To see the other types of publications on this topic, follow the link: DFT approach.
Dissertations / Theses on the topic 'DFT approach'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'DFT approach.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Bagchi, Bhaskar. "Quantum chemical calculation and structure activity relationship of bioactive terpenoids." Thesis, University of North Bengal, 2016. http://ir.nbu.ac.in/handle/123456789/2762.
Full text
2
John, Richard. "Rationalising reactivity : a combined DFT and hyperpolarisation approach." Thesis, University of York, 2014. http://etheses.whiterose.ac.uk/15397/.
Full textAbstract:
The complexes Ru(CO)3(dpae) and Ru(CO)2(dpae)(PPh3) have been found experimentally to undergo various reactions with para-hydrogen and substrates. Reactions with para-hydrogen and diphenylacetylene led to the detection of hydrogenation products, confirming the complexes as hydrogenation catalysts. The catalytic behaviour was identified to be different to that of the equivalent phosphine containing complex. High level DFT investigations have revealed significant insight into the mechanism of reaction. The experimentally detected dihydride complex Ru(H)2(CO)(dpae) was calculated to be a viable reaction product, with various pathways modelled for rearrangement. In contrast, the rearrangements for the complex Ru(H)2(CO)dpae)(PPh3) were found to compete with the reductive elimination of dihydrogen. The routes of reaction by initiation method was examined, with the high energy 14-electron intermediates only accessible photochemically. Routes for the hydrogenation of diphenylacetylene were identified, alongside the mechanism of cis-trans scrambling of stilbene and formation of 1,2-diphenylethane. The formation of 1,2,3,4-tetraphenylbutadiene was also rationalised. The reaction of hydrogen with W(N2)2(dppe-κ2P)2 was shown theoretically to involve an intra-molecular ortho-metallation reaction from the reactive 14-electron intermediate W(dppe-κ2P)2. Low barriers were obtained from the 16-electron intermediate W(H)2(dppe-κ2P)2. This rationalised the formation of the experimentally proposed complex W(H)3(dppe-κ2P)(PPh(C6H4CH2CH2Ph2P)-κ2P). The 14-electron intermediate W(dppe-κ2P)2 was calculated to adopt a butterfly geometry in a singlet state, which than rearranges upon reaction to form 16-electron intermediates. The observation of PHIP in the end products confirms the involvement of an electronic singlet state. Limited solvation was predicted from THF despite its ability to coordinate to metal centres. In summary, the combination of high level DFT models and the use of para-hydrogen reactions is demonstrated to be a powerful tool for probing chemical processes and pathways, and contributes to achieving a greater understanding of reactivity in these metal complex systems.
3
Husowitz, Barry Charles. "Effect of Confinement and Heterogeneity on Phase Behavior: A Density Functional Approach." Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/196124.
Full textAbstract:
Density functional theory of statistical mechanics in a square gradient approximation was used to study nucleation in confined systems such as a cylindrical pore and in-between two cylindrical disks. This approximation was further applied to study the evaporation and condensation in nanopores with finite lengths. Confinement effects induced nucleation phenomena that are not observed in more open systems. Density functional theory was also used to explore the solvation properties of a spherical solute immersed in a supercritical diatomic fluid. The solute was modeled as a hard core Yukawa particle surrounded by a diatomic Lennard-Jones fluid represented by two fused tangent spheres using an interaction site approximation. The results of this study indicate that local density augmentation and the solvation free energies are particularly sensitive to changes in solute and solvent particle geometry and solute/solvent anisotropic interactions. Density functional theory allowed us to systematically study the effect of a variety of geometric and interaction parameters on the properties and behavior of all the systems. Although more sophisticated, but computationally more demanding, theoretical approaches can be used, our results provide fundamental physical insights into the behavior of real systems and create a solid basis for the development of more realistic models.
4
Fernández, Alvarez Víctor Miguel. "A computational approach to the mechanism of light-driven reactions in solution." Doctoral thesis, Universitat Rovira i Virgili, 2017. http://hdl.handle.net/10803/402464.
Full textAbstract:
Aquesta tesi doctoral descriu l'aplicació, d'una combinació de mètodes DFT (Teoria del Funcional de la Densitat) i models cinètics, per elucidar el mecanisme de reaccions en solució iniciades per llum. Aquesta estratègia és usada per estudiar dos tipus de reaccions d'interès comercial. A la primera part, s'analitza el mecanisme de transformacions químiques activades directament per llum. En canvi, la segona part abasta reaccions en què l'activació lumínica passa a través d'un foto-catalitzador. En tots dos casos, els resultats i les propietats experimentals, com ara la selectivitat o el rendiment quàntic, van ser reeixidament reproduïts, i racionalitzats d'acord a les propietats d'estructura electrònica que defineixen els sistemes involucrats. A més, es va demostrar que els models cinètics són crucials per calcular aspectes del mecanisme de transformacions foto-induïdes, ja que la mera comparació de barreres d'energia no té en compte les grans diferències de concentracions presents.Esta tesis doctoral describe la aplicación, de una combinación de métodos DFT (Teoría del Funcional de la Densidad) y modelos cinéticos, para elucidar el mecanismo de reacciones en solución iniciadas por luz. Esta estrategia es usada para estudiar dos tipos de reacciones de interés comercial. En la primera parte, se analiza el mecanismo de transformaciones químicas activadas directamente por luz. En cambio, la segunda parte abarca reacciones en las que la activación lumínica ocurre a través de un foto-catalizador. En ambos casos, los resultados y las propiedades experimentales, tales como la selectividad o el rendimiento cuántico, fueron exitosamente reproducidos, y racionalizados de acuerdo a las propiedades de estructura electrónica que definen a los sistemas involucrados. Además, se demostró que los modelos cinéticos son cruciales para calcular aspectos del mecanismo de transformaciones foto-inducidas, ya que la mera comparación de barreras de energía no tiene en cuenta las grandes diferencias de concentraciones presentes.
This doctoral thesis describes the application of a combination of Density Functional Theory (DFT) methods and kinetic models to elucidate the mechanism of light-driven synthesis reactions in solution. This strategy is applied to study two types of reactions of commercial interest. In the first part, the mechanism of chemical transformations directly activated by visible light is analyzed. On the other hand, the second part covers reactions in which light activation takes place via a photocatalyst. For both cases, experimental outcomes and properties such as selectivity and quantum yield were correctly reproduced and rationalized on the basis of the electronic structure properties that define the systems involved. In addition, kinetic models proved vital in the computation of mechanistic aspects of photo-induced transformations as mere comparisons of energy barriers fail to account for large differences in concentration present.
5
Martins, Ana Caroline Vasconcelos. "GluA2 - Glutamatergic Receptor Study: A Molecular Approach." reponame:Repositório Institucional da UFC, 2017. http://www.repositorio.ufc.br/handle/riufc/28258.
Full textAbstract:
Submitted by José Orlando Soares de Oliveira (orlando.soares@bol.com.br) on 2017-11-30T12:23:47Z
No. of bitstreams: 1
2017_tese_acvmartins.pdf: 10270409 bytes, checksum: f2b0eb40db54875e0e40a6d040ce7336 (MD5)Rejected by Weslayne Nunes de Sales (weslaynesales@ufc.br), reason: A aluna optou por publicar apenas os elementos pré-textuais. on 2017-12-01T12:36:51Z (GMT)
Submitted by José Orlando Soares de Oliveira (orlando.soares@bol.com.br) on 2017-12-01T13:50:35Z No. of bitstreams: 1 Tese corrigida - elementos pretextuais.pdf: 159585 bytes, checksum: 9531b29bc8c5a46f5ed5753442df383f (MD5)
Approved for entry into archive by Weslayne Nunes de Sales (weslaynesales@ufc.br) on 2017-12-01T13:57:30Z (GMT) No. of bitstreams: 1 Tese corrigida - elementos pretextuais.pdf: 159585 bytes, checksum: 9531b29bc8c5a46f5ed5753442df383f (MD5)
Made available in DSpace on 2017-12-01T13:57:30Z (GMT). No. of bitstreams: 1 Tese corrigida - elementos pretextuais.pdf: 159585 bytes, checksum: 9531b29bc8c5a46f5ed5753442df383f (MD5) Previous issue date: 2017-11-17
Glutamate receptors are the mediators of most excitatory neurotransmission processes in the central nervous system, acting as prominent targets for the treatment of several neurological disorders such as Epilepsy, Amyotrophic Lateral Sclerosis, Parkinson’s disease and Alzheimer’s disease. Hence an improved understanding of how glutamate and other ligands interact with the binding domain, of these receptors, can bring relevant insights to the development of new ligands. Therefore, this work aims to study the GluA2–ligand interaction using the structure of GluA2 co-crystallized with the ligands glutamate, AMPA, kainate and DNQX applying a method based on the Density Functional Theory combined with the molecular fractionation with conjugate caps scheme. To address that the dielectric constant of the GluA2 receptor is not homogeneous, a novel molecular approach was proposed and it was applied to study the interaction between the GluA2 and the ligands glutamate, AMPA, kainate and DNQX. The results obtained, considering the inhomogeneous model, were compared with those obtained using an uniform dielectric function for the GluA2 receptor and with data published in the literature establishing a more detailed description of the relevant amino acid residues for the protein-ligand binding interaction. Molecular dynamics studies and protein DFT calculations usually consider a fixed value for the protein dielectric function. In this work when ε = 1 is considered, many amino acid residues seem important, but when the dielectric constant shield was considered, they lost their relevance. The results for the GluA2-ligand total interaction energy and the D1-ligand and D2-ligand total interaction energy also shed some light on the differentiation between full and partial agonists, and between agonists and antagonists. Additionally, the results allow a hypothesis on the correlation between the Glu705-ligand interaction energy and the ligand action, paving the way for the use of the inhomogeneous dielectric function to study glutamate receptors and other protein-ligand systems. Finally, the results also suggests that for different ligands, different homogeneous dielectric constant will be able to well represent the system GluA2-ligand, making it necessary the previous analyses with the inhomogeneous dielectric constant approach.
Os receptores de glutamato são os mediadores da maioria dos processos de neurotransmissão excitatória no sistema nervoso central, atuando como alvos proeminentes para o tratamento de vários distúrbios neurológicos, como Epilepsia, Esclerose Lateral Amiotrófica, Doença de Parkinson e Doença de Alzheimer. Assim, uma compreensão aprimorada de como o glutamato e outros ligantes interagem com o domínio de interação, desses receptores, pode trazer informações relevantes para o desenvolvimento de novos ligantes. Portanto, este trabalho teve por objetivo estudar a interação GluA2-ligante utilizando a estrutura de GluA2 co-cristalizada com os ligantes Glutamato, AMPA, Cainato e DNQX utilizando método baseado na Teoria do Funcional da Densidade combinado com o esquema de fracionamento molecular com capas conjugadas. Para abordar que a constante dielétrica do receptor GluA2 não é homogênea, foi proposta uma nova abordagem molecular, que foi aplicada para estudar a interação entre a GluA2 e os ligantes Glutamato, AMPA, Cainato e DNQX. Os resultados obtidos, considerando o modelo não-homogêneo, foram comparados com aqueles obtidos usando uma função dielétrica uniforme para o receptor GluA2 e com dados publicados na literatura, estabelecendo uma descrição mais detalhada dos resíduos de aminoácido mais relevantes para a interação proteína-ligante. Estudos de dinâmica molecular e cálculos DFT de sistemas proteicos normalmente consideram um valor fixo para a função dielétrica proteica. Nesse trabalho quando ε = 1 é considerado, muitos resíduos de aminoácido parecem relevantes, mas quando a blindagem da constante dielétrica foi considerada, eles perderam sua relevância. Os resultados apresentados para a energia de interação total GluA2-ligante e a energia de interação total D1-ligante e D2-ligante contribuiu com a diferenciação entre agonistas totais e agonistas parciais e entre agonistas e antagonistas. Além disso, os resultados permitem que seja feita hipótese sobre a correlação entre a energia de interação Glu705-ligante e a ação do ligante, abrindo caminho para o uso da função dielétrica não-homogênea para estudar receptores de glutamato e outros sistemas proteína-ligante. Por fim, os resultados também sugerem que para diferentes ligantes, diferentes constantes dielétricas homogêneas serão capazes de representar bem o sistema GluA2-ligante, tornando necessária a análise prévia com a abordagem da constante dielétrica não-homogênea.
6
Zhang, Xuan. "High Precision Dynamic Power System Frequency Estimation Algorithm Based on Phasor Approach." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/31001.
Full textAbstract:
An internet-based, real-time, Global Positioning System (GPS) ---synchronized relative to the wide-area frequency-monitoring network (FNET) ---has been developed at Virginia Tech. In this FNET system, an algorithm that employs the relationship between phasor angles and deviated frequency [13] is used to calculate both frequency and its rate of change. Tests of the algorithm disclose that, for non-pure sinusoidal input (as compared to pure sinusoidal input), significant errors in the output frequency will result. Three approaches for increasing the accuracy of the output frequency were compared. The first---increasing the number of samples per cycle N---proved ineffective. The second---using the average of the first estimated frequencies rather than the instant first estimated frequency as the resampling frequency---produces a moderate increase in accuracy of the frequency estimation. The third---multiple resampling---significantly increased accuracy. But both the second and the third become ineffective to the extent the input is not pure sinusoidal.
From a practical standpoint, attention needs to be paid toward eliminating noise in the input data from the power grid so as to make it more purely sinusoidal. Therefore, it will be worthwhile to test more sophisticated digital filters for processing the input data before feeding it to the algorithm.Master of Science
7
Ponnuchamy, Veerapandian. "Towards A Better Understanding of Lithium Ion Local Environment in Pure, Binary and Ternary Mixtures of Carbonate Solvents : A Numerical Approach." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GRENY004/document.
Full textAbstract:
En raison de l'augmentation de la demande d'énergie, ressources écologiques respectueux de l'environnement et durables (solaires, éoliennes) doivent être développées afin de remplacer les combustibles fossiles. Ces sources d'énergie sont discontinues, étant corrélés avec les conditions météorologiques et leur disponibilité est fluctuant dans le temps. En conséquence, les dispositifs de stockage d'énergie à grande échelle sont devenus incontournables, pour stocker l'énergie sur des échelles de temps longues avec une bonne compatibilité environnementale. La conversion d'énergie électrochimique est le mécanisme clé pour les développements technologiques des sources d'énergie alternatives. Parmi ces systèmes, les batteries Lithium-ion (LIB) ont démontré être les plus robustes et efficaces et sont devenus la technologie courante pour les systèmes de stockage d'énergie de haute performance. Ils sont largement utilisés comme sources d'énergie primaire pour des applications populaires (ordinateurs portables, téléphones cellulaires, et autres). La LIB typique est constitué de deux électrodes, séparés par un électrolyte. Celui-ci joue un rôle très important dans le transfert des ions entre les électrodes fournissant la courante électrique. Ce travail de thèse porte sur les matériaux complexes utilisés comme électrolytes dans les LIB, qui ont un impact sur les propriétés de transport du ion Li et les performances électrochimiques. Habituellement l'électrolyte est constitué de sels de Li et de mélanges de solvants organiques, tels que les carbonates cycliques ou linéaires. Il est donc indispensable de clarifier les propriétés structurelles les plus importantes, et leurs implications sur le transport des ions Li+ dans des solvants purs et mixtes. Nous avons effectué une étude théorique basée sur la théorie du fonctionnelle densité (DFT) et la dynamique moléculaire (MD), et nous avons consideré des carbonates cyclique (carbonate d'éthylène, EC, et carbonate de propylène, PC) et le carbonate de diméthyle, DMC, linéaire. Les calculs DFT ont fourni une image détaillée des structures optimisées de molécules de carbonate et le ion Li+, y compris les groupes pures Li+(S)n (S =EC,PC,DMC et n=1-5), groupes mixtes binaires, Li+(S1)m(S2)n (S1,S2=EC,PC,DMC, m+n=4), et ternaires Li+(EC)l(DMC)m(PC)n (l+m+n=4). L'effet de l'anion PF6 a également été étudié. Nous avons aussi étudié la structure de la couche de coordination autour du Li+, dans tous les cas. Nos résultats montrent que les complexes Li+(EC)4, Li+(DMC)4 et Li+(PC)3 sont les plus stables, selon les valeurs de l'énergie libre de Gibbs, en accord avec les études précédentes. Les énergies libres de réactions calculés pour les mélanges binaires suggèrent que l'ajout de molécules EC et PC aux clusters Li+ -DMC sont plus favorables que l'addition de DMC aux amas Li+-EC et Li+-PC. Dans la plupart des cas, la substitution de solvant aux mélanges binaires sont défavorables. Dans le cas de mélanges ternaires, la molécule DMC ne peut pas remplacer EC et PC, tandis que PC peut facilement remplacer EC et DMC. Notre étude montre que PC tend à substituer EC dans la couche de solvation. Nous avons complété nos études ab-initio par des simulations MD d'une ion Li immergé dans les solvants purs et dans des mélanges de solvants d'intérêt pour les batteries, EC:DMC(1: 1) et EC:DMC:PC(1:1:3). MD est un outil très puissant et nous a permis de clarifier la pertinence des structures découvertes par DFT lorsque le ion est entouré par des solvants mélangés. En effet,la DFT fournit des informations sur les structures les plus stables de groupes isolés, mais aucune information sur leur stabilité ou de la multiplicité (entropie) lorsqu'il est immergé dans un environnement solvant infinie. Les données MD, ainsi que les calculs DFT nous ont permis de donner une image très complète de la structure locale de mélanges de solvants autour le ion lithium, sensiblement amélioré par rapport aux travaux précédentsDue to the increasing global energy demand, eco-friendly and sustainable green resources including solar, or wind energies must be developed, in order to replace fossil fuels. These sources of energy are unfortunately discontinuous, being correlated with weather conditions and their availability is therefore strongly fluctuating in time. As a consequence, large-scale energy storage devices have become fundamental, to store energy on long time scales with a good environmental compatibility. Electrochemical energy conversion is the key mechanism for alternative power sources technological developments. Among these systems, Lithium-ion (Li+) batteries (LIBs) have demonstrated to be the most robust and efficient, and have become the prevalent technology for high-performance energy storage systems. These are widely used as the main energy source for popular applications, including laptops, cell phones and other electronic devices. The typical LIB consists of two (negative and positive) electrodes, separated by an electrolyte. This plays a very important role, transferring ions between the electrodes, therefore providing the electrical current. This thesis work focuses on the complex materials used as electrolytes in LIBs, which impact Li-ion transport properties, power densities and electrochemical performances. Usually, the electrolyte consists of Li-salts and mixtures of organic solvents, such as cyclic or linear carbonates. It is therefore indispensable to shed light on the most important structural (coordination) properties, and their implications on transport behaviour of Li+ ion in pure and mixed solvent compositions. We have performed a theoretical investigation based on combined density Functional Theory (DFT) calculations and Molecular Dynamics (MD) simulations, and have focused on three carbonates, cyclic ethylene carbonate (EC) and propylene carbonate (PC), and linear dimethyl carbonate (DMC). DFT calculations have provided a detailed picture for the optimized structures of isolated carbonate molecules and Li+ ion, including pure clusters Li+(S)n (S=EC, PC, DMC and n=1-5), mixed binary clusters, Li+(S1)m(S2)n (S1, S2 =EC, PC, DMC, with m+n=4), and ternary clusters Li+(EC)l(DMC)m(PC)n with l+m+n=4. Pure solvent clusters were also studied including the effect of PF6- anion. We have investigated in details the structure of the coordination shell around Li+ for all cases. Our results show that clusters such as Li+(EC)4, Li+(DMC)4 and Li+(PC)3 are the most stable, according to Gibbs free energy values, in agreement with previous experimental and theoretical studies. The calculated Gibbs free energies of reactions in binary mixtures suggest that the addition of EC and PC molecules to the Li+-DMC clusters are more favourable than the addition of DMC to Li+-EC and Li+-PC clusters. In most of the cases, the substitution of solvent to binary mixtures are unfavourable. In the case of ternary mixtures, the DMC molecule cannot replace EC and PC, while PC can easily substitute both EC and DMC molecules. Our study shows that PC tends to substitute EC in the solvation shell. We have complemented our ab-initio studies by MD simulations of a Li-ion when immersed in the pure solvents and in particular solvents mixtures of interest for batteries applications, e.g. , EC:DMC (1:1) and EC:DMC:PC(1:1:3). MD is a very powerful tool and has allowed us to clarify the relevance of the cluster structures discovered by DFT when the ion is surrounded by bulk solvents. Indeed, DFT provides information about the most stable structures of isolated clusters but no information about their stability or multiplicity (entropy) when immersed in an infinite solvent environment. The MD data, together the DFT calculations have allowed us to give a very comprehensive picture of the local structure of solvent mixtures around Lithium ion, which substantially improve over previous work
8
Sirikumara, Henaka Rallage Hansika Iroshini. "Engineering structural/electronic properties of layered Selenides : A multi-scale modeling approach." OpenSIUC, 2020. https://opensiuc.lib.siu.edu/dissertations/1840.
Full textAbstract:
Since the discovery of graphene, a new era of physics called "Two Dimensional (2D)Materials" has emerged. Group IV and Group III Selenides such as SnSe and InSe arepromising members of the 2D family. Structure of Group IV selenides is unique and highlysensitive to pressure and temperature. To further tweaking their properties by structuralchanges, thorough understanding of how the structure relates to the electronic bands is veryimportant. Based on the results from DFT calculations, I carefully analyzed electronic bandstructures of layered SnSe with various interlayer stacking. The first part of this dissertationdiscussed the possible stacking-dependent indirect-direct transition of bilayer SnSe.By further analysis, these results reveal that the directionality of interlayer interactionsdetermine the critical features of their electronic band structures. Further, it demonstratedthat such changes can be achieved by substitutional chemical doping. Using a multi-scalemodeling approach by combining the result of DFT and Boltzmann Transport Theory, Idiscussed the electron transport properties of co-doped SnSe, a class of thermodynamicallyand dynamically stable structures. The second part discussed on charge transfer across InSe/Gas interface, which showsbi-polar transport properties. This finding is in a good agreement with the recent experimentalobservations. Fundamental understanding of charge transfer in few-layer InSe /gasinterfaces at the atomic level is expected to pave the path for designing gas sensing devices.
9
Kuchi, Jayasurya. "AN EFFICIENT APPROACH TO REDUCE TEST APPLICATION TIME THROUGH LIMITED SHIFT OPERATIONS IN SCAN CHAINS." OpenSIUC, 2017. https://opensiuc.lib.siu.edu/theses/2182.
Full textAbstract:
Scan Chains in DFT has gained more prominence in recent years due to the increase in the complexity of the sequential circuits. As the test time increases along with the number of memory elements in the circuit, new and improved methods came in to prominence. Even though scan chain increases observability and controllability, a big portion of the time is wasted while shifting in and shifting out the test patterns through the scan chain. This thesis focus on reducing the number of clock cycles that are needed to test the circuit. The proposed Algorithm uses modified shift procedures based on 1) Finding hard to detect faults in the circuit. 2) Productive way to generate test patterns for the combinational blocks in between the flip flops. 3) Rearranging test patterns and changing the shift procedures to achieve fault coverage in reduced number of clock cycles. In this model, the selection process is based on calculating the fault value of a fault and total fault value of the vector which is used to find the hard faults and the order in which the vectors are applied. This method reduces the required number of shifts for detecting the faults and thereby reducing the testing time. This thesis concentrates on appropriate utilization of scan chains for testing the sequential circuits. In this context, the proposed method shows promising results in reduction of the number of shifts, thereby reducing the test time. The experimental results are based on the widely cited ISCAS 89 benchmark circuits.
10
Pueschel, Charles A. "First principles approach to understanding stability and phase transitions of metal A(II)B(IV)hexafluorides." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54484.
Full text
11
Pubill, Ulldemolins Cristina. "Catalytic activation of diboron reagents towards their addition to alkenes: experimental and theoretical approach." Doctoral thesis, Universitat Rovira i Virgili, 2012. http://hdl.handle.net/10803/97206.
Full textAbstract:
Els compostos organoborats són potencialment utilitzats en un extens nombre de camps, des de la medicina, en la teràpia de captura neutrònica amb bor o altres molècules amb activitat biològica, fins a l’ús de molècules funcionals com els polímers. A més a més, els compostos organoborats són curcials com a intermedis de síntesis per a productes d’alt valor afegit. El tema principal d’aquesta tesi és el desenvolupament de noves metodologies sintètiques per a l’obtenció de compostos organoborats de manera eficient. Ens hem centrat en entendre els diferents modes d’activació d’agents diborans i el mecanisme dels processos d’addició de diborans a alquens. Amb aquest propòsit s’han dut a terme estudis d’RMN juntament amb càlculs teòrics basats en la Teoria del Funcional de la Densitat (DFT).The organoborane products are highly used in a broad number of fields, from their use in medicine as a 10B carrier for neutron capture therapy, or other molecules with biological activity, to their use as functional molecules such as polymers. Importantly, organoboranes are very versatile and powerful intermediates in the synthesis of high value products. This thesis focuses on the development of novel methodologies for catalytic boron addition to alkenes, with particular attention to the understanding of the activation mode of the diboron reagent and the mechanism of their addition to olefins. For this purpose NMR studies together with DFT (Density Functional Theory) calculations are carried out.
12
Bohorquez, Ballen Jaime. "Thermal transport in low dimensional semiconductor nanostructures." OpenSIUC, 2014. https://opensiuc.lib.siu.edu/dissertations/798.
Full textAbstract:
We have performed a first principles density functional theory (DFT) calculations to study the thermal conductivity in ZnO nanotubes, ZnO nanowires, and Si/Ge shell-core nanowires. We found the equilibrium configuration and the electric band structure of each nanostructure using DFT, the interatomic force constants and the phonon dispersion relations were calculated using DFPT as implemented in Quantum Espresso. In order to fundamentally understand the effect of atomic arrangements, we calculated the phonon conductance in a ballistic approach using a Green's function method. All ZnO nanostructures studied exhibit semiconducting behavior, with direct bandgap at the Gamma point. The calculated values for the bandgaps were larger than the value of the bandgap of the bulk ZnO. We were able to identify phonon modes in which the motion of Zn atoms is significant when it is compared with the motion of oxygen atoms. The thermal conductivity depends on the diameter of the nanowires and nanotubes and it is dramatically affected when the nanowire or nanotube is doped with Ga. For Si/Ge nanowires, the slope and the curvature of acoustic modes in the phonon dispersion relation increases when the diameter increases. For nanowires with the same number of atoms, the slope and curvature of acoustic modes depends on the concentration of Si atoms. We were able to identify phonon modes in which the motion of core atoms is significant when it is compared with motion of atoms on the nanowire's shell. The thermal conductivity in these nanostructures depends on the nanowire's diameter and on the Si atoms concentration.
13
Costa, Davide. "Modelling the thermal ageing evolution of Fe-Cr alloys using a lattice kinetic Monte Carlo approach based on DFT calculations." Thesis, Lille 1, 2012. http://www.theses.fr/2012LIL10037/document.
Full textAbstract:
Cette thèse aborde l'étude du vieillissement thermique du système Fe-Cr. Nous avons étudié le mécanisme de diffusion de la lacune dans le cadre de la théorie de la fonctionnelle de la densité (Density Functional Theory - DFT) et examiné la capacité d'un potentiel empirique de la classe EAM (Embedded Atom Method) à reproduire les résultats DFT. Nous avons montré que l'énergie de migration de la lacune dépend fortement de l'environnement atomique du point de col où les interactions chrome-chrome et chrome-lacune déterminent en partie l’énergie de point de col. Nous avons proposé trois approches pour la paramétrisation d'un modèle Monte Carlo Cinétique (MCC) atomique : l’une entièrement basée sur le potentiel EAM, les autres partiellement basées sur nos calculs DFT. Les simulations par MCC du vieillissement thermique des alliages Fe-20% at. Cr et Fe-25% at. Cr à 773 K montrent la formation de précipités riches en chrome dont la croissance avec le temps suit une loi de puissance avec un exposant 1/3, en accord avec la théorie de Lifshitz-Slyozov-Wagner. La paramétrisation des simulations par MCC entièrement basée sur le potentiel EAM prédit une taille moyenne des précipités supérieure à celle observée expérimentalement, alors que cette dernière est sous-estimée par les paramétrisations partiellement basées sur nos calculs DFT. Ce désaccord semble avoir une origine cinétique plutôt que thermodynamique. La composition de la phase riche en chrome varie au cours de la séparation de phase, indiquant ainsi que la démixtion se produit par nucléation non-classique ou par décomposition spinodale. Des précipités interconnectés sont plus susceptibles de se former dans le système Fe-25% at. Cr plutôt que dans l’alliage Fe-20% at. Cr suggérant ainsi que, lorsque la concentration en soluté augmente, le mécanisme de démixtion se rapproche de la décomposition spinodaleIn this thesis, we address the study of the microstrucutre evolution of the Fe-Cr system under thermal ageing. The vacancy diffusion mechanism was investigated in the framework of the density functional theory (DFT) and the capability of a recently developed embedded atom method (EAM) empirical cohesive model to reproduce the DFT results was examined. We have shown that the vacancy migration energy strongly depends on the saddle point atomic environment where the chromium-chromium and the chromium-vacancy interactions partially determine the saddle point energy. We proposed three approaches for the parameterisation of an atomistic kinetic Monte Carlo (AKMC) model: one fully based on the EAM potential, the others partially based on our DFT calculations. The AKMC simulations of the thermal ageing of the Fe-20 at.%Cr and Fe-25 at.%Cr alloys at 773 K show the formation of chromium-rich precipitates whose growth with time follows a power law with exponent 1/3. This is consistent with the Lifshitz-Slyozov-Wagner theory of coarsening. The AKMC parameterisation fully based on the EAM potential predicts a mean precipitate size higher than the experimentally observed one, whereas the parameterisations partially based on our DFT calculations underestimate it. This disagreement seems to have a kinetic rather than thermodynamic origin. The composition of the precipitating phase varies during the phase separation thus indicating that the unmixing is driven by either a non-classical nucleation or a spinodal decomposition. Interconnected precipitates are more likely to form in the Fe-25 at.%Cr alloy than in the Fe-20 at.%Cr thus suggesting that, as the solute concentration increases, the spinodal decomposition is more likely to occur
14
Das, S. "Theoretical investigation on structure and reactivity properties of molecule and metal clusters: a conceptual DFT and Ab initio molecular dynamics approach." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2015. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2015.
Full text
15
Okhrimenko, Ivan Grigoryevich. "Implementation of Optical Spectra Calculations in FIREBALL: A Local-Orbital Density Functional Theory Approach." Diss., CLICK HERE for online access, 2008. http://contentdm.lib.byu.edu/ETD/image/etd2620.pdf.
Full text
16
Zhu, Jingwen. "Study of B-H agostic interactions andc onsequence sfor hydrogen storage." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS182/document.
Full textAbstract:
Dans le cadre de la recherche de vecteurs d'énergie “propres”, le borazane et ses dérivés amine-boranes sont devenus des candidats intéressants en tant que matériaux de stockage de l'hydrogène en raison de leur pourcentage massique relativement élevé en hydrogène (19,6% pour borazane) et de la réversibilité potentielle de la réaction de déshydrogénation. Pour des applications réelles, le contrôle des réactions se produisant à la température ambiante est fondamental. Dans ce contexte, la compréhension du processus de la déshydrogénation/déshydrocouplage catalytique de l'amine-borane apparaît comme un élément important. Dans cette thèse, les catalyseurs de types métallocènes du Groupe IV (Cp2M, M = Ti, Zr et Hf) sont étudiés en détail. Le déshydrocouplage de HMe2N·BH3 catalysé par le titanocène a été étudié à la fois expérimentalement et théoriquement mais aucun accord n'avait été atteint auparavant. Dans ce travail, les caractérisations systématiques des interactions 3-centre 2-électron M···H-B impliquées dans les intermédiaires réactionnels ont été réalisées avec des approches topologiques QTAIM et ELF. Par la suite, des mécanismes réactionnels détaillés ont été étudiés. Les résultats théoriques ont démontré que la méthode DFT corrigée avec la dispersion (DFT-D) étaient nécessaire et suffisantes pour une description énergétique correcte des chemins réactionnels. Mon travail a également permis l'identification d'un complexe de van der Waals jouant un rôle clé dans le mécanisme réactionnel en accord avec les observations expérimentalesWith the increasing demand of clean energy carriers, ammonia borane and its related amine-borane compounds have emerged as attractive candidates for hydrogen storage materials due to their relatively high weight percentage of available hydrogen (19.6% for ammonia borane) as well as the potential reversibility for the hydrogen release reactions. Actual applications would benefit from controlled reactions occurring close to room-temperature. In this context, catalytic dehydrogenation/dehydrocoupling of amine-borane appears as a promising solution. In this thesis the Group IV metallocene (Cp2M, M = Ti, Zr and Hf) are mainly discussed. The dehydrocoupling of HMe2N·BH3 catalyzed by titanocene was investigated both experimentally and theoretically but no agreement were reached. In this work, systematic characterization of M···H-B 3-center 2-electron interactions involved in reaction intermediates were carried out with QTAIM and ELF topological approaches. Afterwards, detailed mechanisms were further studied. Computational results have demonstrated that the dispersion corrected DFT (DFT-D) method was indispensable for a correct enegetic prediction for reaction pathways. The identification of a van der Waals complexe also plays a central role for a reaction mechanism with good agreement with experimental observations
17
Cousins, Morgan. "I. Designing Brighter Fluorophores: A Computational And Spectroscopic Approach To Predicting Photophysical Properties Of Hydrazone-Based Dyes Ii. Developing Spectroscopic Methods To Better Understand The Cofactors Of Metalloproteins." ScholarWorks @ UVM, 2017. https://scholarworks.uvm.edu/graddis/787.
Full textAbstract:
Luminogens are molecules that emit light upon exposure to high-energy light, and fluorophores are one class of luminogens. Applications of fluorophores range from microviscosity sensors to light emitting diodes (LEDs), as well as biosensors, just to name a few. Many of these applications require the fluorophore to be in the aggregate or solid state. Some fluorophores become highly emissive in the aggregate state; these fluorophores are aggregation-induced emission (AIE) luminogens. Currently, very few quantum mechanical mechanisms have been proposed to describe the unique AIE behavior of luminogens.
Boron difluorohydrazone (BODIHY) dyes are a new type of AIE fluorophore. The bright emission is from the S>1 excited state (“anomalous” emission) contrary to Kasha’s Rule. Thus, the mechanism Suppression of Kasha’s Rule (SOKR) was proposed to be responsible for the family of BODIHY dyes. We hypothesize that the SOKR mechanism can explain AIE as well as the anomalous emission of other fluorophores. New BODIHY derivatives (para-CO2H BODIHY, aluminum difluorohydrazone (ALDIHY), and paranitro ALDIHY) were predicted to be bright anomalous fluorophores through density functional theory (DFT) and time-dependent DFT (TDDFT) investigations. In addition, a series of anomalous fluorophores were investigated to determine if their photophysical properties could be explained by the SOKR mechanism (azulene, 1,6-diphenyl-1,3,5hexatriene, and zinc tetraphenylporphyrin). Finally, several triazolopyridinium and triazoloquinolinium dyes were computationally investigated by DFT and TDDFT calculations, and an accurate computational model for the large Stokes shifts of these dyes was developed. In conclusion, a better understanding of the photophysical properties through DFT and TDDFT modeling and spectroscopic investigation of hydrazone-based fluorophores has been achieved.
In addition, the metal active sites and cofactors of metalloproteins were probed by optical spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and DFT modeling. In conjunction, these techniques can be used to elucidate the electronic structure responsible for the unique function of these metalloproteins. Specifically, a novel ironsulfur cluster of a metalloprotein that may be involved in endospore formation of Clostridium difficile, CotA, was characterized by magnetic circular dichroism (MCD) spectroscopy. We propose that CotA contains a high-spin [4Fe-4S] cluster and a Rieske [2Fe-2S] cluster. It appears that the multimerization of the protein is related to the cluster conversion at the interface of monomeric subunits where two [2Fe-2S] clusters combine to form the [4Fe-4S] cluster. In addition, a putative cobalamin acquisition protein from Phaeodactylum tricornutum, CBA1, was not expressed at sufficient concentrations in Escherichia coli for spectroscopic investigation. Finally, a new technique was developed using cobalt-59 NMR spectroscopy to better understand the nucleophilic character of cobalt tetrapyrroles, such as cobalamin (vitamin B12), as biological cofactors as well as synthetic catalysts. New insight into the electronic structure provides valuable information related to the mechanism of these metalloproteins.
18
Telyatnyk, Lyudmyla G. "Density functional studies of EPR and NMR parameters of paramagnetic systems." Doctoral thesis, Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4116.
Full text
19
Kavakure, Jules. "Managing risk factors for caries with behaviour change approach : a systematic literature review and observational registry study." Thesis, Högskolan Kristianstad, Fakulteten för hälsovetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:hkr:diva-21445.
Full textAbstract:
It is estimated that nearly 100% of adults had dental caries worldwide. The disease can be approached with a biopsychosocial perspective. Overall, the aim of this study was to assess how behaviour change approach is used to manage risk factors for caries, which was divided in two sub-objectives;1. To illuminate behaviour change methods used to manage risk factors for caries, 2. To explore caries incidence among adult patients who have received behaviour change therapy treatment against caries.To answer the first sub-objective a systematic literature review was performed. To explore dental health status among adults who received behaviour change therapy due to caries, data from the national register in odontology SKaPa was analysed with descriptive and analytic statistics.The findings of the systematic literature review retrieved one RCT-study in the field of behaviour change therapy and caries. Findings from the register study showed there was no corralation between behaviour change therapy and DFT, no differences in inqualities among gender regardning DFT, no differences in DFT related to behaviour change therapy, that among therapy codes for behaviour change therapy behavioural therapy, 60 minutes or more was less frequently used and that dental professionals most frequently used behaviour change therapy when treating initial caries.The conclusion of this study are that there is a lack of scientific evidence regarding managing risk factors for caries with behaviour change approach. The study indicate that qualitative as well as randomized controlled studies would contribute to more knowledge about managing risk factors for caries with behaviour change approach.
20
Visciarelli, Michele. "Modeling transport properties of molecular devices by a novel computational approach." Doctoral thesis, Scuola Normale Superiore, 2014. http://hdl.handle.net/11384/85807.
Full text
21
Dupont, Céline. "A model surface approach to CO oxidation aiming at the purification of H2 combustible : the Pt3Sn(111) surface investigated by HREELS, PM-IRRAS and DFT." Lyon, École normale supérieure (sciences), 2008. http://www.theses.fr/2008ENSL0464.
Full textAbstract:
Les piles à combustibles représentent une alternative prometteuse au pétrole. L'énergie y est produite par oxydation de l'hydrogène, usuellement sur un catalyseur de platine. Cependant la grande affinité entre monoxyde de carbone (polluant de H2) et le platine conduit à l'empoisement du catalyseur. Une solution proposée est l'utilisation de catalyseurs bimétalliques permettant l'oxydation sélective de CO en présence d'un excès d'H2 (PROX). Nous étudions ici les deux terminaisons connues de l'alliage Pt3Sn(111). Les sites préférentiels et les propriétés vibrationnelles de CO, o, o2 et CO+CO2 sont tout d'abord considéré par une double approche théorique (DFT) et expérimentale (HREEELS, PM-IRRAS). La réactivité est ensuite envisagée : dans un premier temps, les actes élémentaires de l'oxydation de CO sont étudiées par DFT et spectrométrie de masse. Finalement une étude préliminaire du PROX est réalisée pour expliquer la plus grande efficacité de Pt3Sn(111) par rapport à Pt(111)An interesting solution to produce clean energy ist the use of fuel cells, in which hydrogen is oxidized on a platinium catlyst. However, H2 is usually polluted by carbon monoxide, a catalyst poison, due ton the strong CO/Pt affinity. In order to achieve the Preferential Oxydation of CO in presence of a large excess of H2 (PROX), bimetallic alloys are a promising solution. In this work, the adsorption and vibrational properties of the intermediate involved in CO oxidation are addressed on both terminations of the Pt3Sn(111) alloy. First preferential sites antd relative stabilities of CO, O, O2 and CO + O2 adsorbates are investigated from a combined experimental (HREELS, PM-IRRAS) and theorical (DFT) study. Then, the elementary acts of CO oxidation are explored by DFT and mass spectrometry. Last the PROX mechanism is considered theoretically and preliminary experimental results are presented, leading ton an explanation of the higher efficiency of Pt3Sn(111) compared to Pt(111)
22
Rodier, Fabien. "Nouvel accès chimio-, régio- et stéréosélectif aux motifs spirolactones polycycliques via une réaction de cycloaddition [3+2]." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4324.
Full textAbstract:
Le système spirocyclique (7,5) est un motif récurrent dans un certain nombre de produits naturels tels que les Micrandilactones ou les Rubriflordilactones. Ces structures polycycliques représentent un réel défi synthétique pour les chimistes organiciens puisqu'elles présentent au moins neuf centres stéréogènes dont plusieurs sont quaternaires. L'objectif principal de ce travail était de développer de nouvelles réactions de cycloaddition [3+2] et de les utiliser comme étape clé afin d'obtenir rapidement et efficacement le squelette polycylique de ces composés. La première partie de ces travaux a été consacrée au développement d'une réaction de cycloaddition [3+2] intra- et intermoléculaire mettant un jeu un nouveau partenaire dipolarophile, les γ-alkylidènes-buténolides. Cette étape clé conduit à la formation de cycloadduits hautement fonctionnalisés de façon rapide et efficace avec d'excellents rendements et de façon hautement chimio-, régio- et diastéréosélective. De plus, des calculs théoriques ont permis d'appréhender le mécanisme réactionnel entre un 2-diazo-1,3-cétoester et la protoanémonine catalysé par un sel de rhodium mis en jeu dans ce type de processus et ainsi d'expliquer les résultats obtenus.Dans une deuxième partie, deux approches aux cœurs ABC et CD de la micrandilactone C ont été développées mettant respectivement en jeu une cycloaddition [3+2] formellement intermoléculaire utilisant un lien de type acétal de silicium et suivie par une réaction de Diels Alder. Ainsi, le motif tétracyclique devrait être rapidement accessible après quelques aménagements de la voie de synthèse initialeThe spiro (7, 5) ring system is a recurring structural moiety in numerous natural products such as Micrandilactones and Rubriflordilactones. In term of complexity, these polycyclic structures represent a synthetic challenge for organic chemist. Indeed, these molecules present at least nine stereogenic centres including several quaternary ones. The main goal of this work was to use unprecedented partners in the [3+2] cycloaddition reaction to obtain quickly and efficiently the polycyclic core of those natural products. The first part of these studies was dedicated to the development of an intra- and intermolecular [3+2] cycloaddition using for the first time a γ-alkylidene-butenolide dipolarophile. This approach provides rapid and facile access to highly functionalised polycyclic molecules along with excellent regio-, chemo- and stereoselectivities. In addition, thanks to computational studies an overall picture of the mechanism of the intermolecular rhodium catalysed [3+2] cycloaddition between 2-diazo-1,3-ketoester and protoanemonin was apprehended, and experimental results have been rationalised.Finally, two approaches to the ABC and CD cores of Micrandilactone C were developed using respectively a formal intermolecular [3+2] cycloaddition reaction in presence of a silicon acetal linker followed by a Diels Alder reaction. The ACDE tetracyclic moiety should be quickly accessible after few modifications of the initial strategy
23
Burema, Shiri. "Inelastic Electron Tunneling Spectroscopy with the Scanning Tunneling Microscope : a combined theory-experiment approach." Thesis, Lyon, École normale supérieure, 2013. http://www.theses.fr/2013ENSL0821.
Full textAbstract:
La Spectroscopie par Effet Tunnel Inélastique (IETS) avec un Microscope à Effet Tunnel (STM) est une nouvelle technique de spectroscopie vibrationnelle, qui permet de caractériser des propriétés très fines de molécules adsorbées sur des surfaces métalliques. Des règles de selection d’excitation vibrationnelle basées sur la symétrie ont été proposées, cependant, elles ne semblent pas exhaustives pour expliquer la totalité du mécanisme et des facteurs en jeu; elles ne sont pas directement transposables pour les propriétés d'un adsorbat et sont lourdes d'utilisation. Le but de cette thèse est donc d'améliorer ces règles de selection par une étude théorique. Un protocole de simulation de l'IETS a été développé, paramétré, et évalué, puis appliqué pour calculer des spectres IETS pour différentes petites molécules, qui sont systématiquement liées, sur une surface de cuivre. Des principes additifs de l'IETS ont été developpés, notamment concernant l’extension dans le vide de l’état de tunnel, l'activation/ quench sélectif de certains modes du aux propriétés électroniques de certains fragments moléculaires, et l'application de certaines règles d'addition de signaux IETS. De plus, des empreintes vibrationnelles par des signaux IETS ont été determinées pour permettre de différentier entre les orientations des adsorbats, la nature chimique des atomes et les isomères de structures. Une stratégie simple utilisant les propriétés de distribution de la densité électronique de la molécule isolée pour prédire les activités IETS sans des couts importants de calculs a aussi été développée. Cette expertise a été utilisée pour rationaliser et interpréter les mesures expérimentales des spectres IETS pour des métalloporphyrines et métallophtalocyanines adsorbées. Ces études sont les premières études IETS pour des molécules aussi larges et complexes. L'approche expérimentale a permis de déterminer les limitations actuelles des simulations IETS. Les défauts associés à l'identification ont été résolus en faisant des simulations d'images STM complémentairesInelastic Electron Tunneling Spectroscopy (IETS) with the Scanning Tunneling Microscope (STM) is a novel vibrational spectroscopy technique that permits to characterize very subtle properties of molecules adsorbed on metallic surfaces. Its proposed symmetry-based propensity selection rules, however, fail to fully capture its exact mechanism and influencing factors; are not directly retraceable to an adsorbate property and are cumbersome. In this thesis, a theoretical approach was taken to improve them. An IETS simulation protocol has been developed, parameterized and benchmarked, and consequently used to calculate IETS spectra for a set of systematically related small molecules on copper surfaces. Extending IETS principles were deduced that refer to the tunneling state’s vacuum extension, the selective activating/quenching of certain types of modes due to the moieties’ electronic properties, and the applicability of a sum rule of IETS signals. Also, fingerprinting IETS-signals that enable discrimination between adsorbate orientations, the chemical nature of atoms and structural isomers were determined and a strategy using straightforward electronic density distribution properties of the isolated molecule to predict IETS activity without (large) computational cost was developed. This expertise was used to rationalize and interpret experimentally measured IETS spectra for adsorbed metalloporphyrins and metallophthalocyanines, being the first IETS studies of this large size. This experimental approach permitted to determine the current limitations of IETS-simulations. The associated identification shortcomings were resolved by conducting complementary STM-image simulations
24
Lourenço, Mirtha Alejandra de Oliveira. "Tuning functionalized periodic mesoporous organosilicas for CO2/CH." Doctoral thesis, Universidade de Aveiro, 2016. http://hdl.handle.net/10773/21817.
Full textAbstract:
Doutoramento em Ciência e Engenharia de MateriaisEsta tese de doutoramento teve como principal objetivo a conceção de novas organossílicas mesoporosas periódicas (PMOs) para aplicação na separação de misturas gasosas de dióxido de carbono e metano. Materiais PMOs, com grupos fenileno e bifenileno bissililados, foram modificados por introdução de grupos funcionais amina, utilizando uma das seguintes metodologias: i) reação de co-condensação; ii) pós-modificação da ponte orgânica; iii) "grafting". O tamanho dos poros das PMOs funcionalizadas e não funcionalizadas foi definido pelo tamanho da cadeia alquilada da molécula molde (surfactante) utilizada na síntese do material poroso. Estudou-se o efeito do diâmetro dos poros na separação de CO2/CH4. Investigou-se também estratégias alternativas para modificar as propriedades físico-químicas dos materiais através de reações de superfície utilizando irradiação de micro-ondas; deposição de camada atómica (ALD) de óxido de alumínio; e carbonização dos materiais em atmosfera inerte. A investigação experimental foi efectuada em paralelo com estudos computacionais. Realizou-se um estudo de simulação molecular recorrendo ao método de DFT, e usando um arranjo regular de grupos fenileno-sílica, para determinar as características ideais dos materiais para promover a separação de metano do dióxido de carbono em misturas destes gases. Foi utilizado um modelo simples, obtido pela repetição de uma célula unitária com 3 anéis fenileno, para simular a parede dos materiais PMOs e desta forma selecionar e avaliar as interações entre os gases e os grupos funcionais presentes na superfície dos materiais. A tendência do rácio entre energias de interação entre a estrutura da parede do fenileno - PMO e as moléculas de CO2 e de CH4 foi concordante com os rácios das constantes de Henry obtidos pela técnica de adsorção. Demonstrou-se uma boa sinergia entre tarefas experimentais e computacionais, o que permite a otimização de recursos, evitando a síntese desnecessária de materiais que se antecipem serem pouco eficazes para o processo de separação de misturas gasosas CO2 e CH4. Assim, a abordagem seguida nesta tese para alcançar adsorventes eficazes foi baseada numa conjugação interdisciplinar envolvendo troca de informação entre as tarefas de síntese, modelação computacional e adsorção.
The main objective of this PhD Thesis was the design of periodic mesoporous organosilicas (PMOs) for applications in carbon dioxide and methane separation. Novel PMOs were prepared by the modification of phenylene and biphenylene PMO materials with different amine functionalities through one of the three following synthetic strategies: i) co-condensation reaction; ii) organic bridge post-modification; or/and iii) grafting. The pore size of both functionalized and non-functionalized phenylene PMOs was regulated by the size of the alkyl-chain in the surfactant template. Materials with different pore sizes were used to understand the influence of the pore diameter on the CO2/CH4 separation. Additionally, it was aimed to explore alternative strategies to modify the physical-chemical properties of the materials such as microwave-assisted functionalization; atomic layer deposition (ALD) of aluminum oxide at the PMO surfaces; and carbonization of the PMO materials. The experimental research was performed in parallel with computational studies. A molecular simulation study, using the DFT method and a regular arrangement of phenylene-silica groups, of the ideal characteristics of the adsorbent materials, for CO2/CH4 separation was performed. It was used a simple model of the wall of the PMO materials obtained by the repetition of a unit cell with 3 phenylene rings, to select and evaluate interactions between gases and functional groups in the surface of the materials. The tendency between the ratio of the interaction energies between the wall structure of the phenylene-PMO and the CO2 and CH4 molecules was in good agreement with the ratio of the Henry constants achieved by the adsorption technique. Therefore, a good synergy between experimental and computational tasks was implemented to optimize the resources, avoiding the synthesis of ineffective materials. Thus, the strategy of this PhD Thesis to achieve effective adsorbents was based on an interdisciplinary approach and on the ability to link and interchange information between synthetic, computer modeling and adsorption experiments
25
Malheiro, Carine. "Adsorption de systèmes gaz/eau en milieu confiné : modélisation par une approche DFT/SAFT couplée à une étude expérimentale." Thesis, Pau, 2014. http://www.theses.fr/2014PAUU3022/document.
Full textAbstract:
La compréhension des phénomènes d’adsorption de gaz en présence d’eau dans des milieux confinés est une problématique importante tant d’un point de vue fondamental que du point de vue des applications industrielles Les travaux menés dans cette thèse ont principalement porté sur le développement d’un nouveau couplage NLDFT/SAFT-VR (Non-Local Density Functional Theory/ Statistical Associating Fluid Theory for potentials of Variable Range) pour modéliser les propriétés interfaciales et l’adsorption de méthane, d’eau et de leur mélange en milieu confiné. Les résultats théoriques obtenus sur ces fluides ont été comparés avec succès à des calculs de simulation moléculaire. Par ailleurs, des isothermes d’adsorption expérimentales de méthane et d’eau sur des charbons actifs ont été mesurées par la technique gravimétrique sur une balance à suspension magnétique. Afin de pouvoir comparer les isothermes expérimentales et théoriques, il est nécessaire de connaître la distribution en taille de pore des solides poreux. C’est pourquoi un nouveau modèle thermodynamique de caractérisation des milieux microporeux a été développé. Les comparaisons des isothermes d’adsorption de méthane ont montré un excellent accord entre résultats théoriques et expérimentauxUnderstanding the gas/water adsorption phenomena in confined media is an important issue from a fundamental point of view and for industrial applications. The main aim of this thesis was to develop a new NLDFT/SAFT-VR coupling (Non-Local Density Functional Theory/ Statistical Associating Fluid Theory for potentials of Variable Range) to model the interfacial properties and the adsorption of methane, water and their binary mixture in porous media. A successful comparison was found between theoretical results from this model and molecular simulation calculations. Moreover, experimental adsorption isotherms of methane and water were measured on activated carbons by gravimetric method on a magnetic suspension balance. In order to compare experimental and modeled adsorption isotherms, it is necessary to get the pore size distribution of the porous solids. To do this, a new thermodynamic model for the characterization of microporous media was developed. The comparison between adsorption isotherms of methane has shown an excellent agreement between theoretical results and experimental measurements
26
Groizard, Thomas. "Vers de nouvelles machines moléculaires organométalliques à ligands carbonés : une approche théorique." Thesis, Rennes 1, 2018. http://www.theses.fr/2018REN1S034/document.
Full textAbstract:
Les fils moléculaires, systèmes organiques conjugués incorporant plusieurs greffons organométalliques, constituent une famille de composés de grand intérêt pour l'électronique moléculaire. Les travaux présentés dans ce manuscrit s'inscrivent dans la suite logique de précédentes études de ces complexes de métaux de transition et constituent une analyse théorique, s'appuyant sur la fonctionnelle de la densité, de l'arrangement structural et des propriétés physiques de nouveaux assemblages moléculaires aux propriétés électroniques ou optiques originales. Ce manuscrit se divise en deux parties distinctes. La première traite de l'emploi des fils moléculaires organométalliques dans le domaine des automates cellulaires quantiques, un nouveau paradigme pour l'électronique fondé sur la localisation des charges de cellules moléculaires comme digit binaire et sur les répulsions coulombiennes comme moyen de transfert de l'information. Le concept, le moyen d'application à l'échelle moléculaire et l'étude de différents composés virtuels y sont développés. La seconde partie porte sur l'introduction de greffons organométalliques au sein de composés ayant des propriétés optiques linéaires et non linéaires et leur influence sur ces dernières. Deux familles de composés ont été étudiés : des systèmes émissifs à base de cycle phosphole et des dendrimères organométalliques à cœur porphyrineMolecular wires, conjugated organic systems bearing several organometallic fragments, form a family of compounds of great interest for molecular electronics. The research works in this manuscript follow on from previous studies of transition metal complexes and constitute a density functional theory-based analysis of both structural arrangement and physical properties of new molecular devices, with unusual electronic or optical properties. This manuscript is divided in two parts. The first one concerns the application of molecular organometallic wires in the quantum cellular automata field, a new paradigm for electronics based on the charge configuration of a molecular cell as a binary digit and using Coulombic repulsion as an information transfer mode. Both the concept, its application to molecular scale et the study of several virtual compounds are discussed. The second part focuses on the incorporation of organometallic fragments in optical active compounds with linear or nonlinear properties, and the influence of metals on those properties. Two compound families have been studied: phosphole-based conjugated emitters and organometallic porphyrine-based dendrimers
27
Petit, Ivan. "Vers une meilleure description des interfaces entre biominéraux et milieux biologiques par une approche combinée théorique et expérimentale." Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLET031/document.
Full textAbstract:
On appelle biominéraux l’ensemble des minéraux fabriqués par le vivant. Ce sont des matériaux essentiels, présents dans la quasi-totalitédes espèces vivantes. Néanmoins les caractéristiques structurales, chimiques ainsi que les mécanismes de formation, et l’évolution de cesmatériaux sont encore fortement débattus. Cela s’explique notamment par les difficultés à étudier expérimentalement des espèces chimiquesévoluant en milieux biologiques.Bien que tout aussi complexe, une approche théorique, à l’échelle moléculaire, peut aider à la caractérisation de ces matériaux biologiqueset notamment la caractérisation de leurs interfaces formées avec les milieux biologiques environnants. Cela étant essentiel pour une meilleurecompréhension de la formation et de l’évolution de ces minéraux.Les oxalates de calcium constituent une famille de biominéraux très importante dans le monde du vivant. Ils constituent notamment les principales espèces cristallinesrencontrées dans les calculs rénaux où ils peuvent exister sous trois phases possédant différents degrés d'hydratation. Au cours de cette thèse, nous avons effectuéles simulations des propriétés spectroscopique IR et RMN des ces trois phases, ce qui permet d'obtenir une signature propre à chacune d'entre elle, aidant ainsi àl'identification de ces phases à partir des spectres obtenus expérimentalement.Les phosphates de calcium font aussi partie des biominéraux. Ils composent la majeure partie du minéral osseux des mammifères. Ce minéral se trouvesous la forme de nanoparticules décrites comme possédant un cœur cristallin d’hydroxyapatite substituées entourée d'une couche hydratée et désordonnée en surface.Durant ce travail de thèse, nous nous sommes intéressés à ces deux composantes. Concernant le cœur cristallin des particules, nous avons étudié en particulierle cas des substitutions par des carbonates car il s'agit de la substitution prédominante dans les apatites biologiques. En couplant ce travail à des expériencesde RMN solide nous pouvons proposé une localisation précise de ces substituants au sein de la maille d’hydroxyapatite.La couche désordonnée de surface est encore très mal comprise à l'heure actuelle et de nombreux modèles structuraux sont proposés dans la littérature pour la décrire. Nous avonsconsidéré un certain nombre d'entre eux pour lesquels nous avons modélisé les propriétés RMN, qui confrontées à celle issues de l'expérience nous ontpermis d'identifier les points forts et faibles des différentes hypothèsesBiominerals are all the minerals produced by living organisms. They are essential materials, present in almost all living species. Nevertheless,the structural, chemical properties and, formation mechanisms and the evolution of these materials are still heavily debated. This is due in particular to thedifficulties of experimentally studying chemical species evolving in biologicalenvironments. Although, equally complex, a theoretical approach at the molecular level can help in the characterization of these biological materialsand in particular the characterization of their interfaces formed with the surrounding biological media. This is essential for a better understandingof the formation and evolution of these minerals.Calcium oxalates are essential biominerals that are very common in the living world. They constitute the main crystalline speciesencountered in kidney stones where they can exist in three phases possessing different degrees of hydration. In this, thesis we carried outsimulations to predict the IR and NMR spectroscopic properties of these three phases. Thsi enabled us to obtain specificsignature of each polyhydrate, and thus makes it possible to obtain a signature specific to each of them, thus helpingthe identification of these phases from the experimentally spectra obtained.Calcium phosphates are part of the bio/biological minerals. They make up the major part of the bone mineral of mammals. This mineral is in the form of nanoparticles havinga crystalline core of hydroxyapatite and a hydrated and disordered surface layer.During this thesis we were interested in these two components. Concerning the crystalline core of the particles, we studied in particularthe case of carbonate substitutions because of its predominant substitution in biological apatites. By combining this work with solid state NMR experimentswe can propose a precise localization of these substituents within the hydroxyapatite crystalline cell.The disordered surface layer is still very poorly understood and many structural models are proposed in the literature to describe it. We haveconsidered a number of them for which we have modeled the NMR properties which were then confronted with experimental results. The comparaisonmade it possible to identify the strengths and weaknesses of the various hypotheses
28
Zenkri, Mariem. "Etude de la cinétique de la corrosion localisée. Approche mésoscopique par automates cellulaires." Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLEC017.
Full textAbstract:
Dans cette thèse, on va étudier plus particulièrement la corrosion localisée qui se caractérise par des réactions anodiques et cathodiques ayant lieu en des endroits distincts. Cette séparation des deux demi-réactions électrochimiques couplée avec le transfert de charge (chute ohmique) ou de matière (diffusion des ions) déterminent en grande partie la cinétique de ce type de corrosion ainsi que les morphologies de la corrosion piqûres, crevasses ... qui en résultent. L'objectif de la thèse sera de développer un modèle réaliste susceptible de rendre compte des couplages importants déterminant la cinétique de la corrosion et de le valider sur la base d'observations en vue de permettre des prédictions à plus long terme. D'un point de vue pratique, les simulations seront développées sur GPU (graphical processing unit) en optimisant l'efficacité du parallélisme sur ce type d'architectureIn this thesis, we will study in particular the localized corrosion characterized by the anodic and cathodic reactions taking place in separate places. This separation of the two electrochemical half-reactions coupled with the charge transfer (IR drop) or matter (ionic diffusion) will contribute in the explanation of the corrosion's kinetic. the morphologies of corrosion pitting, crevice ... that result. The aim of the thesis is to develop a realistic model that realize significant couplings determining the kinetics of corrosion and validate it on the basis of observations to allow predictions in the longer term. From a practical standpoint, the simulations will be developed on GPU (Graphical processing unit) by optimizing the efficiency of this parallelism type of architecture
29
Chéron, Nicolas. "Approche théorique de la réactivité des isonitriles en chimie organique." Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2011. http://tel.archives-ouvertes.fr/tel-00662613.
Full textAbstract:
Les isonitriles sont des espèces connues depuis longtemps, mais étudiées depuis peu. Une approche théorique a permis de s'intéresser en détails aux réactions de Nef et de Ugi. Nous nous sommes tout d'abord focalisés sur la première. Après en avoir élucidé le mécanisme, nous avons étudié l'effet du solvant et nous avons proposé de nouvelles conditions expérimentales. Nous avons ensuite étudié l'influence des groupements de l'acyl, de l'isonitrile et du groupe partant. L'ensemble des variations considérées a pu être rationalisé en reliant l'énergie d'activation au pKa du groupe partant. En parallèle, nous avons étudié la réaction de Ugi. Le mécanisme proposé par Ugi pour cette réaction complexe n'avait toujours pas été vérifié 50 ans après sa découverte. Une étude quasi-exhaustive des différents mécanismes possibles a été menée, en utilisant une approche originale mêlant théorie et expériences. Le mécanisme de cette réaction a ainsi été démontré, tant dans le méthanol que dans le toluène. Les étapes cinétiquement déterminantes et les forces motrices ont été mises en lumière et diffèrent de celles proposées par Ugi. Une variation de la réaction de Ugi est le couplage Ugi-Smiles pour lequel de nombreux résultats expérimentaux n'ont toujours pas trouvé d'explications. Nous nous sommes donc intéressés au réarrangement de Smiles. Nous avons montré l'importance d'une liaison hydrogène intramoléculaire sur la faisabilité de la réaction, et nous avons étendu cette observation aux réactions intermoléculaires. Nous avons également étudié l'influence des substituants des quatre réactifs sur les barrières afin de construire un modèle prédictif.
30
Coiffier, Claire. "Approche Top-down pour la synthèse de substrats biologiquement actifs : analyse des conformations préférentielles de C-furanosides à l'aide de la chimie théorique." Thesis, Reims, 2011. http://www.theses.fr/2011REIMS021/document.
Full textAbstract:
Dans notre laboratoire rémois, le travail sur les sucres est à la base de toutes les recherches, que ce soit pour la synthèse de molécules d'intérêt biologique telles que des analogues du KRN 7000 (un glycolipide présentant une activité antitumorale), ou encore la mise en place de stratégies de synthèse (avec par exemple la stratégie NOE : addition nucléophile stéréosélective suivie d'une ouverture intramoléculaire régiosélective d'un époxyde). Mon trravail a consisté à étudier la flexibilité, et donc les conformations stables ou moins stables, de petites molécules que sont les C-furanosides, le but étant d'établir un certain nombre de règles permettant d'anticiper les questions concernant à la fois l'entrée et la pose de la structure dans un site actif. J'ai donc débuté avec une étude théorique dans le vide, puis j'ai considéré le milieu solvaté, l'objectif à long terme étant la prise en compte d'un site actif. Durant ces études, jai aussi eu la possibilité de réaliser un certain nombre de travaux en synthèse organique, allant jusqu'à l'établissement d'une voie de synthèse vers différents C-furanosides possédant un bras alcyne pouvant être personnalisé par notre partenaire lyonnais via une réaction de chimie click, pour la synthèse de molécules actives contre le diabèteIn our laboratory (in Reims), working on sugars is the base of all researches, whether for biologically interesting molecules synthesis as analogues of KRN 7000 (a glycolipid showing antitumor effects), or for the development of strategies for synthesis (for example the NEO stragegy : stereoselective nucleophilic addition followed by a regioselective intramolecular epoxide opening). My work was about studying the flexibility, and consequently stable and less stable conformations of small molecules : C-furanosides, the aim being the establishment of several rules anticipating the questions concerning the entry and the pose of the structure in an active site. So I have started with a theoretical study in vacuum, then I have considered solvation. The long term goal being the consideration of an active site. During these stdies, I have also realized several works in the field of organic chemistry, going to the establishment of a synthetic pathway to different C-furanosides with an alkyne arm, which could be functionalized by our partner (in Lyon) with a click reaction, for the synthesis of bioactive molecules against diabetes
31
Guil, López Alejandro, and Valadez Isabel María Guerrero. "Design of a set of stool and table with a sustainable approach by using DFA and DFE principles." Thesis, Högskolan i Skövde, Institutionen för ingenjörsvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-13790.
Full textAbstract:
This report covers the conduction of a final thesis project for the University of Skövde in collaboration with Carlos Jimenez Design studio (Spain). The aim of this project was to design and present a set of furniture consisting in a high stool and a high chair of a similar nature to the ones which are usually found in bars, oriented to the domestic environment and to the Scandinavian market. The main special characteristic of this project is that the design has been carried out with a focus on environmental sustainability, which has been approached in such a way that assembly has a big part in it, which at the same time relates to user experience. Therefore, the project combines design for assembly (DFA), design for environment (DFE) and user experience design (UXD) in such a way that all the approaches taken for each of these factors are interrelated in complete and thorough design process, were all the aspects of the final product have been taken into account.
32
Ciro, Guido. "TD-DFT and TD-DFT/PCM approaches to molecular electronic excited states in gas phase and in solution." Doctoral thesis, Scuola Normale Superiore, 2011. http://hdl.handle.net/11384/85797.
Full text
33
Aguado, Ullate Sonia. "Modeling of homogeneous catalysis: from dft to qspr approaches." Doctoral thesis, Universitat Rovira i Virgili, 2012. http://hdl.handle.net/10803/79119.
Full textAbstract:
La catálisis es un campo de la ciencia que explora soluciones a los problemas ambientales como la contaminación, la eliminación de los residuos generados en el proceso de síntesis de materiales o la regeneración de los recursos naturales. En la presente Tesis, hemos reportado un estudio de cálculos DFT para la σ activación del enlace NH de amoníaco considerando las especies μ3-alquilidinos de titanio utilizando el complejo modelo [{Ti(η5-C5H5)(μ-O)}3(μ3-CH)]. Posteriormente, con el fin de analizar la hidroformilación asimétrica de estireno catalizada por complejos Rh-Binaphos, se han combinando estudios basados en la aproximación de la determinación del estado de transición y un análisis cualitativo a través de un descriptor molecular recién definido (volumen de distancia ponderada, VW). Usando nuestro conocimiento mecanicista anterior, hemos presentado un estudio QSPR para predecir la actividad y la enantioselectividad de la hidroformilación de estireno catalizada por complejos Rh-difosfinas. También, hemos desarrollado una nueva metodología 3D-QSSR para predecir la enantioselectividad basada en la cuantificación de la representación de diagramas por cuadrantes y aplicándola en el ciclopropanación asimétrica de alquenos catalizadas por complejos de cobre.Catalysis is a field of science that explores solutions to environmental problems such as pollution, elimination of waste generated in the process of materials synthesis or regeneration of natural resources. In the present Thesis, we have reported a DFT study on the N-H σ-bond activation of ammonia by the µ3-alkylidyne titanium species using the [{Ti(η5-C5H5)(µ-O)}3(µ3-CH)] model complex. Afterwards, we have combined the TS-based approach and qualitative analysis through a newly defined molecular descriptor (distance-weighted volume, VW), in order to analyze the asymmetric hydroformylation of styrene catalyzed by Rh-binaphos complexes. Using our previous mechanistic knowledge, we have presented a QSPR study to predict the activity and the enantioselectivity in the hydroformylation of styrene catalyzed by Rh-diphosphane complexes. We have also developed a new methodology to predict enantioselectivity based on the quantitative quadrant-diagram representation of the catalysts and 3D-QSSR modeling; and we have applied it in the asymmetric cyclopropanation of alkenes catalyzed by copper complexes.
34
Tougerti, Asma. "Elaboration de catalyseurs MoOx/Al2O3 : une approche science des surfaces en phase aqueuse." Paris 6, 2010. http://www.theses.fr/2010PA066137.
Full textAbstract:
Ce travail avait pour but de développer une approche réductionniste de type science des surfaces pour la description et la compréhension de l’élaboration de catalyseurs hétérogènes à l’interface oxyde/phase aqueuse à partir du système modèle MoOx/α‑Al2O3. Grâce à une approche DFT périodique et un modèle thermodynamique nous avons pu déterminer la stabilité des différentes terminaisons potentielles des faces (0001) et (1 02) du support modèle utilisé (l’alumine α) en fonction du taux de recouvrement en eau et ainsi identifier les sites OH de surface exposés par ce support. La caractérisation des systèmes modèles MoOx/α‑Al2O3 par spectroscopie EXAFS en incidence rasante (GI-EXAFS), XPS et AFM a montré que le mode d’adsorption des oxoanions du Mo est fonction de la méthode de préparation, de la concentration de la solution d’imprégnation et de l’orientation de la face utilisée, révélant ainsi le rôle multiple joué par le support oxyde. Pour la face (0001), le support joue le rôle de simple réceptacle physique et on observe la précipitation de l’espèce (NH4)2MoO4. Pour la face (1 02), le support est un véritable ligand supramoléculaire avec une interaction précurseur/support qui diffère selon la méthode de préparation utilisée. Dans le cas d’une imprégnation, il y a reconnaissance chimique et complémentarité géométrique entre les sites de surface et l’heptamolybdate (précurseur du Mo). Dans le cas d’une adsorption à l’équilibre, l’espèce molybdique adsorbée est greffée par établissement de liaisons covalentes sur des sites Al4C-μ1-OH. Les résultats obtenus sur alumine α monocristalline nous permettent de préciser la réactivité individuelle des faces exposées par l’alumine γ.
35
Chizallet, Céline. "Nature et réactivité des sites basiques de l'oxyde de magnésium : rôle des hydroxyles : approche mixte expérimentale et théorique." Paris 6, 2006. http://www.theses.fr/2006PA066350.
Full text
36
Kutudila, Pricilia. "Structure et réactivité des triarylbismuths : approche théorique et expérimentale." Thesis, Paris Est, 2017. http://www.theses.fr/2017PESC1123/document.
Full textAbstract:
Les triarylbismuths sont des réactifs organométalliques d’un intérêt croissant en synthèse organique, pour leur aptitude à transférer leurs trois groupements aryles dans les réactions de couplage croisé C-C pallado-catalysées. Ces réactifs essentiellement non toxiques et « économiques en atomes » sont attrayants dans le cadre d’une chimie plus respectueuse de l’environnement, et présentent des applications en chimie pharmaceutique et en science des matériaux. Cependant, leur développement est ralenti par le manque de connaissances théoriques à leur sujet. Cette thèse vise alors à comprendre la réactivité de ces espèces en confrontant les données expérimentales avec celles obtenues à travers une étude théorique fondamentale (propriétés structurelles, spectroscopiques, thermodynamiques et cinétiques) résultant de calculs DFT. Le but ultime est de prévoir de nouvelles réactivités et sélectivités. Un premier volet se rapporte à une étude comparative de relation structure-propriétés sur des composés incluant un pnictogène comme atome central, tel que le bismuth, et sur différents organobismuths. Les données expérimentales existantes (cristallographiques, RMN, IR) ont été comparées aux résultats théoriques (structures, énergies, modes de vibration, indices de réactivité, etc.). Une fois les propriétés intrinsèques de ces composés mises en évidence et la méthode DFT validée, une nouvelle étude de relation structure-réactivité a été entreprise. Dans ce deuxième volet, nous avons validé le mécanisme des réactions de couplage croisé impliquant des triarylbismuths catalysées par le palladium. Les trois étapes principales du cycle catalytique ont été examinées, à savoir l'addition oxydante, la transmetallation et l'élimination réductrice, et validées en caractérisant les différents intermédiaires et états de transition. La deuxième étape de transmetallation impliquant les triarylbismuths a également fait l'objet d'une étude approfondie. En particulier, la transférabilité des trois groupements aryles et l'influence des substituants (effets électroniques et stériques) sur les barrières de transfert ont été évaluées. Enfin, la réactivité des triarylbismuths a été comparée avec celle d’autres organométalliques afin de développer de nouvelles voies de synthèseTriarylbismuths are organometallic reagents of growing interest for organic synthesis, for their ability to transfer the three aryl moieties in C-C Pd-catalysed cross-coupling reactions. These essentially non-toxic, atom efficient reactants are attractive in the context of environment-friendly chemistry and have applications in pharmaceutical chemistry and in material science. However, their development is hampered by lack of theoretical understanding. This thesis aims to explore the reactivity of these species by comparing the experimental data to fundamental theoretical studies (structural, spectroscopic, thermodynamic and kinetic properties) resulting from DFT calculations. The ultimate goal is to predict new reactivities and selectivities. A first approach consists in a comparative study on the relation between structure and properties in compounds having a pnictogen central atom like bismuth, and in different organobismuths. The existing experimental data (crystallographic, NMR, IR) were compared to the results of theoretical calculations (structures, energies, vibrational modes, reactivity parameters, etc.). After highlighting the intrinsic properties of these compounds and validating the DFT method, a new study was undertaken to elucidate the relations between structure and reactivity. This second investigation enabled us to validate the mechanism of the cross-coupling reaction involving triarylbismuths under palladium catalysis. The three major steps of the catalytic cycle have been examined, i.e. the oxidative addition, transmetallation and reductive elimination, and validated by characterizing the different intermediates and transition states. The second transmetalation step involving the triarylbismuths has also been deeply investigated. The transferability of the three aryl groups and the influence of the electronic and steric effects of the substituents on the energy barrier have been evaluated. Finally, the reactivity of triarylbismuths has been compared with that of other organometallics, to develop new synthetic approaches
37
Aloui, Asma. "Approche combinée théorie-expérience pour la catalyse d’hydrogénation asymétrique." Thesis, Lyon 1, 2010. http://www.theses.fr/2010LYO10291/document.
Full textAbstract:
Plusieurs études ont rapporté l’influence de la pression d’hydrogène, plus précisément la concentration réelle en hydrogène dissous dans le milieu réactionnel, sur l’énantiosélectivité des réactions d’hydrogénations catalytiques intervenant des catalyseurs à base de rhodium. Cependant, l’identification de l’étape ou les étapes enantiodéterminantes ou limitantes ainsi que l’explication de l’effet de la pression d’hydrogène sur cet étape, exigent la détermination des constantes cinétiques de chaque étape élémentaire. Ce projet de recherche vise une telle détermination en combinant deux études expérimentale et théorique. Dans un premier temps, un système catalytique présentant deux effets opposés de la pression de l’hydrogène en fonction de la nature du substrat, a été identifié : un effet néfaste avec le M-acrylate (MAA) et un effet bénéfique avec l’E-emap. Ensuite, deux études ont été menées sur les réactions d’hydrogénation de ces deux substrats par le Rh(I) /(R,R)-Me-BPE. L’étude cinétique expérimentale est basée sur le modèle cinétique proposé par Halpern dans le but d’estimer les paramètres cinétiques des différentes étapes élémentaires, alors que celle théorique consiste à étudier les différents chemins réactionnels possibles par calcul DFT en utilisant le logiciel de modélisation Gaussian 03. L’exploitation des résultats obtenus a permis de revisiter les concepts clés de la catalyse d’hydrogénation asymétrique et de mener une discussion par rapport à la fiabilité des méthodes théoriques à prévoir l’expérienceSeveral studies brought back the influence of the hydrogen pressure, more precisely the real hydrogen concentration dissolved in solution, on the enantioselectivity of the catalytic asymmetric hydrogenation for rhodium based catalysts. However to identify the enantiodetermining step(s), and to gain some further understanding on the hydrogen pressure-enantioselectivity relationship, the determination of the kinetic constants is required. We have thus embarked a project aiming such determination by coupling experimental work and theoretical chemistry. Two studies were undertaken on the asymmetric hydrogenation of both substrates by the Rh (I)/ (R,R)-Me-bpe catalyst. The experimental kinetic work study is based on the kinetic model suggested by Halpern in order to estimate the parameters kinetic of each elementary step, whereas that theoretical, consists in studying the various possible pathways by DFT calculation using the software of modelling Gaussian 03. The analysis of the obtained results made it possible to revisit the concepts’ key of the catalytic asymmetric hydrogenation and to hold a discussion about the reliability of the theoretical methods to envisage the experiment
38
Chesneau, Erwan. "Développement d'une nouvelle approche pour la modélisation structurale de verres boratés : combiner Résonance Magnétique Nucléaire (RMN) et Dynamique Moléculaire." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLV058/document.
Full textAbstract:
Les verres sont des matériaux utilisés dans de très nombreux domaines. Cependant leur structure reste à ce jour peu connue du fait de l’absence d’ordre à longue distance rendant difficile la résolution de la structure à l’échelle atomique. Il est admis que les verres sont constitué d’un enchainement désordonné d’unités élémentaires par exemple des triangles et tétraèdres de bore dans le cas des verres de borates. La résonance magnétique nucléaire (RMN) a démontré être une technique de choix pour l’étude des verres, permettant de mesurer la proportion de chaque unités. Toutefois, la résolution structurale du verre reste aujourd’hui un enjeu scientifique majeur afin de mieux comprendre les relations propriétés-composition. Cette thèse a pour objectif de développer des méthodes combinant des expériences de RMN 1D et 2D avec des calculs DFT de paramètres RMN effectués sur des modèles numériques afin de caractériser la signature spectrale de l’ordre à moyenne distance. Sur une première série de verres de borates de sodium, il a été mis en évidence que seul la dynamique moléculaire (DM) ab-initio permet de reproduire des unités superstructurale telle que des anneaux, qui ont pu être caractérisées expérimentalement notamment grâce à la prise en compte fine des effet de distributions des paramètres RMN. La deuxième série sont des verres d’aluminoborate de lanthane pour laquelle les simulations par DM ne permettent pas un accord satisfaisant avec l’expérience. De ce fait, nous avons exploré une méthode par Reverse Monte Carlo contraintes par les données expérimentales. Cette méthode permet d’améliorer significativement l’accord des modèles avec l’expérience et reste donc à poursuivreGlasses are materials used in many fields. However, their structures still not well known because of the lack of long range order, making it difficult to extract the structural information of these materials. It is accepted that the glassy network is made of many elementary unit chains, being boron triangles and tetrahedron in the case of borate glasses. Nuclear magnetic resonance (NMR) has proven to be a vital characterization technique for the glasses study. It allows the measurement of proportion of each unit. The determination of the structural resolution of glasses remains a major scientific challenge for understanding of the relationship between the glass properties and it elemental compositions. This thesis aims to develop new NMR approach combining 1D, 2D and oxygen-17 NMR with DFT-GIPAW calculations on numerical models in order to characterize the intermediate ranger order NMR fingerprint. The first study is on sodium borate glasses. It highlighted that only ab-initio molecular dynamics (MD) can reproduce the boron rings, which have been confirmed by the NMR data, taking into account of the fine NMR parameters distributions effects. The second study is on aluminoborate glasses. Unlike the previous, the computed MD structures are not in agreement with NMR data. Thereby, a diferente stuctural simulation is applied. Refined models have been determined by Reverse Monte Carlo by constraining few experimental NMR data. This method allows to significantly improve the agreement between sumulated models and the experiment
39
Åkerlind, Amanda. "Elastic properties of the Singö zone from a discrete approach." Thesis, KTH, Skolan för arkitektur och samhällsbyggnad (ABE), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-268640.
Full textAbstract:
A rock mass is characterised by the properties of the intact rock and the fractures. Considering the impact of both constituents is of vital importance for assessing the behaviour of the rock mass. In particular in the case of complex or heterogeneous rock mass compositions. A discrete approach, by using the Discrete Fracture Network (DFN) methodology, enables for the consideration of these aspects.This master’s thesis concerns the evaluation of elastic properties of the Singö deformation zone. A discrete approach has been applied by three-dimensional discrete fracture network modelling, using previously evaluated DFN parameters. The elastic properties have then been obtained by analytical means by using the methodology developed by Davy et al. (2018).The results show that in comparison to earlier evaluations of the elastic properties of the Singö zone, the respective Young’s moduli and Poisson’s ratios obtained by this thesis may indicate a weaker material. However, this study differs from the earlier evaluation by more extensive DFN modelling and the application of a state of stress which is more representative of the surroundings of the zone in Forsmark. The analysis indicates that theadequate model size is slightly larger than the maximum studied DFN model size. A suggested future improvement would be a re-evaluation and updating of the DFN parameters. As a concluding remark, the methodology of Davy et al. (2018) may prove successful in the future for the application to deformation zones.En bergmassa karakteriseras av egenskaperna hos det intakta berget och dess sprickor. Det är därmed av vikt att båda dessa beståndsdelar beaktas vid utvärdering av bergmassans beteende, speciellt vid komplexa eller heterogena bergartssammansättningar.Detta examensarbete syftar till att utvärdera deformationsegenskaper för den så kallade Singözonen. Ett diskret angreppsätt har tillämpats genom modellering av tredimensionella diskreta spricknätverk med hjälp av tidigare utvärderade DFN-parametrar. Deformationsegenskaperna har sedan utvärderats med hjälp av metodiken som presenteras i Davy et al. (2018).Jämfört med tidigare utvärderade deformationsegenskaper hos Singözonen så indikerar resultaten av denna masteruppsats en svagare bergmassa, med hänsyn till uppskattade värden på E-moduler och tvärkontraktionstal. Däremot skiljer sig modelleringsprocessen i detta arbete mot de som utförts i de tidigare studierna. Detta med hänsyn till omfattningen av DFN-modelleringen samt tillämpandet i detta arbete av en spänningsansats som är mer representativ för Forsmarksområdet. Vidare indikerar resultaten att den representativa modellvolymen är något större än den största modellvolym som tillämpats i detta arbete. Förslagsvis kan en utvärdering och eventuell uppdatering av de använda DFN-parametrarna utgöra en möjlig utveckling eller förbättring av det arbete som utförts i detta mastersarbete. Slutligen kan det konstateras att framtida tillämpningar av den metodik som tagits fram av Davy et al. (2018) verkar lämplig att applicera på deformationszoner.
40
Gautier, Sarah. "Réactivité catalytique à haut recouvrement : une approche théorique." Thesis, Lyon, École normale supérieure, 2015. http://www.theses.fr/2015ENSL1015/document.
Full textAbstract:
L’hydrogénation sélective d’hydrocarbures polyinsaturés présente un fort intérêt pour l’industrie pétrolière. Cette réaction est catalysée par des particules métalliques ou des alliages et a lieu sous pression d’hydrogène. Dans ce travail nous étudions la réaction d’hydrogénation sélective du butadiène en 1-butene en présence des catalyseurs Pt(111) et Sn/Pt-Pt(111). Cette étude a été menée à l’aide du programme VASP (Vienna Abinitio Simulation Package) qui permet de simuler des systèmes solides et surfaciques dans le cadre de la théorie de la fonctionnelle de la densité (DFT). Le choix des catalyseurs a été dicté par les communautés expérimentale et industrielle qui utilisent le plus souvent le platine car très actif, ou des alliages de platine-étain, moins actifs mais beaucoup plus sélectifs. L’hydrogénation du butadiène a déjà été étudiée par le passé mais uniquement à T=0 K et sans prendre en compte les conditions réelles de pression des réactifs. Notre but étant de comprendre les pas élémentaires de cette réaction, nous avons choisi de l’étudier à des conditions de T et de P proches de celles utilisées expérimentalement, c’est-à-dire 300-400 K et 1-10 bar. A cette fin, nous avons mis en place un modèle thermodynamique pour évaluer, dans un premier temps, la composition de la surface lors de la réaction. Il est alors apparu que la configuration de surface la plus stable correspond à une couverture de une monocouche d’hydrogène ce qui suggère un mécanisme de type Eley-Rideal. Puis nous avons étudié l’aspect cinétique ce cette réaction et calculé les chemins réactionnels pour différents recouvrements en hydrogène. Nous avons conclu qu’il existe une forte compétitivité entre le mécanisme pressenti, appelé Langmuir-Hinshelwood et impliquant des espèces fortement adsorbées, et le mécanisme Eley-Rideal proposant une adsorption faible de l’un des réactifs. Les calculs ont été effectués avec les fonctionnelles PBE et optPBE pour apporter un point de comparaison des méthodesPetroleum industry has a strong interest in the selective hydrogenation of polyunsaturated hydrocarbons. This reaction is catalyzed by metallic particles or alloys and happens under pressure of hydrogen. In this work, we study the selective hydrogenation of butadiene into 1-butene, on two model catalysts which are Pt(111) and Sn/Pt-Pt(111). For this, we used the VASP code (Vienna Abinitio Simulation Package) that allows to perform periodic calculations in the framework of the Density Functional Theory (DFT). The choice of the catalysts was driven by the experimental and industrial communities who mostly use platinum because of its high activity, or alloys such as tin-platinum alloy, less active but more selective. Butadiene hydrogenation was already modeled in the past but only at T=0 K and without taking into account the real pressure conditions of the reactants. Our aim is to understand the impact of the reaction conditions which is why we ran this study at T and P conditions close to the one used experimentally, e.g. 300-400 K et 1-10 bar. For this, we setup a thermodynamic model to evaluate in a first step the surface composition when the reaction occurs. It came out that the most stable surface configuration corresponds to a coverage of 1 ML of hydrogen which suggests an Eley-Rideal type mechanism. Then we studied the kinetic aspect of this reaction and we calculated the hydrogenation pathways for different coverages of hydrogen. We concluded that there is a strong competition between the sensed mechanism, called Langmuir-Hinshelwood mechanism and implying strongly adsorbed species, and the Eley-Rideal mechanism, proposing a weak adsorption of one of the two reactants
41
Kopp, A. M., and D. L. Orlovskyi. "An approach and tools for business process mapping diagrams analysis." Thesis, НТУ "ХПІ", 2018. http://repository.kpi.kharkov.ua/handle/KhPI-Press/35952.
Full text
42
Cornette, Pauline. "Approche expérimentale et théorique de l’inhibition de corrosion de surfaces métalliques." Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLEC004.
Full textAbstract:
La corrosion des surfaces d’aluminium et d’alliages aluminium/cuivre, et notamment la corrosion localisée, est un problème majeur dans l’industrie, et l’utilisation d’inhibiteur de corrosion est bien souvent indispensable. Les chromates remplissent parfaitement leurs rôles d’inhibition mais seront d’ici peu interdits en raison de leurs toxicités pour l’homme et l’environnement. La compréhension des mécanismes de corrosion et d’inhibition de la corrosion est alors un réel défi de la recherche aujourd’hui. Ce travail de thèse s’organise autour de trois axes de recherche : la compréhension des mécanismes d’initiation de la corrosion de l’aluminium, la relation entre la composition chimique et la résistance à la corrosion des alliages aluminium/cuivre, et enfin l’étude des acides carboxyliques linéaires en tant qu’inhibiteurs verts de corrosion. Ce projet s’appuie sur deux approches complémentaires : une approche théorique, basée sur des calculs DFT, et une approche expérimentale combinant des techniques d'analyse des surfaces ainsi que des techniques électrochimiques. Dans un premier temps, la réactivité vis-à-vis de O2 de modèles de couches minces d’alumine sur aluminium métallique, a été étudiée par calculs ab initio en présence de lacunes d’oxygène dans l’oxyde, ou de cuivre dans le métal, ainsi qu’en présence d’une monocouche d’acides carboxyliques sur la surface. Des techniques d'analyse de surface (XPS, ToF-SIMS, AFM et MEB) ont ensuite été utilisées pour analyser la composition chimique et la morphologie de surfaces d’aluminium pur et d’alliages modèles Al/Cu avant et après adsorption d’une monocouche d’acides carboxyliques. L’influence de la présence de cette couche en surface sur la corrosion en milieu chloruré est finalement étudiée par mesures électrochimiquesCorrosion of aluminum and aluminum/copper alloy surfaces, including localized corrosion, is a major problem in the industry, and the use of a corrosion inhibitor is often essential. Chromates perfectly fulfill their role of inhibition but will soon be prohibited because of their toxicities for humans and environment. Understanding the mechanisms of corrosion and corrosion inhibition is therefore a real challenge for research today. This thesis work is organized around three lines of research: the understanding of the aluminum corrosion initiation mechanisms, the relationship between the chemical composition of the alloy and the corrosion resistance of aluminum/copper alloys, and finally the study of linear carboxylic acids as green corrosion inhibitors. This project relies on two complementary approaches: a theoretical approach, based on DFT calculations, and an experimental approach combining surface analysis techniques as well as electrochemical techniques. First, the reactivity with respect to O2 of alumina thin film models on metallic aluminum, was studied by ab initio calculations in the presence of oxygen vacancies in the oxide, or copper in the metal, as well as in the presence of a carboxylic acids monolayer on the surface. Surface analysis techniques (XPS, ToF-SIMS, AFM and SEM) were then used to analyze the chemical composition and morphology of pure aluminum surfaces and Al/Cu model alloys before and after adsorption. a carboxylic acids monolayer. The influence of the presence of this surface layer on the corrosion in chloride medium is finally studied by electrochemical measurements
43
Zambon, Adrien. "Modèles chimiques du nitrure de carbone graphitique : lien structure-propriétés." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAV024/document.
Full textAbstract:
Le nitrure de carbone graphitique (gCN) est un semi-conducteur organique ayant dernièrement attiré l'attention par sa capacité à photocatalyser la séparation de l'eau. Il a récemment été montré que le gCN était un polymère basé sur le cycle heptazine C6N7, mais son arrangement tridimensionnel reste encore très peu connu. En effet, sa faible solubilité empêche l'utilisation des techniques de caractérisation classiques, et le terme gCN recouvre en réalité une large gamme de composés différents, selon les conditions de synthèse utilisées (choix du précurseur, température…). L'obtention de modèles moléculaires, de structures maîtrisées et bien définies, serait donc d'une grande aide dans la compréhension du lien structure-propriétés. Ceci est le but des travaux présentés dans ce manuscrit. La réactivité du chlorure de cyaméluryle, un précurseur monomérique, a été étudiée, et un protocole de substitution sélective quantitative par les amines secondaire aliphatique a été déterminé. L'utilisation de synthèses par déprotonation ou par activation thermique ont permis l'obtention de deux dimères et d'un trimère linéaire solubles. Les oligomères synthétisés ont été caractérisés par de nombreuses techniques (diffraction des rayons X, RMN, IR, absorption UV-vis, fluorescence, électrochimie), et les valeurs obtenues ont été corroborées à celle obtenues par DFT. De façon générale, une diminution des énergies des transitions électronique est observée quand la taille de chaîne augmente, et l'application de méthodes d'extrapolation suggère que les oligomères linéaires sont des bon modèle moléculaire du gCNGraphitic carbon nitride (gCN) is an organic semi-conductor which has lately attracted a lot of attention when its photocatalytic properties were highlighted for water splitting. It has been recently shown to be based on the heptazine core, but its three-dimensional structure remains elusive. This is first due to its poor solubility which prevents the use of classical characterization techniques, and second to the fact that changes in synthesis experimental conditions (precursors, temperature…) yield different materials. The synthesis of tailored and well-defined molecular models would therefore certainly be of great interest to better understand the structure-properties relationship of this material. This is the aim of the work presented in this manuscript. The reactivity of cyameluryl chloride, a monomeric precursor, has been studied, and a protocol for a quantitative selective substitution by aliphatic secondary amines has been determined. The use of deprotonation by a strong base or thermal treatment yielded two dimers and one linear trimer. The oligomers have been characterized by several technique (X-ray diffraction, NMR, IR, UV-vis absorption, emission, electrochemistry), and the obtained data were in close agreement to the ones observed in DFT. As a rule of thumb, a decrease of the electronic transition energies is observed for an increasing chain length. The application of extrapolation methods to the experimental data suggests that oligomers are relevant molecular models for gCN
44
Šejvlová, Ludmila. "Porovnání přístupů ke generování umělých dat." Master's thesis, Vysoká škola ekonomická v Praze, 2017. http://www.nusl.cz/ntk/nusl-358804.
Full textAbstract:
The diploma thesis deals with synthetic data, selected approaches to their generation together with a practical task of data generation. The goal of the thesis is to describe the selected approaches to data generation, capture their key advantages and disadvantages and compare the individual approaches to each other. The practical part of the thesis describes generation of synthetic data for teaching knowledge discovery using databases. The thesis includes a basic description of synthetic data and thoroughly explains the process of their generation. The approaches selected for further examination are random data generation, the statistical approach, data generation languages and the ReverseMiner tool. The thesis also describes the practical usage of synthetic data and the suitability of each approach for certain purposes. Within this thesis, educational data Hotel SD were created using the ReverseMiner tool. The data contain relations discoverable with SD (set-difference) GUHA-procedures.
45
Musatoiu, Mihai. "An approach to choosing the right distributed file system : Microsoft DFS vs. Hadoop DFS." Thesis, Blekinge Tekniska Högskola, Institutionen för programvaruteknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-844.
Full textAbstract:
Context. An important goal of most IT groups is to manage server resources in such a way that their users are provided with fast, reliable and secure access to files. The modern needs of organizations imply that resources are often distributed geographically, asking for new design solutions for the file systems to remain highly available and efficient. This is where distributed file systems (DFSs) come into the picture. A distributed file system (DFS), as opposed to a "classical", local, file system, is accessible across some kind of network and allows clients to access files remotely as if they were stored locally. Objectives. This paper has the goal of comparatively analyzing two distributed file systems, Microsoft DFS (MSDFS) and Hadoop DFS (HDFS). The two systems come from different "worlds" (proprietary - Microsoft DFS - vs. open-source - Hadoop DFS); the abundance of solutions and the variety of choices that exist today make such a comparison more relevant. Methods. The comparative analysis is done on a cluster of 4 computers running dual-installations of Microsoft Windows Server 2012 R2 (the MSDFS environment) and Linux Ubuntu 14.04 (the HDFS environment). The comparison is done on read and write operations on files and sets of files of increasing sizes, as well as on a set of key usage scenarios. Results. Comparative results are produced for reading and writing operations of files of increasing size - 1 MB, 2 MB, 4 MB and so on up to 4096 MB - and of sets of small files (64 KB each) amounting to totals of 128 MB, 256 MB and so on up to 4096 MB. The results expose the behavior of the two DFSs on different types of stressful activities (when the size of the transferred file increases, as well as when the quantity of data is divided into (tens of) thousands of many small files). The behavior in the case of key usage scenarios is observed and analyzed. Conclusions. HDFS performs better at writing large files, while MSDFS is better at writing many small files. At read operations, the two show similar performance, with a slight advantage for MSDFS. In the key usage scenarios, HDFS shows more flexibility, but MSDFS could be the better choice depending on the needs of the users (for example, most of the common functions can be configured through the graphical user interface).
46
Louyriac, Elisa. "Catalyse de polymérisation stéréosélective du styrène avec l'éthylène pour la production de matériaux sPSE - Approche par modélisation moléculaire." Electronic Thesis or Diss., Toulouse, INSA, 2019. http://www.theses.fr/2019ISAT0054.
Full textAbstract:
Le polystyrène syndiotactique est un matériau attractif pour divers domaines d’application, notamment ceux de l’emballage ou de l’électronique. En revanche des inconvénients peuvent limiter sa production industrielle : un procédé de synthèse à température élevée et une fragilité qui pose problème dans des applications où les propriétés mécaniques sont importantes. L’amélioration du procédé de fabrication et des propriétés physico-chimiques du polystyrène syndiotactique peut se faire par l’incorporation d’un co-monomère, comme l’éthylène, durant la polymérisation stéréosélective du styrène. Les systèmes catalytiques à base de métaux du groupe 3 présentent une forte syndiospécificité et semblent prometteurs pour la copolymérisation styrène-éthylène. L’optimisation par modélisation moléculaire de tels systèmes permettra à terme de concevoir un procédé moins énergivore et satisfaisant les exigences industrielles pour la production de matériaux haute performance. C’est dans ce contexte que s’inscrivent les travaux de cette thèse, qui présente l’étude de la réaction de copolymérisation stéréosélective du styrène avec l’éthylène catalysée par des complexes de métaux du groupe 3 par une approche théorique au niveau DFT. Cette thèse a été réalisée en collaboration avec un laboratoire expérimental et suivie par un groupe industrielSyndiotactic polystyrene is an attractive material used in several fields, in particular packaging or electronics. Its industrial production may be restricted by: a high temperature synthesis process and its brittleness, which is a drawback for applications with mechanical requirements. The improvement of the production process and the physicochemical properties of the syndiotactic polystyrene can be achieved by copolymerization with ethylene. Catalytic systems based on group 3 metals exhibit a high syndiospecificity and seem promising for styrene-ethylene copolymerization. By using molecular modelling, the optimization of such systems will allow to design a less energy-consuming process that fulfils the industrial requirements for the production of high performance materials. In this context, the work presented within this thesis is a theoretical study of styrene-ethylene stereoselective copolymerization catalysis by using DFT calculations. This PhD thesis was conducted in collaboration with an experimental team and followed by an industrial group
47
Ahlman, Kristina. "Det alternativa livet på landsbygden." Thesis, Örebro universitet, Institutionen för juridik, psykologi och socialt arbete, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-33085.
Full textAbstract:
Det ”alternativa livet” kan ses som en motrörelse till urbanisering, ökad konsumtion och ett allt snabbare tempo i samhället. Detta är en kvalitativ studie med syftet att undersöka det alternativa livet. Sex informanter intervjuades om deras upplevelser och uppfattningar av det alternativa livet. Intervjuerna transkriberades och analyserades utifrån en induktiv tematisk metod. Gemensamt för alla informanter är att de vill leva enkelt utifrån grundläggande behov, leva nära naturen, reducera saker livet som de upplever mindre viktiga, anta utmaningar och få mer tid över för sådant de upplever meningsfullt. Genom reduktion upplever infomanterna en större livskvalité och närvaro i nuet. Kombinationen av individuella faktorer och en vilja att leva mer miljömässigt hållbart kan ses som de stora orsakerna till varför de intervjuade väljer att leva alternativt. Resultaten har tolkats utifrån behovsmässig teori, existentiell psykologi och Antonovskys Känsla av Sammanhang.The “alternative life” can be described as a counter movement to the urban society, increased consummation and a stressful lifestyle. The aim of this qualitative study is to examine the alternative life on the countryside. Six informants were interviewed about their experiences and views about the alternative life. The data is transcribed and analyzed with an inductive, thematic approach. The informants want to live with more simplicity, intimate with their basic needs, live close to nature, reducing less important things in life, challenging themselves and having more time for things they find meaningful. The informants experience more quality in life and presence in the moment through reduction. The main reasons for the informants to live an “alternative life” are the combination of individual factors and a desire to live more environmentally friendly. The results have been analyzed from behavioral theory, existential psychology and Antovskys “Sense of Coherence”.
48
Lin, Yuehua. "A model transformation approach to automated model evolution." Birmingham, Ala. : University of Alabama at Birmingham, 2007. http://www.mhsl.uab.edu/dt/2007p/lin.pdf.
Full text
49
GUANDALINI, ALBERTO. "Eccitazioni cariche e neutre non lineari in sistemi a bassa dimensionalità e molecolari mediante l'utilizzo di approcci basati sui funzionali della densità." Doctoral thesis, Università degli studi di Modena e Reggio Emilia, 2020. http://hdl.handle.net/11380/1199882.
Full textAbstract:
Le eccitazioni elettroniche assumono un ruolo di fondamentale importanza in diverse proprietà fisiche dei materiali, ad esempio nel trasporto quantistico, trasporto termico, conducibilità e proprietà ottiche. A seconda della carica elettrica dello stato finale, possiamo distinguere tra eccitazioni cariche e neutre. Nelle eccitazioni cariche, consideriamo elettroni che vengono aggiunti o sottratti al sistema. Questi processi possono essere studiati tramite esperimenti di fotoemissione diretta o inversa. Invece, nelle eccitazioni neutre, la carica totale del sistema viene conservata durante il processo di eccitazione. Questo tipo di eccitazioni possono essere rilevate attraverso misure di assorbimento ottico, sia in regime lineare che non lineare.
La teoria del funzionale della densità (DFT) e la sua estensione dipendente dal tempo (TDDFT) sono spesso il primo quadro teorico di riferimento nella descrizione a primi principi dei processi di eccitazione. Tuttavia, è noto che la DFT e la TDDFT danno luogo ad errori e limiti di applicabilità a causa delle approssimazioni funzionali che devono essere necessariamente utilizzate in pratica. Pertanto, lo sviluppo di approssimazioni più accurate ed altre estensioni teoriche è un campo di ricerca interessante e attivo.
In questo lavoro, mi occupo dello sviluppo di nuovi metodi per il calcolo delle eccitazioni cariche e neutre.
Nella prima parte, mostro come il gap fondamentale dei punti quantici bidimensionali può essere accuratamente stimato al costo computazionale di un calcolo di stato fondamentale, seguito da uno step non autoconsistente dal costo computazionale trascurabile, il tutto eseguito all'interno dell'approssimazione della densità locale. Nonostante ciò, la procedura include formalmente la discontinuità del potenziale di scambio espressa attraverso il metodo del potenziale effettivo orbitale.
Nella seconda parte, ricavo un'approssimazione del potenziale che include esplicitamente un gap di scambio diverso da zero per sistemi bidimensionali sia finiti che periodici. Sebbene la forma funzionale utilizzata coinvolga direttamente gli orbitali a singola particella, il costo computazionale è paragonabile ai calcoli DFT standard. L'approssimazione del potenziale è applicata al grafene artificiale, in cui una distorsione di Kekulé utilizzata per aprire un gap nei punti di Dirac.
Nella terza parte di questo lavoro mi occupo di studiare le eccitazioni neutre non lineari. In particolare, derivo la sezione d'urto ottica per un sistema a più elettroni soggetto a un campo elettrico impulsivo nel regime non perturbativo, cioè per valori arbitrari dell'intensità del campo incidente, partendo dallo stato fondamentale. Successivamente mostro che la sezione d'urto include assorbimenti da stati eccitati all'aumentare dell'intensità del campo elettrico. Queste transizioni ottiche non sono possibili all'interno del regime lineare. Come esempio di applicazione, considero il caso di un sistema modello unidimensionale composto da due elettroni interagenti. L'analisi rivela che gli stati eccitati di tipo gerade, che non partecipano alle proprietà ottiche nel regime lineare, sono popolati nel regime non lineare a causa dell'assorbimento da stato eccitato. Questa analisi aiuta a interpretare le simulazioni di TDDFT in tempo reale che impiegano campi elettrici impulsivi oltre il regime lineare, come per lo studio dei processi coinvolti nei fenomeni di limitazione ottica.
I risultati ottenuti in questa tesi di dottorato contribuiscono allo sviluppo di metodi accurati e praticabili per studiare le eccitazioni elettroniche nei sistemi quantistici e, in particolare, allo sviluppo teorico nel campo degli approcci a principi primi basati sui funzionali della densità.Electronic excitations play a prominent role in a large variety of physical properties of materials, e.g., quantum transport, heat transport, conductivity, and optical properties. Depending on the electric charge of the final state, we may distinguish between charged and neutral excitations. In charged excitations, we consider electrons that are added or subtracted to the system. Direct or inverse photoemission experiments are a primary tool for the experimental observation of such processes. Instead, in neutral excitations, the total charge of the system is conserved during the excitation process. These can be probed through optical absorption measurements, both in the linear and nonlinear regimes. Density functional theory (DFT) and its time-dependent extension (TDDFT) are often the theoretical framework of first choice in the first-principles description of excitation processes. However, it is well known that DFT and TDDFT show failures and limitations due to the functional approximations which are necessary in practice. Thus, the development of more accurate approximations and theoretical extensions is an interesting and intense field of research. In this work, I develop new advances in the calculation of charged and neutral excitations. In the first part, it is shown that the fundamental gap of two-dimensional quantum dots can be accurately estimated at the effort of a standard ground-state calculation supplemented with a non-self-consistent step of negligible cost, all performed at the level of the local-density approximation. Yet, the procedure formally exploits the exchange discontinuity as expressed through the orbital-effective-potential method. In the second part, I derive an approximate potential that can capture non-vanishing exchange gaps both infinite and periodic two-dimensional systems. Although the procedure involves single-particle orbitals directly, the computational cost is comparable to standard DFT calculations. The potential approximation is applied to the artificial graphene, Kekulé distorted to open a gap at the Dirac points. In the third part of this work, nonlinear neutral excitations are investigated. In particular, I derive the optical cross section of a many-electron system subject to an impulsive electric field in the nonperturbative regime, i.e. for arbitrary values of the field strength, starting from the ground state. I show that the cross section includes absorptions from excited states for increasing intensities of the electric field - which are optical transitions that cannot be captured within the linear regime. As an example, I consider the case of a 1D two-electron model system. The analysis reveals that gerade excited states, which are dark in the linear regime, are populated in the nonlinear regime due to excited-state absorption. This analysis helps to interpret real-time TDDFT simulations which employ impulsive electric fields beyond the linear regime, as for studying processes in optical limiting phenomena. The results obtained in this Ph.D. thesis contribute to the development of accurate and feasible methods to investigate electronic excitations in quantum systems, and, more generally, to the theory development of first-principles density-functional approaches.
50
Aloui, Asma. "Approche combinée théorie-expérience pour la catalyse d'hydrogénation asymétrique." Phd thesis, Université Claude Bernard - Lyon I, 2010. http://tel.archives-ouvertes.fr/tel-00721308.
Full textAbstract:
Plusieurs études ont rapporté l'influence de la pression d'hydrogène, plus précisément la concentration réelle en hydrogène dissous dans le milieu réactionnel, sur l'énantiosélectivité des réactions d'hydrogénations catalytiques intervenant des catalyseurs à base de rhodium. Cependant, l'identification de l'étape ou les étapes enantiodéterminantes ou limitantes ainsi que l'explication de l'effet de la pression d'hydrogène sur cet étape, exigent la détermination des constantes cinétiques de chaque étape élémentaire. Ce projet de recherche vise une telle détermination en combinant deux études expérimentale et théorique. Dans un premier temps, un système catalytique présentant deux effets opposés de la pression de l'hydrogène en fonction de la nature du substrat, a été identifié : un effet néfaste avec le M-acrylate (MAA) et un effet bénéfique avec l'E-emap. Ensuite, deux études ont été menées sur les réactions d'hydrogénation de ces deux substrats par le Rh(I) /(R,R)-Me-BPE. L'étude cinétique expérimentale est basée sur le modèle cinétique proposé par Halpern dans le but d'estimer les paramètres cinétiques des différentes étapes élémentaires, alors que celle théorique consiste à étudier les différents chemins réactionnels possibles par calcul DFT en utilisant le logiciel de modélisation Gaussian 03. L'exploitation des résultats obtenus a permis de revisiter les concepts clés de la catalyse d'hydrogénation asymétrique et de mener une discussion par rapport à la fiabilité des méthodes théoriques à prévoir l'expérience.