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  • 1
    ISSN: 1432-2234
    Keywords: Key words: Nature of bonding for Fe(CO)n(n = 1–3) – Complete-active-space self-consistent-field method – Multireference configuration interaction – Mulliken population analysis – Charge density difference map
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. Geometry optimization was performed for the ground states of FeCO, Fe(CO)2, and Fe(CO)3 at various levels of ab initio calculations, and the bond lengths and dissociation energies obtained were in reasonable agreement with experimental results. The nature of bonding was studied for these molecules using a complete-active-space self-consistent-field method. From the Mulliken population analysis, it was found that the traditional donation and back donation mechanism is valid for these molecules, including Fe(CO)3, which has a pyramidal structure.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2234
    Keywords: Key words: Basis sets – Valence functions – Correlated functions – Contracted Gaussian-type functions – First-row transition atoms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. Contracted Gaussian-type function sets are developed for the valence 4s and 3d orbitals and for correlated functions of the first-row transition atoms from Sc to Zn. A segmented contraction scheme is used for its compactness and computational efficiency. The contraction coefficients and exponents of the valence and correlated sets are determined by minimizing the differences from weighted averages of accurate atomic natural orbitals for the 4s 23d n −2 and 4s 13d n −1 atomic states. The new basis sets give a well-balanced description for these configurations at the Hartree–Fock level and yield more than 97% of the atomic correlation energies predicted by accurate natural orbitals of the same size. Molecular tests of the present basis functions are performed for the FeCO molecule at complete-active-space self-consistent-field and at single and double excitation configuration interaction levels. The present sets show an accuracy similar to that of the averaged atomic natural orbital sets in spite of 3–5 times shorter computation time in the generation of two-electron integrals.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2234
    Keywords: Key words: Polarization functions ; Correlating functions ; Contracted Gaussian-type functions ; First-row atoms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. Contracted Gaussian-type function sets are proposed for polarization functions of the atoms helium through neon, with the exception of lithium. A segmented contraction scheme is used for its compactness and computational efficiency. The contraction coefficients and orbital exponents are fully optimized to minimize the difference from accurate atomic natural orbitals. The present polarization functions yield more than 99% of atomic correlation energies predicted by accurate natural orbitals of the same size.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-2234
    Keywords: Key words: Electron affinity ; Excitation energy ; Ionization potential ; Energy convergence ; Transition metal atoms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. The electron affinities of the Sc and Ti atoms have been obtained by configuration interaction calculations. Energy convergence with respect to the systematic expansion of both the one-electron basis set and the configuration space was investigated for valence electrons, and the inclusion of correlation contributions from core electrons and relativistic effects gave the electron affinities of 0.181 eV and 0.163 eV for Sc and Ti, respectively. These are in excellent agreement with the observed values of 0.189 ± 0.020 eV and 0.080 eV. The same approach was applied for the first excited states and positive ions of both atoms. Excellent agreement with the experimental results was also obtained for these states.
    Type of Medium: Electronic Resource
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