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The impact of system restriction in molecular dynamics applied to the melting of Ne at high pressure
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory. (Condensed Matter Theory Grp)
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science. (Condensed Matter Theory Grp)
2008 (English)In: Computational materials science, ISSN 0927-0256, Vol. 44, no 2, 605-610 p.Article in journal (Refereed) Published
Abstract [en]

There are two major ways to perform molecular dynamics (MD) calculations, namely classical and ab initio MD. As ab initio techniques require considerably longer calculation times, it is of interest to compare the results of the two methods. Furthermore, when melting is studied with MD, the use of coexistent solid and liquid structures (two-phase) in the calculations, instead of only a solid structure (one-phase), can have a substantial impact on the results   obtained. In this work, comparisons have been made between classical and ab initio methods applied to one- and two-phase systems for the melting of Ne at high pressure. The temperatures needed to melt the classical one-phase system are somewhat higher compared to the two-phase temperatures, evaluated at the same pressure. Furthermore,   there is a significant discrepancy comparing the one-phase ab initio curve to previously reported classical predictions. At 150 GPa, the calculations in this work show a melting temperature approximately 1000 K above the estimate based on an exponential-6 potential. However, there is a close match between the one-phase ab initio curve and the classical one-phase results in this work. This suggests a possible agreement between a two-phase ab initio and classical two-phase melting curve.

Place, publisher, year, edition, pages
2008. Vol. 44, no 2, 605-610 p.
Keyword [en]
Classical MD, Ab initio MD, Melting, Ne
National Category
Physical Sciences
URN: urn:nbn:se:uu:diva-97006DOI: 10.1016/j.commatsci.2008.05.011ISI: 000261731700052OAI: oai:DiVA.org:uu-97006DiVA: diva2:171770
Available from: 2008-04-04 Created: 2008-04-04 Last updated: 2010-08-10Bibliographically 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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