First-principles calculations employing density functional theory (DFT) were
performed on the energetic materials PETN, HMX, RDX, nitromethane, and a recently
discovered material, nitrate ester 1 (NEST-1). The aims of the study were to accurately
predict the isothermal equation of state for each material, improve the description of these
molecular crystals in DFT by introducing a correction for dispersion interactions, and
perform uniaxial compressions to investigate physical properties that might contribute to
anisotropic sensitivity.
For each system, hydrostatic-compression simulations were performed. Important
properties calculated from the simulations such as the equilibrium structure, isothermal
equation of state, and bulk moduli were compared with available experimental data to
assess the agreement of the calculation method. The largest contribution to the error was
believed to be caused by a poor description of van der Waals (vdW) interactions within
the DFT formalism.
An empirical van der Waals correction to DFT was added to VASP to increase
agreement with experiment. The average agreement of the calculated unit-cell volumes
for six energetic crystals improved from approximately 9% to 2%, and the isothermal
EOS showed improvement for PETN, HMX, RDX, and nitromethane. A comparison was
made between DFT results with and without the vdW correction to identify possible
advantages and limitations.
Uniaxial compressions perpendicular to seven low-index crystallographic planes
were performed on PETN, HMX, RDX, nitromethane, and NEST-1. The principal
stresses, shear stresses, and band gaps for each direction were compared with available
experimental information on shock-induced sensitivity to determine possible correlations
between physical properties and sensitivity. The results for PETN, the only system for
which the anisotropic sensitivity has been thoroughly investigated by experiment,
indicated a possible correlation between maximum shear stress and sensitivity. The
uniaxial compressions that corresponded to the greatest maximum shear stresses in HMX,
RDX, solid nitromethane, and NEST-1 were identified and predicted as directions with
possibly greater sensitivity. Experimental data is anticipated for comparison with the
predictions.
| Identifer | oai:union.ndltd.org:USF/oai:scholarcommons.usf.edu:etd-4887 |
| Date | 17 September 2009 |
| Creators | Conroy, Michael W. |
| Publisher | Scholar Commons |
| Source Sets | University of South Flordia |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Graduate Theses and Dissertations |
| Rights | default |
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