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 P19: Matter in Extreme Environments: Theoretical and Experimental AdvancesFocus Live
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Sponsoring Units: DCOMP DMP Chair: Xiaoyu Wang, State Univ of NY - Buffalo |
Wednesday, March 17, 2021 3:00PM - 3:12PM Live |
P19.00001: Cij: A Python code for thermoelasticity Chenxing Luo, Xin Deng, Wenzhong Wang, Zhongqing Wu, Renata M Wentzcovitch The Wu-Wenzcovitch semi-analytical method is a concise and predictive formalism to compute the high pressure and high temperature (high-PT) thermoelastic tensor (SAM-Cij) of crystalline materials. In conjunction with ab-initio calculations to compute static elastic coefficients and phonon frequencies, this method has been successfully applied to materials across different crystal systems. Mineral elastic properties under mantle conditions obtained with this method have provided first-hand insights into the origins of seismic heterogeneities in Earth's mantle. Here, we introduce the Cij package, a Python implementation of the SAM-Cij method. It enables a thermoelasticity calculation to be initiated from a single command and is fully-configurable from an available calculation settings file to work with different materials. These features allow SAM-Cij calculations to be easily integrated as a part of high-throughput workflows. In addition to the command-line interface, this package also provides intuitive Python APIs for analysis and plotting. |
Wednesday, March 17, 2021 3:12PM - 3:24PM Live |
P19.00002: Liquid liquid transitions and liquid electrides in the alkali metals Victor Naden Robinson, Sandro Scandolo, Andreas Hermann, Graeme Ackland, Hongxiang Zong, Simon Ayrinhac, Daniele Antonangeli, frederic decremps We demonstrate the existence of a new type of liquid in simple metals under high pressure. We show that liquid alkali metals localize electrons on non-nuclear sites as “pseudoanions” under sufficient pressure during a continuous liquid liquid transition. This results in a two-component mixed electride-metallic bonding, in which the electride character increases until around. We have used atomistic simulations with both density functional theory and machine-learned potentials, as well as picosecond acoustic measurements. We show how the transformation is evident in K, Rb, Cs by anomalous diffusivity, thermal expansion, sound speed, coordination number, reflectivity, and heat capacity across a wide range of pressure associated with their respective melting line minima. The abnormalities stem from a significant change in local electronic and ionic structures. Although primarily a pressure-induced phenomenon, there is also a thermal expansion anomaly. We resolve the long-standing mystery of how a liquid can be denser than a close-packed solid, in this case forming a liquid electride. |
Wednesday, March 17, 2021 3:24PM - 3:36PM Live |
P19.00003: pgm: A Python package for free energy calculation Jingyi Zhuang, Hongjin Wang, Qi Zhang, Zhen Zhang, Renata M Wentzcovitch The quasi-harmonic approximation (QHA) is a powerful method for computing free energy and thermodynamic properties of materials at high pressures (P) and temperatures (T). However, anharmonicity, electronic excitations in metals, or both, introduce an intrinsic T-dependence on the phonon frequencies, which makes the QHA inadequate. Here we present a Python package, pgm, for free energy and thermodynamic property calculations. It is based on the concept of phonon quasiparticles and the phonon gas model (PGM). The free energy is obtained by integrating the entropy, which can be readily calculated for a system of phonon quasiparticles. This method is useful for obtaining free energy in anharmonic insulators and harmonic or anharmonic metals. Calculations of thermodynamic properties and equations of state are also implemented in the code. We demonstrate successful applications of pgm to hcp-iron (ε-Fe) at extreme conditions and cubic CaSiO3-perovskite, a strongly anharmonic system. |
Wednesday, March 17, 2021 3:36PM - 4:12PM Live |
P19.00004: Impact-induced chemistry and physics through high-energy ball milling Invited Speaker: Przemyslaw Dera Mechanochemical activation by high-energy milling has become a widely used method for solid state synthesis, and alternative to high-temperature processes. It has been successfully used for synthesis of crystalline and amorphous alloys, intermetallic compounds, metastable phases, nanomaterials and metal-ceramic composites. Mechanochemical synthesis utilizes high-energy impact phenomena to initiate chemical reactions or structural transformations. The peak impact pressures which the individual sample particles experience vary depending on the type of mill, milling speed, as well as size, shape and density of the attritor components, but can reach 20 GPa, while the temperature typically remains below 100C. Remarkably, this is achieved with significant sample quantities (grams), over a short period of time, and very inexpensively. Whereas mechanisms and kinetics of solid-state reactions induced by temperature or static pressure are fairly well understood, transformations of materials under impact in a milling assembly remain largely unexplored and are based almost exclusively on ex situ studies. During the mechanical activation particles undergo heavy deformation and experience significant strains. This results in formation of dislocations, vacancies, stacking faults and increased number of particle boundaries, making the milled material energetically less stable. This presentation will discuss results of ball milling experiments with simple oxides such as GeO2 and TiO2, aimed at inducing structural phase changes, as well as mechanochemical solid state reactions leading to formation of olivine-type compounds. I will also introduce a new project to develop more economical mechanochemical paths towards synthesis of the cubic phase of boron nitride. |
Wednesday, March 17, 2021 4:12PM - 4:24PM Live |
P19.00005: Life in Extreme Environments: Material Properties of the Enzymes Toshiko Ichiye Life on Earth has been found in many extremes of pressure P and temperature T. Understanding how life works at high P and high T has implications for the origin of life on Earth and for the search for extraterrestrial life. In addition, extremes of P and T are used in sterilization and food preservation. To understand how the proteins necessary for life can function at extremes, we use a combination of molecular dynamics simulations of enzymes in aqueous solution, combined with experimental data, to understand how their material properties affect their biochemical activity. We will discuss the effects of P and T on enzymes, evolutionary timescale adaptations in the material properties of enzymes for extremes, and rapid response changes in the intracellular environment to protect enzymes against extremes. |
Wednesday, March 17, 2021 4:24PM - 5:00PM Live |
P19.00006: Using liquid informed searches to predict high pressure and finite temperature phase transitions Invited Speaker: Stanimir Bonev Recent developments in computational algorithms have enabled crystal structure prediction at high pressure conditions, leading the way to the discovery of materials with unexpected and fascinating properties. However, structure prediction at finite temperature remains a challenge, while advances in experimental platforms and measurement techniques have opened up access to the properties of matter via a wide range of pressure-temperature pathways. In this talk, I will discuss the use of structural information and/or sampling from liquid simulations to predict high pressure phase transitions and crystal structures at finite temperature conditions. The techniques will be illustrated with examples of successful applications on several systems, including magnesium, nitrous oxide, and nitrogen. |
Wednesday, March 17, 2021 5:00PM - 5:12PM Live |
P19.00007: Thermal gradient effect on the helium and intrinsic defects transport properties in Tungsten Enrique Martinez Saez, Nithin Mathew, Danny Perez, Brian Wirth, Dimitrios Maroudas
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Wednesday, March 17, 2021 5:12PM - 5:24PM Live |
P19.00008: Express: nonstop calculations with Quantum ESPRESSO Qi Zhang, Hongjin Wang, Jingyi Zhuang, Pedro da Silveira, Renata M Wentzcovitch Ab initio mineral physics studies' intrinsic complexity inspired the development of workflows to automate long and extensive sequences of the ab initio calculations [1]. Here we introduce Express, a new generation of workflows designed to facilitate calculations of the thermodynamic properties of materials. These workflows are exquisitely designed and well-tested, inspired by their predecessor that is known as VLab [1]. |
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