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  • Hydrogen bonding  (2)
  • Approximate natural orbitals  (1)
  • 1975-1979  (3)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    SCF-CI studies of correlation effects on hydrogen bonding and ion hydration (1975)
    Springer
    Theoretical chemistry accounts 36 (1975), S. 249-274 
    Details
    ISSN: 1432-2234
    Keywords: Configuration interaction ; Hydrogen bonding ; Ion hydration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Previous single-determinant Hartree-Fock studies on the equilibrium structures and stabilities of H2 O, H3 O+ as well as of the monohydrated ionic systems Li+ · H2O, F− · H2O and the hydrogen bonded water dimer, H2 O · HOH, are extended by large scale configuration interaction calculations including all the possible single and double excitations arising from the canonical set of Hartree-Fock molecular orbitals. The correlation energy effects on the equilibrium geometrical parameters of the systems under consideration are found to be quite small. The contributions of the correlation energy to the total binding energies of the weakly interacting composed systems are obtained to be of the order of 1 kcal/mole, leading to a considerable increase of the hydrogen bond strength in F− · H2O and H2O · HOH and to a small decrease of the binding energy in Li+ · H2 O. The observed strengthening of the hydrogen bonding interaction due to correlation is shown to be partly compensated by the change in the vibrational zero-point energy of the composed systems compared to the non-interacting subsystems. Approximate force constants corresponding to the intersystem vibrations in Li+ · H2O, F− · H2 O, and H2O · HOH are deduced from the calculated potential curve data on the SCF and the CI level of accuracy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00549690
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  • 2
    Electronic Resource
    Electronic Resource
    SCF-CI studies of the equilibrium structure and the proton transfer barrier H3O 2 − (1976)
    Springer
    Theoretical chemistry accounts 42 (1976), S. 77-82 
    Details
    ISSN: 1432-2234
    Keywords: Configuration interaction ; Hydrogen bonding ; Ion hydration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Large-scale configuration interaction (CI) calculations have been performed in order to study the effect of the correlation energy on the equilibrium geometrical structure, the stability, and on the energy barrier of the proton transfer reaction in the hydrogen bonded system HO− · HOH. An extended Gaussian basis set including polarization functions on each nuclear centre has been employed to approximate the molecular Orbitals. All possible single and double replacements resulting from a single determinant Hartree-Fock reference state have been taken into account in the CI wavefunction. Compared to the SCF results the equilibrium oxygen/oxygen distance has been obtained from the CI calculations to be smaller by about 0.08 Å and the correlation energy has been found to stabilize the composed system by 3.6 kcal/mole. An almost symmetric equilibrium structure with the hydrogen bonding H-atom midway between the two oxygen centres has been obtained in the CI treatment, whereas SCF calculations yield an asymmetric geometrical configuration with a small energy barrier of 1.4 kcal/mole for the proton transfer process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00548292
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  • 3
    Electronic Resource
    Electronic Resource
    A critical study of basis set effects and the use of approximate natural orbitals in SCF-CI calculations of molecular geometries and heats of reaction (1978)
    Springer
    Theoretical chemistry accounts 48 (1978), S. 59-74 
    Details
    ISSN: 1432-2234
    Keywords: Basis set effects ; Approximate natural orbitals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract SCF-CI calculations have been performed on a number of chemical reactions between closed shell molecules in order to determine the heats of reaction. Contracted Gaussian type atomic basis sets of three different qualities were used and the CI calculations were performed in a truncated approximate natural orbital space. The conclusions to be drawn from these calculations are rather pessimistic. For heats of reaction, errors up to 6 kcal/mole are obtained on the SCF-level with a double zeta plus polarization atomic basis. A further improvement is only possible if extended basis sets are used. Correlation effects on heats of reaction are of the same size and CI calculations are therefore only meaningful with large atomic basis sets. For the CI calculations a one-electron space of approximate natural orbitals, obtained from second order RS perturbation theory, was used. Different truncations, using the occupation number as criterion, were tested. The general conclusion is that errors in energy differences obtained with a truncated basis set are of the same magnitude as the error in the total correlation energy. In practice this means that not more than 20–30% of the approximate natural orbitals can be deleted if the error is to be kept less than a few kcal/mole. Finally the truncation error in calculations of bond distances was tested for a few cases. Errors of around 10% of the total change due to correlation were found when 30% of the lowest occupied natural orbitals were deleted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00550241
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