Orientador: Nelson Henrique Morgon / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-04T16:59:18Z (GMT). No. of bitstreams: 1 Silva_MauricioChagasda_M.pdf: 1448929 bytes, checksum: 5e8a626133912c0e72a209eeccbbfd34 (MD5) Previous issue date: 2005 / Mestrado / Físico-Química / Mestre em Química

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18098号 / 理博第3976号 / 新制||理||1573(附属図書館) / 30956 / 京都大学大学院理学研究科化学専攻 / (主査)教授 吉村 一良, 教授 北川 宏, 教授 寺西 利治 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Electronic band structure of various crystal orientations of relaxed and strained bulk, 1D and 2D confined semiconductors are investigated using nonlocal empirical pseudopotential method with spin-orbit interaction. For the bulk semiconductors, local and nonlocal pseudopotential parameters are obtained by fitting transport-relevant quantities, such as band gap, effective masses and deformation potentials, to available experimental data. A cubic-spline interpolation is used to extend local form factors to arbitrary q and the resulting transferable local pseudopotential V(q) with correct work function is used to investigate the 1D and 2D confined systems with supercell method. Quantum confinement, uniaxial and biaxial strain and crystal orientation effects of the band structure are investigated. Regarding the transport relavant quantities, we have found that the largest ballistic electron conductance occurs for compressively-strained large-diameter [001] wires while the smallest transport electron effective mass is found for larger-diameter [110] wires under tensile stress.

The aim of this study is to investigate the bulk glass forming ability (BGFA) of Ti-based alloy systems. These investigations were carried out in two main parts that are complementary to each other: theoretical and experimental. For theoretical studies, which are based on electronic theory of alloys in pseudopotential approximation, Ti-Zr, Ti-Co and Ti-Cu alloys were chosen as the binary systems. Alloying element additions were performed to each binary for the investigation of the BGFA of multicomponent Ti-based alloys. Among the three studied binary systems, Ti-Cu was found to exhibit better BGFA, and Mn, Al and Ni elements were found to be suitable for improving the BGFA of Ti-Cu binary alloy system. BGFA of Ti-Cu binary and Ti-Cu-(Mn, Al, Ni) multicomponent alloys were investigated with the experimental studies that were carried out with performing arc melting and centrifugal casting operations. The characterizations of these alloys were done with scanning electron microscopy, X-ray diffraction analysis and differential scanning calorimetry. Ti60Cu35Mn5, Ti60Cu35Al5 and Ti60Cu35Ni5 alloys were produced and characterized as examples for ternary systems. Among them, Ti60Cu35Mn5 system was found to have better indications regarding to BGFA. Therefore, it was chosen as the main composition and multicomponent alloys of Ti59Cu35Mn5Al1, Ti59Cu35Mn5Ni1 and Ti58Cu35Mn5Al1Ni1 were synthesized and characterized.

Orientador: Rogério Custodio / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-25T11:52:57Z (GMT). No. of bitstreams: 1 Pereira_DouglasHenrique_D.pdf: 3749609 bytes, checksum: b3ed317231247b116e3bdb8974c60c94 (MD5) Previous issue date: 2014 / Resumo: Este trabalho desenvolveu e aplicou métodos de química quântica, mais especificamente a teoria Gaussian 3, nos estudos de propriedades eletrônicas e estruturais de átomos e molécula e encontra-se dividido em 5 capítulos. No capítulo 1 são apresentados os resultados da implementação de pseudopotencial na teoria G3 para 446 reções envolvendo moléculas contendo átomos do 1º, 2º e 3° período representativo da tabela periódica, método denominado G3CEP. O método G3CEP foi aplicado para cálculos de entalpias de formação, energias de atomização e ionização, afinidade eletrônica e de prótons. A implementação final apresentou um desvio absoluto médio total de 1,29 kcal mol-1 para o G3CEP e 1,16 kcal mol-1 para o método G3. Outro aspecto importante associado ao uso do método G3CEP é a redução do tempo de CPU. Em geral, a redução no tempo de CPU varia entre 7-60%, dependendo do tamanho da molécula e dos tipos de átomos presentes na estrutura. O capítulo 2 mostra a aplicação do método G3CEP juntamente com o método original G3, no estudo de 43 barreiras rotacionais internas. Neste estudo procurou-se analisar a precisão dos métodos, bem como entender os efeitos estereoeletrônicos responsáveis pelas conformações mais estáveis. A comparação dos resultados demonstra que os cálculos G3 e G3CEP são mais precisos do que os cálculos MP4 ou cálculos incluindo a energia do ponto zero em relação aos dados experimentais. Considerando o tamanho das moléculas estudadas, uma redução de 32 % no tempo de CPU foi obtida com a utilização do método G3CEP. No capítulo 3 foram aplicados três métodos de alta precisão, os quais são: método Gaussian-3 (G3), Monte Carlo Quântico de Difusão (MCQD) e Coupled Cluster (CCSD(T)/aug-cc-pVQZ) para os cálculos de potenciais de ionização sucessivos e os conjuntos testes estudados foram os três primeiros períodos da tabela periódica [H-Ar]. O método CCSD(T) apresentou melhor precisão nos resultados para as ionizações do 1° e 2° período, seguido do G3 e por fim o MCQD. Para o 3º período o método MCQD é o mais preciso, seguido dos métodos G3 e CCSD(T). Analisando-se os três períodos juntos, o método MCQD juntamente com o método G3 mostraram resultados similares para o potencial de ionização com um desvio absoluto médio de 1,44 eV. O capítulo 4 mostra os resultados da implementação de pseudopotencial na teoria G3(MP2). Este trabalho vem dando continuidade a teoria desenvolvida no capítulo 1, embora agora, utilizando uma versão de ordem reduzida a qual elimina os cálculos em nível MP4 reduzindo assim a demanda computacional. Os resultados mostram um desvio absoluto médio total de 1,67 kcal mol-1 para o G3CEP(MP2) e 1,47 kcal mol-1 para o método G3(MP2) com uma redução computacional de 10-40 %. Por final, o capítulo 5 traz a aplicação do método G3CEP(MP2) e G3(MP2) no estudo da preferencia endo/exo de reações de Diels-Alder. A reação do anidrido maleico e ciclopentadieno apresentou uma menor energia de ativação para o aduto endo em relação ao aduto exo para ambas as metodologias empregadas. Os parâmetros de avaliação termodinâmicos apontam para o produto exo com o método G3(MP2) e para o produto endo utilizando o método G3CEP(MP2). A reação de acrilonitrila com o ciclo-hexadieno mostrou que a preferencia exo é observado tanto pelo controle cinético como pelo termodinâmico para as metodologias empregadas / Abstract: Abstract This study developed and applied methods of quantum chemistry, specifically the Gaussian 3 theory in studies of electronic and structural properties of atoms and molecule and is divided into five chapters: In Chapter 1, related to the development of methods, the results of the implementation of pseudopotential in the G3 theory for 446 atoms and molecules containing the 1st, 2nd and 3rd representative period of the periodic table, method referred to as G3CEP are presented. The G3CEP method was applied to calculations of enthalpies of formation, atomization and ionization energy, electron and protons affinity. The final implementation presented a total mean absolute deviation of 1.29 kcal mol-1 for G3CEP and 1.16 kcal mol-1 for G3 method. Another important aspect associated with the use of G3CEP is the reduction of CPU time. In general CPU time has been reduced from 7% to 60% depending on the size of the molecule and type of atom present in the structure. Chapter 2 shows the application of the G3CEP method together with the original G3, in the study of 43 internal rotational barriers. This study sought to analyze the accuracy of the methods as well as to understand the stereoelectronic effects responsible for the most stable conformations. The comparison of the results shows that the G3 calculations and G3CEP are more accurate than MP4 calculations or calculations including zero point energy in relation to the experimental data. Considering the size of the molecules studied, a 32% reduction in CPU time was obtained using the G3CEP method. In Chapter 3, three methods of high accuracy were applied. They are: Gaussian-3 theory (G3), Diffusion Quantum Monte Carlo (DQMC) and Coupled Cluster (CCSD(T)/aug-cc-pVQZ) for calculations of successive ionization potentials and test sets studied were the first three periods of the periodic table [H-Ar]. The CCSD(T) method showed better accuracy in the results for the ionization of the 1st and 2nd period, followed by G3 and finally DQMC. For the 3rd period the DQMC method is the most accurate, followed by G3 and CCSD(T). Analyzing the three periods together, the DQMC with the G3 methods showed similar results for the ionization potential with a mean absolute deviation of 1.44 eV. Chapter 4 shows the results of the implementation of pseudopotential in the G3(MP2) theory. This work is continuing the theory developed in Chapter 1, although now using a reduced-order version which eliminates the calculations at MP4, thereby, reducing the computational demand. The results show a total mean absolute deviation of 1.67 kcal mol-1 for G3CEP(MP2) and 1.47 kcal mol-1 for G3(MP2) with a reduced computational of 9-40%. By the end, chapter 5 brings the application of methods G3CEP(MP2) and G3(MP2) in the study of preference endo/exo of Diels-Alder reaction. The reaction of maleic anhydride and cyclopentadiene showed lower activation energy for the endo adduct compared to the exo adduct for both methodologies. The evaluation of the thermodynamic parameters indicate the exo product for the G3(MP2) method, and for the endo product using the G3CEP(MP2) method. The reaction of acrylonitrile with cyclohexadiene showed that the exopreference is observed by both the thermodynamic and kinetic controls to the methodologies applied / Doutorado / Físico-Química / Doutor em Ciências

Orientador: Rogério Custodio / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-23T02:21:16Z (GMT). No. of bitstreams: 1 Rocha_CarlosMuriloRomero_M.pdf: 3181887 bytes, checksum: 92221d4d84e390412b4bdcfb0ae7e206 (MD5) Previous issue date: 2013 / Resumo: No presente trabalho o pseudopotencial CEP foi implementado na teoria G3(MP2)B3 e a adaptação denominada G3CEP(MP2)B3. Tal método foi aplicado no estudo de 247 entalpias padrão de formação, 104 energias de ionização, 63 afinidades eletrônicas, 10 afinidades protônicas e 22 energias de atomização de um conjunto de moléculas contendo elementos representativos do 2º, 3º e 4º períodos da tabela periódica, totalizando 446 dados termoquímicos. Os desvios absolutos médios, em relação aos dados experimentais, foram 1,60 kcal mol e 1,41 kcal mol para as teorias G3CEP(MP2)B3 e G3(MP2)B3, respectivamente, com reduções de 10-40% nos tempos de CPU com a implementação do pseudopotencial CEP. Além disso, a avaliação de outras propriedades tais como cargas atômicas, momentos de dipolo e energias de orbitais HOMO resultou em desvios absolutos médios, em relação ao método G3(MP2)B3 original, de 0,203 e, 0,044 D e 0,002 Eh, respectivamente. Outro objetivo do presente trabalho foi a aplicação do método G3CEP(MP2)B3 no estudo do mecanismo de nitração do fenol, em fase gasosa, promovida pelo eletrófilo NO2 . Tal avaliação mecanística evidenciou-nos a ocorrência de transferências eletrônicas do sistema p aromático ao íon nitrônio em etapas que precedem a formação do complexo-s, resultados que são convergentes à hipótese do mecanismo SET (Single Electron Transfer). Além do mecanismo de substituição eletrofílica aromática, o presente estudo evidenciou a ocorrência, em fase gasosa, de caminhos reacionais alternativos, através dos quais a transferência da espécie O ao sistema p aromático do fenol seria observada. As excelentes concordâncias entre a teoria G3CEP(MP2)B3 e os demais métodos Gn mais acurados (como G3(MP2)B3, G3CEP e G3) na previsão de barreiras de ativação, revelou-nos interessantes perspectivas quanto à aplicabilidade da teoria G3CEP(MP2)B3 na determinação mecanística de reações orgânicas, bem como na previsão acurada de barreiras rotacionais internas, frente a reduzidos custos computacionais / Abstract: In this work, the CEP (Compact Effective Potential) pseudopotential was adapted in the G3(MP2)B3 theory providing a theoretical alternative referred to as G3CEP(MP2)B3 for calculations involving second-, third-, and fourth-row representative elements. The G3CEP(MP2) B3 theory was applied in the study of 247 standard enthalpies of formation, 104 ionization energies, 63 electron affinities, 20 proton affinities and 22 atomization energies of a test set comprising 446 experimental energies. The total mean absolute deviation was 1.60 kcal mol for G3CEP(MP2)B3 theory against 1.41 kcal mol from all-electron G3(MP2)B3 calculations, with reductions of 10-40% in CPU time for the implemented theory. Furthermore, the assessment of other properties such as atomic charges, dipole moments and highest occupied molecular orbital (HOMO) energies resulted in mean absolute deviations, compared with those predicted by the original G3(MP2)B3 theory, of 0.203 e, 0.044 D and 0.002 Eh, respectively. In addition to the adaptation and assessment of G3CEP(MP2)B3 theory, the purpose of this work was also the application of the implemented theory in the study of phenol nitration mechanism, in gaseous phase, promoted by NO2 elepctrophile. The mechanistic evaluation at G3CEP(MP2)B3 level showed the occurrence of a single-electron-transfer step from aromatic p-system to the nitronium ion prior to the s-complex formation, in agreement with the SET (Single Electron Transfer) mechanism. Besides electrophilic aromatic substitution reaction, the present work provided insights into alternative reaction mechanisms through which O species are transferred to the phenol aromatic p-system. Excellent agreement between G3CEP(MP2)B3 theory and other more accurate Gn theories (for instance G3(MP2)B3, G3 and G3CEP) in predicting activation barriers showed that the implemented theory would be a useful tool in the study of reaction mechanisms and also for predicting internal rotational barriers with a significantly reduced computational cost / Mestrado / Físico-Química / Mestre em Química

Parameters of Heine and Abarenkov potential has been computed in this paper for twenty two hexagonal closed pack (hcp) crystals. From the minimization of structure dependent energy of the pure crystal the inter-relation between the two parameters of the potential is first determined. Calculation uses pseudopotential technique with nine different exchange and correlation functions and either only available experimental value of vacancy formation energy (E1vF) or that obtained from an empirical relation based on other experimental parameters (Melting temperature, cohesive energy or activation energy) as tool. The variation of E1vF with parameter A of HAP and different exchange and correlation functions (ECF) show sharp fall in E1vF near very small value of A after which it shows constancy for all hcp crystals. Comparison is made with parameter of Ashcroft model also. For Aschroft this variation is almost flat showing averageness while for Heine and Abarenkov sharp variations are there from one hcp crystal to other.

Parameters of Heine and Abarenkov model potential (HAP) have been computed in this paper for sixteen body centered cubic (bcc) closed pack crystals. From the minimization of structure dependent energy of the pure crystal the inter-relation between the two parameters is first determined. Calculation uses pseudopotential technique with nine different exchange and correlation functions (ECF) and either only available experimental value of vacancy formation energy (VFE) or that obtained from an empirical relation based on other experimental parameters (Melting temperature, cohesive energy or activation energy) as tool. The variation of VFE with one parameter of HAP and different ECF show sharp fall in VFE near very small value of it after which it shows constancy for all bcc crystals. Comparison is made with parameter of Ashcroft model also. For increase in valency this parameter of HAP increases and show distinct different curves.

The emperical pseudopotential method in the large basis approach was used to calculate the electronic bandstructures of bulk semiconductor materials and layered semiconductor heterostructures. The crucial continuous atomic form factor potentials needed to carry out such calculations were determined by using Levenberg-Marquardt optimization in order to obtain optimal cubic spline interpolations of the potentials. The optimized potentials were not constrained by any particular functional form (such as a linear combination of Gaussians) and had better convergence properties for the optimization. It was demonstrated that the results obtained in this work could potentially lead to better agreement between calculated and empirically determined band gaps via optimization / Physics / M. Sc. (Physics)

Este trabalho apresenta o primeiro estudo dos estados aniônicos de baixa energia da para-Benzoquinona (p-BQ) por meio de cálculos de espalhamento elástico de elétrons pela molécula neutra. Foi utilizado o método multicanal de Schwinger implementado com pseudopotenciais de Bachelet, Hamann e Schlüter, na aproximação de núcleos fixos, e nas aproximações estático-troca e estático-troca mais polarização. As seções de choque integrais foram calculadas em duas geometrias do alvo, otimizadas para o estado fundamental da molécula neutra e do ânion. Os estados aniônicos encontrados foram aracterizados e comparados com resultados experimentais, realizados com a técnica de espectroscopia de transferência eletrônica (ETS). Três estados * foram observados, sendo um ligado e dois metaestáveis, em acordo com os experimentos. Uma ressonância de Feshbach foi encontrada nos cálculos, tal qual é observada experimentalmente e sugerida em diversos estudos teóricos de estado ligado. Acredita-se que a aproximação utilizada para descrever estados excitados do alvo poderá ser reconsiderada, em que é sugerida uma proximação mais sofisticada, a ser utilizada em cálculos futuros. Com este estudo, é possível uma melhor compreensão dos resultados experimentais ETS, assim como é permitida uma interpretação de estudos teóricos sobre os estados aniônicos da p-BQ. Ademais, este trabalho possibilita próximos estudos de espalhamento envolvendo quinonas mais complexas. / This work present the first study of low-energy anionic states in para-benzoquinone (p-BQ) by electron scattering calculations. The elastic scattering calculations were done in the fixed-nuclei approximation, with the Schwinger multichannel method implemented with pseudopotentials of Bachelet, Hamann and Schlüter, in the static-exchange and in the static-exchange plus polarization approximations. The integral cross sections were performed in two target geometries optimized for the neutral and anion ground states. The anionic states found were characterized and compared with experimental results obtained by electron transfer spectroscopy (ETS). Three * states were observed, a bound state and two metastable, in good agreement with experimental results. A Feshbach resonance was found in calculations, also it is observed experimentally and it was suggested in several theoretical studies of bound state. It is believed that the approach used to describe the target excited states can be reconsidered, as it is suggested a more sophisticated approach to be used in future calculations. With this study, a better understanding of experimental results ETS is possible, as it allowed an interpretation of theoretical studies of the anionic states of p-BQ. Moreover, this work enables further scattering studies involving more complex quinones.