O presente trabalho é um estudo sobre a importância da informação dos orbitais atômicos no cálculo de propriedades optoeletrônicas de heteroestruturas semicondutoras de baixa dimensionalidade. O trabalho é dividido em duas partes: na primeira parte, é estudada a simetria de reversão temporal no hamiltoniano k . p, analisando a preservação da informação de spin presente nos orbitais atômicos. O hamiltoniano obtido é inserido na equação de massa efetiva expandida para superredes. São calculadas estruturas de bandas de alguns poços quânticos de semicondutores III-V e grupo-IV. Compara-se o novo método com os tradicionais, e então são analisadas algumas grandezas que apresentam alteração significativa entre os métodos usados; A segunda parte é composta por um estudo detalhado do potencial de troca-correlação em semicondutores dopados. A matriz que descreve este potencial é escrita usando a distribuição de portadores presentes nos orbitais atômicos da rede cristalina, e os coeficientes desta matriz foram calculados usando quatro modelos para a correção de muitos corpos, baseadas nas aproximações LDA (Local density approximation) e LSDA (Local spin density approximation), com o objetivo de comparar as diversas parametrizações. Usando o método k . p tradicional, expandido para superredes, foram simulados sistemas δ-doped e hMni-δ-doped de Si, através de um cálculo autoconsistente baseado na equação de Poisson. A magnetização dos portadores é descrita por um modelo de campo médio. Foram analisados os perfis de potencial, estruturas de bandas, polarização de portadores e espectros de fotoluminescência para determinar as diferenças entre as aproximações utilizadas. / This work is a study about the atomic orbitals information importance in the calculation of optoelectronics properties of low dimensionality semiconductors. The work is divided in two parts. In the first one, a study of the time reversal symmetry of the k . p Hamiltonian is realized analyzing the preservation of the spin information present in the atomic orbitals. The obtained Hamiltonian is applied in the effective mass equation expanded to superlattices. Some calculations of quantum wells band structures are made using III-V and group-IV semiconductors, comparing the new method with the conventional ones to obtain an analysis of the difference of some physics properties. The second part is a detailed study of the exchangecorrelation potential in doped semiconductors. The matrix coefficients are calculated using the charge distribution of the crystalline lattice atomic orbitals, applied in some LDA (Local density approximation) and LSDA (Local spin density approximation) parameterizations to compare them. Using the conventional k . p method expanded to superlattices, Si δ-doped and hMni-δ-doped systems were calculated through a self consistent calculation based on Poissons equation. The carriers magnetization is described by an average field model. The potential profiles, band structures, carrier polarization and photoluminescence spectra were analyzed to obtain the difference between the approaches.

Alors qu’il existe de nombreux calculs microscopiques de barrières de fission pour des noyaux composés pair-pairs, il n’y a cependant que relativement peu de tels calculs pour des noyaux de masse impaire. Ceci est dû aux complications induites par la brisure de la symétric de reversement du sens du temps au niveau du champ moyen qui est engendrée par la présence d’un nucleon non apparié. Pour éviter cette difficulté, des calculs existants pour des noyaux de masse impaire ont tout simplement négligé ces effets de brisure de la symétrie de reversement du sens du temps.Dans ce travail, on se donne pour but d’améliorer la description des barrières de fission, aussi bien que des propriétés spectroscopiques du niveau fondamental et de l’état isomérique de fission,pour quelques isotopes de masse impaire dans la région des actinides en prenant en compte de tels effets. Ceci a été réalisé dans le cadre du formalisme de Skyrme–Hartree–Fock plus BCS avec blocking en adaptant ce formalisme à la brisure de la symétrie considérée. L’interaction résiduelle d’appariement a été approchée par une force de séniorité dont les paramètres ont été ajustés pour reproduire les différences de masse pair-impair de quelques noyaux de la région des actinides.Les énergies des têtes de bande rotationnelle de basse énergie ont été calculées dans le cadre du modèle unifié de Bohr-Mottelson pour quatre noyaux bien déformés (235U, 239Pu, 237Np, 241Am)produisant un bon accord qualitatif avec les données pour les noyaux impairs en neutrons. L’accord significativement moins bon obtenu pour les noyaux impairs en protons pourrait résulter de l’usage de l’approximation de Slater pour l’interaction d’échange de Coulomb. Les énergies de déformation de deux noyaux impairs en neutrons (235U, 239Pu) ont été calculées pour quelques configurations de particule individuelle, jusqu’après la barrières de fission externe. La symétrie axiale a été imposée tandis que la brisure de la symétrie droite-gauche (ou de parité intrinsèque) a été permise dans la région de la seconde barrière. Les hauteurs des barrières de fission pour ces noyaux impairs dépendent significativement des configurations de particule individuelle. Un accord qualitatif avec les données disponibles pour les hauteurs de barrières des noyaux impairs considérés et leurs voisins pair-pairs a été généralement obtenu. / While there have been numerous microscopic calculations on fission barriers of even-even compoundnuclei, there are however, relatively few such work dedicated to odd-mass nuclei. This is dueto the complications posed by the breaking of the time-reversal symmetry at the mean-field leveldue to the presence of an unpaired nucleon. In order to circumvent this difficulty, previous fission barriercalculations of odd-mass nuclei have been performed by neglecting the effect of time-reversalsymmetry breaking. This work aims to improve on the description of fission barriers as well asthe spectroscopic properties of ground and fission-isomeric state, of some odd-mass actinide nucleiby taking the effect of time-reversal symmetry breaking into account. This has been perfomedwithin a Skyrme-Hartree-Fock-plus-BCS framework with blocking, where the BCS formalism hasbeen adapted to accomodate this symmetry breaking. The Skyrme nucleon-nucleon effective forcehas been used with various sets of parameters (SIII, SkM*, SLy5*). The residual pairing interactionhas been approximated by seniority forces whose neutron and proton parameters have beenfitted to reproduce the odd-even mass differences of some actinide nuclei. The low-lying rotationalband-head energies evaluated within the Bohr-Mottelson unified model have been determined forfour well-deformed odd-nuclei (235U, 239Pu, 237Np, 241Am) yielding a good qualitative agreementto the data for odd-neutron nuclei. The agreement was significantly less good for the odd-protonnuclei, possibly due to the use of the Slater approximation for the exchange Coulomb interaction.The deformation energies of two odd-neutron nuclei (235U and 239Pu) have been calculated forsome single-particle configurations up to a point beyond the outer fission-barrier. Axial symmetrynuclear shape has been assumed while a breaking of the left-right (or intrinsic parity) symmetryhas been allowed around the outer fission-barrier. The fission-barrier heights of such odd-neutronnuclei depend significantly on the particle configurations. A special attention has been paid tothe very important rotational correction to deformation energies. In particular, the correction ofthe moment of inertia calculated from the usual Belyaev expression was considered. Overall, aqualitative agreement with available data on fission-barrier heights for the considered odd-neutronnuclei and their even neighbours has been obtained.

No description available.