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  • 1
    Electronic Resource
    Electronic Resource
    Near-edge core photoabsorption in polyenes (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 5589-5597 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present calculations on near-edge x-ray absorption fine structures (NEXAFS) in polyenes based on a newly derived direct, atomic orbital, static exchange method. The trends of different NEXAFS features with respect to the site of ionization and with respect to the number of ethylene subunits in the oligomer chain are studied. The trends for energies and intensities are found to be regular and alternant. A substantial reduction of the π to σ intensity ratios with the number of ethylene subunits is predicted, indicating delocalization of the screening π electrons. In contrast to NEXAFS spectra of a heterogeneous group attached to hydrocarbon chains, the NEXAFS spectra of oligomer sequences, here the polyenes, converge slowly. The building block principle is less appropriate than the final state rule for rationalizing the present findings. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469290
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  • 2
    Electronic Resource
    Electronic Resource
    Calculation of NEXAFS spectra for surface–adsorbates: Hydroxyl on Cu(111) (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 8713-8725 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using OH adsorbed on the copper(111) surface as model system we demonstrate the feasibility of calculations of NEXAFS spectra of chemisorbed species. We employ a static exchange method that is implemented for large systems through direct atomic orbital techniques. The general cluster convergence of the spectra ranging up to 49 cluster atoms is investigated and found to be satisfactory. The special character of the strong metal to adsorbate charge transfer involving occupied OH orbitals and of the OH–metal ionic bond are shown to have particular consequences for both the analysis and the computation of the NEXAFS spectra. For the larger clusters the discrete spectra are dominated by adsorbate to cluster transitions, which can be understood from the similarity of electronic structure of the adsorbed OH moiety with that of free OH− for which all transitions end up in the continuum. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470128
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  • 3
    Electronic Resource
    Electronic Resource
    The hypermagnetizability of molecular oxygen (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 8552-8563 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The hypermagnetizability and the hypermagnetizability anisotropy of the oxygen molecule are computed using cubic response theory applied to multi-configurational self-consistent field wave functions. The effects of basis set, electron correlation, frequency dispersion, zero point vibrational averaging and pure vibrational contributions are discussed. The result for the anisotropy (Δη=+2.65 a.u. at λ = 632.8 nm), even taking into account possible limitations in the treatment of electron correlation and in the incompleteness of the basis set, maintains a different sign and is more than two orders of magnitude smaller than the experimental values published in the literature. Possible reasons for this large discrepancy are discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473910
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  • 4
    Electronic Resource
    Electronic Resource
    Spin–orbit coupling constants in a multiconfiguration linear response approach (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 2118-2126 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Spin–orbit coupling constants between singlet and triplet states are evaluated as residues of multiconfiguration linear response functions. In this approach, the spin–orbit coupling constants are automatically determined between orthogonal and noninteracting states. Sample calculations are presented for the X 3Σ−g–b 1Σ+g transition in O2 and the 1A1–3B1 transition in CH2. The convergence of the coupling constants is examined as a function of basis set and level of correlation. An exotic behavior is observed in the correlation of the 1A1 state for CH2 when increasing the active space, demonstrating an intricate coupling between the dynamic and static correlation. In general, the results indicate that reliable spin–orbit coupling constants between valence states may be obtained with a 4s3p2d1f basis set for first row atoms and a modest active orbital space.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462063
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  • 5
    Electronic Resource
    Electronic Resource
    Multiconfigurational quadratic response functions for singlet and triplet perturbations: The phosphorescence lifetime of formaldehyde (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 9178-9187 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A formalism is presented for the calculation of quadratic response functions of multiconfigurational self-consistent field reference wave functions. The formalism is general in the sense that it applies equally well to singlet and triplet perturbations and it does not assume any permutational symmetry in the integrals of the perturbational operators. This formalism can be used to derive expressions for various properties related to singlet or triplet quadratic response functions and their residues. We focus on the spin-forbidden dipole transitions between singlet and triplet electronic states responsible for the long lifetime of phosphorescent states. The singlet–triplet transition moments are evaluated as the residues of quadratic response functions. Sample calculations are presented for the formaldehyde molecule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463344
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  • 6
    Electronic Resource
    Electronic Resource
    Indirect nuclear spin–spin coupling constants from multiconfiguration linear response theory (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 6120-6125 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have used multiconfiguration self-consistent-field theory to determine indirect nuclear spin–spin coupling constants. The Fermi contact, spin dipole, and paramagnetic spin–orbit contributions are evaluated as multiconfiguration linear response functions at zero frequency and the diamagnetic spin–orbit contribution as an average value of the multiconfiguration wave function. Sample calculations on HD and CH4 demonstrate that most of the correlation contributions can be recovered in relatively small complete active space (CAS) reference state calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462654
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  • 7
    Electronic Resource
    Electronic Resource
    Frequency-dependent polarizabilities and first hyperpolarizabilities of H2O (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 7159-7164 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Static and frequency-dependent dipole polarizabilities α and first hyperpolarizabilities β are calculated for H2O using self-consistent field (SCF) and multiconfigurational self-consistent- field (MCSCF) linear and quadratic response theory. With an active orbital space where one correlating orbital is included for each occupied valence orbital excellent agreement is obtained with the experimental hyperpolarizability. Basis set dependency has been investigated and a detailed vibrational analysis has been carried out.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464733
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  • 8
    Electronic Resource
    Electronic Resource
    Direct atomic orbital based self-consistent-field calculations of nonlinear molecular properties. Application to the frequency dependent hyperpolarizability of para-nitroaniline (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 6417-6423 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We outline a method for the calculation of nonlinear properties such as dynamic hyperpolarizabilities for self-consistent-field (SCF) wave functions. In this method, two-electron integrals are only addressed in the evaluation of Fock matrices and Fock matrices with one-index transformed integrals. These matrices are determined directly in terms of integrals evaluated in the atomic orbital basis, avoiding expensive integral transformations between atomic and molecular orbital bases as well as storing and retrieving the two-electron integrals. The method is double direct—direct in the sense of constructing Fock matrices from atomic integrals, and direct in the sense of solving the response equations iteratively using direct linear transformations of a generating matrix times trial vectors. Applications can be performed on species of the same size as in direct SCF. The cost of evaluating a single nonlinear molecular property is comparable to that of optimizing the wave function. Additional properties can be obtained at little extra cost by solving all response equations simultaneously. As a demonstration, we calculate the static and dynamic hyperpolarizabilities of para-nitroaniline.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465099
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  • 9
    Electronic Resource
    Electronic Resource
    Direct SCF direct static-exchange calculations of electronic spectra (1997)
    Springer
    Theoretical chemistry accounts 97 (1997), S. 14-40 
    Details
    ISSN: 1432-2234
    Keywords: Key words: Direct methods ; Excited states ; Oligomers ; Adsorbates ; X-ray spectra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. Applications of the direct SCF direct static-exchange method are reviewed for three different types of systems (free molecules, polymers, and surface adsorbates) and for six types of spectroscopy (X-ray absorption-, -emission-, and -shake-up spectroscopy, ultraviolet photoelectron emission, X-ray Raman and circular dichroism spectroscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002140050234
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  • 10
    Electronic Resource
    Electronic Resource
    Ab initio study of the NMR shielding constants and spin-spin coupling constants in cyclopropene (1993)
    Springer
    Theoretical chemistry accounts 87 (1993), S. 19-28 
    Details
    ISSN: 1432-2234
    Keywords: NMR shielding constants ; Spin-spin coupling constants ; Cyclopropene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Ab initio calculations of parameters which characterize the NMR spectrum are presented for the cyclopropene molecule. The London orbitals CHF (or GIAO-CHF, Gauge-Independent Atomic Orbital Coupled Hartree-Fock) results for the shielding constants are in good agreement with the experimental data, accurately determined, and with otherab initio values. The calculations of the NMR spin-spin coupling constants have been performed using the Multiconfiguration Time-Dependent Hartree-Fock (MC TDHF) approach. Different basis sets and MC SCF wavefunctions were used to estimate the accuracy of the results. Good agreement is obtained with the coupling constants estimated using the available experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01113526
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