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  • 1
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 9246-9252 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The density matrix renormalization group (DMRG) method introduced by White for the study of strongly interacting electron systems is reviewed; the method is variational and considers a system of localized electrons as the union of two adjacent fragments A,B. A density matrix ρ is introduced, whose eigenvectors corresponding to the largest eigenvalues are the most significant, the most probable states of A in the presence of B; these states are retained, while states corresponding to small eigenvalues of ρ are neglected. It is conjectured that the decreasing behavior of the eigenvalues is Gaussian. The DMRG method is tested on the Pariser-Parr-Pople Hamiltonian of a cyclic polyene (CH)N up to N=34. A Hilbert space of dimension 5.×1018 is explored. The ground state energy is 10−3 eV within the full CI value in the case N=18. The DMRG method compares favorably also with coupled cluster approximations. The unrestricted Hartree-Fock solution (which presents spin density waves) is briefly reviewed, and a comparison is made with the DMRG energy values. Finally, the spin-spin and density-density correlation functions are computed; the results suggest that the antiferromagnetic order of the exact solution does not extend up to large distances but exists locally. No charge density waves are present. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 5351-5364 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The harmonic and cubic force field of the triatomic molecules ClNO, FNO, ClSN, and FSN are evaluated by using SCF and various CI methods. The vibration–rotation constants derived from the force field are compared to the experimental values. The computed cubic force field is found to be accurate at the SCF level for ClNO and FNO, despite severe limitations of the HF description for the latter molecule. CI effects are important for some of the harmonic components of the force field of FNO and for its α vibration–rotation constants. The values of the vibration–rotation interaction constants have been predicted for ClSN and FSN.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 674-679 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Amsterdam : Elsevier
    International Journal of Biological Macromolecules 11 (1989), S. 77-80 
    ISSN: 0141-8130
    Schlagwort(e): Collagen fibril ; band pattern ; freeze-etching
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Biologie , Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Amsterdam : Elsevier
    The @Journal of Steroid Biochemistry and Molecular Biology 49 (1994), S. 327-331 
    ISSN: 0960-0760
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Biologie , Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Amsterdam : Elsevier
    Chemical Physics Letters 68 (1979), S. 162-165 
    ISSN: 0009-2614
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 7
    ISSN: 0392-6737
    Schlagwort(e): Molecular spectra ; grouped by wave-length ranges
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Beschreibung / Inhaltsverzeichnis: Riassunto Le costanti di accoppiamento quadrupolare di14N e35Cl della specie isotopica14N32S35Cl del tiazil cloruro sono state determinate attraverso l'analisi della struttura iperfine di sei transizioni di tipoμ a eμ b dello spettro a microonde. Si sono ottenuti i seguenti valori (in MHz): χaa (35CL) = −39.00(3), χbb (35CL) = 23.84(4), χaa (14N) = −1.42(6), χbb (14N) = −4.16(6).
    Kurzfassung: Резюме Из анализа сверхтонкой структуры шестиμ a иμ b переходов в микроволновом спектре определяются ядерные квадрупольные константы связи14N и35Cl в14N32S35Cl. Получены следующие значения (в МГц): χaa (35CL) = −39.00(3), χbb (35CL) = 23.84(4), χaa (14N) = −1.42(6), χbb (14N) = −4.16(6).kg]PACS. 33.20
    Notizen: Summary The14N and35Cl nuclear quadrupole coupling constants of the14N32S35Cl isotopic species of thiazyl chloride have been determined from an analysis of the hyperfine structure of sixμ a andμ b transitions in the microwave spectrum as (in MHz) χaa (35CL) = −39.00(3), χbb (35CL) = 23.84(4), χaa (14N) = −1.42(6), χbb (14N) = −4.16(6).
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Il nuovo cimento della Società Italiana di Fisica 3 (1984), S. 489-508 
    ISSN: 0392-6737
    Schlagwort(e): Corrections to electronic structure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Beschreibung / Inhaltsverzeichnis: 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.
    Kurzfassung: 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.
    Notizen: 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.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Amsterdam : Elsevier
    Chemical Physics Letters 58 (1978), S. 132-136 
    ISSN: 0009-2614
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Il nuovo cimento della Società Italiana di Fisica 2 (1983), S. 1-14 
    ISSN: 0392-6737
    Schlagwort(e): Fluorescence, phosphorescence, radiationless transitions (intersystem crossing, internal conversion)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Beschreibung / Inhaltsverzeichnis: Riassunto È stata esaminata la possibilità di applicare la cosiddetta «approssimazione armonica locale» al calcolo delle funzioni generatrici usate nella teoria delle transizioni non radiative. La suddetta approssimazione tenta di «adattare» punto per punto la funzione generatrice alla curvatura del potenziale, variando in modo opportuno la frequenza dell’oscillatore. Nel caso semplice di due oscillatori di Morse identici separati da un dislivello costante di energia ΔE, la probabilità di transizione non radiativa è stata calcolata per un vasto intervallo di valori di ΔE. I risultati sono stati paragonati con quelli ottenuti eseguendo la somma sulle autofunzioni esatte degli stati legati dell’oscillatore di Morse. Si è riscontrato che la forma di linea è qualitativamente corretta, anche se l’approssimazione introduce dei picchi negativi spurii.
    Notizen: Summary The possibility of applying the «local harmonic approximation» to the calculation of the generating functions used in the theory of radiationless transitions has been investigated. The approximation attempts to «adapt» point by point the generating function to the curvature of the potential, varying the oscillator frequency in a suitable manner. In the simple case of two identical Morse oscillators separated by a constant energy gap ΔE, the radiationless transition probability has been computed for a wide range of ΔE values. The results are compared with those obtained by summing over the exact bound states of a Morse oscillator. It is found that the line shape is qualitatively correct although some spurious negative contribution is introduced by the approximation.
    Materialart: Digitale Medien
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