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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 9548-9557 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have performed vibrationally resolved calculations of the excitation of the symmetric stretch in the photoionization of CS2 leading to the X 2Πg, A 2Πu, B 2Σ+u, and C 2Σ+g states of CS+2. Previous theoretical work has determined that the kπg shape resonance in the (5σu)−1 channel consists mainly of a linear combination of low lying virtual d orbitals on sulfur and is thus essentially atomic in nature. This conclusion was primarily based on the shape of the resonant wave function and the insensitivity of the energy of the resonance to bond stretching. Here, we have determined that the energies of the kπ shape resonances located well above threshold and the σ bound states just below threshold are insensitive to bond length. We have also found nearly constant vibrational branching ratios in all channels and polarization components. This is in qualitative agreement with experimental vibrationally resolved cross sections [S. Kakar, H. C. Choi, and E. D. Poliakoff, J. Chem. Phys. 97, 4690 (1992)] which show nearly constant vibrational branching ratios. Our present results indicate that caution must be exercised when using bond length sensitivity as an exclusive means to determine the existence of shape resonances. © 1994 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 106 (1997), S. 10175-10183 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using a previously introduced weight scheme, microbatching, and grid compression [R. E. Stratmann, G. E. Scuseria and M. J. Frisch, Chem. Phys. Lett. 257, 213 (1996)], we significantly speed up the numerical integration of the exchange-correlation contribution to the Coupled-Perturbed Kohn–Sham equations. In addition, we find that the nature of the integrand is such that it is possible to employ substantially fewer grid points in the quadrature and to use the Gaussian very Fast Multipole Method (GvFMM) with very short multipole expansions for the Coulomb contribution, with negligible loss in accuracy. As a representative example, the computational demand for the exchange-correlation portion of a coronene (C24H12) frequency calculation with a 3-21G basis is reduced by more than one order of magnitude. The overall speed up achieved in this calculation is between a factor of 4 to 6, depending on the specific functional. We also present sample calculations using polarized bases, gradient-corrected functionals, and on even larger systems (C54H18 and C96H24), to illustrate the various effects and improvements that we have accomplished. © 1997 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 104 (1996), S. 8989-9000 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present partial photoionization cross sections and photoelectron asymmetry parameters for the photoionization of NO leading to the (2π)−1X 1Σ+, (5σ)−1b 3Π, (5σ)−1A 1Π, (4σ)−1c 3Π, and (4σ)−1B 1Π states of NO+. The results were obtained with multichannel multiplet-specific interaction potentials derived from correlated target states. The resulting scattering equations were solved using the Schwinger variational method. The calculations considered excitation energies in the 10–40 eV range. It was found that selective orthogonalization eliminated spurious resonances that were encountered. We found that in the channel leading to the (2π)−1X 1Σ+ state of NO+, the structure seen experimentally in the 14–17 eV region is due to two pronounced valence autoionizing states, one of which is broadened by interaction with a shape resonance. We predict the existence of a third strong σ→π* transition of 2Σ− symmetry in the photoabsorption cross section at approximately 14.8 eV photon energy which, due to symmetry restrictions, cannot decay by autoionization. In addition, our results indicate that the broad structure seen experimentally in the 20–40 eV region in the (2π)−1 channel might be due to coupling to shape resonances which occur in other ionization channels. Our predicted total cross sections and photoelectron asymmetry parameters differ from those obtained by previous theoretical approaches, all of which neglected correlation effects. The present results were found to be in good agreement with the available experimental data. We found that the existence and position of the various resonances were sensitive to the level of correlation and interchannel coupling included in the calculation. In particular, we found that the resonant enhancement in the channels leading to both the (5σ)−1b 3Π and (5σ)−1A 1Π states of NO+ was due to a single 5σ→σ* resonant state which decayed into both ionization channels. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 8218-8224 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Time-dependent density-functional (TDDFT) methods are applied within the adiabatic approximation to a series of molecules including C70. Our implementation provides an efficient approach for treating frequency-dependent response properties and electronic excitation spectra of large molecules. We also present a new algorithm for the diagonalization of large non-Hermitian matrices which is needed for hybrid functionals and is also faster than the widely used Davidson algorithm when employed for the Hermitian case appearing in excited energy calculations. Results for a few selected molecules using local, gradient-corrected, and hybrid functionals are discussed. We find that for molecules with low lying excited states TDDFT constitutes a considerable improvement over Hartree–Fock based methods (like the random phase approximation) which require comparable computational effort. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 6384-6395 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photoionization cross sections of CS2 leading to the X 2Πg, A 2Πu, B 2Σu+, and C 2Σg+ states of CS2+ have been computed including the effects of interchannel coupling in the multichannel frozen core Hartree–Fock approximation. The results were obtained using the iterative Schwinger variational method using a partial wave expansion up to l=120. The photoionization cross sections are obtained in the mixed dipole representation which ensures that the Thomas–Reiche–Kuhn sum rule is satisfied. We have found shape resonances in the kπg and kπu continuum channels. In particular, the kπg resonance is seen to affect dramatically both total cross sections and photoelectron asymmetry parameters in all other channels when interchannel coupling is included. The form of the resonant wave function indicates that this resonance is caused by low lying virtual d orbitals on the sulfur atoms. Using a Schwinger-type iterative method we have found the position of the corresponding poles of the single channel T matrix in the complex plane. We have determined that the position of the pole is relatively insensitive to the interatomic bond lengths. This is indicative of the atomic nature of the resonant state. We have also determined cross sections and asymmetry parameters in the region of autoionization in the channel leading to the X 2Πg state of CS2+.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 8493-8505 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have implemented an efficient multichannel configuration–interaction complete-active-space (MCCI-CAS) approximation to study electron–correlation effects in molecular photoionization. This approach is based on the graphical unitary group approach (GUGA) for computing matrix elements of the Hamiltonian and includes target relaxation, correlation, and polarization as well as correlation due to coupling between different asymptotic scattering channels. The statistical rule, which partitions the total cross section into multiplets by simple spin statistics, is easily derived in this formalism. The scattering equations are solved using the Schwinger variational method. We present multiplet specific results of a detailed MCCI-CAS Schwinger study of the photoionization of molecular oxygen in the photon energy region of 12.3–20.4 eV, including up to four coupled electronic channels. Our results show the importance of using correlated target states. We have obtained all of the autoionization structure near threshold that has been assigned experimentally. In addition, we predict structure not yet resolved by experiment. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0168-9002
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Nuclear Instruments and Methods in Physics Research Section A: 323 (1992), S. 542-548 
    ISSN: 0168-9002
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Nuclear Instruments and Methods in Physics Research Section A: 348 (1994), S. 97-104 
    ISSN: 0168-9002
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1617-4623
    Keywords: Key wordsbellwether ; moa ; ATP synthase ; Cyclin B ; Cell cycle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We report the isolation and complementation mapping of lethal mutations within the 59AB region on the second chromosome of Drosophila melanogaster. The newly induced lethal mutations in this region define four different complementation groups. Using existing and newly induced deficiencies, these loci can be assigned to three different chromosomal intervals. Moreover, complementation analysis with chromosomes carrying various P element insertions, in combination with a molecular characterization of the corresponding insertion sites, suggests that the previously described male sterile mutation bellwether is an allele of an essential gene that encodes the alpha subunit of the mitochondrial ATP synthase.
    Type of Medium: Electronic Resource
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