Bulletin of the American Physical Society
22nd Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 67, Number 8
Monday–Friday, July 11–15, 2022; Anaheim, California
Session V03: Molecular Dynamics in Carbon and Carbon-Rich MaterialsFocus Recordings Available
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Chair: Rebecca Lindsey, Lawrence Livermore National Lab Room: Anaheim Marriott Platinum 1 |
Thursday, July 14, 2022 2:00PM - 2:30PM |
V03.00001: Phase transitions of carbon at extreme conditions Invited Speaker: Kien Nguyen-Cong An accurate phase diagram of carbon at extreme pressures and temperatures is of critical importance for constructing interior models of carbon-rich exoplanets as well as for designing ablation capsules for inertial confinement fusion experiments. However, stability of diamond and possible transitions to other high-pressure carbon phases above 1 TPa are a matter of debate. We investigate the phase diagram and phase transitions of carbon materials in both crystalline and amorphous forms at high temperatures and pressures using machine-learning molecular dynamics (MD) simulations. The MD simulations explain extreme metastability of diamond well beyond the region of its thermodynamic stability and predict experimentally viable synthesis pathways of elusive BC8 high pressure phase of carbon. |
Thursday, July 14, 2022 2:30PM - 2:45PM |
V03.00002: A model for ramp compression from ab initio calculations Felipe J Gonzalez, Burkhard Militzer, Raymond Jeanloz, Budhiram K Godwal, Kevin P Driver Ramp compression has emerged as a novel experimental technique to probe matter at extreme pressures, while keeping temperatures lower than shock compression. The compression is thought to be quasi-isentropic, which is ideal to probe the convective zones of planetary interiors. However, a complete theoretical framework to model ramp compression for crystalline materials, such as the Rankine-Hugoniot equations for shock compression, is still lacking. In this work, we present a model of ramp compression that is based on thermodynamics and ab initio calculations where we approximate ramp loading as a series of compression and relaxation steps, which involve both uniaxial and isotropic compression. We apply our model to diamond and we compare with the stress-density data reported from experiments for ramp-compressed diamond [1-3]. We find good agreement between our model and a multiple-shock Hugoniot scheme [4], as well as with a recently proposed strength model for diamond based on plastic work [5]. References: [1] D. Bradley et al., PRL 102, 075503 (2009). [2] R. Smith et al., Nature 511, 330 (2014). [3] A. Lazicki et al., Nature 589, 532 (2021). [4] F. Gonzalez-Cataldo et al., PRB 104, 134104 (2021). [5] D.C. Swift et al., PRB 105, 014109 (2022). |
Thursday, July 14, 2022 2:45PM - 3:00PM |
V03.00003: Progress and Future Directions: The ChIMES Machine Learned Interatomic Model Framework for Chemistry in Energetic Materials Rebecca K Lindsey, Cong Huy Pham, Nir Goldman, Laurence E Fried, Sorin Bastea Many of the safety and performance-related properties of energetic materials are governed by complex condensed phase chemistry under extreme conditions precluding direct experimental investigation. Atomistic simulations can provide valuable insights into such systems while circumventing the challenges of physical experiments, but they rely critically on the availability interatomic potentials that are simultaneously exhibit the quantum accuracy necessary to describe condensed phase chemistry under extreme conditions and the computational efficiency necessary to do so on the largeand associated spatiotemporal scales (e.g., approaching 1 μm and μs). Machine-learned interatomic potentials (ML-IAP), which aim to serve as a computationally efficient surrogate for the quantum mechanical potential energy surface, have provided a promising path forward. However, developing robust ML-IAP for condensed phase chemistry in molecular materials presents a significant challenge due to the expansive associated physicochemical space and disparate governing energy scales (i.e., governing bonded, non-bonded, and reactive interactions). In this presentation, we discuss challenges, progress, and future directions in ground-up ML-IAP development for EM within the context of our ChIMES framework. |
Thursday, July 14, 2022 3:00PM - 3:15PM |
V03.00004: Inelastic Deformations in Shock Compressed Diamond Jonathan Willman, Kien Nguyen-Cong, Ivan Oleynik Understanding diamond response to shock compression at megabar pressures is of critical importance for design of instability-free inertial confinement fusion implosions of diamond ablation capsules. Recent shock experiments on single crystal diamond uncovered strong orientational dependent inelastic response in split elastic-inelastic shock wave regime. However, underlying mechanisms of crystalline anisotropy and atomic-scale mechanisms of inelastic deformations are currently unknown. In this work, large-scale molecular dynamic simulations of diamond shock compression are performed using quantum accurate SNAP machine learning potential for carbon to investigate shock response along three <100>, <110> and <111 crystallographic directions in a wide range of shock intensities. Unusual persistence of anisotropic effects is observed at very high pressures up to complete melting along diamond shock Hugoniot. |
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