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Dissertations / Theses on the topic 'Quantum chemistry'

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Published: 4 June 2021
Last updated: 30 July 2024

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1

Altunata, Serhan. "Generalized quantum defect methods in quantum chemistry." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/36257.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2006.
Vita.
Includes bibliographical references (p. 247-254).
The reaction matrix of multichannel quantum defect theory, K, gives a complete picture of the electronic structure and the electron - nuclear dynamics for a molecule. The reaction matrix can be used to examine both bound states and free electron scattering properties of molecular systems, which are characterized by a Rydberg/scattering electron incident on an ionic-core. An ab initio computation of the reaction matrix for fixed molecular geometries is a substantive but important theoretical effort. In this thesis, a generalized quantum defect method is presented for determining the reaction matrix in a form which minimizes its energy dependence. This reaction matrix method is applied to the Rydberg electronic structure of Calcium monofluoride. The spectroscopic quantum defects for the ... states of CaF are computed using an effective one-electron calculation. Good agreement with the experimental values is obtained. The E-symmetry eigenquantum defects obtained from the CaF reaction matrix are found to have an energy dependence characteristic of a resonance. The analysis shows that the main features of the energy-dependent structure in the eigenphases are a consequence of a broad shape resonance in the 2E+ Rydberg series.
(cont.) This short-lived resonance is spread over the entire 2E+ Rydberg series and extends well into the ionization continuum. The effect of the shape resonance is manifested as a global "scarring" of the Rydberg spectrum, which is distinct from the more familiar local level-perturbations. This effect has been unnoticed in previous analyses. The quantum chemical foundation of the quantum defect method is established by a many-electron generalization of the reaction matrix calculation. Test results that validate the many-electron theory are presented for the quantum defects of the lsagnpo, E+ Rydberg series of the hydrogen molecule. It is possible that the reaction matrix calculations on CaF and H2 can pave the way for a novel type of quantum chemistry that aims to calculate the electronic structure over the entire bound-state region, as opposed to the current methods that focus on state by state calculations.
by Serhan Altunata.
Ph.D.
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2

Njegic, Bosiljka. "Cooking up quantum chemistry." [Ames, Iowa : Iowa State University], 2008.

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3

Rudberg, Elias. "Quantum Chemistry for Large Systems." Doctoral thesis, Stockholm : Bioteknologi, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4561.

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4

Gilbert, A. T. B. "Density methods in quantum chemistry." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599402.

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Density functional theory (DFT) has become a central aspect of quantum chemistry and provides the mainstay of chemical calculations. The advantage of DFT methods lies in their relatively inexpensive computational cost and their dealing with an experimentally tangible quantity, i.e. the density. The chief drawback is its lack of well-defined path from approximation to exactitude. Consequently many models and approaches have emerged, and been enthusiastically advocated, often with little more justification than "it works". This thesis begins with an overview of traditional quantum chemical theory and methods, and places DFT within this framework. In chapters 5 and 6 new model systems are presented, and novel methods to derive exchange functionals that are exact for these model systems are developed. By taking this approach, rather than the more pragmatic one of data fitting, the successes and failures can be traced to the underlying soundness of the model and/or the method used in the derivation. In the development of these functionals some difficulties were encountered with convergence of the self-consistent field calculations. These problems are addressed in chapter 7. The observation that a molecular density is very close to that given by the superposition of its constituent atoms, leads naturally to the idea of modelling a density by a sum of nuclear centred, spherically symmetric 'Stewart Atoms'. However, attempts at constructing Stewart atoms in the past have been thwarted by slow basis set convergence. In chapter 8 we overview the work that has been undertaken on Stewart atoms and present several formalisms in which the theory has been developed. Chapter 9 deals with the problem of constructing accurate representations of Stewart atoms. Several different approaches are considered and the most accurate is determined. Applications of the Stewart atoms are considered in chapter 10.
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5

Strange, Robin. "Electron correlation in quantum chemistry." Thesis, University of Birmingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289793.

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6

Murray, Christopher William. "Quantum chemistry for large molecules." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317841.

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7

Rubensson, Emanuel H. "Matrix Algebra for Quantum Chemistry." Doctoral thesis, Stockholm : Bioteknologi, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9447.

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8

Pye, Cory C. "Applications of optimization to quantum chemistry." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/nq23109.pdf.

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9

Ling, Song. "Aspects of quantum dynamics in chemistry /." Thesis, Connect to this title online; UW restricted, 1990. http://hdl.handle.net/1773/11620.

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10

Bast, Radovan. "Quantum chemistry beyond the charge density." Université Louis Pasteur (Strasbourg) (1971-2008), 2008. https://publication-theses.unistra.fr/public/theses_doctorat/2008/BAST_Radovan_2008.pdf.

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Cette thèse se concentre sur les calculs et la visualisation des propriétés moléculaires dans le cadre relativiste à quatre composantes. La théorie des réponses linéaire et quadratiquecombinée avec la théorie de la fonctionnelle de la densité (DFT) Kohn-Sham sont les outils principaux utilisés dans ce travail. Nous avons présenté la mise en oeuvre relativiste à quatre composantes des réponses linéaire et quadratique dans des systèmes à couche fermée dans le cadre de la DFT dépendant du temps avec la contribution de la densité de spin non-colinéaire. Cette thèse contient les premières études Hartree-Fock relativiste à quatre composantes des contributions électrofaibles de la non-conservation de la parité des paramètres spectraux de la résonance magnétique nucléaire. Nous avons introduit une approche visuelle des propriétés moléculaires au deuxième ordre statiques et dépendant de la fréquence dans l'espace physique à trois dimensions dans le cadre relativiste à quatre composantes. Nous avons démontré comment des perturbations statiques peuvent être imposées et visualisées en utilisant la méthode des perturbations finies
This thesis focuses on the calculation and visualization of molecular properties within the 4-component relativistic framework. Response theory together with density functional theory (DFT) within the Kohn-Sham approach are the main tools. The implementation of closed-shell linear and quadratic response functions within time-dependent DFT in the 4-component relativistic framework is presented with extensions that include contributions from the spin density. This thesis contains the first 4-component relativistic Hartree-Fock study of parity-violating effects on nuclear magnetic resonance parameters. An analytical real-space approach to frequency-dependent second-order molecular properties within the 4-component relativistic framework is introduced together with tools for the visualization of higher-order molecular properties based on the finite perturbation approach
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11

Babbush, Ryan Joseph. "Towards Viable Quantum Computation for Chemistry." Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:17467325.

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Since its introduction one decade ago, the quantum algorithm for chemistry has been among the most anticipated applications of quantum computers. However, as the age of industrial quantum technology dawns, so has the realization that even “polynomial” resource overheads are often prohibitive. There remains a large gap between the capabilities of existing hardware and the resources required to quantum compute classically intractable problems in chemistry. The primary contribution of this dissertation is to take meaningful steps towards reducing the costs of three approaches to quantum computing chemistry. First, we discuss how chemistry problems can be embedded in Hamiltonians suitable for commercially manufactured quantum annealing machines. We introduce schemes for more efficiently compiling problems to annealing Hamiltonians and apply the techniques to problems in protein folding, gene expression, and cheminformatics. Second, we introduce the first adiabatic quantum algorithm for fermionic simulation. Towards this end, we develop tools which embed arbitrary universal Hamiltonians in constrained hardware at a reduced cost. Finally, we turn our attention to the digital quantum algorithm for chemistry. By exploiting the locality of physical interactions, we quadratically reduce the number of terms which must be simulated. By analyzing the scaling of time discretization errors in terms of chemical properties, we obtain significantly tighter bounds on the minimum number of time steps which must be simulated. Also included in this dissertation is a protocol for preparing configuration interaction states that is asymptotically superior to all prior results and the details of the most accurate experimental quantum simulation of chemistry ever performed.
Chemical Physics
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12

McClean, Jarrod Ryan. "Algorithms Bridging Quantum Computation and Chemistry." Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:17467376.

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The design of new materials and chemicals derived entirely from computation has long been a goal of computational chemistry, and the governing equation whose solution would permit this dream is known. Unfortunately, the exact solution to this equation has been far too expensive and clever approximations fail in critical situations. Quantum computers offer a novel solution to this problem. In this work, we develop not only new algorithms to use quantum computers to study hard problems in chemistry, but also explore how such algorithms can help us to better understand and improve our traditional approaches. In particular, we first introduce a new method, the variational quantum eigensolver, which is designed to maximally utilize the quantum resources available in a device to solve chemical problems. We apply this method in a real quantum photonic device in the lab to study the dissociation of the helium hydride (HeH$^{+}$) molecule. We also enhance this methodology with architecture specific optimizations on ion trap computers and show how linear-scaling techniques from traditional quantum chemistry can be used to improve the outlook of similar algorithms on quantum computers. We then show how studying quantum algorithms such as these can be used to understand and enhance the development of classical algorithms. In particular we use a tool from adiabatic quantum computation, Feynman's Clock, to develop a new discrete time variational principle and further establish a connection between real-time quantum dynamics and ground state eigenvalue problems. We use these tools to develop two novel parallel-in-time quantum algorithms that outperform competitive algorithms as well as offer new insights into the connection between the fermion sign problem of ground states and the dynamical sign problem of quantum dynamics. Finally we use insights gained in the study of quantum circuits to explore a general notion of sparsity in many-body quantum systems. In particular we use developments from the field of compressed sensing to find compact representations of ground states. As an application we study electronic systems and find solutions dramatically more compact than traditional configuration interaction expansions, offering hope to extend this methodology to challenging systems in chemical and material design.
Chemical Physics
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13

Bast, Radovan Saue Trond. "Quantum chemistry beyond the charge density." Strasbourg : Université Louis Pasteur, 2008. http://eprints-scd-ulp.u-strasbg.fr:8080/926/01/BAST_Radovan_2008.pdf.

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14

Grimes-Marchan, Thomas V. Cundari Thomas R. "Quantum perspectives on physical and inorganic chemistry." [Denton, Tex.] : University of North Texas, 2007. http://digital.library.unt.edu/permalink/meta-dc-5172.

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15

Nolan, Stephen James. "Systematically imrpovable quantum chemistry for crystalline solids." Thesis, University of Bristol, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.557944.

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This thesis describes the development of a scheme for applying wavefunction-based quantum chemistry techniques to crystalline solids: the hierarchical method. The hierarchical method was first proposed by Manby, Gillan and Alfe [1] for cubic crystals. The contribution of electron correlation to the cohesive energy of a crystal is found from calculations on finite clusters of atoms. These clusters are chosen to mimic the structure of the crystal and the edge-effects are subtracted using the hierarchical equation. The quantum chemistry techniques used offer advantages in accuracy over existing solid-state methodologies, such as density functional theory, as they are ab initio and systematically improvable. The hierarchical method was applied to three crystalline solids: lithium hydride, lithium fluoride and neon. For lithium hydride and lithium fluoride, results of high accuracy are reported and comparisons are made with experimental extrapolations as well as contemporary theoretical techniques. In the case of neon, a new hierarchical equation was derived, one that was general to any crystal structure. The assumptions made in the hierarchical method, regarding cluster sizes and the use of symmetry, were successfully tested against a many-body expansion [2]. The systematic improvability of the quantum chemistry techniques employed in the hierarchical method allowed chemical accuracy (±l kcal/mol or ±1.6 mEh) to be approached. For example, the cohesive energy of lithium hydride at the zero point Eok coh was calculated to be -175.3 mEh [3], within 0.4 mEh of the value extrapolated from experimental measurements -174.9 mEh [4]. As well as the cohesive energy Eok coh the hierarchical method can also be used to calculate the equilibrium lattice parameter ao, bulk modulus Bo and surface formation energy a at the zero point. The predicted values for lithium hydride are ao = 4.062 A, Bo = 33.2 GPa, Eok coh = -175.3 mEh [3] and a = 0.43 J m-2 [5]; and for lithium fluoride ao = 4.011 A, Bo = 70.9 GPa, Eok coh = -325.5 mEh and σ = 0.53 J m-2.
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16

Rosal, Sandberg Jaime Axel. "New efficient integral algorithms for quantum chemistry." Doctoral thesis, KTH, Teoretisk kemi och biologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-149572.

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The contents of this thesis are centered in the developement of new efficient algorithms for molecular integral evaluation in quantum chemistry, as well as new design and implementation strategies for such algorithms aimed at maximizing their performance and the utilization of modern hardware. This thesis introduces the K4+MIRROR algorithm for 2-electron repulsion integrals, a new ERI integral scheme effective for both segmented and general contraction, which surpasses the performance of all previous ERI analytic algorithms published in the literature. The performance of the K4 kernel contraction schemeis further boosted by the use of some new recurrence relations, CDR/AERR family of recurrences, and the algorithms is further refined for spherical GTOs with the also new SKS method. New prescreening methods for two-electron integrals are also derived, allowing a more consistent methodology for discarding negligible ERI batches. This thesis introduces new techniques useful to pack integrals efficiently and better exploit the underlying modern SIMD or stream processing hardware. These algorithms and methods are implemented in a new library, the Echidna Fock Solver, a hybrid parallelized module for computing Coulomb and Exchange matrices which has been interfaced to the Dalton suite of quantum chemistry programs. Self-Consistent Field and Response Theory calculations in Dalton using the new EFS library are substantially accelerated, also enabling for the first time the use of general contraction basis sets as default basis for extended calculations. The thesis further describes the derivation and implementation of an integral algorithm for evaluating the matrix elements needed for the recently introduced QM/CMM method, for which many of the techniques previously derived are also used, along with a suitable prescreening method for the matrix elements. The implementation is also interfaced to the Dalton quantum chemistry program, and used in production calculations. The last chapter of the thesis is devoted to the derivation of a general analytic solution for type-II Effective Core Potential integrals, arguably one of the most troublesome molecular integrals in quantum chemistry. A new recurrence is introduced for the integrals, and a screening method is presented. Based on these results, a new efficient algorithm for computing type-II ECPs is also described.

QC 20140826

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17

Overy, Catherine Mary. "Reduced density matrices and stochastic quantum chemistry." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708241.

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18

Grimes-Marchan, Thomas V. "Quantum Perspectives on Physical and Inorganic Chemistry." Thesis, University of North Texas, 2007. https://digital.library.unt.edu/ark:/67531/metadc5172/.

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Applications of computational quantum chemistry are presented, including an analysis of the photophysics of cyclic trinuclear coinage metal pyrazolates, an investigation into a potential catalytic cycle utilizing transition metal scorpionates to activate arene C-H bonds, and a presentation of the benchmarking of a new composite model chemistry (the correlation consistent composite approach, ccCA) for the prediction of classical barrier heights. Modeling the pyrazolate photophysics indicates a significant geometric distortion upon excitation and the impact of both metal identity and substituents on the pyrazolates, pointing to ways in which these systems may be used to produce rationally-tuned phosphors. Similarly, thermodynamic and structural investigations into the catalyst system points to promising candidates for clean catalytic activation of arenes. The ccCA was found to reproduce classical reaction barriers with chemical accuracy, outperforming all DFT, ab initio, and composite methods benchmarked.
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19

Perveaux, Aurelie. "Study of photo induce process by quantum chemistry and quantum dynamics methods." Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLS144/document.

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C’est dernières années, les progrès des techniques expérimentales combinées avec les simulations théoriques ont données un accès à l’étude et le contrôle des réactions photochimiques dans des systèmes moléculaires de grande taille. Ceci ouvre des portes à de nouvelles applications technologiques. Par exemple, les molécules de la famille du 3-hydroxychromone et de l’aminobenzonitrile sont des types de systèmes où les spectres de fluorescences vont présentés des différences importantes suivant l’environnement du système ou même suivant les substituants utilisés. Ce type de propriété est crucial dans le domaine des matériaux organique, afin de pouvoir comprendre et designer des matériaux qui présentent des propriétés optiques choisis tells que les marqueurs fluorescents dans le domaine médical par exemple.Notre stratégie pour étudier la réactivité photochimique est la suivante: *Explorer la surface d’énergie potentielle et optimiser les points spécifiques avec des calculs de chimie quantiques. Dans un premier temps, on a utilisé des méthodes CASSCF/CASPT2 et la méthode PCM pour décrire les effets de solvant. * Génération des surfaces d énergies potentielles exprimer sous la forme de fonctions analytiques des coordonnées nucléaires. * Résolution de l’équation de Schrödinger dépendant du temps pour les noyaux et pour tout les derges de libertés de la molécule. Cette étape est faite à l’aide de la méthode multilayer multiconfiguration time-dependent hartree (ML-MCTDH)
Over the last decades, progress in experimental techniques combined with theoretical simulations has given access to studying and controlling the photochemical reactivity of large molecular systems with numerous technological applications. 3-hydroxychromone and aminobenzonitrile-like molecules are an example where different fluorescence patterns are observed, depending of the solvent or its substituents. Such properties are crucial in the field of organic materials to understand and design materials with specific optical properties such as fluorescent markers.Our strategy to study the photochemistry reactivity is summarised as follows: * Exploring the potential energy surfaces and optimising specific points with quantum chemistry calculations. In a first stage, these are run at the CASSCF/CASPT2 level of theory with a polarised extended basis set, and the solvent effect is described implicitly with the PCM model. * Generating the full dimension potential energy surfaces as analytical functions of the nuclear coordinates.* Solving the nuclear time-dependent Schrödinger equation for all the degrees of freedom. This is achieved with the multilayer Multi-Configuration Time-Dependent Hartree method (ML-MCTDH)
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20

Adamson, R. D. "Novel methods for large molecules in quantum chemistry." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.595361.

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With the rapid increase in computing power Quantum Chemists are looking towards larger and larger molecules. This thesis presents new ways to reduce the expensive scaling of computational cost with system size, thus allowing the advances in computer science to be utilized. The first chapter is an introduction to Hartree-Fock theory and the traditional methods of calculating electron correlation. This is followed by an introduction to Density Functional Theory, concentrating on Kohn-Sham density functional theory. Chapter 3 presents a new way of assessing the accuracy of a density functional by partitioning the density and examining the energy of the component pieces. Chapter 4 describes a new density functional (EDF1), designed especially for small basis sets, thus making it ideal for large systems. The functional is formed from several other common functionals, grouped together in a way to minimize the error of the chemical energetics of a selection of molecules. Chapter 5 gives an introduction to modern two-electron integral theory and then describes a new method for efficiently calculating integrals arising from charges that are well separated. The new algorithm does not scale with the concentration of the basis set. The efficient algorithm of Chapter 5 is O(N2) overall, and therefore still too slow. To truly examine large molecules O(N) methods are required. Chapter 6 provides an introduction to these linear methods and also presents a new method, the CASE approximation, which neglects long-range interactions. How to implement this new method (in O(N) work) is described in Chapter 7. The method is extended to density functional theory in Chapter 8 by attenuating the Dirac functional. Chapter 9 presents a second way to reduce the magnitude (and speed) of the approximation, and also a correction for the main failure of the original approximation. Chapter 10 examines the accuracy of the approximation on a variety of chemical properties. The final chapter describes a way to improve the accuracy of CASE by correcting for the neglected terms in only O(N) work. This correction however is not without its own problems and work continues in this area.
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21

Womack, James Christopher. "Evaluating many-electron molecular integrals for quantum chemistry." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.687429.

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The evaluation of molecular integrals is a vital but computationally expensive part of electronic structure calculations. This computational expense is particularly problematic for the explicitly correlated methods, in which complicated and numerous integrals over more than two-electrons must be evaluated. The successful R12/F12 methods overcome this difficulty by decomposition of these many-electron integrals by means of approximate resolutions of the identity (RIs). To obtain accurate results with this approach, however, requires large auxiliary basis sets with high angular momentum functions. To address this issue, we present a new RI-free variant of MP2-F12 theory, which uses density fitting to approximate three-electron integrals, rather than RIs. This approach demonstrates improved convergence of calculated energies with respect to the size and maximum angular momentum of the auxiliary basis set compared to the standard RI-based approach. For the systems on which the method was tested, relatively small auxiliary basis sets were sufficient to reduce errors in the correlation energy to less than a millihartree. The software implementation of the three-electron integral types needed in the new MP2-F12 variant proved to be extremely time-consuming. This difficulty inspired us to develop "Intception", a code generator which generates code for molecular integral evaluation. Intception is capable of automatically implementing code for evaluating a wide range of molecular integral types, using a general theoretical framework based on Obara-Saika-type recurrence relations [1] . To flexibly express integral definitions for use in Intception, a new domain-specific language was created. Testing revealed that the generated code evaluated integrals to a high numerical accuracy and on a reasonable timescale, though somewhat slower than existing optimized implementations. A detailed analysis of the performance of the generated code was undertaken, which suggested some possible routes to improving the efficiency of the code.
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22

TIANA, DAVIDE. "ORGANOMETALLIC CHEMISTRY FROM THE INTERACTING QUANTUM ATOM APPROACH." Doctoral thesis, Università degli Studi di Milano, 2010. http://hdl.handle.net/2434/150071.

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The Interacting Quantum Atoms approach(IQA) is a recent development of Bader’s QTAM(Quantum Theory of Atoms in Molecules). During the PhD studies the use of pseudopotential inside IQA was implemented allowing the study of transition metal compounds with this techniques. Furthermore IQA concepts were joined with Ponèc’s DAFH (Domain Avaraged Fermi Hole) giving the so-called IQA-EDF-DAFH analysis (EDF= electron-number distribution function) which provide a complete description of the chemical bond in terms of electron density. In order to make benchmark of this new technique classic metal-organic molecules like metal carbonyls, metal hydrides and simple metal dimeric compounds were studied.
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23

Hessmo, Björn. "Quantum optics in constrained geometries." Doctoral thesis, Uppsala University, Department of Quantum Chemistry, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-1208.

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When light exhibits particle properties, and when matter exhibits wave properties quantum mechanics is needed to describe physical phenomena.

A two-photon source produces nonmaximally entangled photon pairs when the source is small enough to diffract light. It is shown that diffraction degrades the entanglement. Quantum states produced in this way are used to probe the complementarity between path information and interference in Young's double slit experiment.

When two photons have a nonmaximally entangled polarization it is shown that the Pancharatnam phase is dependent on the entanglement in a nontrivial way. This could be used for implementing simple quantum logical circuits.

Magnetic traps are capable of holding cold neutral atoms. It is shown that magnetic traps and guides can be generated by thin wires etched on a surface using standard nanofabrication technology. These atom chips can hold and manipulate atoms located a few microns above the surface with very high accuracy. The potentials are very versatile and allows for highly complex designs, one such design implemented here is a beam splitter for neutral atoms. Interferometry with these confined de Broglie is also considered. These atom chips could be used for implementing quantum logical circuits.

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24

Cave-Ayland, Christopher. "Quantum free energy techniques." Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/375028/.

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25

Murray, Christopher Bruce. "Synthesis and characterization of II-IV quantum dots and their assembly into 3D quantum dot superlattices." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11128.

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26

Allis, Damian Gregory Spencer James T. Hudson Bruce S. "Computational quantum chemistry in initial designs and final analyses." Related electronic resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2004. http://wwwlib.umi.com/cr/syr/main.

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27

Oertel, David C. (David Charles). "Photodetectors based on colloidal quantum dots." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/39737.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2007.
Vita.
Includes bibliographical references (p. 193-212).
Inspired by recent work demonstrating photocurrent enhancement in quantum-dot (QD) solids via post-deposition chemical annealing and by recent successes incorporating single monolayers of QDs in light-emitting devices (QD-LEDs), we set out to develop thin-film, layered photodetectors in which the active layer is a chemically annealed QD solid. This thesis reports initial steps in this development. Chapters 1 and 2 contain introductory material. In Chapter 3, we demonstrate a layered QD photodetector (QD-PD) in which the active layer is a 200-nm thick film of CdSe QDs annealed with n-butylamine. These "thick-slab" devices, active in the visible spectrum, represent a minimal transformation from the transverse channel test structures employed for more fundamental studies to a layered, sandwich geometry. The thick-slab design exhibits a number of desirable characteristics, including near-unity internal quantum efficiency and a 50-kHz bandwidth. More complex QD-PD designs, allowing the successful incorporation of much thinner QD solids, are discussed in Chapter 4, and these devices provide insight into the zero-bias operation of thick-slab QD-PDs.
(cont.) The final three chapters of the thesis focus on PbSe QDs, this group's initial material of choice for accessing the short-wavelength-IR spectral window. Initial study of PbSe QDs as a material for QD-PDs is described in Chapter 5. Chapter 6 discusses an 31P-based NMR investigation of the mechanism of PbSe monomer formation, allowing for rational "doping" of syntheses to increase chronically low yields. Finally, Chapter 7 discusses a brief assessment of the suitability of PbSe QDs for in vivo imaging.
by David C. Oertel.
Ph.D.
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28

Kryvohuz, Maksym. "Quantum-classical correspondence in response theory." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43759.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2008.
Includes bibliographical references (p. 113-118).
In this thesis, theoretical analysis of correspondence between classical and quantum dynamics is studied in the context of response theory. Thesis discusses the mathematical origin of time-divergence of classical response functions and explains the failure of classical dynamic perturbation theory. The method of phase space quantization and the method of semiclassical corrections are introduced to converge semiclassical expansion of quantum response function. The analysis of classical limit of quantum response functions in the Weyl-Wigner representation reveals the source of time-divergence of classical response functions and shows the non-commutativity of the limits of long time and small Planck constant. The classical response function is obtained as the leading term of the h-expansion of the Weyl-Wigner phase space representation and increases without bound at long times as a result of ignoring divergent higher order contributions. Systematical inclusion of higher order contributions improves the accuracy of the h expansion at finite times. The time interval for the quantum-classical correspondence is estimated for quasiperiodic dynamics and is shown to be inversely proportional to anharmonicity. The effects of dissipation on the correspondence between classical and quantum response functions are studied. The quantum-classical correspondence is shown to improve if coupling to the environment is introduced. In the last part of thesis the effect of quantum chaos on photon echo-signal of two-electronic state molecular systems is studied. The temporal photon echo signal is shown to reveal key information about the nuclear dynamics in the excited electronic state surface.
(cont.) The suppression of echo signals is demonstrated as a signature of level statistics that corresponds to the classically chaotic nuclear motion in the excited electronic state.
by Maksym Kryvohuz.
Ph.D.
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29

Pereira, Roy Jawahar Joseph. "The Chemistry of Attention: Neuro-Quantum approaches to Consciousness." Thesis, Boston College, 2011. http://hdl.handle.net/2345/3714.

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Thesis advisor: Ronald K. Tacelli
This dissertation arose from concerns that the prevalent philosophy of materialism which reduces everything to matter has inadvertently contributed to the ecological destruction of the planet, and an impoverished understanding of human nature. Conceptual arguments and empirical data cry out for a philosophy beyond materialism (or its current avatar Physicalism) that moves us beyond 17th century classical science, making use of 20th century quantum science to better understand our world. Such a new philosophy would embed a new scientific paradigm that incorporates both the first person point of view and the third person "no point of view."The main issue I engage in this dissertation is whether consciousness can be explained by Physicalism. While functionalism, the dominant theory of Physicalism, answers many questions related to consciousness, it leaves major ones unanswered. I offer a critique of Physicalism using conceptual arguments and empirical data encompassing what I call the "chemistry of attention." I also offer innovative proposals toward a philosophical approach I term "Aspect Monism" that builds on earlier monist philosophies (Spinoza) while incorporating dualistic features, suggesting that this new approach would better account for consciousness. The proximate history of Physicalism to either explain the mind away or reduce it to the brain from Behaviorism through Identity Theory to Functionalism is laid out as well as the difficulty in establishing the boundaries of Physicalism.The project utilizes conceptual arguments to critique Physicalism in three areas of concern: What is left out? What is assumed? What is causing methodological confusion? The areas of qualia, cognition, intentionality, meaning and personhood are left out. This is demonstrated, in part, by various thought experiments like the inverted spectrum argument, the Chinese nation argument, the zombies' argument, the knowledge argument and the Chinese room argument. The problem of causal closure of the physical is that which is assumed. The ambiguity with respect to method is that which causes confusion.Empirical data from the neurosciences (EEG, ERP, fMRI experiments during meditation; OCD and phobia treatment; placebo and nocebo effect) are used to critically analyze Physicalism with respect to mental states and causation and the analysis of such data points to a close relationship between attention and changes in the brain, and subsequently to the collapse of Physicalism into Epiphenomenalism. Such a metaphysical approach to consciousness is suggested from, and provides a home for, the neurophysical approaches to the origins of consciousness. I present a neuro-quantum perspective using Stapp and Penrose-Hameroff who suggest these origins via neuroscience and quantum physics.As we search for a new scientific paradigm and consequently a new metaphysics that takes into consideration the objective and the subjective, and the inner and the outer, a new philosophy and a new scientific paradigm which incorporates both the first person point of view and the third person "no point of view" data is the need of the hour
Thesis (PhD) — Boston College, 2011
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Philosophy
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30

Peterson, Charles Campbell. "Accurate Energetics Across the Periodic Table Via Quantum Chemistry." Thesis, University of North Texas, 2015. https://digital.library.unt.edu/ark:/67531/metadc822822/.

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Greater understanding and accurate predictions of structural, thermochemical, and spectroscopic properties of chemical compounds is critical for the advancements of not only basic science, but also in applications needed for the growth and health of the U.S. economy. This dissertation includes new ab initio composite approaches to predict accurate energetics of lanthanide-containing compounds including relativistic effects, and optimization of parameters for semi-empirical methods for transition metals. Studies of properties and energetics of chemical compounds through various computational methods are also the focus of this research, including the C-O bond cleavage of dimethyl ether by transition metal ions, the study of thermochemical and structural properties of small silicon containing compounds with the Multi-Reference correlation consistent Composite Approach, the development of a composite method for heavy element systems, spectroscopic of compounds containing noble gases and metals (ArxZn and ArxAg+ where x = 1, 2), and the effects due to Basis Set Superposition Error (BSSE) on these van der Waals complexes.
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31

Quan, Chaoyu. "Mathematical methods for implicit solvation models in quantum chemistry." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066587/document.

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Cette thèse est consacrée à étudier et à améliorer les modèles mathématiques et les méthodes utilisées pour les modèles de solvatation implicite en chimie quantique. Ce manuscrit est composée de deux parties. Dans la première partie où nous analysons l'interface soluté-solvant, nous donnons, pour la première fois, une caractérisation complète de la surface moléculaire lisse, c'est-à-dire la surface exclue du solvant (SES). À partie de cette caractérisation, nous développons un algorithme de maillage par morceaux pour les surfaces moléculaires différentes, en particulier pour la SES, en utilisant la triangulation à front avançant. De plus, la cavité de la SES (la région entourée par la SES) est une description plus précise de la cavité de soluté. Dans la deuxième partie, nous construisons donc un modèle de continuum polarisable basé (PCM) sur la SES, dans lequel le paramètre de permittivité diélectrique est continu. Le problème électrostatique de ce modèle consiste à résoudre une équation de Poisson définie sur R3. Nous développons ensuite une méthode de Schwarz particulière, où seules les équations locales restreintes à des boules doivent être résolues. Enfin, nous étudions le modèle de solvatation de Poisson-Boltzmann, un autre modèle de solvatation implicite, qui tient compte à la fois de la permittivité diélectrique et de la force ionique du solvant. Une méthode de Schwarz similaire est proposée pour résoudre l'équation de Poisson-Boltzmann associée en résolvant des équations locales restreintes aux boules comme pour le PCM basé sur la SES
This thesis is devoted to study and improve the mathematical models and methods used in implicit solvation models in quantum chemistry. The manuscript is composed of two parts. In the first part where we analyze the solute-solvent interface, we give, for the first time, a complete characterization of the so-called “smooth” molecular surface, i.e., the solvent excluded surface (SES). Based on this characterization, we develop a piecewise meshing algorithm for different molecular surfaces, especially the SES, using the advancing-front triangulation. Further, it has been pointed out in the literature that the SES-cavity (the region enclosed by the SES) is a more accurate description of the solute cavity. In the second part, we therefore construct an SES-based polarizable continuum model (PCM), in which the dielectric permittivity parameter is continuous. The electrostatic problem of this model involves solving a Poisson equation defined in R3. We then develop a particular Schwarz domain decomposition method where only local equations restricted to balls need to be solved. Finally, the Poisson-Boltzmann solvation model, another implicit solvation model, is also investigated, which takes into account both the dielectric permittivity and the ionic strength of the solvent. A similar Schwarz domain decomposition method is proposed to solve the associated Poisson-Boltzmann equation by solving local equations restricted to balls as it is for the SES-based PCM
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32

Larsson, Per-Erik. "Modelling Chemical Reactions : Theoretical Investigations of Organic Rearrangement Reactions." Doctoral thesis, Uppsala University, Department of Quantum Chemistry, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3475.

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Chemical reactions are ubiquitous and very important for life and many other processes taking place on earth. In both theoretical and experimental studies of reactivity a transition state is often used to rationalise the outcome of such studies. The present thesis deals with calculations of transition states in radical cation rearrangements, and a principle of least motion study of the rearrangements in the barbaralyl cation.

In particular, alternative quadricyclane radical cation (Q∙+) rearrangements are extensively studied. The rearrangement of Q∙+ to norbornadiene is extremely facile and is often used as a prototype for one-electron oxidations. However, electron spin resonance (ESR) experiments show that there are additional cations formed from Q∙+. Two plausible paths for the rearrangement of Q∙+ to the 1,3,5-cycloheptatriene radical cation are located. The most favourable one is a multistep rearrangement with two shallow intermediates, which has a rate-limiting step of 16.5 kcal/mol. In addition, a special structure, the bicyclo[2.2.1]hepta-2-ene-5-yl-7-ylium radical cation, is identified on these alternative paths; and its computed ESR parameters agree excellently with the experimental spectrum assigned to another intermediate on this path. Moreover, this cation show a homoconjugative stabilization, which is uncommon for radical cations.

The bicyclopropylidene (BCP) radical cation undergoes ring opening to the tetramethyleneethane radical cation upon γ-irradiation of the neutral BCP. This rearrangement proceeds through a stepwise mechanism for the first ring opening with a 7.3 kcal/mol activation energy, while the second ring opening has no activation energy. The dominating reaction coordinate during each ring opening is an olefinic carbon rehybridization.

The principle of least motion is based on the idea that, on passing from reactant to product, the reaction path with the least nuclear change is the most likely. By using hyperspherical coordinates to define a distance measure between conformations on a potential energy surface, a possibility to interpret reaction paths in terms of distance arises. In applying this measure to the complex rearrangements of the barbaralyl cation, a correct ordering of the conformations on this surface is found.

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33

Jansson, Magnus. "Quantum Chemical Calculations on ESR, Core Excitations, and Isotope Effects in Molecular Systems." Doctoral thesis, Uppsala University, Department of Quantum Chemistry, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4226.

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In this thesis, quantum chemical calculations are undertaken mostly in order to interpret experimental results, but also to learn about computational techniques, their performance and their limitations. In paper I, the ionization-cleavage process of alkenes is investigated and two pathways are followed, one of initial cleavage and subsequent ionization and on the opposite, the other one of initial ionization and subsequent cleavage. The calculations reveal that ionization is best described by a vertical process, which is much faster than the relaxation of the molecule to its ionized structural minimum. Further, in paper II, the core hole excited state of ammonia is investigated and found to dissociate in an ultra-fast manner nicely explained by the calculated potential energy surface showing a very low barrier for dissociation. In paper III, the static and dynamic structures of two halogenated dimethyl ether radical cations are studied in ESR experiments, and it is found that, while the chlorinated molecule remains unaffected, the fluorinated molecule undergoes a dissociation or association reaction before the measurement takes place, the resulting fragments are searched for but not identified decisively. In paper IV, the stability of Jahn-Teller distorted selectively deuteriated benzene radical cation isotopomers is investigated by ESR experiments and density functional theory calculations. The temperature dependence, between 4.2 K and 77 K, of the ESR spectra is explained. Finally, in paper V, the hydrogen inversion in aziridine and methyl and dimethyl substituted aziridines is investigated. The rate constants and kinetic isotope effects are calculated using various techniques of transition state theory and tunneling correction methods.

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34

Razzaghi, Mortezaali. "Quantum Tunneling in Hydride Transfer Reactions in Solution." Thesis, Southern Illinois University at Edwardsville, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1549836.

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The secondary kinetic isotope effects for the hydride transfer reactions from aliphatic alcohols to four carbocations (NAD+ models) in acetonitrile were determined. The results suggest that the hydride transfer takes place by tunneling and that the rehybridizations of both donor and acceptor carbons lag behind the H-tunneling. This is quite contrary to the observations in alcohol dehydrogenases where the importance of enzyme motions in catalysis is manifested.

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35

Zimmer, John P. (John Philip). "Quantum dot-based nanomaterials for biological imaging." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/37888.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2006.
Vita.
Includes bibliographical references.
Quantum dot-based fluorescent probes were synthesized and applied to biological imaging in two distinct size regimes: (1) 100-1000 nm and (2) < 10 nm in diameter. The larger diameter range was accessed by doping CdSe/ZnS or CdS/ZnS quantum dots (QDs) into shells grown on the surfaces of pre-formed sub-micron SiO2 microspheres. The smaller diameter range was accessed with two different materials: very small InAs/ZnSe QDs and CdSe/ZnS QDs, each water solubilized with small molecule ligands chosen for their ability not only to stabilize QDs in water but also to minimize the total hydrodynamic size of the QD-ligand conjugates. Indium arsenide QDs were synthesized because nanocrystals of this material can be tuned to fluoresce in the near infrared (NIR) portion of the electromagnetic spectrum, especially in the 700-900 nm window where many tissues in the body absorb and scatter minimally, while maintaining core sizes of 2 nm or less. The QD-containing microspheres were used to image tumor vasculature in living animals, and to generate maps of size-dependent extravasation. With subcutaneously delivered nAs/ZnSe QDs, multiple lymph node mapping was demonstrated in vivo for the first time with nanocrystals. When administered intravenously, < 10 nm QDs escaped from the vasculature, or were efficiently cleared from circulation by the kidney. Both of these behaviors, previously unreported, mark key milestones in the realization of an ideal fluorescent QD probe for imaging specific compartments in vivo. Also presented in this thesis is the growth of single-crystalline cobalt nanorods through the oriented attachment of spherical cobalt nanocrystal monomers.
(cont.) When administered intravenously, < 10 nm QDs escaped from the vasculature, or were efficiently cleared from circulation by the kidney. Both of these behaviors, previously unreported, mark key milestones in the realization of an ideal fluorescent QD probe for imaging specific compartments in vivo. Also presented in this thesis is the growth of single-crystalline cobalt nanorods through the oriented attachment of spherical cobalt nanocrystal monomers.
by John P. Zimmer.
Ph.D.
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36

Kuno, Masaru Kenneth 1971. "Band edge spectroscopy of CdSe quantum dots." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/9698.

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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1998.
Includes bibliographical references (p. 373-381) and index.
In this thesis, I describe work done to understand the band edge exciton fine structure of CdSe quantum dots (QDs). These QDs or nanocrystallites are the result of recent synthetic efforts in the Bawendi group to produce nearly monodisperse nanocrystalline materials. The QDs are roughly spherical in shape and range in size from 10 to 50 A in radius. A number of optical experiments have been conducted on the material to understand its optical properties, particularly, the absorption and luminescence. However, several longstanding questions remain. Among them is the origin of the material's band edge luminescence. The emission is unusual because it displays long ([mu]s) lifetimes and exhibits a characteristic, size dependent, Stokes shift. As a consequence, many past studies have implicated the surface as the origin of the emission. In this respect, the surface localization of photogenerated carriers qualitatively explains both the long lifetimes and redshift of the luminescence. Recent theoretical and experimental studies, however, have suggested that the emission arises from an intrinsic core state analogous to a triplet state in small molecules. We describe the theoretical modeling of the QD electronic structure in.eluding the effects of shape, crystal field and the electron-hole exchange interaction. When all symmetry breaking effects are considered, we predict the presence of five fine structure states underlying the hand edge exciton rather than an eightfold degenerate exciton ground state. Following this, we intentionally modify the surface of the nanocrystallites to see the effect this has on the luminescence. Our results suggest that, to a large extent, the surface plays little role in the energetics of the emission. For QDs passivated with different organic and inorganic ligands we find little or no change in values of the "resonant" and "non-resonant" Stokes shift. This strongly supports the above mentioned fine structure model. Subsequent chapters take the proposed theory a step further, using it to explain the unusual behavior of the nanocrystallites subjected to an external magnetic field. The last two chapters pose the question of what happens when the QDs are intentionally doped with a paramagnetic impurity such as manganese? We expected that spin interactions between host and dopant will result in interesting optical phenomena such as the activation of dark excitons as well as shifts in fine structure energies due to an exchange induced mixing of states.
by Masaru Kenneth Kuno.
Ph.D.
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37

Leatherdale, Catherine A. (Catherine Anne) 1972. "Photophysics of cadmium selenide quantum dot solids." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/8828.

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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2000.
Includes bibliographical references.
Semiconductor quantum dots or nanocrystals have size dependent optical and electronic properties that arise from quantum confinement. While the quantum size effect is reasonably well understood, the effect of abrupt interface between the nanocrystal and its dielectric environment is not. In this thesis we study how the dielectric environment affects the quantum dot electronic structure, the optical absorption ~ross-section, charge separation, and transport in cadmium selenide colloidal quantum dots. The electronic states and optical absorption cross-section are found to be less sensitive to changes in the dielectric environment than predicted from theory unless screening from the ligand shell is taken into account. The absolute absorption cross section is measured as a function of quantum dot size; excellent agreement with theory is obtained for absorption far above the band edge. Three-dimensional close packed solids of quantum dots are predicted to act as model artificial solids. Optical absorption measurements indicate that the electronic states of CdSe quantum dots separated by 11 angstroms or more are essentially uncoupled. Photoconductivity measurements suggest that photoexcited quantum confined excitons are ionized by the applied field with a rate that depends on both the size and surface passivation of the quantum dots. The charge generation efficiency decreases with increasing temperature as non-radiative and radiative recombination pathways increasingly compete with charge separation. A simple tunneling model for the initial charge separation step is presented that qualitatively reproduces both the size and surface dependence of the photoconductivity as a function of applied electric field. Finally, we report observations of amplified spontaneous emission from quantum dot solids. The stimulated emission is tunable with quantum dot size and does not sensitively depend upon surface passivation. These measurements demonstrate the feasibility of nanocrystal quantum dot lasers and amplifiers.
by Catherine A. Leatherdale.
Ph.D.
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38

Gontijo, Campos Andre. "Quantum Control over Vast Time Scales and Length Scales." Thesis, Princeton University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10619678.

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Quantum control theory (QCT) is concerned with the active manipulation of phys- ical and chemical processes on the atomic and molecular scale. For a specified con- trol objective, and with restrictions imposed by many possible constraints, the time- dependent field required to manipulate the system in a desired way can be designed using quantum control theory. This dissertation proposes several novel applications of QCT to actively manipulate the dynamics of both quantum and classical systems with and without interactions with an external environment, in both relativistic and non-relativistic regimes. In Chapter 2, the paradigm of spectral dynamic mimicry (SDM) in which laser fields are shaped to make any atomic and molecular systems look identical spectrally is put forward. SDM successfully avoids optimization rou- tines, and provides a powerful tool to find a laser pulse that induces a desired optical response from an arbitrary dynamical system. As illustrations, driving fields are com- puted to induce the same optical response from a variety of distinct systems (open and closed, quantum and classical). The formulation may also be applied to design materials with specified optical characteristics. These findings reveal unexplored flex- ibilities of nonlinear optics. Little is known about the control of relativistic quantum systems. Therefore, an extension of QCT to the Dirac equation is proposed. The main contributions are: (i) Chapters 3 and 4 reach an unprecedented level of control while providing exciting new insights on the complex quantum dynamics of relativis- tic electrons. The method developed provides a very powerful tool to generate new analytical solutions to the Dirac equation, (ii) Chapters 5 and 6 present an open system interaction formalism for the Dirac equation. The presented framework en- ables efficient numerical simulations of relativistic dynamics within the von Neumann density matrix and Wigner phase space descriptions, an essential requirement for the application of QCT, (iii) Chapter 7 proposes a Lindblad model of quantum elec- trodynamics (QED). The presented formalism enables a very efficient and practical numerical method to simulate QED effects, such as the Lamb shift and the anomalous magnetic moment of the electron, for a broad variety of systems.

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39

Miller, Matthew Dean Holder Andrew J. "Applications of quantum chemistry to polymerization reactions and biological activity." Diss., UMK access, 2004.

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Thesis (Ph. D.)--Dept. of Chemistry and School of Pharmacy. University of Missouri--Kansas City, 2004.
"A dissertation in chemistry and pharmaceutical science." Advisor: Andrew J. Holder. Typescript. Vita. Description based on contents viewed Feb. 27, 2006; title from "catalog record" of the print edition. Includes bibliographical references (leaves 206-221). Online version of the print edition.
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40

Wu, Xin [Verfasser]. "Semiempirical Quantum Chemistry on High-Performance Heterogeneous Computers / Xin Wu." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2014. http://d-nb.info/1047440539/34.

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41

Murphy, Paul. "Development and applications of quantum chemistry to open shell systems." Thesis, Heriot-Watt University, 2017. http://hdl.handle.net/10399/3355.

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This thesis investigates the applicability of a range of computational techniques across a range of open shell chemical systems from the geometrically simple but electronically complex to the geometrically complex but electronically simple. Initially an investigation into a range of geometrically simple but electronically complicated systems is presented. The Monte Carlo Configuration Interaction method (MCCI) is applied to challenging transition metals dimers such as ScNi in order to establish the ground state potential energy surface, from equilibrium bond lengths through to dissociation using highly compact wavefunctions compared to Full Configuration Interaction (FCI). It shall be demonstrated that the ScNi dimer represents the current limit of this technique. Software development of MCCI is then undertaken in order to perform calculations of spin-orbit coupling interactions. Results on B, C, O, F, Si, S, F, Cl, OH, NO, CN and C2 species are shown to be comparable with other techniques using the one-electron Breit-Pauli Hamiltonian. The application of quantum chemistry to geometrically complex but electronically simple systems is then considered. Density Functional Theory (DFT) is used to investigate the mechanism and energetic barriers leading to ring inversion of the biscalix[4]arene supra-molecule. A minimum barrier height of 19.31 kcalmol−1 to inversion is elucidated along with details of the complete mechanistic pathway to inversion. The focus then moves to polymetallic clusters of calix[4]arene. A DFT study is made of the preferential binding of calix[4]arene towards first row transition metals of various oxidation and spin states. Results indicate that Cu3+ (singlet) species will preferentially bind to the lower rim over other metals in the study. The final DFT-related work presented is a study of the preferential binding at the upper rim of polymetallic calix[4]arene clusters towards a range of important small gas molecules. It was found that gases such as NH3 and SO2 bind most strongly to the upper rim with the inclusion of a transition metal at the lower rim providing strengthening of the host-guest binding.
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42

Carter, Emily Ann Goddard William A. "Finesse in quantum chemistry : accurate energetics relevant for reaction mechanisms /." Diss., Pasadena, Calif. : California Institute of Technology, 1987. http://resolver.caltech.edu/CaltechETD:etd-11212003-111159.

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43

Seshagiri, Lakshminarasimhan. "Performance analysis and middleware assisted adaptation for quantum chemistry computations." [Ames, Iowa : Iowa State University], 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1473257.

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44

Fujimoto, Kazuhiro. "Quantum chemistry studies on the functions of some photobiological molecules." 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/136197.

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45

Bartlett, P. "Quantum dynamics of three body systems." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.354808.

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46

Bruno, Juan Diderot 1970. "Quantum mechanical studies of Heisenberg antiferromagnetic spin chains." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/84735.

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47

Lopreore, Courtney Lynn. "Recent applications of the quantum trajectory method." Access restricted to users with UT Austin EID Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3034933.

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48

Dinescu, Adriana. "Metals in Chemistry and Biology: Computational Chemistry Studies." Thesis, University of North Texas, 2007. https://digital.library.unt.edu/ark:/67531/metadc3678/.

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Numerous enzymatic reactions are controlled by the chemistry of metallic ions. This dissertation investigates the electronic properties of three transition metal (copper, chromium, and nickel) complexes and describes modeling studies performed on glutathione synthetase. (1) Copper nitrene complexes were computationally characterized, as these complexes have yet to be experimentally isolated. (2) Multireference calculations were carried out on a symmetric C2v chromium dimer derived from the crystal structure of the [(tBu3SiO)Cr(µ-OSitBu3)]2 complex. (3) The T-shaped geometry of a three-coordinate β-diketiminate nickel(I) complex with a CO ligand was compared and contrasted with isoelectronic and isosteric copper(II) complexes. (4) Glutathione synthetase (GS), an enzyme that belongs to the ATP-grasp superfamily, catalyzes the (Mg, ATP)-dependent biosynthesis of glutathione (GSH) from γ-glutamylcysteine and glycine. The free and reactant forms of human GS (wild-type and glycine mutants) were modeled computationally by employing molecular dynamics simulations, as these currently have not been structurally characterized.
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49

Jarosz, Mirna 1981. "The physics and chemistry of transport in CdSe quantum dot solids." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/16664.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2004.
Vita.
Includes bibliographical references.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Semiconductor quantum dots (QDs) have tunable opto-electronic properties and can be chemically synthesized and manipulated with ease, making them a promising novel material for many diverse applications. An understanding of the physics of charge transport in QDs is not only important for realizing QD based electronic devices, but it also provides crucial insight into the chemical and optical properties of QDs. This thesis highlights how photoconductivity measurements are valuable to advancing our understanding of QD physics because they are exquisitely sensitive to the optical, chemical, and electronic properties of QDs. The work presented in this thesis emphasizes how the chemistry and physics of QD films are deeply entwined. Chapter 2 demonstrates that the photoconductivity and dark conductivity of CdSe QD films are enhanced following annealing at high temperatures. Chapter 3 illustrates that the purity of the QD capping reagent (tri-n-octylphosphine) and the methods used for film preparation can each affect the observed photocurrent by two to three orders of magnitude. In Chapter 4, the methods for CdSe film preparation developed in Chapter 3 are used to make films that exhibit photoconductivity properties consistent with having a low density of trapped charges, in contrast to previous studies. Chapter 5 also uses chemistry to bring CdSe QD films into a new regime of photoconductivity physics. Post-deposition chemical treatments that increase photocurrent by up to three to four orders of magnitude are presented. The voltage dependence of the photocurrent after treatment is consistent with having achieved unity exciton separation efficiency. Furthermore, by bringing CdSe QD films into this
(cont.) new regime of higher photoconductivity physics it is found that energetics prevent the facile injection of charges from gold electrodes into CdSe QDs, but there is no barrier to charge extraction.
by Mirna Jarosz.
Ph.D.
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50

Wohlers-Reichel, Tim Fabian. "Engineering interactions for analog simulation of quantum chemistry in a linear Paul Trap." Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/27748.

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The simulation of chemical reactions, specifically ultrafast photochemical reactions is notoriously difficult. Using classical computers, the computational cost to simulate these interactions scales exponentially. By using a controllable quantum device, the quantum hardware cost scaling is instead linear. With this method, it is possible to directly implement the Hamiltonian evolution of a particular quantum system of interest. This approach is known as analog quantum simulation. This thesis describes the experimental implementation of an analog quantum simulation using a trapped ion system. Using laser-mediated spin-motion interactions at 355 nm, we engineer Hamiltonian terms of the linear vibronic coupling model of pyrazine as well as the the one-dimensional absorption spectrum of SO2. These interactions form the basis of a toolkit enabling the analog quantum simulation of chemical dynamics. In addition to this quantum simulation work, progress in the implementation of a single ion addressing system at a wavelength of 411 nm is outlined. This work demonstrates the viability of using 411 nm light to perform selective single qubit gates
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