The study of strongly correlated materials is currently perhaps one of the most active areas of research in condensed matter physics. Strongly correlated materials contain localized electronic states which are often hybridized with more itinerant electrons. This interplay between localized and delocalized degrees of freedom means that these compounds have highly complex phase diagrams which makes these compounds very challenging to understand from a theoretical standpoint. Computer simulations have proved to be an invaluable tool in this regard with state of the art abinitio simulation techniques harnessing the ever-increasing power of modern computers to produce highly accurate descriptions of a variety of strongly correlated materials. One of the most powerful simulation techniques currently in existence is Dynamical Mean Field Theory (DMFT). This thesis describes this powerful simulation technique and its applications to various material systems, as well as addressing some theoretical questions concerning particular implementations of DMFT. This thesis is divided into two parts. In part 1, we describe the theory behind DMFT and its amalgamation with Density Functional Theory (DFT+DMFT). In chapters 2 and 3, we provide the basic theory theory behind DFT and DMFT respectively. In chapter 4, we describe how these two methods are merged to give us the computational framework that is used in this thesis, namely DFT+DMFT. Finally, we round o part 1 of the thesis in chapter 5, which provides a description of the Continuous Time Quantum Monte Carlo (CTQMC) impurity solver, which is at the heart of the DFT+DMFT algorithm and is used extensively throughout this thesis. In part two of the thesis, we apply the DFT+DMFT framework to address some important problems in condensed matter physics. In chapter 6, we study the Magnetic Spectral Function of strongly correlated f-shell materials to understand two important problems in condensed matter physics, namely the volume collapse transition in Cerium and the valence uctuating state ground state of -Pu. In chapter 7, we study the contribution of lattice parameters and electronic entropy to study the decades-old problem of understanding the spin state transition observed in LaCoO3, where we show how lattice expansion, octahedral rotations and electronic entropy are all essential in stabilizing the high-spin state at high temperature. In chapter 8, we switch to studying a more theoretical problem by looking at the problems with using the highly popular constrained Random Phase Approximation (cRPA) method to estimate the screening of local inter-electronic repulsion in strongly correlated systems. We show that cRPA systematically underestimates screening in such systems which makes it an unsuitable method for estimating the repulsion parameter (U) used in impurity solvers. We then develop an alternate method to estimate the screening using the full local polarization which overcomes many of these limitations. Chapter 9 contains all the conclusions obtained in this thesis, followed by references and appendices.
Subject (authority = RUETD)
Topic
Physics and Astronomy
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TitleInfo
Title
Rutgers University Electronic Theses and Dissertations
Identifier (type = RULIB)
ETD
Identifier
ETD_7813
PhysicalDescription
Form (authority = gmd)
electronic resource
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application/pdf
InternetMediaType
text/xml
Extent
1 online resource (xii, 105 p. : ill.)
Note (type = degree)
Ph.D.
Note (type = bibliography)
Includes bibliographical references
Subject (authority = ETD-LCSH)
Topic
Condensed matter
Note (type = statement of responsibility)
by Bismayan Chakrabarti
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TitleInfo
Title
Graduate School - New Brunswick Electronic Theses and Dissertations
Identifier (type = local)
rucore19991600001
Location
PhysicalLocation (authority = marcorg); (displayLabel = Rutgers, The State University of New Jersey)
Rutgers University. Graduate School - New Brunswick
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License
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Author Agreement License
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I hereby grant to the Rutgers University Libraries and to my school the non-exclusive right to archive, reproduce and distribute my thesis or dissertation, in whole or in part, and/or my abstract, in whole or in part, in and from an electronic format, subject to the release date subsequently stipulated in this submittal form and approved by my school. I represent and stipulate that the thesis or dissertation and its abstract are my original work, that they do not infringe or violate any rights of others, and that I make these grants as the sole owner of the rights to my thesis or dissertation and its abstract. I represent that I have obtained written permissions, when necessary, from the owner(s) of each third party copyrighted matter to be included in my thesis or dissertation and will supply copies of such upon request by my school. I acknowledge that RU ETD and my school will not distribute my thesis or dissertation or its abstract if, in their reasonable judgment, they believe all such rights have not been secured. I acknowledge that I retain ownership rights to the copyright of my work. I also retain the right to use all or part of this thesis or dissertation in future works, such as articles or books.