Molecular and crystal orbital studies of organic crystal formation.
Item
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Title
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Molecular and crystal orbital studies of organic crystal formation.
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Identifier
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AAI9986358
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identifier
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9986358
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Creator
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Masunov, Artem Eduardovich.
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Contributor
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Adviser: J. J. Dannenberg
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Date
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2000
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Physical | Engineering, Materials Science | Physics, Molecular
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Abstract
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Ab initio molecular orbital and crystal orbital methods are applied to the study of the geometry of hydrogen-bonded organic crystals and to predict the relative stability of polymorphic modifications. Cluster calculations of para-benzoquinone, of urea and of thiourea at HF, DFT, and AM1 levels with pseudotranslational constraints allow for the analysis of the energies for each type of H-bonds and their dependence on the cluster size. Periodical calculations on infinite systems are in good agreement with the results of cluster calculations. The cooperative components of intermolecular interaction, which are neglected in the most empirical force-field models account for up to 30% of the total interactions in the systems considered. This non-additivity is shown to lead to experimentally observed differences in crystal packing between urea and thourea, and can be successfully reproduced at the practically justified approximations.;One important application of MO calculations is to build simple yet accurate models for intermolecular interactions. Modifications of the basis set by optimizing the centroid positions of each basis function (floating basis set) combined with semiempirical values for exponent factors are suggested for this purpose. Such a wavefunction satisfies the Hellman-Feynman theorem and its electron density can be exactly represented by point charges.;The methodology developed in this work, may be applied to the rational design of crystals with required properties. This will be useful to solve practical problems of crystal engineering, and material science.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
