Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session L23: Matter at Extreme Conditions II |
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Sponsoring Units: DCMP DCOMP Chair: Zsolt Jenei, Lawrence Livermore National Laboratory Room: 202B |
(Author Not Attending)
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L23.00001: First Principles Simulations of P-V-T Unreacted Equation of State of LLM-105 Riad Manaa, I-Feng Kuo, Laurence Fried Equations of states (EOS) of unreacted energetic materials extending to high-pressure and temperatures regimes are of particular interest since they provide fundamental information about the associated thermodynamic properties of these materials at extreme conditions. Very often, experimental and computational studies focus only on determining a pressure-volume relationship at ambient to moderate temperatures. Adding elevated temperature data to construct a P-V-T EOS is highly desirable to extend the range of materials properties. Atomic scale molecular dynamics simulations are particularly suited for such a construct since EOSs are the manifestation of the underlying atomic interactions. In this work, we report dispersion-corrected density functional theoretical calculations of unreacted equation of state (EOS) of the energetic material 2,6-diamino-3, 5-dinitropyrazine-1-oxide (LLM-105). We performed large-scale constant-volume and temperature molecular dynamics simulations for pressures ranging from ambient to 35 GPa, and temperatures ranging from 300 K to 1000 K. These calculations allowed us to construct an unreacted P-V-T EOS and obtain bulk modulus for each P-V isotherm. We also report the thermal expansion coefficient of LLM-105 in the temperature range of this study. [Preview Abstract] |
Wednesday, March 4, 2015 8:12AM - 8:24AM |
L23.00002: Ultrafast Shocked Single Crystal PETN and Beta-HMX: Shock Hugoniot Measurements to Guide the Development of Continuum Models Joseph Zaug, Michael Armstrong, Jonathan Crowhurst, Louis Ferranti, Ryan Austin, Laurence Fried We report results from ultrafast shockwave experiments conducted on single crystal high explosives. Ultrafast shock studies can enable high throughput characterizations of unreacted equations of state to higher pressures than previously reported and also quantify the magnitude of anisotropic mechanical response to shock waves. Our previous results derived from a 372 ps drive duration yielded anisotropic elastic wave response in single crystal beta-HMX ((110) and (010) impact planes). Here we provide results using a \textgreater 2x drive duration to extend measurements into the plastic or bulk wave regime. We compare our ultrafast time domain interferometry (TDI) results with previous gun platform results. These 10 ps time scale resolution TDI measurements guide the development of a continuum model to study pore collapse and energy localization in shock-compressed crystals of beta-HMX. [Preview Abstract] |
Wednesday, March 4, 2015 8:24AM - 8:36AM |
L23.00003: Dynamic response of matter heated by ultrafast laser pulses Eliseo Gamboa, Luke Fletcher, Sebastian Goede, Ulf Zastrau, Hae-Ja Lee, Eric Galtier, Will Schumaker, Rohini Mishra, Philipp Sperling, Maxence Gauthier, Alessandra Ravasio, Michael MacDonald, Siegfried Glenzer The material properties of the light elements at extreme conditions are of utmost importance to a diverse set of fields, from astrophysics and cosmology to research into controlled nuclear fusion energy production. These high-energy density states, defined as solid density plasmas with T\textgreater 10 eV, may be produced in the laboratory by irradiation of materials with high-energy or high-power lasers. Characterizing these material conditions using optical means is challenging because the plasma is above critical density and the experimental conditions are maintained over only very brief timescales. We present a preliminary analysis of x-ray scattering data from ultrafast, isochorically-heated hydrogen and carbon in experiments conducted at the Matter in Extreme Conditions endstation at the Linac Coherent Light Source (LCLS) x-ray free electron laser, SLAC National Accelerator Laboratory. By observing the collective and non-collective x-ray scattering of the LCLS beam at multiple pump-probe delays, we infer the time-history of the electron and ion temperatures and thus the equilibration rate. [Preview Abstract] |
Wednesday, March 4, 2015 8:36AM - 8:48AM |
L23.00004: Micron-scale Reactive Atomistic Simulation of Void Collapse and Hotspot Growth in PETN Tzu-Ray Shan, Ryan Wixom, Aidan Thompson Material defects and other heterogeneities such as dislocations, micro-porosity, and grain boundaries play key roles in the shock-induced initiation of detonation in energetic materials. We performed non-equilibrium molecular dynamics simulations to explore the effect of nanoscale voids on hotspot growth and initiation in micron-scale pentaerythritol tetranitrate (PETN) crystals under weak shock loading (Up $=$ 1.25 km/s; Us $=$4.5 km/s). We used the ReaxFF potential implemented in LAMMPS. We built a pseudo-2D PETN crystal with dimensions 0.3 $\mu$m $\times$ 0.22 $\mu$m $\times$ 1.3 nm containing a 20 nm cylindrical void. Once the initial shockwave traversed the entire sample, the shock-front absorbing boundary condition was applied, allowing the simulation to continue for $\sim$ 0.5 nanoseconds. Results show an exponentially increasing hotspot growth rate. The hotspot morphology is initially symmetric about the void axis, but strong asymmetry develops at later times, due to strong coupling between exothermic chemistry, temperature, and divergent secondary shockwaves emanating from the collapsing void. [Preview Abstract] |
Wednesday, March 4, 2015 8:48AM - 9:00AM |
L23.00005: Post-stishovite transition in hydrous aluminous SiO$_{2}$ Renata Wentzcovitch, Koichiro Umemoto, Katsuyuki Kawamura, Kei Hirose Incorporation of aluminum and some water into SiO$_{2}$ significantly reduces the post-stishovite transition pressure in SiO$_{2}$. This behavior suggests that the ferroelastic post-stishovite transition in subducted Earth's crust could be the source of seismic anomalies with low shear velocities observed in the mid to upper lower mantle. Using ab initio static calculations and molecular dynamics with inter-atomic potentials, we show that hydrogen bonds play a crucial role in lowering the transition pressure. A cooperative redistribution of hydrogen atoms is the main mechanism responsible for the transition pressure reduction in hydrous aluminous stishovite. The effect is enhanced by increasing the water content and suggests a relationship between the depth of these seismic anomalies and degree of hydration of stishovite in the subducted crust. [Preview Abstract] |
Wednesday, March 4, 2015 9:00AM - 9:12AM |
L23.00006: The Dilemma of the High-Spin Persistence Into the Mbar Range of Some Ferric-Metal Oxides Moshe P. Pasternak, Gregory Kh. Rozenberg, Eran Greenberg, Weiming Xu, Mark Nikolaevsky The fate of the strongly correlated $d-d$ Mott-Hubbard (MH) insulators at extreme conditions of pressure is determined by two main reactions: ($i)$ correlation breakdown due to broadening leading to bands overlap of the \textit{empty-filled }band resulting in metallization consequently loss of magnetic moment, and, (\textit{ii}) spin crossover due to the augmented \textit{crystal-field} (10Dq $\sim$ $r^{-5})$ which in the case of the Fe$^{3+}$ - oxides results in $S=$5/2 \textgreater $S=$1/2 transition. The experimental observation of these high pressure phenomena using Diamond-Anvils-Cells and the experimental methods of resistance and $^{57}$Fe M\"{o}ssbauer effect at varying (P,T) and Synchrotron XRD at RT. This presentation will focus on the recent discovered cases of some Fe$^{3+}M$O where the \textit{high-spin} state prevails into the Mbar region; showing no signs of correlation breakdown. The persistence of correlated, HS states to such pressures cannot be explained. This will be preceded by a short introduction to the experimental methods and cases of pressure-induced spin-crossover or MH transitions. [Preview Abstract] |
Wednesday, March 4, 2015 9:12AM - 9:24AM |
L23.00007: Semiempirical equations of state for NaCl Michel Santos, Renata Wentzcovitch Despite diamond anvil cell experiments having reached pressures of hundreds of GPa, measuring high pressures is still a challenge. One of the strategies adopted in high pressure measurements is to measure the lattice spacing, via x-ray diffraction, of a calibrant whose equation of state is well known. Several calibrants have been widely used, but pressure scales based on them still have great uncertainties at high pressures and temperatures (PT). NaCl has been widely used as a pressure standard, but the lack of good high P and high T equations of state limits the use of this material. We have developed strategies to produce predictive high PT equations of state by combining ab initio results with available data at low T and high P or high T and low P. The high PT equations of state obtained in this way for NaCl show excellent agreement with high PT data by Bohler and Kennedy \footnote{R. Boehler and G. Kennedy, J. Phys. Chem. Solids, 41, pp 517 (1980)}. Semi-empirical equations will play an important role in the development of predictive databases of thermodynamics properties of materials. [Preview Abstract] |
Wednesday, March 4, 2015 9:24AM - 9:36AM |
L23.00008: Phase stability and elasticity of CaSiO3 perovskite Fawei Zheng, Tao Sun, Renata Wentzcovitch CaSiO3 perovskite (CaPv) is the third most abundant mineral in the Earth's lower mantle and is a major component of mid-ocean ridge basalt (MORB). This perovskite is stable only at high pressures, it is highly anharmonic, and undergoes a tetragonal to cubic transition at conditions that are still debated. We have used a recently developed hybrid method combining ab initio molecular dynamics with vibrational normal mode analysis to compute its free energy, thermal equation of state, and phase boundary at relevant geophysical conditions. These results are essential for understanding several aspects of mantle convection. [Preview Abstract] |
Wednesday, March 4, 2015 9:36AM - 9:48AM |
L23.00009: Nonlinear THz signatures of energetic molecular crystals David Moore, Mitchell Wood, Diego Dalvit Several methods exist for detecting energetic materials, yet no method is available to surmount the simultaneous challenges of rapid screening, areal coverage, sensitivity and selectivity. Nonlinear coupling of penetrating THz radiation to explosives is a promising new tool for stand-off detection. Here, we report on reactive molecular dynamics simulations of the emission spectra of energetic molecular crystals under electromagnetic insults. The THz emission spectrum, calculated from the time dependent dipole accelerations, is altered due to anharmonic coupling between modes in the material, providing a unique fingerprint for each material. The efficiency of the nonlinear frequency conversion mechanism is studied as a function of various parameters of an incoming electromagnetic pulse, including its carrier frequency, polarization, peak power, and duration. Two common energetic materials, PETN and RDX, were studied wherein we have found unique emission peaks in the frequency range of 0-10THz that arise from select carrier frequencies. [Preview Abstract] |
Wednesday, March 4, 2015 9:48AM - 10:00AM |
L23.00010: Thermoelasticity of (Mg,Fe)SiO$_3$ perovskite Gaurav Shukla, Zhongqing Wu, Han Hsu, Matteo Cococcioni, Renata Wentzcovitch We present LDA+U calculations of high temperature elastic properties of (Mg$_{(1-x)}$Fe$_{x}^{2+}$)SiO$_3$ bridgemanite ($0\le{x}\le0.125$), the most abundant constituent of Earth's lower mantle. Calculations of aggregate elastic moduli and acoustic velocities for the Mg-end member (x=0) are in excellent agreement with the latest high pressure and high temperature experimental measurements. In the iron bearing system, we particularly focus on the change in thermoelastic parameters across the state change that occurs in ferrous iron above $\sim$30 GPa, often attributed to a high-spin (HS) to intermediate spin (IS) crossover but explained by calculations as a lateral displacement of substitutional iron in the perovskite cage. We show that the measured effect on the equation of state of this change in the state of iron can be explained by the lateral displacement of substitutional iron, not by the HS to IS crossover. Calculated elastic properties of (Mg$^{\ }_{0.875}$Fe$^{2+}_{0.125}$)SiO$_3$ along an adiabatic mantle geotherm, somewhat overestimate longitudinal velocities but produce densities and shear velocities consistent with Preliminary Reference Earth Model data throughout most of the lower mantle. [Preview Abstract] |
Wednesday, March 4, 2015 10:00AM - 10:12AM |
L23.00011: Thermoelasticity of Al$^{3+}$- and Fe$^{3+}$-bearing bridgemanite Juan Valencia-Cardona, Gaurav Shukla, Matteo Cococcioni, Renata Wentzcovitch We present quasi-harmonic LDA+U calculations of thermoelastic properties of Fe$^{3+}$- and Al$^{3+}$-bearing bridgemanite (MgSiO$_3$), the main Earth forming phase, at relevant P,T conditions and compositions. Three charge-coupled substitutions, namely, Al$^{3+}$-Al$^{3+}$, Fe$^{3+}$-Fe$^{3+}$, and Fe$^{3+}$-Al$^{3+}$ have been investigated. Aggregate elastic moduli and sound velocities are successfully compared with limited experimental measurements available. The effect of the pressure induced high-spin to low-spin state change in Fe$^{3+}$ in the B-site has been investigated in great detail since it has potentially dramatic effects on seismic velocities in the Earth's lower mantle. [Preview Abstract] |
Wednesday, March 4, 2015 10:12AM - 10:24AM |
L23.00012: Molecular modeling of high-pressure ramp waves in tantalum J. Matthew D. Lane, Hojun Lim, Justin L. Brown Ramp wave compression experiments of bcc metals under extreme conditions have produced differing measurements of material strength response. These variations are often attributed to differing experimental techniques, and varying material factors such as microstructure, and strain-rate. We present non-equilibrium molecular dynamics simulations of tantalum for single crystal and two polycrystalline nanostructures out to 250 GPa, over strain states ranging from 10$^8$ to 10$^{11}$ 1/s. Results will be compared to recent Z-machine strength experiments, meso-scale crystal plasticity models and continuum-scale polycrystalline model. Sandia National Laboratories is a multi program 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] |
Wednesday, March 4, 2015 10:24AM - 10:36AM |
L23.00013: Singly Bonded Layered Polymeric Nitrogen (LP-N) Choong-Shik Yoo, Dane Tomasino, Minseob Kim, Jesse Smith We report the discovery of novel nitrogen phase synthesized using laser-heated diamond anvil cells at pressures well above the stability field of cg-N. This new phase is characterized by its singly bonded, layered polymeric (LP) structure similar to the predicted Pba2 and two colossal Raman bands, arising from two groups of highly polarized nitrogen atoms in the bulk and surface of the layer, respectively. The present result also provides a new constraint for the nitrogen phase diagram, highlighting an unusual symmetry lowering 3D cg-N to 2D LP-N transition and thereby the enhanced electrostatic contribution to the stabilization of this densely packed LP-N. [Preview Abstract] |
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