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Investigation of lattice thermal conductivity of α′ borophene and hydrogenated α′-4H borophene using reverse nonequilibrium molecular dynamics simulation

Summary

Lattice thermal conductivity (LTC) and thermal anisotropy of two-dimensional α′ borophene and hydrogenated α′-4H borophene are computed at 300 K using reactive molecular dynamics in LAMMPS with a ReaxFF potential, with heat transport evaluated by reverse non-equilibrium molecular dynamics (rNEMD) and the enhanced heat exchange (eHEX) algorithm. The Phys. Lett. A abstract motivates the study by noting strong electronic anisotropy in borophene allotropes alongside growing experimental realization of 2D boron structures, then focuses on how hydrogenation and in-plane orientation modify phonon-dominated thermal transport in the ReaxFF framework.

Methods

Interaction model (A/B)

  • Software: LAMMPS with ReaxFF for borophene / hydrogenated borophene (α′ and α′-4H phases as defined in the article).

Equilibration

  • Relaxation: Polak–Ribière conjugate-gradient structural optimization.
  • Thermostat: Nosé–Hoover at 300 K for 0.1 ns with timestep 0.1 fs.
  • Structure checks: RDF/ADF accumulated over 100 fs to verify local geometry.

Thermal transport protocol (B)

  • Method: Reverse NEMD with the enhanced heat exchange (eHEX) algorithm.
  • Geometry: Periodic in-plane; 50 slabs along the heat-flow direction; hot/cold slab energy exchanges impose steady flux; transverse width ~6 nm for comparing orientations.
  • Steady state: 0.1 ns at 0.1 fs in NESS before averaging slab T; longer >0.2 ns segments used to build temperature profiles.

Extraction of κ

κ from Fourier’s law using imposed flux, area, and ∇T; size scaling via κ(L\(_x\)) = κ\(_∞\)/(1 + λ/L\(_x\)) to discuss finite-length effects.

MD application (integrated, same as above detail)

Engine / code: LAMMPS and ReaxFF. System & composition: 2D α′ and hydrogenated α′-4H borophene; PBC in-plane; rNEMD with eHEX uses ~50 slabs in the heat-flow direction, ~6 nm transverse width, hot/cold slab thermostating to impose flux. Timestep 0.1 fs; 0.1 ns Nosé–Hoover equilibration at 300 K; 0.1 ns NESS and >0.2 ns temperature profile accumulation as stated. NVT-class thermostated segments for the thermal workflow; N/A — NPT not used in the κ setup summarized here. N/A — barostat / hydrostatic pressure in this NEMD protocol. N/A — static electric field; N/A — umbrella / metadynamics for κ in this paper’s main line.

Findings

Hydrogenation effect

Hydrogenation increases LTC along armchair for α′ vs pristine in the authors’ ReaxFF rNEMD setup.

Anisotropy

α′ and α′-4H show strong in-plane thermal anisotropy.

Length dependence

Armchair κ increases with sample length in the studied range; zigzag κ decreases with length—attributed to defects, phonon interference, and dispersion effects along that direction.

The abstract further summarizes that α′-4H hydrogenated sheets exhibit higher LTC than pristine α′ along armchair in their parametrization, consistent with hydrogenation stiffening certain phonon branches while preserving strong in-plane anisotropy between armchair and zigzag transport directions. Comparisons to DFT/experiment in the text should be read from the PDF; sensitivity of κ to sample length is explicit above.

Limitations

ReaxFF is empirical; absolute κ values and trends should be cross-checked against experiment or higher-level theory where available.

Relevance to group

Demonstrates ReaxFF + LAMMPS thermal transport workflow (rNEMD/eHEX) for 2D boron allotropes, adjacent to the group’s broader reactive-MD tooling experience.

Citations and evidence anchors

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