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  • Computational Chemistry and Molecular Modeling  (19)
  • 1
    Electronic Resource
    Electronic Resource
    The effect of electric field on the electronic structure of DNA. I. Calculation of the polarizability and of the permanent dipole moment for the nucleotide bases and base pairs (1969)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 3 (1969), S. 621-634 
    Details
    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: Generalizing the method of Hirschfelder, Curtiss and Bird for the calculation of the polarizability of molecules, we have calculated both the diagonal and off-diagonal polarizability tensor elements of the nucleotide bases and base pairs. In the course of calculations also the components of the permanent dipole moments have been computed for these systems.On the basis of the results obtained we have determined also the critical field strengths necessary to break off a base pair and thus to induce the unwinding of the DNA double helix. According to the data obtained, a field strength of the order 108 V/cm can induce the unwinding of DNA if its direction lies in the plane of the base pairs.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560030509
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  • 2
    Electronic Resource
    Electronic Resource
    CNDO/2 and MINDO/2 energy band structures of some homopolynucleotides (1973)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 7 (1973), S. 547-560 
    Details
    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 all-valence electron band structures of the periodic DNA models polyC, polyT, and polyA have been calculated with the aid of the CNDO/2 and MINDO/2 crystal orbital (CO) method.According to the obtained results the valence and conduction bands are always of π type. The widths of the bands are usually larger in the CNDO case, than those obtained for the same systems in the PPP CO approximation. On the other hand the MINDO results show similar widths as the PPP ones. The forbidden bandwidths are by 3-4 eV larger in the CNDO/2 case, than in the PPP one, while the MINDO/2 CO method has resulted in similar gaps like the PPP calculation.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560070310
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  • 3
    Electronic Resource
    Electronic Resource
    Theoretical treatment of chemisorption using an Ab initio SCF Green-matrix formalism (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 839-849 
    Details
    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: We present a treatment of chemisorption that uses the Green matrix of the surface and the admolecule, as well as a cluster calculation of a small surface cluster. Since full HF-SCF-band structures with nonlocal exchange are available now for larger systems for a couple of years, it is possible to treat the substrate surface and the admolecule on equal footing. This offers a natural way to solve the embedding problem. We have applied the formalism to the adsorption of H2 on beryllium and show that in contrast to cluster calculations there appears a binding, which is experimentally verified.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390608
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  • 4
    Electronic Resource
    Electronic Resource
    The first excited triplet states of the nucleotide bases calculated with different semiempirical SCF schemes (1969)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 3 (1969), S. 79-92 
    Details
    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 π-electron distributions, spin densities, and energies of the first triplets of the nucleotide bases, uracil, thymine, cytosine, adenine, and guanine, were investigated in various semiempirical approximations. Results are presented for calculations using the semiempirical form of the closed-shell SCF configuration interaction method, of the different orbitals for different spins (unrestricted Hartree-Fock) treatment, with and without spin projection, and of the Roothaan's open-shell procedure.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560030112
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  • 5
    Electronic Resource
    Electronic Resource
    Concept of charge transfer: Investigation of charge transfer in the glyoxal-formamide, water dimer, and water-lithium cation systems (1980)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 18 (1980), S. 1143-1155 
    Details
    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: In this paper an attempt is made to define charge transfer trying also other ways than Mulliken's population analysis. To illustrate this the amount of transferred charge (q) in the complexes HCONH2 + OHC - CHO in two relative geometrical positions, H2O + H2O and H2O + Li+ has been calculated with the help of Mulliken's population analysis using the wave function of the complex on the one hand and in the framework of different methods to subdivide the total space of the complex into subspaces for the acceptor and donor molecule, respectively, on the other hand. The results obtained show that Mulliken's population analysis gives a qualitatively correct description of the charge transfer process but to obtain the finer details most probably the use of a single number (q) is not sufficient. Further, the change in the total energy with respect to an effective charge transfer of a water dimer and of a solvent-cation complex has been investigated using the new mutually consistent field method. In this way the amount of transferred charge as well as the charge transfer interaction energy have been obtained in one step. These results have been compared with calculations applying second-order perturbation theory including overlap and the supermolecule method.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560180503
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  • 6
    Electronic Resource
    Electronic Resource
    Interaction between polymers: Dispersion energy of two infinite linear chains (1981)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 20 (1981), S. 683-692 
    Details
    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: Using the newly developed discrete variant of the k · p perturbation theory for linear chains an expression is derived for the dispersion interaction between two infinite chains valid for both insulating and metallic polymers. It is shown that the formally divergent dispersion energy is also finite for metallic systems, but it may be considerably enhanced in polymers with partly filled bands as compared with insulting ones. The accuracy of the proposed k · p expansion is investigated on model chains through comparisons with direct ab initio Hartree-Fock crystal orbital calculations. Applying second order perturbation theory an explicit formula in terms of band parameters is given for the numerical calculation of the dispersion energy.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560200310
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  • 7
    Electronic Resource
    Electronic Resource
    Cluster CPA calculations for infinite and half-infinite chains and applications to coupled polymer chains (1982)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 21 (1982), S. 917-926 
    Details
    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: It is shown how the cluster CPA can be used to obtain the local density of states p(E) in a half-infinite or infinite random polymer chain. Calculations were performed for p(E) in a system composed of two coupled random chains with nearest neighbors interaction.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560210517
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  • 8
    Electronic Resource
    Electronic Resource
    Intermolecular and intramolecular interactions calculated with ab initio perturbative configuration interaction method using strongly localized orbitals (1982)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 22 (1982), S. 169-182 
    Details
    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: We have applied the ab initio formulation of the perturbative configuration interaction using localized orbitals (PCILO) method up to third order to calculate intermolecular and intramolecular interaction energies going beyond the ab initio Hartree-Fock calculation. For the rotational barrier in ethane our results agree well with the experimental value and the cis- and even the trans-barriers in HOOH are at least qualitatively reproduced with the aid of the STO-3G basis set. In the case of the water dimer we obtain an equilibrium intermolecular distance and interaction energy which are confirmed by other calculations. We can further conclude from our studies that one has to include higher orders in the perturbation expansion as the system becomes more complicated. It is especially the last aspect which hinders the application of the ab initio PCILO to estimate the major part of the electron correlation energy for large molecules.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560220115
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  • 9
    Electronic Resource
    Electronic Resource
    Spin projected extended Hartree-Fock equations (1973)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 7 (1973), S. 583-608 
    Details
    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 (spin projected) extended Hartree-Fock equations are derived and discussed in the general (“many λi”) case. The derivation is based on the corresponding generalized Brillouin theorem, substituting in its expression the spin projected DODS Slater determinant as a linear combination of determinants. The expressions obtained for the elements of the different matrices εcd (c = a or b, and d = a or b) occurring in the equations are analyzed. The transformation of the equations into the form of a pseudoeigenvalue problem and the LCAO form of the equations are given, too. Finally the relation to the Goddard's GF equations is discussed in detail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560070313
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  • 10
    Electronic Resource
    Electronic Resource
    Breit-type three-electron equation in the Pauli approximation (1977)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 12 (1977), S. 925-935 
    Details
    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: We have reduced the Breit-type equation written down for 3 electrons to the 8 large components of the wave function in the (v/c)2 (Pauli) approximation. This procedure required appropriate handling of the 64 scalar equations which result in this instance. According to the results obtained within the accuracy of (v/c)2 all the terms are the same as those obtained by summing up the terms of the reduced 2-electron Breit's equation to 3 electrons. This statement is no longer valid, however, if during the reduction procedure we would go beyond the (v/c)2 approximation. Finally there is a discussion about how to begin developing a relativistic many-electron theory valid for the inner shell electrons of heavy atoms within the accuracy of the fine structure constant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560120513
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