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Catalyzed growth of encapsulated carbyne

Corpus PDF role

Second registered PDF bytes for the Carbon 2019 article on Ni-catalyzed endohedral carbyne inside a double-walled nanotube (same DOI). Narrative alignment: 2019khalilov-carbon-153-2-catalyzed-growth (alternate path).

Summary

Endohedral carbyne—a one-dimensional carbon chain—inside carbon nanotubes is a long-standing target in nanocarbon synthesis, but atomistic mechanisms of catalytic chain growth under hydrocarbon feedstock remain difficult to probe experimentally at the insertion step. This work combines ReaxFF reactive molecular dynamics (parameters from Zou et al.) with DFT (VASP, GGA-RPBE, PAW pseudopotentials) to study nickel clusters hosted inside a (5,5)@(10,10) double-walled tube. C\(_2\), C\(_2\)H, and C\(_2\)H\(_2\) species are injected as feedstock at 500 K versus 1700 K effective flux conditions (controlled by insertion interval). The study emphasizes sticking and adsorption energetics as a function of hydrogen content, Ni facet geometry (step-like versus flatter (111)-like regions), and how ReaxFF and DFT agree on trends even when absolute binding strengths differ.

Methods

Narrative matches the version-of-record curation on 2019khalilov-carbon-153-2-catalyzed-growth (same DOI and science; alternate PDF bytes here).

1 — MD application (RMD, ReaxFF)

ReaxFF (parameters of Zou et al.) in a (5,5)@(10,10) DWNT with PBC along the axis; Ni in the inner tube (d\(_\mathrm{in}\)≈0.70 nm, d\(_\mathrm{out}\)≈1.39 nm). NpT preequilibration (Berendsen), then NVT with Bussi; C\(_2\)/C\(_2\)H/C\(_2\)H\(_2\) insertion every 25 ps (1700 K) or 250 ps (500 K). Timestep (fs): N/A in the Methods text of the indexed PDF—use 2019khalilov-carbon-153-2-catalyzed-growth or SI for reproducibility. Barostat in production / pressure in NVT: N/A for NVT stages as written. Electric field / enhanced sampling: N/A.

2 — Force-field training

N/A — published ReaxFF parameters (Zou et al.), not a new fit in this article.

3 — Static QM (VASP, NEB)

VASP RPBE+PAW, 400 eV, Γ (1×1×1), ~20×20 Å in-plane supercells; PBE+TS negligible in author tests; NEB for dimer nucleation with ~0.1–0.3 eV barriers as reported.

Findings

Sticking and adsorption energies anti-correlate with H/C ratio in the feedstock family: hydrogen-rich species behave differently from bare C\(_2\) in both ReaxFF and DFT, preserving qualitative ordering across methods. Step-like Ni facets promote C–H cleavage pathways compared with flatter facets, shaping whether dimerization or dehydrogenation dominates early chemistry. DFT consistently reports stronger absolute binding than ReaxFF, but relative trends (which site binds more strongly, which feedstock sticks more readily) remain aligned between models. Ni-terminated carbon chains allow hydrogen to modulate electronic response, linking hydrocarbon identity to whether C–C polymerization or C–H scission is favored on curved Ni surfaces inside the confining nanotube (see version-of-record text on 2019khalilov-carbon-153-2-catalyzed-growth for table / figure locators).

Limitations

ReaxFF and DFT adsorption energies can differ by roughly two-fold in magnitude for some configurations; the paper focuses on mechanistic trends and barrier order-of-magnitude estimates rather than quantitative agreement with experiment for long carbyne stability or growth rates.

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