Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session P17: Matter in Extreme Environments: Theoretical Methods and Applications IFocus
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Sponsoring Units: DCOMP Chair: Tiange Bi Room: BCEC 156A |
Wednesday, March 6, 2019 2:30PM - 3:06PM |
P17.00001: Equation of State Calculations With First-Principles Computer Simulations of Matter at Extreme Conditions Invited Speaker: Burkhard Militzer The properties of materials at extreme pressure and temperature conditions are important in astrophysics and fusion science. When models for the interiors of Saturn and Jupiter are constructed to match gravity data from the NASA missions Cassini and Juno, an accurate knowledge of the equation of state of hydrogen-helium mixtures is essential. Modern dynamic compression experiments typically probe megabar and gigabar pressures. In order to provide a comprehensive theoretical description of materials at such extreme conditions, we combine results from path integral Monte Carlo (PIMC) and density functional molecular dynamics simulations. We present equation of state results for first-row elements and compounds such as boron, CH plastic, and oxygen. The shock Hugoniot curves are derived and compared with experimental data. Then we discuss how bound states can be incorporated efficiently into the nodal structure in the PIMC simulations, which enables us to simulate second row elements. We present results from equation of state computations for sodium, aluminum, silicon, and magnesiosilicates. |
Wednesday, March 6, 2019 3:06PM - 3:18PM |
P17.00002: The Challenge of Assessing Uncertainty in Equation of State (EOS) Generation Christine J Wu, Carrie Prisbrey, Miguel Morales We have recently developed multiphase EOSs for a number of materials including Beryllium and Gallium, based not only on experiments, but also on theoretical calculations for regions where experiments are not available or in conflict. Building EOSs unavoidably involves multiple sources of uncertainties, including experimental error bars, and uncertainties due to theoretical approximations and different choices of the free energy model. We will discuss our baseline EOS models and preliminary attempt to address and bound EOS uncertainties. |
Wednesday, March 6, 2019 3:18PM - 3:30PM |
P17.00003: Determining temperature-pressure-density relations of shock-compressed post-transition metals using optimal functionals Shuai Zhang, Miguel Morales, Richard Briggs, Martin G Gorman, Dayne Fratanduono Dynamic compression techniques offer very useful ways of measuring the equation of state (EOS) of materials at extreme conditions. Many properties, in particular the pressure-density relation along the shock Hugoniot curve, can usually be determined with high accuracy. However, there lacks a generic way to measure temperature. This is problematic when studying phase transformation boundaries of non-transparent materials, which can have large uncertainties depending on the EOS model being used. We propose a method for determining the temperature-pressure-density relation of materials under shock compression using quantum simulations based on optimal functionals. The choice of the functional is constrained by well-established experimental data, such as pressure-density Hugoniot and static compression results. These constraints are from multiple regions of the phase space, therefore making our predictions widely reliable. We apply this method to studying post-transition metals, of which the phase and structural property changes are of great interest to the high-pressure and materials physics communities. |
Wednesday, March 6, 2019 3:30PM - 3:42PM |
P17.00004: First-principles calculation of third-order elastic constants via numerical
differentiation of the second Piola-Kirchhoff stress tensor David Cuffari, Angelo Bongiorno Third-order elastic constants (TOECs) of materials are difficult to measure experimentally and |
Wednesday, March 6, 2019 3:42PM - 3:54PM |
P17.00005: Analysis of heating curves and optical properies for the liquid-liquid transition to metallic hydrogen Jacques Tempere, Matthew Houtput, Isaac Silvera Hydrogen at high temperatures and pressures undergoes a phase transition from liquid molecular to liquid atomic metallic hydrogen. This transition takes place on the planet Jupiter and has been studied in the laboratory. Experiments in a diamond anvil cell for temperatures up to 2000 K and pressures of 100-170 GPa determine heating curves and optical properties. Heating curves (the temperature of the sample as a function of heating power) have a positive slope with increasing power with a plateau in temperature, most likely associated with the latent heat of transformation. Plateaus are associated with an abrupt rise in reflectance and absorption of visible light as expected for a metal. We carry out a realistic finite element analysis of heating curves and optical properties. The simulation shows that the plateaus and onset of absorption are related to the phase transition. However much larger values of latent heat are required than have been predicted by theory. The transition may be more complex than considered in current models. |
Wednesday, March 6, 2019 3:54PM - 4:06PM |
P17.00006: Free energies of reaction for aqueous glycine condensation chemistry at extreme temperatures Nir Goldman, Matthew Kroonblawd We have performed high throughput quantum molecular dynamics simulations to determine the free energy surface for aqueous glycine condensation reactions from moderate to extreme temperatures similar to oceanic hydrothermal vents (1g/cm3 and temperatures ranging from 300 K to 1000 K). Our simulations identify significant changes in the free energy surface topology and subsequent chemical reactivity with increasing temperature. We predict that temperatures at 400 K and below glycine favor dipeptide formation whereas higher temperatures facilitate the reverse hydrolysis reaction, with solvated glycine molecules showing greater stability. This change in favorability is correlated with a shift in the location and characteristics of specific reaction bottlenecks or barriers. Simultaneously, we observe that relative free energy barriers (total energy plus entropic contributions) for both condensation and hydrolysis reactions generally decrease with increasing temperature. Our results indicate that relatively modest temperatures near 400 K may best facilitate formation of oligoglycine molecules in oceanic systems related to the synthesis of life-building compounds. Prepared by LLNL under Contract DE-AC52-07NA27344. |
Wednesday, March 6, 2019 4:06PM - 4:18PM |
P17.00007: First principles simulation of the non-linear Peltier effect Xavier Andrade, Alicia R. Welden, Alfredo A. Correa When matter is subject to large electric fields or temperature gradients, the usual linear approximations for the transportation of charge and heat, Ohm's and Fourier's law, break down. This gives rise to non-linear transport phenomena like negative-differential conduction. |
Wednesday, March 6, 2019 4:18PM - 4:30PM |
P17.00008: Optical absorption properties of laser-dressed matter Bing Gu, Ignacio Franco We develop a theory for the optical absorption of electronic materials driven far from equilibrium by resonant and non-resonant lasers. In it, the interaction between matter and the driving light is treated exactly through a Floquet analysis, while the effects of the probing light are captured to first order in perturbation theory. The formalism is employed to characterize the optical properties of a nanoscale semiconductor dressed by non-resonant light of intermediate intensity (non-perturbative, but non-ionizing). As shown, non-resonant light can reversibly turn this transparent semiconductor into a broadband absorber and open strong absorption/stimulated emission bands at very low frequencies (~meV). These developments offers a platform to understand and predict the emergent optical properties of materials dressed by the electric field of light, and catalyze the design of laser-dressed materials with desired optical properties. |
Wednesday, March 6, 2019 4:30PM - 4:42PM |
P17.00009: Radiation Induced Dissociation Pathways and Charge Redistribution in X-ray Free-Electron Laser Imaging Oscar Grånäs Historically, structure determination of nano-crystals, proteins and macromolecules required the growth of high-quality crystals sufficiently large to diffract x-rays efficiently while withstanding radiation damage. The development of the x-ray free-electron laser (XFEL) has opened the door for high resolution single particle imaging using x-rays, as the extreme intensity ensures that enough diffraction statistics is collected before the sample is destroyed by radiation damage. Still, recovery of the structure is a challenge, in part due to the partial fragmentation of the sample during the diffraction event. |
Wednesday, March 6, 2019 4:42PM - 5:18PM |
P17.00010: Matter in Extreme Environments: Theoretical Studies of Light Elements Under Pressure Invited Speaker: Miguel Morales Despite their apparent simplicity, light elements at extreme conditions of pressure and temperature display remarkable properties that have fascinated theoreticians and experimentalists for over a century. Recent advances in first-principles simulation methods have allowed us to elucidate ever more properties of these materials giving us predictive capabilities which, when combined with continuously improving experimental platforms, allow us to obtain new insight into the behavior of matter at extreme conditions. In this talk I will present an overview of the current state of the art in first-principles simulation capabilities for light elements at extreme environments. I will pay particular attention to simulation methods that operate directly in the physical picture of electrons and ions, including density functional theory and quantum Monte Carlo. As a demonstrative example of the predictive capabilities of these methods, I will present recent predictions in the phase diagram of hydrogen during metallization and molecular dissociation in connection with recent experimental observations of metallization. I will present the most recent predictions for the location of the metal-insulator transition in the compressed liquid along with predictions of the optical properties near the dissociation regime. We show how state-of-the-art simulations are able to provide a comprehensive picture of molecular dissociation and metallization in the liquid which explains the conflicting experimental results obtained for several different platforms. |
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