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1999 (1)
1997 (2)
1Author    MichaelC. Böhm, Johannes SchüttRequires cookie*
 Title    On the Role of the Pauli Antisymmetry Principle in Pericyclic Reactions  
 Abstract    In the present work we discuss the role of the Pauli antisymmetry principle (PAP) in synchronous pericyclic reactions. These reactions are allowed in the electronic ground state whenever the PAP does not act as a quantum constraint in the transition state. The possible suppression of the influence of the PAP is a peculiarity of Tr electron systems. The PAP is a hidden (= deactivated) variable in the 7t electron subspace of polyenes and (An + 2) annulenes (n = 0, 1, 2,...). In An annulenes (n = 1, 2, 3,...) it leads to minority signs in the kinetic hopping matrix of the 7r electronic wave function and thus to an energetic destabilization. The quantum statistical difference between the above families of 7r systems renders possible a microscopical definition of the quantities "aromaticity" and "antiaromaticity". The sign behaviour of the kinetic hopping elements is used in the discussion of pericyclic reactions. The present quantum statistical description of these reactions is related to the Dewar-Zimmermann and Woodward-Hoffmann rules. 
  Reference    Z. Naturforsch. 52a, 727—738 (1997); received September 4 1997 
  Published    1997 
  Keywords    IT Electron Systems, Pericyclic Reactions, Quantum Statistics, Pauli Antisymmetry Principle 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0727.pdf 
 Identifier    ZNA-1997-52a-0727 
 Volume    52 
2Author    MichaelC. Böhm, Christoph SaalRequires cookie*
 Title    On a Direct Superconducting Pairing Mechanism  
 Abstract    We suggest that superconductivity can be traced back to a first-order interaction between the charge carriers which does not necessarily involve second-order electron-phonon coupling. For small molecular model systems it is demonstrated that the formation of Cooper pairs can lead to an attenuation of the destabilizing influence of the Pauli antisymmetry principle (PAP). We suggest that this attenuation of a fermionic quantum constraint is the driving force for the superconducting transition. Whenever the PAP is activated in single-particle hoppings of electrons, the corresponding moves reduce the electronic derealization; they raise the ensemble energy. The stability of a fermionic system is enhanced with decreasing influence of the PAP. Moves of Cooper pairs are not influenced by any quantum constraint of the intersite type. This behaviour differs from the well-known fermionic constraints. The quantum statistics of Cooper pairs is of a mixed type combining a fermionic on-site and a bosonic intersite behaviour. It coincides with the quantum statistics of so-called hard core bosonic ensembles. In the present work Cooper pair formation has been studied for smaller molecular models. The electronic Hamiltonian employed is of the two-parameter Hubbard-type. The solid state phenomenon superconductivity is correlated with the molecular concepts of "antiaromaticity" and "aromaticity". Arguments are given which support the present interpretation. 
  Reference    Z. Naturforsch. 54a, 718—738 (1999); received May 26 1999 
  Published    1999 
  Keywords    Superconductivity, Possible First-Order Pairing Interaction, Quantum Statistics, Pauli Antisymmetry Principle, Superconductivity vs Antiaromaticity and Aromaticity 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0718.pdf 
 Identifier    ZNA-1999-54a-0718 
 Volume    54 
3Author    MichaelC. Böhm, Johannes Schiitt, K G Dr, WeilRequires cookie*
 Title    Quantum Constraints in 7r Systems: The Role of the Pauli Antisymmetry Principle for 7r Electronic Properties  
 Abstract    It is demonstrated that the Pauli antisymmetry principle (PAP) is without influence in the 7r electron subspace of polyenes and (4n + 2) annulenes (n = 0, 1, 2...) as long as the hoppings are restricted to nearest-neighbour centers. Here the 7r electrons behave like a hard core bosonic (heb) ensemble where fermionic on-site and bosonic intersite properties are combined. In An and (In + 1) annulenes (n = 1,2, 3...) 7r electron jumps between the first and last ring atom lead to a Pauli antisymmetry-based destabilization. The second quantum constraint in fermionic systems is the Pauli exclusion principle (PEP). In the many-electron basis adopted in the present work it is possible to treat the PAP and PEP as two decoupled constraints. The electronic destabilization due to the PEP is enhanced with increasing size of the system. The influence of the PAP and PEP on the 7t electrons is discussed in terms of 7r energies and charge fluctuations. The model Hamiltonians adopted are of the Hückel molecular orbital (HMO) and Pariser-Parr-Pople (PPP) type. We suggest quantum statistical definitions of the quantities "aromaticity" and "antiaromaticity", qualitative descriptors which are widely employed in the chemical literature. 
  Reference    Z. Naturforsch. 52a, 717—726 (1997); received July 31 1997 
  Published    1997 
  Keywords    tt Electronic Properties, Quantum Statistics, Pauli Antisymmetry and Exclusion Prin-ciple, Green's Function Quantum Monte Carlo Simulations, Aromaticity vs Antiaro-maticity 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0717.pdf 
 Identifier    ZNA-1997-52a-0717 
 Volume    52