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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.advisor Papaconstantopoulos, Dimitrios A. Koufos, Alexander P.
dc.creator Koufos, Alexander P. 2014-12 2015-03-30T17:34:14Z 2016-01-16T08:24:20Z 2015-03-30
dc.description.abstract In 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.language.iso en_US en_US
dc.rights Copyright 2014 Alexander P. Koufos en_US
dc.subject Coherent Potential Approximation en_US
dc.subject Electronic Structure en_US
dc.subject Electron-Phonon Coupling en_US
dc.subject Iron-based Superconductivity en_US
dc.subject Linearized Augmented Plane Wave Method en_US
dc.subject Tight-Binding Method en_US
dc.title A First-Principles, Tight Binding and Coherent Potential Study of 1-1 Type Iron-based Superconductor FeSe(x)Te(1-x) en_US
dc.type Dissertation en
dc.description.note This work was embargoed by the author and will not be publicly available until January 1, 2016. en_US PhD in Computational Sciences and Informatics en_US Doctoral en Computational Sciences and Informatics en George Mason University en

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