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        Prediction of structures and properties of high-pressure solid materials using first principles methods

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        GRESCHNER-THESIS.pdf (4.497Mb)
        Date
        2016-03-21
        Author
        Greschner, Michael
        Type
        Thesis
        Degree Level
        Masters
        Abstract
        The purpose of the research contained in this thesis is to allow for the prediction of new structures and properties of crystalline structures due to the application of external pressure by using first-principles numerical computations. The body of the thesis is separated into two primary research projects. The properties of cupric oxide (CuO) have been studied at pressures below 70 GPa, and it has been suggested that it may show room-temperature multiferroics at pressure of 20 to 40 GPa. However, at pressures above these ranges, the properties of CuO have yet to be examined thoroughly. The changes in crystal structure of CuO were examined in these high-pressure ranges. It was predicted that the ambient pressure monoclinic structure changes to a rocksalt structure and CsCl structure at high pressure. Changes in the magnetic ordering were also suggested to occur due to superexchange interactions and Jahn-Teller instabilities arising from the d-orbital electrons. Barium chloride (BaCl) has also been observed, which undergoes a similar structural change due to an s – d transition, and whose structural changes can offer further insight into the transitions observed in CuO. Ammonia borane (NH3BH3) is known to have a crystal structure which contains the molecules in staggered conformation at low pressure. The crystalline structure of NH3BH3 was examined at high pressure, which revealed that the staggered configuration transforms to an eclipsed conformation stabilized by homopolar B–Hδ-∙∙∙ δ-H–B dihydrogen bonds. These bonds are shown to be covalent in nature, comparable in bond strength to conventional hydrogen bonds, and may allow for easier molecular hydrogen formation in hydrogen fuel storage.
        Degree
        Master of Science (M.Sc.)
        Department
        Physics and Engineering Physics
        Program
        Physics
        Supervisor
        Yao, Yansun
        Committee
        Chang, Gap Soo; Tse, John S.; Bowles, Richard; Moewes, Alex
        Copyright Date
        February 2016
        URI
        http://hdl.handle.net/10388/ETD-2016-02-2441
        Subject
        Condensed matter theory
        First principles calculations
        Structure prediction
        Density functional theory
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