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@ARTICLE{Mller:4823,
      author       = {Müller, T.},
      title        = {{L}arge-{S}cale {P}arallel {M}ultireference-{A}veraged
                      {Q}uadratic {C}oupled {C}luster: {T}he {G}round {S}tate of
                      the {C}hromium {D}imer {R}evisited},
      journal      = {The journal of physical chemistry / A},
      volume       = {113},
      issn         = {1089-5639},
      address      = {Washington, DC},
      publisher    = {Soc.},
      reportid     = {PreJuSER-4823},
      pages        = {12729 - 12740},
      year         = {2009},
      note         = {The calculations have been carried out on the supercomputer
                      resources provided by the John-von-Neumann Institute for
                      Computing (NIC) at the Research Centre, Julich. A generous
                      supply of computing time is gratefully acknowledged. This
                      work has been partially supported by the European Community
                      (COST Action D37).},
      abstract     = {The accurate prediction of the potential energy function of
                      the X1Sigmag+ state of Cr2 is a remarkable challenge; large
                      differential electron correlation effects, significant
                      scalar relativistic contributions, the need for large
                      flexible basis sets containing g functions, the importance
                      of semicore valence electron correlation, and its
                      multireference nature pose considerable obstacles. So far,
                      the only reasonable successful approaches were based on
                      multireference perturbation theory (MRPT). Recently, there
                      was some controversy in the literature about the role of
                      error compensation and systematic defects of various MRPT
                      implementations that cannot be easily overcome. A detailed
                      basis set study of the potential energy function is
                      presented, adopting a variational method. The method of
                      choice for this electron-rich target with up to 28
                      correlated electrons is fully uncontracted
                      multireference-averaged quadratic coupled cluster (MR-AQCC),
                      which shares the flexibility of the multireference
                      configuration interaction (MRCI) approach and is, in
                      addition, approximately size-extensive (0.02 eV in error as
                      compared to the MRCI value of 1.37 eV for two noninteracting
                      chromium atoms). The best estimate for De arrives at 1.48 eV
                      and agrees well with the experimental data of 1.47 +/- 0.056
                      eV. At the estimated CBS limit, the equilibrium bond
                      distance (1.685 A) and vibrational frequency (459 cm-1) are
                      in agreement with experiment (1.679 A, 481 cm-1). Large
                      basis sets and reference configuration spaces invariably
                      result in huge wave function expansions (here, up to 2.8
                      billion configuration state functions), and efficient
                      parallel implementations of the method are crucial. Hence,
                      relevant details on implementation and general performance
                      of the parallel program code are discussed as well.},
      keywords     = {J (WoSType)},
      cin          = {JSC},
      ddc          = {530},
      cid          = {I:(DE-Juel1)JSC-20090406},
      pnm          = {Scientific Computing},
      pid          = {G:(DE-Juel1)FUEK411},
      shelfmark    = {Chemistry, Physical / Physics, Atomic, Molecular $\&$
                      Chemical},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:19725509},
      UT           = {WOS:000271428100050},
      doi          = {10.1021/jp905254u},
      url          = {https://juser.fz-juelich.de/record/4823},
}