Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session E2: Materials in Extremes IIFocus
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Sponsoring Units: DCOMP DMP SHOCK Chair: Tim Germann, Los Alamos National Laboratory Room: 261 |
Tuesday, March 14, 2017 8:00AM - 8:36AM |
E2.00001: Dynamics of chemical reactions under pressure Invited Speaker: Margherita Citroni High pressure is a powerful tool to finely and widely change the intermolecular geometries in molecular liquids and crystals. Many molecular systems are known to chemically react under pressure, reversibly or irreversibly. In the last years, much work has been done in our laboratory to understand the mechanisms of pressure-induced reactivity at a microscopic level. Experiments relying on static techniques, particularly vibrational and electronic spectroscopy and X-ray diffraction, in combination with MD simulations, have revealed fundamental aspects of the interplay among structure, anisotropic compressibility, and electronic states in opening specific reactions paths$^{\mathrm{1,2}}$. Presently, the experimental and theoretical focus is the time resolution of the reactive processes. Infrared pump-probe experiments on compressed liquid water$^{\mathrm{3,4}}$, unveiling the behavior of the H-bonded network vibrational dynamics under pressure, have been the introductory work to investigate how density affects the dynamics of more complex and reactive systems. At the same time, the dynamics of ice melting (in ice I$_{\mathrm{h}}$ and ice VI) is under study through the use of ultrafast spectroscopic techniques, which will then be employed to investigate the mechanism of formation of hydrates and of solid-state reactions. $^{\mathrm{1}}$ M. Citroni et al. \textit{Role of excited electronic states in the high-pressure amorphization of benzene.} Proc. Natl. Acad. Sci. 105, 7658 -7663 (2008). $^{\mathrm{2}}$ M. Citroni, et al., \textit{Nitromethane Decomposition under High Static Pressure, }J. Phys. Chem. B, 114, 9420-9428 (2010). $^{\mathrm{3}}$ S. Fanetti et al., \textit{Structure and Dynamics of Low-Density and High-Density Liquid Water at High Pressure} J. Phys. Chem. Lett. 5 , 235--240 (2014). $^{\mathrm{4}}$ A. Lapini et al. \textit{Pressure Dependence of Hydrogen-Bond Dynamics in Liquid Water Probed by Ultrafast Infrared Spectroscopy, } J. Phys. Chem. Lett. 7, 3579-3584 (2016). [Preview Abstract] |
Tuesday, March 14, 2017 8:36AM - 8:48AM |
E2.00002: Reaction profiles and energy surfaces of compressed species under extreme conditions Noham Weinberg, Jacob Spooner, Brandon Yanciw, Brandon Smith Both experiment and first principles calculations unequivocally indicate that properties of elements and their compounds undergo a tremendous transformation at ultra-high pressures exceeding 1 Mbar due to the fact that the difference between intra- and intermolecular interactions disappears under such conditions. Yet, even at much milder pressures of 50-300 kbar, when molecules still retain their individual identity, their chemical properties and reactivity change dramatically. Since kinetics and mechanisms of condensed-phase reactions are described in terms of their potential energy (PES) or Gibbs energy (GES) surfaces, chemical effects of high pressure can be assessed through analysis of pressure-induced deformations of GES of solvated reaction systems. We use quantum mechanical and molecular dynamics simulations to construct GES and reaction profiles of compressed species, and analyze how topography of GES changes in response to compression. We also discuss the important role of volume profiles in assessing pressure-induced deformations and show that the high-pressure GES are well described in terms of these volume profiles and the reference zero-pressure GES. [Preview Abstract] |
Tuesday, March 14, 2017 8:48AM - 9:00AM |
E2.00003: Evolutionary optimization of PAW data-sets for accurate high pressure simulations Kanchan Sarkar, Mehmet Topsakal, Natalie Holzwarth, Renata Wentzcovitch We examine the challenge of performing accurate electronic structure calculations at high pressures by comparing the results of all-electron full potential linearized augmented-plane-wave calculations with those of the projector augmented wave (PAW) method. In particular, we focus on developing an automated and consistent way of generating transferable PAW data-sets that can closely produce the all electron equation of state defined from zero to arbitrary high pressures. The technique we propose is an evolutionary search procedure that exploits the ATOMPAW code to generate atomic data-sets and the Quantum ESPRESSO software suite for total energy calculations. We demonstrate different aspects of its workability by optimizing PAW basis functions of some elements relatively abundant in planetary interiors. In addition, we introduce a new measure of atomic data-set goodness by considering their performance uniformity over an enlarged pressure range. [Preview Abstract] |
Tuesday, March 14, 2017 9:00AM - 9:12AM |
E2.00004: Order parameter aided efficient phase space exploration under extreme conditions Amit Samanta Physical processes in nature exhibit disparate time-scales, for example time scales associated with processes like phase transitions, various manifestations of creep, sintering of particles etc. are often much higher than time the system spends in the metastable states. The transition times associated with such events are also orders of magnitude higher than time-scales associated with vibration of atoms. Thus, an atomistic simulation of such transition events is a challenging task. Consequently, efficient exploration of configuration space and identification of metastable structures in condensed phase systems is challenging. In this talk I will illustrate how we can define a set of coarse-grained variables or order parameters and use these to systematically and efficiently steer a system containing thousands or millions of atoms over different parts of the configuration. This order parameter aided sampling can be used to identify metastable states, transition pathways and understand the mechanistic details of complex transition processes. I will illustrate how this sampling scheme can be used to study phase transition pathways and phase boundaries in prototypical materials, like SiO2 and Cu under high-pressure conditions. [Preview Abstract] |
Tuesday, March 14, 2017 9:12AM - 9:24AM |
E2.00005: Stable and Metastable Mixed Polymeric Carbon, Nitrogen, and Oxygen Compounds at High Pressures Brad Steele, Ivan Oleynik Polymeric C$_{\mathrm{x}}$N$_{\mathrm{y}}$O$_{\mathrm{z}}$ compounds are promising candidates for novel high energy density materials. Both nitrogen and carbon monoxide transform into polymeric high energy density materials at high pressures: over 100 GPa for nitrogen and just over a few GPa for polymeric carbon monoxide (p-CO). The recovery of polymeric nitrogen at ambient conditions remains problematic while p-CO is found to decompose at ambient conditions. In spite of the potential usefulness of C$_{\mathrm{x}}$N$_{\mathrm{y}}$O$_{\mathrm{z}}$ compounds, very little is known about their high pressure chemistry. In this work, extensive first principles variable-composition evolutionary structure prediction calculations are performed to predict the mixed C$_{\mathrm{x}}$N$_{\mathrm{y}}$O$_{\mathrm{z}}$ phase diagram at pressures up to 100 GPa. The search reveals the polymeric C$_{\mathrm{2}}$N$_{\mathrm{2}}$O structure in the space group Cmc2$_{\mathrm{1}}$, which is a known structure of Si$_{\mathrm{2}}$N$_{\mathrm{2}}$O, to be stable at just 10 GPa. We also predict several metastable mixed (CO)$_{\mathrm{x}}$-(N$_{\mathrm{2}})_{\mathrm{y}}$ structures energetically favorable compared to p-CO and N$_{\mathrm{2}}$. Several materials are predicted to have an energy density comparable to p-CO at ambient conditions. Predicted structures are characterized by their Raman spectra and equations of state. [Preview Abstract] |
Tuesday, March 14, 2017 9:24AM - 9:36AM |
E2.00006: Ab initio study of properties of BaBiO$_3$ at high pressure Roman Marto\v{n}\'{a}k, Davide Ceresoli, Tomoko Kagayama, Erio Tosatti BaBiO$_3$ is a mixed-valence perovskite which escapes metallic state by creating a Bi-O bond disproportionation or CDW pattern, resulting in a Peierls semiconductor with gap of nearly 1 eV at zero pressure. Evolution of structural and electronic properties at high pressure is, however, largely unknown. Pressure, it might be natural to expect, could reduce the bond-disproportionation and bring the system closer to metalicity or even superconductivity. We address this question by ab initio DFT methods based on GGA and hybrid functionals in combination with crystal structure prediction techniques based on genetic algorithms. We analyze the pressure evolution of bond disproportionation as well as other order parameters related to octahedra rotation for various phases in connection with corresponding evolution of the electronic structure. Results indicate that BaBiO$_3$ continues to resist metalization also under pressure, through structural phase transitions which sustain and in fact increase the diversity of length of Bi-O bonds for neighboring Bi ions, in agreement with preliminary high pressure resistivity data. [Preview Abstract] |
Tuesday, March 14, 2017 9:36AM - 9:48AM |
E2.00007: Modeling Ultra-fast assembly and sintering of gold nanostructures J. Matthew D. Lane, K. Michael Salerno, Gary S. Grest, Hongyou Fan We use fully atomistic simulations to understand the role of extreme pressure in the assembly and sintering of fcc superlattices of alkanethiol-coated gold nanocrystals into larger nanostructures. Recent quasi-isentropic experiments have shown that 1D, 2D and 3D nanostructures can be formed and recovered from dynamic compression experiments on Sandia’s Veloce pulsed power accelerator. Here, we describe the role of coating properties, such as ligand length and grafting density, on ligand migration and deformation processes during pressure-driven coalescence of metal nano cores into permanent nanowires, nanosheets and 3D structures. The role of uniaxial vs isotropic pressure and the effects of compression along various superlattice orientations will be discussed. Sandia National Laboratories is a multi-mission 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] |
Tuesday, March 14, 2017 9:48AM - 10:00AM |
E2.00008: Initial reaction mechanisms in crystalline and molten RDX from ab initio molecular dynamics simulations Igor Schweigert Extreme temperatures and pressures are typically thought to have opposing effects on the initial decomposition reactions in energetic molecular crystals: extreme temperatures promote direct bond homolysis (large activation entropies), while extreme pressures should promote concerted reactions (small activation volumes). However, no quantitative data exists regarding the range of temperatures and pressures at which these effects become pronounced. In this presentation, I will describe density functional theory based molecular dynamics simulations aimed at indentifying the mechanism of initial decomposition of crystalline and molten RDX under elevated temperatures (1500 K and above) and pressures (a few GPa and above). [Preview Abstract] |
Tuesday, March 14, 2017 10:00AM - 10:12AM |
E2.00009: The Isothermal Equation of State of a Polymer Blended Composite Measured Directly via \textit{in-situ} Tabletop Optical Microscopy and Interferometry (OMI) Joseph Zaug, Elissaios Stavrou, Donald Hansen, Steve Falabella, Sam Weir There is a paucity of high-pressure isothermal equation of state (EOS) data from composite and alloyed materials. Recently, we reported on an approach using a diamond-anvil cell to directly measure the EOS of a pressurized triclinic symmetry material (alpha-NTO, 5-nitro-2,4-dihydro-1,2,4,-triazol-3-one). Using commonly available in-house tabletop diagnostics we directly measured pressure dependent single crystal surface area by making Optical Microscopy measurements and single crystal heights via optical Interferometry (OMI) measurements. Here we report tabletop OMI measurements, V(P), conducted on a composite material, LX-17, which is a polymer blended energetic formulation consisting of 92.5 {\%} TATB and 7.5{\%} of Kel-F 800 plastic binder. We modified 400-mm diamond culets to encapsulate 10s of GPa pressurized samples that are 100-microns tall and wide. The modification enabled a 3x increase in sample height. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344 [Preview Abstract] |
Tuesday, March 14, 2017 10:12AM - 10:24AM |
E2.00010: Molecular Mechanisms in the shock induced decomposition of FOX-7 Ankit Mishra, Subodh C. Tiwari, Aiichiro Nakano, Priya Vashishta, Rajiv Kalia Experimental and first principle computational studies on FOX 7 have either involved a very small system consisting of a few atoms or they did not take into account the decomposition mechanisms under extreme conditions of temperature and pressure. We have performed a large-scale reactive MD simulation using ReaxFF-lg force field to study the shock decomposition of FOX 7. The chemical composition of the principal decomposition products correlates well with experimental observations. Furthermore, we observed that the production of N$_{2}$ and H$_{2}$O was inter molecular in nature and was through different chemical pathways. Moreover, the production of CO and CO$_{2}$ was delayed due to production of large stable C,O atoms cluster. These critical insights into the initial processes involved in the shock induced decomposition of FOX-7 will greatly help in understanding the factors playing an important role in the insensitiveness of this high energy material. [Preview Abstract] |
Tuesday, March 14, 2017 10:24AM - 10:36AM |
E2.00011: Launch Characterization of Laser-Driven Flyer Plates Steven Dean, Frank De Lucia, Jennifer Gottfried Laser-driven flyer plates represent a bench-scale means of studying shock impact of energetic materials. The flyer plates are formed by means of a focused Nd:YAG laser. The laser pulse generates a rapidly expanding plasma between the flyer plate foil and the substrate to which it is adhered. As the plasma grows, a section of the metal foil is ejected at high speed, forming the flyer plate. Simultaneously, many small particles are also ejected that travel in the direction of the flyer plate. We term these particles ``launch products''. This hot, fast moving debris can create an environment adverse to the study of impacting energetic materials at longer time scales (100s of ns to $\mu $s). High speed video and schlieren imaging were used to examine the formation of launch products. Control of launch product formation through altering the driving laser energy, the spatial energy profile of the laser pulse, and the flyer plate foil thickness and composition has been investigated. [Preview Abstract] |
Tuesday, March 14, 2017 10:36AM - 10:48AM |
E2.00012: 3D Printed Shock Mitigating Structures Amanda Schrand, Edwin Elston, Mitzi Dennis, Tammy Metroke, Chenggang Chen, Steven Patton, Sabyasachi Ganguli, Ajit Roy Here we explore the durability, and shock mitigating potential, of solid and cellular 3D printed polymers and conductive inks under high strain rate, compressive shock wave and high g acceleration conditions. Our initial designs include a simple circuit with 4 resistors embedded into circular discs and a complex cylindrical gyroid shape. A novel ink consisting of silver-coated carbon black nanoparticles in a thermoplastic polyurethane was used as the trace material. One version of the disc structural design has the advantage of allowing disassembly after testing for direct failure analysis. After increasing impacts, printed and traditionally potted circuits were examined for functionality. Additionally, in the open disc design, trace cracking and delamination of resistors were able to be observed. In a parallel study, we examined the shock mitigating behavior of 3D printed cellular gyroid structures on a Split Hopkinson Pressure Bar (SHPB). We explored alterations to the classic SHPB setup for testing the low impedance, cellular samples to most accurately reflect the stress state inside the sample (strain rates from 700 to 1750 s-1). We discovered that the gyroid can effectively absorb the impact of the test resulting in crushing the structure. Future studies aim to tailor the unit cell dimensions for certain frequencies, increase print accuracy and optimize material compositions for conductivity and adhesion to manufacture more durable devices. [Preview Abstract] |
Tuesday, March 14, 2017 10:48AM - 11:00AM |
E2.00013: Force Field Accelerated Density Functional Theory Molecular Dynamics for Simulation of Reactive Systems at Extreme Conditions Rebecca Lindsey, Nir Goldman, Laurence Fried Understanding chemistry at extreme conditions is crucial in fields including geochemistry, astrobiology, and alternative energy. First principles methods can provide valuable microscopic insights into such systems while circumventing the risks of physical experiments, however the time and length scales associated with chemistry at extreme conditions (ns and $\mu $m, respectively) largely preclude extension of such models to molecular dynamics. In this work, we develop a simulation approach that retains the accuracy of density functional theory (DFT) while decreasing computational effort by several orders of magnitude. We generate $n$-body descriptions for atomic interactions by mapping forces arising from short density functional theory (DFT) trajectories on to simple Chebyshev polynomial series. We examine the importance of including greater than 2-body interactions, model transferability to different state points, and discuss approaches to ensure smooth and reasonable model shape outside of the distance domain sampled by the DFT training set. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
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