Crystalline anisotropy of shock-induced phenomena: Omni-directional multiscale shock technique

Shimamura, Kohei; Misawa, Masanaru; Ohmura, Satoshi; Shimojo, Fuyuki; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya

doi:10.1063/1.4942191

Cited by 16 publications

(18 citation statements)

References 27 publications

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“…Quantum-based simulation methods such as Density Functional Theory 34 (DFT) are often used to accurately model physical and chemical changes in materials progressing through the range of states visited during a shock on atomistic scales. 12,[35][36][37][38] However, DFT molecular dynamics simulations require immense computational effort per simulation time step that can consequently impose harsh limits on the system sizes and time scales that can be studied. The density functional tight binding method (DFTB) holds promise to approach DFT-level accuracy over a wide range of phases and states, 37,39,40 while affording up to a thousand-fold reduction in computational expense.…”

Section: Introductionmentioning

confidence: 99%

Mechanochemical formation of heterogeneous diamond structures during rapid uniaxial compression in graphite

Kroonblawd

Goldman

2018

Phys. Rev. B

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We predict mechanochemical formation of heterogeneous diamond structures from rapid uniaxial compression in graphite using quantum molecular dynamics simulations. Ensembles of simulations reveal the formation of different diamond-like products starting from thermal graphite crystal configurations. We identify distinct classes of final products with characteristic probabilities of formation, stress states, and electrical properties, and show through simulations of rapid quenching that these products are nominally stable and can be recovered at room temperature and pressure. Some of the diamond products exhibit significant disorder and partial closure of the HOMO-LUMO gap. Seeding atomic vacancies in graphite significantly biases toward forming products with small HOMO-LUMO gaps. We show that a strong correlation between the HOMO-LUMO gap and disorder in tetrahedral bonding configurations informs which kinds of structural defects are associated with gap closure. The rapid diffusionless transformation of graphite is found to lock vacancy defects into the final diamond structure, resulting in configurations that prevent sp 3 bonding and lead to localized HOMO and LUMO states with a small gap.

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Section: Introductionmentioning

confidence: 99%

Mechanochemical formation of heterogeneous diamond structures during rapid uniaxial compression in graphite

Kroonblawd

Goldman

2018

Phys. Rev. B

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“…The energy functional was minimized iteratively using a preconditioned conjugate-gradient method. 31,32 The MSST 19,20 was used to simulate a stable planar shock wave by correcting the equations of motion of atoms so that the volume of the simulation cell evolved over time, while imposing constraints on the Rayleigh line for the stress and the Hugoniot relation for the energy. 33 The dynamics of the system is governed by the extended Lagrangian,…”

Section: Methods Of Calculationmentioning

confidence: 99%

“…The question is why the desorption reaction eq. (11) (or (19) and (20)) occurred in the 6 km/s shock-wave simulation, which is involved with the rapid NH 3 production. The reason is discussed in subsection 3.4.…”

Section: Time Evolution Of Number Of Produced Nh 3 Moleculesmentioning

confidence: 99%

“…In order to address these issues, we performed computer simulations based on ab initio molecular dynamics (AIMD) method. Moreover, to reproduce atomic motions during the passing of a shock wave generated by the meteorite collision, we used Multi-Scale Shock Technique (MSST) method 19,20 in combination with the AIMD simulation (referred to as MSST-AIMD simulation).…”

Section: Introductionmentioning

confidence: 99%

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Meteorite impacts on ancient oceans opened up multiple NH₃ production pathways

Shimamura

Shimojo

Nakano

et al. 2017

Phys. Chem. Chem. Phys.

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A recent series of shock experiments by Nakazawa et al. starting in 2005 (e.g. [Nakazawa et al., Earth Planet. Sci. Lett., 2005, 235, 356]) suggested that meteorite impacts on ancient oceans would have yielded a considerable amount of NH to the early Earth from atmospheric N and oceanic HO through reduction by meteoritic iron. To clarify the mechanisms, we imitated the impact events by performing multi-scale shock technique-based ab initio molecular dynamics in the framework of density functional theory in combination with multi-scale shock technique (MSST) simulations. Our previous simulations with impact energies close to that of the experiments revealed picosecond-order rapid NH production during shock compression [Shimamura et al., Sci. Rep., 2016, 6, 38952]. It was also shown that the reduction of N took place with an associative mechanism as seen in the catalysis of nitrogenase enzymes. In this study, we performed an MSST-AIMD simulation to investigate the production by meteorite impacts with higher energies, which are closer to the expected values on the early Earth. It was found that the amount of NH produced further increased. We also found that the increased NH production is due to the emergence of multiple reaction mechanisms at increased impact energies. We elucidated that the reduction of N was not only attributed to the associative mechanism but also to a dissociative mechanism as seen in the Haber-Bosch process and to a mechanism through a hydrazinium ion. The emergence of these multiple production mechanisms capable of providing a large amount of NH would support the suggestions from recent experiments much more strongly than was previously believed, i.e., shock-induced NH production played a key role in the origin of life on Earth.

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“…Atomistic investigation is indispensable to clarify the conditions necessary for the generation of the remaining molecular building blocks (e.g., the remaining 11 kinds of amino acids that have not yet been detected in the experiment). To obtain the fundamental insights from the atomistic point of view, therefore, we have investigated the production mechanisms using ab initio molecular dynamics simulation combined with multiscale shock technique (MSST‐AIMD). Through this attempt, we would like to find heterogeneous chemical reactions due to shock waves which are difficult to analyze in chemical equilibrium theory.…”

Section: Introductionmentioning

confidence: 99%

Ab initio molecular dynamics study of prebiotic production processes of organic compounds at meteorite impacts on ocean

et al. 2018

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Recent experiments concerning prebiotic materials syntheses suggest that the iron-bearing meteorite impacts on ocean during Late Heavy Bombardment provided abundant organic compounds associated with biomolecules such as amino acids and nucleobases. However, the molecular mechanism of a series of chemical reactions to produce such compounds is not well understood. In this study, we simulate the shock compression state of a meteorite impact for a model system composed of CO 2 , H 2 O, and metallic iron slab by ab initio molecular dynamics combined with multiscale shock technique, and clarify possible elementary reaction processes up to production of organic compounds. The reactions included not only pathways similar to the Fischer-Tropsch process known as an important hydrocarbon synthesis in many planetary processes but also those resulting in production of a carboxylic acid. It is also found that bicarbonate ions formed from CO 2 and H 2 O participated in some forms in most of these observed elementary reaction processes. These findings would deepen the understanding of the full range of chemical reactions that could occur in the meteorite impact events.

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Crystalline anisotropy of shock-induced phenomena: Omni-directional multiscale shock technique

Cited by 16 publications

References 27 publications

Mechanochemical formation of heterogeneous diamond structures during rapid uniaxial compression in graphite

Mechanochemical formation of heterogeneous diamond structures during rapid uniaxial compression in graphite

Meteorite impacts on ancient oceans opened up multiple NH₃ production pathways

Ab initio molecular dynamics study of prebiotic production processes of organic compounds at meteorite impacts on ocean

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Crystalline anisotropy of shock-induced phenomena: Omni-directional multiscale shock technique

Cited by 16 publications

References 27 publications

Mechanochemical formation of heterogeneous diamond structures during rapid uniaxial compression in graphite

Mechanochemical formation of heterogeneous diamond structures during rapid uniaxial compression in graphite

Meteorite impacts on ancient oceans opened up multiple NH3 production pathways

Ab initio molecular dynamics study of prebiotic production processes of organic compounds at meteorite impacts on ocean

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Meteorite impacts on ancient oceans opened up multiple NH₃ production pathways