Coexistence of Normal and Auxetic Behavior in a Thermally and Chemically Stable sp³ Nanothread: Poly[5]asterane

A one-dimensional nanostructure with sp³-hybridized carbon atoms, namely, poly[5]asterane (PA), is predicted by means of electronic structure calculations and reactive molecular dynamics simulations. Thermochemical analysis based on homodesmotic reactions showed that the formation of poly[5]asterane is more favorable than that of polytriangulane and comparable to that of polytwistane. A plane-wave DFT approach gave a computed Young's modulus of about 0.84 TPa, which is quite promising and comparable to those of other sp³-hybridized nanothreads. Simulations of the desorption of hydrogen atoms from PA showed a high activation energy (E_a≈52 kcal mol⁻¹), which again indicates substantial chemical stability. Interestingly, PA was shown to exhibit auxetic behavior (negative Poisson's ratio). Thus, PA is advocated as a new mechanically and chemically stable nanothread with exotic auxetic behavior.