Tese (doutorado)—Universidade de Brasília, Instituto de Física, 2009. / Submitted by Larissa Ferreira dos Angelos (ferreirangelos@gmail.com) on 2010-04-19T18:09:55Z
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Previous issue date: 2009-04 / Recentemente, vários modelos estruturais, baseados na Teoria do Funcional da Densidade, têm sido amplamente empregados para representar nanopartículas. Dentre os modelos mais comuns, citamos os aglomerados de 1 a 10 átomos, superfícies planas e pequenas nanopartículas com até 100 átomos. Sabemos que os aglomerados e as superfícies planas descartam a curvatura da nanopartícula e os efeitos de confinamento de exciton. Por outro lado, são modelos muito econômicos do ponto de vista computacional e seriam úteis para o estudo de adsorção de moléculas grandes. Com o intuito de avaliar os pontos positivos e as limitações de cada modelo, nós investigamos rigorosamente a representatividade da nanopartícula de CdS na fase cúbica. Para tanto, nós utilizamos a Teoria do Funcional da Densidade implementada no programa VASP. Assim, comparamos os protótipos dos tipos nanopartícula pequena, conjunto de superfícies planas e aglomerados a partir da avaliação da relaxação das superfícies, das imagens de densidade de carga e dos espectros de densidade de estados eletrônicos. Identificamos o deslocamento para o azul, a anisotropia de carga superficial, a formação de dipolos e de superestruturas. Finalmente, estudamos a adsorção do grupo tiol (HS) na superfície dos modelos de nanopartícula de CdS. A partir da avaliação dos modelos estudados foi possível sugerir um protocolo para a construção de protótipos de nanopartículas que representassem uma nanopartícula maior sem desprezar aspectos relevantes do sistema. __________________________________________________________________________________________ ABSTRACT / Nowadays, several structural models based on the Density Functional Theory have been widely employed in order to represent nanoparticles. The most significant models are clusters containing up to ten atoms, flat surfaces, and small nanoparticles containing up to a hundred atoms. It is well-known that clusters and flat surface models do not take the nanoparticle's curvature and the exciton's confinement effects into account. On the other hand, such models are very economical from the computation point of view and because of this, studying bigger molecules would be quite suitable. With the intention of evaluating the advantages and limitations of each model, the representativity of cubic CdS nanoparticles was extensively and rigorously investigaded herein. For this purpose, the VASP code (where computations are performed within the Density Functional Theory formalism) was applied to compare nanoparticles prototypes represetended by each one of the structural models above. In order to make such comparisons, the following physical properties were evaluated: surface relaxation, charge-density images, and electronic density of state spectra. Numerical findings are as follows: Occurence of band gap blue-shift, surface-charge anisotropy, dipoles and super-structures formation. In addition to this, the tiol-group (HS) adsorption on the surface of CdS nanoparticles prototypes was studied. By means of the evaluation of each structural model investigated herein, it has been possible to suggest a routine for constructing nanoparticles which may represent bigger nanoparticles, overcoming typical computational difficulties without neglecting crucial aspects of the system.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.unb.br:10482/4393 |
| Date | 04 1900 |
| Creators | Fávero, Priscila Pereira |
| Contributors | Miotto, Ronei |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | Portuguese |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Source | reponame:Repositório Institucional da UnB, instname:Universidade de Brasília, instacron:UNB |
| Rights | info:eu-repo/semantics/openAccess |
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