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  • 1
    Electronic Resource
    Electronic Resource
    Quantum-statistical kinetic equations (1989)
    Springer
    Journal of statistical physics 56 (1989), S. 175-201 
    Details
    ISSN: 1572-9613
    Keywords: Kinetic equations ; exchange effects ; renormalized cluster series ; quantum-statistical Boltzmann and Choh-Uhlenbeck equations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Considering a homogeneous normal quantum fluid consisting of identical interacting fermions or bosons, we derive an exact quantum-statistical generalized kinetic equation with a collision operator given as explicit cluster series where exchange effects are included through renormalized Liouville operators. This new result is obtained by applying a recently developed superoperator formalism (Liouville operators, cluster expansions, symmetrized projectors,P q rule, etc.) to nonequilibrium systems described by a density operatorρ(t) which obeys the von Neumann equation. By means of this formalism a factorization theorem is proven (being essential for obtaining closed equations), and partial resummations (leading to renormalized quantities) are performed. As an illustrative application, the quantum-statistical versions (including exchange effects due to Fermi-Dirac or Bose-Einstein statistics) of the homogeneous Boltzmann (binary collisions) and Choh-Uhlenbeck (triple collisions) equations are derived.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01044240
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  • 2
    Electronic Resource
    Electronic Resource
    A new quantum statistical evaluation method for time correlation functions (1989)
    Springer
    Journal of statistical physics 54 (1989), S. 765-795 
    Details
    ISSN: 1572-9613
    Keywords: Time correlation functions ; Liouville operators ; cluster expansion ; exchange effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Considering a system ofN identical interacting particles, which obey Fermi-Dirac or Bose-Einstein statistics, we derive new formulas for correlation functions of the type $$C(t) = \langle \Sigma _{i = 1}^N A_i (t) \Sigma _{j = 1}^N B_j \rangle $$ (whereB j is diagonal in the free-particle states) in the thermodynamic limit. Thereby we apply and extend a superoperator formalism, recently developed for the derivation of long-time tails in semiclassical systems. As an illustrative application, the Boltzmann equation value of the time-integrated correlation functionC(t) is derived in a straightforward manner. Due to exchange effects, the obtained t-matrix and the resulting scattering cross section, which occurs in the Boltzmann collision operator, are now functionals of the Fermi-Dirac or Bose-Einstein distribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01019775
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    1,2-Diphosphetes with Unusual Structures - A Quantum Chemical Investigation of Bonding Properties⋆ (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 951-955 
    Details
    ISSN: 1434-1948
    Keywords: Ab initio calculations ; Phosphorus ; Strained molecules ; Substituent effects ; Pericyclic reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: According to quantum chemical calculations at an ab initio level parent 1,2-diphosphete is slightly more stable than its corresponding 1,4-diphosphabutadiene structural isomer. The quantum chemical calculations indicate that substituents at phosphorus and to a much less extent at carbon exert strong influences on the equilibrium geometries of 1,2-diphosphete structures: π donors at phosphorus strongly elongate the P-P bond while electronegative substituents at phosphorus increase the interflap angle of the four-membered ring systems, bringing an envelope conformation to the fore. The lengthening of the P-P bond gives rise to a Möbius-type delocalization within the ring moiety.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 4
    Electronic Resource
    Electronic Resource
    On the Electronic Properties of Substituted Phosphanylcarbenes (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 369-374 
    Details
    ISSN: 1434-1948
    Keywords: Phosphanylcarbenes ; Substituent effects ; Quantum chemical calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A phosphanyl group exerts much less π-conjugation properties than an amino group. On this basis, corresponding carbene structures exhibit much smaller singlet-triplet energy separations. Of the various structures investigated quantum-chemically the largest singlet-triplet energy separations are predicted for cyclic diphosphanylcarbenes, in which the two functional groups are incorporated into a ring system and the phosphorus atoms are substituted by phosphoraniminato groups. Then the singlet-triplet energy separations become essentially larger than for the Bertrand-type (push-pull) carbenes.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 5
    Electronic Resource
    Electronic Resource
    Linear and cyclic sweep voltammetry at a rotating disk electrode. A digital simulation (1996)
    Weinheim : Wiley-Blackwell
    Electroanalysis 8 (1996), S. 1034-1039 
    Details
    ISSN: 1040-0397
    Keywords: Rotating disk electrode ; Digital simulation ; Mass transport ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The transport equation for the rotating disk electrode is solved numerically with appropriate boundary conditions for reversible and nonreversible redox reactions. A comparison of the computational mode with experimentel data is presented. The adaption of a steady state under variations of experimental parameters ν (scan rate) and ω (angular frequency of rotation) is investigated. It is shown that a triangular voltage scan can be used to indicate the attainment of a steady state in every zone of the current-voltage curve.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140081111
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  • 6
    Electronic Resource
    Electronic Resource
    Digital simulation of potential step experiments using the extrapolation method (1997)
    Weinheim : Wiley-Blackwell
    Electroanalysis 9 (1997), S. 1403-1408 
    Details
    ISSN: 1040-0397
    Keywords: Digital simulation ; Potential step experiment ; Extrapolation method ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: For large values of the model diffusion coefficient the Crank-Nicolson scheme produces poor numerical results, if it is used for the simulation of a potential step experiment. On the other hand the Backward Euler or fully implicit scheme, not suffering from this drawback, is of lower accuracy. We apply the extrapolation method introduced by Morris et al. to the simulation of Cottrellian diffusion and to a simple catalytic mechanism. The extrapolation method, does not show the oscillating behavior of numerical solutions and is of higher accuracy than the fully implicit scheme. Comparison to other implicit difference schemes are presented. The extrapolation schemes show superior results for the diffusional problem and for the short time behavior of the catalytic mechanism.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140091806
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    Paper (German National Licenses)
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