Topology as a Design Variable for Multiproperty Engineering in Synthesized 4-5-6-8 Carbon Nanoribbons

Abstract

Nonbenzenoid carbon frameworks expand low-dimensional material design via controlled asymmetry. Here, we show the experimentally realized 4-5-6-8 carbon nanoribbon establishes a topology-driven paradigm for multiproperty engineering, not just a graphene variant. Using hybrid DFT, tight-binding, and molecular dynamics in a multiscale framework, we demonstrate the symmetry-broken lattice stabilizes hierarchical bonds within standard energy ranges. This geometry produces a robust semiconducting state (hybrid gap >1 eV) and enables strain as a controllable modulation parameter. A tight-binding Hamiltonian fitted only at equilibrium accurately captures strain-dependent band evolution, proving the essential physics is topology-dominated. Mechanical analysis reveals high stiffness with fracture governed by the largest polygons, showing asymmetry redistributes stress without compromising integrity. Intrinsic phonon scattering suppresses thermal conductance, enabling favorable thermoelectric performance without extrinsic disorder. Optical response confirms non-equivalent ring connectivity reorganizes interband transitions, promoting strong visible absorption and efficient photocarrier generation. These results position topology as a governing parameter coupling elasticity, electronics, thermal transport, and optics, establishing the 4-5-6-8 nanoribbon as a unified platform for predictive design of multifunctional carbon materials.

Figures (5)

• Figure 1: Structural characterization and stability of the 4-5-6-8 carbon nanoribbon. (a) Atomic structure highlighting the periodic incorporation of nonhexagonal rings within the ribbon backbone. (b) Cohesive energy comparison with a width-matched armchair graphene nanoribbon, indicating similar energy stability. (c) Optimized geometry and representative C-C bond lengths, revealing pronounced bonding heterogeneity induced by the mixed polygonal network. (d,e) Statistical distributions of bond lengths and bond angles, thereby providing a consistent framework for analyzing a uniform hexagonal environment. (f) Phonon dispersion confirming dynamical structural stability through the absence of imaginary modes. (g) Ab initio molecular dynamics simulations at multiple temperatures demonstrating structural thermal robustness. (h) Final ab initio molecular dynamics snapshot at 1500 K, showing preservation of the ribbon morphology.
• Figure 2: Electronic and transport properties. (a) Electronic structure overview showing the band structure (left), the corresponding Density of States (DOS) (middle), and quantum conductance (right). The results are compared among the PBE (blue), HSE06 (red), and Tight-Binding (TB, black) methods. The calculated electronic band gaps are 0.59 eV (PBE), 1.08 eV (HSE06), and 1.07 eV (TB), respectively. (b) Electron Localization Function (ELF) map. (c) Local Density of States (LDOS) comparing DFT and TB spatial distributions. (d) Local Transmission Density (LTD) showing bond currents. Both (c) and (d) are visualized at the valence band peak ($E = -0.75$ eV) and conduction band valley ($E = 0.68$ eV).
• Figure 3: Selected physical properties of 4-5-6-8 nanoribbon as a function of an externally applied uniaxial strain at $T=0$ K. (a) DFT-based stress-strain curve showing an estimated Young’s modulus of $Y_{M} = 419.4 \pm 2.4$ GPa. (b) Evolution of the energy gap versus strain, comparing ab initio calculations (PBE in blue, HSE06 in red) with Tight-Binding (TB in black) results. (c) Electronic conductance and (d) electric current as a function of bias voltage, calculated using the TB method for strain strengths ranging from 0% to 10%.
• Figure 4: Thermal and thermoelectric transport properties. (a) Lattice thermal conductance ($\kappa_{ph}$) as a function of temperature, calculated using molecular dynamics. The inset shows the phonon thermal conductivity ($\sigma_{ph}$) as a function of length ($L$). (b) Seebeck coefficient, (c) Power factor, and (d) thermoelectric figure of merit ($ZT$) plotted as a function of chemical potential. The curves represent different temperatures ranging from $300$ K to $600$ K.
• Figure 5: Optical properties of the 4-5-6-8 nanoribbon. (a) Real and imaginary parts of the dielectric function. (b) Absorption coefficient spanning the near-visible and ultraviolet spectral regions. (c) Refractive index. (d) Reflectivity. (e) Optical conductivity. (f) Energy loss function. The shaded region denotes the visible range, emphasizing the spectral window relevant for optoelectronic applications.