Bulletin of the American Physical Society
15th APS Topical Conference on Shock Compression of Condensed Matter
Volume 52, Number 8
Sunday–Friday, June 24–29, 2007; Kohala Coast, Hawaii
Session C2: First Principles and Molecular Dynamics Calculations I |
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Chair: Carter White, Naval Research Laboratory Room: Fairmont Orchid Hotel Amphitheater |
Monday, June 25, 2007 1:45PM - 2:00PM |
C2.00001: Anisotropic constitutive relationships in energetic materials: nitromethane, RDX, and TATB Ivan Oleynik, Michael Conroy, Carter White We extend our first-principles studies of isotropic equation of states (EOS) of energetic materials to include stress-dependent relationships that describe the anisotropic materials response upon dynamic loading. We will discuss the results of first-principles density functional theory calculations of the energetic materials nitromethane, RDX, and TATB. The behavior of the materials is investigated upon both hydrostatic and uniaxial compressions along different crystallographic directions and compressions resulting in pressures up to 50 GPa. We will examine the equations of state for each material, its structural and electronic properties as a function of compression ratio, and compare with available experimental results. The behavior of shear stresses upon uniaxial compression will be discussed in relationship with the sensitivity properties of these materials. [Preview Abstract] |
Monday, June 25, 2007 2:00PM - 2:15PM |
C2.00002: Molecular simulations of Crussard curves of detonation product mixtures at chemical equilibrium: Microscopic calculation of the Chapman-Jouguet state Emeric Bourasseau, Vincent Dubois, Nicolas Desbiens, Jean-Bernard Maillet The simultaneous use of the Reaction Ensemble Monte Carlo (ReMC) method and the Adaptative Erpenbeck EOS (AE-EOS) method allows us to calculate direclty the thermodynamical and chemical equilibrium of a mixture on the hugoniot curve. The ReMC method allow to reach chemical equilibrium of detonation products and the AE-EOS method constraints ths system to satisfy the Hugoniot relation. Once the Crussard curve of detonation products has been established, CJ state properties may be calculated. An additional NPT simulation is performed at CJ conditions in order to compute derivative thermodynamic quantities like Cp, Cv, Gruneisen gama, sound velocity, and compressibility factor. Several explosives has been studied, of which PETN, nitromethane, tetranitromethane, and hexanitroethane. In these first simulations, solid carbon is eventually treated using an EOS. [Preview Abstract] |
Monday, June 25, 2007 2:15PM - 2:30PM |
C2.00003: Ab Initio Equation of State for $\beta $-HMX Frank Zerilli, Maija Kuklja An ab initio equation of state for the molecular crystal $\beta $-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine ($\beta $-HMX) has been calculated for temperatures between 0 and 400 K, and for specific volumes from 0.42 to 0.55 cm$^{3}$/gm, corresponding to relative volumes from 0.8 to 1.03. The calculated 300 K isotherm agrees well with the experimentally measured pressure-volume relation reported by Gump and Peiris (\textit{J. Appl.} \textit{Phys.} \textbf{97}, 053513 (2005)), and by Yoo and Cynn (\textit{J. Chem. Phys.} \textbf{111}, 10229 (1999\textbf{)}). The calculated specific heat agrees well with experimental data reported over the range from 300 to 400 K (Hanson-Parr and Parr, \textit{J. Energetic Mater}. \textbf{17}, 1-47 (1999)). The main source of error in the calculations is due to the absence of an adequate ab inito treatment of non local van der Waals interactions which are important in molecular crystals. Work is underway to include these interactions. [Preview Abstract] |
Monday, June 25, 2007 2:30PM - 2:45PM |
C2.00004: Anisotropic constitutive relationships in energetic materials: PETN and HMX Michael Conroy, Ivan Oleynik, Sergey Zybin, Carter White One of the important goals in energetic materials (EM) research is predicting EM properties from first principles based upon underlying atomic structure. Special attention is being focused on obtaining accurate equations of state for several important classes of EMs. In this presentation, we will discuss the results of first-principles density functional theory calculations of the energetic materials PETN and HMX. For each material, we have simulated both hydrostatic compression and uniaxial compression in the crystallographic directions [100], [010], [001], [110], [101], [011], and [111] up to V/V$_{0}$ = 0.50 ($\sim $40-50 GPa). We will examine the equations of state for each material and other structural properties of the unit cell as a function of volume and compare with available experimental results. Also, we will discuss the correlation between calculated shear stresses upon uniaxial compression with experimentally observed anisotropies in sensitivity to shock-induced detonation. [Preview Abstract] |
Monday, June 25, 2007 2:45PM - 3:00PM |
C2.00005: First principles calculation of the structure and vibrational modes for RDX crystals under static and shock compression M.S. Miao, Z.A. Dreger, J.M. Winey, Y.M. Gupta The structure and vibrational modes for RDX crystals, under hydrostatic pressures up to 4 GPa and uniaxial strains along [100] and [111] directions, were calculated at the first principles level by use of the VASP program. The PW91 generalized gradient approximated (GGA) exchange and correlation energy functional and ultrasoft pseudopotentials were employed and a cutoff of 550 eV was used for plane wave basis. The calculated volume and lattice constants at ambient pressure are larger than the experimental value. With increasing pressure, both volume and lattice constants agree better with experimental values. Despite the large deformation of the lattice, the geometry of each molecule changes only slightly as a function of pressure or uniaxial strain. For the vibrational modes, the calculated pressure dependencies of the frequencies agree well with experimental results. For example, the C-H stretching modes and lattice modes show large pressure dependences whereas many other modes such as the ONO stretching modes change only slightly with pressure. The comparison between the effects of hydrostatic pressure and uniaxial strain on vibrational modes will also be presented. [Preview Abstract] |
Monday, June 25, 2007 3:00PM - 3:15PM |
C2.00006: Calculation of RDX molecular crystal geometry and vibrational frequencies under hydrostatic pressure Warren Perger, Wil Slough First-principles calculations of the effects of hydrostatic pressure on RDX are performed using the all-electron CRYSTAL06 program. The lattice constants and optimized internal co-ordinates are simulanteously obtained at ambient pressure and hydrostatic pressure up to 4 GPa. A variety of density functionals and basis sets are used and presented for comparison. The vibrational frequencies as a function of pressure are also calculated and compared with previous gas-phase calculations. [Preview Abstract] |
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