Reactive molecular dynamics simulation of the thermal decomposition mechanisms of 4,10-dinitro-2,6,8,12-tetraoxa-4,10-diazatetracyclo[5.5.0.05,9.03,11]dodecane (TEX)
TEX is a cage-structured energetic nitramine whose thermal decomposition chemistry is studied with ReaxFF/lg reactive MD at several thousand Kelvin to catalog bond-breaking sequences, gas-phase products, and carbon-rich clusters.
Summary¶
The publication applies the ReaxFF/lg reactive force field in periodic boundary conditions to a TEX supercell and heats the system isothermally at 2000 K, 2500 K, 3000 K, and 3500 K to accelerate thermal decomposition. Trajectory analysis extracts dominant initiation steps, stable small-molecule products, evolving cage fragmentation, composition of condensed carbonaceous clusters, and effective kinetic staging as temperature increases. The abstract positions TEX as an isowurtzitane cage explosive with favorable casting properties and cites literature on N–NO₂ bond energy as a sensitivity correlate, motivating systematic reactive MD across temperatures where clusters and gas products compete.
Methods¶
1 — MD application (atomistic dynamics). Simulations use LAMMPS with the ReaxFF/lg reactive force field. A 3 × 3 × 2 supercell of crystalline TEX contains 36 TEX molecules (see Fig. 1 in the article). Three-dimensional periodic boundary conditions enclose the cell. The protocol first relaxes the geometry to a force tolerance of 10⁻⁷ kcal mol⁻¹ Å⁻¹, assigns Maxwell–Boltzmann speeds at 300 K, then equilibrates in NVT at ~300 K for 10 ps with a Berendsen thermostat, followed by NPT at 300 K and 0 atm for 10 ps with a Nosé–Hoover barostat/thermostat (as stated in the paper’s Methods). Isothermal–isochoric (NVT) MD is then run at 2000 K, 2500 K, 3000 K, and 3500 K with a 0.1 fs timestep and a Berendsen thermostat (damping 100 fs). Molecular species are recorded every 10 fs; bond orders and atomic trajectories every 200 fs (per the article). Production trajectories extend to the hundreds of picoseconds range in the reported potential-energy and species-count analyses (e.g. order 10² ps at the higher temperatures in the text).
2 — Force-field training: N/A — the study applies the published ReaxFF/lg nitramine parameterization; it does not re-fit the force field.
3 — Static QM / DFT-only: N/A as a primary method; the Introduction cites prior DFT and AIMD on TEX for context only.
Barostat in production: N/A — thermal decomposition production stages are NVT (constant volume).
Electric field / bias: N/A.
Replica / enhanced sampling: N/A — direct hot NVT trajectories; no umbrella or metadynamics.
Findings¶
Decomposition initiates with N–NO₂ bond cleavage, followed by C–O stretching and progressive cage rupture that releases NO₂ and related fragments in stages. The authors report major gas-phase products including NO₂, NO, H₂O, CO₂, N₂, H₂, HNO₂, and HNO, together with larger clusters such as C₁₂H₁₂N₆O₁₂ and C₁₈H₁₃N₇O₁₄ whose prevalence depends on temperature and reaction progress. Cluster evolution is temperature sensitive: lower temperatures leave the cage largely intact and limit cluster growth, whereas higher temperatures promote large clusters that may subsequently fragment. Hydrogen, nitrogen, and oxygen partition differently between clusters and gas-phase species, with oxygen retained more strongly in condensed fragments—a trend the authors connect to later autoxidation behavior. The introduction contrasts this temperature-swept ReaxFF survey with prior AIMD on small TEX supercells that did not simultaneously address clusters and high-temperature kinetics at scale.
Limitations¶
High-temperature reactive MD uses empirical reactive potentials; quantitative rates should be cross-checked against experiment and quantum benchmarks where available.
Relevance to group¶
Example of ReaxFF/lg applied to nitramine cage decomposition chemistry relevant to energetic materials modeling.