Applications of methods beyond density functional theory to the study of correlated electron systems

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dc.contributor Gupta, Arunava
dc.contributor LeClair, Patrick R.
dc.contributor Mewes, Claudia K. A.
dc.contributor Mryasov, Oleg N.
dc.contributor Townsley, Dean M.
dc.contributor.advisor Butler, W. H. Sims, Hunter Robert 2017-03-01T16:47:10Z 2017-03-01T16:47:10Z 2013
dc.identifier.other u0015_0000001_0001223
dc.identifier.other Sims_alatus_0004D_11395
dc.description Electronic Thesis or Dissertation
dc.description.abstract The difficulty in accurately treating systems in which electron-electron interactions are the dominant physics has plagued condensed matter physics for decades. Currently, there exist many different computational techniques designed to improve upon density functional theory to varying degrees of accuracy. To date, no unified, parameter-free method exists that is guaranteed to yield the correct answer for all materials. Consequently, proper treatment of such systems often requires a combination of several methods, allowing one to check them against one another when their regions of validity overlap and to expand one's reach when a single method cannot reliably describe all of the physics at work. In this dissertation, I present discussion and, when appropriate, brief derivations of several of the most prominent electronic structure methods currently in use---from the local density approximation through LDA+DMFT. I then present several investigations into the electronic and magnetic structure of materials of potential interest for information technology that also illustrate the current state of affairs in computational condensed matter physics. I explore the intersite exchange interactions in CrO_2 within density functional theory (with and without Hubbard “+U” corrections) and evaluate these results through analytic and numerical means. I study the dependence of the mysterious magnetization of Fe_16 N_2 on crystal and electronic structure and employ a wide range of techniques in an attempt to bring greater rigor and deeper understanding to the widely-varying reports on this material. In conjunction with others' careful experimental analysis, I provide a picture of the band structure of the magnetic insulator NiFe_2 O_4 that reveals a novel hierarchy in its band gaps and suggests applications in spintronics and possibly other areas. Finally, I employ dynamical mean-field theory to study the behavior of impurity states in elemental semiconductors, using H impurities in Ge as a base system.
dc.format.extent 119 p.
dc.format.medium electronic
dc.format.mimetype application/pdf
dc.language English
dc.language.iso en_US
dc.publisher University of Alabama Libraries
dc.relation.ispartof The University of Alabama Electronic Theses and Dissertations
dc.relation.ispartof The University of Alabama Libraries Digital Collections
dc.relation.hasversion born digital
dc.rights All rights reserved by the author unless otherwise indicated.
dc.subject.other Condensed matter physics
dc.subject.other Theoretical physics
dc.subject.other Materials Science
dc.title Applications of methods beyond density functional theory to the study of correlated electron systems
dc.type thesis
dc.type text University of Alabama. Dept. of Physics and Astronomy Physics The University of Alabama doctoral Ph.D.

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