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  • Computational Chemistry and Molecular Modeling  (9)
  • Corrections to electronic structure  (1)
  • asymptotic behavior  (1)
  • 1
    ISSN: 0392-6737
    Keywords: Corrections to electronic structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto È ben noto che l'efficienza dei convertitori fotochimici e fotobiologici dipende dalle proprietà spettrali della radiazione incidente. In questo lavoro si analizza l'efficienza di lungo periodo di sistemi con immagazzinamento interno d'energia nel caso di convertitori con uno o due fotosistemi e sezione d'urto d'assorbimento gaussiana. Si discute quindi la dipendenza dell'efficienza dal livello energetico della banda d'assorbimento del sistema e dalle perdite d'energia nella reazione d'immagazzinamento. I risultati ottenuti sono infine paragonati con il comportamento di alcuni dispositivi reali. In particolare, si paragona lo spettro d'assorbimento teorico che rende massima l'efficienza di conversione con lo spettro d'assorbimento sperimentale dei batteri purpurei e delle piante verdi. Anche se questo schema non prende in considerazione la piena complessità delle reazioni fotosintetiche, esso è sufficiente a mostrare che lo spettro d'assorbimento dei convertitori fotosintetici si è adattato alla radiazione solare incidente in modo da ottenere la massima efficienza di conversione.
    Abstract: Пезюме Известно, что зффективность фотобиологических преобразователей зависит от спектраляных свойств падающего излучения. В этой статье анализируется эффективность аккумулирующих устройств с гауссовым поперечным сечением поглощения в случае преобразователй с дной или двумя фотосистемами. Затем обсуждается зависимость от энергетической запрещенной зоны системы и от энергетических потерь в накопиаеле. В частноти, слектр поглощения, который максимизирет эффективностя преобразования, сравнивается с эксперименталяным спектром поглощения пурпурнын бактерий и зеленых станций. Даже беа учета всей сложности фотосинтетических реакций, показано, что спектр поглощения фотосинтетичетических преобразователей, согласванный с падающей солхечной радиацией, дает наивысшую эффективность преобразования.
    Notes: Summary An algorithm has been implemented for the evaluation of one-electron density matrices from correlated wave functions obtained by using a variation-perturbation procedure recently proposed, which allows the inclusion of several reference configurations. The algorithm has been applied to evaluate the dipole moment and the chlorine and nitrogen quadrupole coupling constants of the NSCl molecule.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 55 (1995), S. 347-359 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The extension of the PPP Hamiltonian for alternant cyclic polyenes to noninteger values of the pseudomomentum by imposing modified boundary conditions is discussed in detail. It is shown that a computer program for periodic boundary conditions can be easily adapted to the new boundary conditions. Full CI computations are carried out for some low-lying states of the PPP model of altemant cyclic polyenes (CH)N, (N even) at half-filling. The energy values obtained by using periodic (Bloch) and antiperiodic (Möbius) orbitals are used to perform energy extrapolations for N → ∞. © 1995 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 66 (1998), S. 397-407 
    ISSN: 0020-7608
    Keywords: cyclic polyenes ; exchange energy ; asymptotic behavior ; finite size correction ; Pariser-Parr-Pople ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The large N expansion of the restricted Hartree-Fock (RHF) exchange energy per atom E(N) of the Pariser-Parr-Pople (PPP) model of cyclic polyenes (annulenes) CNHN is derived in detail. We explicitly derive the coefficients E0 and E1 of the asymptotic expansion: E(N)=E0+E1 ln N/N2+O(N-2), N→∞, in the very simple case of half-filling and no bond alternation. The exchange energy per atom in the infinite chain can be written as Eex=(2/π2)∑∞j=1{[γ∞(2j-1)]/[(2j-1)2]}, where γ∞ is the two-electron repulsion integral in the infinite chain. On the other hand, the second coefficient E1 giving a finite-size correction is found to be 1/2b, where b is the bond length. This value of E1 differs slightly from that of a linear chain with periodic boundary conditions because the distance between sites depends upon the radius of the ring, i.e., upon N.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 397-407, 1998
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 7 (1973), S. 223-232 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Approximate and ab initio molecular wave functions are obtained using Gaussian expansions of different length for the Slater orbitals. The expectation values of several one-electron operators are obtained and the accuracy of different wave functions discussed.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 8 (1974), S. 941-950 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Standard sets of Gaussian atomic orbitals (STO-3G, STO-4.31G) are used to evaluate spin-orbit coupling constants in linear molecules (CO2+, NNN) and spin-orbit effects on singlet-triplet transition intensities in formaldehyde. All spin-other orbit effects have been included. In all cases spin-other orbit interactions form a large fraction of the matrix elements. Simple formulae to evaluate spin-orbit one- and two-electron integrals over atomic orbitals are presented. Standard molecular integral programs can be used for the computation of spin-orbit integrals.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 663-672 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Iterative methods for computing eigenvalues and eigenvectors of large symmetric matrices are discussed using the language of multidimensional partitioning technique. New variants are proposed and found useful particularly for the computation of highly excited states of CI matrices.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 5 (1971), S. 497-503 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A MO-LCAO-SCF treatment is performed on water, ammonia and methane using a recently proposed approximate method.The procedure is found capable of predicting total and orbital energies in close agreement with the results of accurate computations using double ζ basis sets of Slater type orbitals.A comparison is made with the results of similar approximate ab initio procedures.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 18 (1980), S. 1393-1404 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By introducing a finite basis, the inhomogeneous equations of perturbation theory are approximated by systems of linear equations. We present and discuss a Padé-type algorithm suitable for large-order systems and having better convergence properties than the classical Jacobi procedure.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 673-684 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An interative technique to solve nearly singular systems of linear equations of quantum chemical interest is described and tested. The solution is split into regular and singular parts, the last being the resonating eigenvector.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 9 (1975), S. 537-544 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Spin-orbit interactions among the ground and the first few excited electronic states of SO2, are computed with ab initio molecular wave functions and Gaussian atomic orbitals. All spin-other orbits contributions to the matrix elements are included.The computed intensity of the first singlet-triplet transition is found to be in broad agreement with experiment and sensitive to an extension of the configuration interaction expansion of molecular wave functions. Also, the splitting of sulfur LII,III states in SO2 is derived as an example of large spin-orbit interactions among electronic states.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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