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Some studies of small reactive intermediates with ultraviolet photoelectron spectroscopyHooper, Nicole January 2002 (has links)
No description available.
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Gas-phase structures of molecules containing heavy p-block elementsWann, Derek A. January 2005 (has links)
Gas-phase electron diffraction (GED) is the method of choice for determining the structures of molecules containing between two and 100 atoms, free from intermolecular interaction. However, for many molecules it becomes necessary to augment the experimental GED data with information from other sources. The SARACEN method, used routinely at Edinburgh when determining structures, allows computed parameters from ab initio and density functional theory (DFT) calculations to be used as extra data in the GED refinement process. This thesis describes the determinations of the gas-phase structures of molecules that contain heavy p-block elements, including examples from Groups 13, 14, 15 and 16. Each of the compounds studied was solid at room temperature, requiring heating to produce a suitable vapour pressure and vaporisation rate and testing the existing electron diffraction apparatus to its limits. Use was made of a new heated reservoir, recently developed in Edinburgh by a previous PhD student, which has allowed compounds to be studied that were previously inaccessible. The molecules that were studied during the course of this degree are: In(P3C2But2), In(P2C3But3), Sn(P2C2But2), Sb2(C6F6)3, Bi2(C6F6)3, Se(SCH3)2 and Te(SCH3)2. While determining the structures of these molecules, accurate theoretical geometries have been obtained using both ab initio and DFT methods. As a result a better understanding has been achieved of which methods are suitable for use in calculating the structures of molecules with heavy p-block elements. The use of pseudopotentials as opposed to all-electron basis sets proved necessary when performing calculations on such large molecules with heavy atoms. The extent to which these pseudopotentials, especially ones that consider very few electrons to be in the valence shell of an atom, can affect the calculated geometries has been shown to be considerable. In addition, methods being developed to compute vibrational corrections for gas-phase structure determination have been extended to the crystalline phase. Molecular dynamics simulations have been used to derive the effects of vibrations on average nuclear positions, relative to equilibrium positions. The differences, when applied to coordinates obtained experimentally by neutron diffraction yield experimental equilibrium structures.
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Many-body effects in interionic interactionsDomene, Carmen January 2000 (has links)
No description available.
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First-principles calculations of Cu adsorption on an H-terminated Si surfaceFoster, A. S., Gosálvez, M. A., Hynninen, T., Nieminen, R. M., Sato, K. 08 1900 (has links)
No description available.
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Spectroscopic and ab initio studies on the conformations and vibrational spectra of selected cyclic and bicyclic moleculesAl-Saadi, Abdulaziz A. H. 15 May 2009 (has links)
The structure, potential energy functions and vibrational spectra of several cyclic
and bicyclic molecules have been investigated using several spectroscopic techniques
and high-level ab initio and density functional theory (DFT) calculations. Laser induced
fluorescence and Raman spectroscopies were used to study the conformation of 2-
indanol in the electronic ground and excited states. These, along with detailed ab initio
calculations, confirmed the existence of four different stable conformations with the one
undergoing an intermolecular hydrogen bonding being the most stable. A theoretical
two-dimensional surface in terms of the ring-puckering and the hydroxyl group internal
rotation vibrations was constructed. This work was extended to obtain preliminary
insights on the conformations and ring-puckering frequencies of 3-cyclopenten-1-ol
using ab initio and DFT calculations.
Infrared and Raman spectra were also utilized to study the structures and
vibrational spectra of -crotonolactone and 2,3-cyclopentenopyridine (pyrindan). Ab initio results showed that -crotonolactone is rigidly planar in the electronic ground state
and has a nearly harmonic ring-puckering potential function. The calculated vibrational
levels were shown to be in very good agreement with the experimental ring-puckering
frequency from vapor-phase Raman observations.
The structures, vibrational spectra, and potential energy functions of several
cyclic molecules were reinvestigated using high-level ab initio computations, and
detailed vibrational analyses based on DFT-B3LYP calculated frequencies were also
carried out. A number of new insights were presented by re-evaluating the available
experimental data for several cyclopentenes, silacyclobutanes and silacyclopentenes. It
was found that the vibrational spectra of some deuterated cyclopentenes possess
extensive coupling between several ring modes and other low-frequency modes.
Reassignments of these spectra have been proposed. Frequencies from DFT-B3LYP
calculations showed very good agreement with the experimental values for
silacyclobutane and its derivatives. The presence of silicon and halogen atoms did not
affect the accuracy of the DFT calculations. In addition, the ring-puckering potential
energy function for silacyclopent-2-ene was studied and alternative assignments of the
far-infrared results were proposed. The new assignments are in good agreement with
computational results. Silacyclopent-2-ene and its -1,1-d2 isotopomer were shown to be
slightly puckered with barriers of less than 50 cm-1.
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X-ray absorption near-edge structures of disordered Mg_1−xZn_xO solid solutionsMizoguchi, Teruyasu, Seko, Atsuto, Yoshiya, Masato, Yoshida, Hisao, Yoshida, Tomoko, Ching, W. Y., Tanaka, Isao 11 1900 (has links)
No description available.
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Theoretical Evidence for Reassignment of Two Fundamental Vibrational Modes of Tetrafluorooxirane-<sup>16</sup>O and -<sup>18</sup>OLiu, Ruifeng, Clark, Jeffrey A., Krauser, Joel A., Tate, Dennis R., Moody, Paula R., Vanburen, Alex S. 01 January 1996 (has links)
Ab initio and density functional theory calculations confirm Craig's assignment of the fundamental vibrational modes of tetrafluorooxirane with the exception that assignments of the C-F stretching modes v9 (b1) and v13 (b2) should be exchanged. The calculated structural parameters are in good agreement with results of microwave studies except for the C-C bond length for which all the calculated results are slightly too long.
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Inverted Zintl phases and ions - A search for new electronic properties.Lindsjö, Martin January 2002 (has links)
No description available.
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Détermination ab initio de potentiels électroniques pour le calcul de données spectroscopiques / Ab Initio Determination of Electronic Potentials for Spectroscopic Datas ComputationBrites, Vincent 17 September 2010 (has links)
La structure et la spectroscopie de molécules d'intérêt astrophysique ont été étudiées par des méthodes de calcul électronique ab initio hautement corrélées. Notre démarche a tout d'abord été d'étudier des systèmes allant de deux à quatre atomes, afin de voir l'influence du niveau de calcul électronique utilisé lors de la détermination de données comparables aux résultats expérimentaux. Ainsi, l'étude de la spectroscopie des états électroniques de la molécule AlCl a été entreprise. Les résultats obtenus pour ce système reproduisent parfaitement les mesures expérimentales existantes tout en introduisant la compréhension des phénomènes observés. Nous avons ensuite prédit un ensemble de données pour les ions AlCl+ et AlCl2+, en utilisant la même méthodologie. Nous avons également entrepris des calculs de durée de vie de prédissociation pour les molécules SH et SH+. Nos courbes d'énergie potentielle hautement corrélée nous ont permis de reproduire avec une grande précision les durées de vie de prédissociation des niveaux rovibrationnels de SH. Par la suite, nous avons étudié une molécule d'intérêt astrophysique, détectée dans l'atmosphère de Titan, N2H+. Nous avons généré des surfaces d'énergie potentielle multidimensionnelles pour les états fondamentaux des molécules N2H+, N2H2+ et N2HAr+. Ces surfaces ont été utilisées pour le calcul des niveaux rovibrationnels de ces ions et de leurs espèces deutérées. Un excellent accord avec les donné es expérimentales disponibles a été obtenu, et un ensemble de constantes spectroscopiques a été prédit. Enfin, nous nous sommes intéressés à une molécule plus grande, Si(C2H3)4. Cette étude nous a permis d'établir une méthodologie pour le calcul de la structure et des états électroniques excités de molécules de taille moyenne. Nous avons également effectué des calculs sur l'ion Si(C2H3)4+, afin d'interpréter sa fragmentation mesurée lors de l'expérience d'impact d'électron réalisée à l'Université de Bratislava durant cette thèse / Highly correlated ab initio methodologies were used to investigate the structure and the spectroscopy of small and medium sized molecules at different levels of theory. Our results are compared to the available experimental data. For the AlCl molecule, our computed spectroscopic constants were in good agreement with the experimental ones, allowing us to predict a set of predictive data for the less known AlCl+ and AlCl2+ ions. After that, we treated the predissociation lifetimes of the A state of SH and SH+. Our highly correlated calculations allowed us to reproduce the lifetimes measured experimentally. Thereafter, multidimensional potential energy surfaces of the ground state of N2H+, N2H2+ and N2HAr+ were generated. These surfaces were used for the calculations of rovibrational levels of these ions and their respective deuterated species. An overall excellent agreement was obtained comparing to the available experimental measurements. Finall y, we investigated the Si(C2H3)4 molecule in order to establish a methodology for the treatment of the structure and electronic excited states of medium sized molecules. We also studied the reactivity of the Si(C2H3)4+ ion for a tentative assignment of the mass spectra obtained in the University of Bratislava by an electron impact experiment
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Propriedades eletrônicas em nanossistemas baseados em nanotubos de carbono e grafeno / Eletronic properties in nanosystems based on carbono nanotubes and grapheneKirch, Alexsandro 13 March 2014 (has links)
Neste trabalho foram realizadas simulações computacionais para investigar as propriedades eletrônicas de nanossistemas baseados em nanotubos de carbono e grafeno por meio de cálculos de primeiros princípios. Um dos nanossistemas investigados é formado por um nanotubo de carbono acoplado a eletrodos de nanofios de paládio encapsulados. Foi mostrado que estados provenientes dos eletrodos interagem fortemente com os estados do nanotubo de carbono. Cálculos de transporte eletrônico foram realizados para investigar a potencialidade desse nanossistema em aplicações como transistor de efeito de campo. Foi mostrado que a intensidade da corrente elétrica desse nanossistema pode ser variada com o campo elétrico de gate. Outro trabalho desenvolvido no presente trabalho tem como base um nanossistema formado pelo grafeno depositado nos substratos SiO2 amorfo e h-BN. Foi determinada a energia de adsorção e a quantidade de carga transferida para investigar a influênicas desses substratos na adsorção da molécula de H2 pelo grafeno. Foi mostrado que a energia de adsorção da molécula de H2 adsorivda na interface grafeno/SiO2 amorfo é menor em comparação com o grafeno suspenso ou disposto sobre o substrato h-BN. Além disso, a adsorção do H2 nessa região resulta em uma transferência de carga de uma ordem de grandeza maior em comparação com a adsorção no grafeno suspenso, sendo observado um deslocamento do Cone de Dirac em relação ao nível de Fermi. Esse estudo poderá contribuir para a construção de futuros sensores de H2 à base de grafeno. / In this work, ab initio calculations were performed within DFT framework to analyse electronic properties of Carbon nanotubes and grapheme nano systems. In this work, computer simulations were performed to investigate the electronic properties of nanosystems based on carbon nanotubes and graphene within DFT framework. One of these systems studied is a Carbon nanotube semiconductor coupled to encapsulated leads of Pd nanowires. It has been shown that leads states interact strongly with the carbon nanotube states. Electronic transport calculations were performed to unfold new applications of this system, such as the field effect transistor. We noticed that charge current intensity can be tuned by electrical field. We also described the influence of amorphous SiO2 and h-BN, in H2 energy adsorption and charge transfer, where both materials are used as graphene substrates. It was shown that the latter adsorption energy in the graphene/Si02 is smaller than graphene/h-Bn and the graphene suspended itself. In fact this adsorption results in a charge transference one order greater than in the suspended graphene, which can be seen as a vertical shift of the Dirac Cone. This study may improve the construction of future H2 sensors based on graphene.
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