Reaction Rates in Nitromethane under High Pressure from Density Functional Tight Binding Molecular Dynamics...

Area of Science:

• Computational Chemistry
• Materials Science
• Chemical Kinetics

Background:

• Nitromethane (NM) is a high explosive requiring detailed understanding of its reaction dynamics.
• Investigating NM's reactivity under extreme conditions is crucial for safety and performance prediction.

Purpose of the Study:

• To determine the reaction rates of nitromethane (NM) under high pressure (14-28 GPa) and temperature (1450-1850 K).
• To develop a simplified model for NM explosion dynamics.
• To provide reaction rates for implementation in hydrocodes.

Main Methods:

• Density Functional Tight Binding (DFTB) molecular dynamics (MD) simulations were employed.
• Multiple MD simulations were run to capture stochastic reaction behaviors.
• Data was fitted to a Frank-Kamenetskii model to extract kinetic parameters.

Main Results:

• DFTB-MD simulations revealed stochastic reaction times and chemical pathways for NM.
• A two-step model (ignition/explosion) was devised, identifying aci-ion formation as a key early step.
• Prefactors, activation energies, and volumes for ignition and explosion stages were extracted.

Conclusions:

• The study provides an efficient method for investigating high explosive reactivity using electronic structure-based MD simulations.
• The developed two-step model accurately represents NM explosion dynamics and can be integrated into hydrocodes.
• This research offers valuable kinetic data for understanding and modeling energetic materials.