Bulletin of the American Physical Society
16th APS Topical Conference on Shock Compression of Condensed Matter
Volume 54, Number 8
Sunday–Friday, June 28–July 3 2009; Nashville, Tennessee
Session U2: EOS-2: Equations of State |
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Chair: Cynthia Schwartz, Los Alamos National Laboratory Room: Hermitage AB |
Thursday, July 2, 2009 11:00AM - 11:15AM |
U2.00001: Equation of State of Warm Dense Hydrogen at Megabar Pressure Range V.K. Gryaznov, I.L. Iosilevskiy Improved model for equation of state of warm dense hydrogen (SAHA-D) is developed in frames of ``chemical picture.'' Hydrogen is considered as multi-component strongly interacted mixture of atoms, molecules, ions and electrons. Intense short-range repulsion of neutral particles is presented in frames of soft sphere approximation. Parameters of interaction potentials for atoms and molecules are chosen in accordance with non-empirical atom-atom approach. Modified pseudopotential approximation is used for Coulomb corrections. Partial degeneracy of electrons is taken into account also. SAHA-D model has good asympthotics at the low (room temperature) and very high temperature limits. Detailed comparison of our results with all available experiments on the first and secondary shock is presented in the intermediate temperature range. Results of calculations of equation of state and thermodynamic properties in frames of SAHA-D model of isoentropically compressed liquid deuterium as well as comparison with new experimental data are presented and discussed. [Preview Abstract] |
Thursday, July 2, 2009 11:15AM - 11:30AM |
U2.00002: Planar Impact Study of a Shear Thickening Fluid Oren Petel, Andrew Higgins Dense suspensions of particles in liquids often exhibit non-Newtonian behavior, such as shear thickening, under the appropriate stimulus. Recently, there has been increasing interest in these materials for protective applications, but their dynamic response has not yet been extensively characterized. The current study examines the behavior of these types of suspensions under a plate impact loading scenario. The impacts were generated by steel flyer plates launched at velocities of up to 500 m/s from a single-stage 64-mm-bore gas gun. The shear thickening fluids consisted of micron-scale ceramic powders (amorphous silica and silicon carbide) suspended in ethylene glycol at near-limit volume fractions. Shock velocity and dynamic strain gage measurements are reported. [Preview Abstract] |
Thursday, July 2, 2009 11:30AM - 12:00PM |
U2.00003: Shock-Wave Exploration of the High-Pressure Phases of Carbon Invited Speaker: The high energy density behavior of carbon, particularly in the vicinity of the shock melt boundary and the theoretically predicted diamond-liquid-bc8 triple point, is of broad scientific interest, and is of particular interest to those studying planetary astrophysics and inertial confinement fusion. Previous experimental data in the several hundred GPa pressure range in the vicinity of the melt boundary have only been able to provide data with accuracy levels that permit qualitative comparison with theory. Here we present shock-wave experiments on carbon using a magnetically driven flyer plate technique with sufficient accuracy to enable quantitative comparison with quantum molecular dynamics (QMD) simulations. Our QMD simulations indicate subtle but measurable changes in the shock {$U_s-u_p$} behavior as the shock Hugoniot traverses the diamond-liquid and the bc8-liquid coexistence regions and a distinct change in slope at the diamond-liquid-bc8 triple point. The data is in very good agreement with the theoretical predictions and provides strong evidence for the existence of the diamond-liquid-bc8 triple point along the principal Hugoniot for diamond. [Preview Abstract] |
Thursday, July 2, 2009 12:00PM - 12:15PM |
U2.00004: Optimized Nested Markov Chain Monte Carlo Sampling: Theory Joshua Coe, Thomas D. Sewell, M. Sam Shaw Metropolis Monte Carlo sampling of a reference potential is used to build a Markov chain in the isothermal-isobaric ensemble. At the endpoints of the chain, the energy is reevaluated at a different level of approximation (the ``full'' energy) and a composite move encompassing all of the intervening steps is accepted on the basis of a modified Metropolis criterion. By manipulating the thermodynamic variables characterizing the reference system we maximize the average acceptance probability of composite moves, lengthening significantly the random walk made between consecutive evaluations of the full potential at a fixed acceptance probability. This provides maximally decorrelated samples of the full potential, thereby lowering the total number required to build ensemble averages of a given variance. The efficiency of the method is illustrated using model potentials appropriate to molecular fluids at high pressure. Implications for ab initio or density functional theory (DFT) treatment are discussed. [Preview Abstract] |
Thursday, July 2, 2009 12:15PM - 12:30PM |
U2.00005: Optimized Nested Markov Chain Monte Carlo Sampling: Application to the Liquid Nitrogen Hugoniot Using Density Functional Theory M. Sam Shaw, Joshua D. Coe, Thomas D. Sewell An optimized version of the Nested Markov Chain Monte Carlo sampling method is applied to the calculation of the Hugoniot for liquid nitrogen. The ``full'' system of interest is calculated using density functional theory (DFT) with a 6-31G* basis set for the configurational energies. The ``reference'' system is given by a model potential fit to the anisotropic pair interaction of two nitrogen molecules from DFT calculations. The EOS is sampled in the isobaric-isothermal (NPT) ensemble with a trial move constructed from many Monte Carlo steps in the reference system. The trial move is then accepted with a probability chosen to give the full system distribution. The P's and T's of the reference and full systems are chosen separately to optimize the computational time required to produce the full system EOS. The method is numerically very efficient and predicts a Hugoniot in excellent agreement with experimental data. [Preview Abstract] |
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