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Agradecimentos: A.G.F. and M.H.F.B acknowledge support from the Brazilian Agency Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) under Finance Code 001 (A.G.F) and CAPES/PrInt Programme (M.H.F.B.). M.H.F.B. and M.A.P.L. acknowledge support from the Brazilian Agency Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). M.H.F.B. also acknowledges computational support from Professor Carlos M. de Carvalho at LFTC-DFis-UFPR and at LCPAD-UFPR. This research used the computing resources and assistance of the John David Rogers Computing Center (CCJDR) in the Institute of Physics "Gleb Wataghin," University of Campinas. This paper is also Honoring Prof. Vincent McKoy. For being very focused on ab initio calculations, he end up motivating our Brazilian community to explore several approximations that can proper describe the scattering process. Our applications of the SMC method with norm conserving pseudopotentials represent our effort of mixing ab initio calculation (electronic valence) with pseudo-potentials (electronic core). The present paper represents the first step to another mixture of strategies, the ab initio electronic excitation description with a pseudo (model) potential to represent the ionization process. During the review process of this manuscript by the Referees our dear friend and senior author of this manuscript, Professor Luiz Guimarães Ferreira (Guima), has passed away. Guima had a huge impact in our careers and in our lives Abstract: We propose a model potential for computing total ionization cross sections for atoms and molecules by electron impact. The potential is obtained by a fitting procedure using the Binary-Encounter-Bethe model cross sections as a starting point. We present total ionization cross section for hydrogen, carbon, nitrogen and oxygen atoms and for hydrogen, nitrogen, water, methane and benzene molecules. The results obtained with our model potential are compared with results obtained with the Binary-Encounter-Bethe model and with the first Born approximation, and agreement is quite good. Our results show that this potential could be used to account for the ionization channel in an electron-molecule collision calculation COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

Agradecimentos: A.G.F. acknowledges support from Coordenaão de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001, and M.A.P.L. and R.F.C. acknowledge the Brazilian agency Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). This research used the computing resour- ces and assistance of the John David Rogers Computing Center (CCJDR) in the Institute of Physics "Gleb Wataghin," University of Campinas. M.J.B. acknowledges funding from the Australian Research Council through Grant # DP180101655 Abstract: Benzene is undoubtedly one of the most studied target molecules in electron scattering experiments and calculations. However, there is still a huge knowledge gap on the electronic excitation cross sections of this fundamental collision. Here, we report calculated differential and integral cross sections for elastic and electronic excitation, as well as total cross sections, for electron scattering by the benzene molecule, for impact energies in the 10-50 eV range. We have employed the Schwinger multichannel method, in two levels of approximation. By including extra diffuse functions in the second calculation, the role of higher lying Rydberg states in the multichannel coupling scheme was assessed. We found that such states have minor effects on the elastic and total cross sections. In contrast, the electronic excitation cross sections of the lower-lying bands decrease in magnitude when accounting for the higher Rydberg states, and this effect becomes more pronounced at lower impact energies. Our computed elastic cross sections are in quite good agreement with the available experimental data, whereas the comparison for the electronic excitation channels is still satisfactory. We also discuss the need for accurate excitation energies in order to properly compare theoretical and experimental electronic excitation cross sections COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

Orientador: Marco Aurélio Pinheiro Lima Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin Resumo: Nesta dissertação apresentamos seções de choque diferenciais (DCSs) para a excitação eletrônica para os estados de mais baixa energia dos tautômeros trans e gauche da molécula de etanol, assim como seções de choque totais para a faixa de energia de 15-50 eV. Os cálculos foram realizados utilizando o Método Multicanal de Schwinger (SMC) implementado com pseudopotenciais. Levamos em conta 11, 41, 183, 317 e 431 canais abertos para o tautômero trans e, para o gauche, os três primeiros acoplamentos multicanais citados, devido à limitação computacional associada ao grupo pontual C1 desse tautômero. Até o momento, os nossos cálculos foram os mais sofisticados com respeito ao número de canais abertos já realizados com o método SMC. Encontramos, no geral, um bom acordo em relação aos resultados experimentais disponíveis na literatura para ângulos intermediários e em energias de impacto maiores (a partir de 15 eV). Entretanto, mesmo utilizando o procedimento Born-closure para melhorar a descrição de interações de longo alcance de dipolo (deficiente devido ao uso de funções quadraticamente integráveis), não obtivemos uma boa descrição dos ângulos pequenos nas DCSs calculadas com o SMC para estados com transições permitidas por dipolo. Esses resultados indicaram que o pobre acordo em baixos ângulos está associado à má descrição das menores ondas parciais. Com respeito às DCSs em menores energias de impacto, no geral, superestimamos os resultados experimentais. A falta de mais canais abertos pode estar associada com as discrepâncias remanescentes em relação ao experimento, mas aqui argumentamos que outros fatores também devem estar envolvidos. Visando uma descrição melhorada dos estados excitados do alvo, propomos um procedimento simples para selecionar pares de orbitais buraco e partícula, preservando a descrição de excitações simples da implementação atual do SMC. Uma avaliação quantitativa do processo de colisão deve ainda considerar a contribuição individual de cada tautômero, os quais apresentaram DCSs bastante distintas em alguns casos. Nossas energias de excitação calculadas suportam que a segunda banda de absorção do etanol compreende três estados singletos, em vez de dois ou quatro, que foram sugeridos em trabalhos anteriores Abstract: In this dissertation we present differential cross sections (DCSs) for the electronic excitation of the lower-lying states of the trans and gauche tautomers of the ethanol molecule, as well as total cross sections for the energy range of 15-50 eV. The calculations were performed using the Schwinger Multichannel method (SMC) implemented with pseudopotentials. We took into account 11, 41, 183, 317 and 431 open channels for the trans tautomer and the first three levels of multichannel coupling mentioned for the gauche, due to the computational limitation associated with the C1 point group of this tautomer. So far, our calculations using the SMC method are the most sophisticated in terms of the number of open channels. In general, we found a good agreement with the experimental results available in the literature for intermediate angles and higher impact energies (above 15 eV). However, even when using the Born-closure procedure to improve the long range dipole interaction (deficient due to the use of quadratically integrable functions), we did not obtain a good description of the forward scattering in the DCSs calculated with the SMC method for dipole allowed transitions. These results indicated that the unsatisfactory agreement on smaller scattering angles is associated with a poor description of the lower partial waves. In general, with regard to the DCSs at lower impact energies, we overestimated the experimental data. Missing open channels are usually evoked to explain the remaining discrepancies to experiment, but here we argue that other factors should also be involved. Aiming at an improved description of the target states, we have proposed a simple procedure for selecting the pairs of hole and particle orbitals, while keeping the single excitation prescription of the current SMC implementation. A quantitative assessment of the collision process should further consider the individual contribution of each tautomer, which presented quite distinct DCSs in some cases. Our computed excitation energies also support that the second absorption band of ethanol is comprised of three singlet states of each tautomer, rather than the previously suggested two or four states Mestrado Física Mestre em Física CNPQ 135900/2018-2