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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 7583-7596 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The x-ray photoionization spectra of large saturated hydrocarbons have been investigated by means of one-particle Green's function calculations. These spectra saturate overall rather quickly to their asymptotic form with increasing system size. The results obtained indicate a severe breakdown of the molecular orbital picture of ionization above a binding energy threshold of about 23 eV, for n-alkane chains ranging from n-propane to n-nonane, or cycloalkane compounds such as cyclobutane, cyclopentane, and cyclohexane. In spite of the fast multiplication of satellite solutions, shake-up lines remain confined above that threshold, as a result of the delocalization properties of one-electron canonical states. The ring closure is shown to emphasize the dispersion of photoionization intensity into satellites. Conformational changes, on the other hand, have only marginal effects on the convoluted correlation bands. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 7012-7026 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An exhaustive investigation of the outer-valence ionization spectra of azulene, phenanthrene, pyrene, chrysene, triphenylene, and perylene is presented. The analysis is based on one-particle Green's function calculations performed upon correlated [density-functional theory/Becke three-parameter Lee–Yang–Parr (DFT/B3LYP)] geometries using the third-order outer-valence Green's function [OVGF] and algebraic-diagrammatic construction [ADC(3)] schemes, as well as basis sets of improving quality (6-31G, 6-31G*, cc-pVDZ). The ionization bands of polycyclic aromatic hydrocarbons show a great diversity, which reflects the strong impact of the molecular architecture on orbital energies. Despite the intricacy of ionization spectra and the extent of the shake-up contamination in the π- and σ-band systems, the ADC(3) results enable consistent insights into available ultraviolet photoelectron measurements, up to the inner-valence region. They also indirectly support recent assignments of low-lying π*←π doublet excitations in the electronic absorption spectrum of the pyrene and perylene cations by means of time-dependent density functional theory [J. Chem. Phys. 111, 8904 (1999)]. It has been found that OVGF pole strengths smaller than 0.85 very systematically foretell a breakdown of the orbital picture of ionization at the ADC(3) level. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 5859-5882 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The valence ionization bands of benzene and of polyacenes ranging from naphthalene to pentacene have been entirely assigned by means of one-particle Green's function calculations, performed using the third-order algebraic-diagrammatic construction [ADC(3)] scheme and series of basis sets of improving quality. For the sake of consistency, the computations are based on correlated (DFT/B3LYP) rather than uncorrelated geometries. Ionization bands pertaining to π-orbitals are subject to a severe shake-up contamination at already quite low binding energies (e.g., down to 8.0 eV in the case of pentacene). In sharp contrast, the orbital picture of ionization holds to a much greater extent within the σ-band system (e.g., for pentacene, up to binding energies of 14.6 eV). Despite the intricacy of ionization bands, and, possibly, vibrational complications, ADC(3) spectra consistently match photoionization measurements up to the inner-valence region, where the orbital picture completely breaks down. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 63 (1997), S. 483-509 
    ISSN: 0020-7608
    Keywords: linear response ; quadratic response ; perturbation theory ; electronic correlation ; Green's function ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The equations satisfied by the first-order perturbed electron propagator in an applied external field are examined at a level equivalent to the two-particle-hole Tamm-Dancoff and extended two-particle-hole Tamm-Dancoff approximations (2ph-TDA). These schemes are derived with the intention of evaluating linear and quadratic response properties through second and third order in correlation. Their derivation is based on a combination of the diagrammatic and algebraic superoperator methods. Both schemes account for the polarization of the 2p-1h and 2h-1p responses and bielectron interactions under an external field. The 2ph-TDA scheme is correct up to second order in electronic correlation and includes infinite geometric series of mixed RPA-ladder-type character. Its extended version is derived consistently through third order and accounts for a first-order screening of the external field and bielectron interaction by the effects of electronic correlation. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 483-509, 1997
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 63 (1997), S. 465-481 
    ISSN: 0020-7608
    Keywords: excited states ; shake-up ; relaxation ; electronic correlation ; Green's function ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The x-ray photoemission spectra of the ethylene, butadiene, and hexatriene compounds were investigated using one-particle Green's function calculations which are exact up to third order in correlation. This study points to the importance of initial-state correlation and cross-section effects for a consistent reproduction of satellite bands recorded under x-ray photoionization. By extrapolating the results obtained to larger unsaturated hydrocarbons, it is clear that the signal recorded in the inner-valence region of polyacetylene must be exclusively assigned to many-body structures. This study also provides evidence for a partial contamination of the outer-valence band by shake-up lines. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 465-481, 1997
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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