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@ARTICLE{Shepard:496,
      author       = {Shepard, R. and Kedziora, G. and Lischka, H. and Shavitt,
                      I. and Müller, T. and Szalay, P.G. and Kallay, M. and Seth,
                      M.},
      title        = {{T}he {A}ccuracy of {M}olecular {B}ond {L}engths {C}omputed
                      by {M}ultireference {E}lectronic {S}tructure {M}ethods},
      journal      = {Chemical physics},
      volume       = {349},
      issn         = {0301-0104},
      address      = {Amsterdam [u.a.]},
      publisher    = {Elsevier Science},
      reportid     = {PreJuSER-496},
      year         = {2008},
      note         = {Record converted from VDB: 12.11.2012},
      abstract     = {We compare experimental R-e values with computed R-e values
                      for 20 molecules using three multireference electronic
                      structure methods, MCSCF, MR-SDCI, and MR-AQCC. Three
                      correlation-consistent orbital basis sets are used, along
                      with complete basis set extrapolations, for all of the
                      molecules. These data complement those computed previously
                      with single-reference methods. Several trends are observed.
                      The SCF R-e values tend to be shorter than the experimental
                      values, and the MCSCF values tend to be longer than the
                      experimental values. We attribute these trends to the ionic
                      contamination of the SCF wave function and to the
                      corresponding systematic distortion of the potential energy
                      curve. For the individual bonds, the MR-SDCI R-e values tend
                      to be shorter than the MR-AQCC values, which in turn tend to
                      be shorter than the MCSCF values. Compared to the previous
                      single-reference results, the MCSCF values are roughly
                      comparable to the MP4 and CCSD methods, which are more
                      accurate than might be expected due to the fact that these
                      MCSCF wave functions include no extra-valence electron
                      correlation effects. This suggests that static valence
                      correlation effects, such as near-degeneracies and the
                      ability to dissociate correctly to neutral fragments, play
                      an important role in determining the shape of the potential
                      energy surface, even near equilibrium structures. The
                      MR-SDCI and MR-AQCC methods predict R-e values with an
                      accuracy comparable to, or better than, the best
                      single-reference methods (MP4, CCSD, and CCSD(T)), despite
                      the fact that triple and higher excitations into the
                      extra-valence orbital space are included in the
                      single-reference methods but are absent in the
                      multireference wave functions. The computed R-e values using
                      the multireference methods tend to be smooth and monotonic
                      with basis set improvement. The molecular structures are
                      optimized using analytic energy gradients, and the timings
                      for these calculations show the practical advantage of using
                      variational wave functions for which the Hellmann-Feynman
                      theorem can be exploited. (c) 2008 Elsevier B.V. All rights
                      reserved.},
      keywords     = {J (WoSType)},
      cin          = {JSC},
      ddc          = {540},
      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},
      UT           = {WOS:000257538300005},
      doi          = {10.1016/j.chemphys.2008.03.009},
      url          = {https://juser.fz-juelich.de/record/496},
}