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Molecular dynamics simulations of shock waves in oriented nitromethane single crystals: plane-specific effects
Lan He1, Thomas D Sewell, Donald L Thompson
1Department of Chemistry, University of Missouri-Columbia, Columbia, Missouri 65211-7600, USA.
The Journal of Chemical Physics
|January 28, 2012
Summary
Molecular dynamics simulations reveal shock waves in crystalline nitromethane cause plane-specific structural disordering. Kinetic energy redistribution, however, shows no such directional preference.
Area of Science:
- Materials Science
- Physical Chemistry
- Computational Physics
Background:
- Understanding the behavior of energetic materials under shock compression is crucial for safety and performance.
- Crystalline nitromethane is a model energetic material whose response to shock waves provides insights into fundamental decomposition mechanisms.
Purpose of the Study:
- To investigate the post-shock relaxation phenomena in crystalline nitromethane under various shock wave propagation directions.
- To characterize the plane-specific structural and orientational disordering induced by shock waves.
- To analyze the kinetic energy partitioning and redistribution following shock compression.
Main Methods:
- Molecular dynamics simulations were performed using the Sorescu-Rice-Thompson force field.
- Simulations covered shock waves propagating along [110], [011], [101], [111], [100], [010], and [001] directions.
- Analysis involved calculating 1D mean square displacement (MSD), 2D radial distribution function (RDF), 2D orientation order parameter P(2)(θ), and kinetic energy components.
Main Results:
- Shocks along [010] and [101] induced crystal-crystal structure transformations.
- Shocks along other directions ([011], [110], [111], [100], [001]) resulted in plane-specific structural disordering, evident in 2D RDF.
- Disordering was most extensive in (010) and (110) planes, less in (100), and minimal in (001).
- Orientational and translational disordering, as indicated by 2D P(2)(θ) and 1D MSD, were also plane-specific.
- Kinetic energy partitioning and redistribution showed no plane specificity.
Conclusions:
- Shock wave propagation direction significantly influences the post-shock relaxation and disordering in crystalline nitromethane.
- The observed plane-specific disordering arises from anisotropic orientational and translational relaxation.
- Kinetic energy dynamics are isotropic, suggesting a decoupling between structural changes and energy redistribution mechanisms.
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