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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 16 Apr 2024 14:59:27 +0000Theoretical Studies of Ziegler-Natta Catalysis: Structural Variations and Tacticity Control
https://resolver.caltech.edu/CaltechAUTHORS:20180529-145628341
Authors: {'items': [{'id': 'Bierwagen-E-P', 'name': {'family': 'Bierwagen', 'given': 'Erik P.'}}, {'id': 'Bercaw-J-E', 'name': {'family': 'Bercaw', 'given': 'John E.'}}, {'id': 'Goddard-W-A-III', 'name': {'family': 'Goddard', 'given': 'W. A., III'}, 'orcid': '0000-0003-0097-5716'}]}
Year: 1994
DOI: 10.1021/ja00083a037
Models for the likely active catalysts in homogeneous Ziegler-Natta systems have been studied using ab initio quantum chemical methods. We investigated the geometries of the isoelectronic model complexes, X_2M-R where X = Cl or Cp = (η^5-C_5H_5); where M = Sc and Ti^+ (and also Ti); and where R = H, CH_3, or SiH_3. The general trend is that the M = Sc compounds strongly prefer a planar configuration, whereas the M = Ti^+ cases generally prefer pyramidal geometries. This difference in geometry can be related to the differing ground-state electronic configurations for the metals: Sc is (4s)^2(3d)^1, whereas Ti^+ is (4s)^1(3d)^2. The nonplanar geometry for [Cp_2Ti-R]^+ suggests an explanation for the origin of stereospecificity in the syndiotactic polymerization by unsymmetric metallocene catalysts. These results suggest that {(η^5-C_5H_4)CMe_2(η^5-fluorenyl)}Sc-R would not catalyze syndiotactic polymerization under these conditions.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/dmwh6-g0506Parallel Calculation of Electron-Transfer and Resonance Matrix Elements of Hartree-Fock and Generalized Valence Bond Wave Functions
https://resolver.caltech.edu/CaltechAUTHORS:20180406-080326206
Authors: {'items': [{'id': 'Bierwagen-E-P', 'name': {'family': 'Bierwagen', 'given': 'Erik P.'}}, {'id': 'Coley-T-R', 'name': {'family': 'Coley', 'given': 'Terry R.'}}, {'id': 'Goddard-W-A-III', 'name': {'family': 'Goddard', 'given': 'William A., III'}, 'orcid': '0000-0003-0097-5716'}]}
Year: 1995
DOI: 10.1021/bk-1995-0592.ch007
We review the theory for the computation of the Hamiltonian matrix element between two distinct electronic wave functions ψ_A and ψ_B sharing the same nuclear configuration but differing electronic density distributions. For example, ψ_A and ψ_B might describe two endpoints in an electron transfer reaction or two configurations in a resonance description of a molecule. In such cases the calculation of the rate of electron transfer or resonance energy requires evaluation of <ψ_A\Ĥ\ψ_B> = H_(AB) matrix elements. Because the orbitals of ψ_A and ψ_B have complicated (non-orthogonal) relationships, the calculation of H_(AB) had been computationally intensive. In this paper we consider ψ_A, ψ_B having the form of closed or open-shell Hartree-Fock or Generalized Valence Bond wave functions and show the parallel structure of the theory. Using this parallel structure we present an efficient computational implementation for shared memory multiprocessors.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/cvpr8-hxn15