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  • 1975-1979  (745)
  • Computational Chemistry and Molecular Modeling  (745)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 15 (1979), S. 15-35 
    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: For a few organic semiconductors we present calculations performed on a simple model by means of the field-theoretical formulation of the “different-orbitals-for-different-spins” method. The numerical methods are extensively described and the results are discussed in comparison with other methods existing in the same domain.
    Additional Material: 3 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 15 (1979), S. 49-56 
    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 diatomics-in-molecules method is applied to calculate the ground state 1A′ potential energy surface for LiOH. Three different sets of polyatomic basis functions are investigated. An adequate description of the surface is obtained only with the set including both neutral and ionic atomic states.
    Additional Material: 2 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 15 (1979), S. 37-47 
    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 semiempirical molecular orbital (MO) method is outlined that is designed for correlation and prediction of the spectra and other properties of complex molecules. Within the ZDO approximation, the reactive (π-bonding and nonbonding) electrons are treated explicitly considering the σ electrons as an unreactive static potential. The electronic repulsion integrals are evaluated using the multipole expansion formulas, which allow the characterization of each orbital by specification of its quadrupole moment, from which all two-center repulsion integrals involving it would be computed. A preliminary application of the all reactive electron self-consistent field (ARE-SCF-CI) MO method is made to organic carbonyls as well as some selected cyanine dyes. The predicted n → π* and π → π* transition energies and intensities are in good agreement with experimental data. The calculated ionization potentials are 0.2-0.7 eV lower than the observed values. The present method, although it requires further possible refinements, bridges the gap between the simplicity of the PPP method and the required overall interpretation of the electronic properties.
    Additional Material: 1 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 15 (1979), S. 57-71 
    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 minimal number of independent nonzero atomic integrals that occur over arbitrarily oriented basis orbitals of the form R(r) · Ylm(Ω) is theoretically derived. The corresponding method can be easily applied to any point group, including the molecular continuous groups C∞v and D∞h. On the basis of this (theoretical) lower bound, the efficiency of the permutational approach in generating sets of independent integrals is discussed. It is proved that lobe orbitals are always more efficient than the familiar Cartesian Gaussians, in the sense that GLOs provide the shortest integral lists. Moreover, it appears that the new axial GLOs often lead to a number of integrals, which is the theoretical lower bound previously defined. With AGLOs, the numbers of two-electron integrals to be computed, stored, and processed are divided by factors 2.9 (NH3), 4.2 (C5H5), and 3.6 (C6H6) with reference to the corresponding CGTOs calculations. Remembering that in the permutational approach, atomic integrals are directly computed without any four-indice transformation, it appears that its utilization in connection with AGLOs provides one of the most powerful tools for treating symmetrical species.
    Additional Material: 3 Tab.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 15 (1979), S. 73-81 
    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 PCILO method was applied to complexes where dispersion energy forms the dominant attractive contribution of the intermolecular interaction energy. With alkane dimers, especially with dimers of higher alkanes (C4H10)2, (C5H12)2, etc., and the ethylene dimer PCILO was successful as to stabilization energy, equilibrium distance, optimal dimer structure, and energy composition. The dispersion energy part is always underestimated, however. With (X2)2 dimers (X = N, F, Cl) PCILO failed, which might be explained by the presence of lone pairs in the subsystems.
    Additional Material: 4 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 15 (1979), S. 83-95 
    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 screened potential model (SPM) is formulated with Slater-type functions to reproduce the density of the electron shells. The orbital exponent for the valence shell is optimized to calibrate the SPM against experimental valence and Rydberg s and p energy levels for the alkali metals (Li, Na, and K) rare gases (He, Ne, Ar, and Kr), second-row atoms, and Cu, Zn, Mg, S, and Ga. The resulting one-electron wave functions are used to calculate the dipole and velocity forms of the oscillator strengths and 〈1/r3〉 for spin-orbit coupling. The excellent agreement with the averaged experimental results suggests that the SPM atomic orbitals are a good starting point for the evaluation of one-electron properties.
    Additional Material: 1 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 15 (1979), S. 97-107 
    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 validity of two models used in comparisons of the UHF and PHF methods in hyperfine structure calculations is investigated for the lowest 2P state of Li. An improved model for the angular splitting of the core orbitals is proposed and shown to give an accurate description of both the UHF and the PHF wave functions.
    Additional Material: 5 Tab.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 15 (1979), S. 109-120 
    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 random-walk method of solving the Schrödinger equation is applied to the 1B1g and 1B2g states of the H4 square with side length 2.4 a.u. The results provide an independent check of the accuracy of prior variational calculations for these states. With node structures for the 1B1g state taken from a variational calculation with a single-zeta basis set and taken in the simplest form meeting symmetry requirements, the calculated energies are lower than the expectation value of the energy for the single-zeta basis set but not as low as the expectation value for an optimized-exponent double-zeta basis set with polarization terms. Comparisons of results give no suggestion of a barrier height lower than ∼120 kcal/mol for passage through the square configuration in the exchange reaction H2 + D2 → 2HD. For the 1B2g state with node structure in the simplest form meeting symmetry requirements the calculated energy is ∼65 kcal/mol lower than the expectation value of the energy for variational calculations with a double-zeta basis set.
    Additional Material: 6 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 15 (1979), S. 121-129 
    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 molecular electrostatic potentials computed by the overlap-multipole-expansion procedure (OMTP) are compared to exact electrostatic potentials computed with the same Gaussian basis set, for different molecular species. It is shown that at distances of the molecule larger than 2.2 Å, the OMTP values compared to those of the exact ones are within an error of 0.5 kcal/mol. This error decreases with increasing distance. For distances below this limit the OMTP potentials may be used as a first indication of the trends of the molecule, provided the values to compare are not too close.
    Additional Material: 4 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 15 (1979), S. 281-291 
    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 simple model for surface reconstruction is developed utilizing the next-nearest-neighbor approximation within the framework of molecular-orbital theory. Exact energy expressions for this model and various special cases are derived, and they are illustrated by numerical results. The influence of a very weak surface deformation on the energy spectrum of surface states is also discussed.
    Additional Material: 4 Ill.
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  • 11
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 15 (1979), S. 271-280 
    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: This paper offers a unified presentation of the main ring conformers of the diol expoxides, triol carbonium ions, and tetrols related to the “bay-region” benzo ring of carcinogenic metabolites of PAH and brings forward quantitative information through ab initio SCF computations about their relative energies. It substantiates and evaluates the energy of the syn epoxide-OH4 hydrogen bond and, on the contrary, refutes the significance of an O⃛H—O or an O-⃛H—O bond in the triol carbonium ions. It provides an explanation for the similar rates of acid-catalyzed hydrolysis of the syn and anti diol expoxides. It evaluates the stabilization of the triol carbonium ions due to the presence of a neighboring double bond and accounts for the spontaneous opening of protonated epoxides. Finally it accounts for cis hydrolysis of the syn diol epoxide and trans hydrolysis of the anit diol epoxide under acid conditions.
    Additional Material: 6 Ill.
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  • 12
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 15 (1979), S. 379-387 
    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 new theoretical approach to the cooperativity of an enzyme has been proposed. When we applied the present theory to the allosteric effect of hemoglobin, we obtained a so-called Koshland-Nemethy-Filmer formula. Our theory suggested that the sigmoid curve becomes sharper when the affinity of the first oxygen molecule of the hemoglobin is smaller.
    Additional Material: 4 Ill.
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  • 13
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 15 (1979), S. 491-497 
    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: Several analogs of valinomycin have been simulated. These are analogs obtained by changing the configuration of the amino acid and hydroxy acid residues one at a time. Nonbonded interactions have been calculated for three conformations of each analog. The electrostatic and polarization contributions to the energy are conformation selective, whereas the Pauli repulsion is the only component which is isomer selective. For the ring chirality considered here the analog of valinomycin having all the three L-valyl residues replaced by D-valyl residues is predicted to be frozen in a “top open” conformation.
    Additional Material: 3 Ill.
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  • 14
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 16 (1979) 
    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
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  • 15
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 15 (1979), S. 783-792 
    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: Giving explicit consideration to the lone pairs of the carbonyl oxygen of the amide group it is found that the polarity of the amide group resides essentially in the lone pair. As a confirmation, the lone pairs of the ester group are also found to account for most of its polarity. This localization of amide dipole affects the dipeptide conformation map only in the unallowed regions of the map, but has significant impact on the dipole moment of the dipeptide in different conformations. The experimentally observed dipole moments of dipeptides in solution are in conformity with our assignment of polarity of the amide group.
    Additional Material: 3 Ill.
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  • 16
    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
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  • 17
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 16 (1979), S. 1-2 
    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
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  • 18
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 16 (1979), S. 3-4 
    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: No. Abstract.
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  • 19
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 16 (1979), S. 5-17 
    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 properties of exciton and soliton excitations in one-dimensional molecular systems and in α-helical protein molecules are investigated. It is shown that collective excitations - solitons, corresponding to a combination of vibrational excitations in peptide groups and a local deformation of molecules - are possible in α-helical protein molecules. These excitations move along the molecule without energy losses and are perfect energy carriers. A qualitative description of the shortening in the length of muscular fibers is given using the concept of solitons occurring under the hydrolysis of ATP molecules at the ends of thick fibers contained in the sarcomeres of muscular fibers.
    Additional Material: 6 Ill.
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  • 20
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 16 (1979), S. 19-29 
    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: Preferred conformations of phospholipids have been predicted through quantum-chemical techniques and classical potential functions. An essential condition for a conformation to exist in a biomembrane is that it should be possible for it to organize in the form of a bilayer. Taking into consideration the conformational flexibility of the polar head group, organization at the lipid-water interface has been considered. The biological implications of such an organization in terms of formation of “hydrophobic channels” is discussed. Quantum-mechanical investigations on the transport phenomenon have shown that the “selectivity” of biological membranes is connected with the “organization.” Calculations of the quantum-mechanical transmission coefficients for different model potential profiles indicate that minor differences in the height of potential barriers in certain regions can lead to significant changes in transmission coefficients. The “directional selectivity” of substrates (differences in transmission coefficients for flow in and out of the cell) can be explained on the basis of differences in membrane organization. These results have some important consequences in the evolutionary process in biological membranes.
    Additional Material: 7 Ill.
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  • 21
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 16 (1979), S. 31-42 
    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 new electron structural mechanism is proposed for interpretations in molecular biology, in addition to the already existing theories of Szent-Györgyi (semiconductivity) and Fröhlich (long-range coherence). The hypothetical “intermediate-” or “zigzag states” (ZZS) of solids are investigated by the recursion (transfer matrix) method. The physical reality of the ZZS is discussed up to an SCF DODS-type theory and the necessity of additional less approximate investigations is emphasized. The possible role of ZZS in the explanation of: (i) translation in protein synthesis, (ii) energy and charge transfer processes, as well as (iii) initiation of protein formation is outlined.
    Additional Material: 3 Ill.
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  • 22
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 16 (1979), S. 43-50 
    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 the myosin-auramine O system 10 or 11 binding sites of auramine O on the rod-like part of myosin were discovered. The myosin fluorescence decreases with an increase in auramine O concentration. This is evidence of the excitation energy transfer from tryptophanyls situated near the binding sites to auramine O. The effective distance of energy transfer is 35 Å. It is suggested that the light meromyosin has binding sites with periodicities of 77-86 Å. Every binding site has a negative charge and hydrophobic locus.
    Additional Material: 5 Ill.
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  • 23
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    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 16 (1979), S. 51-56 
    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 transition from quantum chemistry to quantum biology is discussed, and the contributions that quantum biology can make to the study of biological structure and process are outlined. The need for extensions to the theory to deal with larger systems, to include solvent effects and to account for specificity, are emphasized.
    Additional Material: 1 Tab.
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  • 24
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 16 (1979), S. 57-64 
    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: Pseudopotential theory is introduced into the ab initio FSGO molecular fragment method. Pseudopotential molecular fragments using pseudopotentials of double-zeta quality are characterized, and a method of their assembly into larger molecules is presented. Core-valence electron separation is achieved at both levels of the molecular calculations. Heteroatom incorporation into the method is also considered. Applications of the pseudo-FSGO molecular fragment method to hydrocarbons and simple molecular systems containing heteroatoms are discussed. Results are compared to those of the original FSGO method and experiment.
    Additional Material: 2 Ill.
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  • 25
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 16 (1979), S. 175-188 
    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 quantum-mechanical model study, aided by classical potential calculations, of the formation of adducts between the candidate ultimate carcinogen benzo(a)pyrene diol epoxide and the amino groups of guanine, adenine, and cytosine is presented. An explanation for the preferential reactivity of guanine is proposed and conformational aspects of adduct formation are discussed for both nucleosides and B-DNA.
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  • 26
    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: This survey covers the following topics: (1) Theoretical calculation of the total multitude of the energetically permitted regular DNA helices. (2) Theoretical study of flexibility of the double helix with emphasis on nucleosome structure. (3) Experimental data on the properties of the B to A transition of DNA in solution: the degree of cooperativity and influence of sequence. (4) The B-A transition and its possible role in genes activation.
    Additional Material: 7 Ill.
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  • 27
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 16 (1979) 
    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
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  • 28
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    International Journal of Quantum Chemistry 16 (1979), S. 203-213 
    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 use of empirical 0-1-6-12 atom-atom potential functions and the PCILOCC method intra- and intermolecular interactions of glycero-phosphoryl-ethanolamine model head groups in a planar layer crystal were calculated. Starting from investigations of the two-dimensional energy-contour diagrams the minima of energy as a function of all head group torsion angles were calculated using a gradient procedure. Within an interval of 15 kcal/mol above the energy of the global minimum we obtained about 30 local minima. These results demonstrate a high flexibility of the investigated phosphorylethanolamine head group in agreement with experiment. The ethanolamine moiety exists in enantiomeric conformations. With the torsion angles of the 0-1-6-12 energy minimization procedure PCILOCC calculations were carried out. These calculations yield the x-ray conformation as the most stable one (unit-cell stabilization energy = -36.3 kcal/mol). The PCILOCC as well as the potential function calculations show that the conformation of phospholipid head groups in layer crystals is determined by intramolecular as well as by intermolecular interactions with neighboring phospholipid molecules.
    Additional Material: 5 Ill.
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  • 29
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    International Journal of Quantum Chemistry 16 (1979), S. 215-219 
    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 new approach is proposed to derive the equation of elementary excitation motion along chains and it is used to obtain an important correction of the equation.
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  • 30
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    International Journal of Quantum Chemistry 16 (1979), S. 243-256 
    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: Absolute rate theory (ART) was applied to a series of reactions of the type A+BC → AB+C containing H, F, HF, H2, and F2, trans-cis isomerization of dideuteroethylene, and processes H + CH4 → H2 + CH3 and H′+CH4 → H′CH3 + H. Geometries and energies of activated complexes were taken from the best ab initio studies reported in the literature in which at least a DZ + P basis set was used and a large portion of the correlation energy was included. Vibrational frequencies needed for the zero-point energies and vibrational partition functions were estimated from the reported potential surfaces (HHF and HFF) or evaluated from SCF 4-31G calculations (HFH, FHF, twisted C2H4, and CH5 complexes). Compatability of calculated rate constants with the experimental data was examined.
    Additional Material: 39 Ill.
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  • 31
    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: Methods for determining the thermal measurements of biological objects have found ever increasing application in biology. This paper analyzes the temperature dependence of the heat capacity of biopolymer solutions between 4-400°K. Four distinct temperature regions were discovered, and experiments on these temperature intervals are given.
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  • 32
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 16 (1979) 
    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
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  • 33
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    International Journal of Quantum Chemistry 16 (1979), S. 437-444 
    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 present work is devoted to investigation of thermal transitions in the crystals of seven proteins to compare the protein globule stability in crystal and solution. Calorimetry methods, electron and optical microscopy, as well as x-ray diffraction studies are used. It is found that protein crystals do not melt and that the destruction of the crystal lattice is a result of protein globule denaturation within the crystal. It is demonstrated that during the heating of pepsin and DF-trypsin crystals it is possible to observe phase transition of the first order. Equilibrium temperatures of protein denaturation in crystals and in solution coincide. The peculiarities of the crystal state are revealed in the increasing thermal transition cooperativity and the system relaxation period.
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  • 34
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    International Journal of Quantum Chemistry 16 (1979), S. 445-465 
    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 concept of potential surfaces and classification of various types of intermolecular forces are given. The possibilities and the criteria of applicability of modern methods for potential surface calculation at short, intermediate, and long distances are discussed. Special attention is paid to the methods for calculating interactions between large molecules.
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  • 35
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    International Journal of Quantum Chemistry 16 (1979), S. 605-613 
    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 semiempirical MINDO/3 method with complete optimization of geometry is employed to calculate the electronic ground-state properties (dipole moments and ionization potentials) and the energies of various tautomeric forms of uracil, uracil monoanion, cytosine, and isocytosine. The results are shown to be consistent with most of the experimental data. Accuracy of various quantum-mechanical methods is discussed. Particular attention is paid to the influence of the geometry optimization on energy differences between various tautomers. Some qualitative conclusions of biological importance are drawn from these calculations.
    Additional Material: 2 Ill.
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  • 36
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    International Journal of Quantum Chemistry 16 (1979), S. 631-639 
    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: Ab initio SCF computations indicate that the formation of an adduct of glyoxal to the guanidinium ion occurs in two steps. The first addition should occur on an NH2 group, rather than on NHCH3, and the formation of an unsymmetrical adduct IV is competitive and may be even favored over that of the symmetrical adduct III suggested by Takahashi. The barrier for that reaction is higher than for a similar reaction with guanine. The formation of a Schiff base between glyoxal and the guanidinium ion is disfavored because of the large endothermicity calculated for the process, much larger than that predicted for Schiff base formation with simple neutral or protonated amines.
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  • 37
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    International Journal of Quantum Chemistry 16 (1979), S. 669-689 
    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: This paper presents a critical discussion of recent discoveries on the metabolic transformations of polycyclic aromatic hydrocarbons and their interactions with nucleic acids in the light of quantum-mechanical theories of chemical carcinogenesis.
    Additional Material: 8 Ill.
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  • 38
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    International Journal of Quantum Chemistry 16 (1979), S. 641-653 
    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 view of building a workable molecular model of tetraliganded zinc at the active site of carbonic anhydrase, an ab initio SCF study using pseudopotentials is performed on Zn2+(OH2)n from n = 2 to 6, Zn2+(NH3)n-1 (OH2) for n = 2 and 4, Zn2+(NH3)2 (imidazole) (OH2), and their ionized species involving OH- or imidazolate, considering in particular the evolution of the properties of the ligands and of the bound cation upon increasing n and upon replacement of one ligand by another. (Comparison of NH3 and imidazole binding was made in a full SCF calculation.) The results obtained in the tetraliganded complex confirm that zinc binding facilitates water deprotonation more than imidazole deprotonation, so as to reverse the order of their intrinsic ease of ionization. A study of the approach of CO2 toward the active site is made in an electrostatic approximation using as models the most representative of the computed four-ligand complexes.
    Additional Material: 1 Ill.
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  • 39
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 16 (1979) 
    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
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  • 40
    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: New “reference” circular dichroism spectra of α helix, β-structure (both parallel and antiparallel), β-bends, and the unordered form are obtained from circular dichroism spectra and x-ray data for six proteins (myoglobin, lysozyme, lactate dehydrogenase, papain, ribonuclease, and subtilisin BPN′). Circular dichroism spectra for α-helix and antiparallel β-structure are similar to those for poly(Llysine). The circular dichroism spectrum of the parallel β-structure is qualitatively similar to that theoretically calculated by Madison and Schellman. The circular dichroism spectrum of β-bends is qualitatively similar to that theoretically calculated by Woody. The spectrum of the unordered form is close to that of the denaturated proteins. These “reference” circular dichroism spectra used for the analysis of the secondary structure of ten globular proteins (besides the six reference proteins D-glyceraldehyde 3-phosphate dehydrogenase, concanavalin A, cytochrome c, and insulin).
    Additional Material: 1 Ill.
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  • 41
    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: Quantum-chemical calculation of the energies of the electronic transitions and the electronic structures of the neutral and ionic species of the nucleic acids components in their ground and lower excited singlet and triplet ππ* and nπ* states has been carried out in the all-valence-electron approximation CNDO/S. The results of the calculation allow one to identify the most photoreactive sites of the molecules and to consider the dependence of the location of these sites on the ionic state of the molecules. The calculated data are compared with our previous results obtained in a π-electron approximation. The individual absorption spectra of various ionic and tautomeric species of the nucleic acids components obtained by us earlier have been decomposed into bands corresponding to separate electronic transitions. As a rule, there is a good agreement between the calculated data in the two approximations and the experimental results.
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  • 42
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    International Journal of Quantum Chemistry 16 (1979), S. 833-837 
    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: Excited π-electronic states of cytosine and uracil are calculated by the CI method. The effects of a transition from the single-excited configuration set to the set involving all double-excited configurations are considered. The set expansion is shown to affect essentially the transition energies and oscillator strengths, in particular, an additional electron transition related to the first absorption band occurs in the singlet uracil spectrum. When doubly excitations are taken into account the triplet transition energies considerably increase and become practically insensitive to repulsion integral parametrization.
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  • 43
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    International Journal of Quantum Chemistry 16 (1979), S. 839-845 
    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: Rotational isomerization of bipyridines C5H4N—C5H4N was studied by CNDO/2, PPP/CI, and CNDO/CI methods. It is shown that CNDO/2 overestimates the angle of rotation φ between the pyridine rings ca. two times. The angle φ was determined for 2,2′-bipyridine by means of correlation of the theoretical (CNDO/2) and experimental dipole moment. It was also found from the correlation between the theoretical and experimental UV spectra. It is shown that there is an explicit dependence of the results upon the distance between heteroatoms (PPP/CI). It has been found that the CNDO/CI method correctly predicts the value of the rotational angles and their sequence in bipyridines.
    Additional Material: 2 Ill.
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  • 44
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    International Journal of Quantum Chemistry 16 (1979), S. 847-855 
    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 investigation of the factors determining the formation and stability of the higher biopolymers structures is one of the most important trends of the development of molecular biophysics. A feature common to most macromolecular systems under physiological conditions is that they function in an aqueous environment. Thus, it is natural to assume that the peculiarities of biological macromolecules structures and their functional activity as well are closely related to the specific properties of such a unique solvent as water. The investigations of the conformational changes of biopolymer, induced by dehydration of the macromolecule, give information about the nature of the forces stabilizing its structure. The dehydration of the macromolecule in solution can be attained by addition of a nonaqueous cosolvent. Generally low-molecular-weight aliphatic alcohols, amides, and amines are used as a nonaqueous component. At present a vast number of experimental and theoretical data concerning the properties of water and aqueous systems are available. The specificity of water as a solvent arises primarily from the spatial hydrogen-bonded structure. The addition of a nonaqueous component exerts changes in this structure, which evolve to the singularities of the physical characteristics of water-nonelectrolyte mixtures. It is generally assumed that nonelectrolytes may be divided, according to their effect on the spatial water structure, largely into two basic classes: (1) the structure makers, i.e., the compounds of aliphatic alcohols type; (2) the structure breakers, i.e., the compounds of urea type. The agents belonging to the first class show a stabilizing effect in the range of low nonelectrolyte content. At a certain critical concentration, Ccrit, characteristic of each substance, the nonaqueous solute molecules leave the cavities of the spatial water structure which leads to a disruption of the latter. The agents belonging to the second class exert a structure-breaking effect even in the range of extremely low concentrations, which arises from their high competitive ability for hydrogen bonding.
    Additional Material: 7 Ill.
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  • 45
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    International Journal of Quantum Chemistry 16 (1979), S. 857-862 
    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 representation of a completely stiff macromolecule as a long rigid rod and the representation of a semiflexible macromolecule as a chain of freely rotating connected effective rigid rods, the conditions of formation of the liquid-crystalline phase in the solutions of such macromolecules are obtained and the diagram of states for the corresponding phase transitions in the variables temperature-volume fraction of polymer in the solution is constructed.
    Additional Material: 2 Ill.
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  • 46
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    International Journal of Quantum Chemistry 16 (1979), S. 863-868 
    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: Atom-atom potential functions for calculation of nonbonded interaction energies of nucleic acids are proposed. Quantitative reliability of the obtained results is checked by using the calculations of intermolecular interaction energy in crystals. Based on the calculations of the interaction energy of the nucleic acid bases the molecular mechanisms of spontaneous mutations are suggested.
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  • 47
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    International Journal of Quantum Chemistry 16 (1979), S. 869-875 
    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 method of correlation functions used in the theory of liquids is suggested for investigation of the solvation shell structure in the vicinity of nonpolar surfaces. An approach making it possible to obtain the molecule correlation functions in the solvation shell is worked out. In this approach the correlation functions are the product of the interatomic correlation functions.
    Additional Material: 2 Ill.
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  • 48
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    International Journal of Quantum Chemistry 16 (1979), S. 877-882 
    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 physical aspects of the primary charge separation processes in bacterial photosynthesis are discussed. The donor-acceptor model of electron transfer due to participation of protein current states is used. The kinetics of photosynthetic reaction center (PRC) processes is investigated and the PRC energetic scheme is constructed using the nonequilibrium density matrix method. It is shown that with allowance for the effect of vibrational sublevels of states participating in transitions the theory describes well experimental data.
    Additional Material: 3 Ill.
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  • 49
    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: This paper analyzes the low-temperature magnetic circular dichroism of NO-Fe(II)hemoproteins in detail. We include the Jahn-Teller effect in our consideration of the low-temperature MCD results.
    Additional Material: 3 Ill.
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  • 50
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    International Journal of Quantum Chemistry 16 (1979), S. 891-895 
    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 unrestricted HF method in the INDO approximation with optimized geometry was used to describe the electronic structure of the hetero-ring of verdazyl and the derivatives of the latter. The results obtained are in good agreement with the experimental EPR spectra of triphenylverdazyl radical and its dipole moment. These data may be a basis for understanding and predicting the chemical properties and reactivity of verdazyl and its derivatives.
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  • 51
    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 interaction energy between water and B-DNA in the single and double helix is computed at a number of planar cross sections perpendicular to the helix long axis and for a few cylindrical surfaces enclosing the helix. In addition, Monte Carlo simulations are presented for a small cluster of water around regions of energy minima. On the base of these simulations the structure of water for B-DNA in solution, the quaternary structure of B-DNA, is proposed and discussed. The intermolecular interaction used in the Monte Carlo computation has been derived from ab initio computations of complexes between water and the DNA bases, diethylphosphate, a ribose derivative, and other model compounds.
    Additional Material: 11 Ill.
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  • 52
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    International Journal of Quantum Chemistry 16 (1979), S. 917-930 
    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 free radical was produced enzymatically by incubating benzo(a)pyrene with liver microsomes. This radical, identified as the 6-oxybenzo(a) pyrene radical, was sufficiently reactive to bind covalently with nucleic acid bases. Similar reactive free radicals were produced enzymatically from anthanthrene and 10-aza-benzo(a)pyrene, which are carcinogenic in spite of lacking so-called “bay regions.” Hepatocarcinogens such as 3′-methyl-4-dimethylaminoazobenzene and related compounds, naphthylamines, and 2-acetylaminofluorene yield free radicals after being incubated with liver microsomes. Thus, various kinds of chemical carcinogens are found to be converted to free radicals, suggesting causal significance for the formation of free radicals in chemical carcinogenesis.
    Additional Material: 13 Ill.
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  • 53
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    International Journal of Quantum Chemistry 16 (1979), S. 1033-1049 
    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: For each of HNO, FNO, LiNO, LiON and HF2-, ab initio valence-bond wave functions are reported for the four-electron three-center bonding unit which involves one of the following sets of atomic orbitals: (a) NX σ-bond (X = H, For Li) and oxygen 2pπ′; (b) LiO σ-bond and nitrogen 2pπ′; (c) hydrogen 1s and fluorine 2pσ. Six S = 0 valence-bond structures pertain for this type of bonding unit. For HF2- and FNO, the calculated bond-eigenfunction coefficients for some of these valence-bond structures differ appreciably according to whether the Slater determinants include only the electrons of the four-electron three-center bonding unit, or all of the valence-shell ± inner-shell electrons. For HNO, LiNO, and LiON, the all-electron and all valence-shell electron calculations generate similar sets of bond-eigenfunction coefficients. For each of the nitrosyl systems, the bond-eigenfunction coefficient with largest magnitude is calculated to be that for which zero atomic formal charges occur in the valence-bond structure. Qualitative valence-bond and “increased-valence” descriptions of the bonding are presented.
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  • 54
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    International Journal of Quantum Chemistry 16 (1979), S. 1051-1068 
    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: Various electronic indices calculated by the CNDO/s-CI method for uracil, 5-fluorouracil, thymine, and cytosine and the Woodward-Hoffmann rule applied to the photodimerization of these molecules lead us to the following conclusions: (i) decrease of the C5—C6 bond order consequent to excitation is generally correlated with the photodimerization reaction for all the biological pyrimidines; (ii) excited pyrimidine molecules may be nonplanar and the excitation would be delocalized over both the molecules which photodimerize; (iii) electrostatic interactions may play a significant role in the initial stages of the photodimerization reaction; (iv) singlet precursors to the stable triplet photodimers may exist; and (v) electron density does not, in general, increase in the C5—C6 bond in the excited state as compared to the ground state, contradicting the proposals of some earlier workers. Hybrid population densities and σ-bond orders have been calculated for the first time for the molecules. Fluorine in 5-fluorouracil perturbs the hybrid populations as compared to those of uracil mainly in its vicinity.
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  • 55
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    International Journal of Quantum Chemistry 16 (1979), S. 1069-1101 
    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 novel approach is developed for optimizing molecular orbitals within the context of a multiconfiguration self-consistent-field problem. The MCSCF wave function is determined through a sequence of eigenvalue problems in the multiconfiguration space and the single-excitation space. They are used to iteratively improve the natural orbitals, which in turn are related, by successively improved transformations, to the MCSCF orbitals. The mathematical problems arising out of this general concept are solved and the computational implementation is discussed. In many applications the method has proven itself as a powerful approach in forcing rapid convergence. Adaptation to spin and spatial symmetry is maintained throughout and the procedure is applicable to excited states as well as to ground states.
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  • 56
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    International Journal of Quantum Chemistry 16 (1979), S. 1103-1139 
    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 direct dissociation of ethylene into two methylenes is studied along the least motion reaction path by means of an ab initio multiconfiguration self-consistent-field (MCSCF) calculation. All eight configurations arising from those valence orbitals that form the CC bonds, seven of them singlet coupled and one triplet coupled, are taken into account. The HCH bond angle is optimized along the entire reaction path. Separate MCSCF optimizations are carried through for the lowest two states of 1Ag symmetry. The (1Agσ2π2) ethylene ground state dissociates into two (3B1σπ) ground-state methylenes. The (1Agσ2π*2) excited state of ethylene dissociates into two (1A1σ2) excited methylenes. It is established that both these dissociations proceed without any barrier in the energy curve. In the ground state, where orbital symmetry is conserved, the π-bond breaks before the σ-bond, and the calculated heat of reaction agrees within 6 kcal/mol with the experimental value. In the excited state, where orbital symmetry is not conserved, the nonbonded repulsion between methylene σ2 lone pairs is found to blend into the antibonding character of the excited ethylene, yielding an energy curve that is everywhere repulsive. However, the variation of the HCH angle during the dissociation process is not simple, initially it expands and subsequently it contracts. Quantitative analytical approaches are developed which furnish conceptual interpretations of the orbital changes and configurational changes along the reaction path.
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  • 57
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    International Journal of Quantum Chemistry 16 (1979), S. 1141-1148 
    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 semiempirical MINDO/3 method is employed to calculate the energies of various tautomers of model tautomeric compounds -  2-oxo- and 4-oxopyridines and pyrimidines. The results are compared with experimental data in the gas phase, where the solute-solvent interactions not included in theoretical calculations are absent. Although the relative energies obtained by the MINDO/3 method appear to be superior to other semiempirical and ab initio calculations, the accuracy of the method was determined to be as low as 3-4 kcal/mol. It indicates that it is exceedingly difficult to account theoretically for intrinsic stabilities of the tautomers. The importance of various factors influencing calculated free-energy differences is discussed. Particular attention is paid to the problem of geometry optimization.
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  • 58
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    International Journal of Quantum Chemistry 16 (1979), S. 1149-1150 
    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
    Additional Material: 1 Tab.
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  • 59
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    International Journal of Quantum Chemistry 16 (1979), S. 1151-1155 
    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
    Additional Material: 3 Ill.
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  • 60
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    International Journal of Quantum Chemistry 16 (1979) 
    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
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  • 61
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    International Journal of Quantum Chemistry 16 (1979), S. 1157-1157 
    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
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  • 62
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    International Journal of Quantum Chemistry 16 (1979), S. 1161-1194 
    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
    Description / Table of Contents: Quelques relations essentielles pour la théorie de la représentation et l'algèbre de Wigner et Racah d'un groupe fini ou compact sont discutées et transcrites en termes de diagrammes. Une attention toute particulière est réservée au cas d'un groupe simplement réductible et tous les diagrammes donnés ici sont applicables à SU2 sans aucun changement.
    Abstract: Einige grundlegende Beziehungen für die Darstellungstheorie und die Wigner-Racah-Algebra einer endlichen oder kompakten Gruppe werden diskutiert und mit Diagrammen beschrieben. Besonders betont wird der Fall einer einfach reduziblen Gruppe. Alle Diagramme können ohne Modifizierung auf SU2 angewandt werden.
    Notes: Some basic relations for the representation theory and the Wigner-Racah algebra of a finite or compact continuous group are discussed and transcribed in terms of diagrams. Special emphasis is placed on the case of a simply reducible group and all the diagrams are applicable to SU2 without any change.
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  • 63
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    International Journal of Quantum Chemistry 16 (1979), S. 1195-1207 
    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
    Description / Table of Contents: La détermination des coefficients de sousduction pour les états du groupe unitaire U(n) avec les restrictions U(n) ↓ U(n1) ⊗ U(n2) a été considérée pour les états sans spin d'un système à plusieurs électrons. Un procédé simple et adapté à la programmation pour déterminer ces coefficients a été développé en utilisant les propriétés de transformation de la base tensorielle correspondant à la représentation irréductible 〈2N/2-S, 12S〉 de U(n). Ce procédé est illustré par un simple exemple.
    Abstract: Die Bestimmung der Subduzierungskoeffiziente für Zustären Gruppe U(n) mit den Einschränkungen U(n) ↓ U(n1) ⊗ U(n2) ist für die spinfreien Zustände von Vielelektronensystemen untersucht worden. Ein einfaches programmierbares Verfahren für die Bestimmung dieser Koeffiziente ist entwickelt worden, das die Transformationseigenschaften des der irreduziblen Darstellung 〈2N/2-S, 12S〉 von U(n) gehörenden Tensorbasissatzes benutzt. Dieses Verfahren ist mit einem einfachen Beispiel illustriert worden.
    Notes: The determination of the subduction coefficients for states of the unitary group U(n) under the restrictions U(n) ↓ U(n1) ⊗ U(n2) have been considered for the spin free states of many electron systems. Using the transformation properties of the tensor basis spanning the irreducible representation 〈2N/2-S, 12S〉 of U(n) under the permutations of electron coordinates, a simple programmable procedure has been developed for the determination of these coefficients. The procedure has been illustrated using a simple example.
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  • 64
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    International Journal of Quantum Chemistry 16 (1979), S. 1239-1247 
    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
    Description / Table of Contents: On a calculé des polarisabilités multipolaires dépendantes de la fréquence pour la série de He à partir d'un modèle hydrodynamique de la mécanique quantique dans le cadre d'un Hamiltonien de particules indépendantes. Notre méthode est équivalente à l'approximation de Hartree-Fock noncouplée, ce qui veut dire, que nos valeurs des polarisabilités, des énergies de transition et des coefficients pour les forces de dispersion sont comparables aux résultats précédents obtenus par cette approximation.
    Abstract: Frequenzabhängige Multipolpolarisierbarkeiten für die He-Folge sind mittels eines hydrodynamischen Modells der Quantenmechanik im Rahmen eines Hamiltonoperators für unabhängige Teilchen berechnet worden. Unser Verfahren ist der ungekoppelten Hartree-Fock-Näherung äquivalent und deswegen sind unsere Werte für die Polarisierbarkeiten, die Übergangsenergien und die Dispersionskraftkoeffizienten mit früheren Ergebnissen dieser Näherung vergleichbar.
    Notes: Frequency-dependent multipole polarizabilities of the He sequence have been calculated from a hydrodynamic model of quantum mechanics and using an independent-particle model Hamiltonian. Our present scheme is parallel to the uncoupled Hartree-Fock approximation so our values of polarizabilities, multipole transition energies and dispersion force coefficients between the He—He pair are comparable with earlier works using the uncoupled Hartree-Fock approximation.
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  • 65
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    International Journal of Quantum Chemistry 16 (1979), S. 1209-1237 
    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
    Description / Table of Contents: Le formalisme des fonctions de Green de polarisation dans la notation utilisant les superopérateurs de Goscinski et Lukman a été réétabli avec un état de référence MC-SCF pour obtenir le métrique des superopérateurs. Les avantages potentiels de cet état de référence plus général ainsi que certains points faibles inhérents associés aux états de référence utilisés traditionnellement dans les théories de perturbation Hartree-Fock ou Rayleigh-Schrödinger sont discutés brièvement. L'hermiticité des superopérateurs est analysée dans le cadre des états de référence MC-SCF. Utilisant une notion d'ordre propre à cet état de référence on présente des formules explicites et des procédés de calcul pour la réalisation de cette théorie des fonctions de Green, qui sont spécialisés pour inclure des termes consistants jusqu'au second ordre.
    Abstract: Der Formalismus für Green'sche Funktionen von Polarisierungstyp in der Superoperatorbezeichnung von Goscinski und Lukman wird mittels eines MC-SCF-Referenzzustands hergeleitet. Die möglichen Vorteile mit diesem allgemeineren Referenzzustand und gewisse mit den in den traditionellen Hartree-Fock- oder Rayleigh-Schrödinger-Störungstheorien verwendeten Referenzzuständen verbundene eigene Schwächen werden kurz diskutiert. Die Hermitizität der Superoperatoren wird im Rahmen des MC-SCF-Referenzzustands analysiert. Mittels eines für diesen Referenzzustand geeigneten Ordnungsbegriffs werden explizite Formeln und Rechnungsverfahren für die Implementierung dieser Theorie von Green'schen Funktionen vorgelegt und spezialisiert um Glieder bis zur zweiten Ordnung einzuschliessen.
    Notes: The polarization Green's-function formalism in the superoperator notation of Goscinski and Lukman is re-derived using a multiconfiguration self-consistent-field (MC-SCF) reference state to establish the superoperator metric. The potential advantages of employing this more general reference state in Green's-function theories and certain inherent weaknesses associated with the traditional Hartree-Fock or Rayleigh-Schrödinger perturbation theory reference state choices are briefly discussed. The Hermiticity of the superoperators is analyzed within the framework of the MC-SCF reference state. Using a concept of order appropriate for this reference state choice, explicit formulas and computational procedures for the implementation of this Green's-function theory are presented and specialized to include terms consistent through second order.
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    International Journal of Quantum Chemistry 16 (1979), S. 1249-1263 
    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
    Description / Table of Contents: Le problème de la diffusion colinéaire d'un atome par une molécule diatomique homonucléaire est formulé comme une équation différentielle matricielle non-linéaire du premier ordre pour le coefficient de réflexion variable. Quand l'Hamiltonien de la cible est invariant sous une transformation de parité, seulement des transitions entre des états pairs ou impairs sont possibles. Cette règle de sélection réduit le nombre de canaux ouverts ou fermés qui contribuent aux coefficients de réflexion et de transmission. Les conditions du problème permettent d'approximer l'Hamiltonien de la cible par celui d'un oscillateur harmonique déplacé. Dans cette approximation la symétrie de réflexion de l'Hamiltonien n'est pas conservée et des transitions entre des niveaux arbitraires sont possibles. Pour simplifier le problème encore plus, on admet que l'interaction entre le projectile et la cible est une somme de deux termes Gaussiens. Pour cette combinaison-ci l'interaction multi-canal peut ětre exprimiée dans une forme analytique finie. Des probabilités de transition sont obtenues pour la collision He—H2, par la solution de l'équation différentielle matricielle, obtenue d'une représentation du potentiel de Lennard-Jones par une somme de deux potentiels Gaussiens. Les résultats numériques sont comparés à ceux obtenus par Secrest-Johnson et Clark-Dickinson.
    Abstract: Die kolineare Streuung eines Atoms von einem homonuklearen zweiatomigen Molekül wird als eine nichtlineare Matrixdifferentialgleichung erster Ordnung für den variablen Reflexionskoefficient formuliert. Wenn der Hamiltonoperator für das Ziel unter Paritätstransformationen invariant ist, sind nur Übergänge zwischen geraden oder ungeraden Zuständen möglich. Diese Auswahlsregel reduziert die Anzahl von offenen oder abgeschlossenen Kanälen, die zu den Reflexions- oder Transmissionskoeffizienten beitragen. Die Bedingungen des Problems erlauben dass der Hamiltonoperator des Ziels mit dem eines verschiebenen harmonischen Oszillators angenähert wird. In dieser Näherung wird die Reflexionssymmetrie des Hamiltonoperators nicht beibehalten und Übergänge zwischen willkürlichen Niveaus sind daher möglich. Um das Problem weiter zu vereinfachen wird die Wechselwirkung zwischen Projektil und Ziel als eine Summe von zwei Gauss'schen Gliedern angenähert. Für diese Kombination der Potentiale kan die Multi-Kanal-Wechselwirkung analytischückt werdn. Durch Anpassung des Lennard-Jones'schen Potentials zu einer Summe von zwei Gauss'schen Potentialen und Lösung der Matrixdifferentialgleichung sind Übergangswahrscheinlichkeiten für die Kollison He—H2 erhalten worden. Die numerischen Ergebnisse werden mit denen von Secrest-Johnson und Clark-Dickinson verglichen.
    Notes: The problem of collinear scattering of an atom from a homonuclear diatomic molecule is formulated in terms of a first-order nonlinear matrix differential equation for the variable coefficient of reflection. For a homonuclear molecule when the target Hamiltonian is invariant under the parity transformation, only transitions between even states or odd states are possible. This selection rule reduces the number of open or closed channels that contribute to the reflection and transmission coefficients. But for numerical calculation, under the conditions of the problem, one can approximate the target Hamiltonian by the Hamiltonian of a displaced harmonic oscillator. In this approximation, the reflectional symmetry of the Hamiltonian is not preserved and transitions between any two levels of the target are possible. To simplify the problem further, the interaction between the projectile and the target is assumed to be a sum of two Gaussian terms. For this combination of the potentials the many-channel interaction can be expressed analytically. By fitting the Lennard-Jones potential with a sum of two Gaussian potentials and solving the matrix differential equation, transition probabilities are obtained for the He—H2 collision. The numerical results are compared with the results found by Secrest and Johnson, and by Clark and Dickinson.
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  • 67
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    International Journal of Quantum Chemistry 16 (1979), S. 1301-1305 
    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
    Description / Table of Contents: Nous étudions l'influence de la composition du développement en ondes partielles dans les calculs de type MSXα sur les énergies de liaison et les énergies orbitalaires pour N2, O2, et F2.
    Abstract: Wir untersuchen wie die Zusammensetzung der Partialwellenentwicklung in MSXα-Berechnungen Total- und Orbitalenergien für N2, O2, und F2 beeinflusst.
    Notes: We explore how the composition of the partial wave expansion in MSXα calculations affects the binding energies and orbital energies for N2, O2, and F2.
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  • 68
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    International Journal of Quantum Chemistry 16 (1979), S. 1265-1277 
    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
    Description / Table of Contents: Dans la méthode ab initio ordinaire pour calculer des orbitales molćulaires le nombre d'intégrales à évaluer augmente comme M4, où M est le nombre de fonctions de base. Dans le présent article une méthode alternative est discutée où le temps de calcul augmente beaucoup moins rapidement. Les éléments de matrice du potentiel de déformation sont calculés par des méthodes utilisant des transformées de Fourier, tandis que les éléments de matrice du potentiel des atomes neutres sont calculés par des intégrales transmissibles. Ces intégrales transmissibles (moments des potentiels des atomes neutres) peuvent ětre évaluées une fois pour toutes et incorporées comme input dans des programmes d'ordinateur. Dans un appendice on discute un théorème de développement général. Ce théorème permet un développement d'une fonction radiale arbitraire autour d'un autre centre.
    Abstract: In der üblichen ab-initio-Methode für Molekülorbitalberechnungen wächst die Anzahl von Integralen, die berechnet werden müssen, wie M4, wo M die Anzahl von Basisfunktionen ist. In diesem Artikel wird ein alternatives Verfahren diskutiert, wo die Rechnungszeit viel weniger schnell mit M wächst. Matrixelemente des Deformationspotentials werden mit Fourier-transformmethoden berechnet, während Matrixelemente des Potentials der neutralen Atome mit Hilfe von übertragbaren Integralen berechnet werden. Diese übertragbaren Integrale (Momente der Potentiale für neutrale Atome) können ein für allemal berechnet und als Inputdaten in Computerprogramme eingegliedert werden. In einem Appendix wird ein allgemeiner Entwicklungssatz diskutiert, der eine Entwicklung einer wilkürlichen kugelsymmetrischen Funktion um ein anderes Zentrum erlaubt.
    Notes: In the usual ab initio method of calculating molecular orbitals, the number of integrals to be evaluated increases as M4, where M is the number of basis functions. In this paper, an alternative method is discussed, where the computation time increases much less violently with the number of basis functions. Matrix elements of the deformation potential are evaluated by Fourier transform methods, while matrix elements of the neutral-atom potential are evaluated by means of transferable integrals. The transferable integrals (moments of the neutral-atom potentials) can be evaluated once and for all and incorporated as input data in computer programs. In an appendix to the paper, a general expansion theorem is discussed. This theorem allows an arbitrary spherically symmetric function to be expanded about another center.
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  • 69
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    International Journal of Quantum Chemistry 16 (1979), S. 1347-1356 
    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
    Description / Table of Contents: La méthode de relaxation optimale pour la recherche des valeurs propres d'une matrice symétrique, proposée par Shavitt, est adaptée pour résoudre le problème des équations de mouvement. Les matrices Z et Y sont obtenues en une seule diagonalisation; les matrices A et B ne sont pas modifiées par le calcul. La méthode est particulièrement utile quand la base est de grande dimension ou quand elle n'est pas orthogonale, si l'on ne recnerche que les énergies de transition le plus basses.
    Abstract: Die von Shavitt vorgeschlagene Methode mit Optimalrelaxierung für die Bestimmung der Eigenwerte von symmetrischen Matrizen, ist zur Lösung des Bewegungsgleichungsproblems angepasst worden. Die Matrizen Z und Y werden durch eine einzige Diagonalisierung erhalten, wobei die Matrizen A und B unverändert bleiben. Dieses Verfahren ist besonders anwendbar, wenn die Basis hochdimensional oder nicht orthogonal ist, und nur die tiefsten Übergangsenergien gebraucht werden.
    Notes: The method of optimal relaxation to determine the eigenvalues of symmetric matrices, as proposed by Shavitt, has been adapted to solve the equation-of-motion problem. Matrices Z and Y are obtained by one diagonalization, while matrices A and B remain unchanged. This procedure is particularly useful for high-dimensional or nonorthogonal bases, if one needs only the lowest transition energies.
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    International Journal of Quantum Chemistry 16 (1979), S. 1337-1346 
    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
    Description / Table of Contents: La position et l'intensité des bandes d'absorption d'un nombre de colorants chalcone ont été calculées par la méthode FEMO. Les trois à quatre maximums d'absorption de ces molécules ont été calculés en admettant que la molécule consiste de deux parties, avec le clivage hypothétique au site de la liaison C=O de façon à fournir six et huit électrons π à ces parties, respectivement. Puis chaque partie est traitée comme une entité indépendante. Les maximums d'absorption obtenus par l'application des conditions de Kuhn sont en accord avec les valeurs expérimentales. Ces maximums ont été corrigés par rapport aux perturbations dues aux groupes fonctionnels substitués avec une électronégativité plus importante que celle du carbone. Les forces d'oscillateurs correspondant aux maximums d'absorption ont aussi été calculés.
    Abstract: Die Lage und Intensität der Absorptionsbanden einer Reihe von Chalconfarben sind mit der FEMO-Methode berechnet worden. Die drei bis vier Absorptionsmaxima dieser Moleküle wurden unter der Annahme berechnet, dass das Molekül aus zwei Teilen besteht. Die hypothetische Spaltung befindet sich in der C=O-Bindung, so dass die zwei Teilen 6 und 8 π-Elektronen, bzw., enthalten. Jeder Teil wird dann als eine unabhängige Einheit behandelt. Die mit den Kuhn'schen Bedingungen erhaltenen Absorptionsmaxima stimmen mit den Experimentalwerten überein. Die von den substituierten Funktionalgruppen mit höherer Elektronegativität als Kohlenstoff herrührenden Störungsenergiekorrektionen zu den Absorptionsmaxima sind auch berechnet worden. Die diesen maxima entsprechenden Oszillatorstärken sind weiter berechnet worden.
    Notes: The position and intensity of the absorption bands of a number of chalcone dyes have been calculated on the basis of the free-electron molecular-orbital (FEMO) theory. The three to four absorption maxima of the chalcones are calculated by assuming the molecule to consist of two parts. The hypothetical cleavage is affected at the site of C=O bond such that first and second part of the molecule contains six and eight π electrons, respectively. Each part is then treated as an independent entity and the absorption maxima obtained by the application of joint and continuity condition of Kuhn are in agreement with the experimental values. The perturbation energy correction due to the substituted functional groups with higher electronegativity than carbon have also been made in the absorption maxima. The oscillator strengths corresponding to the values of the absorption maxima have been obtained as well.
    Additional Material: 3 Ill.
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    International Journal of Quantum Chemistry 16 (1979), S. 1321-1335 
    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
    Description / Table of Contents: Les expressions explicites des éléments de matrice des générateurs du groupe unitaire entre des configurations à N électrons, antisymétriques géminalement et adaptées au spin, données comme des éléments de matrice par rapport aux fonctions de spin de certaines permutations orbitalaires, sont obtenues à l'aide des techniques diagrammatiques de la théorie à N corps indépendante du temps. Il est démontré aussi comment ce procédé peut ětre combiné avec les méthodes graphiques des algèbres de spin pour obtenir des expressions explicites des facteurs de spin, quand un schéma de couplage a été choisi. Cette méthode-ci fournit des expressions explicites pour les permutations orbitalaires qui définissent les facteurs de spin. Si préférable la détermination explicite des permutations “line-up” peut ětre évitée, parce qu'elles sont contenues implicitement dans les diagrammes orbitalaires. Ceci explique aussi la raison de choisir des fonctions de spin géminalement antisymétriques, si on demande un formalisme simple.
    Abstract: Die expliziten Ausdrücke für die Matrixelemente der Generatoren der unitären Gruppe ziwschen geminal-antisymmetrischen spinanggepassten N-Elektronenkonfigurationen, gegeben als Spinfunktionenmatrixelemente gewisser Orbitalpermutationen, werden mittels der Diagrammverfahren der zeitunabhängigen Vielteilchentheorie abgeleitet. Es wird auch gezeigt, wie dieses Verfahren mit der in den Spinalgebren benutzten graphischen Methoden kombiniert werden kann, um explizite Ausdrücke der Spinfaktoren zu erhalten, wenn ein bestimmtes Kopplungsschema gewählt worden ist. Diese Methode gibt explizite Ausdrücke für die Orbitalpermutationen, die die Spinfaktoren definieren. Wenn gewünscht kann die explizite Bestimmung der “line-up”-Permutationen in diesem Verfahren vermieden werden, da diese implizit in den Orbitaldiagrammen enthalten sind. Dieses erklärt auch warum die geminal-antisymmetrischen Spinfunktionen benutzt werden müssen, wenn einen einfachen Formalismus gewünscht wird.
    Notes: The explicit expressions for the matrix elements of unitary group generators between geminally antisymmetric spin-adapted N-electron configurations in terms of the orbital occupancies and spin factors, given as spin function matrix elements of appropriate orbital permutations, are derived using the many-body time-independent diagrammatic techniques. It is also shown how this approach can be conveniently combined with graphical methods of spin algebras to obtain explicit expressions for the spin factors, once a definite coupling scheme is chosen. This method yields explicit expressions for the orbital permutations defining the spin factors. However, if desired, the explicit determination of line-up permutations can be avoided in this approach, since they are implicitly contained in the orbital diagrams. It also clearly indicates why the geminally antisymmetric spin functions have to be used when a simple formalism is desired.
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    International Journal of Quantum Chemistry 15 (1979), S. 131-131 
    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
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The atomic dipole approximation has been employed to calculate the energies of electrostatic interaction between adenine and various pyrimidine derivatives. Minima of the interaction energy for various planar configurations were determined. Inclusion of the “monopole-dipole” and “dipole-dipole” terms in the multipole expansion improves considerably the agreement with experimental data. The effect of sulfur substitution has been investigated in detail. Formation of N—H…S hydrogen bonds is less favorable than of N—H…O bonds, due largely to the lower atomic dipole of the sulfur atom resulting from the shift of the π-electron charge toward the neighboring carbon. The results are relevant to the interactions of thiouracils in nucleic acids.
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  • 74
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    International Journal of Quantum Chemistry 15 (1979), S. 389-401 
    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 found that ordinary STOs fall off too fast in the atomic region in many cases. A new type of basis set, which is more adaptable to the rather different requirements of the various atomic orbitals in an atom, is developed. The suggested functional form χ(r) = Nrn-1 exp{-α[(βr + 1)1/2 - 1]} contains the STOs as a limiting case. Calculations on a series of atoms from H to Zn show that the new basis gives better results than STOs for equal basis set size. The necessary integrals do not present any problem to evaluate.
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    International Journal of Quantum Chemistry 15 (1979), S. 403-410 
    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 valence spectrum of CoO has been calculated using the CoO610- cluster, stabilized by an electrostatic field, as a model of bulk CoO. The wave functions were generated using basis sets of better than double-zeta quality. SCF wave functions were obtained for the ground state and for the first ionized state of the cluster. Limited CI calculations were performed using these orbital sets. The lowest states of the ion correspond to the main lines in the spectrum, while higher states can give rise to high-energy satellites to the main lines. The relative intensities of these satellites were estimated in the case of high-energy incident photons.
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    International Journal of Quantum Chemistry 15 (1979), S. 411-421 
    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: Pseudospectra from Gaussian basis set calculations within a frozen-core approximation have been used in a moment analysis to obtain Tchebychev profiles for the photoabsorption process in the valence shell of Ne. The profiles show good agreement with cross sections obtained in equivalent calculations using numerical atomic wave functions and continuum orbitals, particularly when the dipole-velocity form is employed. Variation of the basis sets shows that it is possible to obtain meaningful photoabsorption profiles using 13-15 virtual orbitals to describe the outgoing electron.
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    International Journal of Quantum Chemistry 15 (1979), S. 445-445 
    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
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  • 78
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    International Journal of Quantum Chemistry 15 (1979) 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    International Journal of Quantum Chemistry 15 (1979), S. 423-443 
    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 expectation energy values EK, Vee, Vnn, Ven, and ET have been calculated for H2 and the C1, C2, and C3 hydrocarbons using a (9,5) basis set and the experimental geometries. Treating the theoretical reaction heat, ΔET, as the resultant of the nuclear repulsion term, ΔVnn, and the net electron energy term, ΔEelec = ΔEK + ΔVee + ΔVen, the contribution of inner and outer shell electron energies to ΔEelec, and hence to ΔET, has been calculated for a large number of hydrocarbon reactions by evaluating the Coulson-Neilson energies ηi, where Σηi = Eelec. For the vast majority of reactions, 67/84, the change in inner shell electron energy, (Σηi)inner, accounts for more than 10% of ΔEelec, in many cases being as high as 20-35%. Furthermore, in addition to these cases in which the change in inner shell electron energy serves to augment (significantly) the change in outer shell electron energy, there are other cases in which the change in inner shell electron energy either exceeds in magnitude the change in outer shell energy, or is even opposite in sign, indicative of inner and outer shell electrons acting contrariwise. Inner shell electron energies contribute to the reaction heats because they are structure dependent, like the more familiar orbital energies ε, but the dependence is of a different kind.
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 15 (1979), S. 463-479 
    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 coupled-cluster variational-like direct approach to the calculation of ionization and electron attachment energies and of excitation energies is applied to several π-electron model systems, using the PPP Hamiltonian with various parametrizations. A simple approximation, which represents the triexcited clusters in terms of disconnected W1T2 terms, is employed. All the necessary diagrams for both excitation energy and ionization potential (electron affinity) calculations are given in the compact Hugenholtz nonoriented form. The results of the calculations for benzene, trans-butadiene, all-trans-hexatriene, and fulvene are compared with the corresponding full CI results, and the conclusions about the validity and efficiency of this approach are drawn.
    Additional Material: 6 Ill.
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  • 81
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    International Journal of Quantum Chemistry 15 (1979), S. 481-489 
    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 paper reports the study of a possible mechanism of Ca+2 activation of prostaglandin PGF2α on the basis of molecular-orbital and conformation-energy calculations. The electronic charges on various atoms of the molecule have been evaluated from the available crystallographic data by the extended Hückel theory (EHT). Conformation energies were calculated for intrinsic torsional rotations around the C11—C12, C7—C8, and C14—C15 bonds. The minimum energy conformation was found to differ from the crystallographic conformation by 9.3 kcal/mol. Some additional local energy minima are also reported within this range. The calculation of the long-range interchain interaction energy between the α and ω chains shows variation with conformation. The binding site for the Ca+2 ion has been estimated on the basis of the molecular electrostatic potentials. Such a binding site was found near the carboxyl group, which agrees with the current chemical thinking. Changes in the electronic charge distribution due to Ca+2 complexation were studied by EHT method using the supramolecular approach. Calcium complexation decreases the conformation energy by 2-3 kcal/mol and has a small effect on the interchain interaction energy.
    Additional Material: 4 Ill.
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  • 82
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    International Journal of Quantum Chemistry 15 (1979), S. 499-510 
    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 ab initio SCF LCAO-MO method is used to compute the main electronic properties of a purine nucleoside, adenosine, in two specific conformational arrangements (3′-endo conformation of the ribose, gt orientation of the extracyclic CH2OH group, anti orientation of the base with respect to the sugar and 3′-endo conformation of the ribose, gg orientation of the extra-cyclic CH2OH group, syn orientation of the base with respect to the sugar). The results are compared with those performed for the isolated component fragments, adenine and 3′-endo riboses.
    Additional Material: 7 Ill.
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  • 83
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    International Journal of Quantum Chemistry 15 (1979), S. 611-643 
    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 definition is given for the spin-tensorial components of a p-electron density matrix for arbitrary p. Certain of these are defined to be standard components, and it is shown that all others can be obtained from them by linear combinations of permutations. When the density matrix is reduced, the standard components either map into standard components of the fewer-electron density matrix or into the origin. One- and two-electron density matrices are treated in greater detail. Reducing bases are given for the spaces in which the spatial coefficients of the spin components are elements. For spin eigenstates traces of all components are determined, and the π = 1 parts of all components are determined in terms of two independent components, which are themselves determined by the two-electron charge density matrix. Geometric consequences are investigated.
    Additional Material: 15 Tab.
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  • 84
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    International Journal of Quantum Chemistry 15 (1979), S. 663-682 
    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 Desargues-Levi graph represents important chemical transformations: (1) isomerization routes for some carbonium ion rearrangements, (2) isomerization of trigonal bipyramidal structures, and (3) some pseudorotations of octahedral complexes. The symmetry properties of this graph have not been fully investigated in the past. Using the concept of the smallest binary code, all permutations which form the symmetry operations in the graph are registered. The resulting symmetry group can be represented as the direct product of S5 (the full symmetric permutation group on five objects) and Ci (the inversion in the center). There are 14 classes belonging to the following partitionings: 120(1), 1826(1), 1428(1), 1236(1), 123262(1), 2 63(2), 2244(2), 210(3), 54(1), and 102(1). The total of 240 symmetry operations are distributed among the above 14 classes as follows: 1, 10, 15, 20, 20, 20, 20, 30, 30, 15, 10, 1, 24, and 24, respectively. Since partitioning cannot uniquely characterize a class, it is suggested that the distance between vertices in a cycle be introduced as an additional parameter to discriminate among classes having identical partitioning. Also, a suggestion to a generalization of the Mulliken notation for irreducible representations of the point molecular groups valid for more versatile symmetry groups of graphs is indicated.
    Additional Material: 5 Ill.
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  • 85
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    International Journal of Quantum Chemistry 15 (1979), S. 683-692 
    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: Third-order diagrammatic perturbation theory provides a simple and accurate description of the electronic structure of atoms and molecules beyond that afforded by independent electron models. The largest corrections to such treatments, the fourth-order terms, are presented and discussed. All of the diagrams, which arise when the closed-shell Hartree-Fock function is utilized as a reference function, are given through fourth order.
    Additional Material: 6 Ill.
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  • 86
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    International Journal of Quantum Chemistry 15 (1979), S. 693-700 
    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 new iterative scheme for a simultaneous calculation of the m lowest eigenvalues together with their eigenvectors has been derived for a real symmetric matrix. The scheme is based on the orthogonal gradient method and is easy to use for large-scale configuration-interaction calculations of electronic wave functions. A variant of the scheme deals with nonorthogonal basis functions, which are particularly simple in the case of the bonded-function method of Boys.
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  • 87
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    International Journal of Quantum Chemistry 15 (1979), S. 713-715 
    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 Longuet-Higgins group is used to obtain an alternative formulation of a criterion for optical activity of nonrigid molecules recently given by Frei and Günthard.
    Additional Material: 2 Ill.
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  • 88
    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 physical interpretation of intermolecular interactions is usually based on the well-known multipole expansion of the inverse of the interparticle distance. The interaction energy is then interpreted as a sum of terms arising from the interaction of various multipole moments of both systems. It is supposed that the interaction energy calculated via the truncated multipole expansion generally depends on the choice of local coordinate systems through the coordinate dependence of the multipole moments. In this paper we prove that each term of the multipole expansion given in the form ∑k = 1 Ck/Rk is invariant with respect to identical translations and arbitrary rotations of the local coordinate systems. The invariant form of the convergence criterion of the multipole expansion is given and discussed.
    Additional Material: 1 Ill.
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  • 89
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    International Journal of Quantum Chemistry 15 (1979), S. 717-729 
    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: Power moments for all of the reduced hydrogenic Green's functions have been computed. These moments have the same form as the corresponding moments of the free-particle Green's functions. Green's functions of the second kind are defined, and uses for these objects in model potential theory and the theory of many-body Green's functions are pointed out. In the case of the ground state of the hydrogenic atom, the Green's function of the second kind has been given.
    Additional Material: 1 Ill.
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  • 90
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    International Journal of Quantum Chemistry 15 (1979), S. 745-750 
    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: Different kinds of improved uncoupled Hartree-Fock methods are proposed for the calculation of second-order perturbation energies. Using these methods inequalities are derived for the error of the uncoupled procedure with geometric approximation.
    Additional Material: 1 Tab.
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  • 91
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    International Journal of Quantum Chemistry 15 (1979), S. 731-744 
    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 use of multiple scattering techniques combined with a statistical exchange potential for the description of the electronic structure of atoms, molecules, and solids depends strongly on the geometry (muffin tin, overlapping spheres, or cellular potentials) and on the form of the electron gas exchange. In this work we compare only the effects of using different geometries. For that purpose we have done calculations on the hydrogen molecular ion and Hartree-type calculations on the hydrogen molecule so that no exchange effects are involved. To avoid arbitrariness in the choice of the sphere sizes we propose a nonempirical criterion that consists of using the set of radii that will minimize the charge in the interstitial region of the molecule or cluster. Some arguments are given to justify this criterion, and to clarify the differences between cellular, overlapping spheres, and muffin-tin geometries. It is found that the cellular geometry gives a very good description around the equilibrium internuclear distance. However, for most systems of interest, exchange will be present. Thus, we have done, for comparison, the calculation on H2 using Xαβ statistical exchange. It is shown through this calculation that some of the correlation energy may be obtained by redefining the molecular orbitals in terms of non-paired-spins spatial orbitals, this formulation being required to obtain the correct free-atom limit.
    Additional Material: 6 Ill.
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  • 92
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    International Journal of Quantum Chemistry 15 (1979), S. 751-767 
    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 theory of the open-and closed-shell restricted Hartree-Fock method is given a unitary group formulation. Both extremum and stability conditions are employed, the former leading to a generalized Brillouin theorem.
    Additional Material: 2 Tab.
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  • 93
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    International Journal of Quantum Chemistry 15 (1979), S. 769-782 
    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 improved interaction potential has been devised for diatomic alkali halide molecules. This potential, in addition to similar attraction terms as in the Rittner potential, includes a new exponential for the short-range repulsion. The constant m in the exponential is seen to be well expressible in terms of the parameters of the Rittner potential. The new potential is also correlated with different properties, as for example, effective charges, effective radii, effective principal quantum numbers, etc., of the combining ions. Various spectroscopic constants, viz., the ionic dissociation energy Di, the vibrational-rotational coupling constant αe, the vibrational anharmonicity constant ωexe, as well as two second-order spectroscopic constants γe and βe have been calculated for this and for the Rittner potential. From comparisons between these two potentials, the new one has been observed better than the other.
    Additional Material: 3 Tab.
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  • 94
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    International Journal of Quantum Chemistry 16 (1979), S. 111-117 
    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 circular dichroism of molecules, which are large compared to the wavelength of light, is considered. Explicit expressions are obtained for the circular dichroism and absorption of an exciton dimer and of a free particle on a helix. The dimensions are described for which the dipole approximation for the optical properties fails.
    Additional Material: 1 Ill.
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  • 95
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    International Journal of Quantum Chemistry 16 (1979), S. 133-152 
    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 analysis of modern physical mechanisms of electron transfer in proteins is given. The tunnel electron transfer and donor-acceptor electron transfer through conducting states of a protein chain are discussed in detail. The expressions for the values of the electron resonance interaction and the formulas for probabilities of electron transfer between vibronic levels of donor and acceptor states in the presence of “transverse” and “longitudinal” relaxation are given.
    Additional Material: 6 Ill.
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  • 96
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    International Journal of Quantum Chemistry 16 (1979), S. 119-132 
    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 expressions for the polymer absorption band hypochromism and oscillator strength are studied in frames of the first-order perturbation theory. The physically justified approximations for a polymer hypochromism calculation are indicated. The uniform interpretation of the effect origin is given independently on the approximation used. In frames of the perturbation theory the DNA hypochromism formula is obtained, from which the known experimental dependences of hypochromism on chain length and polymer helicity degree follows directly. The analytic expression of the DNA hypochromism dependence on AT pairs content is obtained. It is established that in most cases for natural DNA the nucleotide sequence does not influence in practice the value of the hypochromic effect.
    Additional Material: 1 Ill.
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  • 97
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    International Journal of Quantum Chemistry 16 (1979), S. 261-264 
    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 geometrical parameters of the ammonia molecule in the lowest-lying triplet state have been estimated by means of the SCF method and by making an extrapolation to take into account electron correlation effects. The planar configuration has been obtained as the most probable geometrical arrangement (3 A2″).
    Additional Material: 2 Tab.
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  • 98
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    International Journal of Quantum Chemistry 16 (1979), S. 265-272 
    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 new method for the calculation of electrostatic isopotential maps, based on completely transferable bond orbitals, is proposed. According to the simple form of the potential term the amount of computational work is proportional to the first power of the number of valence electrons. Slater-type atomic orbitals are used to construct the bond orbitals, thus all integrals can be calculated explicitly. The subtilisin charge-relay system is studied as an example. It is found, in agreement with the results of Beppu and Yomosa, that the two protons transfer in a stepwise manner.
    Additional Material: 3 Ill.
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  • 99
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    International Journal of Quantum Chemistry 16 (1979), S. 273-275 
    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 report here a summary of a limited CI calculation carried out on the C∞v and D∞h electronically excited states of bifluoride ion. This species is interesting as the prototype of a hydrogen-bonded system. It is determined that the lowest-lying excited states of the system are dissociative and/or autoionizing.
    Additional Material: 1 Ill.
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  • 100
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    International Journal of Quantum Chemistry 16 (1979), S. 293-298 
    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 role of some amino acids and metal ions in the catalytic activity of carbonic anhydrase (carbonate dehydratase EC 4.2.1.1) has been investigated. The additional stabilization of the transition state complex was used as the qualitative measure of the effect of molecular surrounding on CO2 hydration reaction calculated within the approximate CNDO/2 approach. The effect of the molecular environment has been simulated by inclusion into the SCF LCAO MO Hamiltonian, a term representing the interaction with a set of point charges and atomic dipoles centered on experimentally determined position of Zn2+ ion and all atoms of histidine 94, 96, 119 and threonine 199, 200 (or histidine 200 in the case of carbonic anhydrase B). The possible molecular mechanism of CO2 hydration inside the active site has been also discussed.
    Additional Material: 1 Ill.
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