Dissertations / Theses on the topic 'Density matrices'
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Rodríguez, Mayorga Mauricio. "Reduced density matrices: development and chemical applications." Doctoral thesis, Universitat de Girona, 2018. http://hdl.handle.net/10803/664261.
Full textEn esta tesis, nos enfocamos en metodologías alternativas que se basan en la reconstrucción de matrices de densidad. Mientras que en DFT varias calibraciones se pueden encontrar en la literatura, para el resto de metodologías alternativas no hay ninguna calibración donde la calidad de la matrices sea analizada. Por lo tanto, en esta tesis, desarrollamos una calibración exhaustiva para las aproximaciones disponibles en la literatura que reconstruyen matrices de orden 2 y 3. Las matrices densidad proporcionan acceso a magnitudes físicas como la densidad de probabilidad intracular (IPD). Nos centramos en una comprensión profunda de esta magnitud y, para ese fin, analizamos la evolución del IPD radial en átomos aislados y en el proceso de formación de enlaces. Finalmente, desde las matrices densidad también podemos evaluar el orden de los enlaces, y lo usamos para caracterizar el llamado mecanismo de arpón
Overy, Catherine Mary. "Reduced density matrices and stochastic quantum chemistry." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708241.
Full textScholz, Timothy Theodore. "Density matrix theory of diatomic molecules." Title page, contents and summary only, 1989. http://web4.library.adelaide.edu.au/theses/09SM/09sms368.pdf.
Full textRubensson, Emanuel. "Sparse Matrices in Self-Consistent Field Methods." Licentiate thesis, Stockholm : KTH Biotechnology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4219.
Full textYam, Chi-yung, and 任志勇. "Linear-scaling time-dependent density functional theory." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2003. http://hub.hku.hk/bib/B31246199.
Full textSchäfer-Bung, Boris, and Mathias Nest. "Correlated dynamics of electrons with reduced two-electron density matrices." Universität Potsdam, 2008. http://opus.kobv.de/ubp/volltexte/2010/4177/.
Full textLiang, Wanzhen. "Localized-denisty-matrix method and its application to nano-size systems." Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B22718771.
Full textFung, Russell. "Trajectory calculation in an electrostatic positron beam using a reformulated extended charge density model /." Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B20567017.
Full textRaynal, Philippe. "Unambiguous state discrimination of two density matrices in quantum information theory." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=981136737.
Full textClin, Lucien Cyril. "Cholesky decomposed density matrices in laplace transform Møller-Plesset perturbation theory." Diss., lmu, 2012. http://nbn-resolving.de/urn:nbn:de:bvb:19-152656.
Full textMinor, Bill. "Density matrix renormalization group study of the enhanced hole-hopping model of high temperature superconductivity /." *McMaster only, 1996.
Find full textNg, Man-fai, and 吳文暉. "Studies of the excited states of poly (p-phenylenevinylene) (PPV) derivatives and the light harvesting system II." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2003. http://hub.hku.hk/bib/B31244658.
Full text馮德操 and Russell Fung. "Trajectory calculation in an electrostatic positron beam using a reformulated extended charge density model." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31220836.
Full text梁万珍 and Wanzhen Liang. "Localized-denisty-matrix method and its application to nano-size systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31242042.
Full textFriedrich, Oliver [Verfasser], and Ralf [Akademischer Betreuer] Bender. "Statistical properties of the cosmic density field beyond 2-point statistics : covariance matrices and density split statistics / Oliver Friedrich ; Betreuer: Ralf Bender." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2018. http://d-nb.info/1178323749/34.
Full textFriedrich, Oliver Verfasser], and Ralf [Akademischer Betreuer] [Bender. "Statistical properties of the cosmic density field beyond 2-point statistics : covariance matrices and density split statistics / Oliver Friedrich ; Betreuer: Ralf Bender." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2018. http://d-nb.info/1178323749/34.
Full textWaller, Mark Paul. "Experimental and theoretical studies of the electron distribution in weak molecular interactions." Thesis, The University of Sydney, 2006. https://hdl.handle.net/2123/28058.
Full textDianzinga, Mamy Rivo. "N-representable density matrix perturbation theory." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0285/document.
Full textWhereas standard approaches for solving the electronic structures present acomputer effort scaling with the cube of the number of atoms, solutions to overcomethis cubic wall are now well established for the ground state properties, and allow toreach the asymptotic linear-scaling, O(N). These solutions are based on thenearsightedness of the density matrix and the development of a theoreticalframework allowing bypassing the standard eigenvalue problem to directly solve thedensity matrix. The density matrix purification theory constitutes a branch of such atheoretical framework. Similarly to earlier developments of O(N) methodology appliedto the ground state, the perturbation theory necessary for the calculation of responsefunctions must be revised to circumvent the use of expensive routines, such asmatrix diagonalization and sum-over-states. The key point is to develop a robustmethod based only on the search of the perturbed density matrix, for which, ideally,only sparse matrix multiplications are required. In the first part of this work, we derivea canonical purification, which respects the N-representability conditions of the oneparticledensity matrix for both unperturbed and perturbed electronic structurecalculations. We show that this purification polynomial is self-consistent andconverges systematically to the right solution. As a second part of this work, we applythe method to the computation of static non-linear response tensors as measured inoptical spectroscopy. Beyond the possibility of achieving linear-scaling calculations,we demonstrate that the N-representability conditions are a prerequisite to ensurereliability of the results
Clin, Lucien Cyril [Verfasser], and Christian [Akademischer Betreuer] Ochsenfeld. "Cholesky decomposed density matrices in laplace transform Møller-Plesset perturbation theory / Lucien Cyril Clin. Betreuer: Christian Ochsenfeld." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2012. http://d-nb.info/1030475377/34.
Full textSushma, Kumari. "Topics in random matrices and statistical machine learning." Kyoto University, 2018. http://hdl.handle.net/2433/235047.
Full textMichaïl, Alkéos. "Eigenvalues and eigenvectors of large matrices under random perturbations." Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCB214.
Full textThe present thesis is devoted to the study of the effect of a perturbation on the spectrum of a Hermitian matrix by a random matrix with small operator norm and whose entries in the eigenvector basis of the first one were independent, centered and with a variance profile. This is carried out through perturbative expansions of various types of spectral laws of the considered perturbed large matrices. First, we demonstrate different perturbative expansions of the empirical spectral measure in the cases of the perturbative regime and the semi-perturbative regime and highlight well known heuristic patterns in Physics, as the transition between semi-perturbative and perturbative regimes. Secondly, we provide a thorough study of the semi-perturbative regime and prove the new fact that this regime could be decomposed into infinitely many sub-regimes. Finally, we prove, through a perturbative expansion of spectral measures associated to the state defined by a given vector, a perturbative expansion of the coordinates of the eigenvectors of the perturbed matrices
Price, Aiden K. "Improved constructions of low-density parity-check codes." Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/128373/1/Aiden_Price_Thesis.pdf.
Full textPaulino, Neto Romain. "Développement et application de méthodes corrélées pour la description de systèmes moléculaires." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066216/document.
Full textIn the last few years, a lot of energy has been put forward in the area of quantum chemistry to develop new methods, or to improve existing methods, that are able to describe very precisely the electronic structure of molecular systems. In this manuscript, a precise overview of such a method (namely the Density Matrix Renormalization Group, DMRG method) is given. A software able to carry out DMRG calculations has indeed been developed from scratch in the laboratory during this thesis. This method can be seen as a post-Hartree-Fock method, in which only the electronic states that are relevant for the correct description of the molecule are kept. In this way, the computational cost remains acceptable, and the results are in line with those given by "exact" methods such as full-CI. Density Functional Theory (DFT) has also been investigated in this work. DFT and TD-DFT calculations have indeed also been carried out. The performances of two middle-range-separated functionals, namely HISS-A and HISS-B, to describe electronic transitions in conjugated molecules have been probed in a theory vs. theory study. Those functionals, which had been first developed for the study of metals, show to be adequate for the correct description of electronic excitations of chromophores and of push-pull molecules. Optical properties of a dual emittor have also been studied using TD-DFT. The dual emission of this molecule has been shown to stem from the presence of two distinct emissive states, respectively of Intramolecular Charge Transfer (ICT) and locally excited (LE) nature. TD-DFT has allowed us to link those two emissive states to two different conformations of the molecule
Rudberg, Elias. "Quantum Chemistry for Large Systems." Doctoral thesis, Stockholm : Bioteknologi, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4561.
Full textVizzotto, Juliana Kaizer. "Structuring general and complete quantum computations in Haskell : the arrows approach." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2006. http://hdl.handle.net/10183/13154.
Full textQuantum computation can be understood as transformation of information encoded in the state of a quantum physical system. The basic idea behind quantum computation is to encode data using quantum bits (qubits). Differently from the classical bit, the qubit can be in a superposition of basic states leading to “quantum parallelism”, which is an important characteristic of quantum computation since it can greatly increase the speed processing of algorithms. However, quantum data types are computationally very powerful not only due to superposition. There are other odd properties like measurement and entangled. In this thesis we argue that a realistic model for quantum computations should be general with respect to measurements, and complete with respect to the information flow between the quantum and classical worlds. We thus explain and structure general and complete quantum programming in Haskell using well known constructions from classical semantics and programming languages, like monads and arrows. In more detail, this thesis focuses on the following contributions. Monads and Arrows. Quantum parallelism, entanglement, and measurement certainly go beyond “pure” functional programming. We have shown that quantum parallelism can be modelled using a slightly generalisation of monads called indexed monads, or Kleisli structures. We have also build on this insight and showed that quantum measurement can be explained using a more radical generalisation of monads, the so-called arrows, more specifically, indexed arrows, which we define in this thesis. This result connects “generic” and “complete” quantum features to well-founded semantics constructions and programming languages. Understanding of Interpretations of QuantumMechanics as Computational Effects. In a thought experiment, Einsten, Podolsky, and Rosen demonstrate some counter-intuitive consequences of quantum mechanics. The basic idea is that two entangled particles appear to always communicate some information even when they are separated by arbitrarily large distances. There has been endless debate and papers on this topic, but it is interesting that, as proposed by Amr Sabry, this strangeness can be essentially modelled by assignments to global variables. We build on that, and model this strangeness using the general notions of computational effects embodied in monads and arrows. Reasoning about Quantum Programs Using Algebraic Laws. We have developed a preliminary work to do equational reasoning about quantum algorithms written in a pure sublanguage of a functional quantum programming language, called QML.
Baydemir, Tuncay. "Effect Of Natural Polysaccharides On The Integrity And Texture Of Sugar Based Matrices In Three Dimensional Printing." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/4/1045392/index.pdf.
Full textBurow, Asbjörn Manfred. "Methoden zur Beschreibung von chemischen Strukturen beliebiger Dimensionalität mit der Dichtefunktionaltheorie unter periodischen Randbedingungen." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2011. http://dx.doi.org/10.18452/16415.
Full textThis work contributes to the field of theoretical chemistry and is aimed at the development of efficient methods for computation of the electron density and the energy belonging to the ground state of molecular and periodic systems. It is based on the use of Kohn Sham density functional theory (Kohn Sham DFT) and local basis functions. In this scope, the molecular and the periodic systems of any dimensionality (e.g., bulk crystals, thin films, and polymers) are treated on an equal footing using methods which are easy to implement, numerically accurate, and highly efficient. For this, the author has augmented established methods of molecular simulations for their use with periodic boundary conditions applying novel techniques. These methods have been combined to a complete DFT method. Among these methods, the innovative approach for the RI (resolution of identity) method applied to the Coulomb term represents the key technology of this work. As a striking feature, this approach operates exclusively in real space. Although the RI method is the chief ingredient, the development of further methods is required to achieve overall efficiency for the consumption of storage and time. One of these methods is used to compress the density and Kohn Sham matrices. Moreover, numerical integration of the exchange-correlation term has been improved applying an adaptive numerical integration scheme. The methods presented in this thesis are combined to the prototype of an RI-DFT program. Using this program single point energies on the gamma point can be calculated for systems with closed shells. Calculations have been performed and the results are used to assess the accuracy and efficiency achieved. This program forms the foundation of an efficient and competitive DFT code. It works numerically accurate and treats molecules and periodic systems on an equal footing.
Atas, Yasar Yilmaz. "Quelques aspects du chaos quantique dans les systèmes de N-corps en interaction : chaînes de spins quantiques et matrices aléatoires." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112221/document.
Full textMy thesis is devoted to the study of some aspects of many body quantum interacting systems. In particular we focus on quantum spin chains. I have studied several aspects of quantum spin chains, from both numerical and analytical perspectives. I addressed especially questions related to the structure of eigenfunctions, the level densities and the spectral properties of spin chain Hamiltonians. In this thesis, I first present the basic numerical techniques used for the computation of eigenvalues and eigenvectors of spin chain Hamiltonians. Level densities of quantum models are important and simple quantities that allow to characterize spectral properties of systems with large number of degrees of freedom. It is well known that the level densities of most integrable models tend to the Gaussian in the thermodynamic limit. However, it appears that in certain limits of coupling of the spin chain to the magnetic field and for finite number of spins on the chain, one observes peaks in the level density. I will show that the knowledge of the first two moments of the Hamiltonian in the degenerate subspace associated with each peak give a good approximation to the level density. Next, I study the statistical properties of the eigenvalues of spin chain Hamiltonians. One of the main achievements in the study of the spectral statistics of quantum complex systems concerns the universal behaviour of the fluctuation of measure such as the distribution of spacing between two consecutive eigenvalues. These fluctuations are very well described by the theory of random matrices but the comparison with the theoretical prediction generally requires a transformation of the spectrum of the Hamiltonian called the unfolding procedure. For many-body quantum systems, the size of the Hilbert space generally grows exponentially with the number of particles leading to a lack of data to make a proper statistical study. These constraints have led to the introduction of a new measure free of the unfolding procedure and based on the ratio of consecutive level spacings rather than the spacings themselves. This measure is independant of the local level density. By following the Wigner surmise for the computation of the level spacing distribution, I obtained approximation for the distribution of the ratio of consecutive level spacings by analyzing random 3x3 matrices for the three canonical ensembles. The prediction are compared with numerical results showing excellent agreement. Finally, I investigate eigenfunction statistics of some canonical spin-chain Hamiltonians. Eigenfunctions together with the energy spectrum are the fundamental objects of quantum systems: their structure is quite complicated and not well understood. Due to the exponential growth of the size of the Hilbert space, the study of eigenfunctions is a very difficult task from both analytical and numerical points of view. I demonstrate that the groundstate eigenfunctions of all canonical models of spin chain are multifractal, by computing numerically the Rényi entropy and extrapolating it to obtain the multifractal dimensions
Solomon, Lazarus. "Study of spin-lattice relaxation rates in solids lattice-frame method compared with quantum density-matrix method, and Glauber dynamic /." Master's thesis, Mississippi State : Mississippi State University, 2006. http://library.msstate.edu/etd/show.asp?etd=etd-11062006-114635.
Full textAbreu, Bruno Ricardi de 1990. "Matriz densidade a baixas temperaturas para sistemas com interação de pares." [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/276983.
Full textDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: A matriz densidade é um objeto fundamental na mecânica estatística de sistemas de muitos corpos quânticos. Através dela pode ser encontrado o valor esperado de qualquer observável do sistema de interesse. Neste trabalho calculamos a matriz densidade a baixas temperaturas para sistemas de muitos corpos que interagem via um potencial de pares através de convolucões da matriz densidade a altas temperaturas, onde é possível utilizar aproximações semi-clássicas
Abstract: The density matrix is a fundamental object in statistical mechanics of quantum many-body systems. Through it the observed value of any observable of a quantum mechanical system of interest can be found. In this work we calculate the density matrix at low temperatures of manybody systems that interact through pairwise potentials using a convolution procedure of the density matrix at high temperatures, where is possible to apply semi-classical approximations
Mestrado
Física
Mestre em Física
Seigneur, Hubert P. "Modeling and design of a photonic crystal chip hosting a quantum network made of single spins in quantum dots that interact via single photons." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4614.
Full textID: 029049734; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references (p. 247-254).
Ph.D.
Doctorate
Optics and Photonics
Ragot, Sébastien. "Matrices densité : modélisation des densités de charge et d'impulsion : prédiction des propriétés solides." Châtenay-Malabry, Ecole centrale de Paris, 2001. http://www.theses.fr/2001ECAP0709.
Full textYan, Zeyin. "Reconstruction de densité d'impulsion et détermination de la matrice densité réduite à un électron." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLC001/document.
Full textHigh resolution X-ray diffraction (XRD) and polarized neutron diffraction (PND) are commonly used to model charge and spin densities in position space. Additionally, Compton scattering (CS) and magnetic Compton scattering (MCS) are the main techniques to observe the most diffuse electrons and unpaired electrons by providing the “Directional Compton Profiles" (DCPs) and ”Directional magnetic Compton Profiles" (DMCPs), respectively. A set of such DCPs (DMCPs) can be used to reconstruct two-dimensional or three-dimensional electron momentum density. Since all these techniques describe the same electrons in different space representations, we concentrate on associating the electron momentum density reconstructed from DCPs (resp. DMCPs) with electron density refined using XRD (resp. PND) data.The confrontation between theory and experiment, or between different experiments, providing several sets of experimental data, is generally obtained from the reconstructed electron densities and compared with theoretical results in position and momentum spaces. The challenge of comparing the results obtained by ab-initio computations and experimental approaches (in the Nit(SMe)Ph case) shows the necessity of a multiple experiments joint refinement and also the improvement of theoretical computation models. It proves that, in the case of a spin resolved electron density, a mere Hartree-Fock or DFT approach is not sufficient. In the YTiO3 case, a joint analysis of position and momentum spaces (PND & MCS) highlights the possible ferromagnetic pathway along Ti--O1--Ti. Therefore, a “super-position" spin density is proposed and proves to allow cross-checking the coherence between experimental electron densities in posittion and momentum spaces, without having recourse to ab initio results. Furthermore, an ”isolated Ti model" based on PND refined orbital coefficients emphasizes the importance of metal-oxygen coherent coupling to properly account for observations in momentum space.A one-electron reduced density matrix (1-RDM) approach is proposed as a fundamental basis for systematically combining position and momentum spaces. To reconstruct 1-RDM from a periodic ab initio computation, an "iterative cluster" approach is proposed. On this basis, it becomes possible to obtain a theoretical spin resolved 1-RDM along specific chemical bonding paths. It allows a clarification of the difference between Ti--O1--Ti and Ti--O2--Ti spin couplings in YTiO3. It shows that interaction contributions between atoms (metal and oxygen atoms) are different depending on whether the property is represented in position or momentum spaces. This is clearly observed in metal-oxygen chemical bonds and can be illustrated by an orbital resolved contribution analysis. Quantities for electron descriptions in phase space, such as the Moyal function, can also be determinerd by this "cluster model", which might be of particular interest if Compton scattering in Bragg positions could be generalized. The preliminary results of a simple spin resolved 1-RDM refinement model are exposed. The model respects the N-representability and is adapted for various experimental data (e.g.: XRD, PND, CS, MCS, XMD etc.). The potential of this model is not limited to a spin analysis but its use is limited here to the unpaired electrons description. The limitations of this model are analysed and possible improvements in the future are also proposed
Taillebois, Emile Raymond Ferreira. "Traço parcial em sistemas relativísticos: uma nova visão." Universidade Federal de Goiás, 2013. http://repositorio.bc.ufg.br/tede/handle/tede/7484.
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Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq
In this dissertation, the use of the partial trace of momentum degrees of freedom in the construction of spin reduced density matrices for relativistic massive systems is analyzed. In the regime considered here, massive particles can be described by irreducible unitary representations of the Poincar e group, and the base states are labeled by the dynamical variables of momentum and spin. The reduced density matrices obtained by the partial trace of momenta have unusual properties, since they are not covariant under the action of restricted Lorentz transformations. That behavior produces some important consequences in the study of quantum information in relativistic systems. However, recent arguments have been presented against the use of those matrices in the description of processes involving the transfer of information stored in spin degrees of freedom of relativistic massive particles. Those criticisms are discussed in this dissertation and a connection with the structure of the space of states associated with a given unitary representation is established through a detailed study of the induced representation method applied to the Poincar e group. This allows rewriting the criticisms in literature without the need of a speci c model of interaction for the spin measurement. Besides that, the analysis performed here allows to establish a new method to construct e ective spin reduced density matrices. The presented approach allows recovering the results in the literature and, at the same time, to incorporate the criticisms in a consistent way. However, it is necessary to abandon the usual partial trace of the momentum degrees of freedom and the interpretation in the literature for the spin reduced density matrices. The examples presented in the arguments against the usual spin reduced density matrices are studied using the approach proposed in this dissertation.
Nesta dissertação, a utilização do traço parcial dos momentos na construção de matrizes densidade reduzidas de spin para partículas massivas relativisticas é analisada. No regime considerado, as partículas massivas podem ser descritas por representações unitárias do grupo de Poincaré, e os estados de base são rotulados pelas variáveis dinâmicas de momento e spin. As matrizes reduzidas obtidas por meio do traço parcial dos momentos possuem propriedades inusitadas, pois não são covariantes sob a ação de transformações de Lorentz restritas. Essa característica traz consequências importantes para o estudo da teoria da informação quântica em sistemas relativísticos. No entanto, argumentos recentes têm sido apresentados contra o uso dessas matrizes nos processos de transmissões de informação envolvendo os graus de spin de partículas massivas. Essas críticas são discutidas neste trabalho e uma conexão com a estrutura do espaço de estados associado a representação unitária em questão é estabelecida por meio de um estudo detalhado do método das representações induzidas aplicado ao grupo de Poincaré. Isso permite reescrever as críticas presentes na literatura sem a necessidade de se introduzir um modelo específico de interação associado à medida do spin das partículas. Alem disso, a análise realizada nesta dissertação permite estabelecer um novo método para a construção de matrizes densidade reduzidas efetivas de spin. A proposta apresentada permite recuperar os resultados presentes na literatura e, ao mesmo tempo, incorporar as críticas de maneira consistente. No entanto, para isso é necessário abandonar o traço parcial usual dos graus de liberdade de momento e a interpretação dada na literatura para as matrizes densidade reduzidas de spin. Os exemplos apresentados nas argumentações contra as matrizes densidade reduzidas de spin usuais são estudados utilizando o método proposto neste trabalho.
Stojanovic, Alexandre. "Sur la distribution limite des valeurs propres dans des matrices aléatoires." Paris 7, 2003. http://www.theses.fr/2003PA077184.
Full textLopez-Sandoval, Roman. "Théorie de la fonctionnelle de la matrice densité pour les hamiltoniens modèles." Toulouse 3, 2000. http://www.theses.fr/2000TOU30180.
Full textLacombe, Lionel. "On dynamics beyond time-dependent mean-field theories." Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30185/document.
Full textThis thesis presents various quantal approaches for the exploration of dynamical processes in multielectronic systems, especially after an intense excitation which can possibly lead to dissipative effects. Mean field theories constitute useful tools in that respect. Despite the existence of numerous works during the past two decades, they have strong difficulties to capture full 2-body correlations. Thermalization is one of these effects that stems from electron-electron collisions. After an introductory chapter, we present in Chapter 2 the formalism of the various schemes studied in this thesis toward the description of such an effect by including collisional terms on top of a mean field theory. These schemes are called Stochastic Time-Dependent Hartree Fock (STDHF), Extended TDHF (ETDHF) and Collisional TDHF (CTDHF). The latter scheme constitutes in some sense the main achievement of this thesis. The numerical realizations of each scheme are also discussed in detail. In Chapters 3, 4 and 5, we apply the approaches discussed in Chapter 2 but in various systems. In Chapter 3, we first explore a rare reaction channel, that is the probability of an electron to attach on small water clusters. Good agreement with experimental data is achieved. In Chapter 4, a model widely used in nuclear physics is exactly solved and quantitatively compared to STDHF. The time evolution of 1-body observables agrees well in both schemes, especially what concerns thermal behavior. However, to allow a good description of the dynamics, one is bound to use a large statistics, which can constitute a hindrance of the use of STDHF in larger systems. To overcome this problem, in Chapter 5, we go for a testing of CTDHF developed in Chapter 2 in a one-dimensional system (and without electronic emission). This system consists in electrons in a jellium potential with a simplified self-consistent interaction expressed as a functional of the density. The advantage of this 1D model is that STDHF calculations are numerically manageable and therefore allows a direct comparison with CTDHF calculations. In this proof of concept study, CTDHF compares remarkably well with STDHF. This thus paves the road toward an efficient description of dissipation in realistic 3D systems by CTDHF
Baguet, Lucas. "États périodiques du jellium à deux et trois dimensions : approximation de Hartree-Fock." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066389/document.
Full textThe jellium model is a fundamental model in condensed matter. It is formed by a set of electrons and a uniform background insuring global neutrality. At zero temperature and without external field, the ground-state depends only on the electronic density. Despite its simplicity, the jellium ground-state is still an open problem. We studied the jellium model in 2 and 3 dimensions within the Hartree-Fock approximation using a numerical descent method. Assuming periodic states, we greatly reduce the number of unknowns and the system may contain up to one million of electrons. At fixed lattice symmetry and polarization, the ground-state is a Wigner crystal at low density, and a «metallic state» above a critical density value. These metallic states are crystals with a lattice constant smaller than in Wigner phase, and interpolate between the latter and the Fermi gas. The metallic states exists in two and three dimensions, for a polarized and unpolarized gas, and for various lattice symmetries. Therefore, the jellium phase diagram at zero temperature is rich : it contains several Wigner crystal phases at low density, polarized and unpolarized, and an unpolarized metallic state at high density. These states are well described by a superposition of spin-density waves, as predicted by Overhauser in 1962
Paulin, Sébastien. "Approximations simples d'intégrales de chemins à température finie." Lyon, École normale supérieure (sciences), 2007. http://www.theses.fr/2007ENSL0445.
Full textRoche, Stéphane. "Chondrocytes en culture en haute densité et dans des matrices collagène : application à la réparation du cartilage." Lyon 1, 1999. http://www.theses.fr/1999LYO10150.
Full textPernet, Clément. "Algèbre linéaire exacte efficace : le calcul du polynôme caractéristique." Phd thesis, Université Joseph Fourier (Grenoble), 2006. http://tel.archives-ouvertes.fr/tel-00111346.
Full textLe calcul du polynôme caractéristique est l'un des problèmes classiques en algèbre linéaire. Son calcul exact permet par exemple de déterminer la similitude entre deux matrices, par le calcul de la forme normale de Frobenius, ou la cospectralité de deux graphes. Si l'amélioration de sa complexité théorique reste un problème ouvert, tant pour les méthodes denses que boîte noire, nous abordons la question du point de vue de la praticabilité : des algorithmes adaptatifs pour les matrices denses ou boîte noire sont dérivés des meilleurs algorithmes existants pour assurer l'efficacité en pratique. Cela permet de traiter de façon exacte des problèmes de dimensions jusqu'alors inaccessibles.
VASCONCELOS, Marcos Müller. "Decodificação iterativa de códigos baseados em matrizes de verificação de paridade esparsas." Universidade Federal de Pernambuco, 2007. https://repositorio.ufpe.br/handle/123456789/5436.
Full textCódigos baseados em matrizes esparsas têm desempenhado um importante papel em teoria da codificação. Os códigos low-density parity-check (LDPC) constituem uma famosa família de códigos definidos a partir de matrizes de verificação de paridade esparsas que apresentam desempenhos excelentes no canal com ruído aditivo Gaussiano branco (RAGB). O sucesso desses códigos se deve a sua representação através de grafos, que permite a operação de um algoritmo de decodificação iterativo cuja complexidade cresce linearmente com o comprimento dos blocos. Esta dissertação apresenta um estudo sobre códigos LDPC e sua principal ferramenta de análise, a density evolution. Para isso, a representação gráfica de códigos de bloco lineares e o funcionamento do algoritmo de decodificação Soma-Produto são apresentados. Algumas técnicas de projeto de códigos LDPC são discutidas e seu desempenho no canal RAGB é avaliado por meio de simulações. Baseando-se nestas ferramentas, a density evolution para os canal RAGB é derivada em forma integral e em forma aproximada. Por fim, uma modificação no algoritmo Soma-Produto é proposta para decodificação de códigos LDPC no canal Gilbert-Elliott
Meziani, Katia. "Estimation non paramétrique en tomographie quantique homodyne." Paris 7, 2008. http://www.theses.fr/2008PA077172.
Full textIn the setting of quantum optics, the reconstruction of the quantum state (Wigner function or infinite-dimensional density matrix) of a light beam can be seen as a statistical severely ill-posed inverse problem. First, we propose estimators of the density matrix and the Wigner function respectively, using pattern functions in the first case and kernel functions in the second. We assume that the unknown density matrix belongs to a nonparametric class which corresponds to typical states prepared in the laboratory. We translate these classes in terms of properties of the associated Wigner function. In an other part, we estimate the integrated squared Wigner function by a kernel-based second order U-statistic on a larger regularity class. This quadratic functional is a physical measure of the purity of the state. We deduce an adaptive estimator for the Wigner function that does not depend on the smoothness parameters. In the last part of the thesis, we are interested in the problem of goodness-of-fit testing. We give a testing procedure derived from a projection-type estimator on \textit{pattern} functions. We study the upper bounds of the minimax risk for all our procedures. The density matrix estimation and the testing procedure are implemented and their numerical performances are studied
Perez, Jean-Philippe. "Caractérisation de photodétecteurs quantiques d'ondes refroidis à base de Hg0. 7Cd0. 3Te : Etude du bruit électrique basse fréquence à l'obscurité et sous flux infrarouge." Montpellier 2, 2004. http://www.theses.fr/2004MON20062.
Full textPAVLOV, ROSSEN. "Contribution a la theorie de la fonctionnelle de la densite. Application de la methode de la transformation d'echelle locale aux matrices densites reduites avec ou sans spin ; effets de correlation et effets de couche." Paris 6, 1999. http://www.theses.fr/1999PA066392.
Full textNechita, Ion. "États aléatoires, théorie quantique de l'information et probabilités libres." Phd thesis, Université Claude Bernard - Lyon I, 2009. http://tel.archives-ouvertes.fr/tel-00371592.
Full textDillmann, Baudouin. "Electromagnetic fields mapping in the HR-MAS probes, used to perform solid-state NMR at high field." Université Louis Pasteur (Strasbourg) (1971-2008), 2007. https://publication-theses.unistra.fr/public/theses_doctorat/2007/DILLMANN_Baudouin_2007.pdf.
Full textGomes, Andre Severo Pereira. "Desenvolvimento teorico e computacional do modelo de matriz densidade aplicado ao metodo da coordenada geradora em calculos "ab initio" relativisticos." [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/249226.
Full textTese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica
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Doutorado
Físico-Química
Doutor em Quimica
Abadie, Sacha. "Vibrational excitation of molecules in the gas phase or embedded in matrices by ab initio molecular dynamics." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLE057/document.
Full textIn the thesis we have studied two prototypical systems in both condensed and gas phase,to follow and quantify the vibrational energy flow through normal modes after vibrational excitation.For the condensed phase, we considered a host Formic Acid immersedin an argon matrix, while for the gas phase we have studied the N-Methyl Acetamid... Cl.. Ar cluster. After the preparation of initial conditions using a semi-classical Wigner sampling, several DFT-MD trajectories have been performed to analyse the Intra/Inter vibrational energy relaxation. Two theoretical methods have been used to follow the evolution with time of the vibrational quantum numbers: a new method based on the study of vibrational density of states (VDOS)compared with a more traditional method based on the study of the amplitude of a specificmotion of the molecule (i.e. distance or angle). Both methods reveal similar results.In the condensed phase, the quantum yield of the trans/cis isomerisation process of theFormic Acid molecule has been compared to the experimental data. We have shown that thevibrational excitation of two combination modes involves in some cases the isomerisation ofthe Formic Acid molecule. This initial vibrational excitation of the Formic Acid has also animpact on the surrounding matrix: the energy initially contained into the FA is redistributedto the matrix leading to the deformation and the melting (solid-liquid transition) of theargon matrix.In the gas phase, we have shown that vibrational excitation of the N-H stretching motion ofthe (Cl...NMA) involves the systematic loss of the argon atom. Finally, the two models have shown that in both condensed or gas phase environment, after the vibrational excitation (n=1) of a normal modeat t=0 of the dynamics, this normal mode comes back in its ground state (n=0)
Cangiotti, Francesco. "Realizzazione di macchine termiche basate su sistemi a due livelli." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18413/.
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