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  • 1
    Electronic Resource
    Electronic Resource
    On the theoretical determination of the electron affinity of ozone (1993)
    Springer
    Theoretical chemistry accounts 86 (1993), S. 467-476 
    Details
    ISSN: 1432-2234
    Keywords: Ozone ; Electron affinity ; CAS ; SCF
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Multiconfigurational electron correlation methods have been analyzed in order to theoretically compute the electron affinity (EA) of ozone. The near-degeneracy correlation effects, which are so important in O3 and O 3 − , have been described using complete active space (CAS) SCF wave functions. Remaining dynamic correlation effects are computed using second-order perturbation theory (the CASPT2 method). The best calculated adiabatic value (including zero-point energy corrections), 2.19 eV, is about 0.09 eV larger than the experimental value. Comparative studies using size-consistent coupled pair functional approaches (CPF and ACPF) have also been performed. The harmonic frequencies in O 3 − have been determined to be: ω1=992, ω2=572, and ω3=879 cm−1, which gives a zero-point energy of 0.151 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01113945
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  • 2
    Electronic Resource
    Electronic Resource
    The internal rotational barrier of biphenyl studied with multiconfigurational second-order perturbation theory (CASPT2) (1995)
    Springer
    Theoretical chemistry accounts 91 (1995), S. 17-29 
    Details
    ISSN: 1432-2234
    Keywords: Biphenyl ; Rotational barrier ; Perturbation theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A detailedab initio study of the molecular structure and rotational barriers of biphenyl has been performed. First, non-dynamical correlation effects involving the π system are taken into account at the CASSCF level. These wave functions are subsequently employed as reference functions in a multiconfigurational second-order perturbation treatment (CASPT2). The performance single-reference approaches is in addition analysed. The molecular geometries of biphenyl in twisted, coplanar, and perpendicular conformations have been optimized at the CASSCF level. A rotational angle of 44.3° is predicted for the minimum energy conformer in agreement with gas-phase electron diffraction data (44.4±1.2°). The highest level of theory employed yields the values 12.93 (6.0±2.1) and 6.40 (6.5±2.5) kJ/mol for the barrier heights at 0° and 90°, respectively (electron diffraction data within parentheses). In the light of the present findings, the reliability of the available experimental data is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01113859
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  • 3
    Electronic Resource
    Electronic Resource
    Density matrix averaged atomic natural orbital (ANO) basis sets for correlated molecular wave functions (1995)
    Springer
    Theoretical chemistry accounts 92 (1995), S. 149-181 
    Details
    ISSN: 1432-2234
    Keywords: Basis sets ; Atomic natural orbitals ; General contraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Generally contracted basis sets for the first row transition metal atoms Sc-Zn have been constructed using the atomic natural orbital (ANO) approach, with modifications for allowing symmetry breaking and state averaging. The ANOs are constructed by averaging over the three electronic configurationsd n ,d n−1 s, andd n−2 s 2 for the neutral atom as well as the ground state for the cation and the ground state atom in an external electric field. The primitive sets are 21s15p10d6f4g. Contraction to 6s5p4d3f2g yields results that are virtually identical to those obtained with the corresponding uncontracted basis sets for the atomic properties, which they have been designed to reproduce. Slightly larger deviations are obtained with the 5s4p3d2f1g for the polarizability, while energetic properties still have only small errors. The design objective has been to describe the ionization potential, the polarizability and the valence spectrum as accurately as possible. The result is a set of well-balanced basis sets for molecular calculations, which can be used together with basis sets of the same quality for the first and second row atoms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01114922
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  • 4
    Electronic Resource
    Electronic Resource
    A theoretical determination of the electronic spectrum of formaldehyde (1995)
    Springer
    Theoretical chemistry accounts 92 (1995), S. 227-239 
    Details
    ISSN: 1432-2234
    Keywords: Formaldehyde ; Electronic spectrum ; Perturbation theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The electronically excited states of formaldehyde are examined by means of multiconfigurational second-order perturbation (CASPT2) theory with extended ANO-type basis sets. The calculations comprised five valence excited states plus all singlet 3s, 3p, and 3d members of the Rydberg series converging on the first ionization. The computed vertical excitation energies were found to be within 0.2 eV of the available experimental energies. Full geometry optimization has been performed for five valence excited states. Assuming a planar geometry, the “0-0” transition for the valence1A1(π → π*) state is calculated to appear near 7.9 eV, close to the (n y → 3p) region. This state is, however, not planar and the true adiabatic energy is 7.4 eV, which is 2.3 eV below the corresponding vertical transition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01125948
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  • 5
    Electronic Resource
    Electronic Resource
    A restricted active space (RAS) SCF study of the lifetime of theA 3Π state of OH+ (1991)
    Springer
    Theoretical chemistry accounts 79 (1991), S. 81-92 
    Details
    ISSN: 1432-2234
    Keywords: Hydroxyl ionA 3Π state ; Restricted active space (RAS) SCF ; Active orbitals ; Bond distances
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Restricted Active Space (RAS) SCF calculations have been performed of the potential curves for theX 3Σ− andA 3Π states of the OH+ ion and on the lifetime of thev=0−2 vibrational levels of theA state. The convergence of the transition moment integral as a function of the size of the active orbital space was used to select the active orbitals. The calculated value of thev=0 lifetime is 2.4 µs. An estimate of the errors remaining in the calculation leads to a final theoretical value of 2.7±0.1 µs. Computed bond distances and bond energies are 1.031 (1.029) Å and 5.05 (5.01) eV, respectively, for theX state, and 1.137 (1.135) Å and 1.57 eV, respectively, for theA state (experimental values within parenthesis).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01127097
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  • 6
    Electronic Resource
    Electronic Resource
    A theoretical determination of the dissociation energy of the nitric oxide dimer (1994)
    Springer
    Theoretical chemistry accounts 88 (1994), S. 425-435 
    Details
    ISSN: 1432-2234
    Keywords: Nitric oxide dimer ; Dissociation energy ; Structure, ACPF Method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Multi-reference CI methods have been applied to determine the dissociation energy and structure of thecis-N2O2 molecule. The convergence of the theoretical result has been checked with respect to a systematic expansion of the one-electron basis set and the multi-reference CI wave function. The best calculated value, 13.8 kJ/mol, is in agreement with the experimental value, 12.2 kJ/mol. It has been obtained with an extended ANO-type basis set [6s5p3d2f], including the effect of the basis set superposition error (BSSE) in the geometry optimization, and additional effects, such as the electron correlation of core electrons and relativistic corrections, using the average coupled pair functional (ACPF) approach. The optimal geometry computed at this level was found to be:r(NN)=2.284 Å,r(NO)=1.149 Å, and 〈NNO=96.1°. Employing the [6s5p3d2f] basis set, the BSSE was found to be ≈2 kJ/mol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01113292
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  • 7
    Electronic Resource
    Electronic Resource
    An ab initio CI study on the rotational barrier of the allyl anion (1986)
    Springer
    Theoretical chemistry accounts 69 (1986), S. 101-106 
    Details
    ISSN: 1432-2234
    Keywords: Rotational barrier ; Allyl anion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract All-electron and pseudopotential non-empirical calculations have been performed on C 2v and C s (syn, anti) allyl anion conformations. Using a double-zeta valence-shell basis set within the Epstein-Nesbet definition of the unperturbed Hamiltonian, a value about 19 kcal/mol is found for the barrier to rotation of the allyl anion. This value is the theoretical value obtained with greater accuracy, and the lowest one for the rotational barrier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00527682
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  • 8
    Electronic Resource
    Electronic Resource
    The internal rotational barrier of biphenyl studied with multiconfigurational second-order perturbation theory (CASPT2) (1995)
    Springer
    Theoretica chimica acta 91 (1995), S. 17-29 
    Details
    ISSN: 0040-5744
    Keywords: Key words: Biphenyl ; Rotational barrier ; Perturbation theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary.  A detailed ab initio study of the molecular structure and rotational barriers of biphenyl has been performed. First, non-dynamical correlation effects involving the π system are taken into account at the CASSCF level. These wave functions are subsequently employed as reference functions in a multiconfigurational second-order perturbation treatment (CASPT2). The performance single-reference approaches is in addition analysed. The molecular geometries of biphenyl in twisted, coplanar, and perpendicular conformations have been optimized at the CASSCF level. A rotational angle of 44.3° is predicted for the minimum energy conformer in agreement with gas-phase electron diffraction data (44.4±1.2°). The highest level of theory employed yields the values 12.93 (6.0±2.1) and 6.40 (6.5±2.5) kJ/mol for the barrier heights at 0° and 90°, respectively (electron diffraction data within parentheses). In the light of the present findings, the reliability of the available experimental data is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01113859
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  • 9
    Electronic Resource
    Electronic Resource
    Density matrix averaged atomic natural orbital (ANO) basis sets for correlated molecular wave functions III. First row transition metal atoms (1995)
    Springer
    Theoretica chimica acta 92 (1995), S. 149-181 
    Details
    ISSN: 0040-5744
    Keywords: Key words: Basis sets ; Atomic natural orbitals ; General contraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract.  Generally contracted basis sets for the first row transition metal atoms Sc–Zn have been constructed using the atomic natural orbital (ANO) approach, with modifications for allowing symmetry breaking and state averaging. The ANOs are constructed by averaging over the three electronic configurations d n , d n-1 s,  and d n-2 s 2 for the neutral atom as well as the ground state for the cation and the ground state atom in an external electric field. The primitive sets are 21s15p10d6f4g. Contraction to 6s5p4d3f2g yields results that are virtually identical to those obtained with the corresponding uncontracted basis sets for the atomic properties, which they have been designed to reproduce. Slightly larger deviations are obtained with the 5s4p3d2f1g for the polarizability, while energetic properties still have only small errors. The design objective has been to describe the ionization potential, the polarizability and the valence spectrum as accurately as possible. The result is a set of well-balanced basis sets for molecular calculations, which can be used together with basis sets of the same quality for the first and second row atoms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01114922
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  • 10
    Electronic Resource
    Electronic Resource
    A theoretical determination of the electronic spectrum of formaldehyde (1995)
    Springer
    Theoretica chimica acta 92 (1995), S. 227-239 
    Details
    ISSN: 0040-5744
    Keywords: Key words: Formaldehyde ; Electronic spectrum ; Perturbation theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary.  The electronically excited states of formaldehyde are examined by means of multiconfigurational second-order perturbation (CASPT2) theory with extended ANO-type basis sets. The calculations comprised five valence excited states plus all singlet 3s, 3p, and 3d members of the Rydberg series converging on the first ionization. The computed vertical excitation energies were found to be within 0.2 eV of the available experimental energies. Full geometry optimization has been performed for five valence excited states. Assuming a planar geometry, the “0–0” transition for the valence 1A1(π→π*) state is calculated to appear near 7.9 eV, close to the (n y →3p) region. This state is, however, not planar and the true adiabatic energy is 7.4 eV, which is 2.3 eV below the corresponding vertical transition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01125948
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