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@ARTICLE{Mller:818076,
      author       = {Müller, Mathias Christian Thomas David and Friedrich,
                      Christoph and Blügel, Stefan},
      title        = {{A}coustic magnons in the long-wavelength limit:
                      {I}nvestigating the {G}oldstone violation in many-body
                      perturbation theory},
      journal      = {Physical review / B},
      volume       = {94},
      number       = {6},
      issn         = {2469-9950},
      address      = {Woodbury, NY},
      publisher    = {Inst.},
      reportid     = {FZJ-2016-04610},
      pages        = {064433},
      year         = {2016},
      abstract     = {Collective spin excitations in magnetic materials arise
                      from the correlated motion of electron-hole pairs with
                      opposite spins. The pair propagation is described by the
                      transverse magnetic susceptibility, which we calculate
                      within many-body perturbation theory from first principles
                      employing the full-potential linearized augmented-plane-wave
                      formalism. Ferromagnetic materials exhibit a spontaneously
                      broken global rotation symmetry in spin space leading to the
                      appearance of acoustic magnons (zero gap) in the
                      long-wavelength limit. However, due to approximations used
                      in the numerical scheme, the acoustic magnon dispersion
                      exhibits a small but finite gap at Γ. We analyze this
                      violation of the Goldstone mode and present an approach that
                      implements the magnetic susceptibility using a renormalized
                      Green function instead of the Kohn-Sham one. This much more
                      expensive approach shows substantial improvement of the
                      Goldstone-mode condition. In addition, we discuss a possible
                      correction scheme, which involves an adjustment of the
                      Kohn-Sham exchange splitting, which is motivated by the
                      spin-wave solution of the one-band Hubbard model. The new
                      exchange splittings turn out to be closer to experiment. We
                      present corrected magnon spectra for the elementary
                      ferromagnets Fe, Co, and Ni.},
      cin          = {IAS-1 / PGI-1 / JARA-FIT / JARA-HPC},
      ddc          = {530},
      cid          = {I:(DE-Juel1)IAS-1-20090406 / I:(DE-Juel1)PGI-1-20110106 /
                      $I:(DE-82)080009_20140620$ / $I:(DE-82)080012_20140620$},
      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)16},
      UT           = {WOS:000382125200003},
      doi          = {10.1103/PhysRevB.94.064433},
      url          = {https://juser.fz-juelich.de/record/818076},
}