The multiconfiguration time-dependent Hartree-Fock (MCTDHF) and multiconfiguration time-dependent Hartree (MCTDH) methods are employed to investigate nonperturbative multielectron dynamics in finite quantum systems. MCTDHF is a powerful tool that allows for the investigation of multielectron dynamics in strongly perturbed quantum systems. We have developed an MCTDHF code that is capable of treating problems involving three dimensional (3D) atoms and molecules exposed to strong laser fields. This code will allow for the theoretical treatment of multielectron phenomena in attosecond science that were previously inaccessible. These problems include complex ionization processes in pump-probe experiments on noble gas atoms, the nonlinear effects that have been observed in Ne atoms in the presence of an x-ray free-electron laser (XFEL) and the molecular rearrangement of cations after ionization. An implementation of MCTDH that is optimized for two electrons, each moving in two dimensions (2D), is also presented. This implementation of MCTDH allows for the efficient treatment of 2D spin-free systems involving two electrons; however, it does not scale well to 3D or to systems containing more that two electrons. Both MCTDHF and MCTDH were used to treat 2D problems in nanophysics and attosecond science. MCTDHF is used to investigate plasmon dynamics and the quantum breathing mode for several electrons in finite lateral quantum dots. MCTDHF is also used to study the effects of manipulating the potential of a double lateral quantum dot containing two electrons; applications to quantum computing are discussed. MCTDH is used to examine a diatomic model molecular system exposed to a strong laser field; nonsequential double ionization and high harmonic generation are studied and new processes identified and explained. An implementation of MCTDHF is developed for nonuniform tensor product grids; this will allow for the full 3D implementation of MCTDHF and will provide a means to investigate a wide variety of problems that cannot be currently treated by any other method. Finally, the time it takes for an electron to tunnel from a bound state is investigated; a definition of the tunnel time is established and the Keldysh time is connected to the wavefunction dynamics.

La théorie covariance de la fonctionnelle de la densité (CDF), basée sur un petit nombre de paramètres ajustables, a été utilisée avec succès pour décrire l’état fondamental et les états excités des noyaux de la carte nucléaire, pour A>12. Cette approche permet de décrire les systèmes nucléaires finis avec un Lagrangien hadronique universel résolu dans le cadre de l'approche Relativiste-Hartree-Fock-Bologuibov (RHFB). Ce modèle est également utilisé pour l'étude des étoiles compactes, car il peut être étendu à des densités élevées où la relativité restreinte ne peut pas être ignoré. Ce modèle peut également être étendu pour inclure la contribution des hypérons et ainsi que d'autres particules exotiques. Dans ce travail, la description et des prédictions basées sur l'approche RHFB pour les noyaux dans des conditions extrêmes de la masse, d'isospin et de température sont présentés.Dans la première partie de cette thèse, nous explorons l'apparition de nouvelles fermetures de couches sphériques pour des noyaux super-lourds, où les fermetures de couches sont caractérisées en termes de gap à deux nucléons. Les résultats dépendent légèrement des Lagrangians effectifs utilisés, mais les nombres magiques au-delà de ^{208} Pb sont prédit pour un nombre de protons Z=120 et 138, et pour un nombre de neutrons N=172, 184, 228, et 258. Les effets de couche sont sensibles à différents termes de champ de moyen, tels que le couplage spin-orbite, la masse scalaire et la masses effective, ainsi que l'interaction de tensorielle de Lorentz. Ces termes ont des poids différents dans les Lagrangians effectifs employées, expliquant les variations, somme toute petites, dans leurs prédictions. Employant le modèle RHFB le plus avancé, nous avons trouvé que le nucléide ^{304} 120 est favorisée comme étant le prochain noyau sphérique doublement magique au-delà de ^{208} Pb.Dans la deuxième partie de cette thèse, nous étudions l'apparition de nouveaux nombres magiques pour les noyaux de masse intermédiaire riches en neutrons, et nous analysons le rôle des interactions pseudo-vecteur et de tensorielle de Lorentz. Basé sur la transformation de Foldy-Wouthuysen, nous discutons en détail le rôle joué par les différents termes des interactions pseudo-vecteur et de tensorielle de Lorentz. Dans l'apparition des nouveaux nombres magiques N=16 , 32 et 34. Les noyaux ^{24} O ^{48} Si et ^{52,54} Ca sont prédits avec un grand gap au niveau de Fermi et un gap d'appariement zéro (^{24} O,^{54}Ca ) ou quasi-nul (^{48} Si,^{54} Ca), les rendant candidats pour de nouveaux nombres magiques des noyaux riches en neutrons. Nous constatons que les interactions de Lorentz pseudo-vecteur et tensorielle induisent des évolutions très spécifiques des énergies à une particule, ce qui pourrait signer la présence et la nécessité d'approches relativistes avec des interactions d'échanges de mésons.Dans la dernière partie de cette thèse, nous étudions les transitions de phase et excitations thermiques des deux noyaux stables et faiblement liés. Les prédictions de divers Lagrangiens relativistes et des différentes interactions d'appariement sont discutées. La température critique de la transition d'appariement dépend linéairement du gap d'appariement à température nulle, et cette dépendance est similaire pour une interaction de portée nulle ou bien finie. Les calculs présentés montrent des caractéristiques intéressantes des corrélations d'appariement à température finie, comme la persistance d'appariement et les phénomènes de re-entrance superfluide. En outre, nous analysons la réponse thermique de certains noyaux.En conclusion, le travail présenté dans cette thèse montre des résultats très intéressants et nouveaux pour trois des questions les plus importantes en physique nucléaire: la quête d'un nouvel îlot de stabilité dans la région des super-lourds, l'apparition de nouveaux nombres magiques dans les noyaux exotiques, et la réponse d'un système finis aux excitations thermiques. / The covariant density functional (CDF) theory with a few number of parameters has been successfully employed to describe ground-state and excited-states of nuclei over the entire nuclear landscape for A > 12. It describes finite nuclear systems with a universal hadronic Lagrangian, which is solved considering the relativistic-Hartree-Fock-Bologuibov approach (RHFB). This model is also employed for the study of compact stars, since it can be extended to high densities where special relativity cannot be ignore. This model can also be extended to include the contribution of hyperons and as well as other exotic particles. In this work, the description and some predictions based on RHFB approach for nuclei under extreme conditions of mass, isospin and temperature are presented.In the first part, we explore the occurrence of spherical shell closures for superheavy nuclei, where shell closures are characterized in terms of two-nucleon gaps. The results depend slightly on the effective Lagrangians used, but the magic numbers beyond ^{208}Pb are generally predicted to be Z = 120 and 138 for protons, and N = 172, 184, 228, and 258 for neutrons. Shell effects are sensitive to various terms of the mean-field, such as the spin-orbit coupling, the scalar and the effective masses, as well as the Lorentz-tensor interaction. These terms have different weights in the effective Lagrangians employed, explaining the (relatively small) variations in the predictions. Employing the most advanced RHFB model, we founded that the nuclide ^{304}120 is favored as being the next spherical doubly-magic nucleus beyond ^{208}Pb.In the second part, we investigate the formation of new shell gaps in intermediate mass neutron-rich nuclei, and analyze the role of the Lorentz pseudo-vector and tensor interactions. Based on the Foldy-Wouthuysen transformation, we discuss in detail the role played by the different terms of the Lorentz pseudo-vector and tensor interactions in the appearance of the N=16, 32 and 34 shell gaps. The nuclei ^{24}O, ^{48}Si and ^{52,54}Ca are predicted with a large shell gap and zero (^{24}O, ^{52}Ca) or almost zero (^{48}Si, ^{54}Ca) pairing gap, making them candidates for new magic numbers in neutron rich nuclei. We find that the Lorentz pseudo-vector and tensor interactions induce very specific evolutions of single-particle energies, which could clearly sign their presence and reveal the need for relativistic approaches with exchange interactions.In the last part, we study the phase transitions and thermal excitations of both stable and weakly-bound nuclei. The predictions of various relativistic Lagrangians and different pairing interactions are discussed. The critical temperature of the pairing transition is found to depend linearly on the zero-temperature pairing gap, and this dependence is similar for a zero-range or a finite-range pairing interaction. The present calculations show interesting features of the pairing correlations at finite temperature, such as the pairing persistence and pairing re-entrance phenomena. Also, we analyze the thermal response of some nuclei.In conclusion, the work presented in this thesis shown interesting and new results for three of the most important questions in nuclear physics: the quest for a new island of stability in the superheavy region, the appearance of new magic numbers in exotic nuclei, and the response of finite-systems to thermal excitations.

Cette thèse est consacrée à l’étude mathématique de divers systèmes de particules classiques et quantiques, en milieu désordonné. Elle comprend quatre travaux publiés ou soumis. Dans le premier nous fournissons une nouvelle formule permettant de prouver la localisation d’Anderson en une dimension d’espace et de caractériser la décroissance des fonctions propres à l’infini. Le second contient l’une des premières preuves de la localisation pour une infinité de particules en intéraction, dans l’approximation d’Hartree-Fock. Le troisième est dédié au modèle d’Anderson soumis à une perturbation périodique en temps. Sous certaines conditions sur la fréquence d’oscillation nous prouvons l’absence de diffusion. Dans le dernier travail nous montrons la décroissancedes corrélations pour le modèle du Jellium en une dimension dans un fond inhomogène, en utilisant la distance de Hilbert sur les cônes et le théorème de Birkhoff-Hopf. / This thesis is devoted to the mathematical study of some systems of classical and quantum particles, in a disordered medium. It comprises four published or submitted works. In the first one we provide a new formula allowing to prove Anderson localisation in one space dimension and to characterise the decay at infinity of the eigenfunctions. The second contains one of the first proofs of localisation for infinitely many particles in interaction, in the Hartree-Fock approximation. The third work is dedicated to the Anderson model in a time-periodic perturbation. Under certain conditions on the oscillation frequency we prove the absence of diffusion. In the last work we show the decay of correlations for the one-dimensional Jellium model in an inhomogeneous background, using the Hilbert distance on cones and the Birkhoff-Hopf theorem

Thesis (PhD (Physics))--University of Stelllenbosch, 2010. / ENGLISH ABSTRACT: In this dissertation a fully relativistic model for polarized inclusive quasielastic proton-nucleus scattering is developed. Using a standard relativistic impulse approximation (RIA) treatment of quasielastic scattering and a two-body SPVAT form of the current operator, it is shown how the behaviour of projectile and target can be decoupled. Subsequently, different models for projectile and target can be adopted and combined to examine a variety of relativistic effects. The most simplistic model of the target is provided by a mean-field nuclear matter approximation to the relativistic meson-nucleon model, quantum hadrodynamics (QHD). Here relativistic effects manifest as an effective mass, which is lower than the free mass, of the constituent nucleons. This model is improved upon by including many-body correlations through medium-modification of meson propagators in the relativistic random-phase approximation (RPA). Since it is generally accepted that the strong nuclear force and the extended range of the nuclear potential lead to distortion effects on the projectile and ejectile (seen as a modulation of the wave functions), our formalism is geared towards the use of relativistic distorted waves (RDWIA). The distorted waves are written as partial wave expansions and are solutions to the Dirac equation with potentials. The inclusion of distortions, however, greatly increases the computational burden and we show how a number of analytical and numerical techniques can be used to facilitate the process of calculation. It is also shown how the standard relativistic plane wave treatment (RPWIA) can, instead, be easily employed to obtain a baseline for determining the impact of distortions. A calculation is performed for the reaction 40Ca(!p, !p !) at a beam energy of 500 MeV. Here it is found that the effect of correlations on the RPWIA calculation can be seen as a quenching of the cross section that is expected to become more pronounced at lower energies or for higher density targets. A RDWIA calculation shows additional reduction and if target correlations are included this effect is enhanced. To our knowledge this is the first calculation that attempts to include both these effects (RPA and RDWIA) in the context of quasielastic proton-nucleus scattering. / AFRIKAANSE OPSOMMING: In hierdie proefskrif word ’n ten volle relatiwistiese model vir die berekening van inklusiewe kwasielastiese proton-kern verstrooiing daargestel. Deur gebruik te maak van ’n standaard relatiwistiese impulsbenadering (RIA) vir kwasi-elastiese verstrooiing asook ’n twee-deeltjie-SPVAT-vorm vir die stroom-operator, word daar gewys hoedat die gedrag van die projektiel en teiken ontkoppel kan word. Verskillende modelle kan dus vir die projektiel en teiken gebruik word om ’n verskeidenheid relatiwistiese effekte te bestudeer. Die mees simplistiese model vir die teiken word verskaf deur ’n gemiddelde-veld kernmateriaalbenadering tot die relatiwistiese meson-nukleon-model, kwantum-hadrodinamika (QHD). In hierdie model manifesteer relatiwistiese effekte as ’n effektiewe massa, wat kleiner is as die vrye massa, van nukleone in die kern. Hierdie model word verbeter deur die inagneming van veeldeeltjie korrelasies deur medium-gewysigde meson-propagators in die relatiwistiese ewekansige-fase-benadering (RPA). Aangesien dit algemeen aanvaar word dat die sterk-wisselwerking en die reikwydte van die kernpotensiaal aanleiding gee tot vervormingseffekte op die projektiel en ejektiel (gesien as die modulasie van golffunksies), is ons model optimaal geformuleer om gebruik te maak van relatiwistiese vervormde golwe (RDWIA). Die vervormde golwe word geskryf as parsi¨elegolf uitbreidings en dien as oplossings vir die Dirac-vergelyking met potensiale. Insluiting van vervormings vermeerder egter die berekeningslas geweldig en ons toon hoedat ’n aantal analitiese en numeriese tegnieke gebruik kan word om die proses te vergemaklik. Daar word ook aangetoon hoe die standaard- relatiwistiese-vlakgolf-benadering (RPWIA), in plaas van vevormde golwe, maklik gebruik kan word om ’n verwysingspunt vir die meting van die effek van vervormings te bepaal. ’n Berekening vir die reaksie 40Ca(!p, !p !) teen ’n projektiel-energie van 500 MeV word getoon. Hier word dit gevind dat die effek van korrelasies op die RPWIA-berekening gesien kan word as ’n verlaging van die kansvlak. Daar word verwag dat hierdie effek duideliker sal word by laer energie¨e en ho¨er kerndigthede. ’n RDWIA-berekening word getoon wat daarop dui dat addisionele verlaging in die kansvlak voorkom en indien korrelasies hier ingesluit word, word hierdie effek vergroot. Sover ons kennis strek, is hierdie die eerste berekening wat poog om beide hierdie effekte (RPA en RDWIA) in die konteks van kwasi-elastiese proton-kern verstrooiing in te sluit.

No description available.

Na primeira parte, estudamos os efeitos da temperatura sobre o emparelhamento normal e quase-dêuteron na matéria nuclear assimétrica usando a interação do tipo Bonn para a interação via troca de mésons. Analisamos os campos médios de emparelhamento como função da densidade, assimetria nêutron-próton e temperatura. Na segunda parte estudamos um dos ingredientes básicos para o cálculo estatístico do decaimento do núcleo quente, a densidade de estados. Bonche, Levit e Vautherin estudaram as propriedades estatísticas do núcleo quente usando um cálculo de Hartree-Fock estático para temperaturas finitas que descreve um núcleo quente em equilíbrio com um vapor de nucleons externo e após o cálculo extraiam a contribuição do vapor. Uma maneira alternativa para o cálculo de tais propriedades é através da contribuição dos estados ligados de partícula única. Calculamos as propriedades do núcleo quente usando ambos os formalismos em uma aproximação de Hartree relativística com as interações NL3 e DDME1 e comparamos os resultados obtidos nos dois formalismos. Por fim, obtivemos uma parametrização para a energia livre de Helmholtz para os quatro conjuntos de cálculos citados. Calculamos as propriedades estatísticas para um amplo conjunto de núcleos até temperaturas onde soluções auto-consistentes não existem mais e com estas propriedades realizamos ajustes globais a uma expressão estendida do modelo da gota-líquida dependente da temperatura similar às utilizadas em modelos de multifragmentação estatística.

Submitted by Cleide Dantas (cleidedantas@ufpa.br) on 2014-06-30T16:38:37Z No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Tese_EstudoTransporteEletronico.pdf: 1675927 bytes, checksum: 8d1dbfaef64dc73b80969f1a77221068 (MD5) / Rejected by Irvana Coutinho (irvana@ufpa.br), reason: Para substituição do PDF. on 2014-07-22T11:35:22Z (GMT) / Submitted by Cleide Dantas (cleidedantas@ufpa.br) on 2014-07-22T11:38:12Z No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Tese_EstudoTransporteEletronico.pdf: 4423348 bytes, checksum: 5f46b9fabf64f22e3aac0040ed71c181 (MD5) / Approved for entry into archive by Ana Rosa Silva (arosa@ufpa.br) on 2014-09-04T13:52:44Z (GMT) No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Tese_EstudoTransporteEletronico.pdf: 4423348 bytes, checksum: 5f46b9fabf64f22e3aac0040ed71c181 (MD5) / Made available in DSpace on 2014-09-04T13:52:44Z (GMT). No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Tese_EstudoTransporteEletronico.pdf: 4423348 bytes, checksum: 5f46b9fabf64f22e3aac0040ed71c181 (MD5) Previous issue date: 2013 / Neste Trabalho é apresentado um estudo teórico da estrutura eletrônica de uma molécula de fulereno C60 com junções em quatro terminais baseados em grupos doadores de elétron – etratiofulvaleno (TTF) – e grupos aceitadores de elétrons – fenilpropanodinila (FPP) e dispositivos moleculares baseados em derivados dos Carotenoides. O mecanismo de transporte investigado para os derivados dos Carotenoides foram utilizados para o melhor entendimento das curvas de Fowler- Nordheim (FN) e Millikan-Lauritsen (ML) para os sistemas baseados em fulereno C60. Em todos os casos foi possível confirmar que a análise empírica de Millikan-Lauritsen (ML) também é suficiente para descrever em todos os aspectos a espectroscopia de voltagem de transição (TVS). Para estudar os sistemas, foram feitas otimizações de geometria sistematicamente e observado uma transferência eletrônica calculada por métodos derivados de Hartree-Fock e Teoria do Funcional Densidade (DFT). Os resultados apresentados mostram um estudo detalhado do rearranjo de carga molecular para a estrutura, que sob a ação de um campo elétrico externo apontou que o transporte de carga está diretamente ligado ao tipo de junção que esse sistema é submetido de forma que a voltagem aplicada é intensa o bastante para criar um potencial de saturação nos sistemas em estudo: fulereno C60 com três terminais de tetratiofulvaleno e um terminal de fenil-propanodinila (C60-(TTF)3-FPP); fulereno C60 com quatros terminais de fenil-propanodinila (C60-(FPP)4). Os resultados mostram que se tem um retificador molecular que pode trabalhar corretamente como um retificador macroscópico. / In this work it is presented a theoretical study on the electronic structure of a fullerene molecule (C60) with junctions in four terminals based on groups electron donors. tetrathiafulvalene (TTF) – and groups acceptors of electrons – fenilpropanodinilla (FPP) and molecular devices based on Carotenoid derivatives. The transport mechanism investigated for the carotenoids derivatives were utilized for better understanding of Fowler-Nordheim (FN) and Millikan-Lauritsen (ML) plots for the systems based in fullerene C60. In all cases it was possible to confirm that the Millikan- Lauritsen (ML) analysis empirical is also sufficient to describe all aspects the transition voltage spectroscopy (TVS). To study this class of systems, optimize the geometry systematically and observe the electronic transfer calculated by Hartree-Fock and Density Functional Theory (DFT). The results show through a detailed analysis of the molecular charge rearrangement due to an external electric field shows that the charge transport is directly on to the type of junction that this system is submitted of form that the applied voltage suffices to create a saturation potential in the systems in study: fullerene C60 with three terminals of tetrathiafulvalene and one terminal of fenilpropanodinilla (C60-(TTF)3-FPP); fullerene C60 with four terminals of fenilpropanodinilla (C60-(FPP)4). The particularity observed in C60-(FPP)4 is the disposal of the structure to operate with rectifying character for the electronic transport in the presence of orthogonal electric field to terminal data. The results show that we have a Molecular rectifier that works as a macroscopic rectifier.

Submitted by Cleide Dantas (cleidedantas@ufpa.br) on 2014-04-30T12:33:42Z No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_InvestigacaoCaracteristicasNCPS.pdf: 10527727 bytes, checksum: 7e320cfba4c6a329c0c2d91d6adbdff3 (MD5) / Approved for entry into archive by Ana Rosa Silva (arosa@ufpa.br) on 2014-06-11T13:18:53Z (GMT) No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_InvestigacaoCaracteristicasNCPS.pdf: 10527727 bytes, checksum: 7e320cfba4c6a329c0c2d91d6adbdff3 (MD5) / Made available in DSpace on 2014-06-11T13:18:53Z (GMT). No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_InvestigacaoCaracteristicasNCPS.pdf: 10527727 bytes, checksum: 7e320cfba4c6a329c0c2d91d6adbdff3 (MD5) Previous issue date: 2006 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Neste trabalho, fizemos uma investigação sobre o estudo teórico das características I x V e C x V de Nanotubo Carbono de Parede Simples (NCPS) puro, com Nitrogênio substitucional carregado com cargas -1 (caracterizando um indicativo de dopagem tipo n) e +1 (caracterizando um indicativo de dopagem tipo p) e na presença de grupos doador (NO2)-aceitador (NH2), através da simulação computacional do estado fundamental de NCPS, bem como de sua estrutura eletrônica e propriedades ópticas, utilizando parametrizações semi-empíricas AM1 (Austin Mudel 1) e ZINDO/S-ClS (Zerner´s lntermediate Neglect of Differential Orbital/Spectroscopic - Cunfiguration lnteraction Single) derivadas da Teoria de Hartree-Fock baseada em técnicas de química quântica. Por meio deste modelo teórico analisamos as propriedades ópticas e eletrônicas, de maior interesse para esses materiais, a fim de se entender a melhor forma de interação desses materiais na fabricação de dispositivos eletrônicos, tais como TECs (Transistores de Efeito de Campo) ou em aplicações em optoeletrônica tais como DEL (Dispositivo Emissor de Luz). Observamos que NCPS com Nitrogênio substitucional apresentam defeitos conformacionais do tipo polarônico. Fizemos as curvas dos espectros UV-visível de Absorção para NCPS armchair e zigzag puro, com Nitrogênio substitucional carregado com cargas (-1 e +1) e na presença de grupos doador (NO2)-aceitador (NH2), quando perturbados por intensidades diferentes de campo elétrico. Verificamos que em NCPS zigzag ao aumentarmos a intensidade do campo elétrico, suas curvas sofrem grandes perturbações. Obtivemos as curvas p x E, I x V e C x V para esses NCPS, concluímos que NCPS armchair possui comportamento resistor, pois suas curvas são lineares e zigzag possui comportamento semelhante ao dos dispositivos eletrônicos importantes para o avanço tecnológico. Assim, nossos resultados estão de bom acordo com os resultados experimentais e teóricos de NCPS puro e com Nitrogênio encontrados na literatura. / In this work, we relate an investigation on the theoretical study of the I x V and C x V characteristics os SWCN pure, with substitutional Nitrogen charged with charge -1 (n-type material) and +1 (p-type material) and in the presence of donor (NO2)-aceptor (NH2) grups, through of the computational simulation of the SWCN ground states as well as your electronic structure and optics properties utilizing quantum chemical approaches: AM1 (Austin Model 1) and ZINDO/S-CIS (Zerner’s Intermediate Neglect of Differential Orbital/Spectroscopic – Configuration Interaction Simple) semi-empirical parametrization, Hartree-Fock based theory. By mean of this theoretical model, we analyse the electrons and optics properties, of more interest for that materials, the end understand the best shape of interation of this materials in the fabrication of electronic devices such as FETs (Field-Effect Transistors) or in optoelectronic applications such as LEDs (Light-Emitting Devices). We observate that SWCN with substitutional Nitrogen presents conformational defects of the polaron type. We made the curves of the UV-visivel Absorpion Spectra for armchair and zigzag SWCN pure, with substitutional Nitrogen charged with charge -1 (n-type material) and +1 (p-type material) and in the presence of donor (NO2)-aceptor (NH2) grups, when they are perturbed by different intensity of electric field. We examine in zigzag SWCN when it has na increase in the intensity of the electric field, yours curves suffer large perturbations. We get the curves p x E, I x V and C x V for this SWCN, we conclude that armchair armchair possess resistor behavior, therefore yours curves are linears and zigzag possess similar behavior at the importants electronic devices for the tecnologics advance. Our results are good agreement with the experimentals and theoretical results of the SWCN pure and with Nitrogen found in the literature.

Molecular modeling, using both ab initio and semi-empirical methods has been undertaken for a series of dirhodium complexes in order to improve the understanding of the nature of the chemical bonding in this class of homogeneous catalysts. These complexes, with carboxylamidate and carboxylate ligands, are extremely functional metal catalysts used in the synthesis of pharmaceuticals and agrochemicals. The X-ray crystallography shows anomalies in the bond angles that have potential impact on understanding the catalysis. To resolve these issues, minimum energy structures of several examples (e.g. Rh2(NHCOCH3)4, Rh2(NHCOCH3)4NC, Rh2(CO2CH3)4, Rh2(CO2CH3)4NC, Rh2(CHO2)4, and Rh2(CHO2)4NC) were calculated using Hatree-Fock and Density Functional Theory/B3LYP with the LANL2DZ ECP (Rh), and cc-pVDZ (all other atoms) basis sets.

We study the application of Bose-Einstein condensates (BECs) to simulations of phenomena across a number of disciplines in physics, using theoretical and computational methods. ¶ Collapsing condensates as created by E. Donley et al. [Nature 415, 39 (2002)] exhibit potentially useful parallels to an inflationary universe. To enable the exploitation of this analogy, we check if current quantum field theories describe collapsing condensates quantitatively, by targeting the discrepancy between experimental and theoretical values for the time to collapse. To this end, we couple the lowest order quantum field correlation functions to the condensate wavefunction, and solve the resulting Hartree-Fock-Bogoliubov equations numerically. Complementarily, we perform stochastic truncated Wigner simulations of the collapse. Both methods also allow us to study finite temperature effects. ¶ We find with neither method that quantum corrections lead to a faster collapse than is predicted by Gross-Pitaevskii theory. We conclude that the discrepancy between the experimental and theoretical values of the collapse time cannot be explained by Gaussian quantum fluctuations or finite temperature effects. Further studies are thus required before the full analogue cosmology potential of collapsing condensates can be utilised. ¶ As the next project, we find experimental parameter regimes in which stable three-dimensional Skyrmions can exist in a condensate. We show that their stability in a harmonic trap depends critically on scattering lengths, atom numbers, trap rotation and trap anisotropy. In particular, for the Rb87 |F=1,m_f=-1>, |F=2,m_f=1> hyperfine states, stability is sensitive to the scattering lengths at the 2% level. We find stable Skyrmions with slightly more than 2*10^6 atoms, which can be stabilised against drifting out of the trap by laser pinning. ¶ As a stepping stone towards Skyrmions, we propose a method for the stabilisation of a stack of parallel vortex rings in a Bose-Einstein condensate. The method makes use of a ``hollow'' laser beam containing an optical vortex, which realises an optical tunnel for the condensate. Using realistic experimental parameters, we demonstrate numerically that our method can stabilise up to 9 vortex rings. ¶ Finally, we focus on analogue gravity, further exploiting the analogy between flowing condensates and general relativistic curved space time. We compare several realistic setups, investigating their suitability for the observation of analogue Hawking radiation. We link our proposal of stable ring flows to analogue gravity, by studying supersonic flows in the optical tunnel. We show that long-living immobile condensate solitons generated in the tunnel exhibit sonic horizons, and discuss whether these could be employed to study extreme cases in analogue gravity. ¶ Beyond these, our survey indicates that for conventional analogue Hawking radiation, simple outflow from a condensate reservoir, in effectively one dimension, has the best properties. We show with three dimensional simulations that stable sonic horizons exist under realistic conditions. However, we highlight that three-body losses impose limitations on the achievable analogue Hawking temperatures. These limitations vary between the atomic species and favour light atoms. ¶ Our results indicate that Bose-Einstein condensates will soon be useful for interdisciplinary studies by analogy, but also show that the experiments will be challenging.