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 N2: TMS: First-principles and Molecular Dynamics VI |
Hide Abstracts |
Chair: Nicolas Pineau, CEA Room: Grand Ballroom II |
Wednesday, June 19, 2019 9:15AM - 9:30AM |
N2.00001: Diamond Formation from Hydrocarbons in Planetary Conditions: An ab initio Study Maitrayee Ghosh, S. X. Hu Shock-wave experiments have indicated the formation of diamond from polystyrene under planetary interior thermodynamic conditions ($P$ \textasciitilde 150 GPa, $T$ \textasciitilde 5000 K),$^{\mathrm{\thinspace }}$yet a theoretical understanding still remains far-fetched.\footnote{D. Kraus\textit{ et al.}, Nat. Astron. \textbf{1}, 606 (2017).\par } \footnote{ D. Kraus\textit{ et al.}, Phys. Plasmas \textbf{25}, 056313 (2018).}In this work, we have applied a reverse strategy based on quantum molecular-dynamics (QMD) simulations to demonstrate that a diamond-hydrogen separated phase is indeed more energetically favorable than a randomly mixed (C$_{\mathrm{8}}$H$_{\mathrm{8}})_{\mathrm{n}}$ system at the said thermodynamic conditions. Our QMD simulations show that hydrogen atoms should remain outside the diamond and not within its interstitial spaces. Hydrogen atoms, if present inside, will escape out and destroy the diamond structure. Depression of the melting curve of diamond also occurs because of increased C--H chemical bonding. We are now constructing a $P$--$T$ phase diagram (up to $T$ \textasciitilde 9000 K and $P$ \textasciitilde 500~GPa) of (C$_{\mathrm{8}}$H$_{\mathrm{8}})_{\mathrm{n}}$. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. [Preview Abstract] |
Wednesday, June 19, 2019 9:30AM - 9:45AM |
N2.00002: Critical point, liquid-vapor coexistence, and melting of Mg$_{2}$SiO$_{4}$ from ab-initio simulations Joshua Townsend, Gil Shohet, Luke Shulenburger, Michael Desjarlais We report density functional theory-based molecular dynamics calculations (DFT-MD) of Mg$_{2}$SiO$_{4}$ liquid and vapor across the liquid-vapor coexistence boundary that spanned 0.22-3.22 g/cc in density and 5000-10000 K in temperature. The critical point was estimated through a bootstrap analysis of a collection of DFT-MD isotherms above and below the critical point. Additionally, we describe the structure and composition of the liquid and vapor around the critical point. Finally, we discuss melting behavior at $P$=1 bar. [Preview Abstract] |
Wednesday, June 19, 2019 9:45AM - 10:00AM |
N2.00003: Rapid Compression of Prototype Sand-like Systems using Atomistic Molecular Dynamic Simulations ShinYoung Kang, Daniel Orlikowski Porous materials offer many challenges in modeling because stress-chains, phase transitions and/or chemical reactions may be occurring. The granular Hugoniot response like for SiO$_{\mathrm{2}}$ compacts and at low initial macro-densities will yield a stiffer response compared to a fully dense sample [Trunin 2001]. K. Cochrane \textit{et al}.$^{\mathrm{\thinspace }}$[2017] introduced the hypothesis of surface energy for the initial Hugoniot energy E$_{\mathrm{o}}$ using DFT constrained by a Hugoniot-stat. We test this hypothesis but allowing the system to dynamically respond within the atomistic microcanonical (NVE) ensemble. We use atomistic MD simulations using Tersoff potential for nanometer-sized granules to investigate the underlying mechanism for the SiO$_{\mathrm{2}}$ Hugoniot. We first establish a Hugoniot baseline for a single crystal SiO$_{\mathrm{2}}$ system, then we use nearly spherical granules of SiO$_{\mathrm{2}}$ in close-packed configurations. Additionally, we have applied the similar methodology to SiO$_{\mathrm{2}}$ systems with voids for comparison. [Preview Abstract] |
Wednesday, June 19, 2019 10:00AM - 10:15AM |
N2.00004: Hydrocarbon and water desorption from oxide surfaces using non-reactive and reactive molecular dynamics Jason Koski, Matthew Lane Hydrocarbon and water desorption from oxide surfaces can significantly influence the performance of high-voltage pulsed power machines, such as Sandia's Z-machine. The extreme temperatures and field strengths present in the Z-machine form plasmas and result in overall current loss. Previously, we have studied the desorption of water from a Fe2O3 (0001) surface and fit the desorption profiles to Temkin isotherm models using non-reactive molecular dynamics (MD). Here, we expand on that work by analyzing hydrocarbon/water mixtures and comparing both non-reactive and reactive MD simulations. The reactive MD allows for bond breaking and ionization; phenomena that are present in the extreme environments of pulsed power machines. Specifically, we look at the desorption of hydrocarbon molecules of different chain lengths and chain architectures (i.e. linear or branched) as well as hydrocarbon/water mixtures of varying concentrations. Finally, we look at the effect of uniform external electric fields of varying strength and direction on the desorption profiles. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525. [Preview Abstract] |
Wednesday, June 19, 2019 10:15AM - 10:30AM |
N2.00005: Numerical modeling of the phase transition kinetics for the sub-microsecond solidification of water under dynamic compression Dane Sterbentz, Philip Myint, Jean-Pierre Delplanque, Jonathan Belof Several landmark experimental studies on the solidification of liquid water to the high-pressure ice VII phase under multiple-shock and ramp dynamic compression have been carried out over the past two decades, yet modeling this rapid phase transition has proven challenging. The application of classical nucleation theory (CNT)-based approaches to rapid phase transition kinetics occurring under extreme temperatures and pressures presents a variety of new opportunities for predictive computational modeling. This work attempts to model the liquid water---ice VII phase transformation using a numerical discretization scheme to solve the Zel'dovich---Frenkel partial differential equation, a fundamental CNT-based kinetic equation describing the statistical time-dependent behavior of solid cluster formation. One major result of this research is that the Zel'dovich---Frenkel equation is able to model---without the need for empirical scaling parameters---the duration of the lag time prior to the onset of the phase transformation. [Preview Abstract] |
Wednesday, June 19, 2019 10:30AM - 10:45AM |
N2.00006: Shock Processes in Water: multi-scale comparison and experimental results Longhao Huang, John Borg The motivation for this research is developing a better understanding of shock processes in water. This work seeks a better understanding of how simulations at various scales (continuum and molecular dynamic) result in differing estimates of the shock thickness in water. This is accomplished utilizing and comparing Direct Numerical Simulation (DNS) to Molecular Dynamic (MD) simulations. Shock experiments were performed in order to better understand the simulated results. The DNS simulations utilize pressure dependent viscosity models in order to match experimental results. The Large-Scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) under-predicts the experimentally determined shock thickness. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700