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 Y03: Molecular Dynamics-Driven Property PredictionsFocus Recordings Available
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Chair: Mary Alice Cusentino, Sandia National Laboratories Room: Anaheim Marriott Platinum 1 |
Friday, July 15, 2022 9:15AM - 9:45AM |
Y03.00001: Phase behavior of super-ionic water at planetary conditions. Invited Speaker: Sebastien Hamel Most water in the universe may be superionic, and its thermodynamic and transport properties are crucial for planetary science but difficult to probe experimentally or theoretically. We use machine learning and free energy methods to overcome the limitations of quantum mechanical simulations, and characterize hydrogen diffusion, superionic transitions, and phase behaviors of water at extreme conditions. The machine learned potentials allow us to explore in detail the nature of the phase transitions and the free energy surface of water and clarifies the phase behaviour of the high-pressure insulating and superionic ices and reveals peculiar solid–solid transition mechanisms not known in other systems. |
Friday, July 15, 2022 9:45AM - 10:00AM |
Y03.00002: Non-perturbation electron-vibration interaction simulations of quantum effects in phase transitions under high pressure Anguang Hu A long-standing challenge in high-pressure physics and chemistry is determining locations of phase transitions in the pressure-volume-temperature space and simultaneously characterizing them. Accurate non-perturbation electron-vibration interaction simulations recently developed applied to computationally studies of phase transitions under high pressure. Simulations show that some quantum effects in phase transitions play an important role at high pressure. These quantum effects include the quantum degeneracy in energy band structures and electron-vibration interactions. Under mechanical compression, electron-vibration interactions can strongly couple the quantum degeneracy to stretch chemical bonds through a specific reaction vibrational mode and thus induce a phase transition. The vibrational amplitude of the reaction mode can apply to estimate transformation temperature in good agreement with experiments. Therefore, non-perturbation electron-vibration interaction simulations can identify phase transition locations in the pressure-volume-temperature space. More importantly, such simulations provide numerical modelling access to the physics and chemistry of quantum materials under high pressure. |
Friday, July 15, 2022 10:00AM - 10:15AM |
Y03.00003: Prediction of crystalline structure and properties of nitryl cyanide solids at high pressure. Iskander G Batyrev, Jonnathan C Bennion
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Friday, July 15, 2022 10:15AM - 10:30AM |
Y03.00004: Many-Body Mechanochemistry Simulations: Exploring the initial events inside a hotspot Brenden W Hamilton, Alejandro H Strachan When molecular materials experience high velocity impacts, the resulting shockwave can induce a variety of complex intra-molecular deformations, leading to mechanochemistry. Mechanochemistry can enable novel reaction pathways, lower the thermal energy cost of reactions, and is relevant to thermochemical phenomena such as detonation, with mounting indication that these effects are highly relevant to the initiation of “hotspots” in high explosives. However, these effects are difficult to assess under non-equilibrium and shock loading simulations, and the state-of-the-art simulation techniques for mechanochemistry typically apply linear forces to individual molecules. Therefore, we develop a novel technique of an external biasing potential to apply ‘many-bodied steered molecular dynamics’ in which we mimic intra-molecular deformations of a shock induced hotspot in TATB. Independent simulations of two different deformation types show different levels of acceleration of reaction kinetics for the applied work and results in different alterations to first-step reaction pathways. We believe these results help to solve the puzzling difference between thermal and shock-loaded kinetics in HEs and provide a more general methodology for assessing mechanochemical affects in bulk, covalent solids. |
Friday, July 15, 2022 10:30AM - 10:45AM |
Y03.00005: Modeling Decomposition of Energetically Functionalized Dodecanes Tammie R Nelson, Patricia L Huestis, Virginia W Manner High explosives (HE) experience radiation in a variety of settings, from environmental sources to space applications. Degradation of HE in sunlight is also of interest. Understanding the decomposition of energetic functional groups (EFGs) in response to radiation is critical. Computational modeling provides a predictive view of HE degradation and reveals mechanistic details that can be difficult to obtain experimentally. We have designed a dodecane-X system, where X = H or the EFG azide, nitro, nitramine, nitrate ester. These molecules are investigated in order to obtain a systematic view of EFG degradation under UV radiation while keeping the molecular backbone constant. Dynamics following electronic excitation is modeled using the Non-Adiabatic Excited State Molecular Dynamics (NEXMD) software. NEXMD uses Fewest Switches Surface Hopping (FSSH) to model internal conversion. The open-shell configuration interaction singles (CIS) implementation coupled with the semi-empirical AM1 Hamiltonian accurately describes bond breaking barriers. An ensemble of trajectories is propagated allowing statistical determination of timescales (relaxation, bond breaking, and energy transfer) as well as quantum yields (QY), which are related to relative stability. We find that the primary low energy pathway involves only the EFG. The QY of the most probable pathway is generally reduced at higher energy as new pathways involving exciton energy transfer and decomposition of the alkane chain are introduced. |
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