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Wetzel, Thiele Lee. "Ab initio computational studies." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/26023.
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Northey, Thomas. "Ab initio molecular diffraction." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/28772.
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In 1915, Debye derived his well-known equation for the X-ray scattering from a sample of randomly orientated gas-phase molecules. He approximated the molecular scattering by adding the contributions of isolated atomic constituents. This is known as the Independent Atom Model (IAM). However, it omits the redistribution of valence electrons due to bonding, and is limited to the electronic ground state. The main proposition of this thesis is that it is worthwhile going beyond the IAM when interpreting X-ray scattering data. In part, this is motivated by the arrival of new X-ray sources called X-ray Free-Electron Lasers (XFELs). A new method called Ab Initio X-ray Diffraction (AIXRD) is introduced. It calculates the elastic X-ray molecular scattering factor directly from wave functions calculated by ab initio electronic structure theory, for instance Hartree-Fock or multiconfigurational self-consistent field. In this way, the valence electrons are correctly taken into account, and calculations based on electronically excited wave functions become possible. The wave functions must be constructed from spatial orbitals made up of Gaussian-Type Orbitals (GTOs), giving an analytical solution to the Fourier transform integrals involved, and is key to computationally efficient and accurate results. This is compared to a fast Fourier transform (FFT) method, where the electron density is computed on a 3D grid and an FFT algorithm is used to obtain the elastic X-ray molecular scattering factor. Inspired by post-crystallography experiments such as serial femtosecond crystallography and single-particle imaging at XFELs, the AIXRD method is expanded to allow accurate X-ray diffraction calculations from large molecules such as proteins. To make the underlying ab initio problem tractable, the molecule is split into fragments. In other words, the electron density is constructed by a sum of fragment contributions, as is the corresponding molecular form-factor. In this way, it is analogous to the IAM approach except that instead of isolated atoms, there are isolated fragments. A pairwise summation of fragment contributions is also used to account for fragment-fragment interactions. Various fragment definitions are compared based on their effect on the X-ray diffraction signal, and are compared to the IAM method. Finally, X-ray diffraction from molecules in specific quantum states is calculated, revealing a distinct quantum fingerprint in the X-ray diffraction, and a comparison to experiment is made. In particular, the elastic X-ray diffraction is calculated from gas-phase H2 pumped to various electronic, vibrational, and electronic states. This is expanded upon for polyatomic molecules using the harmonic approximation for the vibrational states.
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Schweigert, Igor Vitalyevich. "Ab initio Density Functional Theory." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0011614.
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Delle, Site Luigi. "Ab initio study of water." Thesis, Queen's University Belfast, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322621.
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Thomas, Geraint Llewllyn. "Ab initio protein fold prediction." Thesis, University of Leeds, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.436019.
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Chang, Qiang. "Ab Initio Calculation on UO2." The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1391705586.
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Sommer, Jan. "Ab initio Berechnung des Elektronentransports in metallbeschichteten Kohlenstoffnanoröhrchen: Ab initio Berechnung des Elektronentransports inmetallbeschichteten Kohlenstoffnanoröhrchen." Bachelor's thesis, Fraunhofer Institut für elektronische Nanosysteme, 2011. https://monarch.qucosa.de/id/qucosa%3A18639.
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Kohlenstoffnanoröhrchen (engl. carbon nanotube, CNT) sind vielversprechende Kandidaten für den Ersatz von Kupferleitbahnen die bei weiterer Strukturverkleinerung von integrierten Schaltkreisen notwendig wird. In dieser Arbeit wird mit Hilfe von ab-initio Simulationen auf Basis der Dichtefunktionaltheorie die elektronische Struktur von halbleitenden CNTs beispielhaft anhand des (8,4)-CNTs untersucht. Nach Besetzung des CNT mit Metallatomen, hier Kobalt, zeigen sich massive Änderungen der Bandstruktur. Es reichen bereits überraschend kleine Mengen des Metalls aus, um einen starken Effekt zu erreichen. Die Änderungen der elektronischen Struktur sind stark abhängig von der genauen Position der Metallatome relativ zum Kohlenstoffgerüst der CNTs, der Einfluss der mechanischen Verformung des CNTs als Reaktion auf die Anlagerung ist hingegen sehr gering. Die relevanten Bänder der Kobaltatome liegen leicht unterhalt der Fermi-Energie und sorgen bei der Integration in die Bandstruktur des CNTs für die Schließung der Bandlücke und somit für die Transformation eines vorher halbleitenden CNTs in ein leitendes.
Diese Transformation konnte auch mit Simulationsrechnungen zum Elektronentransport bestätigt werden. Ferner wurden bei weiteren Rechnungen eine ausgeprägte Spinabhängigkeit der Bandstruktur ermittelt, welche noch weiterer Untersuchung bedarf.
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Langer, Holger. "Nichtadiabatische Ab-initio-Molekulardynamiksimulationen photoangeregter Nukleobasen." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980630452.
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Binder, Jörg. "Giant Magnetoresistance - eine ab-initio Beschreibung." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2001. http://nbn-resolving.de/urn:nbn:de:swb:14-997704395015-96808.
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Die vorliegende Arbeit ist ein Beitrag zur Theorie des spinabhängigen Transports in magnetischen Vielfachschichten. Es wird erstmalig eine parameterfreie Beschreibung des Giant Magnetoresistance (GMR) vorgelegt, welche detaillierte Einsichten in die mikroskopischen Vorgänge gestattet. Die ab-initio Berechnung der Elektronenstruktur der magnetischen Vielfachschichten basiert auf der Spindichtefunktionaltheorie unter Verwendung eines Screened Korringa-Kohn-Rostoker-Verfahrens. Die Streueigenschaften von Punktdefekten werden über die Greensche Funktion des gestörten Systems selbstkonsistent bestimmt. Die Transporteigenschaften werden durch Lösung der quasiklassischen Boltzmann-Gleichung unter Berücksichtigung der Elektronenstruktur der Vielfachschicht und der Anisotropie der Streuung an Fremdatomen berechnet. Die Boltzmann-Gleichung wird iterativ unter Einbeziehung der Vertex-Korrekturen gelöst. Der Formalismus wird auf Co/Cu- und Fe/Cr-Vielfachschichten, die Standardsysteme der Magnetoelektronik, angewandt. Es werden die Abhängigkeit der Streuquerschnitte, der spezifischen Restwiderstände und des GMR von der Art und der Lage der Übergangsmetalldefekte in Co/Cu- und Fe/Cr-Vielfachschichten diskutiert. Darüber hinaus wird der Einfluß des Quantum Confinements auf den GMR eingehend untersucht. Vorteile und Grenzen der vorliegenden theoretischen Beschreibung werden aufgezeigtA new theoretical concept to study the microscopic origin of Giant Magnetoresistance (GMR) from first principles is presented. The method is based on ab-initio electronic structure calculations within the spin density functional theory using a Screened Korringa-Kohn-Rostoker method. Scattering at impurity atoms in the multilayers is described by means of a Green's-function method. The scattering potentials are calculated self-consistently. The transport properties are treated quasi-classically solving the Boltzmann equation including the electronic structure of the layered system and the anisotropic scattering. The solution of the Boltzmann equation is performed iteratively taking into account both scattering out and scattering in terms (vertex corrections). The method is applied to Co/Cu and Fe/Cr multilayers. Trends of scattering cross sections, residual resistivities and GMR ratios are discussed for various transition metal impurities at different positions in the Co/Cu or Fe/Cr multilayers. Furthermore the relation between spin dependence of the electronic structure and GMR as well as the role of quantum confinement effects for GMR are investigated. Advantages and limits of the approach are discussed in detail
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Li, Sa. "Materials Design from ab initio Calculations." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4274.
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Waldron, Derek. "Ab-initio simulation of spintronic devices." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=18470.
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In this thesis, we present the mathematical and implementation details of an ab initio method for calculating spin-polarized quantum transport properties of atomic scale spintronic devices under external bias potential. The method is based on carrying out density functional theory (DFT) within the Keldysh non-equilibrium Green's function (NEGF) formalism to calculate the self-consistent spin-densities. This state-of-the-art technique extends previous work by: i) reformulating the theory in spin-space such that the non-equilibrium charge density can be evaluated for different spin-channels, and ii) introducing k-point sampling to treat transverse periodic devices such that correct bulk as well as surface magnetism can be described. Computational details including k-point sampling to converge the Brillouin zone integration, optimization of pseudopotentials and basis sets, and efficient O(N) calculation of the Green's function are presented. We apply this method to investigate nonlinear and non-equilibrium spin-polarized transport in several magnetic tunnel junctions (MTJs) as a function of external bias voltage. Firstly, we find that for an Fe/MgO/Fe trilayer structure, the zero-bias tunnel magnetoresistance (TMR) is several thousand percent, and it is reduced to about 1000% when the Fe/MgO interface is oxidized. The TMR for devices without oxidization reduces monotonically to zero with a voltage scale of about 0.5-1V, consistent with experimental observations. We present an understanding of the nonequilibrium transport by investigating microscopic details of the scattering states and the Bloch bands of the Fe leads. Secondly, we investigate a molecular MTJ composed of Ni leads sandwiching a benzenedithiol(BDT) molecule. We find a TMR of ~27% which declines toward zero as bias voltage is increased. The spin currents are nonlinear functions of bias voltage, even changing sign at certain voltages due to specific features of the coupling between molecular statesDans cette thèse, nous présentons les détails mathématiques et d'implémentation d'une méthode \emph{ab initio} pour le calcul des propriétés de transport quantique polarisé en spin de dispositifs spintroniques de taille atomique sous un différence de potentiel appliquée. La méthode est basée sur la théorie des fonctionnelles de la densité (DFT) dans le cadre du formalisme des fonctions de Green hors équilibre (NEGF) de Keldysh pour calculer les densités de spin auto-consistantes. Cette technique de pointe étend les travaux précédents: i) en reformulant la théorie dans l'espace de spins de telle manière que la densité de charge hors équilibre peut être évaluée pour différents canaux à spin, et ii) en présentant l'échantillonnage de k-point pour traiter les dispositifs périodiques transversaux de telle façon que le magnétisme de surface et de volume peuvent être décrits correctement. Les détails informatiques, y compris l'échantillonnage de k-points pour la convergence de l'intégration sur la zone de Brillouin, la construction et l'optimisation de la base et des pseudo-potentiels, et un calcul efficace O(N) de la fonction de Green sont présentés. Nous appliquons cette méthode pour étudier le transport polarisé en spin, non linéaire et hors équilibre, dans plusieurs jonctions tunnel magnétiques (MTJs), comme fonction du potentiel appliqué. Premièrement, nous constatons que pour une structure tri-couche de Fe/MgO/Fe, la magnétorésistance tunnel (TMR) à différence de potentiel nulle est de plusieurs milliers de pourcents, et se réduit environ à 1000% lorsque l'interface de Fe/MgO est oxydée. La TMR pour des dispositifs sans oxydation se réduit à zéro de façon monotone avec une différence de potentiel de l'ordre de 0.5-1V, conformément aux observations expérimentales. Nous interprétons nos résultats en étudiant les détails microscopiques d'états de diffusion et des bandes de Bloch dans les électrodes
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Somasundram, K. "Ab initio calculation of molecular properties." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383905.
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黃新祥 and Sun-cheung Wong. "Ab initio calculations of silicon clusters." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B3122197X.
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Su, Ming-Der. "Ab initio calculation of molecular surfaces." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239130.
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Pickard, Christopher James. "Ab initio electron energy loss spectroscopy." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627420.
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Tillack, Natalie. "Ab initio modelling of magnetoelectric materials." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:94f92598-be2b-4e4f-b861-11a370b72c2d.
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The search for magnetoelectric materials, i.e. materials that respond with a polarisation (magnetisation) when an external magnetic (electric) field is applied, has become more important in recent years---both for the standalone magnetoelectricity and as part of the cross-coupling in modern multiferroics. To date, applications of magnetoelectrics (MEs) in technology are hampered by either small coupling strengths or low operating temperatures. In the present work, the linear magnetoelectric coupling is examined by means of density functional theory with the aim to understand the physics of the coupling, and in turn open up pathways in the search for improved coupling properties. The spin part of the ME coupling tensor was shown to be the sum of the electronic and the lattice contribution. Recently developed first-principles frameworks allow us to gain insights into the microscopic mechanisms of the coupling and are applied to compute the response in modifications of the prototypical ME Cr2O3 and isostructural compounds. We find that strains at ambient pressures influence the lattice contribution significantly. At higher pressures, a magnetic phase transition is shown to destabilise magneto-active phonon modes and lead to a divergence of the longitudinal lattice response due to magnetic softness, with a coupling strength 650 times larger than its zero-pressure value. Equivalently, a divergence of the electronic response is measured at the transition from insulator to metal---previously suggested in literature, but to date not measured. The largest value of the electronic response is shown to be 31.4ps/m, which is larger than the ambient value by a factor of 70, and also large in terms of the absolute value. We exemplify both the magnetic softness and band-gap alterations by doping the Cr2O3 parent structure with Fe and Ti. We show that doping provides a powerful way to include magnetic frustration resulting in a ten-fold increase of magnetic contributions to the lattice response. When the dopants lower the Cr2O3 band gap, the electronic response is measured to be ten times larger than reported for pure Cr2O3. Finally, the high-symmetry configurations of the spin flop phase of Cr2O3 are modelled. A combined phenomenological and group-theoretical analysis reveals a novel ME coupling mechanism only present in the spin flop phases. Akin to the ferroaxial mechanism in multiferroics, a chiral in-plane transverse coupling term is observed, whose Landau invariant is of 5th order.
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Binder, Jörg. "Giant Magnetoresistance - eine ab-initio Beschreibung." Doctoral thesis, Technische Universität Dresden, 2000. https://tud.qucosa.de/id/qucosa%3A24782.
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Die vorliegende Arbeit ist ein Beitrag zur Theorie des spinabhängigen Transports in magnetischen Vielfachschichten. Es wird erstmalig eine parameterfreie Beschreibung des Giant Magnetoresistance (GMR) vorgelegt, welche detaillierte Einsichten in die mikroskopischen Vorgänge gestattet. Die ab-initio Berechnung der Elektronenstruktur der magnetischen Vielfachschichten basiert auf der Spindichtefunktionaltheorie unter Verwendung eines Screened Korringa-Kohn-Rostoker-Verfahrens. Die Streueigenschaften von Punktdefekten werden über die Greensche Funktion des gestörten Systems selbstkonsistent bestimmt. Die Transporteigenschaften werden durch Lösung der quasiklassischen Boltzmann-Gleichung unter Berücksichtigung der Elektronenstruktur der Vielfachschicht und der Anisotropie der Streuung an Fremdatomen berechnet. Die Boltzmann-Gleichung wird iterativ unter Einbeziehung der Vertex-Korrekturen gelöst. Der Formalismus wird auf Co/Cu- und Fe/Cr-Vielfachschichten, die Standardsysteme der Magnetoelektronik, angewandt. Es werden die Abhängigkeit der Streuquerschnitte, der spezifischen Restwiderstände und des GMR von der Art und der Lage der Übergangsmetalldefekte in Co/Cu- und Fe/Cr-Vielfachschichten diskutiert. Darüber hinaus wird der Einfluß des Quantum Confinements auf den GMR eingehend untersucht. Vorteile und Grenzen der vorliegenden theoretischen Beschreibung werden aufgezeigt.A new theoretical concept to study the microscopic origin of Giant Magnetoresistance (GMR) from first principles is presented. The method is based on ab-initio electronic structure calculations within the spin density functional theory using a Screened Korringa-Kohn-Rostoker method. Scattering at impurity atoms in the multilayers is described by means of a Green's-function method. The scattering potentials are calculated self-consistently. The transport properties are treated quasi-classically solving the Boltzmann equation including the electronic structure of the layered system and the anisotropic scattering. The solution of the Boltzmann equation is performed iteratively taking into account both scattering out and scattering in terms (vertex corrections). The method is applied to Co/Cu and Fe/Cr multilayers. Trends of scattering cross sections, residual resistivities and GMR ratios are discussed for various transition metal impurities at different positions in the Co/Cu or Fe/Cr multilayers. Furthermore the relation between spin dependence of the electronic structure and GMR as well as the role of quantum confinement effects for GMR are investigated. Advantages and limits of the approach are discussed in detail.
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Tam, Mary Christina. "Ab initio Calculations of Optical Rotation." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/27214.
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Coupled cluster (CC) and density functional theory (DFT) are highly regarded as robust quantum chemical methods for accurately predicting a wide variety of properties, such as molecular structures, thermochemical data, vibrational spectra, etc., but there has been little focus on the theoretical prediction of optical rotation. This property, also referred to as circular birefringence, is inherent to all chiral molecules and occurs because such samples exhibit different refractive indices for left- and right- circularly polarized light. This thesis focuses on the theoretical prediction of this chiroptic property using CC and DFT quantum chemical models. Several
small chiral systems have been studied, including (S)-methyloxirane, (R)-epichlorohydrin, (R)-methylthiirane, and the conformationally flexible molecules, (R)-3-chloro-1-butene and
(R)-2-chlorobutane. All predicted results have been compared to recently published gas-phase cavity ringdown polarimetry data. When applicable, well-converged Gibbs free energy differences among confomers were determined using complete-basis-set extrapolations of CC energies in order to obtain Boltzmann-averaged specific rotations. The overall results indicate that the theoretical rotation is highly dependent on the choice of optimized geometry and basis set (diffuse functions are shown to be extremely important), and that there is a large difference between the CC and DFT predicted values, with DFT usually predicting magnitudes that are larger than those of coupled cluster theory.Ph. D.
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Boyer, Frédéric. "Reconstruction ab initio de voies métaboliques." Phd thesis, Université Joseph Fourier (Grenoble), 2004. http://www.theses.fr/2004GRE10076.
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La reconstruction des voies métaboliques d'un organisme est une tâche importante pour les biologistes et plusieurs approches ont déjà été proposées pour assister ce travail mais il y a un besoin pour des approches plus exploratoires. La première partie de cette thèse s'intéresse à la reconstruction ab initio de voies métaboliques. Cela consiste en la recherche d'un réseau réactionnel qui connecte au moins deux composés en se basant uniquement sur une base de réactions autoriées. Nous proposons une nouvelle formulation de ce problème qui considère les réactions comme transferts d'atomes entre composés chimiques. Une voie métabolique est ainsi associée à un transfert d'atomes entre deux composés. Le problème de la reconstruction est exprimé comme la recherche d'une composition d'injections partielles dont la taille de l'image est maximale. La complexite de ce problème a été étudiée et un algorithme le résolvant est présenté. La seconde partie présente la formalisation d'un problème de comparaison de graphes. Le cas particuliers traité dans cette thèse concerne la comparaison d'un réseau de réactions avec l'organisation spatiale des gènes sur le génome. Cette comparaison permet l'identification de voies métaboliques codées en opérons dans les génomes bactériensReconstructing the metabolic pathways of an orgnanism is a task of major importance and several approaches have already been proposed in order to help biologists in this task but more exploratory approaches are needed. The first part of this thesis emphasis on what we call ab initio metabolic pathway reconstruction. This is the problem of finding a reaction network connceting two or more compounds relying only on a database of feasible reactions. We propose here a new formulation for this problem. Given a set of biochemical reactions together with their substrates and products, we consider the reactions as transfers of atoms between the chemical compounds and we look for sequences of reactions transferring a maximal (or preset) number of atoms between a source and a sink compound. We state this problem as the one of finding a composition of partial injections that maximises the image size. The theoretical complexity of this problem has been studied and a practical algoritm to solve it is presented. Ths second part presents a formalization of a problem concerning graphs comparison. The particular case treated in this thesis concerns the comparison of a network of reactions with the spatial organization of genes on the genome. This comparison permits to identify operons encoded metabolic pathways
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Bailey, Christine Lynn. "Ab initio studies of aluminium halides." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/6162.
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The catalytic fluorination of hydrocarbons facilitates the large-scale production of chlorofluorocarbons for a wide range of applications including aerosol propellants, refrigerants and solvents. Lewis acid catalysts, such as Swarts catalysts based on antimony pentafluoride, are commonly used. Recently, a sol-gel based synthesis method has been developed which yields very high surface area aluminium fluoride (HS-AlF3) that has a Lewis acidity comparable to that of the Swarts catalysts. This makes HS-AlF3 a promising candidate for use in several Lewis acid catalysed reactions. Despite the importance of the surface in the catalytic process little is known about the detailed atomic scale structure of AlF3 surfaces. Surface thermodynamics calculations, based on hybrid-exchange density functional theory, are employed to predict the composition and structure of AlF3 surfaces. The surfaces of AlF3 expose under coordinated Al ions that are potential Lewis acid sites. Under standard atmospheric conditions the AlF3 surfaces are shown to adsorb water above the under coordinated Al ions. Theoretical characterisation of the under coordinated Al ions shows that the most reactive type of site is not exposed on crystalline α-AlF3 samples, however, it is predicted to occur in small quantities on β crystallites. It is speculated that such sites occur in higher quantities on the high surface area materials. This result may explain the different reactivity of α-, β- and HS-AlF3. Our detailed understanding of AlF3 surfaces allows us to propose a reaction centre and mechanism for the dismutation of CCl2F2 on β-AlF3. Aluminium chloride is extensively used as a catalyst in Friedal-Crafts reactions. It is therefore, commonly assumed that pure crystalline AlCl3 is strongly Lewis acidic. Ab initio surface thermodynamics calculations are used to study the surfaces of crystalline AlCl3 and show that it is chemically inert.
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Wong, Sun-cheung. "Ab initio calculations of silicon clusters." Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B20192708.
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Destandau-Léonard, Céline. "Calculs ab-initio de données spectroscopiques." Marne-la-Vallée, 2000. http://www.theses.fr/2000MARN0081.
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Le but de ce travail a ete de determiner des donnees spectroscopiques fiables pour les molecules a 2, 3 et 4 atomes en utilisant les methodes ab-initio de la chimie quantique. La premiere etape consiste en la construction des fonctions d'energie potentielle a l'aide des methodes mrci et ccsd+t qui incluent une grande partie de la correlation electronique. A partir de la, les energies des niveaux rovibrationnels sont obtenues par des methodes numeriques pour les molecules diatomiques, perturbativement et variationnellement pour les molecules triatomiques et tetra-atomiques. Les grandeurs issues de ces calculs ont ete employees pour simuler l'excitation selective des niveaux vibrationnels des molecules. Nous avons utilise une approche basee sur le developpement de la fonction d'onde totale dependant du temps sur les etats stationnaires. Elle a ete appliquee sur oh, of, ocl, obr, oi et h2cs. Dans chaque cas, une grande selectivite a pu etre atteinte. Pour la premiere fois, ce type de controle a ete mis en place sur la molecule h 2cs en prenant en compte toute la dimension du systeme. En collaboration avec l'equipe experimentale de bale (suisse), une etude theorique concernant des anions triatomiques a ete effectuee, l'observation de tels ions dans le milieu interstellaire etant l'un des challenges actuels en astrophysique. Nous avons traite l'etat a 2 + de c 2o , l'etat x 2 g de c 3 et les etats x 1 + et a 1 de c 2b. Dans deux cas, il a fallu prendre en compte l'effet renner-teller. Nous avons aussi caracterise l'etat x 2a 1 de c 2b qui presente des mouvements de grande amplitude. Enfin, les etats electroniques fondamentaux des complexes a transfert de charge n 4 +, n 2co + et occo + ont ete etudies. Ces molecules isoelectroniques
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Mohamed, Fawzi Roberto. "Advanced methods in Ab-initio molecular dynamics /." Zürich : ETH, 2006. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16893.
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Jung, Daniel Yong Chu. "Ab initio studies in high pressure geochemistry /." Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17730.
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Wagener, Thomas. "Ab-initio-Rechnungen zur Struktur von Übergangsmetallkomplexen." [S.l.] : [s.n.], 1999. http://archiv.ub.uni-marburg.de/diss/z1999/0395/.
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Brémond, Eric. "Simulation ab initio de spectres UV-visibles." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2012. http://pastel.archives-ouvertes.fr/pastel-00760600.
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Les facteurs de réponse UV-visible sont des éléments clés utilisés en chimie analytique afin d'évaluer les proportions des différents constituants d'un mélange. Particulièrement prisés par le monde de l'industrie, ces facteurs sont le plus souvent difficiles à obtenir, surtout lorsque les composés mis en jeu sont des impuretés difficiles à isoler ou à synthétiser. Dans ce contexte, la chimie théorique, et plus particulièrement la Théorie de la Fonctionnelle de la Densité Dépendant du Temps peut devenir un atout non négligeable, capable d'apporter des réponses en un minimum de temps. Afin de parvenir à ce type d'informations, une étude approfondie de la spectroscopie UV-visible est nécessaire. Cette étude met en lumière les capacités de la TD-DFT à simuler, non seulement la position des bandes d'absorption d'un spectre, mais également à être utilisée pour faire de la quantification de composés. À ce titre, plusieurs nouvelles fonctionnelles de la densité ont ici été développées afin de tenter d'améliorer la précision de la méthode, à la fois d'un point de vue structural, et d'un point de vue de la simulation de propriétés comme les énergies d'excitations. En somme, plusieurs modèles ont été éprouvés, dont certains développés, tous visant principalement à reproduire au mieux la structure parfois complexe des bandes d'absorption d'un spectre UV-visible. Non seulement centrée sur le processus d'absorption, cette étude s'étend également au processus de fluorescence, montrant et démontrant l'utilité de la chimie théorique en science et dans l'industrie.
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Nazé, Cédric. "Relativistic ab initio calculations of isotope shifts." Doctoral thesis, Universite Libre de Bruxelles, 2012. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209637.
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Quand les effets de la masse finie du noyau et de la distribution de charge spatiale sont pris en compte dans l’Hamiltonien décrivant un système atomique, les isotopes d’un élément, caractérisés par le même nombre de protons mais un nombre différent de neutrons, ont des niveaux d’énergie électronique différents. Le déplacement entre les niveaux d’énergie (pour un même état quantique) de deux isotopes différents est appelé le déplacement isotopique de niveau. De manière générale, on peut distinguer les déplacements isotopiques de champ (field shift) et les déplacements isotopiques de masse (mass shift). Pour les systèmes à plus d’un électron, le specific mass shift (SMS) apparaît. Grâce à sa faible pondération, le paramètre SMS peut être traité comme une perturbation de l’Hamiltonien ;son estimation fait appel aux intégrales de Vinti [5].Dans un contexte relativiste, les programmes grasp2K [2] et mcdf-gme [1] permettent de résoudre les équations de Dirac-Fock associées à un état multiconfigurationnel et d’en fournir l’énergie ainsi que la représentation numérique des orbitales monoélectroniques. Nous avons créé et introduit dans le programme mcdf-gme une sous-routine capable d’estimer les paramètres de masse et de champ à partir des fonctions d’onde multiconfigurationnelles. Pour le programme GRASP2K, un module indépendant à été créé.
Par ailleurs, un opérateur plus complet impliquant des corrections en αZ, a été dérivé par Shabaev [4] et, de manière indépendante, par Palmer [3]. Nous avons déduit la forme tensorielle de cet opérateur et avons également implémenté dans les programmes cités ci-dessus le calcul de ses éléments de matrice.
Grâce à ces outils nous avons pu étudier la détérioration de l’opérateur d’énergie cinétique pour estimer le normal mass shift et travailler divers systèmes comme le lithium neutre et sa séquence isoélectronique. Par la suite nous avons également travaillé sur les séquences isoélectroniques du bore, du béryllium, du carbone et de l’azote. Enfin, certains effets isotopiques ont été étudiés pour plusieurs transitions dans le baryum neutre.
Bibliographie
[1] J. P. Desclaux. A relativistic multiconfiguration Dirac-Fock package. In E. Clementi, editor, Methods and Techniques in Computational Chemistry - vol. A :Small Systems of METTEC, page 253. STEF, Cagliari, 1993.
[2] P. Jönsson, X. He, C. Froese Fischer and I. P. Grant. The GRASP2K relativistic atomic structure package. Comput. Phys. Commun. 177 :597–622, 2007.
[3] C. W. P. Palmer. Reformulation of the theory of the mass shift. J. Phys. B :At. Mol. Phys. 20 :5987–5996, 1987.
[4] V. M. Shabaev and A. N. Artemyev. Relativistic nuclear recoil corrections to the energy levels of multicharged ions. J. Phys. B :At. Mol. Phys. 27 :1307–1314, 1994.
[5] J. P. Vinti. Isotope shift in magnesium. Phys. Rev. 56 :1120–1132, 1939.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished
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Marzari, Nicola. "Ab-initio molecular dynamics for metallic systems." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285270.
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Thorpe, Aaron J. "Ab initio studies of strained ring molecules." Thesis, University of Canterbury. Department of Chemistry, 1999. http://hdl.handle.net/10092/8323.
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The work reported in this thesis concerns the acid catalysed rearrangement of epoxides in the presence and absence of intramolecular nucleophiles. The potential energy surface (MP2/6-31G*//MP2/6-31G* and B3LYP/6-31G*) for rearrangement of protonated propene oxide to protonated propanal has been established. The rearrangement exhibits a 2 kcal/mol preference for rotation of oxygen away from the more hindered face of the oxirane plane containing the methyl. The rearrangement pathway involves two distinct steps; first, rupture of the oxirane and second, hydride migration. The latter does not commence until rupture of the C-O bond is complete. The combination of these two steps defines a concerted asynchronous rearrangement pathway and exhibits a 20 : 1 preference for migration of the proton trans to the methyl over the cis.
Kinetic isotope effects of the acid and BF₃-catalysed rearrangement of methyl propene oxide to methylpropanal are consistent with a 1,2 hydride shift to a carbocation intermediate (B3LYP/6-31G*). Inverse secondary kinetic isotope effects for hydride migration reflect changes in Cl-H(D) stretching and out of plane bending frequencies. A calculated correction applied to the experimentally observed migration of hydrogen/deuterium (MH/MD = 1.92) results in a primary kinetic isotope effect for the reaction (kH/kD = 1.557) close to the theoretically calculated value (kH/kD = 1.677).
The inversion and retention transition structures for intramolecular reaction of protonated cis- and trans-3,4-epoxypentan-1-ol which give protonated cis- and trans-2-methylfuran-3-ols have been determined at the ab initio MP2/6-31G* and hybrid density functional B3LYP/6-31G* levels of theory. Intrinsic reaction coordinate calculations for the lower energy inversion pathways for formation of the 2-methylfuran-3-ols show that intramolecular attack occurs in concert with ring opening. A complex of the 5-membered transition structure from the trans-epoxide with the Houk theozyme 3.5 kcal/mol lower in energy than the complex previously reported as a model for the antibody IgG26D9 catalysed intramolecular cyclisation of trans-4,5-epoxyhexan-1-ol reverses the preference of that theozyme to favour furan formation. This negates the theozyme as a model for the antibody reaction. A new theozyme is reported which favours pyran formation over furan formation consistent with the antibody result.
The potential energy surface for the acid and BF₃ catalysed rearrangement of cis- and trans-4,5-epoxyhexan-1-ol involving inversion and retention of configuration at the reaction centre at the HF/6-31G* and B3LYP/6-31G* levels are reported. The preference for furan formation over pyran is attributed to the more favourable O-Cep-O bond angles at the transition structures for furan formation.
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Menconi, Giuseppina. "Exchange-correlation functionals from ab initio potentials." Thesis, Durham University, 2002. http://etheses.dur.ac.uk/4178/.
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An accurate description of the exchange-correlation energy is central to density functional theory (DFT). In this thesis a series of exchange-correlation functionals are developed using new approaches based on exchange-correlation potentials and enhancement factors. The functionals are assessed for a wide range of molecular properties. Chapter 1 describes Hartree Fock theory, introducing the key concepts of exchange and correlation. Chapter 2 describes the fundamental ideas of DFT and the implementation of Kohn-Sham theory. Chapter 3 describes a new approach for determining exchange-correlation functionals solely from ab initio potentials. A series of functionals are developed and assessed. Chapter 4 investigates the performance of one of these functionals, which provides particularly high quality structural predictions. A challenging benchmark of sulfur-containing compounds and a new benchmark of diatomic molecules are considered. Results are assessed in terms of the enhancement factor. In Chapter 5, the enhancement factor is used to develop new functionals that satisfy several exact physical conditions. The potential energy curve of the Helium dimer is investigated, since this is known to be sensitive to the enhancement factor. In Chapter 6 a series of hybrid functionals are determined. Particular attention is paid to their performance for chemical reactions and the relationship of these results to self-interaction errors. Chapter 7 investigates a new definition of the exchange-correlation charge (hole), which is directly related to the exchange-correlation potential. The first such calculations on molecular systems are presented. Concluding remarks are presented in Chapter 8.
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Sarker, Prodip Kumar. "Reactive polymers by ab initio cationic polymerisation." Thesis, University of Sheffield, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.400001.
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Briddon, Patrick Roy. "Defects in solids : an ab initio study." Thesis, University of Exeter, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253562.
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Chichkine, Maxim. "Ab initio study of defects in silicon." Thesis, De Montfort University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.416700.
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Hasnip, Philip James. "Ab initio simulations of transition metal surfaces." Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272735.
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Engeness, Torkel Dyrbaek 1972. "Multiscale ab initio approaches to materials physics." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/8023.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2003.Includes bibliographical references (leaves 157-162).
This work presents new ab initio approaches to materials physics. We first introduce the multiscale approach to determination of thermal properties and changes in free energy. With this approach one can perform thermal averaging of ensembles of states with ab initio methods, thus enabling ab initio calculations of free energy changes. We use this method to perform an ab initio calculation of the free energy of reconstruction in the 300 reconstruction of silicon. In the next chapters we introduce a completely new approach to electronic structure calculations, using a new, real-space bais set (wavelets) which enables all-electron calculations of complex systems. By eliminating the need for pseudopotentials for decsribing the core, one can for the first time access the true density functional energy of a system through systematic convergence. In the final chapter we combine this method with the generalized gradient approximation to perform calculations on high-pressure phases of boron.
by Torkel D. Engeness.
Ph.D.
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Richards, William D. (William Davidson). "Ab-initio simulation of novel solid electrolytes." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/88398.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014.30
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 41-43).
All solid-state batteries may be a solution to some of the problems facing conventional organic electrolytes in Li and Na-ion batteries, but typically conductivities are very low. Reports of fast lithium conduction in Li 0GeP 2S1 2 (LGPS), with conductivity of 12 mS/cm at room temperature, have shown that Li -diffusion in solid electrolytes can match or exceed the liquid electrolytes in use today. I report results of ab-initio calculations on a related system of materials, Nai0 MP 2SI 2 (M = Ge, Si, Sn), which are predicted to have similar properties to LGPS as candidates for electrolytes in Na-ion batteries. I also derive methods to estimate the error associated with diffusion simulations, so that appropriate tradeoffs between computational time and simulation accuracy can be made. This is a key enabler of a high throughput computational search for new electrolyte materials.
by William D. Richards.
S.M.
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Segall, Matthew David. "An ab initio study of biological systems." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627280.
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Binnie, S. J. "Ab initio surface energetics : beyond chemical accuracy." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1318067/.
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Density functional theory (DFT) is the work–horse of modern materials modeling techniques, but scattered evidence indicates it often fails for important surface properties. This thesis investigates how DFT estimates of the surface energy (σ) and molecular adsorption energies of ionic systems are affected by the choice of exchange–correlation (xc) functional. Accurate diffusion Monte–Carlo (DMC) and quantum chemistry (QC) calculations are presented for these quantities showing marked improvement over DFT and agreement of much better than chemical accuracy. DFT estimates of σ are presented for the (001) surfaces of LiH, LiF, NaF and MgO. Five xc functionals, LDA, PBE, RPBE, Wu–Cohen and PW91 are used. A clear xc functional bias is demonstrated with σLDA > σWC > σPBE > σPW91 > σRPBE. To improve the picture detailed pseudopotential DMC calculations are presented for LiH and LiF. The lattice parameters and cohesive energies agree with experiment to better than 0.2 % and 30 meV respectively. For LiH novel all–electron DMC calculations are also presented showing significant improvement over pseudopotential DMC. Accurate all–electron Hartree–Fock calculations of σ for LiH(001) and LiF(001) are presented along with calculations of the LiF bulk using specially adapted Gaussian basis–sets. Combined with existing QC correlation estimates the bulk and surface properties of LiH and LiF show excellent agreement to both experiment and DMC and allow a longstanding disagreement between two experimental estimates for σLiF to be resolved. Finally the adsorption energy curve for water on LiH(001) is obtained by both DMC and incremental QC techniques leading to agreement of better than 10 meV. DFT and dispersion corrected DFT estimates are also presented highlighting the large xc functional dependence. Thus we demonstrate that is possible and necessary to obtain agreement between higher levels of theory and produce benchmark values beyond DFT.
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Swift, D. C. "Ab fere initio equations of mechanical state." Thesis, University of Edinburgh, 2000. http://hdl.handle.net/1842/11446.
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This thesis describes the development and application of models to predict the equation of mechanical state of materials from first principles, concentrating on the regime of strong shock waves. Most effort was devoted to crystalline solids, though extensions to the fluid phase and higher temperatures are proposed. Equations of state and phase diagrams were predicted for aluminium, silicon and beryllium. The method used is based on quantum mechanical treatments of the electrons in the solid and of the phonon modes. The importance of anharmonic effects (phonon-phonon interactions) was investigated, but was not included rigorously because it did not appear to contribute significantly. With fully ab initio methods, the equation of state and phase diagram could be predicted to a few percent in mass density, the discrepancy being caused mainly by the use of the local density approximation in predicting electron states. The accuracy of the equation of state could be improved considerably by adjusting the internal energy to reproduce the observed mass density at STP. The resulting ab fere initio equation of state could essentially reproduce the observed states on the shock Hugoniot to within the scatter in the experimental data. Because these equations of state are built on firm quantum mechanical and thermodynamic principles, they should predict accurate properties away from the principal Hugoniot, unlike traditional empirical equations of state. Accurate temperatures are important in the development of models of material strength (elasticity and plasticity) based on microstructural phenomena. As an illustration of the versatility of the equations of state, hydrocode simulations were made of the splitting of a shock wave in silicon, caused by the phase change. The splitting appears to be in reasonable agreement with laser-driven shock experiments.
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Lima, Filipe Camargo Dalmatti Alves. "Modelagem ab initio da interação proteína-carboidrato." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-21102010-110913/.
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A Frutalina é uma proteína tetramérica ligante de carboidratos obtida através de sementes Artocarpus incisa. Os interesses biomédicos da Frutalina estão em sua alta afnidade de ligação por carboidratos presentes em algumas células tumorais específicas. Até agora, nenhum estudo teórico computacional foi realizado para investigar as características de ligação da Frutalina. Neste trabalho, através de um estudo multidisciplinar, investigamos as propriedades de ligação e óticas da Frutalina com carboidratos. Utilizamos um modelo-corte teórico, considerando apenas o sítio ativo de ligação com o carboidrato construído com o auxílio de docking molecular e mecânica molecular clássica. As energias de ligação são obtidas através de uma abordagem quântica ab initio all electron, dentro da Teoria do Funcional da Densidade (DFT), no espaço recíproco que combina o método Projector Augmented Waves (PAW) e a dinâmica molecular de Car-Parrinello (CP). Uma metodologia Hartree-Fock (HF) semi-empírica é utilizada para obter as propriedades óticas. A investigação deste problema muito complexo pode ser dividido em seis etapas principais: a) estudamos as propriedades estruturais da proteína para avaliar a sua mobilidade e escolhemos um conjunto de dados de raios-X para descrever o sistema; b) aplicamos a técnica de docking molecular para ligar quatro carboidratos ( alfa-metil-D-galactose, beta-D-galactose, O1-metil-manose e alfa-metil-D-glucopiranose) na proteína; c) otimizamos a geometria do sistema lectina-carboidrato utilizando mecânica molecular clássica; d) criamos o modelo-corte ; e) investigamos as propriedades óticas utilizando HF; f) estudamos as propriedades eletrônicas do sistema proteína-carboidrato e calculamos energias de ligação através do cálculo DFT. O modelo aqui proposto, além de apresentar uma adequada concordância com dados experimentais, abre a possibilidade de investigar propriedades eletrônicas através de uma abordagem quântica estado da arte na área de estrutura eletrônica.Frutalin is a tetrameric carbohydrate-binding protein obtained from breadfruit seeds. Biomedical interest on Frutalin comes from the high afinity exhibited by these molecules toward carbohydrates expressed by specific tumor cells. So far, no theoretical computational studies have been carried out to investigate the binding characteristics of frutalin, which is probably due to the large number of atoms that should be considered for in silicon calculations. We investigate the binding of frutalin and optical properties with specific carbohydrate molecules using a theoretical cutmodel considering only the carbohydrate binding site. This model has been constructed with the aid of molecular docking and classical molecular mechanics. We use the ab initio all electron reciprocal space Projector Augmented Waves (PAW) method and the Car-Parrinello scheme as embodied in the CP-PAW code to obtain the binding energies. To evaluate the optical properties, we employed the Hartree-Fock Semi-empirical ZINDO method from the Materials Studio 4.0 computational package. The investigation of this very complex problem can be divided into 6 main steps. Firstly, we study the structural properties of the protein to evaluate its mobility and we choose a x-ray data to describe reliably the system. In the second step, we performed molecular docking to link up four carbohydrates (alpha-methyl-D-galactoside, beta-D-galactoside, O1-methyl-mannose and methyl-alpha-D-glucopyranoside) in the protein. We optimize the geometry of the system lectin-carbohydrate using molecular mechanics in the third step. In the fourth step, we created the cutmodel based on the final geometries obtained in the previous step. In the fifth and sixth steps we investigate the quantum interaction of the protein with each carbohydrate. Our theoretical results are compared with available measurements in each step. The study of the interaction between the active binding site and carbohydrates allows us to demonstrate that our methodology is well suited to predict the electronic properties of the system.
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Rêgo, Celso Ricardo Caldeira. "Ab-initio studies of adsorbate-surface interactions." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-29012018-093011/.
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This thesis supplies a contribution to the understanding of the interaction between carboncarbon surfaces, atoms with carbon-surfaces, and atoms with metallic surfaces. It is well established that the surface-surface and atom-surface interactions are interesting, important and challenging for reasons that vary from industrial interest up to the academic necessity of understanding it deeply. Currently, there are many measurements and simulations for the geometric and electronic properties of Graphite, these differ by more than 40%. This implies that our understanding of the nature of this material is quite poor. The interaction between small transition-metals clusters with a Graphene sheet is another example where our knowledge is very limited. There are many theoretical studies in the literature that describe the interaction between these clusters with a Graphene sheet, but they agree and disagree on many points, which calls for systematic study of this issue. In this thesis we will focus our efforts on studying the surface-surface and atom/clusters-surface interactions. This thesis is split into three projects. The first aims to contribute to the understanding of the interlayer interactions of the bulk Graphite. In the second, we intend to shed some light on comprehending the interaction of an adatom with a Graphene sheet. Both of these projects, are studied within DFT framework with the inclusion of the van der Waals (vdW) corrections. In the Graphite project, we found that the electronic and geometric properties depend on the vdW correction employed in the calculation. In the adatom supported on Graphene project, we combined a modified Anderson-Newns model to describe the coupling between the adatom with Graphene. In addition, we found the existence of competition between quantum and classical forces, which determine the type of site in which the adatom prefers to adsorb. The last project is a dynamical study of an atom that impinges upon a metallic surface. In this project, we focus on the calculation of the sticking coefficient, a measure of the amount of nuclear density attached to the metal surface after collision. At this time the project is not one 100% ready, but our preliminary results indicates that, a small part of the nuclear density stays stuck on the metal.Esta tese ajuda a entender as interações entre duas superfícies de carbono. A natureza da interação de átomos ou aglomerados atômicos adsorvidos sobre uma superfície de carbono. Além disso, visa esclarecer a dinâmica de um átomo sendo adsorvido sobre uma superfície metálica. As interações superfície-superfície e átomos-superfícies são importantes por razões que variam desde o interesse industrial até a necessidade acadêmica para compreendê-la profundamente. Entendê-las ainda é um desafio. Diversos trabalhos apresentam medidas experimentais e simulações para as propriedades geométricas e eletrônicas do grafite. Tais medidas diferem em mais ide 40% umas da outra. Isso mostra que nossa compreensão sobre a natureza desse material ainda é bastante pobre. A interação entre pequenos grupos de metais de transição com uma folha de grapheno é outro exemplo em que nosso conhecimento é limitado. Existem muitos estudos teóricos na literatura que descrevem a interação desse tipo de aglomerado com uma folha de grafeno, porém há numerosas discordâncias. Tais controvérsias parecem suplicar por um estudo sistemático. Nesta tese focamos nossos estudos nas interações superfície-superfície e de átomos ou aglomerados atômicos com superfícies de carbono e de um metal. A tese foi dividida em três projetos. O primeiro visa compreender melhor a interação entre as camadas do grafite. No segundo, pretendemos lançar alguma luz no entendimento da interação de átomos e aglomerados atômicos com uma folha de grafeno. Esses dois projetos, são estudados à luz da Teoria do Funcional da Densidade com a inclusão das correções van der Waals (vdW). No Projecto sobre o grafite, mostramos que as propriedades eletrônicas e geométricas dependem do tipo de correção de vdW empregada no cálculo. No projeto sobre átomos e aglomerados atômicos adsorvidos no grapheno, combinamos um modelo modificado de Anderson-Newns para descrever o acoplamento entre um átomo adsorvido e o grafeno. Além disso, encontramos uma competição entre forças quânticas e clássicas, a qual determina o tipo de sítio no qual o átomo prefere ser adsorvido. O último projeto é um estudo dinâmico de um átomo colidindo contra uma superfície metálica. Nesse projeto o foco é posto no cálculo do coeficiente de aderência, o qual mede a taxa de densidade nuclear presa na superfície metálica após a colisão. Resultados preliminares indicam que, uma pequena parte da densidade nuclear permanece aderida ao metal depois da colisão.
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Gilbert, Christopher Andrew. "Ab initio modelling of defects in oxides." Thesis, Loughborough University, 2009. https://dspace.lboro.ac.uk/2134/35706.
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Two materials, magnesium oxide and magnesium aluminate spinel, have been studied using the ab initio methodology, density functional theory. In the case of MgO, energetics of a variety of point defects were considered. These defects were isolated Schottky and Frenkel defects and interstitial pairs, along with a number of Schottky defects and di-interstitials. Comparisons were made between the density functional theory results and results obtained from empirical potential simulations and these generally showed good agreement. Both methodologies predicted the first nearest neighbour Schottky defects to be the most energetically favourable of the considered Schottky defects and that the first, second, and fifth nearest neighbour di-interstitials were of similar energy and were favoured over the other di-interstitial configurations. Relaxed structures of the defects were analysed, which showed that empirical potential simulations were accurately predicting the displacements of atoms surrounding di-interstitials, but overestimated O atom displacement for Schottky defects.
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Shukri, Abdullah. "Ab initio electronic stopping power in materials." Palaiseau, Ecole polytechnique, 2015. https://tel.archives-ouvertes.fr/tel-01269549/document.
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Le pouvoir d'arrêt électronique est essentiel pour de nombreuses applications qui dépendent du transport des ions dans la matière, comme par exemple, la protonthérapie utilisée en médecine. Tandis que de nombreuses données expérimentales sont disponibles pour les élements purs, les données sont beaucoup plus parcellaires pour les matériaux binaires. Au cours de cette thèse, nous avons développé une approche numérique complètement ab initio fondée sur l'approximation de la réponse linéaire dans le cadre de la théorie de la fonctionnelle de la densité dépendente du temps, afin de prédire le pouvoir d'arrêt moyen d'un ion dans un matériau, sans recourrir à des ajustements sur l'expérience. Le code développé a été inséré dans le projet libre ABINIT. Tout d'abord, nous démontrons l'importance de la description réaliste de la structure électronique en comparant nos résultats à des calculs modèles de gaz d'électrons libres. Nous montrons que le pouvoir d'arrêt calculé est en bon accord avec l'expérience, pourvu que les calculs soient bien convergés et que les effets tels que l'excitation des électrons de coeur et l'échange-corrélation soient pris en compte. De façon surprenante, les effets au-delà de l'approximation linéaire restent limités pour les protons. Finalement, nous explorons le domaine de validité de quelques règles empiriques, communément utilisées par les expérimentateursThe knowledge of the stopping power is essential for a variety of applications which depend on the transport of ions in matter: for instance, the use of proton or heavier ion beams in radiotherapy. Whereas experimental data are readily available for elemental solids, the data are much more scarce for compounds. In this thesis, we develop a fully ab initio scheme based on linear response time-dependent density functional theory to predict the impact parameter averaged quantity named the random electronic stopping power (RESP) of materials without any empirical fitting. Our developments have been done within the open-source ab initio code named ABINIT, where two approximations are now available: the Random Phase Approximation (RPA) and the Adiabatic Local Density Approximation (ALDA). First, we demonstrate the importance of describing the realistic ab initio electronic structure by comparing ab initio against models based on the free-electron gas. We show that the calculated RESP compares well with experimental data, when at full convergence, with the inclusion of the core states and of the exchange-correlation. Also, we evaluate the unexpectedly limited magnitude of the non-linear terms in the RESP by comparing with other approaches based on the time-propagation of time-dependent density-functional theory. In addition, we check the validity of a few empirical rules of thumbs that are commonly employed for the experimental interpretation or for the prediction with empirical codes
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Bhattarai, Bishal. "Ab initio Structure Inversion for Amorphous Materials." Ohio University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1537349044469989.
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Adams, Donat Jozsef. "Ab initio simulations of Earth forming minerals /." kostenfrei, 2007. http://e-collection.ethbib.ethz.ch/view/eth:30017.
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Goll, Erich. "Kopplung von Dichtefunktional- und ab-initio-Methoden." [S.l. : s.n.], 2008. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-35842.
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Hardcastle, Trevor Peter. "Ab initio modelling of low-dimensional systems." Thesis, University of Leeds, 2014. http://etheses.whiterose.ac.uk/6828/.
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In this thesis, theoretical electronic structure methods have been used to study systems of interest to materials science and engineering. The many-body problem of quantum mechanics has been reviewed, and it has been explained that the density functional theory (DFT) of Hohenberg, Kohn and Sham is a very practical approach to solving it. The core details of DFT have been explicitly laid out. Having then demonstrated an awareness of the many different powers and varied capabilities of DFT in predicting material properties, systems laying at the current frontiers in nanoelectronics (chapters 3 and 5) and theoretical surface science (chapter 4) have then been focused on. In chapter 3, the behaviour of metal adatoms on graphene substrates has been predicted using DFT. From adatom binding energy and migration energy calculations, it has been theoretically suggested that single Cr, Au and Al adatoms diffuse randomly on graphene at room temperature until they collide with edge sites or defects, where they form stable bonds. This prediction has been used to explain experimental electron microscopy data which shows that metal adatoms evaporated onto graphene by chemical vapour deposition (CVD) have only ever been observed at edge sites and defects, and never on the pristine regions. In chapter 4, a new methodology has been developed for predicting the energies of step defects on crystalline solid surfaces, and it has been applied to steps on the (110) surface of TiO2 rutile. The limitations of currently published methods of calculating step energies have been explained in detail, and it has been demonstrated that this new method is much more reliable. The method has been used to predict the shape of a terrace island on the (110) surface of TiO2 rutile, and the prediction has been found to compare well with published experimental electron microscopy data. In chapter 5, current progress on an ongoing project has been summarised which investigates whether there is an energetic advantage to multiple substitutional nitrogen dopants in graphene occupying the same sublattice. The results are inconclusive so far, although it has been shown so far that magnetic effects are unlikely to be playing a role. In chapter 6, the accomplishments of this thesis have been summarised and future directions suggested.
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Fikar, Ondřej. "Ab initio výpočty křivek rozpustnosti tuhých roztoků." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-400461.
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This diploma thesis is focused on a theoretical study of the phase stability of solid solutions in selected aluminium and silver alloys. The ab initio calculations were performed using projected augmented waves method and the thermal dependencies of thermodynamic quantities were acquired using phonon calculations. The main focus of this work is the of aluminium-germanium alloy, while the other examined alloys (Al-Pb, Ag-Ge and Ag-Pb) serve the purpose of comparison of the solid solubility prediction and its reliability in systems with different composition. The temperatures, at which the solid solutions become stable, were evaluated using the energy difference between possible states and this evaluation was carried out for different contributions to the total energy. Also the electronic and phonon densities of states were calculated for all pure elements and solid solutions. The temperatures of solubility were compared to the experimental ones provided by the CALPHAD method and the individual contributions to the total energy were determined and depicted. The results obtained in this work tend to underestimate temperatures of solubility of individual solid solutions by hundreds of Kelvin.
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Bortoletto, Daiana Ribeiro. "Modelo computacional "ab-initio" para carcinoma espinocelular." reponame:Repositório Institucional da UFABC, 2017.
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Avezac, Mayeul d'. "Ab initio study of magnetic resonance spectroscopies." Paris 6, 2005. http://www.theses.fr/2005PA066264.
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