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Atomistic simulation of orientation dependence in shock-induced initiation of pentaerythritol tetranitrate

Evidence and attribution

Authority of statements

Prose below summarizes the publication identified by doi, title, and pdf_path. Authors are Sandia National Laboratories; no van Duin-group affiliation.

Summary

ReaxFF MD with the multiscale shock technique (MSST) shocks PETN single crystals along [110], [001], and [100] with shock speeds 3–10 km/s. Chemistry turns on at ≥ ~6 km/s, initiated by nitro/nitrate-group cleavage. Sensitivity ranks [110] most sensitive, [100] least; for [001], nitro loss dominates initiation, whereas [110] and [100] show mixed nitro/nitrate pathways. Energy partitioning into C–NO\(_2\) vs C–ONO\(_2\) modes differs by orientation, matching the trend that orientations with stronger steric hindrance to shear localize more plastic work and heat.

Methods

Grounding: papers/ReaxFF_others/Shan_PETN_JPCB_2013.pdf; normalized/extracts/2013shan-venue-jp310473h_p1-2.txt (abstract + Theoretical Methods opening).

1 — MD application (shock-driven reactive MD with MSST)

  • Engine / code: Molecular dynamics simulations using ReaxFF with shocks driven by the multiscale shock technique (MSST) (abstract). LAMMPS is not named on the indexed excerpt pages.
  • System size & composition: PETN single crystal simulated as a 4 × 4 × 4 supercell containing several thousand atoms (abstract / Methods excerpt).
  • Shock / strain rate: Shocks propagate along [110], [001], and [100] with shock speeds 3–10 km/s (abstract).
  • Boundaries / periodicity: Bulk PETN supercell shock setup (abstract framing); exact boundary conditions of MSST implementation are not restated on p1–2 beyond standard MSST usage—confirm in pdf_path.
  • Ensemble / thermostat (pre-shock equilibration excerpt): Prior to compression/shock work, the excerpted protocol includes NVT relaxation at 300 K using a Nosé–Hoover thermostat for up to 6 ps (DFT-MD) and 10 ps (ReaxFF-MD) (papers/ReaxFF_others/Shan_PETN_JPCB_2013.pdf, Sec. 2 excerpt).
  • Timestep / duration (MSST production): N/A — full MSST production timestep/duration tables are not on p1–2; read pdf_path shock Methods.
  • Temperature: N/A — explicit thermodynamic temperature protocol for shocked states is not stated separately from MSST shock strength on p1–2.
  • Pressure / stress: Shock loading implies uniaxial compression along selected orientations; stress tensor reporting is not stated on p1–2.
  • Electric field: N/A.
  • Replica / enhanced sampling: N/A — not stated beyond MSST-driven shocks.

2 — Force-field training

N/A — uses the ReaxFF parametrization of Budzien et al. as cited (abstract / Methods excerpt).

3 — Static QM / AIMD (supporting EOS context)

DFT-based molecular dynamics (DFT-MD) on the unreacted Hugoniot uses AM05 in VASP 5.2 with 800 eV cutoff and k-point sampling at mean-value point (¼,¼,¼), ionic timestep 0.4 fs, referencing experimental PETN lattice parameters (Methods excerpt).

Findings

  • Outcomes & mechanisms: For shocks ≥ ~6 km/s, chemistry initiates via dissociation of nitro and nitrate groups (abstract). Steric hindrance arguments tie slip-system constraints to localized plastic heating and orientation-dependent sensitivity (abstract + introduction excerpt).
  • Comparisons: The introduction contrasts prior small-cell / pair-collision studies with this work’s larger supercell shocks intended to capture local deformation mechanisms (abstract/intro excerpt).
  • Sensitivity / design levers: Shock orientation and shock speed (3–10 km/s) are the primary knobs; sensitivity order is reported as [110] most sensitive, [001] intermediate, [100] least sensitive (abstract).
  • Limitations & outlook: The abstract distinguishes dominant initiation channels by orientation ([001] nitro-loss-dominated vs [110]/[100] mixed nitro/nitrate pathways) and discusses kinetic energy partitioning among C–NO\(_2\) vs C–ONO\(_2\) modes (abstract).
  • Corpus honesty: Indexed excerpt includes DFT-MD settings for the unreacted Hugoniot but does not include full MSST parameter tables; read pdf_path for complete shock MD protocol.

Limitations

Ideal crystal blocks omit defects, porosity, and continuum-scale hydrodynamics. MSST is an approximate shock-driving framework; quantitative initiation thresholds should be cross-checked against the paper’s full shock protocol and any continuum/hydro validation literature cited there.

Relevance to group

Corpus energetic materials / shock example using ReaxFF (external to van Duin group) for MST benchmarking.

Citations and evidence anchors

  • DOI: 10.1021/jp310473h
  • Extract: normalized/extracts/2013shan-venue-jp310473h_p1-2.txt
  • Shock-to-chemistry coupling in condensed explosives
  • reaxff-family