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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 98 (1976), S. 2659-2660 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 100 (1978), S. 392-395 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 96 (1974), S. 11-16 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 289-294 
    ISSN: 0392-6737
    Keywords: Electron correlation and CI calculations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Valence Full Configuration Interaction (FCI) calculations are reported for the N2 molecule with a 4s3p triple-zeta basis set at different distances. The size of the FCI space is more than 225 000 000 symmetry-adapted Slater determinants. The computation requires about 1400 s of c.p.u. time per iteration on a CRAY C90, and is one of the largest FCI calculations ever converged. Our results, as is in general the case for FCI computations, can be used to test the performance of approximated methods used to study electronic correlation in molecules.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 1 (1982), S. 21-27 
    ISSN: 0392-6737
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Il metodo veloce d'interazione delle configurazioni è esteso in modo da tener conto anche dell'effetto delle configurazioni con tre o quattro elettroni eccitati.
    Abstract: Резюме Быстрый метод для анализа конфигурационного взаимодействия обобщается для вычисления эффекта конфигураций с тремя или четырьмя возбуж-денными электронами.
    Notes: Summary The fast CI method is extended in order to account for the effect of triply and quadruply excited configurations.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 9 (1987), S. 45-54 
    ISSN: 0392-6737
    Keywords: Specific calculations and results
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Si mostra come calcolare elementi di matrice che governano l’assorbimento bifotonico in molecole partendo da funzioni d’onda approssimate come sviluppi CI per la parte elettronica o splines cubiche per quella vibrazionale. Sono state fatte applicazioni alle transizioni2Σ+ A←2∏X di OH e1Σ g + E,F←1Σ g + X di H2 usando i metodi seguenti: I) somma sugli stati nell’approssimazione di Born-Oppenheimer con inclusione delle funzioni d’onda vibrazionali e 2) soluzione diretta dell’equazione della teoria delle perturbazioni per mezzo di uno sviluppo CI a nuclei fissi seguita da una media vibrazionale. I risultati sono stati paragonatti ai dati sperimentali e discussi.
    Notes: Summary We show how conventional linear expansion techniques for both electronic and vibrational wave functions can be used for the computation of matrix elements governing the two-photon absorption probability in molecules. In particular, the2Σ+ A←2∏X transition matrix elements of OH and the1Σ g + E,F←1Σ g + X of H2are computed using 1) the sum over states in the Born-Oppenheimer approximation with inclusion of vibrational wave functions, 2) solution of perturbation theory equations by expansion in the CI basis at fixed nuclei, followed by a kind of vibrational averaging. The results are compared with experiment and discussed.
    Type of Medium: Electronic Resource
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 674-679 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A multireference perturbative-variational method, proposed by the authors to compute the molecular energies and wave functions is investigated to assess the importance of the choice of the orbital basis and of the "zeroth order'' Hamiltonian on the computed energies. A new definition is presented of single particle energy suitable to perform perturbative-variational computations with any type of orbital sets. Test computations performed with various orbital sets for the Be+H2 system at various geometries indicate that the computed energies are not very sensitive to the choice of the single particle energies but they are sensitive to the choice of the orbitals. The MCSCF orbitals appear to provide the best starting set of orbitals to perform this type of computation. The computed energies are compared to those evaluated by single and multireference coupled cluster, MBPT, and CI methods.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A CI program is described for the evaluation of two-photon electronic transitions, based on time dependent second order perturbation theory. The expression of the transition amplitudes is obtained by directly solving first order perturbation equations over the CI components, avoiding the second order expression with summation over the full set of the intermediate CI eigenstates. The procedure has been implemented as part of a general CI program for ab initio computations of these properties. To test the program, the relative intensities of the "hot'' vibronic components of the A1g→B2u transition of the benzene molecule have been evaluated on a minicomputer and compared to the experiment.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 1277-1282 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We apply the density matrix renormalization group method to the Pariser–Parr–Pople Hamiltonian and investigate the onset of dimerization. We deduce the parameters of the hopping term and the contribution of the σ bonds from ab initio calculations on ethylene. Denoting by Rij the C–C distances, we perform a variational optimization of the dimerization δ=(Ri,i+1−Ri−1,i)/2 and of the average bond length R0 for chains up to N=50 sites. The critical value of N at which the transition occurs is found to be between N=14 and N=18 for the present model. The asymptotic values for large N for R0 and δ are given by 1.408(3) Å and 0.036(0) Å. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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