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Simulation of shock-induced melting of Ni using molecular dynamics coupled to a two-temperature model
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
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2006 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 1, 012101- p.Article in journal (Refereed) Published
Abstract [en]

Using nonequilibrium molecular dynamics (MD) simulations we study shock-induced melting in Ni with an embedded atom method (EAM). Dynamic melting is probed by the pair correlation function, and we find a melting lattice temperature of T-melt=6400 +/- 300 K for a melting pressure of P-melt=275 +/- 10 GPa. When a combined MD+TTM (two-temperature model) approach is used to include electronic heat conduction and electron-phonon coupling, P-melt and T-melt change. For a given pressure, the temperature behind the shock decreases due to electronic heat diffusion into the cold, unshocked material. This cooling of the material behind the shock slightly increases the melting pressure compared to simulations without electronic heat conduction and electron-phonon coupling. The decrease in the temperature behind the shock front is enhanced if the electron-phonon coupling is artificially made larger. We also explore the feasibility of using x-ray diffraction to detect melting.

Place, publisher, year, edition, pages
2006. Vol. 74, no 1, 012101- p.
National Category
Physical Sciences
URN: urn:nbn:se:uu:diva-97014DOI: 10.1103/PhysRevB.74.012101ISI: 000239426400001OAI: oai:DiVA.org:uu-97014DiVA: diva2:171778
Available from: 2008-04-04 Created: 2008-04-04 Last updated: 2012-03-05Bibliographically 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.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 422
Atomic and molecular physics, molecular dynamics, phase transitions, melting, elasticity, equation of state, metals, rare gases, Atom- och molekylfysik
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
Available from: 2008-04-04 Created: 2008-04-04Bibliographically approved

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Ahuja, Rajeev
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