This doctoral study consists of three parts. In the first part, structural and electronic properties of Al_kTi_lNi_m (k+l+m=2,3) microclusters have been investigated by performing density functional theory (DFT) calculations within the B3LYP [which comprises the Becke-88 exchange functional and the correlation functional of Lee, Yang, and Parr] and the effective core potential (ECP) level. Dimers and trimers of the elements aluminum, titanium, and nickel, and their binary and ternary combinations have been studied in their ground states. The optimum geometries, possible dissociation channels, vibrational properties, and electronic structure of the clusters under study have been obtained. In the second part, after an empirical potential energy function (PEF) has been parametrized for the AlTiNi ternary system, stable (minimum-energy) structures of Al_kTi_lNi_m (k+l+m=4) microclusters have been determined by molecular dynamics (MD) simulations. The energetics of the microclusters in 1K and 300 K have been discussed. By performing, again, DFT calculations (within the B3LYP and ECP level), the possible dissociation channels and electronic properties of the obtained clusters have been calculated. In the last part, using the empirical PEF parametrized previously for the AlTiNi ternary system, minimum-energy structures of Al_nTi_nNi_n (n= 1-16) ternary alloy nanoparticles have been determined by performing MD simulations. The structural and energetic features of the obtained nanoparticles have been investigated.

Thermodynamic stabilities of eighteen cyclic C5H6 isomers were explored computationally both on singlet and triplet state potential energy surfaces (PES). All isomers have singlet ground states except for bicyclo[2.1.0]pent-5-ylidene (B5) having no stable geometry on the singlet C5H6 PES. Cyclopenta-1,3-diene (M1) is the most stable cyclic C5H6 isomer while cyclopent-1,4-diylidene is the least stable one among all. Cyclopenta-1,2-diene (M2) and cyclopentyne (M3) have biradical characters of 46.9 and 21.5%, respectively. Seven unimolecular isomerization reactions occurring among several of these molecules were investigated by DFT and ab initio methods. The conversion of bicyclo[2.1.0]pent-2-ene (B1) and tricyclo[2.1.0.02,5]-pentane (T1) into 1,3-cyclopentadiene (M1) are shown to be concerted processes whose reaction paths pass through TSs with a high degree of biradical character. The reaction enthalpies (DH0) are predicted to be -47.7 kcal/mol for B1 and -63.8 kcal/mol for T1 at UB3LYP/6-31G(d) level. The activation enthalpy (DH0&sup1 / ) for the ring opening of B1 was calculated by the CR-CCSD(T) method to be 25.2 kcal/mol, in good agreement with experiment. Furthermore, the DH0&sup1 / for the ring opening of T1 was obtained by the CR-CCSD(T) method to be 48.2 kcal/mol. The self-conversion of M1 via 1,5-hydrogen shift is a facile and concerted reaction with aromatic TS. The DH0&sup1 / estimations of B3LYP and CC methods are 25.24 and 28.78 kcal/mol, respectively. For 1,2-hydrogen shift reactions of cyclopent-3-enylidene (M4) and cyclopenten-2-ylidene (M5), the single point CC calculations predicted the DH0&sup1 / values of 3.13 and 10.12 kcal/mol, as well as, the DH0 values of -71.28 and -64.05 kcal/mol, respectively. The reason of M5 being more stable than M4 is due to the conjugation of the carbene carbon and the double bond in M5. The reaction path of cyclobutylidene methylene to cyclopentyne rearrangement is found to be rather shallow. The DH0&sup1 / and DH0 values predicted by the RCCSD(T) method to be 3.65 and -5.72 kcal/mol, respectively. Finally, triplet state isomerization of bicyclo[2.1.0]pent-5-ylidene to cyclopenta-1,2-diene, as well as, its parent reaction, cyclopropylidene to 1,2-propadiene were investigated at several levels of theory including DFT, CASSCF and CC methods. The UCCSD(T) method estimated a moderate barrier whose value is 8.12 kcal/mol for the isomerization of 3B5 with the reaction enthalpy of -44.63 kcal/mol.

19 Dec 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 2009" Ivana Adamovic. 12/19/2004. Report is also available in paper and microfiche from NTIS.

19 Dec 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 1930" Heather Marie Netzloff. 12/19/2004. Report is also available in paper and microfiche from NTIS.

Made available in DSpace on 2015-05-14T13:21:51Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 1010298 bytes, checksum: a5a24de3f4abc4b3987d2584b46eea8f (MD5) Previous issue date: 2009-07-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The waste from fruit and vegetables and the discharge of domestic and industrial wastewaters in an unacceptable way cause serious problems for the majority of cities in Brazil and the rest of the world. The residues from fruit and vegetables and domestic and industrial wastewater could be treated jointly by the process of anaerobic digestion resulting in the production of energy and a reduction in negative environmental impacts. The principal objective of this work was to study the kinetics of the process of anaerobic biostabilization of vegetable residual solids (RSV), treated at different concentrations of total solids with the view to optimizing energy production and anaerobic biostabilization. To execute this study a completely mixed, compartmentalized anaerobic reactor comprising three compartments separated by glass plates with unit volumes of 25 litres, was designed, installed and monitored,. The resulting products from anaerobic biostabiliztion in the form of semi-solids were monitored weekly except for pH, total alkalinity and volatile fatty acids which jointly with biogas production were monitored twice weekly during a the total monitoring period of 294 days. The work was divided into two stages. In the first stage a substrate comprising twelve different types of vegetable solid waste with a total solids concentration equal to 75, 4 g/L was used. In the second stage the concentration of total solids applied to compartments C1, C2 and C3 were 40, 22.6 and 23.2 g/L respectively, with the with the level of humidity being adjusted by the addition of domestic sewage. The maximum percentage of methane in the biogas was 61.5% obtained in the first compartment (C1) of the reactor during the second experimental stage. The maximum kinetic constants for bioconversion (k) for COD total and soluble, TKN and sulphate during the first stage were respectively 3.86 x 10-2, 3.01 x 10-2, 4.75 x 10-2 and 2.13 x 10-2d-1. During the second stage of the study the values maximum obtained were 1.28 x 10-2, 1.90 x 10-2, 2.90 x 10-2 and 3.22 x 10-2d-1, for COD total and soluble, TKN and sulphate respectively. / O desperdício de frutas e verduras e o lançamento de águas residuárias domésticas ou industriais de forma inadequada representam sérios problemas para maioria das cidades do Brasil e do mundo. Os resíduos de frutas e verduras e as águas residuárias domésticas e industriais podem ser tratados de forma conjugada pelo processo de digestão anaeróbia, resultando no aproveitamento energético e na redução de impactos ao meio ambiente. O objetivo principal deste trabalho foi o estudo cinético do processo de bioestabilização anaeróbia de resíduos sólidos vegetais (RSV), tratados com diferentes concentrações de sólidos totais, visando o aproveitamento do potencial energético e consequentemente a bioestabilização anaeróbia do material orgânico. Para realização deste trabalho foi projetado, construído, instalado e monitorado um reator anaeróbio compartimentado de mistura completa, contendo três câmaras individuais de reação, construídas com placas de vidro, com volumes unitários de 25 litros. Os produtos resultantes do processo de bioestabilização anaeróbia que se encontravam na forma semi-sólida foram monitorados semanalmente, exceto pH, alcalinidade total e ácidos graxos voláteis que juntamente com o biogás foram monitorados duas vezes por semana; o período total de monitoração foi de 294 dias. O trabalho foi dividido em duas etapas. Na primeira etapa, o substrato constituído por doze diferentes tipos de (RSV) foi digerido a uma concentração de sólidos totais igual a 75,4 g/L. Para realização da segunda etapa, a concentração de sólidos totais aplicada às câmaras C1, C2 e C3 foram de 40; 22,8 e 23,2 g/L respectivamente, haja vista o teor de umidade do substrato preparado ter sido ajustado com adição esgoto doméstico. A porcentagem máxima de metano contido no biogás foi de 61,5%, obtida para primeira câmara de reação, no decorrer da segunda etapa. A produção máxima de biogás foi de 56 litros, também obtida na primeira câmara C1, ao longo da segunda etapa. Os valores máximos das constantes cinéticas de bioconversão (k) obtidos no decorrer da primeira etapa para DQOt, DQOs, NTK e sulfato foram respectivamente 3,86.10-2, 3,01.10-2, 4,75.10-2 e 2,13.10-2d-1. Durante a segunda etapa do trabalho os valores máximos obtidos foram de 1,28.10-2, 1,90.10-2, 2,90.10-2 e 3,22.10-2d-1 para DQOt, DQOs, NTK e sulfato, respectivamente.

Essa tese tem o objetivo modelar um subconjunto de peças de um compressor hermético de refrigeração idealizado utilizando um programa de elementos finitos para estudar a pressão de contato na junta da placa de válvulas com e sem pressão de gás refrigerante. Nessa pesquisa também se faz a modelagem dinâmica da bomba de um compressor acadêmico com vistas a estudar a vibração gerada durante seu funcionamento. No estudo da junta de vedação se faz um modelo geométrico do conjunto cabeçote e juntas com um programa CAD. A partir da geometria do subconjunto um modelo físico é construído no ANSYS®, que leva em consideração as diferentes propriedades dos materiais do conjunto cabeçote e juntas, inclusive a não linearidade do material da junta. São feitas simulações aplicando diferentes valores de força normal nos parafusos do cabeçote. No estudo de vibração do compressor faz-se o modelo de CAD da bomba de onde se obtém seu peso e propriedades de inércia. A matriz de rigidez do sistema de suspensão da bomba é calculada e se faz a análise modal da bomba. Os resultados das análises de pressão de contato foram mostrados através de gráficos da normal closure e da normal pressure da junta. Eles indicam de forma clara as regiões de baixa pressão de contato aplicada pelas peças que estão ou deveriam estar comprimindo a junta de vedação, que seriam regiões de falhas. Na análise dinâmica da bomba do compressor, é calculada a matriz de rigidez total do sistema com as molas de suspensão, levando em consideração a rigidez compressiva, de flexão e cisalhante das molas. Com a solução do modelo dinâmico criado, calcula-se a matriz dinâmica, a matriz modal normalizada, a matriz de frequências características, o deslocamento <span style=\"font-style:italic\">X <span style=\"position: relative; bottom: 1.3ex; letter-spacing: -1.2ex; right: 1.2ex\">&#8594; da bomba e também as energias cinética e potencial da bomba devido às forças de agitação. O modelo de elementos finitos da junta da placa de válvulas tem resultados coerentes e o modelo dinâmico da bomba fornece vários resultados para a análise de vibração de compressores. / This thesis has as objective to model a subset of parts of an idealized hermetic compressor for refrigeration using a program of finite elements intended to study the contact pressure on the valve plate gasket with and without pressure from the refrigerant gas. In this research a dynamic modelling of an academic compressor pump is also made with the aim of studying the vibration generated during its functioning. In the study of the sealing gasket, a geometric model of the cylinder head and gasket assembly is made by using a CAD program. From the geometric of the subset a physical model is built on the ANSYS®, which takes into account the different properties of the cylinder head and gasket assembly materials, including the non-linearity of the gasket material. Simulations are made by applying different normal force values on the cylinder head screws. In the compressor vibration study, a CAD pump model is made, thus obtaining its weight and inertia properties. The stiffness matrix of the pump suspension system is calculated and a modal analysis of the pump is made. The results from the contact pressure analyses were shown through \"normal closure\" and \"normal pressure\" charts of the gasket. They show in clear form the low contact pressure regions applied by the parts that are or should be compressing the sealing gasket, which would the regions of failures. In the dynamic analysis of the compressor pump, the total stiffness matrix of the system is calculated with the suspension springs, taking into account the compressive, flexural and shearing rigidities of the springs. With the solution of the dynamic model created, the following are calculated: the dynamic matrix, the normalized modal matrix, the characteristics frequency matrix, the <span style=\"font-style:italic\">X <span style=\"position: relative; bottom: 1.3ex; letter-spacing: -1.2ex; right: 1.2ex\">&#8594; displacement from the pump, as well as the kinetic and potential energy of the pump due to shaking forces. The finite elements model of the valve plate gasket has coherent results and the dynamic model of the pump provides various results for the analysis of the compressor vibration.

Este projeto tem dois objetivos. Primeiramente estudou-se a aplicabilidade dos splines tricúbicos para a construção de superfícies de energia potencial globais. Um dos obstáculos que este método tem de superar e a escolha de um sistema de coordenadas apropriado, que minimize a influência de pontos não físicos. Para isto, propôs-se o uso do sistema de coordenadas de Pekeris, nunca usado para este fim. Este procedimento foi realizado para três sistemas químicos bem descritos na literatura, [Cl,H2], [F,H,D] e [H,O,Cl], cujas superfícies de energia potencial e propriedades das reações foram usadas como referência. Com base nestes modelos, aplicamos o método proposto variando-se a quantidade e a disposição dos nós das interpolações, a fim de verificar sua influência na qualidade das superfícies interpoladas. Os resultados mostram que as superfícies construídas por este método reproduzem muito bem os cálculos de dinâmica química, tanto por métodos quânticos quanto por métodos clássicos. Para isto, os nós da interpolação devem cobrir as regiões mais importantes da superfície de energia potencial e os valores mais baixos das coordenadas de Pekeris devem ser priorizados. O segundo objetivo consiste na aplicação deste procedimento na construção da superfície de energia potencial [H,S,F]. Com esta superfície, diversas características deste sistema foram analisadas, tais como geometrias dos pontos estacionários, energias relativas e frequências vibracionais. Os valores obtidos estão de acordo com os dados descritos na literatura. A superfície construída também foi usada para a realização de cálculos de dinâmica para a reação F+HS &#8594; S+FH. Observamos a existência de dois tipos de mecanismos, um com a formação de um intermediário de longa duração e outro com a abstração direta do átomo de hidrogênio. / This project has two goals. First, we studied the applicability of the tricubic splines to construct global potential energy surfaces. One of the diculties this approach has to overcome is the choice of an appropriate coordinate system that minimises the in uence of non-physical points. For such, we proposed the use of the Pekeris coordinate system, never employed for this purpose. This procedure was carried out for three well described systems, [Cl,H2], [F,H,D] and [H,O,Cl], whose potential energy surfaces and reaction properties were taken as references. Based on these models, we applied the proposed method varying the amount and arrangement of the interpolation knots, to verify their influence on the quality of the interpolated surfaces. The results showed that surfaces constructed by this approach reproduce very well the chemical dynamics calculations, both for the quantum as well as for the classical methods, provided that the interpolation knots cover the most important regions of the potential energy surfaces, and the lower values of the Pekeris coordinates are prioritised. The second goal was the application of this procedure to the construction of the [H,S,F] potential energy surface. With this surface, several characteristics of this system were analysed, such as the geometry of the stationary points, relative energies and vibrational frequencies. The values obtained are in agreement with the data described in the literature. The constructed surface was also used for quantum dynamics calculations on the reaction F + HS &#8594; S + FH. We observed two kinds of mechanisms, one of them with the formation of a long-living intermediate and the other with the direct abstraction of the hydrogen atom.

No description available.

Les processus de transfert de charge sont très importants dans de nombreux domaines de la physique et de la chimie. Ils interviennent en particulier dans la conception ds plasmas astrophysiques ainsi que des plasmas de fusion. Les particules secondaires, électrons lents ou ions, générés le long du trajet des radiations jouent également un rôle crucial dans l’action des radaitions sur le milieu biologique, en relation en particulier avec les traitements du cancer. Il est donc fondamental d’avoir une connaissance approfondie des mécanismes mis en jeu dans ce type de processus, à l’échelle moléculaire. Pour cela, nous avons étudié dans cette thèse deux systèmes voisins, la collision des ions C2+ avec les molécules HF et HCI afin d’ananllyser en détail le mécanisme de transfert de charge dans ces deux réactions en d’en déduire des éléments permettant d’avoir une vue plus générals de ce type de processus. Nous nous sommes en particulier intéressés à l’anisotropie de la réaction de transfert de charge ainsi qu’aux effets dus à la vibration de la molécule diatomique cible lors de la collision. Une étude comparée des ces deux système a montré un mécanisme différent dans chaque cas liés aux interactions non-adiabatiques mises en jeu / Collisiosns of slow multiply charged ions with molecular species have been widely investigated in the past few years. Imortant experimental and theoretical effort has been focused on reactions with simple targets. Consideration of more complex molecular targets are now of increasing interest, in particular with regardto possible direect or indirect processes occuring in the irradiation of the biological medium.. In these reactions generally at relativity low energies, different processes have to be considered: exitation and fragmentation on the molecule, ionization of the gaseous target, and also possible charge transfer from the multicharged ion toward the biomolecule..Charge transfer can be investigated theoretically in the framework of the molecular representation of the collision. Such studies provides important information on the mecanism as well as on the electronic structure of the projectile and target during the reaction. The charge-transfer process in collisions on C2+ ions with hydrogen halide molecule (HF, HCI) has been studied by means of ab initio quantum chemistry molecular methods followed by semiclassical dynamical treatment in the keV collision energy range. The mechanism has been investigated in detail in each reaction, in connection with nonadiabatic interactions around avoided crodssings between states involved in the process.

Le but principal de ce travail est d'examiner la capacité des méthodes clusters couplés explicitement corrélées (CCSD(T)-F12) pour la génération des surface de potentiel (SEPs) multidimensionnelles à courte, moyenne et longue portée intermoléculaires et leur utilisation dans la détermination des spectres des systèmes van der Waals (vdW) et des données de collision sur une large gamme d'énergie de collision. Ceci a été fait par une comparaison directe des surfaces de potentiel et des résultats générés à partir de l'utilisation des méthodes clusters couplés standards avec simple, double et un traitement perturbatif des excitations triples (CCSD(T)) et explicitement corrélée CCSD(T)-F12. En effet, nous démontrons que la méthode CCSD(T)-F12 en connexion avec la base aug-cc-pVTZ est la méthode de choix pour la génération de ces surfaces de potentiel avec une très grande réduction du coût computationnel (temps CPU et occupation disque). Ceci est illustré à travers l'étude des systèmes vdW HCl/DCl-He et CO2 -CO2 qui sont importants pour l'astrophysique et les atmosphères planétaires. Pour HCl/DCl-He, nous avons comparé les résultats issus des SEPs explicitement corrélées et celles calculées avec les méthodes cluster couplés standards. Ces SEPs ont été générées le long des coordonnées intermonomères. A travers ces comparaisons, nous avons montré que l'utilisation des méthodes CCSD(T)-F12/aug-cc-pVTZ explicitement corrélées permet de dépasser la précision de l'approche CCSD(T)/CBS (prise comme référence) avec un coût computationnel très réduit. La qualité de la surface de potentiel explicitement corrélée a été vérifiée par le calcul des sections efficaces et des taux de collision d'excitation rotationnelle de HCl/DCl par He. Par la suite, Nous étendons, notre étude aux systèmes moléculaires plus larges à travers l'étude du dimère de dioxyde de carbone,(CO2 )2 . Ainsi, nous avons généré une SEP d'interaction à 4 dimensions pour le dimère de dioxyde de carbone (CO2 )2 en utilisant la méthode CCSD(T)-F12/aug-cc-pVTZ qui a été comparée avec d'autres surfaces et spécialement avec celle générée par les approches de référence CCSD(T)/CBS et SAPT. Cette comparaison a bien prouvé la performance des méthodes explicitement corrélées pour la description de la corrélation électronique. Ceci, a été validé par des calculs de dynamique qui ont permis de déterminer le second coefficient du viriel, le premier moment spectral et les niveaux vibrationnels du dimère de CO2 et leur comparaison aux résultats expérimentaux et théoriques existants. Nous recommandons donc l'utilisation de la méthode CCSD(T)-F12/aug-cc-pVTZ pour l'étude des interactions moléculaires impliquant des systèmes polyatomique-polyatomique faiblement liés / The main goal of this work is to examine the capabilities of explicitly correlated coupled cluster (CCSD(T)-F12) methods for the mapping of multidimensional potential energy surfaces (PESs) at short, medium and long intermolecular ranges and therefore their use in the determination of accurate collisional data for a wide range of collision energies after dynamical computations. This is done through close comparisons of these PESs and corresponding data to those deduced using standard coupled cluster approaches with perturbative treatment of triple excitations (CCSD(T)). Therefore, we definitely establish that CCSD(T)-F12 in connection with the aug-cc-pVTZ basis set is the method of choice for the generation of such accurate PESs with strong reduction of computational cost (CPU and disk occupancy). As a benchmark, we treated the rotational excitation induced by collision of HCl/DCl-He and CO2 -CO2 van der Waals molecular systems, which are relevant for astrophysics and planetary atmospheres, respectively. For HCl-He and DCl-He, we closely compared the results deduced from PESs calculated with explicitly correlated and standard coupled cluster methods. These PESs were generated over the intermonomer degrees of freedom. Through these comparisons, we have shown that the use of explicitly correlated CCSD(T)-F12/aug-cc-pVTZ method overcomes the accuracy of the reference approach CCSD(T) associated with the complete basis set (CBS) with a very low computational cost (2 orders of magnitude less). The quality of the explicitly correlated potential surface was verified by cross sections and collision rate calculations. Then, we extended our findings to the CO2 -CO2 larger molecular systems. Hence, we generated four-dimentional (4D) PES of the carbon dioxide dimer (CO2 )2 using the CCSD(T)-F12 method and we compared it with other surfaces specially with that generated by the CCSD(T)/CBS and SAPT approaches. Again, we established the performance of explicitly correlated method to account fully for electron correlation. This was validated after dynamical calculations, where second virial coefficient, first spectral moment and vibrational energies of the CO2 dimer were computed and compared to previous experimental and theoretical data. In total, we recommend the use of CCSD(T)/aug-cc-pVTZ method for the investigation of weak interactions occurring between polyatomic-polyatomic systems for a wide range of applications