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Twin induced sensitivity enhancement of HMX versus shock: A molecular reactive force field simulation

Evidence and attribution

Authority of statements

Prose below summarizes the publication identified by doi, title, and pdf_path. Authors are CAEP / Sichuan University; no van Duin-group affiliation.

Summary

ReaxFF plus the multi-scale shock technique (MSST) shocks twinned and perfect HMX crystals at 6–10 km/s for ~50 ps to probe how crystallographic defects influence shock initiation and early decomposition in energetic materials. The twin lowers shock initiation stress, raises decomposition rates, and produces larger temperature and stress rises than the perfect crystal under identical shock conditions—trends the authors connect to experimental sensitivity differences between defective and ideal HMX. The twin plane is the hottest region shortly after shock, with temperature decreasing away from it—supporting hot-spot nucleation localized at the defect. The work is an external CAEP / Sichuan University contribution in the corpus (no van Duin-group affiliation).

Methods

1 — MD application (atomistic dynamics). Molecular dynamics (MD) is carried out in LAMMPS using ReaxFF_lg7 together with the multiscale shock technique (MSST) to shock twinned (TH) vs perfect (PH) HMX along (001) (normal to the twin plane) at 6–10 km/s (papers/ReaxFF_others/Wen_HMX_twin_JPC_C_2013.pdf; normalized/extracts/2013wen-venue-jp4072795_p1-2.txt). The supercell contains 320 HMX molecules (8960 atoms) including a twinning plane for TH (Section 2.1), with three-dimensional periodic boundary conditions (3D PBC) as standard for the bulk HMX shock cell in this MSST setup. Trajectories extend 50 ps with Δt = 0.1 fs, writing frames every 1 ps for analysis. Thermostat: MSST couples shock heating to a thermostat-like multiscale control as defined by Reed et al. and implemented in LAMMPS (see pdf_path for equations and parameters). FindMole post-processes species; stress diagnostics use the virial stress tensor as defined in LAMMPS output. Ensemble: the MSST propagator implements the MSST shock equations (a non-equilibrium route distinct from equilibrium NVT/NPT sampling); any explicit NVE/NVT preshock legs are only in pdf_path beyond this summary. Electric field: N/A — not used. Replica / enhanced sampling: N/A — MSST replaces umbrella/metadynamics here.

2 — Force-field training. N/A — ReaxFF_lg7 is selected and justified via SI references rather than being newly fit in this article’s main text (as framed on this page).

3 — Static QM / DFT-only. N/A — shock MD is central.

Findings

Outcomes & mechanisms. The twin lowers shock initiation stress, increases reactant decay rates, and produces larger temperature and stress rises than the perfect crystal for the same shock—matching experimental sensitivity trends discussed by the authors. The twin plane is the hottest region shortly after shock, with temperature falling away from it—supporting hot-spot nucleation at the defect rather than uniform heating. The study argues microstructure (twinning) can focus energy dissipation and accelerate early chemistry versus ideal crystals in this ReaxFF+MSST setup.

Comparisons. Trends are discussed relative to experimental sensitivity of defective vs ideal HMX in the article’s framing.

Sensitivity & design levers. Shock speed (6–10 km/s), twin vs perfect microstructure, and post-shock T/stress fields are the primary levers summarized here.

Limitations & outlook. Idealized twin geometry and ~50 ps horizons limit direct connection to continuum detonation; MSST approximates steady shocks with constraints that differ from full Eulerian shock treatments (## Limitations).

Corpus honesty. External CAEP / Sichuan University corpus entry (no van Duin-group affiliation); confirm ReaxFF_lg7 identity against SI before cross-corpus numerical comparisons.

Limitations

Idealized twin geometry; short simulation time; continuum detonation and long-time burn are not resolved. MSST approximates steady shock response with thermostat-like constraints that differ from full non-equilibrium Eulerian shock simulations.

Relevance to group

External HMX shock study in corpus showing ReaxFF + MSST sensitivity to twin defects.

Citations and evidence anchors

  • DOI: 10.1021/jp4072795
  • Extract: normalized/extracts/2013wen-venue-jp4072795_p1-2.txt

Reader notes (navigation)

MSST shock simulations here use ReaxFF_lg7; confirm parameter file identity against Supporting Information S2 before comparing HMX twin results to other HMX shock studies in the corpus that may use different ReaxFF variants.