Bulletin of the American Physical Society
20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017; St. Louis, Missouri
Session S6: Equation of State IV |
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Chair: Carl Greeff, Los Alamos National Laboratory Room: Regency Ballroom E |
Thursday, July 13, 2017 9:15AM - 9:30AM |
S6.00001: Sesame style decomposition of KS-DFT molecular dynamics for direct interrogation of nuclear models Sarah Burnett, Daniel Sheppard, Kevin Honnell A common paradigm used in the construction of equations of state is to decompose the thermodynamics into a superposition of three terms: a static lattice cold curve, a contribution from the thermal motion of the ions, and a contribution from the thermal excitation of the electrons. While statistical mechanical models for crystals provide tractable framework for the ionic contribution in the solid phase, much less is understood about the ionic contribution above the melt temperature ($C_v \approx 3R$) and how it should transition to the high-temperature limit ($C_v \sim \frac{3}{2}R$). In this work, we use the VASP Quantum Molecular Dynamics package to probe thermal ionic behavior in the liquid and to compare the results to two semi-empirical models -- the Johnson model and the Chisolm high-temperature liquid model. For each temperature and density of interest, we begin by performing a full Kohn-Sham QMD simulation of the system. The average of the resulting internal energies and pressures is recorded for each particular temperature. Taking the derivative of the energy with respect to temperature using Gram polynomials returns the specific heat, $C_v$. We describe the general methodology and compare predictions for the constant volume heat capacity of Al to common ionic models. [Preview Abstract] |
Thursday, July 13, 2017 9:30AM - 9:45AM |
S6.00002: The Equation of State of Triamino-Trinitrobenzene from Density Functional Theory Molecular Dynamics Ryan R. Wixom The U$_{\mathrm{S}}$-u$_{\mathrm{P}}$ shock Hugoniot has long been the fundamental relationship used to experimentally define the unreacted equations of state of explosives. These experiments are typically performed on porous or composite samples, providing data that is specific to the density of the samples being tested. However, If the crystalline Hugoniot is known, analytical or numerical methods can be used to transform the U$_{\mathrm{S}}$-u$_{\mathrm{P}}$ relationship to describe the shock response of the porous material. To obtain an accurate crystalline equation of state for TATB, density functional theory based molecular dynamics were used to map out points on the Hugoniot. Since this method provides the pressure, temperature, density, and internal energy at each point on the Hugoniot, a complete equation of state can be constructed. Isotropic, uniaxial, hydrostatic, and isothermal compression of the simulation cell were used to examine TATB under different thermodynamic conditions. A cusp is observed in the Hugoniot that correlates to loss of aromaticity of the molecule. Results of the calculations will be presented and compared to the available experimental data. [Preview Abstract] |
Thursday, July 13, 2017 9:45AM - 10:00AM |
S6.00003: Rice-Walsh equation of state for metals based on the shock Hugoniot data for porous samples Kunihito Nagayama The dimensionless material parameter $R$ introduced by Wu and Jing into the Rice-Walsh equation of state (EOS) has been deduced from the published shock Hugoniot data for porous samples of ten metals. It was found that the parameter $R/p$ decays smoothly with shock pressure $p$ and displays small experimental scatter in the high pressure region. The parameter has only a weak temperature dependence and is well approximated by a function of pressure alone, and the Gr\"{u}neisen parameter should be temperature dependent under compression. The thermodynamic formulation of the Rice-Walsh EOS for these metals was realized using the empirically determined function $R(p)$ and their known shock Hugoniot. It was then possible to reproduce porous shock Hugoniot for these metals, and agreement between the porous data and the calculated Hgoniots using the empirical function described was very good for most degrees of porosity. The Gr\"{u}neisen parameters along full-density and porous Hugoniot curve were calculated using a thermodynamic identity connecting $R$ and the Gr\"{u}neisen parameter. Extended Rice-Walsh EOS was also formulated to explain anomalous Hugoniots with extremely high porosities. [Preview Abstract] |
Thursday, July 13, 2017 10:00AM - 10:15AM |
S6.00004: Validation for equation of state of Tantalum in wide regime Haifeng Liu, Gongmu Zhang, Haifeng Song, Hongzhou Song, Yanhong Zhao, Mingfeng Tian, Shuaichuang Wang We introduce the wide regime equation of state (WEOS) developed in Institute of Applied Physics and Computational Mathematics (IAPCM). A semi-empirical model of the WEOS is given by a thermodynamically complete potential of the Helmholtz free energy which combines several theoretical models and has some adjustable parameters calibrated via some experimental and theoretical data. The validation methods of the equation of state in wide regime are presented in Tantalum. The results of the WEOS are well consistent with the available theoretical and experimental data, including isotherm, Hugoniot, off-Hugoniot and sound velocity data. It enhances our confidence in the accuracy of the WEOS, which is very important for the validation and verification of equation of state in high temperature and pressure technology. [Preview Abstract] |
Thursday, July 13, 2017 10:15AM - 10:45AM |
S6.00005: Using Sandia’s Z Machine and Density Functional Theory Simulations to Understand Planetary Materials Invited Speaker: Seth Root The use of Z, NIF, and Omega have produced many breakthrough results in high pressure physics. One area that has greatly benefited from these facilities is the planetary sciences. The high pressure behavior of planetary materials has implications for numerous geophysical and planetary processes. The continuing discovery of exosolar super-Earths demonstrates the need for accurate equation of state data to better inform our models of their interior structures. Planetary collision processes, such as the moon-forming giant impact, require understanding planetary materials over a wide-range of pressures and temperatures. Using Z, we examined the shock compression response of some common planetary materials: MgO, Mg$_2$SiO$_4$, and Fe$_2$O$_3$ (hematite). We compare the experimental shock compression measurements with density functional theory (DFT) based quantum molecular dynamics (QMD) simulations. The combination of experiment and theory provides clearer understanding of planetary materials properties at extreme conditions. Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
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