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Showing 1 to 20 of 37 for “"Semiempirical"”.
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Decomposition of perfluoropolyether lubricating oil: experimental and semiempirical results
Includes bibliographical references.
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Ab initio and Direct Quasiclassical Trajectory Study of the F + CH₄ → HF + CH₃ and F + C₂H₆ → HF + C₂H₅ Reactions
The reparametization of semiempirical Hamiltonians is an emerging method used in direct dynamics studies. The use of semiempirical Hamiltonians in direct dynamics studies diminishes the computational cost of trajectory calculations and negates the need for an analytical potential energy surface …
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Air pollution modeling
… pollution over a mesoscale region. MAXPOL-A is a semiempirical, source-oriented, microscal0, deterministic, climatological air pollution model which uses a simplex search algorithm to walk, one step at a time, towara the area of maximum concentration. Input parameters govern the length of walk and …
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Feynman-Dyson perturbation theory applied to model linear polyenes
… from quantum field theory, was employed in semiempirical calculations on trans - polyacetylene. A variety of soliton-like excited states of the molecule were studied by the PPP-UHF-RPA method. The results of this study provide useful information on the nature of these states, which are …
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An experimental investigation of the effect of slit length on the bursting strength of film and fabric plastic cylindrical shells
… bursting strength obtained from two different semiempirical analyses, one based on notch strength analysis and the other employing fracture mechanics concepts. The comparison demonstrates that large errors can result from the application of the notch-strength analysis yields a scatter band …
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Theoretical studies of the dynamics of gas-phase and gas/surface atom+alkane reactions and of the structure and dynamics of water confined between hydrophobic surfaces
… gas-phase chemical dynamics, we reparametrized semiempirical Hamiltonians so that they can accurately describe the potential energy surfaces for two distinct atom+alkane reactions. In addition to their demonstrated accuracy, these methods possess the attractive quality of being computationally …
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Part One: The Quantitative Prediction and Analysis of Enthalpies for The Interaction of Gas Phase Ion-Ion, Gas Phase Ion-Molecule, and Molecule-Molecule Lewis Acid-Base Systems. Part Two: The Study of Intervalence Transfer in Mixed Valence Systems Using Time Domain Reflectometry
… intuition regarding acid-base properties and a semiempirical justification for the electron transfer term is presented. New insights regarding the comparison of gas phase and solution data are provided. The quantitative correlation can be used to indicate instances where variations may occur in …
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Determinação experimental do coeficiente de reaeração, em rios e canais abertos, com o emprego de traçadores
… obtained from predictive models and are fit to a semiempirical equation involving hidraulic parameters. An analysis is made of losses of Amidorodamina G. E., and these are compared with those of conservative tracer, HTO.
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A simplified means of providing first estimates to laminar heating rates on isothermal axisymmetric blunt bodies
… heat transfer parameter which is shown, from a semiempirical study, to undergo only moderate variation in regions where the heat transfer experiences order of magnitude changes. Based on these results, a series expansion for the parameter of interest is obtained through the fourth order term. …
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Studies of and methods for electronic properties of large chemical systems
… of many embedding methods. Fourth, we employ semiempirical neglect of diatomic differential overlap (NDDO) methods as force fields for liquid water. Using force matching, we design a reparameterized NDDO model and find that it qualitatively reproduces the experimental radial distribution …
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Direct QM/MM Simulations of the Excited State Dynamics of Retinal Protonated Schiff Base in Isolation and in Complex Environments
… environments. A reparameterized multireference semiempirical method is used to describe the ground and excited electronic states of the chromophore and the environment is represented with an empirical force field (QM/MM). The potential energy surfaces and their couplings are determined "on the …
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Electronic structure of strongly correlated low-dimensional spin ½ systems: cuprates and vanadates
… the basics of density functional theory and semiempirical LSD+U approximation, which was implemented in the full-potential local-orbital (FPLO) minimal-basis calculation scheme. In the third chapter we tested the implemented version of LSDA+U on 3d transitional metal monoxides. Essential …
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Synthesis, Chemical Behavior, and Spectroscopic and Theoretical Probes of Cyamelurine and Related Compounds
… spectrum has been aided by results from semiempirical HAM/3, and from ab initio, Gaussian 70, quantum mechanical calculations. The detailed picture of valence orbital structure provides insight concerning the low basicity and the overall high chemical stability of cyamelurine, the …
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Tunneling spectroscopy of highly ordered organic thin films
… the Local Density Approximation (LDA) as well as semiempirical quantum chemistry calculations.
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A STUDY OF PROTON-INDUCED L-SHELL CROSS SECTIONS
… of L-subshell ionization cross sections using a semiempirical expression were obtained. The parameters were derived by fitting an analytical function to the experimental L-subshell ionization cross sections. A series of experiments were also carried out to measure the proton-induced L x-ray …
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Towards the Design of Carnitine Acyltransferase Inhibitors: Modeling the Conformational Behavior of (<em>R</em>)-Carnitine, (<em>R</em>)-Acetylcarnitine, Morpholinium rings, and 2-Oxo-1,3,6-dioxazaphosphacinium rings
Full grid-search semiempirical calculations (AM1 and AM1/COSMO) on zwitterionic acetylcarnitine and carnitine, cationic acetylcholine and choline, and 3-acetoxypropanoate and 3-hydroxypropanoate in the gas phase and solution were performed. The calculated ΔH<sub>hydr</sub> for hydrolyses of …
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Reconstructing the Atomic Number of Cargo X-ray Images using Dual Energy Radiography
… number of radiographic images by introducing a semiempirical transparency model. By incorporating a simple calibration step, this model captures second-order effects such as bulk scattering and uncertainties in the source energy spectrum and the detector response function. This methodology was …
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Development of polarizable force fields for proteins
… the convergence and the transferability of semiempirical parameters in the X-Pol potential. The molecular dynamics simulation of a solvated bovine pancreatic trypsine inhibitor reveals significant polarization and charge transfer effects in the protein.
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Radical rearrangement in the spiro(cyclopropane-1,1'-indan) and 3',4'-dihydrospiro(cyclopropane-1,1'(2H)-naphthalene) systems. An investigation of fast radical clocks
… transition state by the adjacent phenyl ring. Semiempirical AM1 and MNDO calculations failed to provide a reasonable correlation with these experimental results. Attempts to evaluate the effect of cyclopropane methyl substituents on the rate of rearrangement of spiroindanyl radicals by an …
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The Ab Initio Calculation of the Chemical Shift Tensor and its Application for the Structure Determination in Ordered and Disordered Phases by Means of Solid-State Nuclear Magnetic Resonance
… environments the advantages of force field and semiempirical methods, density functional and perturbation theory calculations were combined with the description of the systems in the cluster or embedded cluster approach as well as with calculations under periodic boundary conditions. Such it was …
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