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 C3: First-Principles and Molecular Dynamics Calculations II: Phase Transitions |
Hide Abstracts |
Chair: Tommy Sewell, University of Missouri Room: Renaissance Ballroom AB |
Monday, June 27, 2011 11:00AM - 11:15AM |
C3.00001: Ab Initio investigation of the shock-induced cd to beta-tin phase transition in single-crystal silicon Gabriele Mogni, Andrew Higginbotham, Justin Wark, Katalin Gaal-Nagy An understanding of the mechanisms behind the relief of shear stress in shocked single-crystal silicon and germanium remains elusive. Silicon undergoes a first-order pressure-induced polymorphic phase transition from its ambient pressure cubic-diamond (cd) crystal structure to its first high-pressure stable phase, beta-tin, at about 120 kbar under hydrostatic compression. This phase transition was first the subject of an experimental investigation under shock-wave loading by Gust and Royce (J. Appl. Phys.: 42, 5 (1971)), who interpreted the wave profile measurements as an HEL at 92 kbar and consequent onset of 3D plastic deformation and a subsequent phase transition. By investigating the lowering of the transition pressure and enthalpy barrier as a function of increasing uniaxial shear stress via ab-initio DFT simulations, we predict a significant lowering of the transition stress, down to values close to those associated with the HEL itself. This raises the question as to whether the onset of inelastic response at the HEL is in fact the onset of a phase transition. Our plans for the future involve substantiating these findings in laser-based shock-wave experiments. [Preview Abstract] |
Monday, June 27, 2011 11:15AM - 11:30AM |
C3.00002: Shock-induced phase transition in diamond You Lin, Romain Perriott, Vasily Zhakhovsky, Carter White, Ivan Oleynik Shock wave propagation in diamond crystal along the $<$110$>$ crystallographic direction was simulated by molecular dynamics (MD) using the Reactive Empirical Bond Order (REBO) potential. In addition to usual regimes of shock wave propagation, such as single elastic wave, two split elastic-plastic waves, and single plastic shock wave, a two-zone \textit{elastic-elastic} single shock wave was observed in the range of piston velocities between 2.0 and 4.1 km/s and longitudinal stresses 126 -278 GPa. The elastic-elastic splitting occurs because the crystal undergoes a stress-induced structural phase transition from a normal, low-pressure, to a high-pressure phase of diamond within the interval of pressures below the Hugoniot elastic limit. The existence of a polymorphic phase transition makes possible a rarefaction shock wave, which was observed in our MD simulations of short piston impact of a diamond sample followed by the formation of a rarefaction shock wave that transforms the high-pressure phase back to the low pressure phase of diamond. [Preview Abstract] |
Monday, June 27, 2011 11:30AM - 11:45AM |
C3.00003: High-pressure phase diagrams of liquid CO$_2$ and N$_2$ Brian Boates, Stanimir Bonev The phase diagrams of liquid CO$_2$ and N$_2$ have been investigated using first- principles theory. Both materials exhibit transitions to conducting liquids at high temperatures ($T$) and relatively modest pressures ($P$). Furthermore, both liquids undergo polymerization phase transitions at pressures comparable to their solid counterparts. The liquid phase diagrams have been divided into several regimes through a detailed analysis of changes in bonding, as well as structural and electronic properties for pressures and temperatures up to 200 GPa and 10 000 K, respectively. Similarities and differences between the high-$P$ and $T$ behavior of these fluids will be discussed. Calculations of the Hugoniot are in excellent agreement with available experimental data. [Preview Abstract] |
Monday, June 27, 2011 11:45AM - 12:00PM |
C3.00004: Liquid-liquid phase transition in high pressure hydrogen from ab-initio simulations Miguel A. Morales, Eric Schwegler, Carlo Pierleoni, David M. Ceperley Using Born-Oppenheimer molecular dynamics with Density Functional Theory and Coupled Electron-Ion Monte Carlo simulations, we study molecular dissociation in liquid hydrogen. We observe a range of densities for which (dP/d?)$_T$ = 0 and find sharp discontinuities in the electronic conductivity; both are clear evidence of a liquid-liquid phase transition for temperatures 600K $<$ T $<$ 1500K. Both levels of theory exhibit the transition, although Quantum Monte Carlo predicts higher transition pressures. We estimate the critical point of the transition at temperatures slightly below 2000K using the discontinuity in the electronic conductivity. Using Path Integral Molecular Dynamics we examine the influence of zero point motion on the predicted transition, which still exhibits a first order behavior. We calculate the melting curve of molecular hydrogen up to pressures of 200GPa, finding a reentrant melting line in good agreement with previous calculations. The melting line crosses the metalization line at 700K and 220GPa with density functional theory and at 550K and 290GPa within Quantum Monte Carlo. [Preview Abstract] |
Monday, June 27, 2011 12:00PM - 12:15PM |
C3.00005: Molecular dynamics simulations of diamond shock compression using different interatomic potentials Romain Perriot, Xiang Gu, You Lin, Vasily V. Zhakhovsky, Nicolas Pineau, Jean-Bernard Maillet, Laurent Soulard, Jan H. Los, Carter T. White, Ivan I. Oleynik Shock wave propagation in diamond crystals were simulated by molecular dynamics (MD) using several interactomic potentials: Reactive Empirical Bond Order (REBO) potential; Screened REBO (S-REBO); and, long-range carbon bond-order potential (LCBOP II). Several shock-wave regimes were observed, including single-wave elastic, plastic, and split two-wave elastic-plastic regimes, as well as a novel steady two-zone elastic-plastic regime. The latter regime is characterized by the leading elastic zone of the metastable material uniaxially compressed above the Hugoniot Elastic Limit, which depends on the specific potential used in the simulations. The results obtained using REBO, S-REBO, and LCBOP II are compared with experiment. [Preview Abstract] |
Monday, June 27, 2011 12:15PM - 12:30PM |
C3.00006: Burnett-Cattaneo continuum theory for shock waves Brad Lee Holian, Michel Mareschal, Ramon Ravelo We model strong shockwave propagation, both in the ideal gas and in the dense Lennard-Jones fluid, using a refinement of earlier work, which accounts for the cold compression in the early stages of the shock rise by a nonlinear, Burnett-like, strain-rate dependence of the thermal conductivity, and relaxation of kinetic temperature components on the hot, compressed side of the shock front. The relaxation of the disequilibrium among the three components of the kinetic temperature, namely, the difference between the component in the direction of a planar shock wave and those in the transverse directions, particularly in the region near the shock front, is accomplished at a much more quantitative level by the first-ever rigorous application of the Cattaneo-Maxwell relaxation equation to a reference solution, namely, the steady shockwave solution of linear Navier-Stokes-Fourier theory, along with the nonlinear Burnett heat-flux term. Our new continuum theory is in nearly quantitative agreement with non-equilibrium molecular-dynamics simulations under strong shockwave conditions, using relaxation parameters obtained from the reference solution. [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