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One-dimensional polymeric carbon structure based on five-membered rings in alkaline earth metal dicarbides BeC2 and MgC2
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
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2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 12, p. 125439-Article in journal (Refereed) Published
Abstract [en]

We studied five alkaline earth dicarbide systems MAEC2 (where M-AE =   Be-Ba) by using ab initio random structure search. For BeC2 and MgC2,   the lowest energy and dynamically stable configuration consists of five-membered carbon rings connected to each other via an individual  arbon atom, stabilized through the donation of electrons from the   surrounding alkaline earth ions. For CaC2, SrC2, and BaC2, our study   shows that the chain crystal structure is more stable than the   predicted structure due to strains induced by the increasing size of   alkaline earth metal ions. The reaction energies of the typical synthesis pathway are comparable to those calculated for the experimental reaction of the known chain-type structure. Finally, the proposed structure should be optically distinguishable due to a   significantly narrower band gap.

Place, publisher, year, edition, pages
2010. Vol. 82, no 12, p. 125439-
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-131049DOI: 10.1103/PhysRevB.82.125439ISI: 000282009000006OAI: oai:DiVA.org:uu-131049DiVA, id: diva2:352658
Available from: 2010-09-22 Created: 2010-09-22 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Computational Studies of Hydrogen Storage Materials: Physisorbed and Chemisorbed  Systems
Open this publication in new window or tab >>Computational Studies of Hydrogen Storage Materials: Physisorbed and Chemisorbed  Systems
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with first-principles calculations based on density functional theory to investigate hydrogen storage related properties in various high-surface area materials and the ground state crystal structures in alkaline earth dicarbide systems.

High-surface area materials have been shown to be very promising for hydrogen storage applications owing to them containing numerous hydrogen adsorption sites and good kinetics for adsorption/desorption. However, one disadvantage of these materials is their very weak interaction with adsorbed hydrogen molecules. Hence, for any feasible applications, the hydrogen interaction energy of these materials must be enhanced.  In metal organic frameworks, approaches for improving the hydrogen interaction energy are opening the metal oxide cluster and decorating hydrogen attracting metals, e.g. Li, at the adsorption sites of the host.  In covalent organic framework-1, the effects of the H2-H2 interaction are also found to play a significant role for enhancing the hydrogen adsorption energy. Moreover, ab initio molecular dynamics simulations reveal that hydrogen molecules can be trapped in the host material due to the blockage from adjacent adsorbed hydrogen molecules.

In light metal hydride systems, hydrogen ions play two different roles, namely they can behave as "promoter" and "inhibitor" of Li diffusion in lithium imide and lithium amide, respectively.  By studying thermodynamics of Li+ and proton diffusions in the mixture between lithium amide and lithium hydride, it was found that Li+ and proton diffusions inside lithium amide are more favorable than those between lithium amide and lithium hydride.

Finally, our results show that the ground state configuration of BeC2 and MgC2 consists of five-membered carbon rings connected through a carbon atom forming an infinitely repeated chain surrounded by Be/Mg ions, whereas the stable crystal structure of the CaC2, SrC2 and BaC2 is the chain type structure, commonly found in the alkaline earth dicarbide systems.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. p. 90
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 782
Keywords
Density functional theory, Ab initio molecular dynamics, Ab initio random structure searching, Hydrogen storage materials, Alkaline earth dicarbide
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-132875 (URN)978-91-554-7933-6 (ISBN)
Public defence
2010-12-10, Å80101, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Note
Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 712Available from: 2010-11-19 Created: 2010-10-28 Last updated: 2011-03-21Bibliographically approved
2. Insights into Materials Properties from Ab Initio Theory: Diffusion, Adsorption, Catalysis & Structure
Open this publication in new window or tab >>Insights into Materials Properties from Ab Initio Theory: Diffusion, Adsorption, Catalysis & Structure
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, density functional theory (DFT) calculations and DFT based ab initio molecular dynamics simulations have been employed in order to gain insights into materials properties like diffusion, adsorption, catalysis, and structure.

In transition metals, absorbed hydrogen atoms self-trap due to localization of metal d-electrons. The self-trapping state is shown to highly influence hydrogen diffusion in the classical over-barrier jump temperature region. Li diffusion in Li-N-H systems is investigated. The diffusion in Li3N is shown to be controlled by the concentration of vacancies. Exchanging one Li for H (Li2NH), gives a system where the diffusion no longer is dependent on the concentrations of vacancies, but instead on N-H rotations. Furthermore, exchanging another Li for H (LiNH2), results in a blockade of Li diffusion. For high-surface area hydrogen storage materials, metal organic frameworks and covalent organic frameworks, the hydrogen adsorption is studied. In metal organic frameworks, a Li-decoration is also suggested as a way to increase the hydrogen adsorption energy. In NaAlH4 doped with transition metals (TM), the hypothesis of TM-Al intermetallic alloys as the main catalytic species is supported. The source of the catalytic effect of carbon nanostructures on hydrogen desorption from NaAlH4 is shown to be the high electronegativity of the carbon nanostructures. A space-group optimized ab initio random structure search method is used to find a new ground state structure for BeC2 and MgC2. The fast change between the amorphous and the crystalline phase of GeSbTe phase-change materials is suggested to be due to the close resemblance between the local amorphous structure and the crystalline structure. Finally, we show that more than 80% of the voltage in the lead acid battery is due to relativistic effects.

 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. p. 81
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 772
Keywords
Density functional theory, Molecular dynamics, Diffusion, Catalysis, Adsorption, Random structure search, Hydrogen-storage materials, Phase-change materials
National Category
Condensed Matter Physics Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-131331 (URN)978-91-554-7907-7 (ISBN)
Public defence
2010-11-12, Siegbansalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Note
Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 702Available from: 2010-10-21 Created: 2010-09-30 Last updated: 2011-04-04Bibliographically approved

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Blomqvist, AndreasScheicher, Ralph H.Ahuja, Rajeev

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