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 U6: Phase Transitions VI |
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Chair: Ben Morrow, Los Alamos National Laboratory Room: Regency Ballroom E |
Thursday, July 13, 2017 2:15PM - 2:45PM |
U6.00001: Generating a Multiphase Equation of State with Swarm Intelligence Invited Speaker: Geoffrey Cox Hydrocode calculations require knowledge of the variation of pressure of a material with density and temperature, which is given by the equation of state. An accurate model needs to account for discontinuities in energy, density and properties of a material across a phase boundary. When generating a multiphase equation of state the modeller attempts to balance the agreement between the available data for compression, expansion and phase boundary location. However, this can prove difficult because minor adjustments in the equation of state for a single phase can have a large impact on the overall phase diagram. Recently, Cox and Christie[1] described a method for combining statistical-mechanics-based condensed matter physics models with a stochastic analysis technique called particle swarm optimisation. The models produced show good agreement with experiment over a wide range of pressure--temperature space. This talk details the general implementation of this technique, shows example results, and describes the types of analysis that can be performed with this method. [1] G A Cox and M A Christie 2015~\textit{J. Phys.: Condens. Matter}~27~405201 [Preview Abstract] |
Thursday, July 13, 2017 2:45PM - 3:00PM |
U6.00002: A mean-field thermodynamic description of the kinetics of overdriven interfaces. Tomorr Haxhimali, Jonathan Belof, Babak Sadigh, Luis Zepeda Zepeda-Ruiz A key aspect of an accurate description of shock-induced structural phase transitions is the rigorous computation of the dynamics of the interfaces between coexisting phases. In the wake of the shock, the system will be exposed to strong gradient fields that give rise to overdriven interfaces during the induced phase transformation. In this work we take a mean-field approach using a time-dependent Ginzburg-Landau formalism to describe the dynamics of such overdriven interfaces. We make a connection of the mean-field result to a quasi-Langevin description, the Kardar-Parisi-Zhang (KPZ) equation, of the kinetics of the interface. Further, larger coarse-grained descriptions of the phase transition such as the Kolmogorov-Johnson-Mehl-Avrami (KJMA) model, which are commonly coupled to hydrodynamic equations that describe the evolution of the temperature and pressure during the shock propagation, ignore the details of the dynamics and structure of the interfacial regions. Overlaying the KPZ description of the interface evolution to these coarse-grained methods will result in physically more accurate multiscale models for shock propagation. We will present results from our efforts in this regard. [Preview Abstract] |
Thursday, July 13, 2017 3:00PM - 3:15PM |
U6.00003: High-pressure/high-temperature polymorphs of energetic materials by first-principles simulations Nam Le, Igor Schweigert Energetic molecular crystals exhibit complex phase diagrams that include solid-solid phase transitions, melting, and decomposition. Sorescu and Rice have recently demonstrated that first-principles molecular dynamics (MD) simulations based on dispersion-corrected density functional theory (DFT) can capture the $\alpha$ to $\gamma$ phase transition in hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) on time scales of several picoseconds [1]. Motivated by their work, we are using DFT-based MD to model the relative stability of solid phases in several molecular crystals. In this presentation, we report simulations of pentaerythritol tetranitrate (PETN) and 2,4,6-trinitrotoluene (TNT) under high pressures and temperatures and compare them with experimentally observed polymorphs [2,3]. [1] Sorescu and Rice, J. Phys. Chem. C, 120, 19547-19557 (2016) [2] Dreger and Gupta, J. Phys. Chem. A, 117, 5306-5313 (2013) [3] Dattelbaum et al., Appl. Phys. Lett., 104, 021911 (2014) [Preview Abstract] |
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