Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session L40: Matter in Extreme Environments III: Warm Dense MatterFocus
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Sponsoring Units: DCOMP DMP Chair: Aidan Thompson, Sandia National Laboratories Room: 705 |
Wednesday, March 4, 2020 8:00AM - 8:36AM |
L40.00001: Understanding Matter Under Warm and Extremely Dense Conditions Invited Speaker: Suxing Hu Understanding Matter Under Warm and Extremely Dense Conditions |
Wednesday, March 4, 2020 8:36AM - 8:48AM |
L40.00002: Ultrafast electron-ion coupled dynamics of iron nano-foil in warm dense matter (WDM) conditions studies by time resolved XANES and ab-initio simulations Amalia fernandez, Alfredo A. Correa, Sebastien Hamel, David Prendergast, Sri Chaitanya Das Pemmaraju, Philip Heimann, Roger Wirth Falcone, Jon Henry Eggert, Yuan Ping, Tadashi Ogitsu In recent years, significant progresses have been made in both ultrafast experimental measurements techniques as well as in computational modeling that allow us to access to fundamental properties such as electron-phonon coupling under electron-ion non-equilibrium conditions. In this presentation, we will discuss how a combination of time-resolved XANES experiment and ab-initio derived two-temperature model coupled with XANES simulation is used to study the spatiotemporal electron-ion relaxation behavior of nano-meter thin iron foil that is exposed to femto second laser pulse. We show that the current level of experimental time resolution is already sufficient to constraint thermophysical properties under non-equilibrium WDM conditions within a few tens of percent, however, for the optimal sensitivity, which depends strongly on the choices of geometrical design of target as well as corresponding laser fluece. |
Wednesday, March 4, 2020 8:48AM - 9:00AM |
L40.00003: First-principles Stopping Power in Warm Dense Matter Attila Cangi, Andrew Baczewski, Stephanie B Hansen Recent experiments provide measurements of fusion-product stopping powers in warm dense targets [1, 2]. State-of-the-art numerical modeling complements these critical advances in our empirical knowledge and phenomenological understanding of transport properties in this thermodynamic regime. In anticipation of future experiments, we assess the ability of real-time time-dependent density functional theory (TDDFT) to reproduce these results and compare its predictions with linear response TDDFT and average-atom models. |
Wednesday, March 4, 2020 9:00AM - 9:12AM |
L40.00004: Thermoelectric properties from time-dependent density functional theory Alicia Welden, Xavier Andrade, Alfredo A. Correa The goal of this work is to develop computational methods to predict electrical and thermal transport properties from ab-initio quantum simulations. We apply a microscopic theory of quantum transport to obtain conductivities from first principles. The new methods, based on simulating real time electron dynamics, are able to access larger systems than the standard Kubo-Greenwood approach and are also applicable in non-linear regimes. We investigate liquid metallic hydrogen at 1400 K and 400 GPa, in order to see if there is nonlinear behavior under conditions that are typically accessible by experiments. |
Wednesday, March 4, 2020 9:12AM - 9:24AM |
L40.00005: Thermal gradient effect on the transport properties of helium and intrinsic defects in tungsten Enrique Martinez Saez, Dimitrios Maroudas, Brian Wirth Plasma-facing materials (PFMs) in a fusion reactor are expected to withstand stringent conditions, with high heat and particle fluxes that modify the materials microstructure. These fluxes create strong gradients of temperature and concentration of diverse species. Besides the He ash, neutron particles will create intrinsic point defects, such as vacancies and self-interstitials atoms (SIAs), and their clusters. These species will then migrate in the presence of the afore-mentioned gradients. In this work, we use nonequilibrium molecular dynamics simulations to study the transport properties of He, vacancies, and SIAs in the presence of a thermal gradient in tungsten. In all cases, the defects and impurity atoms tend to migrate toward the hot regions of the material. The resulting concentration profiles are in agreement with irreversible thermodynamics. We compute a negative heat of transport for all species, which indicates that the respective driven species fluxes are directed opposite to the heat flux. We demonstrate that, when the mass-heat transport coupling is considered, the resulting steady-state profiles vary significantly from those when species transport is decoupled from heat transport. |
Wednesday, March 4, 2020 9:24AM - 9:36AM |
L40.00006: Electronic structure approach to compute Dark Matter-Electron scattering cross-sections in Direct Detection experiments Cheng Zhen, Rouven Essig, Marivi Fernandez Serra The existence of dark matter in the Universe is nowadays overwhelming. Numerous direct detection experiments are currently on going or planned all around the world. As the mass of these dark matter particles is unknown, these experiments explore different mass ranges, with a large majority being sensitive to masses above the GeV range. In these experiments dark matter is assumed to scatter from the nuclei and background models are built upon a combined theoretical and experimental characterization of nuclear recoils in the detectors. Recently, however, dark matter in the sub-GeV mass range has received much attention, and several well-motivated theoretical models exist for candidates in this mass range. The traditional method of detecting the nuclear recoil does not apply for sub-GeV dark matter because the recoil energy falls below the detector threshold. However, the scattering of dark matter with atomic electrons can produce observable ionization signals. In this talk we present the theoretical model to estimate the dark matter-electron scattering event rate using first principle methods. We will show how this rate estimation depends on the underlying theoretical approximations. We also show results for different systems like liquid Xe, Si and Ge. |
Wednesday, March 4, 2020 9:36AM - 9:48AM |
L40.00007: Accurate Calculations of a Solid State Test Set with Quantum Monte Carlo Methods Cody Melton, Jaron Krogel, Fionn Malone, Miguel A Morales, Luke Shulenburger Quantum Monte Carlo (QMC) methods serve as some of the most promising techniques for studying correlated materials across large spans of system size. Here, we revisit a solid state test set for QMC ranging from ionic, metallic, covalent, and van der Waals materials. |
Wednesday, March 4, 2020 9:48AM - 10:00AM |
L40.00008: Materials Informatics for Dark Matter Detection Richard Geilhufe, Bart Olsthoorn, Alfredo Ferella, Timo Koski, Felix Kahlhöfer, Jan Conrad, Alexander V Balatsky Dark Matter particles are commonly assumed to be weakly interacting massive particles (WIMPs) with a mass in the GeV to TeV range. Recent interest has shifted toward lighter WIMPs, which are more difficult to probe experimentally. A detection of sub-GeV WIMPs requires the use of small gap materials in sensors. Using recent WIMP mass estimates, we identify the relevant target space toward small gap materials (100 to 10 meV). Dirac Materials, a class of small- or zero-gap materials, emerge as natural candidates Dark Matter sensors. We propose the use of informatics tools to rapidly assay materials band structures to search for small gap semiconductors and semimetals, rather than focusing on a few preselected compounds. As a specific example of the proposed strategy, we use the organic materials database (https://omdb.mathub.io) to identify organic candidate materials. We outline a novel and powerful approach to search for dark matter detection sensor materials by means of a rapid assay of materials using informatics tools. |
Wednesday, March 4, 2020 10:00AM - 10:12AM |
L40.00009: Extreme Electric Fields in DFT Michael Ashton, Christoph Freysoldt, Joerg Neugebauer Strong (1010 V/m) electric fields can be used to trigger chemical processes with extreme precision by selectively stabilizing or weakening bonds to initiate reactions which are otherwise slow or do not proceed at all. The ability to manipulate electric fields to tailor and stimulate bond-breaking events is a powerful experimental control knob, but one whose effects are difficult to predict due to a lack of suitable tools to probe its associated atomic-scale mechanisms. Here we introduce a novel approach, which we term the Generalized Dipole Correction (GDC), that enables the direct study of ultra-high fields effecting bond-breaking and desorption at the level of single atoms using Density Functional Theory (DFT). As a prototype application, we consider field evaporation from a kinked W (110) surface. We reveal two qualitatively different competing mechanisms that can be switched by the applied field. |
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