Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session J19: Matter in Extreme Environments: Novel ChemistryFocus Live
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Sponsoring Units: DCOMP DMP Chair: Shuai Zhang, University of Rochester |
Tuesday, March 16, 2021 3:00PM - 3:36PM Live |
J19.00001: Chemistry under high pressure Invited Speaker: Maosheng Miao Thanks to the developments of high-pressure techniques and quantum mechanics based |
Tuesday, March 16, 2021 3:36PM - 3:48PM Live |
J19.00002: Structure of amorphous non-molecular CS2 at high pressure - experiment and simulation Jinwey Yan, Ondrej Tóth, Wan Xu, Xiao-Di Liu, Eugene Gregoryanz, Philip Dalladay-Simpson, Mario Santoro, Federico Aiace Gorelli, Roman Martonak CS2 represents an important simple molecular system with double bonds. It is widely believed that upon compression it converts into a system of (-(C=S)-S-)n polymeric chains (Bridgman's black polymer-BBP). Here we show, combining new Raman, IR and XRD data for pressures up to 40 GPa with ab initio and machine-learned potential simulations, that the structure of BBP is different. Pressure-induced polymerization creates an amorphous system consisting of chains with 3-coordinated C atoms connected via S bridges or double C=C bonds as well as ones with 4-coordinated C atoms within edge-sharing CS4 tetrahedra. Spectral features observed upon compression can be explained without need for decomposition of molecules. Upon decompression, partially reversible transition is observed. Our work uncovers the non-trivial high-pressure structural evolution in one of the simplest and long-studied molecular systems. |
Tuesday, March 16, 2021 3:48PM - 4:00PM Live |
J19.00003: Electronic Structure and Superconductivity of Compressed Metal Tetrahydrides Tiange Bi, Eva Zurek Tetrahydrides crystallizing in the ThCr2Si2 structure type have been predicted to become stable |
Tuesday, March 16, 2021 4:00PM - 4:12PM Live |
J19.00004: Superconductivity in sodalite-like yttrium hydride clathrates Christoph Heil, Simone di Cataldo, Giovanni Bachelet, Lilia Boeri Motivated by the discovery of near-room-temperature superconductivity in the sodalite-like clathrate hydride LaH10, we report ab initio calculations of the superconducting properties of two closely related hydrides YH6 and YH10 [1], for which an even higher Tc has been predicted. Using fully anisotropic Migdal-Eliashberg theory with Coulomb corrections, we find almost isotropic superconducting gaps, resulting from a uniform distribution of the coupling over states of both Y and H sublattices. The Coulomb screening is rather weak, resulting in a Morel-Anderson pseudopotential μ* = 0.11, at odds with claims of unusually large μ* in lanthanum hydrides. The corresponding critical temperatures at 300 GPa exceed room temperature (Tc = 290 and 310 K for YH6 and YH10), in agreement with a previous isotropic-gap calculation. We estimate anharmonic effects to be weak. |
Tuesday, March 16, 2021 4:12PM - 4:24PM Live |
J19.00005: Quantum Crystal Structure in the 250 K Superconducting Lanthanum Hydride Ion Errea Hydrogen-rich materials at high pressures are at the verge of reaching room-temperature superconductivity. Electrical and x-ray diffraction measurements determined a weakly pressure-dependent Tc for LaH10 between 137 and 218 gigapascals in a structure with a fcc arrangement of La atoms. Here we show that quantum atomic fluctuations stabilize in this pressure range a high-symmetry Fm-3m crystal structure consistent with experiments. Even if ab initio classical calculations predict this structure to distort below 230 GPa, the inclusion of quantum effects evidences the Fm-3m as the true ground state. The agreement between the calculated and experimental Tc values further supports this phase as responsible for the 250 K superconductivity. The relevance of quantum fluctuations questions many of the crystal structure predictions made for hydrides within a classical approach that at the moment guide experiments. Furthermore, quantum effects are revealed to be crucial to stabilize solids with extraordinary electron-phonon coupling, reducing the pressures needed for their synthesis. |
Tuesday, March 16, 2021 4:24PM - 5:00PM Live |
J19.00006: Crystal Structure and Reflectivity of Laser Ramp-Compressed Sodium Invited Speaker: Danae Polsin Extreme compression can alter the free-electron behavior of “simple” metals such as sodium. At pressures exceeding 200 GPa, Na was observed to become transparent to visible light under static compression. First-principles calculations suggest this is caused by a transformation to an electride phase where electrons are localized in interstitial positions. Laser-driven ramp compression is used to compress Na into an unexplored pressure regime to investigate the crystalline structure, reflectivity, and melting behavior of Na. X-ray diffraction is used to constrain the crystalline structure and detect melting. Optical reflectivity measurements at 532 nm are used to detect a transition to the observed insulating electride phase. We show the highest-pressure solid x-ray diffraction and reflectivity data on Na to date. The results indicate the Na phase diagram is more complicated than predicted by zero-temperature density functional theory. |
Tuesday, March 16, 2021 5:00PM - 5:12PM Live |
J19.00007: The change of basic chemical behavior of elements under high pressure Yuanhui Sun, Maosheng Miao The chemistry at ambient condition has implicit boundaries rooted in the atomic shell structure: The inner-shell electrons and the unoccupied outer-shell orbitals do not involve as major component in chemical reactions and in chemical bonds. The chemical properties of atoms are determined by the electrons in the outermost shell; hence, these electrons are called valence electrons. These general rules govern our understanding of chemical structures and reactions. |
Tuesday, March 16, 2021 5:12PM - 5:24PM Live |
J19.00008: The Van Der Waals Radii at High Pressure and the Atoms-Under-Pressure Database Martin Rahm, Mattias Ångqvist, J. Magnus Rahm, Paul Erhart, Roberto Cammi We describe a quantum mechanical model for calculating van der Waals radii of non-reactively compressed atoms. Radii are presented for 93 atoms in a pressure range from 0 to 300 gigapascal. Trends in radii are shown to be largely maintained under pressure compared to ambient conditions, but atoms also change place in their relative size ordering. Isobaric contractions of radii are predicted and are explained by pressure-induced changes to the electronic ground state configurations of the atoms. The presented radii are predictive of drastically different chemistry and physics under high pressure and permit an extension of atom-based rationales to different thermodynamic regimes. For example, they can aid in assignment of bonded and non-bonded contacts, for distinguishing molecular entities, and for estimating available space inside compressed materials. An open interactive web application, the Atoms-Under-Pressure Database, containing radii, electronegativities and atomic ground state electron configurations for compressed atoms is also demonstrated. |
Tuesday, March 16, 2021 5:24PM - 5:36PM Live |
J19.00009: Theoretical Prediction of Superhard Materials with the XtalOpt Evolutionary Algorithm Xiaoyu Wang, Eva Zurek, Davide Proserpio The XtalOpt evolutionary algorithm for crystal structure prediction has been extended to enable the prediction of materials with specific properties. A fitness function has been implemented wherein the user can denote the percent contribution that enthalpy and the property (e.g. Vickers hardness obtained via a macroscopic hardness model and the shear modulus as determined via machine learning, percentage of hydrogen atoms that do not form H-H bonds, or density of states at the Fermi level) have on the fitness function. We have used XtalOpt to search for hard and stable carbon allotropes. Several novel carbon allotropes that are superconducting or posess super-long sp3-sp3 bonds were found. We also discovered novel hydrides that could potentially be conventional superconductors. |
Tuesday, March 16, 2021 5:36PM - 5:48PM Live |
J19.00010: Shared structural motifs and bonding in new families of boron structures found via XtalOpt evolutionary algorithm Katerina Hilleke, Eva Zurek The complex chemistry of elemental boron is demonstrated in both the large number of predicted and experimentally-realized allotropes as well as the curious structural motifs that arise. As a consequence of electron deficiency, multicenter bonding is prevalent in boron-based systems, demonstrated in the combination of two- and three-center bonding in α-rhombohedral boron. In an attempt to clarify potential metastable structural adaptations of boron at high pressures, crystal structure searches were performed at 100 GPa using the XtalOpt evolutionary algorithm. In addition to the experimentally-observed Cmca α-Ga allotrope, a series of dynamically stable metastable structures were identified. Several are directly recognizable as adaptations of the α-Ga structure, with others displaying channels throughout. The SSAdNDP analysis, which generates a chemically-intuitive bonding representation within solid systems, revealed networks of four-, three- and two-center bonding interactions, with different bonding motifs reflecting the multiple structural families. The relationships among the identified structures hint at many possible variations of elemental boron structures. |
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