Bulletin of the American Physical Society
21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 64, Number 8
Sunday–Friday, June 16–21, 2019; Portland, Oregon
Session L6: TMS: First-principles and Molecular Dynamics V |
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Chair: Thomas Mattsson, Sandia National Labs (SNL) Room: Broadway III/IV |
Tuesday, June 18, 2019 4:00PM - 4:30PM |
L6.00001: Calculation of elastic constants at high pressure from first-principles Invited Speaker: Shailesh Mehta Elastic constants can be defined via either the energy-strain or stress-strain relationships. Although the formal theory is well established, their computation using the energy-strain relationship can lead to erroneous results at non-zero pressure. This talks discusses various corrective solutions that have been put forward to address this issue. An alternative method that is physically transparent and avoids the complexities of previous suggestions is then proposed. [Preview Abstract] |
Tuesday, June 18, 2019 4:30PM - 4:45PM |
L6.00002: First-principles calculations of multiple-shock conductivity measurements in hydrogen and deuterium Marcus Knudson, Michael Desjarlais, Martin Preising, Ronald Redmer We present a detailed comparison of previous multiple-shock electrical conductivity measurements in hydrogen and deuterium near molecular-to-atomic (MA) transition with finite temperature density functional theory (FT-DFT) calculations employing various exchange-correlation (xc) functionals. The measurement results are found to be inconsistent with the semilocal xc functional PBE and are in much better agreement with the nonlocal xc functionals vdW-DF1 and vdW-DF2. Furthermore, we show that the inconsistency with PBE likely stems from pressure errors associated with the PBE xc functional that result from premature dissociation, leading to calculated pressures that are too low at these temperature (T) and density ($\rho )$ conditions. Together with previous comparisons at high-T, low-$\rho $ and low-T, high-$\rho $, these results provide a consistent picture for the MA transition over a wide T and $\rho $ range. This picture may also provide insight into differences in experimental observations of the metallization of liquid hydrogen and deuterium in the low-T regime. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. [Preview Abstract] |
Tuesday, June 18, 2019 4:45PM - 5:00PM |
L6.00003: Multiphase equation of state of beryllium Joshua Coe, Sven Rudin, Boris Maiorov We will present a new Sesame equation of state (EOS) for beryllium comprising the hcp, bcc, and liquid/plasma phases. The EOS was calibrated based on a combination of first principles calculations and a wide variety of experimental data. After reviewing the correspondence between theory and experiment for the ambient phase, we will discuss phase boundaries and the location of the triple point relative to the principal Hugoniot. [Preview Abstract] |
Tuesday, June 18, 2019 5:00PM - 5:15PM |
L6.00004: Predictive simulations of metastable phases of carbon at high compression Ashley Huff, Kien Nguyen Cong, Jonathan Willman, Nir Goldman, Ivan Oleynik Carbon exhibits a relatively simple phase diagram under hydrostatic compression: thermodynamically stable sp2-bonded graphite and metastable sp3-bonded cubic diamond at ambient conditions and bc8 and simple cubic phases at high pressures above 1 TPa. There have been reports of appearance of hexagonal phase of diamond in shock experiments, but these results have been questioned by interpreting associated diffraction peaks as deformation twinning on (111) planes as a result of plastic deformations in cubic diamond. We explore unknown metastable phases of carbon under both hydrostatic and uniaxial compression by using combination of first-principles density functional theory and semi-empirical density functional tight-binding combined with evolutionary crystal structure prediction. Shear stresses play a key role in transformation of diamond to new lower energy metastable phases. Their appearance provides a plausible interpretation of recent experimental observations. [Preview Abstract] |
Tuesday, June 18, 2019 5:15PM - 5:30PM |
L6.00005: Modeling Sensitivity Analysis of the Interface Temperature of Dynamically Compressed Iron David Brantley, Eric Shi, Minta Akin Precise measurements of the bulk temperature of iron at Earth's core pressures provides a critical constraint on the iron equation of state, and is a vital input in generating accurate models of the Earth's core. Dynamic compression experiments offer a promising path into the relevant high pressure -- high temperature regime, however temperature measurements of shock compressed opaque materials are challenging due to the small optical depth, non-ideal effects, and often poorly known physical properties in this sector of P-T space. In this talk, I present a detailed sensitivity analysis of the iron interface temperature resulting from dynamic compression of iron at our two-stage light gas gun facilities. Hydrocode simulations are employed to examine the impact of several effects including equation of state, thermal conductivity, and the presence of gaps. [Preview Abstract] |
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