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Analysis of dynamical exchange and correlation in terms of coupled multipoles
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
(English)Manuscript (Other academic)
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-98062OAI: oai:DiVA.org:uu-98062DiVA: diva2:173231
Available from: 2009-02-12 Created: 2009-02-12 Last updated: 2012-08-01Bibliographically approved
In thesis
1. Distorted Space and Multipoles in Electronic Structure Calculations
Open this publication in new window or tab >>Distorted Space and Multipoles in Electronic Structure Calculations
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis concerns methods for electronic structure calculations and some applications of the methods.

The augmented planewave (APW) basis set and it’s relatives LAPW (linearised APW) and APW+lo (local orbitals) have been widely used for electronic structure calculations. Here a modification of the APW basis set based on a transformation of the basis functions from a curvilinear coordinate system. Applications to a few test systems show that the modified basis set may speed up electronic structure calculations of sparse systems.

The local density approximation (LDA) is used in density functional theory. Although it is the simplest possible approximation possible for the unknown exchange-correlation energy functional, it has proven to give quite accurate results for a wide range of systems. LDA fails in systems where the non-local effects are important. By including non-local effects by adding an orbital dependent term to the energy functional, through for example the LDA+U method, the calculated properties of many materials are closer to experimental observations. In the thesis the most general formulation of the LDA+U method is presented and a new way of interpreting the results of a calculations by formulating the orbital dependent part of the energy functional in terms of multipole momentum tensors. Applications to some early actinide systems leads to a reformulations of Hund’s rules for polarisations associated with the spin and orbital magnetic moment and a suggestion for similar rules, Katt’s rules, valid in the strong spin orbit coupling regime.

Place, publisher, year, edition, pages
Uppsala: Universitetsbiblioteket, 2009. 64 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 601
Keyword
Physics, materials science, condensed matter theory, density functional theory, Magnetism
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-9553 (URN)978-91-554-7407-2 (ISBN)
Public defence
2009-03-06, Å80101, Ångsträmlaboratoriet, Lägerhyddsv. 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2009-02-12 Created: 2009-02-12 Last updated: 2009-05-28Bibliographically approved
2. Multipoles in Correlated Electron Materials
Open this publication in new window or tab >>Multipoles in Correlated Electron Materials
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Electronic structure calculations constitute a valuable tool to predict the properties of materials. In this study we propose an efficient scheme to study correlated electron systems with essentially only one free parameter, the screening length of the Coulomb potential. A general reformulation of the exchange energy of the correlated electron shell is combined with this method in order to analyze the calculations. The results are interpreted in terms of different polarization channels, due to different multipoles. The method is applied to various actinide compounds, in order to increase the understanding of the complicate behaviour of 5f electrons in these systems. We studied the non-magnetic phase of δ-Pu, where the spin polarization is taken over by a spin-orbit-like term that does not break the time reversal symmetry. We also find that a non-trivial high multipole of the magnetization density, the triakontadipole, constitutes the ordering parameter in the mysterious hidden order phase of the heavy-fermion superconductor URu2Si2. This type of multipolar ordering is also found to play an essential role in the hexagonal-based superconductors UPd2Al3,  UNi2Al3 and UPt3 and in the dioxide insulators UO2, NpO2 and PuO2. The triakontadipole moments are also present in all magnetic actinides we considered, except for Cm. These results led us to formulate a new set of rules for the ground state of a system, that are valid in presence of strong spin-orbit coupling interaction instead of those of Hund; the Katt's rules. Finally, we applied our method to a new class of high-Tc superconductors, the Fe-pnictides, where the Fe 3d electrons are moderately correlated. In these materials we obtain the stabilization of a low spin moment solution, in agreement with experiment, over a large moment solution, due to the gain in exchange energy in the formation of large multipoles of the spin magnetization density.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. 84 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 775
Keyword
correlated electrons, magnetic ordering, multipoles, actinides, hidden order, high temperature superconductors, Fe pnictides, electronic structure calculations
National Category
Condensed Matter Physics Condensed Matter Physics Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-132068 (URN)978-91-554-7917-6 (ISBN)
Public defence
2010-11-26, Siegbahnsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Note
Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 705Available from: 2010-11-04 Created: 2010-10-13 Last updated: 2011-03-21Bibliographically approved
3. Theoretical Studies of Magnetism and Electron Correlation in Solids
Open this publication in new window or tab >>Theoretical Studies of Magnetism and Electron Correlation in Solids
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This work presents new development and applications of ab-initio simulation tools for material science. Focus lies on materials with strong electronic correlation and strong spin-orbit coupling. Improvements on methods for solving the impurity problem in LDA+DMFT is presented, as well as a reliant method for charge self-consistency in a LMTO based electronic structure code. A new adaptive scheme for Brillouin zone integration is developed, where we show a strong reduction of numerical noise compared to standard techniques. A reformulation of the standard LDA+U method aiming to reduce the number of free parameters is introduced. Fast and realistic reduction of the number of free parameters provides the possibility of high throughput calculations and enabled us to study a large number of compounds. An analysis method for polarization in terms of coupled multipoles, and their corresponding energy contributions is developed and applied. This led to the formulation of Katt's rules, a set of rules complementary to Hund's rules. Katt's rules applies for occupying the orbitals of an electronic shell with strong spin-orbit coupling. The analysis is also used to investigate the unconventional Uranium based superconductors URu2Si2, UPt3, UPd2Al3 and UNi2Al3, as well as the high temperature superconductor LaOFeAs. We also investigate the non-magnetic delta-phase of Plutonium, providing insight to the electronic structure and the branching ratios of 4d to 5f transitions seen in photo emission spectra.The influence of surface reconstruction on the magneto crystalline anisotropy is investigated in multilayer Fe/ZnSe, showing that Fe deposited on an unreconstructed interface strongly reduces the uniaxial component of the MAE. We provide a detailed understanding of the magnetic properties of Fe2P, opening possible routes for enhancing the MAE in this system. A general route to strong MAE in nano-laminates is presented, we apply this to propose a candidate with extremely strong anisotropy energy density, 5Fe/2W1-xReX for x=[0.6-0.8].

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. xii+70 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 920
Keyword
Magnetism, Superconductivity, Electron Correlation, DMFT, DFT, Actinides, multipoles, hidden order, magnetic anisotropy
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-172334 (URN)978-91-554-8337-1 (ISBN)
Public defence
2012-05-22, Siegbahnsalen, Lägerhyddsv. 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2012-04-26 Created: 2012-04-04 Last updated: 2012-08-01Bibliographically approved

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Grånäs, OscarNordström, Lars

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