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@PHDTHESIS{Schultze:974989,
      author       = {Schultze, Jil},
      othercontributors = {Lüchow, Arne and Bannwarth, Christoph Nils},
      title        = {{T}ackling multi-reference systems with quantum monte carlo
                      methods},
      school       = {RWTH Aachen University},
      type         = {Dissertation},
      address      = {Aachen},
      publisher    = {RWTH Aachen University},
      reportid     = {RWTH-2023-11746},
      pages        = {1 Online-Ressource : Illustrationen},
      year         = {2023},
      note         = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
                      University 2024; Dissertation, RWTH Aachen University, 2023},
      abstract     = {For nearly a century, the quest to accurately describe the
                      correlation of electrons has been pursued by scientists.
                      However, the challenging task of recovering both dynamic and
                      static electron correlation, which is crucial for systems
                      dominated by multiple configurations, has been encountered.
                      In the last few decades, researchers have developed a
                      multitude of methods carefully tailored to capture both
                      types of correlation. Among the techniques capable of
                      addressing this challenge are quantum Monte Carlo methods,
                      known for their ability to provide accuracy beyond
                      mean-field theory. The objective of this work is to explore
                      the effectiveness and accuracy of the multi-reference
                      diffusion Monte Carlo (MR-DMC) approach for various systems
                      exhibiting multi-reference character. In the first part of
                      this work, we focus on the late transition metal compounds,
                      utilizing initial full valence complete active space
                      self-consistent field wave functions. Accurate bond
                      dissociation energies are reported for a variety of
                      transition metal dimers, demonstrating close agreement with
                      experimental results. The optimization of molecular orbitals
                      using variational Monte Carlo in the presence of a Jastrow
                      correlation function is identified as a key factor
                      contributing to this success. Additionally, spectroscopic
                      constants are investigated by fitting a Morse potential to
                      the recorded MR-DMC potential energy curves, resulting in a
                      good agreement with experimental and theoretical data. In
                      the second part, we shift our attention to selected
                      configuration interaction approaches, with a primary
                      emphasis on a rigorous investigation of the ground state of
                      the carbon dimer using truncated CIPSI-Jastrow wave
                      functions. The influence of the Jastrow factor on the
                      redistribution of importance among the different
                      configurations is discussed. Furthermore, accurate MR-DMC
                      absolute energies and bond dissociation energies for the
                      carbon dimer are presented. Lastly, a selected configuration
                      interaction algorithm in conjunction with a Jastrow
                      correlation function is introduced.},
      cin          = {153420 / 150000},
      ddc          = {540},
      cid          = {$I:(DE-82)153420_20140620$ / $I:(DE-82)150000_20140620$},
      typ          = {PUB:(DE-HGF)11},
      doi          = {10.18154/RWTH-2023-11746},
      url          = {https://publications.rwth-aachen.de/record/974989},
}