Design rules for 1D sp–carbon devices: contact effects, length, and strain control

We use density-functional theory combined with nonequilibrium Green's-function transport calculations (DFT + NEGF) to study electronic transport across a systematic series of alkynic/carbyne junctions (families FA-1…FA-10). Device geometries and contact registries were sampled to identify stable contact configurations and to extract channel-resolved transmission eigenvalues and TVS/Fowler–Nordheim/Millikan–Lauritsen diagnostics.Our computed cohesion energies cluster tightly around ≈ −7.0 eV per atom across the series, indicating similar thermodynamic stability for all families. Eigenchannel analysis and transport diagnostics reveal three transport regimes: (i) short bridges (e.g., FA-1) are essentially non-conducting at zero bias (T₁ ≈ 6.28 × 10 −4 ) but develop a near-open resonant channel under bias (T₁ ≈ 0.787 at 1.0 V), (ii) intermediate families show partial bias activation with moderate T₁ growth (e.g., FA-2: 0.00035 → 0.173 at 1.0 V; FA-4: 0.0042 → 0.0528 at 1.0 V), and (iii) long bridges (FA-8…FA-10) remain tunneling-dominated with T₁ typically in the 10 −6 –10 −3 range even at high bias. These findings yield concrete, experimentally testable signatures (parity oscillations in low-bias conductance, systematic transition-voltage shifts with length/strain, and eigenchannel-resolved spatial fingerprints) and therefore provide direct guidance for STM/MCBJ validation and future device integration.