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Wang ZQ, Gu YJ, Tang J, Yan ZX, Xie Y, Wang YX, Chen XR, Chen QF. Ab initio determination of melting and sound velocity of neon up to the deep interior of the Earth. J Chem Phys 2024; 160:204711. [PMID: 38804489 DOI: 10.1063/5.0200412] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2024] [Accepted: 05/13/2024] [Indexed: 05/29/2024] Open
Abstract
The thermophysical properties and elemental abundances of the noble gases in terrestrial materials can provide unique insights into the Earth's evolution and mantle dynamics. Here, we perform extensive ab initio molecular dynamics simulations to determine the melting temperature and sound velocity of neon up to 370 GPa and 7500 K to constrain its physical state and storage capacity, together with to reveal its implications for the deep interior of the Earth. It is found that solid neon can exist stably under the lower mantle and inner core conditions, and the abnormal melting of neon is not observed under the entire temperature (T) and pressure (P) region inside the Earth owing to its peculiar electronic structure, which is substantially distinct from other heavier noble gases. An inspection of the reduction for sound velocity along the Earth's geotherm evidences that neon can be used as a light element to account for the low-velocity anomaly and density deficit in the deep Earth. A comparison of the pair distribution functions and mean square displacements of MgSiO3-Ne and Fe-Ne alloys further reveals that MgSiO3 has a larger neon storage capacity than the liquid iron under the deep Earth condition, indicating that the lower mantle may be a natural deep noble gas storage reservoir. Our results provide valuable information for studying the fundamental behavior and phase transition of neon in a higher T-P regime, and further enhance our understanding for the interior structure and evolution processes inside the Earth.
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Affiliation(s)
- Zhao-Qi Wang
- College of Science, Xi'an University of Science and Technology, Xi'an 710054, China
| | - Yun-Jun Gu
- National Key Laboratory for Shock Wave and Detonation Physics Research, Institute of Fluid Physics, Chinese Academy of Engineering Physics, Mianyang 621900, China
| | - Jun Tang
- Science and Technology on Surface Physics and Chemistry Laboratory, Mianyang 621908, China
| | - Zheng-Xin Yan
- College of Science, Xi'an University of Science and Technology, Xi'an 710054, China
| | - You Xie
- College of Science, Xi'an University of Science and Technology, Xi'an 710054, China
| | - Yi-Xian Wang
- College of Science, Xi'an University of Science and Technology, Xi'an 710054, China
| | - Xiang-Rong Chen
- College of Physics, Sichuan University, Chengdu 610065, China
| | - Qi-Feng Chen
- School of Science, Southwest University of Science and Technology, Mianyang 621010, China
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2
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Rehman ZU, Rehman MA, Rehman B, Sikiru S, Qureshi S, Ali EM, Awais M, Amjad M, Iqbal I, Rafique A, Bibi S. Ab initio insight into the physical properties of MgXH 3 (X = Co, Cu, Ni) lead-free perovskite for hydrogen storage application. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2023; 30:113889-113902. [PMID: 37858013 DOI: 10.1007/s11356-023-30279-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2023] [Accepted: 09/30/2023] [Indexed: 10/21/2023]
Abstract
Renewable energy systems are vital for a sustainable future, where solid-state hydrogen storage can play a crucial role. Perovskite hydride materials have attracted the scientific community for hydrogen storage applications. The current work focuses on the theoretical study using density functional theory (DFT) to evaluate the characteristics of MgXH3 (X = Co, Cu, Ni) hydrides. The structural, vibrational, electronic, mechanical, thermodynamic, and hydrogen storage properties of these hydrides were investigated. The equilibrium lattice parameters were calculated using the Birch-Murnaghan equation of state-to-energy volume curves. The elastic constants (Cij) and relevant parameters, such as Born criteria, were calculated to confirm the mechanical stability of the hydrides. The Cauchy pressure (Cp) revealed brittle or ductile behavior. The outcomes of the Pugh ratio, Poisson ratio, and anisotropy were also calculated and discussed. The absence of negative lattice vibrational frequencies in phonon dispersion confirmed the lattice's dynamic stability. The heat capacity curves of thermodynamic properties revealed that hydrides can conduct thermal energy. The metallic character and ample interatomic distances of hydrides were confirmed by the band structure and population analysis, which confirmed that hydrides can conduct electrical energy and adsorb hydrogen. The density of state (DOS) and partial DOS unveiled the role of specific atoms in the DOS of the crystal. The calculated gravimetric hydrogen storage capacity of MgCoH3, MgCuH3, and MgNiH3 hydrides was 3.64, 3.32, and 3.49wt%, respectively. Our results provide a deeper understanding of its potential for hydrogen storage applications through a detailed analysis of MgXH3 (X = Co, Cu, Ni) perovskite hydride material.
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Affiliation(s)
- Zia Ur Rehman
- Department of Mathematics, Namal University, 30 Km Talagang Road, Mianwali, 42250, Pakistan.
| | - Muhammad Awais Rehman
- Department of Physics, Khwaja Fareed University of Engineering and Information Technology, Rahim Yar Khan, Pakistan
| | - Bushra Rehman
- Department of Environmental Science, Quaid-i-Azam University Islamabad, Islamabad, 45320, Pakistan
| | - Surajudeen Sikiru
- College of Engineering, Institute of Power Engineering, Universiti Tenaga Nasional, 43300, Kajang Selangor, Malaysia
| | - Saima Qureshi
- Faculty of Technical Sciences, University of Novi Sad, Fruškogorska 11, 21000, Novi Sad, Serbia
| | - Esraa Mousa Ali
- Faculty of Aviation Science, Amman Arab University, 2234, Amman, 11953, Jordan
| | - Muhammad Awais
- Department of Mathematics, Namal University, 30 Km Talagang Road, Mianwali, 42250, Pakistan
| | - Mahnoor Amjad
- Department of Chemistry, Hazara University, Dhodial, Mansehra, 21120, Khyber Pakhtunkhwa, Pakistan
| | - Iqra Iqbal
- Department of Mathematics, Namal University, 30 Km Talagang Road, Mianwali, 42250, Pakistan
| | - Anam Rafique
- Department of Mathematics, Namal University, 30 Km Talagang Road, Mianwali, 42250, Pakistan
| | - Saira Bibi
- Department of Chemistry, Hazara University, Dhodial, Mansehra, 21120, Khyber Pakhtunkhwa, Pakistan
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3
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Erba A, Desmarais JK, Casassa S, Civalleri B, Donà L, Bush IJ, Searle B, Maschio L, Edith-Daga L, Cossard A, Ribaldone C, Ascrizzi E, Marana NL, Flament JP, Kirtman B. CRYSTAL23: A Program for Computational Solid State Physics and Chemistry. J Chem Theory Comput 2023; 19:6891-6932. [PMID: 36502394 PMCID: PMC10601489 DOI: 10.1021/acs.jctc.2c00958] [Citation(s) in RCA: 20] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2022] [Indexed: 12/14/2022]
Abstract
The Crystal program for quantum-mechanical simulations of materials has been bridging the realm of molecular quantum chemistry to the realm of solid state physics for many years, since its first public version released back in 1988. This peculiarity stems from the use of atom-centered basis functions within a linear combination of atomic orbitals (LCAO) approach and from the corresponding efficiency in the evaluation of the exact Fock exchange series. In particular, this has led to the implementation of a rich variety of hybrid density functional approximations since 1998. Nowadays, it is acknowledged by a broad community of solid state chemists and physicists that the inclusion of a fraction of Fock exchange in the exchange-correlation potential of the density functional theory is key to a better description of many properties of materials (electronic, magnetic, mechanical, spintronic, lattice-dynamical, etc.). Here, the main developments made to the program in the last five years (i.e., since the previous release, Crystal17) are presented and some of their most noteworthy applications reviewed.
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Affiliation(s)
- Alessandro Erba
- Dipartimento
di Chimica, Università di Torino, via Giuria 5, 10125 Torino, Italy
| | - Jacques K. Desmarais
- Dipartimento
di Chimica, Università di Torino, via Giuria 5, 10125 Torino, Italy
| | - Silvia Casassa
- Dipartimento
di Chimica, Università di Torino, via Giuria 5, 10125 Torino, Italy
| | - Bartolomeo Civalleri
- Dipartimento
di Chimica, Università di Torino, via Giuria 5, 10125 Torino, Italy
| | - Lorenzo Donà
- Dipartimento
di Chimica, Università di Torino, via Giuria 5, 10125 Torino, Italy
| | - Ian J. Bush
- STFC
Rutherford Appleton Laboratory, Chilton Didcot, Oxfordshire OX11 0QX, United Kingdom
| | - Barry Searle
- SFTC
Daresbury Laboratory, Daresbury, Cheshire WA4 4AD, United Kingdom
| | - Lorenzo Maschio
- Dipartimento
di Chimica, Università di Torino, via Giuria 5, 10125 Torino, Italy
| | - Loredana Edith-Daga
- Dipartimento
di Chimica, Università di Torino, via Giuria 5, 10125 Torino, Italy
| | - Alessandro Cossard
- Dipartimento
di Chimica, Università di Torino, via Giuria 5, 10125 Torino, Italy
| | - Chiara Ribaldone
- Dipartimento
di Chimica, Università di Torino, via Giuria 5, 10125 Torino, Italy
| | - Eleonora Ascrizzi
- Dipartimento
di Chimica, Università di Torino, via Giuria 5, 10125 Torino, Italy
| | - Naiara L. Marana
- Dipartimento
di Chimica, Università di Torino, via Giuria 5, 10125 Torino, Italy
| | - Jean-Pierre Flament
- Université
de Lille, CNRS, UMR 8523 — PhLAM — Physique des Lasers, Atomes et Molécules, 59000 Lille, France
| | - Bernard Kirtman
- Department
of Chemistry and Biochemistry, University
of California, Santa
Barbara, California 93106, United States
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4
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Lin J, Tamura R, Futamura Y, Sakurai T, Miyazaki T. Determination of hyper-parameters in the atomic descriptors for efficient and robust molecular dynamics simulations with machine learning forces. Phys Chem Chem Phys 2023. [PMID: 37377109 DOI: 10.1039/d3cp01922e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/29/2023]
Abstract
The atomic descriptors used in machine learning to predict forces are often high dimensional. In general, by retrieving a significant amount of structural information from these descriptors, accurate force predictions can be achieved. On the other hand, to acquire higher robustness for transferability without overfitting, sufficient reduction of descriptors should be necessary. In this study, we propose a method to automatically determine hyperparameters in the atomic descriptors, aiming to obtain accurate machine learning forces while using a small number of descriptors. Our method focuses on identifying an appropriate threshold cut-off for the variance value of the descriptor components. To demonstrate the effectiveness of our method, we apply it to crystalline, liquid, and amorphous structures in SiO2, SiGe, and Si systems. By using both conventional two-body descriptors and our introduced split-type three-body descriptors, we demonstrate that our method can provide machine learning forces that enable efficient and robust molecular dynamics simulations.
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Affiliation(s)
- Jianbo Lin
- Center for Basic Research on Materials, National Institute for Materials Science, Tsukuba 305-0044, Japan.
| | - Ryo Tamura
- Center for Basic Research on Materials, National Institute for Materials Science, Tsukuba 305-0044, Japan.
- Graduate School of Frontier Sciences, The University of Tokyo, Chiba 277-8568, Japan
| | - Yasunori Futamura
- Department of Computer Science, University of Tsukuba, Tsukuba 305-8573, Japan
- Center for Artificial Intelligence, University of Tsukuba, Tsukuba 305-8573, Japan
- Master's/Doctoral Program in Life Science Innovation, University of Tsukuba, Tsukuba 305-8577, Japan
| | - Tetsuya Sakurai
- Department of Computer Science, University of Tsukuba, Tsukuba 305-8573, Japan
- Center for Artificial Intelligence, University of Tsukuba, Tsukuba 305-8573, Japan
- Master's/Doctoral Program in Life Science Innovation, University of Tsukuba, Tsukuba 305-8577, Japan
| | - Tsuyoshi Miyazaki
- Master's/Doctoral Program in Life Science Innovation, University of Tsukuba, Tsukuba 305-8577, Japan
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba 305-0044, Japan.
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5
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Deng X, Xu Y, Hao S, Ruan Y, Zhao Y, Wang W, Ni S, Wu Z. Compositional and thermal state of the lower mantle from joint 3D inversion with seismic tomography and mineral elasticity. Proc Natl Acad Sci U S A 2023; 120:e2220178120. [PMID: 37339202 PMCID: PMC10293858 DOI: 10.1073/pnas.2220178120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2022] [Accepted: 04/17/2023] [Indexed: 06/22/2023] Open
Abstract
The compositional and thermal state of Earth's mantle provides critical constraints on the origin, evolution, and dynamics of Earth. However, the chemical composition and thermal structure of the lower mantle are still poorly understood. Particularly, the nature and origin of the two large low-shear-velocity provinces (LLSVPs) in the lowermost mantle observed from seismological studies are still debated. In this study, we inverted for the 3D chemical composition and thermal state of the lower mantle based on seismic tomography and mineral elasticity data by employing a Markov chain Monte Carlo framework. The results show a silica-enriched lower mantle with a Mg/Si ratio less than ~1.16, lower than that of the pyrolitic upper mantle (Mg/Si = 1.3). The lateral temperature distributions can be described by a Gaussian distribution with a standard deviation (SD) of 120 to 140 K at 800 to 1,600 km and the SD increases to 250 K at 2,200 km depth. However, the lateral distribution in the lowermost mantle does not follow the Gaussian distribution. We found that the velocity heterogeneities in the upper lower mantle mainly result from thermal anomalies, while those in the lowermost mantle mainly result from compositional or phase variations. The LLSVPs have higher density at the base and lower density above the depth of ~2,700 km than the ambient mantle, respectively. The LLSVPs are found to have ~500 K higher temperature, higher Bridgmanite and iron content than the ambient mantle, supporting the hypothesis that the LLSVPs may originate from an ancient basal magma ocean formed in Earth's early history.
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Affiliation(s)
- Xin Deng
- Deep Space Exploration Laboratory / School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui230026, China
| | - Yinhan Xu
- Deep Space Exploration Laboratory / School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui230026, China
| | - Shangqin Hao
- Deep Space Exploration Laboratory / School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui230026, China
- Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA92092
| | - Youyi Ruan
- School of Earth Sciences and Engineering, Nanjing University, Nanjing, Jiangsu210023, China
- Institute of Earth Exploration and Sensing, Nanjing University, Nanjing, Jiangsu210023, China
| | - Yajie Zhao
- Deep Space Exploration Laboratory / School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui230026, China
| | - Wenzhong Wang
- Deep Space Exploration Laboratory / School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui230026, China
- Chinese Academy of Sciences, Center for Excellence in Comparative Planetology, University of Science and Technology of China, Hefei, Anhui233500, China
- National Geophysical Observatory at Mengcheng, University of Science and Technology of China, Hefei, Anhui233500, China
| | - Sidao Ni
- State Key Laboratory of Geodesy and Earth’s Dynamics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan, Hubei430077, China
| | - Zhongqing Wu
- Deep Space Exploration Laboratory / School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui230026, China
- Chinese Academy of Sciences, Center for Excellence in Comparative Planetology, University of Science and Technology of China, Hefei, Anhui233500, China
- National Geophysical Observatory at Mengcheng, University of Science and Technology of China, Hefei, Anhui233500, China
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6
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Mao Z, Sun N, Wei W. Perspective for elasticity of minerals in the Earth's top lower mantle. Natl Sci Rev 2021; 8:nwaa270. [PMID: 34691617 PMCID: PMC8288362 DOI: 10.1093/nsr/nwaa270] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Revised: 10/20/2020] [Accepted: 10/27/2020] [Indexed: 11/24/2022] Open
Affiliation(s)
- Zhu Mao
- Laboratory of Seismology and Physics of Earth's Interior, School of Earth and Space Sciences, University of Science and Technology of China, China
| | - Ningyu Sun
- Laboratory of Seismology and Physics of Earth's Interior, School of Earth and Space Sciences, University of Science and Technology of China, China
| | - Wei Wei
- Laboratory of Seismology and Physics of Earth's Interior, School of Earth and Space Sciences, University of Science and Technology of China, China
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7
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Maul J, Ongari D, Moosavi SM, Smit B, Erba A. Thermoelasticity of Flexible Organic Crystals from Quasi-harmonic Lattice Dynamics: The Case of Copper(II) Acetylacetonate. J Phys Chem Lett 2020; 11:8543-8548. [PMID: 32969662 PMCID: PMC7901648 DOI: 10.1021/acs.jpclett.0c02762] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2020] [Accepted: 09/18/2020] [Indexed: 06/11/2023]
Abstract
A computationally affordable approach, based on quasi-harmonic lattice dynamics, is presented for the quantum-mechanical calculation of thermoelastic moduli of flexible, stimuli-responsive, organic crystals. The methodology relies on the simultaneous description of structural changes induced by thermal expansion and strain. The complete thermoelastic response of the mechanically flexible metal-organic copper(II) acetylacetonate crystal is determined and discussed in the temperature range 0-300 K. The elastic moduli do not just shrink with temperature but they do so anisotropically. The present results clearly indicate the need for an explicit account of thermal effects in the simulation of mechanical properties of elastically flexible organic materials. Indeed, predictions from standard static calculations on this flexible metal-organic crystal are off by up to 100%.
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Affiliation(s)
- Jefferson Maul
- Dipartimento di Chimica,
Università di Torino, via Giuria 5, 10125 Torino,
Italy
| | - Daniele Ongari
- Laboratory of Molecular Simulation (LSMO), Institut
des Sciences et Ingénierie Chimiques, École Polytechnique
Fédérale de Lausanne (EPFL), Rue de l’Industrie 17,
Sion, Valais CH-1951, Switzerland
| | - Seyed Mohamad Moosavi
- Laboratory of Molecular Simulation (LSMO), Institut
des Sciences et Ingénierie Chimiques, École Polytechnique
Fédérale de Lausanne (EPFL), Rue de l’Industrie 17,
Sion, Valais CH-1951, Switzerland
| | - Berend Smit
- Laboratory of Molecular Simulation (LSMO), Institut
des Sciences et Ingénierie Chimiques, École Polytechnique
Fédérale de Lausanne (EPFL), Rue de l’Industrie 17,
Sion, Valais CH-1951, Switzerland
| | - Alessandro Erba
- Dipartimento di Chimica,
Università di Torino, via Giuria 5, 10125 Torino,
Italy
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8
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Zhang H, Wang X, Chremos A, Douglas JF. Superionic UO2: A model anharmonic crystalline material. J Chem Phys 2019; 150:174506. [DOI: 10.1063/1.5091042] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Affiliation(s)
- Hao Zhang
- Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 1H9, Canada
| | - Xinyi Wang
- Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 1H9, Canada
| | - Alexandros Chremos
- Material Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - Jack F. Douglas
- Material Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
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9
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Geng M, Jónsson H. Density functional theory calculations and thermodynamic analysis of bridgmanite surface structure. Phys Chem Chem Phys 2019; 21:1009-1013. [PMID: 30525142 DOI: 10.1039/c8cp06702c] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Bridgmanite, a high temperature and pressure form of MgSiO3, is believed to be Earth's most abundant mineral and responsible for the observed seismic anisotropy in the mantle. Little is known about surfaces of bridgmanite but knowledge of the most stable surface terminations is important for understanding various geochemical processes as well as likely slip planes. A density functional theory based thermodynamic approach is used here to establish the range of stability of bridgmanite as well as possible termination structures of the (001), (010), (100) and (011) surfaces as a function of the chemical potential of oxygen and magnesium. The vibrational contribution to the Gibbs free energy is found to be essential for obtaining a stability region of bridgmanite in the phase diagram. The most stable surface termination of bridgmanite varies between three different atomic structures depending on the chemical potential of oxygen and magnesium. The results presented provide a basis for further theoretical studies of the chemical processes on bridgmanite surfaces in the Earth's mantle and slip plane analysis.
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Affiliation(s)
- Ming Geng
- Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China.
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10
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Mantle dynamics inferred from the crystallographic preferred orientation of bridgmanite. Nature 2016; 539:81-84. [DOI: 10.1038/nature19777] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2015] [Accepted: 08/15/2016] [Indexed: 11/08/2022]
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11
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Di Paola C, P Brodholt J. Modeling the melting of multicomponent systems: the case of MgSiO3 perovskite under lower mantle conditions. Sci Rep 2016; 6:29830. [PMID: 27444854 PMCID: PMC4956746 DOI: 10.1038/srep29830] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Accepted: 06/22/2016] [Indexed: 01/11/2023] Open
Abstract
Knowledge of the melting properties of materials, especially at extreme pressure conditions, represents a long-standing scientific challenge. For instance, there is currently considerable uncertainty over the melting temperatures of the high-pressure mantle mineral, bridgmanite (MgSiO3-perovskite), with current estimates of the melting T at the base of the mantle ranging from 4800 K to 8000 K. The difficulty with experimentally measuring high pressure melting temperatures has motivated the use of ab initio methods, however, melting is a complex multi-scale phenomenon and the timescale for melting can be prohibitively long. Here we show that a combination of empirical and ab-initio molecular dynamics calculations can be used to successfully predict the melting point of multicomponent systems, such as MgSiO3 perovskite. We predict the correct low-pressure melting T, and at high-pressure we show that the melting temperature is only 5000 K at 120 GPa, a value lower than nearly all previous estimates. In addition, we believe that this strategy is of general applicability and therefore suitable for any system under physical conditions where simpler models fail.
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Affiliation(s)
- Cono Di Paola
- Department of Earth Sciences, University College London, WC1E 6BT London United Kingdom
| | - John P Brodholt
- Department of Earth Sciences, University College London, WC1E 6BT London United Kingdom
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12
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Zahn D. Nucleation mechanism and kinetics of the perovskite to post-perovskite transition of MgSiO3 under extreme conditions. Chem Phys Lett 2013. [DOI: 10.1016/j.cplett.2013.04.058] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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13
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Liu ZJ, Sun XW, Zhang CR, Hu JB, Song T, Qi JH. Elastic Tensor and Thermodynamic Property of Magnesium Silicate Perovskite from First-principles Calculations. CHINESE J CHEM PHYS 2011. [DOI: 10.1088/1674-0068/24/06/703-710] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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14
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Shang SL, Zhang H, Wang Y, Liu ZK. Temperature-dependent elastic stiffness constants of α- and θ-Al2O3 from first-principles calculations. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:375403. [PMID: 21403195 DOI: 10.1088/0953-8984/22/37/375403] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Temperature-dependent elastic stiffness constants (c(ij)s), including both the isothermal and isoentropic ones, have been predicted for rhombohedral α-Al(2)O(3) and monoclinic θ-Al(2)O(3) in terms of a quasistatic approach, i.e., a combination of volume-dependent c(ij)s determined by a first-principles strain versus stress method and direction-dependent thermal expansions obtained by first-principles phonon calculations. A good agreement is observed between the predictions and the available experiments for α-Al(2)O(3), especially for the off-diagonal elastic constants. In addition, the temperature-dependent c(ij)s predicted herein, in particular the ones for metastable θ-Al(2)O(3), enable the stress analysis at elevated temperatures in thermally grown oxides containing α- and θ-Al(2)O(3), which are crucial to understand the failure of thermal barrier coatings in gas-turbine engines.
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Affiliation(s)
- Shun-Li Shang
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA.
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15
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Sha X, Cohen RE. Finite-temperature magnetism in bcc Fe under compression. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:372201. [PMID: 21403188 DOI: 10.1088/0953-8984/22/37/372201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We investigate the contributions of finite-temperature magnetic fluctuations to the thermodynamic properties of bcc Fe as functions of pressure. First, we apply a tight-binding total-energy model parameterized to first-principles linearized augmented plane-wave computations to examine various ferromagnetic, anti-ferromagnetic, and noncollinear spin spiral states at zero temperature. The tight-binding data are fit to a generalized Heisenberg Hamiltonian to describe the magnetic energy functional based on local moments. We then use Monte Carlo simulations to compute the magnetic susceptibility, the Curie temperature, heat capacity, and magnetic free energy. Including the finite-temperature magnetism improves the agreement with experiment for the calculated thermal expansion coefficients.
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Affiliation(s)
- Xianwei Sha
- Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA
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16
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First-principles constraints on diffusion in lower-mantle minerals and a weak D′′ layer. Nature 2010; 465:462-5. [DOI: 10.1038/nature09052] [Citation(s) in RCA: 178] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2010] [Accepted: 03/26/2010] [Indexed: 11/08/2022]
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17
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Tangney P, Scandolo S. Melting slope of MgO from molecular dynamics and density functional theory. J Chem Phys 2009; 131:124510. [DOI: 10.1063/1.3238548] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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18
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Hafner J. Ab-initiosimulations of materials using VASP: Density-functional theory and beyond. J Comput Chem 2008; 29:2044-78. [DOI: 10.1002/jcc.21057] [Citation(s) in RCA: 1810] [Impact Index Per Article: 113.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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19
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Tan E, Gurnis M. Compressible thermochemical convection and application to lower mantle structures. ACTA ACUST UNITED AC 2007. [DOI: 10.1029/2006jb004505] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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20
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Wan JTK, Duffy TS, Scandolo S, Car R. First-principles study of density, viscosity, and diffusion coefficients of liquid MgSiO3at conditions of the Earth's deep mantle. ACTA ACUST UNITED AC 2007. [DOI: 10.1029/2005jb004135] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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21
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Watanabe M, Adachi M, Morishita T, Higuchi K, Kobatake H, Fukuyama H. Does supercooled liquid Si have a density maximum? Faraday Discuss 2007; 136:279-86; discussion 309-28. [DOI: 10.1039/b616394g] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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22
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Morishita T. How does tetrahedral structure grow in liquid silicon upon supercooling? PHYSICAL REVIEW LETTERS 2006; 97:165502. [PMID: 17155410 DOI: 10.1103/physrevlett.97.165502] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2006] [Indexed: 05/12/2023]
Abstract
We present an extensive set of isothermal-isobaric first-principles molecular-dynamics simulations of liquid silicon over a temperature range of 950-1700 K. We find that the tetrahedral order gradually grows upon cooling to approximately 1200 K, but that the growth accelerates significantly below approximately 1200 K. This growth process gives rise to anomalous changes in density and liquid structure upon supercooling. In particular, we find that the atomic coordination number remains constant to approximately 1200 K and then begins to decrease below approximately 1200 K, which resolves the existing controversy regarding liquid structure in the supercooled regime [T. H. Kim, Phys. Rev. Lett. 95, 085501 (2005)10.1103/PhysRevLett.95.085501].
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Affiliation(s)
- Tetsuya Morishita
- Research Institute for Computational Sciences (RICS), National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki, Japan.
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23
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Wenk HR, Lonardelli I, Merkel S, Miyagi L, Pehl J, Speziale S, Tommaseo CE. Deformation textures produced in diamond anvil experiments, analysed in radial diffraction geometry. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2006; 18:S933-S947. [PMID: 22611103 DOI: 10.1088/0953-8984/18/25/s02] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Diamond anvil cells may not only impose pressure upon a sample but also a compressive stress that produces elastic and plastic deformation of polycrystalline samples. The plastic deformation may result in texture development if the material deforms by slip or mechanical twinning, or if grains have a non-equiaxed shape. In radial diffraction geometry, texture is revealed by variation of intensity along Debye rings relative to the compression direction. Diffraction images (obtained by CCD or image plate) can be used to extract quantitative texture information. Currently the most elegant and powerful method is a modified Rietveld technique as implemented in the software package MAUD. From texture data one can evaluate the homogeneity of strain in a diamond anvil cell, the strain magnitude and deformation mechanisms, the latter by comparing observed texture patterns with results from polycrystal plasticity simulations. Some examples such as olivine, magnesiowuestite, MgSiO(3) perovskite and ε-iron are discussed.
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Affiliation(s)
- H-R Wenk
- Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA
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24
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Oganov AR, Price GD. Ab initio thermodynamics of MgSiO3 perovskite at high pressures and temperatures. J Chem Phys 2006; 122:124501. [PMID: 15836391 DOI: 10.1063/1.1869973] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Using quantum-mechanical simulations based on density-functional perturbation theory, we address the problem of stability of MgSiO3 perovskite to decomposition into MgO and SiO2 at pressures and temperatures of the Earth's lower mantle. We show that MgSiO3 perovskite (and its post-perovskite phase) is more stable than the mixture of oxides throughout the pressure-temperature regime of the Earth's mantle. Structural stability and lattice dynamics of phases in the system MgO-SiO2 are discussed.
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Affiliation(s)
- Artem R Oganov
- Laboratory of Crystallography, Department of Materials, ETH Hönggerberg, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland.
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25
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Wentzcovitch RM, Tsuchiya T, Tsuchiya J. MgSiO3 postperovskite at D'' conditions. Proc Natl Acad Sci U S A 2006; 103:543-6. [PMID: 16407135 PMCID: PMC1334645 DOI: 10.1073/pnas.0506879103] [Citation(s) in RCA: 157] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2005] [Indexed: 11/18/2022] Open
Abstract
The postperovskite transition in MgSiO(3) at conditions similar to those expected at the D'' discontinuity of Earth's lower mantle offers a paradigm for interpreting the properties of this region. Despite consistent experimental and theoretical predictions of this phase transformation, the complexity of the D'' region raises questions about its geophysical significance. Here we report the thermoelastic properties of Cmcm postperovskite at appropriate conditions and evidences of its presence in the lowermost mantle. These are (i) the jumps in shear and longitudinal velocities similar to those observed in certain places of the D'' discontinuity and (ii) the anticorrelation between shear and bulk velocity anomalies as detected within the D'' region. In addition, the increase in shear modulus across the phase transition provides a possible explanation for the reported discrepancy between the calculated shear modulus of postperovskite free aggregates and the seismological counterpart in the lowermost mantle.
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Affiliation(s)
- Renata M Wentzcovitch
- Department of Chemical Engineering and Materials Science, Minnesota Supercomputing Institute for Digital Technology and Advanced Computation, University of Minnesota, 421 Washington Avenue Southeast, Minneapolis, MN 55455, USA.
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26
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Bovolo CI. The physical and chemical composition of the lower mantle. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2005; 363:2811-35. [PMID: 16286292 DOI: 10.1098/rsta.2005.1675] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
This article reviews some of the recent advances made within the field of mineral physics. In order to link the observed seismic and density structures of the lower mantle with a particular mineral composition, knowledge of the thermodynamic properties of the candidate materials is required. Determining which compositional model best matches the observed data is difficult because of the wide variety of possible mineral structures and compositions. State-of-the-art experimental and analytical techniques have pushed forward our knowledge of mineral physics, yet certain properties, such as the elastic properties of lower mantle minerals at high pressures and temperatures, are difficult to determine experimentally and remain elusive. Fortunately, computational techniques are now sufficiently advanced to enable the prediction of these properties in a self-consistent manner, but more results are required.A fundamental question is whether or not the upper and lower mantles are mixing. Traditional models that involve chemically separate upper and lower mantles cannot yet be ruled out despite recent conflicting seismological evidence showing that subducting slabs penetrate deep into the lower mantle and that chemically distinct layers are, therefore, unlikely.Recent seismic tomography studies giving three-dimensional models of the seismic wave velocities in the Earth also base their interpretations on the thermodynamic properties of minerals. These studies reveal heterogeneous velocity and density anomalies in the lower mantle, which are difficult to reconcile with mineral physics data.
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Affiliation(s)
- C Isabella Bovolo
- University of Newcastle upon Tyne School of Civil Engineering & Geosciences Newcastle upon Tyne NE1 7RU, UK.
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27
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Abstract
First-principles molecular-dynamics simulations show that over the pressure regime of Earth's mantle the mean silicon-oxygen coordination number of magnesium metasilicate liquid changes nearly linearly from 4 to 6. The density contrast between liquid and crystal decreases by a factor of nearly 5 over the mantle pressure regime and is 4% at the core-mantle boundary. The ab initio melting curve, obtained by integration of the Clausius-Clapeyron equation, yields a melting temperature at the core-mantle boundary of 5400 +/- 600 kelvins.
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Affiliation(s)
- Lars Stixrude
- Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA.
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28
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Belonoshko AB, Skorodumova NV, Rosengren A, Ahuja R, Johansson B, Burakovsky L, Preston DL. High-pressure melting of MgSiO3. PHYSICAL REVIEW LETTERS 2005; 94:195701. [PMID: 16090187 DOI: 10.1103/physrevlett.94.195701] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2004] [Indexed: 05/03/2023]
Abstract
The melting curve of MgSiO(3) perovskite has been determined by means of ab initio molecular dynamics complemented by effective pair potentials, and a new phenomenological model of melting. Using first principles ground state calculations, we find that the MgSiO(3) perovskite phase transforms into post perovskite at pressures above 100 GPa, in agreement with recent theoretical and experimental studies. We find that the melting curve of MgSiO(3), being very steep at pressures below 60 GPa, rapidly flattens on increasing pressure. The experimental controversy on the melting of the MgSiO(3) perovskite at high pressures is resolved, confirming the data by Zerr and Boehler.
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Affiliation(s)
- A B Belonoshko
- Applied Materials Physics, Department of Material Science and Engineering, The Royal Institute of Technology, Stockholm, Sweden
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29
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30
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Iitaka T, Hirose K, Kawamura K, Murakami M. The elasticity of the MgSiO3 post-perovskite phase in the Earth's lowermost mantle. Nature 2004; 430:442-5. [PMID: 15269765 DOI: 10.1038/nature02702] [Citation(s) in RCA: 215] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2004] [Accepted: 05/27/2004] [Indexed: 11/08/2022]
Abstract
MgSiO3 perovskite has been assumed to be the dominant component of the Earth's lower mantle, although this phase alone cannot explain the discontinuity in seismic velocities observed 200-300 km above the core-mantle boundary (the D" discontinuity) or the polarization anisotropy observed in the lowermost mantle. Experimental and theoretical studies that have attempted to attribute these phenomena to a phase transition in the perovskite phase have tended to simply confirm the stability of the perovskite phase. However, recent in situ X-ray diffraction measurements have revealed a transition to a 'post-perovskite' phase above 125 GPa and 2,500 K--conditions close to those at the D" discontinuity. Here we show the results of first-principles calculations of the structure, stability and elasticity of both phases at zero temperature. We find that the post-perovskite phase becomes the stable phase above 98 GPa, and may be responsible for the observed seismic discontinuity and anisotropy in the lowermost mantle. Although our ground-state calculations of the unit cell do not include the effects of temperature and minor elements, they do provide a consistent explanation for a number of properties of the D" layer.
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Affiliation(s)
- T Iitaka
- Computational Astrophysics Laboratory, RIKEN (The Institute of Physical and Chemical Research), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
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31
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Oganov AR, Ono S. Theoretical and experimental evidence for a post-perovskite phase of MgSiO3 in Earth's D" layer. Nature 2004; 430:445-8. [PMID: 15269766 DOI: 10.1038/nature02701] [Citation(s) in RCA: 769] [Impact Index Per Article: 38.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2004] [Accepted: 05/27/2004] [Indexed: 11/09/2022]
Abstract
The Earth's lower mantle is believed to be composed mainly of (Mg,Fe)SiO3 perovskite, with lesser amounts of (Mg,Fe)O and CaSiO3 (ref. 1). But it has not been possible to explain many unusual properties of the lowermost approximately 150 km of the mantle (the D" layer) with this mineralogy. Here, using ab initio simulations and high-pressure experiments, we show that at pressures and temperatures of the D" layer, MgSiO3 transforms from perovskite into a layered CaIrO3-type post-perovskite phase. The elastic properties of the post-perovskite phase and its stability field explain several observed puzzling properties of the D" layer: its seismic anisotropy, the strongly undulating shear-wave discontinuity at its top and possibly the anticorrelation between shear and bulk sound velocities.
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Affiliation(s)
- Artem R Oganov
- Laboratory of Crystallography, Department of Materials, ETH Zurich, Wolfgang Pauli Strasse 10, CH-8093 Zurich, Switzerland.
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32
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Morishita T. High density amorphous form and polyamorphic transformations of silicon. PHYSICAL REVIEW LETTERS 2004; 93:055503. [PMID: 15323706 DOI: 10.1103/physrevlett.93.055503] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2004] [Indexed: 05/24/2023]
Abstract
Polyamorphic transformations of silicon have been investigated by constant-pressure first-principles molecular-dynamics simulations. By pressurizing a normal amorphous Si with tetrahedral coordination, a new high density amorphous (HDA) form that has a strong resemblance to HDA water is obtained. We find that the HDA form can be also obtained through vitrification of liquid Si under pressure. Both HDA and liquid Si contain deformed tetrahedral configurations with interstitial atoms. These findings indicate that HDA Si is directly connected with liquid Si, which is of particular importance in understanding phase relations of polyamorphs of Si.
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Affiliation(s)
- Tetsuya Morishita
- Department of Applied Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan.
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33
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Wentzcovitch RM, Karki BB, Cococcioni M, de Gironcoli S. Thermoelastic properties of MgSiO(3)-perovskite: insights on the nature of the Earth's lower mantle. PHYSICAL REVIEW LETTERS 2004; 92:018501. [PMID: 14754029 DOI: 10.1103/physrevlett.92.018501] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2003] [Indexed: 05/24/2023]
Abstract
We have determined by means of first principles quasiharmonic calculations the elastic constants and acoustic velocities of MgSiO3 perovskite, the most abundant mineral of the Earth's lower mantle (LM), at pertinent pressures and temperatures. Using these results, along with the effects of low concentration iron alloying and the thermoelasticity of the most important secondary LM phase, MgO, we predict the isotropic elastic moduli of likely LM aggregates. Comparison with seismic values extracted from the preliminary reference Earth model indicates that the top of the LM behaves as a typical aggregate of pyrolitic composition, likewise the upper mantle. But systematic deviations that cannot be accounted for by alterations in the geotherm alone develop toward the deep LM. This result could be viewed as evidence in support of radially inhomogeneous LM models.
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Affiliation(s)
- R M Wentzcovitch
- Department of Chemical Engineering and Materials Science, Minnesota Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455, USA
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34
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Oganov AR, Gillan MJ, Price GD. Ab initio lattice dynamics and structural stability of MgO. J Chem Phys 2003. [DOI: 10.1063/1.1570394] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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35
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Forte AM, Mitrovica JX, Espesset A. Geodynamic and seismic constraints on the thermochemical structure and dynamics of convection in the deep mantle. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2002; 360:2521-2543. [PMID: 12460479 DOI: 10.1098/rsta.2002.1079] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
We revisit a recent study by Forte & Mitrovica in which global geophysical observables associated with mantle convection were inverted and the existence of a strong increase in viscosity near a depth of 2000 km was inferred. Employing mineral-physics data and theory we also showed that, although there are chemical anomalies in the lowermost mantle, they are unable to inhibit the dominant thermal buoyancy of the deep-mantle mega-plumes below Africa and the Pacific Ocean. New Monte Carlo simulations are employed to explore the impact of uncertainties in current mineral-physics constraints on inferences of deep-mantle thermochemical structure. To explore the impact of the high-viscosity peak at a depth of 2000 km on the evolution of lower-mantle structure, we carried out time-dependent convection simulations. The latter show that the stability and longevity of the dominant long-wavelength heterogeneity in the lowermost mantle are controlled by this viscosity peak.
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Affiliation(s)
- Alessandro M Forte
- Department of Earth Sciences, University of Western Ontario, London, Canada
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36
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Brodholt JP, Oganov AR, Price GD. Computational mineral physics and the physical properties of perovskite. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2002; 360:2507-2520. [PMID: 12460478 DOI: 10.1098/rsta.2002.1078] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The inherent uncertainties in modern first-principles calculations are reviewed using geophysically relevant examples. The elastic constants of perovskite at lower-mantle temperatures and pressures are calculated using ab initio molecular dynamics. These are used in conjunction with seismic tomographic models to estimate that the lateral temperature contrasts in the Earth's lower mantle are 800 K at a depth of 1000 km, and 1500 K at a depth of 2000 km. The effect of Al(3+) on the compressibility of MgSiO(3) perovskite is calculated using three different pseudopotentials. The results confirm earlier work and show that the compressibility of perovskites with Al(3+) substituted for both Si(4+) and Mg(2+) is very similar to the compressibility of Al(3+)-free perovskite. Even when 100% of the Si(4+) and Mg(2+) ions are replaced with Al(3+), the bulk modulus is only 7% less than that for Al(3+)-free perovskite. In contrast, perovskites where Al(3+) substitutes for Si(4+) only and that are charge balanced by oxygen vacancies do show higher compressibilities. When corrected to similar concentrations of Al(3+), the calculated compressibilities of the oxygen-vacancy-rich perovskites are in agreement with experimental results.
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Affiliation(s)
- John P Brodholt
- Department of Earth Sciences, University College London, Gower Street, UK
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37
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Wookey J, Kendall JM, Barruol G. Mid-mantle deformation inferred from seismic anisotropy. Nature 2002; 415:777-80. [PMID: 11845205 DOI: 10.1038/415777a] [Citation(s) in RCA: 136] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
With time, convective processes in the Earth's mantle will tend to align crystals, grains and inclusions. This mantle fabric is detectable seismologically, as it produces an anisotropy in material properties--in particular, a directional dependence in seismic-wave velocity. This alignment is enhanced at the boundaries of the mantle where there are rapid changes in the direction and magnitude of mantle flow, and therefore most observations of anisotropy are confined to the uppermost mantle or lithosphere and the lowermost-mantle analogue of the lithosphere, the D" region. Here we present evidence from shear-wave splitting measurements for mid-mantle anisotropy in the vicinity of the 660-km discontinuity, the boundary between the upper and lower mantle. Deep-focus earthquakes in the Tonga-Kermadec and New Hebrides subduction zones recorded at Australian seismograph stations record some of the largest values of shear-wave splitting hitherto reported. The results suggest that, at least locally, there may exist a mid-mantle boundary layer, which could indicate the impediment of flow between the upper and lower mantle in this region.
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Affiliation(s)
- James Wookey
- School of Earth Sciences, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK
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38
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Affiliation(s)
- D L Anderson
- Seismological Laboratory, California Institute of Technology, Pasadena, CA 91125, USA.
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