Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session E3: First-Principles and Molecular Dynamics Calculations IV: Equations of State |
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Chair: Evan Reed, Stanford University Room: Renaissance Ballroom AB |
Monday, June 27, 2011 4:00PM - 4:15PM |
E3.00001: Equation of state of mixtures: density functional theory (DFT) simulations and experiments on Sandia's Z machine R.J. Magyar, S. Root, T.A. Haill, D.G. Schroen, T.R. Mattsson, D.G. Flicker Mixtures of materials are expected to behave quite differently from their isolated constituents, particularly when the constituents atomic numbers differ significantly. To investigate the mixture behavior, we performed density functional theory (DFT) calculations on xenon/hydrogen, xenon/ethane, and platinum/hydrocarbon mixtures. In addition, we performed shock compression experiments on platinum-doped hydrocarbon foams up to 480 GPa using the Sandia Z - accelerator. Since the DFT simulations treat electrons and nuclei generically, simulations of pure and mix systems are expected to be of comparable accuracy. The DFT and experimental results are compared to hydrodynamic simulations using different mixing models in the equation of state. The role of de-mixing and the relative contributions of the enthalpy of mixing are explored. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of the Lockheed Martin company, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Monday, June 27, 2011 4:15PM - 4:30PM |
E3.00002: Equations of state for energetic materials from density functional theory with van der Waals, thermal, and zero-point energy corrections Aaron Landerville, Michael Conroy, Mikalai Budzevich, You Lin, Carter White, Ivan Oleynik Equations of state EOS, which establish fundamental relationships between thermodynamic variables, are important because they provide necessary input for the description of materials at the mesoscopic and continuum levels. 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 non-zero temperatures. This method can be used to predict thermo-physical properties of these materials for a wide range of pressures and temperatures. [Preview Abstract] |
Monday, June 27, 2011 4:30PM - 4:45PM |
E3.00003: DFT Calculations for the Uranium EOS Carl Greeff, Scott Crockett, Sven Rudin, John Wills We present results of density functional theory calculations on the Uranium equation of state. We examine the influence of approximations for the exchange-correlation functional and spin-orbit interaction, as well as numerical methods such as pseudopotentials. We compare calculated properties, such as static lattice energies and electronic specific heats, to their empirically derived counterparts. [Preview Abstract] |
Monday, June 27, 2011 4:45PM - 5:00PM |
E3.00004: Equation of State and Kinetics of Shock Compressed Water, $\alpha $-Quartz and Diamond from Density Functional Tight Binding Simulations Nir Goldman, Larry Fried We present equation of state and chemical kinetics data from density functional tight binding (DFTB) molecular dynamics simulations of covalently bonded materials shock compressed to high pressure and temperatures. DFTB holds promise as an alternative to standard quantum simulations due to its increase in computational efficiency which allows for simulations of up to $\sim $1 ns while retaining the accuracy of quantum codes. However, its accuracy at extreme conditions remains largely unknown. Using a new extension to the Multi-Scale Shock Technique, we have simulated shock compression in water, $\alpha $-quartz and diamond up to high densities where these materials experience significant thermal electronic excitations and quartz and diamond are in a dense fluid state. Our simulations show good agreement with experimentally measured Hugoniot pressures, densities, and temperatures (where available) for all materials. In addition, our simulations of water yield accurate dissociation kinetics over a wide range of pressures. DFTB simulations have the potential to answer open experimental questions for a variety of materials, including the anomalous heat capacities measured in shock compressed $\alpha $-quartz and the transition to a high pressure BC8 phase in diamond. [Preview Abstract] |
Monday, June 27, 2011 5:00PM - 5:15PM |
E3.00005: Thermodynamic properties of solids and liquids at extreme conditions Amanuel Teweldeberhan, Stanimir Bonev A recent work on high pressure phases of calcium using a combination of density functional theory and diffusion quantum Monte Carlo methods will be presented. Various approaches have been used to compute the entropies and free energies of different structures of calcium exhibiting strong anharmonicity to account for their thermodynamic stability at high pressure. We will also discuss efficient methods for computing liquid free energies and their application to predict mixing and de-mixing behavior in low-Z liquid mixtures at high pressure and temperature. [Preview Abstract] |
Monday, June 27, 2011 5:15PM - 5:30PM |
E3.00006: Theoretical phase diagram of beryllium at low pressure and high temperature Gregory Robert, Philippe Legrand, Stephane Bernard Beryllium, although a ``simple'' metal remains a challenge for both theory and experiment. In this presentation, we will try to shed some light on a controversial issue concerning the phase diagram at low pressure and high temperature which is not clearly established [1,2]. In a previous work, we have shown that the bcc structure could be stabilized at high temperature by anharmonic effects [3] and could lead to a bcc pocket located at low pressure-high temperature. This is consistent with recent heated DAC experiments [4]. However to determine if the bcc phase has the lowest Gibbs free energy compared to hcp, we apply the force matching method fitted on quantum molecular dynamics data. \\[4pt] [1] M. Francois and M. Contre in Proc. Grenoble 1965, PUF Paris (1966). \\[0pt] [2] A. Abey in UCRL53567 (1984). \\[0pt] [3] G. Robert et al Phys Rev B 82, 104118 (2010). \\[0pt] [4] Evans et al. cited in Phys. Rev. B 79, 064106 (2009). [Preview Abstract] |
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