Bulletin of the American Physical Society
APS March Meeting 2024
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session D20: Matter at Extreme Conditions: Planetary Science and Warm Dense MatterFocus
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Sponsoring Units: GCCM DCOMP DMP Chair: Alison Altman, Texas A&M University Room: M101ABC |
Monday, March 4, 2024 3:00PM - 3:36PM |
D20.00001: Dynamic compression of iron oxides to multi-megabar pressures Invited Speaker: Ian K Ocampo Laser-driven dynamic compression enables the study of planetary materials at the extreme pressure-temperature (PT) conditions of Earth’s deep interior. When coupled with in situ x-ray diffraction, fundamental properties such as crystal structure and equation of state can be accurately measured which are essential for developing interior structure, dynamics, and evolution models for planets within and outside our solar system. The discovery of over 5500 extrasolar planets has motivated research on matter at even more extreme PT conditions as calculations based on density estimates for these planets suggest PT profiles that greatly exceed those for Earth. As planetary detection techniques and mass-radius measurement precision continue to improve, experimental efforts must accompany these advances to better understand the interiors of these planets which largely control their surface processes, including planet habitability. |
Monday, March 4, 2024 3:36PM - 3:48PM |
D20.00002: Structural prediction of Fe-Mg-O compounds at Super-Earth's pressures Yimei Fang Terrestrial exoplanets are of great interest for being simultaneously similar to and different from Earth. Their compositions are likely comparable to those of solar-terrestrial objects, but their internal pressures and temperatures can vary significantly with their masses/sizes. The most abundant non-volatile elements are O, Mg, Si, Fe, Al, and Ca, and there has been much recent progress in understanding the nature of magnesium silicates up to and beyond ~3 TPa. However, a critical element, Fe, has yet to be systematically included in materials discovery studies of potential terrestrial planet-forming phases at ultra-high pressures. Here, using the adaptive genetic algorithm (AGA) crystal structure prediction method, we predict several unreported stable crystalline phases in the binary Fe-Mg and ternary Fe-Mg-O systems up to pressures of 3 TPa. The analysis of the local packing motifs of the low-enthalpy Fe-Mg-O phases reveals that the Fe-Mg-O system favors a BCC motif under ultra-high pressures regardless of chemical composition. Besides, oxygen enrichment is conducive to lowering the enthalpies of the Fe-Mg-O phases. Our results extend the current knowledge of structural information of the Fe-Mg-O system to exoplanet pressures. |
Monday, March 4, 2024 3:48PM - 4:00PM |
D20.00003: Elasticity and acoustic velocities of δ-AlOOH at geophysical conditions Chenxing Luo, Yang Sun, Renata Maria M Wentzcovitch δ-AlOOH is a prototypical high-pressure hydrous phase for understanding deep water storage and circulation in Earth's deep interior. However, its elasticity and acoustic velocities remain undetermined at high pressures and temperatures. This study evaluates the adiabatic elastic tensor and acoustic velocities of δ-AlOOH at mantle pressures and temperatures. The elastic tensor is computed using molecular dynamics with a machine-learning force field constructed based on the SCAN meta-GGA description of the system. This method enables us to tackle the long-standing issue of anharmonicity across the pressure-induced H-bond symmetrization and reach extreme temperatures up to δ's superionic regime. Our ambient condition results are in excellent agreement with recent single-crystal measurements, showcasing the validity and effectiveness of our approach. |
Monday, March 4, 2024 4:00PM - 4:12PM |
D20.00004: Ab initio study on the stability and elasticity of brucite Hongjin Wang, Chenxing Luo, Renata Maria M Wentzcovitch Brucite, or magnesium hydroxide (Mg(OH)2), is a mineral of great interest owing to its various applications and roles in geological and environmental processes. Its structure, behavior under different conditions, and unique properties have been the subject of numerous studies. As a stable hydrous phase in subduction zones, its elastic anisotropy can significantly contribute to the seismic properties of these regions. Since the brucite structure was first refined in 1967 as having a space group of P-3m1, several possible structures with different symmetries have been proposed. Here, we use ab initio techniques to address different brucite structures' static and dynamic stability. Furthermore, we compute the brucite’s elastic properties and address some consequences for seismic observations. |
Monday, March 4, 2024 4:12PM - 4:24PM |
D20.00005: Mechanical stability of body-centered cubic iron at Earth’s core pressure and temperature conditions using a molecular graph kernel and Gaussian process regression Blaise A Ayirizia Gaussian process regression was performed on graph kernels quantifying the similarity of mathematical graphs that encode the atomic configurations of the body-centered cubic (BCC) crystal lattice of iron with thermal atomic displacements to predict the energy associated with arbitrary atomic configurations. The energies and atomic configurations used in the regression were obtained via density functional theory molecular dynamics (MD) at pressures expected to occur in the Earth's core and at temperatures ranging from several hundred to several thousand kelvin. Random MD simulation time steps were selected and each atom in the supercell was displaced in the direction of the first, second, and third nearest neighbors, calculating the force exerted on the displaced atom by numerical differentiation. The BCC structure is unstable at low temperatures, but the atoms generally experience a restoring force at high temperatures, particularly in the direction of the first and the third nearest neighbors. |
Monday, March 4, 2024 4:24PM - 4:36PM |
D20.00006: Ferrous iron partitioning in the lower mantle: consequences for seismic velocities and heterogeneities Jingyi Zhuang, Renata Maria M Wentzcovitch Iron partitioning among lower mantle phases has non-monotonic behavior owing to the high-spin to a low-spin crossover of iron in ferropericlase (Fp) at pressure-temperature conditions of this region. The potential effects of this partitioning have long been recognized and the actual partitioning coefficient between bridgmanite (Bm) and ferropericlase (Fp), KD, has been investigated in different aggregates multiple times. Here, we systematically investigate the behavior of KD using ab initio simulation methods and non-ideal or quasi-ideal solid solution models for the main phases. We also address the effect of this variable KD on lower mantle velocities and temperature-induced heterogeneities. |
Monday, March 4, 2024 4:36PM - 4:48PM |
D20.00007: Novel Doubly Superionic Behavior in Icy Compounds at Planetary Interior Conditions Kyla de Villa, Felipe J Gonzalez, Burkhard Militzer Superionic phases, in which protons diffuse like a liquid through stable lattices of heavier nuclei, have been observed in water and ammonia at high pressures. Here, we describe a novel state of matter: double superionicity. With density functional molecular dynamics and machine learning molecular dynamics simulations we show that hydrogen and one heavier species become mobilized at elevated temperature while the heaviest nuclei provide a stable sublattice until the entire material melts at yet higher temperature. We further demonstrate that proton superionicity is ubiquitous in H-C-N-O materials at sufficiently high pressure and temperature. Superionic and doubly superionic phases may exist in the interiors of Uranus and Neptune and thus may influence their magnetic dynamo because of their high ionic conductivities. |
Monday, March 4, 2024 4:48PM - 5:00PM |
D20.00008: Pressure engineering negative linear compressibility in various type systems Arthur Haozhe H Liu, Lisa Luhong Wang Liu Various types of negative linear compressibility (NLC) under high pressure conditions were reported but not fully understood. NLC is a rare phenomenon where a crystal expands along one direction under hydrostatic compression. In this presentation, both crystalline and non-crystlline selenium samples were in situ studied in diamond anvil cell under high pressure conditions using synchrotron x-ray diffraction. Two types of NLC mechanism were found at various pressure regions, i. e. at around 10 GPa, and around 120 GPa, respectively, in this same elemental Se sample [1, 2]. By adjusting the preheating history of non-crystalline Se samples [3], we could capture early crystallization process and reveal the physics behind the previous controversy results on this system. Other type of NLC at very low pressure region, i. e. below 0.2 GPa, was also discovered in a Ni(II) complex single crystal [4], follow up with the similar phase transition at low temperature conditions. In practice, the latter case might have potentially bright application future. |
Monday, March 4, 2024 5:00PM - 5:12PM |
D20.00009: An ab initio study of the hydrogen-helium phase separation in the Gibbs ensemble Francois Soubiran, Etienne Jaupart, Christophe Winisdoerffer The giant planets observations lead to significant advances in our understanding of dense plasmas. The detection of a strong magnetic field around Jupiter was an indirect proof of hydrogen metallization at high pressure. The excess luminosity of Saturn as well as the gravitometric measurements by Cassini and Juno strongly support the idea that hydrogen and helium segregate at high pressure. Ab initio simulations confirmed these predictions although a large uncertainty remains regarding the critical surface of the H-He phase separation. Recent experiments were able to detect a phase separation of hydrogen-helium in the megabar regime using reflectivity measurements in laser-shocks. However these experiments place the critical surface of the H-He demixing at much higher temperature than the ab initio studies. |
Monday, March 4, 2024 5:12PM - 5:24PM |
D20.00010: Charge Transport Properties of Matter Under Extreme Conditions from ab initio Molecular Dynamics Vidushi Sharma, Alexander J White, Lee A Collins Warm dense matter (WDM), believed to constitute the cores of giant icy planetary and stellar systems, has been an entity of long-standing interest due to its realization in inertial confinement fusion experiments in a controlled laboratory environment. A quantum mechanical description of this exotic state of matter is crucial for guiding experimental efforts into probing this regime as well as verifying the equation of state and other transport properties typically obtained from analytical models. Recently, density functional theory (DFT) and its time-dependent extension (TDDFT) have emerged as powerful tools for modeling the static and dynamic transport properties of such hot dense systems. In the traditional formulation of DFT, its computational complexity scales cubically with system size and temperature, making it computationally rather expensive. In this talk, I will describe an alternative linear-scaling approach that applies stochastic techniques to the traditional Kohn-Sham DFT framework. Further, I will discuss a novel proposal for a mixed DFT (mDFT) formalism that combines the stochastic and deterministic Kohn-Sham algorithms to study matter at moderate to very high temperatures [1]. Finally, I will highlight targeted physical observables, diffusivity, and conductivities obtained in a computationally efficient fashion within this formalism for multiple testbed WDM single-component systems and mixtures [2]. |
Monday, March 4, 2024 5:24PM - 5:36PM |
D20.00011: Transport Coefficients of Warm Dense Matter from Kohn-Sham Density Functional Theory Cody A Melton, Raymond C Clay, joshua P townsend, Kyle R Cochrane, Amanda E Dumi, Meghan K Lentz Ionic and electronic transport coefficients are fundamentally important to the understanding of the warm dense matter (WDM) regime. These coefficients are consumed by hydrodynamic codes which are used to both design and interpret experiments on high energy density facilities such as the Z-machine, the NIF, and Omega. Experiments in these regimes are exceptionally difficult and often provide limited constraints on models, while theoretical methods originate from either the plasma or condensed matter communities. The WDM regime exists at the coalescence of the two communities and resides at the limits of applicability for some methods. To quantify the uncertainties and capabilities of current theory, the “2nd charged-particle transport coefficient comparison workshop (TCCW2)” brought together multiple methods from different fields to study transport properties in the WDM regime. We present a comprehensive study of self-diffusion, DC electrical conductivity, electrical thermal conductivity, and shear viscosity via ab-initio molecular dynamics and density functional theory for our contribution to the TCCW2. In addition, special care is taken to highlight the sensitivities of statistical estimates and convergence of transport coefficients to rarely discussed aspects of the data analysis. |
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