It is shown that the introduction of zero-point energy and thermal effects to density functional theory with an empirical van der Waals correction results in a significant improvement in the prediction of equilibrium volumes and isothermal equations of state for hydrostatic compressions of energetic materials at nonzero temperatures. This method can be used to predict the thermophysical properties of these materials for a wide range of pressures and temperatures.

First-principles density functional theory ͑DFT͒ calculations have been used to obtain the constitutive relationships of pentaerythritol tetranitrate ͑PETN-I͒, a crystalline energetic material. The isotropic equation of state ͑EOS͒ for hydrostatic compression has been extended to include uniaxial compressions in the ͗100͘, ͗010͘, ͗001͘, ͗110͘, ͗101͘, ͗011͘, and ͗111͘ crystallographic directions up to a compression ratio of V / V 0 = 0.70. DFT predicts equilibrium properties such as lattice parameters and elastic constants, as well as the hydrostatic EOS, in agreement with available experimental data. Our results show a substantial anisotropy of various properties of PETN-I upon uniaxial compression. To characterize the anisotropic traits of PETN, different physical properties of the uniaxially compressed crystal such as the energy per atom, band gap, and stress tensor have been evaluated as a function of compression ratio. The maximum shear stresses were calculated and examined for a correlation with the anisotropy in shock-initiation sensitivity.

First-principles density functional theory calculations have been performed to obtain constitutive relationships in the crystalline energetic material ␤-cyclotetramethylene tetranitramine ͑␤-HMX͒. In addition to hydrostatic loading, uniaxial compressions in the directions normal to the ͕100͖, ͕010͖, ͕001͖, ͕110͖, ͕101͖, ͕011͖, and ͕111͖ planes have been performed to investigate the anisotropic equation of state ͑EOS͒. The calculated lattice parameters and hydrostatic EOS are in reasonable agreement with the available experimental data. The uniaxial compression data show a significant anisotropy in the principal stresses, change in energy, band gap, and shear stresses, which might lead to the anisotropy of the elastic-plastic shock transition and shock sensitivity of ␤-HMX.

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h i g h l i g h t s • Fuel beneath an aqueous firefighting foam increases the rate of foam degradation. • Iso-octane degrades foams faster than methylcyclohexane. • Fuel enhances bubble coalescence at the interface increasing foam degradation. • Fluorinated foams degrade slower than foams with only hydrocarbon surfactants.