A First-Principles, Tight Binding and Coherent Potential Study of 1-1 Type Iron-based Superconductor FeSe(x)Te(1-x)

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dc.contributor.advisorPapaconstantopoulos, Dimitrios A.
dc.contributor.authorKoufos, Alexander P.
dc.creatorKoufos, Alexander P.
dc.date2014-12
dc.date.accessioned2015-03-30T17:34:14Z
dc.date.available2016-01-16T08:24:20Z
dc.date.issued2015-03-30
dc.description.abstractIn this dissertation I performed first-principles calculations of the electronic structure for Iron-Selenium-Tellurium (FeSeTe) systems and applied the results to study superconductivity in these materials. This dissertation discusses new first-principles calculations based on the Linearized Augmented Plane Wave (LAPW) method of Density Functional Theory (DFT) used in the Gaspari-Gyorffy-McMillan (GGM) theories of superconductivity. The LAPW results were also used to construct Tight-Binding (TB) Hamiltonians using the Naval Research Laboratory TB (NRL-TB) method. The code was expanded to include angular momentum contribution to the fits, to improve total and decomposed Density of States (DOS). Final fits for FeSe and FeTe showed total energy and total DOS calculations to compare well with the LAPW results up to the eighteenth band. These fits were further used to develop a computer program to treat disorder effects via the Coherent Potential Approximation (CPA) to the TB method. The new code incorporated diagonal disorder in the CPA and combined with the Virtual Crystal Approximation to study various concentrations of FeSe(x)Te(1-x), where random substitutions of Se by Te were taken into account. Calculated DOS results with the CPA show similar features to the calculated LAPW DOS of FeSe(0.50)Te(0.50) by a supercell approach. The results presented show that the GGM theories based on LAPW results can find good agreement with experimentally measured superconductivity temperatures, T(c). Specifically, we calculate T(c)'s of 5.4K and 14.5K for FeSe and FeSe(0.50)Te(0.50), respectively. The corresponding calculated electron-phonon coupling constants, lambda, are 0.64 and 0.97, respectively. This suggests that the electron-phonon coupling interaction of the Bardeen-Cooper-Schrieffer (BCS) theory is an important mechanism in the superconductivity of these materials.
dc.description.noteThis work was embargoed by the author and will not be publicly available until January 1, 2016.
dc.identifier.urihttps://hdl.handle.net/1920/9241
dc.language.isoen_US
dc.rightsCopyright 2014 Alexander P. Koufos
dc.subjectCoherent Potential Approximation
dc.subjectElectronic Structure
dc.subjectElectron-Phonon Coupling
dc.subjectIron-based Superconductivity
dc.subjectLinearized Augmented Plane Wave Method
dc.subjectTight-Binding Method
dc.titleA First-Principles, Tight Binding and Coherent Potential Study of 1-1 Type Iron-based Superconductor FeSe(x)Te(1-x)
dc.typeDissertation
thesis.degree.disciplineComputational Sciences and Informatics
thesis.degree.grantorGeorge Mason University
thesis.degree.levelDoctoral
thesis.degree.namePhD in Computational Sciences and Informatics

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