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Master's Dissertation
Full name
Antonio Cesar Ferreira
Knowledge Area
Date of Defense
São Paulo, 1990
Title in Portuguese
Keywords in Portuguese
Aglomerado molecular
Defeitos e impurezas em GaAs
Espalhamento múltiplo-X?
Estrutura eletrônica
Abstract in Portuguese
Devido à inconfiabilidade do modelo EM-X?, no cálculo da energia total, consideramos uma correção na densidade de carga "muffin-tin". Com esta correção podemos ajustar a energia total, a partir de parâmetros definidos na teoria. O objetivo deste trabalho é o estudo da curva da energia total associada ao estado excitado do sistema GaAs: AsGa, quando o átomo substitucional de As se desloca na direção <1 1 1>. Partindo de cálculos de primeiros princípios (LARGE UNIT CELL APPROACH), reproduzimos a curva da energia total do estado fundamental. A partir dos parâmetros encontrados na correção não "muffin-tin" da densidade de carga, calculamos a curva do estado excitado utilizando o conceito de estado de transição de Slater. Nossos resultados mostraram que o efeito Jahn-TeIler não ocorre para defeitos tipo antisítio. Vimos também que a curva do comportamento dos autovalores com o deslocamento do átomo substitucional, está de acordo com cálculos recentes encontrados na literatura.
Title in English
Muffin-tin potential correction: antisite in GaAs
Keywords in English
Defects and impurities in GaAs
Electronic structure
Molecular cluster
Quantum mechanics
X?-multiple scattering
Abstract in English
Since total energy calculations within the Multiple Scattering-X? model are not reliable, a non "muffin-tin" correction to the charge density has been considered. With this correction the total energy can be adjusted through parameters defined in the theory. The aim of this work is to study the total energy curve of the excited state of the GaAs: AsGa system when the arsenic substitutional atom is displaced in the <1 1 1> direction. As a first step, the ground-state total energy curve obtained from first-principles calculations (LARGE UNIT CELL APPROACH) was reproduced. From the parameters found for the non "muffin-tin" charge density corrections, we have calculated the excited-state total energy curve by using the Slater transition-state concept. Our results show that the Jahn-Teller effect is not expected to occur for antisite-like defects. Moreover, the obtained behavior of the eigenvalues with displacement of the substitutional atom is in fairly good agreement with recent theoretical calculations found in the literature.
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