanical, electronic, and chemical property characterization of carbyne from first principles, including its tunability and stability.

Findings

Carbyne is twice as stiff as the stiffest known materials.

It has an unrivaled specific strength of up to 7.5×10^7 Nm/kg.

Carbyne's band gap increases significantly under tension.

Abstract

We report an extensive study of the properties of carbyne using first-principles calculations. We investigate carbyne's mechanical response to tension, bending, and torsion deformations. Under tension, carbyne is about twice as stiff as the stiffest known materials and has an unrivaled specific strength of up to 7.5*10^7 Nm/kg, requiring a force of ~10 nN to break a single atomic chain. Carbyne has a fairly large room-temperature persistence length of about 14 nm. Surprisingly, the torsional stiffness of carbyne can be zero but can be 'switched on' by appropriate functional groups at the ends. Further, under appropriate termination, carbyne can be switched into a magnetic-semiconductor state by mechanical twisting. We reconstruct the equivalent continuum-elasticity representation, providing the full set of elastic moduli for carbyne, showing its extreme mechanical performance (e.g. a nominal Young's modulus of 32.7 TPa with an effective mechanical thickness of 0.772 A). We also find an interesting coupling between strain and band gap of carbyne, which is strongly increased under tension, from 3.2 to 4.4 eV under a 10% strain. Finally, we study the performance of carbyne as a nanoscale electrical cable, and estimate its chemical stability against self-aggregation, finding an activation barrier of 0.6 eV for the carbyne-carbyne cross-linking reaction and an equilibrium cross-link density for two parallel carbyne chains of 1 cross-link per 17 C atoms (2.2 nm).