Library

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 99 (1977), S. 4624-4628 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 3063-3070 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The multiconfigurational time-dependent Hartree–Fock (MCTDHF) method is used to study the excitation energies and transition moments of the CH+ ion. A consistent approach to the selection of configurations based on the complete active space (CAS) model is successfully applied. In this approach a large set of orbitals is included in the active space without a substantial increase in the number of configurations, since only for a smaller subset of orbitals is the configuration expansion complete and the remaining orbitals active are considered an auxiliary set. For CH+ the active space includes the valence and additional orbitals, with the valence orbitals constituting the complete subset. Extra configurations involving single and double excitations from the valence to the additional (auxiliary) orbitals are included both for the MCSCF reference state and in the MCTDHF. It is demonstrated that this active space accurately mimics MCSCF and MCTDHF calculations with an enlarged complete active space which includes both the original CAS and the auxiliary orbitals. The calculations for the 1 Π and 1 Σ+ excited states at the equilibrium geometry show that accurate excitation energies and transition moments are obtained in this way. For most of these states for which there are other good ab initio results available, we obtain comparable excitation energies and transition moments. In addition to 1 Π and 1 Σ+ , low lying states of other symmetries are obtained and discussed.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 5652-5659 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The coupling of the intermolecular interaction with the intramolecular correlation effects is considered using the coupled cluster (CC) formalism. The CC equations for the dispersion energy are presented and their relation to the double perturbation theory is analyzed. An approximate scheme based on partial decoupling of the CC equations is applied for the He–He interaction. Numerical results are obtained using explicitly correlated Gaussian geminal basis set. They confirm the importance of the intraatomic (apparent) correlation effects and agree very well with the experimentally derived potential.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 71-72 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effect of the interatomic interaction on the static dipole polarizability has been reexamined in detail for the He dimer at the equilibrium internuclear distance of RHe... He=5.6 a0 by using high-precision explicitly correlated R12 approaches. Our most accurate CCSD(T)-R12 results for the increments of the polarizability are 61.79×10−3 a.u. for the anisotropy and −1.04×10−3 a.u. for the trace, not significantly different from recent literature CCSD data and confirming their high accuracy. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Multiconfigurational self-consistent field (MCSCF) response is used to study the electric field dependence of magnetizabilities and nuclear shielding constants for N2, C2H2, HCN, and H2O. London perturbation-dependent atomic orbitals are used to ensure gauge origin independence. The computed magnetizabilities and shielding derivatives show a strong electron correlation dependence. The N2 results confirm the conclusions of previous ab initio studies. For the other molecules, this is the first study of the above magnetic properties beyond the SCF approximation. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 7229-7235 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio calculations have been performed for the static and dynamic polarizability and hyperpolarizability for a series of polyynes C2nH2 using self-consistent field (SCF) (n=1–6) and multiconfiguration self-consistent field (MCSCF) (n=1–4) wave functions. We have considered the longitudinal component of the static hyperpolarizability and the same component of the dynamic hyperpolarizability measured in electric-field induced second harmonic generation γESHG=γ(−2ω;ω,ω,0). The frequency dependence of the polarizability and hyperpolarizability has been rationalized in terms of the coefficients in expansions in ω2. The static hyperpolarizabilities vary smoothly with the chain length and satisfy γ(C2nH2)=γ (C2H2)×nX, where X≈3.0. The dynamic hyperpolarizability satisfies a similar relation where X increases slowly with ω.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 504-512 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio methods were applied to compute the potential curves for the X 3Σ− and A 3Π states, the transition dipole moment, and the radiative lifetimes of the vibrational levels of the A state of the SO molecule. Extended atomic natural orbital basis sets including up to g-type functions were used. The potential energy curves were computed at the multireference configuration interaction level of approximation. The calculated bond distances and bond energies are 1.498 (1.481) A(ring) and 5.21 (5.36) eV, respectively, for the X state, and 1.694 (1.609) A(ring) and 0.57 (0.64) eV, respectively, for the A state (experimental values within parentheses). Restricted active space self-consistent field (RASSCF) wave functions were used to obtain the transition dipole moments, and the size of the RASSCF active orbital space was increased until stability of the transition moment value was achieved. The calculated transition moment strongly depends on the internuclear distance. The calculated value of the A 3Π, v=0 lifetime is 46.6 μs, while the experimental values are in the range of 36–39 μs. The computed lifetime is a very sensitive function of the relative accuracy of the potential energy and transition moment curves: for example, removing the g-type function on sulphur increases the lifetime to 55 μs.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 27 (1972), S. 135-145 
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die ungekoppelte Hartree-Fock Variationsstörungsrechnung von Karplus u. Kolker wird für die Berechnung von Eigenschaften 2. Ordnung des Wassermoleküls verwendet. Für die Berechnung wird die SCF MO SCGO-Wellenfunktion des Grundzustandes gewählt, und die gestörten Orbitale 1. Ordnung werden in der multiplikativen Form approximiert. Die Konvergenz der Methode und die Frage, ob die Eichinvarianz verletzt wird, werden untersucht. Für den gewählten Potential-Nullpunkt im Zentrum der negativen Ladungsverteilung beträgt die errechnete Protonenabschirmungskonstante 28,30 ppm in guter Übereinstimmung mit den experimentellen Werten (30.20, 30.03 + 0.60 ppm). Die Ergebnisse für die magnetische Suszeptibilität des Wassermoleküls sind gleichfalls in vernünftiger Übereinstimmung mit dem Experiment.
    Notes: Abstract The variation-perturbation uncoupled Hartree-Fock procedure of Karplus and Kolker is employed for the calculation of the second-order properties of the water molecule. The SCF MO LCGO ground state wave function was chosen and the first-order perturbed orbitals were approximated in the multiplicative form. The convergence of the method as well as the violation of the gauge independence are studied. For the preferred gauge origin at the electronic centroid the calculated proton shielding constant is 28.30 ppm and compares favourably with the experimental data (30.20, 30.03 ±0.60 ppm). The results for the magnetic susceptibility of the water molecule are also in reasonable agreement with experimental values.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 99 (1998), S. 175-182 
    ISSN: 1432-2234
    Keywords: Key words: Basis sets ; Basis-set convergence ; NMR parameters ; Spin-spin coupling constants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. The convergence of NMR indirect spin-spin coupling constants with the extension of the basis set is analyzed, based on calculations carried out at the multiconfigurational self-consistent-field level for the HF and H2O systems. For the dominant and difficult Fermi-contact contribution, the standard correlation-consistent basis sets of electronic-structure theory are not suitable, lacking flexibility in the core region. Improved but not satisfactory convergence of the couplings is observed when decontracting the s functions of the correlation-consistent cc-pVXZ basis sets for 2≤X≤6. Next, by systematically extending these basis sets with tight s functions, new sets are obtained that are sufficiently flexible for accurate calculations of indirect nuclear spin-spin couplings, without sacrificing the smooth convergence behavior of the correlation-consistent basis sets.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 30 (1973), S. 257-265 
    ISSN: 1432-2234
    Keywords: Proton magnetic shielding ; Hydrogen bond NMR shift of water molecule and dimer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The proton magnetic shielding constants in the water molecule and its linear perpendicular dimer are computed from SCF-MO-LCGO wave functions by using the uncoupled Hartree-Fock variation-perturbation procedure due to Karplus and Kolker. The convergence of the calculated shielding constants as well as their gauge dependence is studied. The final results for 17-term polynomial variation function indicate that the best choice for the gauge origin corresponds to the molecular electronic centroid. The calculated proton magnetic shielding constant in the water molecule is in remarkable agreement with experimental data and favourably compares with the best coupled Hartree-Fock results. It follows from the calculations for the water dimer that the H-bond NMR-shift amounts in this case —1.0 ppm and qualitatively agrees with the experimental data for the liquid water.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...