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Dynamical stability of the cubic metallic phase of AlH3 at ambient pressure: Density functional calculations
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 10, 100102- p.Article in journal (Refereed) Published
Abstract [en]

We have characterized the high-pressure cubic phase of AlH3 from ab initio using density functional theory to determine mechanical as well as electronic properties and lattice dynamics (phonon-dispersion relations) from the response function method. Our zero-temperature phonon calculations show the softening of a particular mode with decreasing pressure, indicating the onset of a dynamic instability that continues to persist at ambient conditions. This instability can, however, be removed when finite electronic temperature effects are considered in the calculations. We furthermore identify a particular momentum transfer in the phonon-dispersion relation, matching a corresponding momentum transfer in the electronic band structure.

Place, publisher, year, edition, pages
2008. Vol. 78, no 10, 100102- p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-97983DOI: 10.1103/PhysRevB.78.100102ISI: 000259690400002OAI: oai:DiVA.org:uu-97983DiVA: diva2:173132
Available from: 2009-01-30 Created: 2009-01-30 Last updated: 2012-03-29Bibliographically approved
In thesis
1. Ab initio Lattice Dynamics: Hydrogen-dense and Other Materials
Open this publication in new window or tab >>Ab initio Lattice Dynamics: Hydrogen-dense and Other Materials
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents a theoretical study of materials under high pressure using ab initio lattice dynamics based on density functional theory and density functional perturbation theory using both super-cell and linear response approach.

Ab initio lattice dynamics using super-cell approach is applied to compare our theoretical predictions with experimental findings. Phonon dispersion curves of fcc α-γ cerium are calculated and compared with inelastic X-ray scattering data. Pressure dependency of phonon density of states in two cubic phases TiO2 allows us to assign the observed cubic phase in experiments to be of fluorite rather than pyrite structure. Dynamical stability of cotunnite TiO2 phase at low pressure can explain the observed quenching phenomena in experiments. Our calculated O2 vibron mode in both ε-ζ phases of solid oxygen supports the hypothesis that both phases are iso-structural.

Hydrogen-dense materials attract great attention not only because they open a path to study phenomena related to metallization (superconductivity) of solid hydrogen but also because they are closely related to important industrial applications (hydrogen storage). Using linear response method, we find that metallic fcc-AlH3 is dynamically stabilized in the range of 72-106 GPa and can persist at ambient pressure if finite temperature effects are considered. For SiH4, we test dynamical stability, Raman spectra, zero point energy, and utilize GW calculations for self energy correction. We find that a metallic tetragonal phase of SiH4 can be assigned to the experimentally observed one. Our ab initio lattice dynamics calculations based on density functional perturbation theory predict that fcc-YH3 is a pressure-induced superconductor with a high transition temperature of 40 K at 17.7 GPa. With increasing pressure this material undergoes a superconductor-metal-superconductor transition and the underlying mechanism of this transition can simultaneously explains also the observed metal-insulator transition at 25 GPa in YH3-δ.

Place, publisher, year, edition, pages
Uppsala: Universitetsbiblioteket, 2009. 80 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 597
Keyword
Density functional theory, Density functional perturbation theory, Hydrogen-dense materials, Phase transition, High pressure, Ab initio lattice dynamics, Superconductivity, Quasi-particle approximation
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-9535 (URN)978-91-554-7400-3 (ISBN)
Public defence
2009-02-26, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1 Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2009-01-30 Created: 2009-01-30 Last updated: 2010-03-08Bibliographically approved

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Scheicher, Ralph H.Ahuja, Rajeev

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