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Ab initio calculations of the elastic properties of ferropericlase Mg(1-x)Fe(x)O (x<=0.25)
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. (Condensed Matter Theory Group)
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. (Condensed Matter Theory Group)
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. (Condensed Matter Theory Group)
2007 (English)In: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395, Vol. 164, no 3-4, 177-185 p.Article in journal (Refereed) Published
Abstract [en]

Ferropericlase Mg1-xFexO is believed to be the second most abundant mineral in the Earth's mantle. Therefore, the electronic and elastic properties of ferropericlase are important for the understanding of the Earth's interior. Ab initio total energy calculations have been performed for Fe concentrations x ≤ 0.25. The equation of state (EOS) clearly shows a volume expansion as a function of Fe concentration, consistent with experimental data. Magnetic moment calculations as a function of pressure show a high-spin to low-spin transition of Fe2+, and the theoretical transition pressure increases with iron composition. At ambient pressure, we have found that the shear constant C44 reproduces well the experimental data as a function of Fe concentration. The MgO and Mg0.9Fe0.1O minerals show an increasing C44 with pressure, whereas the Δ C44 / Δ P is slightly negative after 26 GPa for Mg0.8Fe0.2O. The C44 softening could be related to the transition from the cubic to a rhombohedrally distorted phase, recently found by experiment.

Place, publisher, year, edition, pages
2007. Vol. 164, no 3-4, 177-185 p.
Keyword [en]
Ferropericlase, Elasticity, Pressure
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-97015DOI: 10.1016/j.pepi.2007.06.012ISI: 000250473900004OAI: oai:DiVA.org:uu-97015DiVA: diva2:171779
Available from: 2008-04-04 Created: 2008-04-04 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Studies of Material Properties using Ab Initio and Classical Molecular Dynamics
Open this publication in new window or tab >>Studies of Material Properties using Ab Initio and Classical Molecular Dynamics
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, material properties have been examined under extreme conditions in computer-based calculations.

The research on iron (Fe), nickel (Ni), and ferropericlase (Mg1-xFexO) are not only important for our understanding of the Earth, but also for an improved knowledge of these materials per se.

An embedded-atom model for Fe demonstrated to reproduce properties such as structure factors, densities and diffusion constants, and was employed to evaluate temperature gradients at Earth core conditions. A similar interaction together with a two-temperature method was applied for the analysis of shock-induced melting of Ni. For Mg1-xFexO, the magnetic transition pressure was shown to increase with iron content. Furthermore, the C44 softening with pressure and iron composition supports the experimentally observed phase transition for Mg0.8Fe0.2O at 35 GPa.

The properties of high density helium (He) is of great interest as the gas is one of the most abundant elements in the solar system. Furthermore, He and neon (Ne) are often used as pressure media in diamond anvil cells. The melting of He showed a possible fcc-bcc-liquid transition starting at T=340 K, P=22 GPa with a Buckingham potential, whereas the bcc phase was not seen with the Aziz form. For Ne, Monte Carlo calculations at ambient pressure showed very accurate results when extrapolating the melting temperatures to an infinite cluster limit. At high pressure, a one-phase ab initio melting curve showed a match with one-phase L-J potential results, which could imply a correspondence between ab initio/classical one-phase/two-phase calculations.

In the search for hard materials, ab initio calculations for four TiO2 phases were compared. Just as imposed by experiment, the cotunnite phase was found to be very hard. The anomalous elastic behavior of the superconducting group-V metals V, Nb, Ta was found to be related to shrinking nesting vectors and the electronic topological transition (ETT).

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. x, 85 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 422
Keyword
Atomic and molecular physics, molecular dynamics, phase transitions, melting, elasticity, equation of state, metals, rare gases, Atom- och molekylfysik
Identifiers
urn:nbn:se:uu:diva-8626 (URN)978-91-554-7154-5 (ISBN)
Public defence
2008-04-25, Häggsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15
Opponent
Supervisors
Available from: 2008-04-04 Created: 2008-04-04Bibliographically approved

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Vitos, LeventeAhuja, Rajeev

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