Abinitio calculations on the electronic properties of an encapsulated pair of polyynes inside a semiconductor zigzag carbon nanotube

Abstract We present a first-principles investigation of the structural and electronic properties of linear carbon chains encapsulated inside a zigzag carbon nanotube (10,0). Using density functional theory as implemented in the SIESTA code, we investigate both single- and double-chain configurations under periodic boundary conditions. Non-covalent functionalization is taken into account through van der Waals interactions.For the single-chain system, confinement inside the nanotube leads to a complete suppression of the bond-length alternation, driving a transition from a polyyne to a cumulene-like structure and inducing metallic behavior. In contrast, the encapsulation of two interacting chains results in an anti-parallel stacking configuration that preserves a finite bond-length alternation (~0.027Å) and opens a narrow indirect band gap of approximately 80 meV. Furthermore, the application of longitudinal mechanical compression progressively reduces the bond-length alternation and triggers a semiconductor-to-metal transition at strain values exceeding −2%. These results demonstrate that interchain coupling and external strain provide effective mechanisms for tuning the electronic properties of one-dimensional carbon-based hybrid nanostructures.