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  • Inorganic Chemistry  (757)
  • ASTROPHYSICS  (566)
  • Computational Chemistry and Molecular Modeling  (333)
  • 1980-1984  (1,656)
  • 1925-1929
  • 1980  (1,656)
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  • 1980-1984  (1,656)
  • 1925-1929
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  • 1
    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 results of calculations of the transition energies and polarization in nucleotide bases performed by the CNDO/S CI method are compared with experimental data for long-wavelength and vacuumabsorption bands. The calculations and the analysis of experimental data testify to the existence of n - π* transitions in the first absorption bands of the bases. The study of double-stranded polynucleotides and DNA hypochromism based on the theoretical electronic characteristics of the bases and perturbation theory is performed. The role of stacking and complementary interactions within the hypochromic effect is cleared up. Two mechanisms for the shift of the fluorescence band maximum are investigated: two-proton transfer along H bonds and excimer formation. The study of H-bond potential curves shows the disadvantage of two-proton phototautomerism in the nucleotide base pairs in contrast to model systems. The possibility of excimer state formation in stacked homo- and heterodimers of nucleotide bases is shown within the extended-Hückel treatment. The nature of excimer minimum for the excited-state potential curve is analyzed.
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  • 2
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 17 (1980), S. 531-547 
    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 time-dependent Hartree-Fock (TDHF) equations are derived up to the second order when the system is perturbed by a monochromatic plane wave. The solutions of the equations are subjected to the orthonormalization conditions satisfied by the orbitals. In the equations, these conditions are expressed by the appearing of coefficients λjkn,ε playing the part of Lagrangian multipliers. Relations between the coefficients λjkn,ε are established. These relations are equivalent to the above-mentioned orthonormalization conditions. This equivalence enables us to substitute for the solution of an integrodifferential equation system subject to constraint conditions, that of a free system. The TDHF equations obtained determine the first- and second-order orbital perturbations, which no doubt verify the orthonormalization conditions. These orbitals can be used in the calculation, up to second order, of different nonlinear optical effects.
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  • 3
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 17 (1980), S. 596-596 
    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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  • 4
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    International Journal of Quantum Chemistry 17 (1980), S. 619-629 
    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: Pair correlation in the ground state of the Li isoelectronic sequence is studied through four approximate wave functions which incorporate inter- and intrashell pair correlation. Of these functions, two possess symmetry appropriate to a three-electron system, while two do not. The functions are not variational functions in the usual sense. They are instead fixed linear combinations of products of orbitals and pair functions for the appropriate states of two-electron atoms. They are considered here as zero-order approximations to the exact wave functions, and the corresponding zero-order Hamiltonians are obtained. The simplest of these functions is improved by the introduction of a screening parameter for the “outer” electron. This latter function is found to be a satisfactory compromise between accuracy and simplicity and is proposed for study via higher-order perturbation theory.
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  • 5
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    International Journal of Quantum Chemistry 17 (1980), S. 599-608 
    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 calculations of various expectation energies have been made for the reactant and product species in six reactions that involve only small linear molecules. The reactions include fission by hydrogen, addition of hydrogen, exchange of triply bonded atoms, fluorination, and oxygen atom transfer. The change in total electronic energy is not invariably the result of changes in inner shell energy and outer shell σ- and π-electron energies simply augmenting each other, but in several cases there is a complex interplay of opposing effects. This approach gives a different insight into the energetic aspects of changes in bonding from that derived from the concept of shared electron pairs in σ and π bonds together with lone pairs in valence shells. Changes in π-electron energy are shown to be important in a reaction in which neither reactant nor product molecules contain π bonds in the usual chemical sense. While in a reaction in which there is a complete change in the nature of the triple bonds, and hence the π bonding, the change in π-electron energy makes a smaller contribution than either the change in inner shell or the outer shell σ-electron energies.
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  • 6
    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 use a previously proposed variation-perturbation method to calculate the electric polarizabilities and the electric dipole moment at equilibrium nuclear distance of the BH molecule. We obtain 3.56 × 10-24 cm3 for the perpendicular polarizability αxx and 3.22 × 10-24 cm3 for the parallel polarizability αzz. Our result for the electric dipole moment μ0 is 1.734 debye units; there is no reliable experimental result to compare it with.
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  • 7
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    International Journal of Quantum Chemistry 17 (1980), S. 549-586 
    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 resonance energy of conjugated benzenoid systems is expressed as contributions arising from independent conjugated circuits. The scheme has been applied to numerous very large conjugated systems. In many cases, it was possible to find regularities in the increments for the resonance energy within a family of benzenoid systems as the number of benzene rings is increased.
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  • 8
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    International Journal of Quantum Chemistry 17 (1980), S. 595-595 
    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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  • 9
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    International Journal of Quantum Chemistry 17 (1980), S. 609-618 
    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 previously given iterative procedure to improve wave functions is analyzed. Its relationship with other well-known approximation methods is investigated. Hypervirial operators depending on a real parameter are proposed and their connection with the employment of an infinite number of hypervirial relations is analyzed. A way to use formulas that are valid for exact eigenfunctions in the case of approximate functions is presented. Formal results are applied to the harmonic oscillator and hydrogen atom models in order to show their practical utilization.
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  • 10
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    International Journal of Quantum Chemistry 17 (1980), S. 651-671 
    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 MO calculations, using both minimal (STO-3G) and extended (Roos-Siegbahn) basis sets are reported for the systems methanethiol-imidazole, methanethiol-imidazole-formaldehyde, and methanethiol-imidazole-formamide, which, together with a point-change representation of a long α-helix, form models for the active site of papain. It is shown that the large electric field exerted by the helix in the active-site region is responsible for the presence of the essential residues Cys 25 and His 159 in the form of an ion pair RS- ··· ImH+, which is crucial for a recently proposed mechanism for the catalytic action of the enzyme. Also, an explanation is given for the anomalies in measured pK values for these residues. Detailed studies on the (sub)systems show that minimal basis sets lack the flexibility necessary for describing the type of proton transfer involved. We conclude that α-helices are essential parts of enzymes and that they play a significant role in the catalytic process.
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  • 11
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    International Journal of Quantum Chemistry 17 (1980), S. 679-687 
    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 generalization of optimized diatomics-in-molecules method that provides an accurate treatment of overlap integrals is presented. The possibilities of the method to reproduce potential surfaces of the 4B2, 2B2, and 2A1 states of the H3 molecule are investigated. It is shown that satisfactory results can be achieved only for a single state under consideration, but not for the three states simultaneously.
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  • 12
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    International Journal of Quantum Chemistry 17 (1980), S. 719-724 
    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 calculations carried out on the planar cluster CuCl42- suggest that the strong satellites at the high-binding energy side of inner-shell ESCA lines of Cu are due to charge relaxations in the σ-bonding orbitals which mix with Cu 3d. The satellite state with the largest intensity may be described as a one-electron excitation Cu 3d → Cl 3p.
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  • 13
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    International Journal of Quantum Chemistry 17 (1980), S. 975-982 
    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 modification of the overlap approximation for triplet pair correlation energies is presented. The modification allows the use of either the canonical absolute overlap or the minimum absolute overlap. When applied to the b 3∑u+ state of H2, this approximation reproduces the observed correlation energy to within 0.0002 hartree (or ±3%) for all internuclear distances from 1.3 bohr to infinity.
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  • 14
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    International Journal of Quantum Chemistry 17 (1980), S. 1039-1041 
    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
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    International Journal of Quantum Chemistry 17 (1980), S. 1042-1042 
    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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  • 16
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    International Journal of Quantum Chemistry 17 (1980), S. 1069-1074 
    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 rǒle de la nonadditivité pour l'énergie d'interaction entre trois molécules de LiH a été examiné dans le cadre de la méthode ab-initio-SCF. La partie nonadditive de l'énergie d'interaction est plus importante pour une structure cyclique que pour un trimère linéaire; elle est stabilisante dans les deux cas. La valeur du rapport entre les termes à deux et à trois corps pour des points différents sur l'hypersurface de l'énergie est discutée.
    Abstract: Die Bedeutung der Nichtadditivität in der Wechselwirkungsenergie zwischen drei LiH-Molekülen ist im Rahmen des ab-initio-SCF-Verfahrens untersucht worden. Der nichtadditive Teil der Wechselwirkungsenergie ist wichtiger für eine zyklische Struktur als in einem linearen Trimer; er ist in beiden Fallen stabilisierend. Das Verhältnis zwischen Zwei- und Dreikörperglieder für verschiedene Punkte auf der Energiehyperfläche wird diskutiert.
    Notes: The role of nonadditivity of the interaction energy between three LiH molecules was investigated within the SCF ab initio framework. The nonadditive part of the interaction energy is more important in the case of a cyclic structure than in a linear trimer, and is stabilizing in both cases. The value of the ratio of three-body and two-body terms for different points on the energy hypersurface is discussed.
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  • 17
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    International Journal of Quantum Chemistry 17 (1980), S. 1099-1109 
    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: Des développments gaussiens complètement optimisés des fonctions hydrogénoïdes de type 1s, 2pz, 3dxy, et 4fxyz ont été pratiquement reproduits par une construction spéciale des paramètres variationnels. L'utilité des fonctions génératrices utilisées est discutée brièvement.
    Abstract: Vollständig optimisierte Gaussentwicklungen wasserstoffähnlicher Funktionen von Typ 1s, 2pz, 3dxy, und 4fxyz sind mittels eines speziellen Verfahrens für die bestimmung der Variationsparameter praktisch reproduziert worden. Der Nutzen der angewandten erzeugenden Funktionen wird kurz diskutiert.
    Notes: Fully optimized lengthy Gaussian expansions of hydrogenic 1s and 2pz functions have been practically reproduced by generating the variational parameters by means of suitably chosen functions involving only few parameters. Hydrogenic 3dxy and 4fxyz functions have been approximated in a similar way. The usefulness of such generating functions is briefly discussed.
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  • 18
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    International Journal of Quantum Chemistry 17 (1980), S. 1125-1141 
    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: L'approximation HF présentée dans la partie I a été testée par rapport à plusieurs propriétés moléculaires. Trois niveaux d'aproximation différents a, b, et c sont considérés. Des résultats satisfaisants - en comparaison avec des calculs HF “exacts” - sont obtenus avec la base STO-3G et le niveau a. A ce niveau-ci l'erreur dans l'énergie de liaison est de 0.001-0.025 a.u. pour toutes les molécules considérées, qui contiennent jusqu'à six atomes de la première ligne comme par exemple le cyclopentanone (C5OH8). L'erreur dans les énergies de réaction traitées ici est d'environ 4 kcal/mol (l'erreur maximale est de 9 kcal/mol). Les énergies orbitalaires, les moments dipolaires, les charges brutes, les géométries d'équilibres et les barrières de rotation interne sont bien reproduits par notre méthode à tous les trois niveaux.
    Abstract: Die HF-Näherungsmethode, welche im Teil I vorgestellt wurde, wird an einigen Moleküleigenschaften getestet. Drei Näherungsstufen a, b, und c werden untersucht. Zufriedenstellende Ergebnisse - verglichen mit entsprechenden “exakten” HF-Rechnungen - erhält man mit der STO-3G Basis und der Näherungsstufe a. Bei dieser Näherung ist der Fehler in der Bindungsenergie 0.001-0.025 a.u. für alle untersuchten Moleküle, welche bis zu 6 Atome der 1. Reihe enthalten, wie z.B. Cyclopentanon (C5OH8). Der Fehler in den hier behandelten Reaktionsenergien beträgt etwa 4 kcal/mol (der maximale Fehler beträgt 9 kcal/mol). Orbitalenergien, Diplolmomente, Bruttoladungen, Gleichgewichtsgeometrien und Rotationsbarrieren werden durch die Näherungsmethode bei allen Näherungsstufen gut wiedergegeben.
    Notes: The HF approximation method that was outlined in Paper I is tested with respect to several molecular properties. Three different levels of approximation a, b, and c are considered. Satisfactory results - compared to corresponding “exact” HF calculations - are obtained with the STO-3G basis and the approximation level a. At this level the error in the binding energy is 0.001-0.025 a.u. for all considered molecules which contain up to six first-row atoms as, e.g., cyclopentanone (C5OH8). The error in the reaction energies considered here is about 4 kcal/mol (the maximal error is 9 kcal/mol). Orbital energies, dipole moments, gross charges, equilibrium geometries, and barriers to internal rotation are well reproduced by the approximation method at all three levels.
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  • 19
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    International Journal of Quantum Chemistry 17 (1980), S. 995-1006 
    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 influence of side-chain disorder on the electronic structure of proteins has been investigated in the case of polypeptides containing two or three different amino acid residues. It has been found that due to the different potentials of different side-chain groups, the original valence and conduction bands of the homopolypeptides are split into narrow bands. The comparison of the densities of electronic states in simple homopolypeptides and in composite polymers shows that new forbidden regions in the energy spectrum of proteins may develop. The consequences of these effects for the semiconductive properties of proteins are discussed.
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  • 20
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    International Journal of Quantum Chemistry 17 (1980), S. 1031-1037 
    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 a previous paper, a scheme of integral approximation was proposed, in which a large number of two-electron integrals containing a certain kind of orbital pairs, i.e., weakly related pairs, can be neglected. A new criterion for partitioning orbital pairs into two groups, i.e., strongly and weakly related pairs, is introduced in order to allow for neglect of more integrals without sacrificing the accuracy of a computation. Test calculations on the BH3—C2H4 complex show that by the use of the new version, results of roughly the same accuracy as was obtained by the old version is obtained by retaining 80% of the integrals used in the old version. This kind of saving is more significant for larger molecules. For example, in a calculation on Cu-porphine with 203 CGTO'S, the revised version will require about 2.0 × 106 integrals, while the original version will require about 4.5 × 106. And these two approximate calculations are expected to give the results of roughly the same accuracy.
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  • 21
    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: Cooperative phenomena may be involved in the biological effects of magnetic fields (H), since its effects on isolated atoms or ions, at room temperature, are very weak. It is suggested that interactions at the social level can considerably increase the efficiency of H in orienting the displacements of animals. This effect is discussed with a simple mathematical model inspired on superparamagnetism. In case of very weak interactions of H with isolated animals, it suggests that orientation could only be made visible through cooperativity at the social level. These results are generalized to other physical stimuli and effects, leading to the concept of cooperative sensory response, i.e., a group response to an external physical agent even when its effect on isolated members of the group is undetectable.
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  • 22
    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: En déterminant les paramètres des jeux de base dans des environnements moléculaires par d'autres critères que l'énergie totale, il est démontré qu'une généralisation de la base pour des fragments moléculaires peut ětre obtenue, dans laquelle les propriétés géométriques et celles de la structure électronique sont prédites considérablement mieux qu'avec des bases de taille semblable. Comme premier pas dans le développement d'une série de bases avec une flexibilité et une précision de plus en plus prononcée, on a construit plusieurs jeux de base de type simple zéta avec une contraction gaussienne pour chaque orbitale de base. Les meilleures de ces bases donnent des propriétés géométriques et électroniques pour une série de molécules organiques avec'une précision meilleure que celle obtenue par la base correspondante de type STO-2G et semblable dans la plupart des cas à STO-3G. En outre cette base peut ětre utilisée soit avec des gaussiennes cartésiennes, soit avec des gaussiennes sphériques flottantes.
    Abstract: Durch eine Bestimmung von Basissatzparametern in Molekülumgebungen mit anderen Kriterien als der Gesamtenergie wird gezeigt, dass eine Verallgemeinerung des Molekülfragmentsbasissatzes erhalten werden kann, mit welchem geometrischen und Elektronstruktureigenschaften beträchtlich besser als mit anderen Basissätzen ähnlicher Grösse vorhergesagt werden können. Als erster Schritt in der Entwicklung einer Reihe von Basissätzen mit sukzessiv grösserer Flexibilität und Genauigkeit werden mehrere Basissätze von Einzelzetatyp durch eine Gauss'sche Kontraktion für jedes Basisorbital konstruiert. Mit den besten dieser Basissätze werden geometrische und elektronische Eigen-schaften für eine Reihe von organischen Molekülen mit besserer Genauigkeit als dem entsprechenden STO-2G Basissatz und in vielen Fallen ähnlich dem STO-2G Satz erhalten. Weiter wird gezeiget, dass dieser Basissatz mit sowohl Cartesischen als fliesseden sphärischen Gaussfunktionen vereinbar ist.
    Notes: By determining basis set parameters in molecular environments using other criteria than total energy, it is shown that a generalization of the molecular fragment basis can be obtained in which calculated geometric and electronic structural properties are predicted substantially better than with other basis sets of similar size. As a first step in the development of a series of basis sets having successively greater flexibility and accuracy, several single-zeta basis sets are created, using a two-Gaussian contraction for each basis orbital. The best of these basis sets produced calculated geometric and electronic properties for a series of molecules that model a wide variety of organic molecules that are of better accuracy than the corresponding STO-2G basis, and similar in most cases to STO-3G. In addition, the basis set is shown to be applicable in either a Cartesian Gaussian basis or a floating spherical Gaussian basis.
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  • 23
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    International Journal of Quantum Chemistry 17 (1980), S. 1111-1123 
    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: Une méthode est proposée, qui réduit considérablement le travail numérique dans un calcul HF en réduisant le nombre d'intégrales à deux électrons qui doivent ětre calculées. Les procédés suivants sont utilisés: (i) la densité électronique est approximée par un petit nombre de fonctions pour la partie de Coulomb de la matrice HF; (ii) cette densité approchée est modifiée pour améliorer son potentiel; (iii) dans la partie d'échange une fonction de base χ est remplacée par une fonction \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \chi $\end{document} avec un nombre moindre de lobes gaussines; (iv) l'érreur causée par ce remplacement-ci est réduite par une modification des densités \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \chi _i \tilde \chi _j $\end{document} dans les intégrales d'échange. Le temps de calcul pour les intégrales est réduit par un facteur 6 pour des molécules contenant cinq atomes de la première ligne comme par exemple CF4, si l'on utilise une base 7S/3P contractée à (5, 1, 1/3). Le temps augmente approximativement avec n3, si n est le nombre de lobes gaussiens.
    Abstract: Eine Methode wird vorgeschlagen, welche den numerischen Aufwand von Hartree-Foch Rechnungen dadurch verringert, indem die Zahl der zu berechnenden Zweielektronenintegrale reduziert wird. Dabei werden folgende Konzepte verwendet: (i) Zur Berechnung des Coulombanteils der HF Matrix wird die Elektronendichte durch wenig Funktionen approximiert. (ii) Die approximierte Dichte wird so modifiziert, daß ihr Potential verbessert wird. (iii) Zur Berechnung des Austauschanteils wird eine Basisfunktion χ durch eine Funktion \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \chi $\end{document} ersetzt, welche weniger Gauss-lobes enthält. (iv) Der dadurch hervorgerufene Fehler wird durch eine Änderung der in den Austauschintegralen vorkommenden Dichten \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \chi _i \tilde \chi _j $\end{document} reduziert. Für Moleküle, welche 5 Atome der 1. Reihe enthalten, wie z.B. CF4, wird die Rechenzeit für den Integralteil um den Faktor 6 reduziert, wenn eine 7S/3P Basis kontrahiert zu (5, 1, 1/3) verwendet wird. Die Integralzeit nimmt etwa mit der 3. Potenz der Zahl der Gauss-lobes zu.
    Notes: A method is proposed that reduces the computational effort of HF calculations considerably by reducing the number of two-electron integrals that have to be calculated. The following concepts are used: (i) approximation of the electron density by only few functions for the Coulomb part of the HF matrix; (ii) modification of this approximate density, to improve its Coulomb field; (iii) in the exchange part, a basis function χ is replaced by a function \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \chi $\end{document} consisting of fewer Gaussian lobes; (iv) the error caused by this replacement is reduced by a modification of the densities \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \chi _i \tilde \chi _j $\end{document} in the exchange integrals. The computation time of the integral part is reduced by a factor 6 for molecules containing five first-row atoms as, e.g., CF4, if one uses a 7S/3P basis set contracted to (5, 1, 1/3). The integral time increases roughly with n3, if n is the number of Gaussian lobes.
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    International Journal of Quantum Chemistry 18 (1980) 
    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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    International Journal of Quantum Chemistry 18 (1980), S. 3-9 
    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 hierarchy of necessary conditions that an exact density matrix of a pure state or an ensemble has to satisfy is derived, namely the hermiticity of certain operators F(k). For k = 1 this reduces to the well-known Hartree-Fock condition. It is then shown that the kth set of conditions is equivalent to stationarity of the energy with respect to unitary k-particle transformations. k-Particle generalizations of Hartree-Fock theory are then discussed both in the spirit of k-particle pseudoeigenvalue equations and in the framework of a Newton-Raphson-type constructive scheme.
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    International Journal of Quantum Chemistry 18 (1980), S. 275-280 
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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 binding energy spectra for the valence orbitals of hydrogen chloride have been obtained using the binary (e,2e) method at 1200 eV. The strength of the innermost valence orbital (4σ) is severely split among several ion states in the energy range 25 to 41 eV. The measured cross sections are compared with results of calculations using contracted Gaussian basis sets of double-zeta quality, and with a one-particle Green's function calculation.
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    International Journal of Quantum Chemistry 18 (1980), S. 307-310 
    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 charge exchange process in the intervalence (mixed-valence) system is interpreted in terms of the nonstationary state mechanism which is a well-known approach for rationalizing the molecular tautomerism process. The two kinds of processes are viewed in a close analogy in the sense that both involve a pair of near-degenerate levels in a double-well potential. However, a comparison is made between the two cases to demonstrate that an electron moves not only faster but also farther in distance than a nucleus does.
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    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: Traditionally, the calculation of the vibrational spectra of molecules involves at one point or another a numerical differentiation procedure. Such a method has some serious drawbacks both in efficiency and in accuracy. In this paper, an alternative method based on linear response theory is presented. The second derivative of the ground-state energy is expressed in terms of the electron density response matrix by means of perturbation theory. The unperturbed wave functions are obtained from the Hartree-Fock equation. First-order perturbation theory applied to this equation leads to the Hartree-Fock linear response. As an illustration of this method the vibrational frequency of a H2 molecule is calculated. The result is 1.348 × 1014 Hz as compared to the experimental value of 1.319 × 1014 Hz. This method is also applicable in the calculation of the phonon dispersion curves of solids.
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    International Journal of Quantum Chemistry 18 (1980), S. 393-396 
    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 brief account of a quantum chemistry literature data base (QCLDB) is described, which contains the key information of about 2000 papers of ab initio calculations of atoms and molecules published in 1977-1979. The QCLDB is stored in a computer and can be sorted and rearranged into author and substance indices. Selection of the items for each paper in a computer-readable data base is discussed.
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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: Metal chelates [(C2H2X2)2M]n with ligating atoms X = NH, O, S and central atoms M = Be2+, Mg2+, Ni2+, Zn2+ (n = 0, ± 2), and M = Li+, Cu+ (n = ± 1, -3), have been studied in our Laboratory for some years by ab initio calculations. In this article it is shown that certain features of the complexes are the same for all the different metals in our series. These features include a drastic reduction of the energy gap between unoccupied and occupied orbitals, when electrons are added to the positively charged complexes. This change of the energy gap is shown to be an effect of the ligand dimer [(C2H2X2)2]n. But this dimer can only exist when a positive ion, e.g., a metal ion, forms a bridge between the two monomers. The reduced energy gap implies a strong bathochromic shift of the electronic spectrum and low electrical resistivity.
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    International Journal of Quantum Chemistry 18 (1980), S. 457-462 
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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 photoisomerization of imine compounds is studied in terms of an ab initio MO CI calculation. The potential curves of the syn-anti isomerization via the rotation and the inversion are examined for benzaldimine. It is suggested that the photoisomerization is initiated through the rotation around the C—N bond in both singlet and triplet states. The ease of the photoisomerization is found to be determined by both the conformation of phenyl ring in the ground state and the energy difference of vertically excited states between two isomers.
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    International Journal of Quantum Chemistry 18 (1980), S. 493-500 
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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: To aid in designing new therapeutic iron chelating agents, the mechanism of iron binding to prototypic heterocyclic carboxaldehyde thiosemicarbazones has been studied. Based on molecular orbital and spectroscopic studies, iron (II) is found to bind in a covalent manner, while iron(III) seems to interact ionically. However, with both iron(II) and iron(III), chelate formation is dependent on charge interaction between the metal and the coordinating atoms of the ligand.
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    International Journal of Quantum Chemistry 18 (1980), S. 515-519 
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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 potential-energy curves for the movement of proton along the hydrogen-bond direction were calculated for the parent and cations produced from the β- decay of pyridine-pyrrole labeled by tritium (3H) or carbon-14(14C). For all cations the double minimum potential is predicted to be formed, and the activation energy for the proton transfer from one well to the other is about 10.0 kcal/mol, which is much lower than that in the (NH2—H—NH2)+ ion. A positional effect of nuclear transformation is scarcely expected in 3H β- decay, whereas a slight positional effect may be expected in 14C β- decay.
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    International Journal of Quantum Chemistry 18 (1980), S. 533-537 
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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: A theoretical study has been made on the translational or “rattling” motion of homonuclear diatomic molecules encaged in β-quinol clathrates. By the use of an adjustable parameter for the van der Waals radius, experimental results have been explained fairly well.
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    International Journal of Quantum Chemistry 18 (1980), S. 501-508 
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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 problem of the existence of a prostaglandin (PG) receptor is still controversial, but it seems to be clear that the main action of the PGs concerns the interface of the cellular membrane (which has a predominantly lipid character) and the extracellular liquid (which mainly consists of water). Also especially in the case of the exogenous PGs, the transport of these substances in the organism in influenced by the hydrophilic-hydrophobic properties of the reactive molecules. These properties can be estimated by MO studies using a solvation model and a semiempirical method of calculation. This paper is concerned with the molecules of PGA1 and PGE1. MO studies were performed for these molecules with the CNDO/SW method in order to calculate ionization potentials, dipole moments, and molecular polarizabilities. With these computed molecular properties, the electrostatic and van der Waals interactions with water and octanol molecules are evaluated and compared within the framework of the original model. This study allows the differentiation of the hydrophilic-hydrophobic character of the PGs investigated and the comparison of the results with experimental data.
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    International Journal of Quantum Chemistry 18 (1980), S. 189-191 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
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    Topics: Chemistry and Pharmacology
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    International Journal of Quantum Chemistry 18 (1980), S. 607-613 
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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 range in ordinary space of a defect in a solid, polymer, or a large molecule is an important parameter in many physical and chemical situations like, e.g., substitutional and interstitial impurities in ionic crystals, deep and shallow energy levels in semiconductors, core holes in systems studied by photoelectron spectroscopy, and hydrogen in metals. Both the electronic structure and the lattice of the host molecule or solid are normally influenced by the defect, and it is desirable to treat, as far as possible, these two aspects together. An explicit procedure for investigating the degree of localization is proposed that is based on the direct calculation of Wannier functions and partitioning technique.
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    International Journal of Quantum Chemistry 18 (1980), S. 619-623 
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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: Exciton transfers in the two-dimensional and spin-canted antiferromagnet (C2H5NH3)2MnCl4 were studied by investigating the absorption spectra 6A1g → 4T2g(4D) of Mn2+. A magnon side band (exciton-magnon simultaneous excitation) which has an anomalous shape with the cutoffs at the low-energy as well as the high-energy sides was observed. This anomalous shape could be reproduced in calculation as magnon side band, considering both the intersublattice and intrasublattice exciton transfers. From the analysis of this band shape, the magnitudes of the intersublattice and intrasublattice exciton transfers are estimated to be 10.2 and 6.8 cm-1, respectively. In the case of simple antiferromagnets without spin canting, the intersublattice exciton transfer process is forbidden because of the spin angular momentum. However, in the case of (C2H5NH3)2MnCl4, the prohibition of the intersublattice exciton transfer is removed by the canted-spin arrangement.
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    International Journal of Quantum Chemistry 18 (1980), S. 695-708 
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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: A new method has been proposed for calculating the Gaussian matrix elements of the interaction operator represented by an arbitrary degree of interelectron distance X12ρ. The method is based on the expansion of two-electron integrals as the sum of one-electron integrals which in turn admit compact operator representation in terms of confluent hypergeometric functions. The generating differential operator has been shown to be related to the modified Hermitian polynomials. The standard structure of the special functions encountered in this approach is useful in studying the analytical behavior of the integrals and makes it possible to obtain for these integrals recurrence relations, direct algebraic expressions in the forms of finite sum of confluent hypergeometric functions, integral representations, and asymptotic properties. Unlike the usual methods based on integral transformation of the interaction operator, the proposed approach has a wider field of application, and in addition, leads to compact and convenient analytical expressions. The idea of using differential properties of integrals to simplify the integrand structure gives the proposed approach a certain resemblance to that suggested by Boys but not developed in detail in his pioneer work.
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    International Journal of Quantum Chemistry 18 (1980), S. 775-782 
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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: Properties of Hückel parameters are investigated by using a mapping concept. The mapping is constructed by means of the Linderberg relation. No efforts are made to get a numerically correct description of the Hückel parameters.
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    International Journal of Quantum Chemistry 18 (1980), S. 797-810 
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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 performance of the MINDO/3 method has been evaluated in simple heteroatomic molecules that are representative of several important biological systems. Molecular geometries are accurate to within 0.04 Å for bond lengths, and 3° for most bond angles. Dipole moments and charge distributions are estimated satisfactorily, and ionization potentials are predicted to an accuracy of 0.5 eV. The method is less accurate in estimating the ionization of some upper level σ orbitals. The overall evaluation shows that MINDO/3 provides a good description of the geometries and electronic properties of the molecules studied. The results of MINDO/3 calculations in several other chemical systems are also reviewed.
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    International Journal of Quantum Chemistry 18 (1980), S. 841-866 
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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: Spin functions that are compatible with orbital ordering and geminal antisymmetry conditions are investigated. It is shown that two widely used classes of spin functions, namely, the spin-bonded functions and Yamanouchi-Kotani (or, equivalently, Gelfand-Tsetlin) functions possess these properties. The relationship of the latter with Young-Yamanouchi spin functions is also outlined using graphical techniques of spin algebras. These techniques are also used to rederive the Hamiltonian matrix elements between spin-bonded functions and to show the relationship among the various schemes used in this case.
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    International Journal of Quantum Chemistry 18 (1980), S. 1109-1131 
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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: A theorem is presented that characterizes approximate states and truncated operator manifolds associated with self-consistent approximate propagators. This theorem establishes a natural relationship between Hermiticity, stationarity, nonredundance and completeness of operator manifolds, model time evolution, and the vacuum condition. For the case of the polarization propagator we describe algorithms by which we can construct states and manifolds that satisfy this theorem and the vacuum condition.
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    International Journal of Quantum Chemistry 18 (1980), S. 1165-1173 
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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: An exchange-correlation potential model to be used in connection with the multiple scattering method is presented. Retaining the main advantages of the multiple scattering method with the Xα potential, particularly its low computational requirements, this new formalism does not require any adjustable parameter. Test calculations on the NiF64- system are reported and compared with experimental and ab initio results.
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    International Journal of Quantum Chemistry 18 (1980), S. 1405-1413 
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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: Semiempirical MO calculations of the self-consistent charge and configuration (SCCC) method are reported for the acetonitrile-metal solvated species (CH3CN)xMn+, where M = Be2+ and Mg2+. Comparison of the delocalization energies for various chemical structures x = 1, 2, 3, 4, 6 leads to an expectation of a tetrahedral structure for the Be2+ species and an octahedral structure for the Mg2+ species. The electronic nature of the donor-acceptor interaction is also discussed.
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    International Journal of Quantum Chemistry 18 (1980), S. 1465-1472 
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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: Analytical formulas are given for the orbital contributions to two-electron properties such as 〈r12n〉, with n = -2, -1, 1, 2, 3, and 4, for atomic systems in which orbitals are expanded as linear combinations of Gaussian functions. Numerical values for all possible contributions in the atoms Li to Ne have been calculated at the Hartree-Fock level. These quantities are compared and discussed to show what kind of information can be obtained from such quantities. The influence of the basis set size has also been considered.
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    International Journal of Quantum Chemistry 18 (1980), S. 1485-1487 
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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 18 (1980), S. 709-713 
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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: Using a modified form of Sharma's method for the expansion of a Slater-type orbital in spherical harmonics about a displaced center, a general expression for the overlap integral between two orbitals is derived that is equivalent to that given by Sharma. By use of a simple kind of “computer algebra” this expression is developed here into a formula that is equivalent to earlier known ones and may have computational advantages when the generated formula coefficients are stored. This method is capable of extension to more complicated integrals.
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    International Journal of Quantum Chemistry 18 (1980), S. 891-904 
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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: This paper reports some theoretical studies of PGA1 using conformational and molecular orbital techniques. The conformation energy (CE) calculations, using empirical potential-energy functions, for intrinsic torsional rotations around C12—C13 (θ), C7—C8 (Ψ), and C14—C15 (φ) show a number of energy minima. The relative value of the CE for these minima ranges from 4.09 to 8.01 kcal/mol. An additional rotation around C4—C5 (χ) giving “twist” to the carboxyl chains lowers the CE value by 2-3 kcal/mol and a conformation with CE value 2.39 kcal/mol less than crystallographic one is obtained. The interchain interaction energy showed changes with conformations. No significant change in the interchain interaction energy was observed due to “twist” in the carboxyl chain. The isopotential mapping study demonstrated the probable ionic binding site near the carboxyl and the ring (O9) oxygens. Conformational and molecular orbital results are discussed in the light of the reduced abortifacient potency of PGA1 with respect to PGF2α and the possible role of Ca2+ ions in this action.
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    International Journal of Quantum Chemistry 18 (1980), S. 1157-1163 
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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 transformation of two-electron integrals from an atomic orbital basis to a symmetry orbital basis is a straightforward procedure, but becomes a time-consuming process when the system has high symmetry. In the conventional transformation algorithm, the number of multiplications is proportional to the fifth power of the basis size. To reduce the computer time, a new transformation algorithm is proposed. In this method, the number of multiplications for the transformation is proportional to the fourth power of the number of atomic orbitals in an equivalent orbital group. A new transformation program has been completed and tested against the conventional n5 method. The present method may be regarded as extension of Almlöf's method to any molecular point group. The program cuts the CPU time for the transformation to one-third in calculations for C4H8 and NiF6. This reduction is quite significant for large systems having high symmetry.
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    Notes: Double-helical polynucleotide conformations, poly(dA)·poly(dT), poly(d(A-T))·poly(d(T-A))·poly(dG)·poly(dC), and poly(d(G-C))·poly(d(C-G)) are analyzed by the atom-atom potential method. The energy optimization is carried out in the space of eight independent geometric parameters using analytical procedures for the constraints, taking into account the flexibility of the β-D-deoxyribose rings. At the first stage, the full screening of atomic partial charges was assumed. The structures of the calculated B and the A forms of DNA are characterized by low energy and absence of short contacts; the dihedral angles are near the average values in the monomers. With the typical energy difference of 3-5 kcal/mol nucleotide pairs in all cases, the B form is more preferable as compared to the A form. At the final step the effect of the Coulomb term is evaluated for poly(dA)·poly(dT) using various values of the effective dielectric constant (ε = 28, 24, 20, 18, 14, 12, 10, 8, 6, 4, and 1). If ε ≤24, the energy optimization leads A to B. We discuss the stereochemical details of the intermediate conformations on the A-B path and hypothesize the nature of stability of the A and the B forms and the mechanism of the A-B transition.
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    International Journal of Quantum Chemistry 17 (1980), S. 377-398 
    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 energy of (H2O)3 has been calculated for 29 geometrical configurations of the trimer using the SCF LCAO MO method and extended as well as minimal basis sets of Gaussian functions. For two configurations two intermediate basis sets have also been tested. The results show the nonadditive component of the interaction energy to be small. They also indicate that fairly reliable results for the trimer can be obtained using minimal basis sets and the counterpoise method to eliminate the basis set superposition error. The nonadditive contribution to the interaction energy is shown to be mainly due to the long-range induction interaction.
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  • 53
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    International Journal of Quantum Chemistry 17 (1980), S. 459-465 
    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: We present two identities that permit a simplification of some lengthy derivations with spherical harmonics. Examples of their use are given.
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
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    Topics: Chemistry and Pharmacology
    Notes: The practical value of a wave function derives from its ability to estimate or predict the chemical and physical properties of the electronic structure which it describes. Reliability is defined as a property to be evaluated on the basis of (i) the magnitude of the difference between the measured and calculated values of the observable together with (ii) the sign of the difference, (ii) the number and nature of observables correctly estimated, and (iv) the number and type of electronic structures that are correctly estimated. Systematic statistical comparison implies the existence of both internally consistent sets of wave functions for homologous series of molecules and their corresponding experimental values together with reliable error estimates. The most complete data base currently available for comparison is the spectroscopic constants for the first and second row diatomic hydrides. Utilizing appropriate statistical comparison techniques, four approximations (CEPA, PNO-CI, GTO-SCF, and STO-SCF) are compared among themselves and against experimentally measured values. The CEPA approximation yields differences from experiment that approximate a normal error distribution, while the other approximations show systematic departures from experiment. Two values, ωe and ωeχe, for SH exhibit differences large enough to cast doubt upon the calculated value, the experimental value, or both.
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    International Journal of Quantum Chemistry 17 (1980), S. 415-428 
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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 Fock generating function method is employed for the separation of spin variables into two-particle transition density matrices. Their spatial components introduced by McWeeny are expressed through Schrödinger's coordinate wave functions. Some nontrivial integral relations between these components and the charge and transition spin density matrices are obtained. The interrelation between the mentioned spatial components and the Matsen-Poshusta symmetrized density matrices of an arbitrary spatial function is found.
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    International Journal of Quantum Chemistry 17 (1980) 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
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    International Journal of Quantum Chemistry 17 (1980), S. 725-736 
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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 SCF theory of multiplet monodeterminantal states is described from a comprehensive viewpoint. In this context, the formalism and derived theorems are developed, as well as the description of a SCF closed-shell-like structure, namely the hypermultiplet. Numerical applications are discussed taking as a model the H2O molecule and its first positive ion. Wave functions of double ζ-quality, with computed molecular properties of 16 states are given.
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    International Journal of Quantum Chemistry 17 (1980), S. 759-774 
    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 Coulomb correlation hole distribution function has been computed with respect to various reference centers in the HCN molecule, using standard SCF+CI type wave functions. The extent to which statistical correlation between unlike-spin electrons is introduced into an SCF wave function through the inclusion of configuration interaction has been assessed by an examination of the range and depth of such holes, and compared with the behavior of analogous Fermi distribution functions. Our results show that the range of Fermi correlation is consistently longer than that of the corresponding Coulomb correlation.
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
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    Topics: Chemistry and Pharmacology
    Notes: The four-center nonplanar electron repulsion integrals over 1s Slater-type atomic orbitals are considered by a numerical Fourier-transform method. It is shown that the highly oscillating integrand appearing in the Fourier inversion formula could be successfully treated by using Tchebyscheff quadrature. The resulting formulas are thoroughly discussed with particular emphasis on their numerical features and convergence properties. It follows that the aforementioned integrals may be calculated with a good accuracy with a moderate amount of computing time.
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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: This work describes the investigation of the space organization of DNA compact forms and DNA-protein complexes by the small-angle x-ray scattering method. A plane texture was disclosed in dehydrated DNP films. Compact DNA particles formed in the presence of poly(ethylene glycol) reveal ordered structures having a periodicity of 84 Å. Various morphological forms of crystals of CTA-DNA were used to obtain small-angle x-ray patterns of the single-crystal type.
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    International Journal of Quantum Chemistry 17 (1980), S. 833-844 
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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: Within the framework of the nonrelativistic Schrödinger equation, the Coulomb field case is used to assess the range of validity of the Thomas-Fermi statistical theory of atoms. In particular, attention is focused on (a) the x-ray scattering factor, which is the Fourier transform of the electron density; and (b) the momentum density. In each case the predictions of the statistical theory are compared with the exact results for the Coulomb potential. These can conveniently be calculated using earlier work of Fock. Some assessment is also made of the accuracy of the statistical approximation for the kinetic energy density; this is of interest in connection with the density functional approach. Finally, some brief comments are made on the relation between the self-consistent Thomas-Fermi method and the Hartree theory for atoms.
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    International Journal of Quantum Chemistry 17 (1980), S. 915-930 
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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 theory of vibrations of a composite particle when vibrational amplitudes are not constrained to be small according to the Eckart conditions is developed using the methods of differential topology. A global classical Hamiltonian appropriate for this system is given, and for the case of the molecular vibration-rotation problem, it is transformed into a global quantum Hamiltonian operator. It is shown that the zeroth-order term in the global Hamiltonian operator is identical to the Wilson-Howard Hamiltonian; higher-order terms are shown to give successively better approximations to the large amplitude problem. Generalized Eckart conditions are derived for the global classical Hamiltonian; the quantum equivalent of these conditions along with the quantum equivalent of the Eckart conditions are given. The spectrum of the global Hamiltonian operator is discussed and it is shown that the calculation of the vibration-rotation energy states of the system reduces to the same straight-forward procedure, the solution of a secular determinant, as was carried out for the Wilson-Howard Hamiltonian at a later time by Nielsen.
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    International Journal of Quantum Chemistry 17 (1980), S. 955-968 
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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: Molecular polarizabilities are computed using ab initio SCF wave functions and second-order perturbation theory with special attention given to the use of a shifted denominator. Rather small basis sets are used, in order to obtain reasonable values at a reduced cost. Results are presented for H2, CO, H2O, C2H4, OCS, C6H6, Cl2, Br2, I2.
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    International Journal of Quantum Chemistry 17 (1980), S. 983-993 
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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: A mathematical model to relate order and rotational motion in lipid hydrocarbon chains in biological membranes is proposed. Schrödinger equations with suitable potential functions for C—C rotations in lipid hydrocarbons chains have been solved to obtain wave functions characterizing these motions. For a free chain a threefold potential function has been assumed. The effect of collisions between neighboring chains in a membrane is considered by including another term (δ function) in the potential function.
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    International Journal of Quantum Chemistry 17 (1980) 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
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    Topics: Chemistry and Pharmacology
    Notes: The individual absorption spectra of various ionic and tautomeric species of some derivatives of nucleic-acid components have been determined by computer handling of the summary spectra of these compounds measured at different pH values. These individual spectra have been decomposed into separate bands represented by log-normal curves and corresponding to different electronic transitions. Using the parameter system calculated earlier for the molecules of the vitamin B6 family, the calculation of the electronic spectra and electronic structure of various ionic and tautomeric species of the molecules studied have been carried out in the π-electron approximation. These properties have also been calculated by the all-valence electronic method CNDOS. The calculated results correlate well with both approximations and with our experimental spectral data. The localization of the molecular electronic excitation studied on the transition to the S1 and T1 states is considered in connection with the reactivity in these states.
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    International Journal of Quantum Chemistry 17 (1980), S. 895-905 
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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: A partitioning of the molecular Hamiltonian into the occupied and virtual orbital spaces and their orthogonal complement is introduced and used to develop a perturbation expansion of the exact ground-state energy relative to the Hartree-Fock energy computed using an incomplete basis set. The leading perturbation corrections to pair energies due to using the incomplete basis set are considered in detail. Summations of certain classes of pair contributions are discussed and a resummed correction is obtained.
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    International Journal of Quantum Chemistry 17 (1980), S. 931-942 
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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 energy levels and perturbation expansions for the expectation values of arbitrary powers of position for a perturbed Morse oscillator are obtained by application of the hypervirial and Hellmann-Feynman theorems, solely in terms of the unperturbed energy. We obtain expressions for the first-order corrections for (1 - e-aq )m for 4 ≤ m ≤ 8 and the expressions to second and third order for the quartic perturbation. A numerical application to the CO molecule is made.
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    International Journal of Quantum Chemistry 17 (1980), S. 969-974 
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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: An ab initio Hartree-Fock-Slater procedure was applied to the calculation of the electronic structure of polysulfanes, H2Sn (n = 1-4) and the ions HSn- and Sn2-. Charge densities, overlap populations, and deprotonation energies are calculated; the latter appear well correlated with the first and second acidity constants.
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    International Journal of Quantum Chemistry 17 (1980), S. 1143-1166 
    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 prouvons par des méthodes géométriques élémentaires et dans le cadre de l'approximation de Born-Oppenheimer, que quand les noyaux d'une molécule sont dissociés en amas séparés dans l'espace, les énergies moléculaires discrètes tendent vers la somme des énergies des sous-systèmes isolés. Nos méthodes montrent aussi que les projections spectrales associées au spectre moléculaire discret tendent asymptotiquement vers des sommes directes de projections spectrales convenables pour les sous-systèmes isolés. Ces résultats s'appliquent à n'importe quel système de particules qui interagissent par des potentiels de paire s'annulant asymptotiquement. Nous prouvons que le développement en 1/R pour des courbes de potentiel moléculaires discrètes est asymptotique quand R → ∞, et nous discutons le comportement des coefficients de ce développement pour l'état fondamental de H2+.Wir beweisen durch elementare geometrische Methoden und im Rahmen der Born-Oppenheimer-Näherung, dass, wenn die Kerne eines Moleküls in räumlich separierten Clusters dissoziiert werden, die diskreten Molekülenergien Summen der Energien der isolierten Untersysteme zustreben. Unsere Methoden zeigen auch, dass die mit dem diskreten Molekularspektrum assoziierten Spektralprojektionen asymptotisch direkten Summen von geeigneten Spektralprojektionen für die isolierten Untersysteme zustreben. Diese Ergebnisse sind für irgendein System von Teilchen gültig, die durch asymptotisch verschwindende Paarpotentiale wechselwirken. Wir beweisen, dass die Entwicklung in 1/R für diskrete molekulare Potentialkurven wenn R → ∞ asymptotisch ist, und wir diskutieren das Verhalten der Koeffizienten dieser Entwicklung für den Grundzustand von H2+.
    Notes: We prove by elementary geometric methods and within the Born-Oppenheimer approximation that as the nuclei of a molecule are dissociated into spatially separated clusters, the discrete molecular energies approach sums of the energies of isolated subsystems. Our methods also show that the spectral projections associated with the discrete molecular spectrum asymptotically approach direct sums of suitable spectral projections for the isolated subsystems. These results apply to any system of particles interacting by asymptotically vanishing pair potentials. We prove that the 1/R expansion for discrete molecular potential curves is asymptotic as R → ∞, and we discuss the behavior of the coefficients of the 1/R expansion for the ground state of H2+.
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    International Journal of Quantum Chemistry 17 (1980), S. 1221-1227 
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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 17 (1980), S. 1191-1200 
    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 le present article on considére un nouveau modèle pour le transport moléculaire à travers des membranes, qui a été introduit antérieurement par Hosur. Dans ce modèle, la membrane est assimilée à une barrière de potentiel, en déterminant le flux matériel à travers de la měme partant dès le coefficient de transmission de la barrière, en supposant l'existence d'une différence d'énergie parmi les molécules qui appartiennent à les fluides d'une et d'autre cǒté de la membrane. On obtient ainsi, une expression pour le flux dans le cas de pétites différences d'énergie, qui a été particularisée au cas ou la difference d'énergie est due à un gradient de température, un gradient de concentration ou à tous les deux gradients agissant ensemble. Dans tous les cas, sous certaines conditions, on obtient des equations qui sont formellement identiques à celles obtenues par la thermodynamique des processus irréversibles.
    Abstract: In vorliegendem Artikel wird ein von Hosur eingeführtes Modell für Transport durch Membranen untersucht. In diesem Modell wird die Membran mit einer Potentialschwelle assimiliert, und der Materialfluss durch die Membran wird vom Transmissionskoeffizient der Schwelle bestimmt, wobei es wird angenommen, dass ein Energieunterschied unter den Molekülen an den beiden Seiten der Membran existiert. Für den Fall wo dieser Energieunterschied klein ist wird eine Gleichung für den Transport erhalten. Diese wird spezialisiert zu den Fallen wo der Energieunterschied von einem Temperatur-oder Konzentrationsgradient oder beiden zusammen verursacht wird. In allen Fallen werden-mit gewissen Begrenzungen-Gleichungen erhalten, die mit denen der Thermodynamik irreversibler Prozesse formal identisch sind.
    Notes: In the present paper a new model for the transport through membranes, introduced previously by Hosur, is considered. In this model, the membrane is assimilated to a potential barrier, and the material flow through the membrane is determined from the transmission coefficient of the barrier, assuming the existence of an energy difference among the molecules placed at both sides of the membrane. An equation for the transport, in the case of small energy differences, is obtained, which is particularized to the cases that the energy difference is caused by a temperature gradient, a concentration gradient, and both gradients acting together. In all cases, under certain limitations, formally identical equations to those of the thermodynamics of irreversible processes are obtained.
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    Topics: Chemistry and Pharmacology
    Notes: The nonrigid molecule symmetry group for methylamine is determined as a set of permutations and permutation inversions for two situations. In the first case the internal rotations of the methyl group and NH2 group are included and the second case the transition of a hydrogen atom from the methyl group to NH2 group is also included. In both cases the energy level splitting of the rigid model of the methylamine is found, nuclear statistical weights of the split levels are calculated, and sections rules for the allowed dipole transitions are given.
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    International Journal of Quantum Chemistry 18 (1980), S. 57-63 
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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: In this paper, a fresh attempt has been made to discuss dual-symmetry groups by which the supra-antarafacial cycloaddition and the chelatropic reactions can be correctly described, as a direct consequence of which the corresponding energy correlation diagrams are successfully constructed. Furthermore, the energy correlation diagrams of sigmatropic reactions are also established by the use of another kind of single-symmetry group.
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    International Journal of Quantum Chemistry 18 (1980), S. 79-87 
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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: A comparison between the construction of symmetry-correlation diagrams and the perturbation method for studying chemical reactions is carried out. The perturbation method consists of decomposing the system Hamiltonian H into a sum, H = H0 + H′. Various symmetry correlation schemes appearing in the literature may be explained by the nonuniqueness of the decomposition scheme. All symmetry selection rules may be viewed as the varieties. By examining the symmetry-correlation diagrams, processes under investigation may be called “forbidden” or “allowed,” depending on the topological feature. Of particular importance is the topology associated with the “avoided crossing.” By making the comparison, we can establish the correspondence of the two methods and conclude that the perturbation order furnishes the origin of the “forbiddenness” of a process.
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    International Journal of Quantum Chemistry 18 (1980), S. 107-116 
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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: Ab initio molecular-orbital theory has been used to study the 1,3-sigmatropic hydrogen rearrangements: propene → propene, formic acic → formic acid, and vinyl alcohol → acetaldehyde. Fully optimized structures of stable molecules and transition states have been determined using gradient procedures and the 4-31G basis set. Improved energies have been obtained using a variety of techniques with basis sets up to the size of double-ζ plus polarization (DZP) and electron correlation up to the CEPA/DZP level. Although both polarization functions and electron correlation lead to a lowering of the calculated barriers, the values remain substantial for all three rearrangements.
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    International Journal of Quantum Chemistry 17 (1980), S. 1179-1184 
    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: Un simple potentiel analytique avec deux paramètres et ajusté pour reproduire les niveaux expérimentaux est utilisé pour engendrer des fonctions d'onde pour l'état fondamental et quelques états excités de l'atome de lithium. Avec ces fonctions d'onde, l'approximation de Born et le schema de couplage LS de Russell-Saunders nous calculons les forces d'oscillateur optiques pour un nombre d'excitations à partier de l'état fondamental 1s22s(2S1/2). Les résultats sont comparés aux valeurs expérimentales et à ceux obtenus d'autres calculs.
    Abstract: Ein einfaches analytisches Zweiparameterpotential, angepasst um die experimentellen Energieniveaus zu reproduzieren, wird für die Erzeugung von Wellenfunktionen für den Grundzustand und einige angeregten Zustände des Lithiumatoms angewandt. Mit diesen Wellenfunktionen, der Bornapproximation und dem Russell-Saunders'schen LS-Kopplungsschema werden die optischen Oszillatorenstärken für verschiedene Anregungen vom Grundzustand 1s22s(2S1/2) berechnet. Die Resultate werden mit Experimentalwerten und Resultaten anderer Berechnungen verglichen.
    Notes: A simple two-parameter analytic potential adjusted so as to reproduce the experimental energy levels is used to generate wave functions for the ground and excited states of the lithium atom. Using these wave functions in conjunction with the Born approximation and the Russell-Saunders LS-coupling scheme, we calculate the optical oscillator strengths for various excitations from the 1s22s(2S1/2) ground state. The results are compared to experiment and other calculations.
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    International Journal of Quantum Chemistry 18 (1980), S. 193-197 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present the results obtained within the CNDO/2 method for the diamagnetic susceptibilities of a series of conjugated molecules including benzene, fulvene, pyridine, pyrrole, and furan. The calculations have been carried out, according to Bley's method, in the framework of coupled Hartree-Fock perturbation theory, using gauge invariant atomic orbitals and the London approximation. The two usual CNDO parametrizations, due respectively to Pople, Santry, and Segal and to Del Bene and Jaffe, did not enable one to obtain the principal susceptibilities of the molecules under consideration. We investigated the effect of the CNDO parametrizations on the different contributions to the susceptibility, and gave a first improvement to Bley's method, which permits the calculation of the mean susceptibility of conjugated molecules with less than 9% error.
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  • 79
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    International Journal of Quantum Chemistry 18 (1980), S. 199-204 
    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 s-p separation model CNDO-MO method has been introduced and developed for both the open- and closed-shell systems since 1975. This method has two chief advantages over most of the other CNDO methods. (1) The ns and np bases of the same atom may be considered independent to infer different bonding behavior. (2) Pariser-Parr and Nishimoto-Mataga approximations are applied to the Coulombic repulsion integrals, which not only simplifies the calculation and saves computer time but also gives reliable computational results. A series of nitrogen fluoride molecules such as NF, NF2, NF3, cis-N2F2, trans-N2F2, and N2F2 have been selected for this MO calculation. In each case, both ionization potential and dipole moment were calculated. The results are closer to the observed values than those reported in other works.
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  • 80
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    International Journal of Quantum Chemistry 18 (1980), S. 227-235 
    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: Calculations of molecular-orbital energies and x-ray photoelectron spectra have been carried out for the third-row oxyanions, transition-metal oxyanions, SiO2 and TiO2, by the discrete variational-Xα cluster method. The calculated orbital energies are consistent with those determined from the XPS experiments. Theoretical XPS line shapes with Gaussian are generally in good agreement with the observed spectra. However, underestimation has been found for the photopeak intensities in the low-binding-energy region of TiO2. The discrepancy is partially attributed to the use of inaccurate photoionization cross-section for the Ti3d orbital.
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  • 81
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    International Journal of Quantum Chemistry 18 (1980), S. 243-250 
    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 general way for drawing the state correlation diagram and seeking the reaction path is presented. If a high-symmetry reacting system is given, its least-motion path that maintains the symmetry is primarily examined. For a given state, it is judged whether the least-motion path is symmetry allowed or forbidden. If allowed, it is called the direct process. If forbidden, the symmetry imposed on the system should be relaxed, resulting in the mixing of MO's. Then, the energy barrier of the avoided crossing for some excited states is removed and the possible reaction path is found. After this procedure, the symmetry-allowed paths may be sought by the geometry optimization with a suitable wave function. By the use of such a procedure, the dissociation of diazomethane and (3H-)diazirine is found to proceed via the Cs and C2 symmetries.
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  • 82
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    International Journal of Quantum Chemistry 18 (1980), S. 281-285 
    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 differential cross-sections for high-energy electrons scattered from water have been measured over a wide range of momentum transfers. The effect of chemical binding was seen from the comparison between the experiment and the calculation for an independent-atom model. The ab initio calculation using SCF MO was carried out with respect to the elastic scattering. It was in a good agreement with the experiment and thus a reliable electron distribution in water was obtained.
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  • 83
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    International Journal of Quantum Chemistry 18 (1980), S. 293-300 
    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: Effects of incident photon field coherence on resonant light scattering have been investigated. In order to obtain the scattering intensity and the photon counting rate, an expression for the reduced density matrix for the scattered field has been derived. The expression involves the first-order correlation function of the incident field. The relation between the line shape of the scattered light and the bandwidth of the incident field has been clarified. Model calculations of the photon counting rate have been performed in the case of an incident field without first-order coherence. In our treatment, the transverse and longitudinal relaxation constants have been taken into account by using the impact approximation.
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  • 84
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    International Journal of Quantum Chemistry 18 (1980), S. 317-321 
    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 vibrational properties of a quantum system are determined by the density response matrix. In linear response theory this quantity is connected to the polarizability matrix, which can be expressed in terms of a double summation over one-particle energies and wave functions. In has been shown that this expression is not useful in the calculation of vibrational frequencies because of the very slow convergence of the summation in terms of the unoccupied states. In this paper, a different but equivalent expression is presented using a continued fraction. The resulting expression contains only one summation over the occupied states, solving in this way all the problems connected with the sum-over-states expression of the polarizability matrix. The elimination of all the unoccupied states via the use of the moment formula turns out to be a crucial step in the solution of the problem of the first-principles calculation of the vibrational spectra of molecules and solids.
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  • 85
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    International Journal of Quantum Chemistry 18 (1980), S. 323-329 
    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: Normal-mode vibrational frequencies were obtained for uracil and 4-hydroxyuracil with the MINDO/3 SCF method. MINDO/3 vibrational frequencies and the moments of inertia for STO-3G optimized geometries yielded a ΔST0 for U ⇄ U* of 1.06 e.u./mol by standard statistical thermodynamic equations. ΔGT0 is then 6.29 kcal/mol in the gas phase for U ⇄ U*. The reaction field continuum model of solvent effect lowers ΔGT0 to 5.3 kcal/mol in aqueous solution. The tautomeric equilibrium constant in solution is then 1.3 × 10-4, in good agreement with experimental values.
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  • 86
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    International Journal of Quantum Chemistry 18 (1980), S. 345-345 
    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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  • 87
    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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  • 88
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    International Journal of Quantum Chemistry 18 (1980), S. 469-479 
    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: A self-consistent modified extended Hückel (SC-MEH) MO method has been extended to study the electronic structure and bonding in the complex ions: PtC42-, Pt(NH3)42+, cis-Pt(NH3)2Cl2, trans-Pt(NH3)2Cl2, and Pt(CN)42-, in which the atomic basis functions were derived from the published relativistic Dirac-Fock functions. Both quasirelativistic (in the frozen spin approximation) and nonrelativistic calculations were made to include the 5s 5p 5d 6s and 6p levels of Pt and the nsnp valence levels of the ligands. Similar calculations have been completed in the nonrelativistic mode for Pt(NH3)2 (OH2)L and Pt(NH3)2L2, where L is the monodentated bond at the N-7 position of guanine in DNA and L2 are the bidentated bonds at the N-7 and O-6 guanine sites, respectively. Based on these initial results specific conclusions have been made regarding a proposed biochemical mechanism that has been advanced to explain the unique anticancer activity of cis-Pt(NH3)2 Cl2 (DDP).
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  • 89
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    International Journal of Quantum Chemistry 18 (1980), S. 539-544 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The steric and electronic structure of the most potent uncoupler of oxidative phosphorylation, SF 6847, was studied. From 1H NMR measurements, it was found that the benzylic protons meta to the hydroxyl group are equivalent in neutral form, and that these protons tend to become non-equivalent on acid dissociation of the phenolic proton. The CNDO/2 calculation of the dimethyl derivative of SF 6847 showed that in the most stable conformation the angle of the malononitrile group with respect to the benzene ring is about 40° and that the planar form is quite unstable. Results on electronic absorption of SF 6847 in various media showed that the acid dissociation of its phenolic group is affected very much by small changes in the nature of the surrounding environment. It was also found that the calculated total energy differences between the anionic and neutral forms are correlated well with the uncoupling activities of 4-substituted 2,6-di-tert-butylphenol derivatives.
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  • 90
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    International Journal of Quantum Chemistry 18 (1980), S. 587-593 
    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: Fluorescence spectra and their temperature dependence of amorphous anthracene films doped with naphthacene were observed. An amorphous film was prepared by vacuum evaporation technique on a quartz plate cooled down to 30-40°K. The obtained results were discussed in relation to the structural change in the amorphous film.
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  • 91
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    International Journal of Quantum Chemistry 18 (1980), S. 641-644 
    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: Neutron scattering spectra from methane molecules adsorbed on a surface of graphite were observed by Newbery et al. They found four inelastic peaks in the temperature range lower than 30°K and assigned them to transitions between rotational tunneling states of methane molecules. This system was investigated by introducing both the interaction between methane molecules and that between a methane molecule and carbon atoms of graphite in order to explain the observed spectrum. It is shown that the system can be analyzed in terms of an effective field with tetrahedral symmetry.
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  • 92
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    International Journal of Quantum Chemistry 18 (1980) 
    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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  • 93
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    International Journal of Quantum Chemistry 18 (1980), S. 675-688 
    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 wave function and total energy of ammonia crystal are determined from the results of a totally optimized STO-3G ab initio calculation of the tetramer, pattern of the crystal. The crystal electronic energy is expressed in terms of the interatomic distances and charge density matrix elements. The geometry obtained from optimization of the tetramer energy on geometric parameters is in very good agreement with the experimental data of the crystal.
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  • 94
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    International Journal of Quantum Chemistry 18 (1980), S. 689-694 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown that trial functions involving Padé approximants yield satisfactory results for the ground state of the helium atom. In particular, the five-parameter form reproduces the best variational function of the type Ψ = e-zsφ(u) obtained numerically, to a remarkable extent.
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  • 95
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    International Journal of Quantum Chemistry 18 (1980), S. 357-363 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The spin densities of the radical anions from 4-methylcatechol, 4-carboxylic catechol, and 3-methylcatechol were calculated by means of the INDO method with the geometrical parameter adjusting method. The observed protion hyperfine coupling constants were exactly reproduced.
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  • 96
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    International Journal of Quantum Chemistry 18 (1980), S. 397-401 
    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
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  • 97
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    International Journal of Quantum Chemistry 18 (1980), S. 421-437 
    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 intermolecular energy of two conformations of stacked hydrated purine dimers is computed for a varying number of molecules of water around the stacks. The results obtained show that hydration can modify the relative stability of the dimers as calculated in vacuo. In addition, the optimized arrangements of the molecules of water around the dimers depict that purine molecules strongly interact with the solvent and that bridges made of water dimers or trimers are formed between the stacked bases.
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  • 98
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    International Journal of Quantum Chemistry 18 (1980), S. 439-448 
    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 order to elucidate further details of RNA conformations we have studied base stacking in dinucleoside monophosphates (DNP's) using UV difference spectra and the hypochromic effect. SCF CI MO calculations according to PPP and MIM approximations were carried out for six pyrimidine-containing DNP's in each of several stacking geometries. The calculated and plotted difference spectra were fitted to the experimental spectra. Different DNP's showed distinct geometries in the range of the helix angle of 35°. From our results we conclude that there is a microstructure in the helix. This would imply an additional content of information in this macromolecule, a higher precision in nucleic acid interactions, and make possible the prediction of the conformation of polynucleotides.
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  • 99
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    International Journal of Quantum Chemistry 18 (1980), S. 463-468 
    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 reaction mechanism of photoisomerization of isoxazoles to oxazoles through azirine intermediates is investigated theoretically by means of ab initio MO CI calculations. Azirine intermediates in S1 state [(n →*) state of the carbonyl chromophore] cause the C—N bond rupture of azirine ring and transform to isoxazoles via intersystem crossing to T1 state. On the other hand, azirine intermediates in S2 state [(n →*) state of the ketimine chromophore] lead to the C—C bond rupture of azirine ring and convert to oxazoles via intersystem crossing to T1 state.
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  • 100
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    International Journal of Quantum Chemistry 18 (1980), S. 481-492 
    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 optical spectrum of a model oxyheme complex has been calculated using a new intermediate neglect of differential overlap (INDO-SCF-CI) method that allows for the inclusion of configuration interaction and transition metals. In addition to the porphyrin π→π* transitions common to all heme proteins, four weak x,y polarized transitions observed only in oxyheme complexes have been calculated and assigned to excitations involving the lowest-empty highly delocalized (Oπ, dπ) orbital. Two broad z-polarized bands observed in the single-crystal polarized absorption spectra of oxymyoglobin and hemoglobin have also been calculated. Controversy exists over the assignment of these transitions and, in particular, over the extent of involvement of the oxygen ligand. Our calculations assign the weaker near-IR visible band mainly to the d σ dπ→ dπ* excitations and the more intense UV band mainly to a2u → dσ* excitations. While significant participation (25%) of the highly delocalized (Oπ, dπ) virtual orbital is also found, these z-polarized transitions need not be totally unique to oxyheme complexes, in keeping with experimental observation.
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