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  • 36.40  (2)
  • Delocalized MOs  (1)
  • PACS. 31.50.+w Excited states[:AND:] 31.70.Dk Environmental and solvent effects  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Possible artifacts occurring in the calculation of intermolecular energies from delocalized pictures (1979)
    Springer
    Theoretical chemistry accounts 52 (1979), S. 55-66 
    Details
    ISSN: 1432-2234
    Keywords: Delocalized MOs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The intermolecular energy between two identical subsystems may be calculated from symmetrydelocalized MO's resulting for instance from a preliminary SCF calculation of the supersystem. Then each second-order energy correction mixes intramolecular correlation,R −6 intermolecular dispersion energy, andR −3 components. TheR −3 components disappear through subtle cancellations. The shifted Epstein-Nesbet energy denominators introduce an artificial second-order intermolecularR −1 component, which would be cancelled by off-diagonal third-order terms, as well as a bad asymptotic limit at infinite distances. TheR −1 artifact will also occur in strong symmetrical chemical bonds calculated in the Epstein-Nesbet perturbation scheme from delocalized MO's. These defects will occur in all variational approximate CI techniques which neglect off-diagonal elements between delocalized doubly excited determinants. These artifacts are avoided when using the Moller-Plesset definition of the zeroth order Hamiltonian or when starting from (SCF)localized MO's (even in the Epstein-Nesbet perturbation). The discussion is exemplified on an accurateab initio calculation of the Ar2 molecule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00581701
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  • 2
    Electronic Resource
    Electronic Resource
    Static, statistical, and dynamical properties of small sodium clusters (1993)
    Springer
    The European physical journal 26 (1993), S. 232-235 
    Details
    ISSN: 1434-6079
    Keywords: 31.20.D ; 31.30 ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper reports results obtained in the study of small alkali metal clusters (2≤n≤34). Properties of interest include static descriptions of the Potential Energy Surfaces (PES) using a Distance-Dependent Tight Binding hamiltonian (DDTB) and new results obtained with the same hamiltonian through a Monte-Carlo Growth Method (MCGM) which is shown to give an efficient way to sample the PES, but may also be helpful to estimate the statistical occurrences of the various isomers (catching areas). The probability for generating a given configuration is proportional to a Boltzmann distribution factor and hence a temperature dependence is introduced in the study of the PES. In section 2, the temperature dependence of the optical response for small clusters (on the example of Na4) is simulated throughab initio calculations of the electronic structure coupled with Monte-Carlo dynamics on the absorbing system in the ground state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01429154
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    A pseudopotential study of molecular spectroscopy in rare gas matrices: absorption of NO in argon (1998)
    Springer
    The European physical journal 4 (1998), S. 219-224 
    Details
    ISSN: 1434-6079
    Keywords: PACS. 31.50.+w Excited states[:AND:] 31.70.Dk Environmental and solvent effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We present a pseudopotential method to study the absorption spectroscopy of NO in an argon matrix modeled by a large albeit finite cluster. The excited states of NO are described with the virtual orbitals of a NO+ Hartree-Fock calculation plus a core-polarization operator to account for the electron-NO+ correlation. The argon atoms of the matrix are replaced by pseudopotentials for the repulsive contributions and core-polarization operators to account for matrix polarization and correlation with the excited electron. The model is shown to account for the matrix-induced transition shifts and also for the cut-off of the Rydberg series for n 〉3 reported in absorption experiments from the ground state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530050202
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  • 4
    Electronic Resource
    Electronic Resource
    Electronic correlation and effective interactions in small alkali clusters (1989)
    Springer
    The European physical journal 12 (1989), S. 341-346 
    Details
    ISSN: 1434-6079
    Keywords: 31.20.D ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The crucial importance of correlation effects versus delocalization, and their nature in small Alkali clusters is analysed from an ab-initio point of view through a detailed investigation of the Li2 dimer. The role of the external correlation (provided by extended basis sets and large Configuration Interaction calculations) is shown to lower the energy of ionic configurations and to increase their weight in the electronic wavefunction, increasing simultaneously the importance of delocalization versus internal correlation within thes-band. Effective interactions are determined from accurate diabatic calculations on dimers and transfered to clusters via an effective hamiltonian spanned bys orthogonal orbitals. Although not including explicitely thep-band, this model provides results in good agreement with abinitio calculations on Lithium clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426968
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    Paper (German National Licenses)
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