Teoria do funcional da densidade aplicada na Caracterização do Catalisador CaSnO3

• Ano de defesa: 2016
• Autor(a) principal: Andrade, Jefferson Maul de
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal da Paraíba; Brasil; Química; Programa de Pós-Graduação em Química; UFPB
• Palavras-chave em Português: CaSnO3; Programa Crystal; Raman; QHA; Hirshfeld-I; Adsorção; Crystal Program; Adsorption; CIENCIAS EXATAS E DA TERRA::QUIMICA
• Link de acesso: https://repositorio.ufpb.br/jspui/handle/tede/9000

This dissertation has as its central point the characterization through the density functional theory (DFT) of the orthorhombic perovskite CaSnO3 belonging to the space group Pbnm, using Gaussian type orbitals. At first, the bulk of the material was explored with the most diverse solids simulation techniques, focusing on the structural evaluation under pressure and frequency calculations, as well as its intensities (Raman and Infrared spectra) evaluated by the newly implemented (In Crystal program) Coupled-Perturbed Hartree-Fock/Kohn- Sham (CPHF/KS). Following, the bulk was again exploited under pressure, including various exchange-correlation type formulations within the DFT theory, as well as the use of routines recently implemented in the Crystal program as: Elastic constants under pressure, directional seismic velocity analysis and quasi-harmonic approximation (QHA). The latter is of great physical, mineralogical and geophysical interest due to its description of a material under conditions of high temperatures and pressures simultaneously. To further explore the possible catalytic properties of the material, the studies the defects, including oxygen vacancies and doping with copper, was carried out focusing on the energy differences and electronic charge analysis, the last, taking into account the Mulliken technique and Hirshfeld-I (available only to developers at present). Those calculation where performed at PBE and PBE0 level (for the doping with Cu only PBE0), with RHF and UHF formulations for the open shell and spin polarized cases. The used supercell (2x2x2) presented an adequate size to work with. The oxygen vacancy formed has the tendency to reduce the Sn neighbors, that form a mid gap close to the Valence Band, and presenting as the most stable formulation the RHF and Singlet (UHF). The oxygen vacancy is here characterized as been a neutral one. In the doping cases, where the tin atom is substituted by a coper one, the most stable case was when the Cu was near the vacancy (first neighbor). To finish the studies on this perovskite, the surface (001) is studied. The surface terminated in -CaO is a bit more stable than the -SnO2 one, however, the first one, using the applied methodology, presented some problems when adsorbing gases, hence been discarded in favor of the -SnO2 one. The CO and NH3 gases are adsorbed over the -SnO2 terminated surface, to evaluate it, charge density maps, density of states (DOS) and Raman intensity where used. The results showed that the CO adsorption is weak, but has a visible response in the Raman spectra. In the NH3 case the adsorption is strong and can be assigned as a chemisorption. In the last, an intense Raman peak appear and it is assigned to a bond between the hydrogen and the surface oxygen and it appear about 3098 cm−1.