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@ARTICLE{Kovacevic:42310,
      author       = {Kovacevic, B. and Baric, D. and Maksic, Z. and Müller, T.},
      title        = {{T}he {O}rigin of {A}romaticity: {I}mportant {R}ole of the
                      {S}igma {F}ramework in {B}enzene},
      journal      = {ChemPhysChem},
      volume       = {5},
      issn         = {1439-4235},
      address      = {Weinheim},
      publisher    = {Wiley-VCH Verl.},
      reportid     = {PreJuSER-42310},
      pages        = {1352 - 1364},
      year         = {2004},
      note         = {Record converted from VDB: 12.11.2012},
      abstract     = {The physical nature of aromaticity is addressed at a high
                      ab initio level. It is conclusively shown that the extrinsic
                      aromatic stabilization energy of benzene E(ease)B, estimated
                      relative to its linear polyene counterpart(s), is very
                      well-reproduced at the Hartree-Fock (HF) level. This is a
                      consequence of the fact that the contributions arising from
                      the zero-point vibrational energy (ZPVE) and electron
                      correlation are rather small. More specifically, they yield
                      together 2.0 kcalmol(-1) to the destabilization of benzene.
                      A careful scrutiny of the HF energies by virial theorem
                      shows further that the kinetic energies of the sigma and pi
                      electrons E(T)HF(sigma) and E(T)HF(pi) are strictly additive
                      in the gauge linear zig-zag polyenes, which also holds for
                      their sum Et(T)HF This finding has the important corollary
                      that E(ease)B is little dependent on the choice of the
                      homodesmic reactions involving zig-zag polyenes. A detailed
                      physical analysis of the sigma- and pi-electron
                      contributions to extrinsic aromaticity requires explicit
                      introduction of the potential energy terms Vne, Vee, and
                      Vnn, which signify Coulomb interactions between the
                      electrons and the nuclei. The Vee term involves repulsive
                      interaction Vee(sigmapi) between the sigma and pi electrons,
                      which cannot be unequivocally resolved into sigma and pi
                      contributions. The same holds for the Vnn energy, which
                      implicitly depends on the electron density distribution via
                      the Born-Oppenheimer (BO) potential energy surface. Several
                      possibilities for partitioning Vee(sigmapi) and Vnn terms
                      into sigma and pi components are examined. It is argued that
                      the stockholder principle is the most realistic, which
                      strongly indicates that E(ease)B is a result of favorable
                      sigma-framework interactions. In contrast, the pi-electron
                      framework prefers the open-chain linear polyenes.},
      keywords     = {J (WoSType)},
      cin          = {ZAM},
      ddc          = {540},
      cid          = {I:(DE-Juel1)VDB62},
      pnm          = {Betrieb und Weiterentwicklung des Höchstleistungsrechners},
      pid          = {G:(DE-Juel1)FUEK254},
      shelfmark    = {Chemistry, Physical / Physics, Atomic, Molecular $\&$
                      Chemical},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:15503393},
      UT           = {WOS:000224147700009},
      doi          = {10.1002/cphc.200400061},
      url          = {https://juser.fz-juelich.de/record/42310},
}