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@PHDTHESIS{Bornemann:861845,
      author       = {Bornemann, Marcel},
      title        = {{L}arge-scale {I}nvestigations of {N}on-trivial {M}agnetic
                      {T}extures in {C}hiral {M}agnets with {D}ensity {F}unctional
                      {T}heory},
      volume       = {195},
      school       = {RWTH Aachen},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2019-02271},
      isbn         = {978-3-95806-394-5},
      series       = {Schriften des Forschungszentrums Jülich. Reihe
                      Schlüsseltechnologien / Key Technologies},
      pages        = {143 S.},
      year         = {2019},
      note         = {RWTH Aachen, Diss., 2019},
      abstract     = {The large-scale Density Functional Theory (DFT) code
                      KKRnano allows one to perform $\textit{ab initio}$
                      simulations for thousands of atoms. In this thesis an
                      extension of KKRnano is presented and utilized which
                      facilitates the investigation of exotic non-collinear
                      magnetic textures in bulk materials on huge length scales.
                      Such an undertakinginevitably involves the utilization of
                      High Performance Computing (HPC) which is itself a
                      scientific field. The work in this context includes the
                      adaptation of new coding paradigms and the optimization of
                      codes on constantly changing hardware architectures. In
                      KKRnano, the runtime of a simulation scales linearly with
                      the number of atoms due to an advanced
                      Korringa-Kohn-Rostoker (KKR) scheme that is applied, in
                      which the sparsity of the matrices in the
                      multiple-scattering equations is exploited. This enables us
                      to investigate phenomena that occur on a length scale of
                      nanometers involving thousands of atoms.The main purpose of
                      this thesis was to generalize the KKR formalism in KKRnano
                      in such a way that a non-collinear alignment of the atomic
                      spins can be treated. In addition to this, the relativistic
                      coupling of spin and orbital degrees of freedom, which
                      arises from the Dirac equation, was introduced to the code.
                      This coupling gives rise to the Dzyaloshinskii-Moriya
                      interaction (DMI) from which the formation of non-collinear
                      magnetic textures usually originates. Other methodological
                      features that were added to KKRnano or were re-established
                      in the context of this thesis are the Generalized Gradient
                      Approximation (GGA), Lloyd’s formula and a semi-core
                      energy contour integration. GGA is known to be a better
                      approximation to the exchange-correlation energy in DFT than
                      the still very popular Local Density Approximation (LDA),
                      Lloyd’s formula allows to determine the charge density
                      exactly, despite the angular momentum expansion of all
                      quantities, and the semi-core energy contour integration
                      facilitates the treatment of high-lying electronic core
                      states. Furthermore, an experimental port of the
                      multiple-scattering solver routine to Graphics Processing
                      Unit (GPU) architectures is discussed and the large-scale
                      capabilities of KKR nano are demonstrated by benchmark
                      calculations on the supercomputer JUQUEEN that include more
                      than 200.000 atoms. The new version of KKRnano is used to
                      investigate the magnetic B20 compounds B20-MnGe and B20-FeGe
                      as well as alloys of B20-Mn$_{1−x}$Fe$_{x}$Ge type with
                      varied concentration of Mn and Ge. These compounds are
                      well-known for exhibiting helicalstates. Recently reported
                      observations of topologically protected magnetic particles,
                      also known as skyrmions, make them promising candidates for
                      future spintronic devices. Initially, the known
                      pressure-induced transition from a high-spin to a low-spin
                      state in B20-MnGe is reproduced with KKRnano and an
                      examination of the magnetocrystalline anisotropy yields
                      unexpected results. [...]},
      cin          = {PGI-1 / IAS-1 / JARA-FIT / JARA-HPC},
      cid          = {I:(DE-Juel1)PGI-1-20110106 / I:(DE-Juel1)IAS-1-20090406 /
                      $I:(DE-82)080009_20140620$ / $I:(DE-82)080012_20140620$},
      pnm          = {142 - Controlling Spin-Based Phenomena (POF3-142) / 143 -
                      Controlling Configuration-Based Phenomena (POF3-143)},
      pid          = {G:(DE-HGF)POF3-142 / G:(DE-HGF)POF3-143},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/861845},
}