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1
au, kaurgurd@willettonshs wa edu, and Gurdeep Kaur. "Electron-helium scattering using analytical and numerical wave functions." Murdoch University, 2002. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20080123.100101.
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Theoretical investigations of electron-inert gas scattering are challenging because of the complex target structure. The electron-Helium system has been the most studied both at low and intermediate energies by sophisticated R-matrix and coupled channels methods. For the other inert gases, few calculations have been attempted at the same level sophistication. One problem is that general target-structure codes provide different forms of wave functions that must be interfaced with the scattering equations. The theoretical work presented in this thesis is based on the momentum-space coupled channels equations. For this formalism only one and two-electron atoms have been studied and purpose-built routines, specific to these atoms, have been developed. For the inert gases however such a task is much more formidable and a more practical approach is to use existing structure codes that have taken several man-years to develop.
The framework of this thesis comprises of two parts. In the first part we discuss the need for, and the way to, modify the existing close-coupling code developed by Berge & Stelbovics in order to interface with other atomic structure packages in the literature. Two mainstream packages, an atomic structure package of Charlotte Froese Fischer and an atomic structure of Alan Hibbert are discussed. Methods to extract the wave functions for Helium and Neon targets using Hibbert's package are given. In the second part, various options and strategies for the calculation of the target structure, including frozen-core and configuration-interaction wave functions, using analytic Slater, Laguerre or numerical orbitals are considered for the Helium target. Hibbert's structure code wave functions are shown to be correctly interfaced into our momentum-space coupled channels code. The pros and cons of the various target structure descriptions are given and applied for lowenergy elastic and inelastic scattering of electron from Helium.
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Faulkner, Helen Mary Louise. "Studies in phase and inversion problems for dynamical electron diffraction." Connect to thesis, 2003. http://repository.unimelb.edu.au/10187/2880.
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This thesis examines problems in electron diffraction and related areas of theoretical optics. It begins with a study of the phase of a quantum mechanical wave function and the behaviour of phase vortices and vortex cores. Several rules for vortex core evolution are given and simulated vortex trajectories are studied. These simulations show that in electron microscopy at atomic resolution and in other similar situations, vortices occur in the wave functions very frequently. This means any image processing methods which deal with the wave function phase must permit vortices to occur. In this context a number of methods of phase retrieval are compared and evaluated. The criteria of evaluation are the accuracy of the phase retrieval, its ability to cope with vortices, its numerical stability and its required computational resources. The best method is found to be an iterative algorithm similar in approach to the Gerchberg-Saxton method, but based on a through focal series of images.Using this phase retrieval method as an essential tool, the thesis continues with a study of inverse problems in electron optics. The first problem considered is that of using a set of images taken to characterise the coherent aberrations present in a general imaging system. This problem occurs in many areas of optics and is studied here with a focus on transmission electron microscopy. A method of using software to simultaneously determine aberrations and subsequently remove them is presented and tested in simulation. This method is found to have a high level of accuracy in aberration determination. The second inverse problem studied in this thesis is the inversion problem in dynamical electron diffraction. This problem is solved for a periodic object, giving an accurate and unique solution for the projected potential in the multiple scattering case. An extension of this solution to objects which are non-periodic in the direction of the incident wave is investigated. Finally a model computation solving the general inversion problem for dynamical diffraction in an aberrated transmission electron microscope is performed, illustrating this and previous material and summing up the advances presented in this work.
3
Lee, R. J. S. "Ion-atom collisions at relativistic and non-relativistic energies." Thesis, Queen's University Belfast, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368591.
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Rvachev, Marat. "Study of the Quasielastic {sup 3}He(e,e{prime}p) Reaction at Q{sup 2}=1.5 (GeV/c){sup 2} up to Missing Momenta of 1 GeV/c." Washington, D.C : Oak Ridge, Tenn. : United States. Dept. of Energy. Office of Energy Research ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2003. http://www.osti.gov/servlets/purl/824894-w3sMWi/native/.
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Thesis (Ph.D.); Submitted to Massachusetts Inst. of Tech., Cambridge, MA (US); 1 Sep 2003.Published through the Information Bridge: DOE Scientific and Technical Information. "JLAB-PHY-03-167" "DOE/ER/40150-2745" Marat Rvachev. 09/01/2003. Report is also available in paper and microfiche from NTIS.
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Zhang, Bin. "Searching for Short Range Correlations Using (e,e'NN) Reactions." Washington, D.C : Oak Ridge, Tenn. : United States. Dept. of Energy. Office of Energy Research ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2003. http://www.osti.gov/servlets/purl/824928-2353Al/native/.
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Thesis; Thesis information not provided; 1 Feb 2003.Published through the Information Bridge: DOE Scientific and Technical Information. "JLAB-PHY-03-38" "DOE/ER/40150-2762" Bin Zhang. 02/01/2003. Report is also available in paper and microfiche from NTIS.
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Moon, Christopher Ryan. "Designing electron wave functions in assembled nanostructures /." May be available electronically:, 2009. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Bawagan, Alexis Delano Ortiz. "Evaluation of wavefunctions by electron momentum spectroscopy." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26958.
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Electron momentum spectroscopy (EMS) provides experimental atomic and molecular electronic structure information in terms of the binding energy spectrum and the experimental momentum profile (XMP), which is a direct probe of the electron momentum distribution in specific molecular orbitals. The measured XMPs permit a detailed quantitative evaluation of theoretical ab initio wavefunctions in quantum chemistry and also provide a means to investigate traditional concepts in chemical reactivity at the fundamental electronic level.
This thesis reports high momentum resolution EMS measurements of the valence orbitals of H₂0, D₂0, NH₃ and H₂CO obtained using an EMS spectrometer of the symmetric, non-coplanar type operated at an impact energy of 1200eV. The measured experimental momentum profiles for the valence orbitals of each molecule have been placed on a common intensity scale, which has allowed a stringent quantitative comparison between experiment and theory. These studies now confirm earlier preliminary investigations that suggested serious discrepancies between experimental and theoretical momentum distributions. Exhaustive consideration of possible rationalizations of these discrepancies indicate that double zeta quality and even near Hartree-Fock quality wavefunctions are insufficient in describing the outermost valence orbitals of H₂0 and NH₃. Preliminary results for H₂CO also indicate that near Hartree-Fock wavefunctions are incapable of describing the outermost 2b₂ orbital. Interactive and collaborative theoretical efforts have therefore led to the development of new Hartree-Fock limit and also highly correlated (CI) wavefunctions for H₂0, NH₃ and H₂CO. It is found that highly extended basis sets including diffuse functions and the adequate inclusion of correlation and relaxation effects are necessary in the accurate prediction of experimental momentum profiles as measured by electron momentum spectroscopy.
New EMS measurements are also reported for the outermost valence orbitals of NF₃, NH₂CH₃, NH (CH₃)₂, N (CH₃)₃ and para-dichlorobenzene. These exploratory studies have illustrated useful chemical applications of EMS. In particular, EMS measurements of the outermost orbitals of the methylated amines have revealed chemical trends which are consistent with molecular orbital calculations. These calculations suggest extensive electron density derealization of the so-called nitrogen 'lone pair' in the methylated amines in comparison to the 'lone pair' in NH₃. EMS measurements of the non-degenerate π₃ and π₂ orbitals of para-dichlorobenzene show different experimental momentum profiles consistent with arguments based on inductive and resonance effects. These experimental trends, both in the case of the amines and para-dichlorobenzene, were qualitatively predicted by molecular orbital calculations using double zeta quality wavefunctions. However more accurate prediction of the experimental momentum profiles of these molecules will need more extended basis sets and the inclusion of correlation and relaxation effects as suggested by the studies based on the smaller molecules.
An integrated computer package (HEMS) for momentum space calculations has also been developed based on improvements to existing programs. Development studies testing a new prototype multichannel (in the ɸ plane) EMS spectrometer are described.Science, Faculty of
Chemistry, Department of
Graduate
8
Kaur, Gurdeep. "Electron-helium scattering using analytical and numerical wave functions." Kaur, Gurdeep (2002) Electron-helium scattering using analytical and numerical wave functions. PhD thesis, Murdoch University, 2002. http://researchrepository.murdoch.edu.au/472/.
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Theoretical investigations of electron-inert gas scattering are challenging because of the complex target structure. The electron-Helium system has been the most studied both at low and intermediate energies by sophisticated R-matrix and coupled channels methods. For the other inert gases, few calculations have been attempted at the same level sophistication. One problem is that general target-structure codes provide different forms of wave functions that must be interfaced with the scattering equations. The theoretical work presented in this thesis is based on the momentum-space coupled channels equations. For this formalism only one and two-electron atoms have been studied and purpose-built routines, specific to these atoms, have been developed. For the inert gases however such a task is much more formidable and a more practical approach is to use existing structure codes that have taken several man-years to develop.
The framework of this thesis comprises of two parts. In the first part we discuss the need for, and the way to, modify the existing close-coupling code developed by Berge & Stelbovics in order to interface with other atomic structure packages in the literature. Two mainstream packages, an atomic structure package of Charlotte Froese Fischer and an atomic structure of Alan Hibbert are discussed. Methods to extract the wave functions for Helium and Neon targets using Hibbert's package are given. In the second part, various options and strategies for the calculation of the target structure, including frozen-core and configuration-interaction wave functions, using analytic Slater, Laguerre or numerical orbitals are considered for the Helium target. Hibbert's structure code wave functions are shown to be correctly interfaced into our momentum-space coupled channels code. The pros and cons of the various target structure descriptions are given and applied for lowenergy elastic and inelastic scattering of electron from Helium.
9
Franck, Odile. "A closer look at wave-function/density-functional hybrid methods." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066303/document.
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La théorie de la fonctionnelle de la densité (DFT) est une reformulation du problème quantique à N corps où l'énergie de l'état fondamental est exprimée sous la forme d'une fonction de la densité électronique. Dans l'approche de Kohn-Sham de la DFT, seule l'énergie dite d'échange-corrélation décrivant la partie non classique de l'interaction électron-électron nécessite d'être approchée comme une fonctionnelle de la densité. Dans le cadre de la thèse nous nous intéressons à une approximation visant à améliorer la précision et qui consiste à combiner de façon rigoureuse une approximation de type " fonctionnelle de la densité " avec un calcul explicite de type " fonction d'onde " à l'aide d'une décomposition de l'interaction électron-électron coulombienne. L'objectif est de disposer de méthodes améliorant la précision de la DFT actuelle avec un effort de calcul restant compétitif. Ce travail de thèse se décompose en trois études distinctes. Une première étude a consisté a étendre l'analyse de la convergence en base à la séparation de portée qui a permit de mettre en évidence une convergence exponentielle pour l'énergie de corrélation MP2 de longue portée. Dans un second temps nous nous sommes intéressés à une approximation auto-cohérente des fonctionnelles double-hybride utilisant la méthode des potentiels-effectifs-optimisés. Finalement la troisième étude propose une analyse de l'approximation adiabatique semi-locale du noyau d'échange et de corrélation de courte portée dans le cadre de la TDDFT avec séparation de portée dans son formalisme de réponse linéaireThe theory of the functional of the density ( DFT) is a reformulation of the quantum problem in N body where the energy of the fundamental state is expressed under the shape of a function(office) of the electronic density. In the approach of Kohn-Sham of the DFT, only the said energy of exchange-correlation describing the not classic part(party) of the interaction electron-electron requires to be approached as a functional of the density. Within the framework of the thesis(theory) we are interested in an approximation to improve the precision and which consists in combining(organizing) in a rigorous way an approximation of type(chap) " functional of the density " with an explicit calculation of type(chap) " function(office) of wave " by means of a decomposition of the interaction electron-electron coulombienne. The objective is to have methods
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Mahler, Andrew. "The One Electron Basis Set: Challenges in Wavefunction and Electron Density Calculations." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849642/.
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In the exploration of chemical systems through quantum mechanics, accurate treatment of the electron wavefunction, and the related electron density, is fundamental to extracting information concerning properties of a system. This work examines challenges in achieving accurate chemical information through manipulation of the one-electron basis set.
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Seth, Priyanka. "Improved wave functions for quantum Monte Carlo." Thesis, University of Cambridge, 2013. https://www.repository.cam.ac.uk/handle/1810/244333.
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Quantum Monte Carlo (QMC) methods can yield highly accurate energies for correlated quantum systems. QMC calculations based on many-body wave functions are considerably more accurate than density functional theory methods, and their accuracy rivals that of the most sophisticated quantum chemistry methods. This thesis is concerned with the development of improved wave function forms and their use in performing highly-accurate quantum Monte Carlo calculations. All-electron variational and diffusion Monte Carlo (VMC and DMC) calculations are performed for the first-row atoms and singly-positive ions. Over 98% of the correlation energy is retrieved at the VMC level and over 99% at the DMC level for all the atoms and ions. Their first ionization potentials are calculated within chemical accuracy. Scalar relativistic corrections to the energies, mass-polarization terms, and one- and two-electron expectation values are also evaluated. A form for the electron and intracule densities is presented and fits to this form are performed. Typical Jastrow factors used in quantum Monte Carlo calculations comprise electron-electron, electron-nucleus and electron-electron-nucleus terms. A general Jastrow factor capable of correlating an arbitrary of number of electrons and nuclei, and including anisotropy is outlined. Terms that depend on the relative orientation of electrons are also introduced and applied. This Jastrow factor is applied to electron gases, atoms and molecules and is found to give significant improvement at both VMC and DMC levels. Similar generalizations to backflow transformations will allow useful additional variational freedom in the wave function. In particular, the use of different backflow functions for different orbitals is expected to be important in systems where the orbitals are qualitatively different. The modifications to the code necessary to accommodate orbital-dependent backflow functions are described and some systems in which they are expected to be important are suggested.
12
Barker, James Alexander. "The electronic properties of semiconductor quantum dots." Thesis, University of Surrey, 2000. http://epubs.surrey.ac.uk/1021/.
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An, Dechang. "Electro-optic polymer-based monolithic waveguide devices with multi-functions of amplification switching and modulation." Access restricted to users with UT Austin EID Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3035933.
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Maltezopoulos, Theophilos. "Wave-function mapping of electronic states in nanostructures by scanning tunneling spectroscopy." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=971435375.
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Li, Peng. "Novel quantum magnetic states in low dimensions." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B36883062.
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Li, Peng, and 李鵬. "Novel quantum magnetic states in low dimensions." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B36883062.
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Vale, Christopher A. W. "Growth-based computer aided design strategies for multimode waveguide design with the aid of functional blocks." Thesis, Stellenbosch : Stellenbosch University, 2001. http://hdl.handle.net/10019.1/52291.
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Thesis (PhD) -- Stellenbosch University, 2001.Some digitised pages may appear illegible due to the condition of the original hard copy.
ENGLISH ABSTRACT: A new technique for the design of multimode devices in overmoded waveguide is presented. The technique applies the principle of growth-based design and uses a conceptual functional block representation of the design structure to provide necessary flexibility to the design algorithms. Two growth based design strategies are proposed and evaluated. The first uses a generalized synthesis-oriented scanning technique, and the second uses an evolutionary strategy. The techniques provide reliable solutions to a variety of multimode design problems. In order to facilitate sufficiently fast numerical analysis, novel enhancements of the mode matching technique are developed and the use of surrogate models is investigated. In addition, to allow physical evaluation of the finished devices, original techniques of measuring multimode devices are formulated and utilised. Two practical problems are used to evaluate the performance of the design procedures. The first is the design of overmoded waveguide chokes for microwave heating facilities, and the second is the design of multimode horns for antenna and spatial power combining applications. Various examples of each type of problem are presented with measurements of manufactured solutions.
AFRIKAANSE OPSOMMING: ’n Nuwe tegniek vir die ontwerp van multimodusstelsels binne multimodus golfleier word voorgestel. Die tegniek maak gebruik van die beginsel van groei-georienteerde ontwerp en ontgin ’n konsepsuele funksionele module-voorstelling van die ontwerpstruktuur om die nodige buigsaamheid aan die ontwerpsalgoritmes te verleen. Twee groei-georienteerde ontwerpstrategiee word aangebied en geevalueer. Die eerste is gebasseer op ’n veralgemeende sintese-georienteerde skandeertegniek, en die tweede maak gebruik van ’n evolusie-strategie. Die tegniek verskaf betroubare oplossings vir ’n verskeidenheid van multimodusontwerpsprobleme. Ten einde ’n numeriese analise-tegniek daar te stel wat vinnig genoeg is, word oorspronklike verbeterings van die modal-pas metode ontwikkel en surrogaatmodelle is ook ondersoek. Verder, vir fisiese evaluasie, word oorspronklike meettegnieke vir multimodusstelsels geformuleer en gebruik. Twee praktiese probleme word gebruik om die ontwerpprosedures te evalueer. Die eerste is die ontwerp van multimodus golfleierdrywingsdempers vir mikrogolfverhitting, en die tweede is die ontwerp van multimodus horings vir antenna- en ruimtelike drywingskombineerdertoepasings. Verskeie voorbeelde van elke tipe probleem word gegee met metings van gei'mplementeerde oplossings.
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Hao, Wei-Da. "Waveform Estimation with Jitter Noise by Pseudo Symmetrical Probability Density Function." PDXScholar, 1993. https://pdxscholar.library.pdx.edu/open_access_etds/4587.
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A new method for solving jitter noise in estimating high frequency waveform is proposed. It reduces the bias of the estimation in those points where all the other methods fail to achieve. It provides preliminary models for estimating percentiles in Normal, Exponential probability density function. Based on the model for Normal probability density function, a model for any probability density function is derived. The resulting percentiles, in turn, are used as estimates for the amplitude of the waveform. Simulation results show us with satisfactory accuracy.
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Zhai, Dawei. "Studies on Electron Dynamics in Deformed Graphene." Ohio University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1540985604827894.
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Fleig, Timo. "Wave function based relativistic multi-reference electron correlation methods development and application to atomic and molecular properties /." [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=984672672.
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López, Ríos Pablo. "Backflow and pairing wave function for quantum Monte Carlo methods." Thesis, University of Cambridge, 2016. https://www.repository.cam.ac.uk/handle/1810/288882.
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Quantum Monte Carlo (QMC) methods are a class of stochastic techniques that can be used to compute the properties of electronic systems accurately from first principles. This thesis is mainly concerned with the development of trial wave functions for QMC. An extension of the backflow transformation to inhomogeneous electronic systems is presented and applied to atoms, molecules and extended systems. The backflow transformation I have developed typically retrieves an additional 50% of the remaining correlation energy at the variational Monte Carlo level, and 30% at the diffusion Monte Carlo level; the number of parameters required to achieve a given fraction of the correlation energy does not appear to increase with system size. The expense incurred by the use of backflow transformations is investigated, and it is found to scale favourably with system size. Additionally, I propose a single wave function form for studying the electron-hole system which includes pairing effects and is capable of describing all of the relevant phases of this system. The effectiveness of this general wave function is demonstrated by applying it to a particular transition between two phases of the symmetric electron-hole bilayer, and it is found that using a single wave function form gives a more accurate physical description of the system than using a different wave function to describe each phase. Both of these developments are new, and they provide a powerful set of tools for designing accurate wave functions. Backflow transformations are particularly important for systems with repulsive interactions, while pairing wave functions are important for attractive interactions. It is possible to combine backflow and pairing to further increase the accuracy of the wave function. The wave function technology that I have developed should therefore be useful across a very wide range of problems.
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Marumoto, Kazuhiro, Shin-ichi Kuroda, Taishi Takenobu, and Yoshihiro Iwasa. "Spatial Extent of Wave Functions of Gate-Induced Hole Carriers in Pentacene Field-Effect Devices as Investigated by Electron Spin Resonance." American Physical Society, 2006. http://hdl.handle.net/2237/8836.
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Calderín, L., V. V. Karasiev, and S. B. Trickey. "Kubo–Greenwood electrical conductivity formulation and implementation for projector augmented wave datasets." ELSEVIER SCIENCE BV, 2017. http://hdl.handle.net/10150/626127.
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As the foundation for a new computational implementation, we survey the calculation of the complex electrical conductivity tensor based on the Kubo-Greenwood (KG) formalism (Kubo, 1957; Greenwood, 1958), with emphasis on derivations and technical aspects pertinent to use of projector augmented wave datasets with plane wave basis sets (BIlichl, 1994). New analytical results and a full implementation of the KG approach in an open-source Fortran 90 post-processing code for use with Quantum Espresso (Giannozzi et al., 2009) are presented. Named KGEC ([K]ubo [G]reenwood [E]lectronic [C]onductivity), the code calculates the full complex conductivity tensor (not just the average trace). It supports use of either the original KG formula or the popular one approximated in terms of a Dirac delta function. It provides both Gaussian and Lorentzian representations of the Dirac delta function (though the Lorentzian is preferable on basic grounds). KGEC provides decomposition of the conductivity into intra- and inter band contributions as well as degenerate state contributions. It calculates the dc conductivity tensor directly. It is MPI parallelized over k-points, bands, and plane waves, with an option to recover the plane wave processes for their use in band parallelization as well. It is designed to provide rapid convergence with respect to k-point density. Examples of its use are given.
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Tatsumi, Kazuyoshi, Shunsuke Muto, and Ján Rusz. "New algorithm for efficient Bloch-waves calculations of orientation-sensitive ELNES." Elsevier, 2013. http://hdl.handle.net/2237/20831.
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Colson, Tobias A., and tobiascolson@gmail com. "Large Angle Plasmon Scattering in Metals and Ceramics." RMIT University. Applied Sciences, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20090212.143048.
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This investigation is primarily concerned with the low loss, or plasmon region of an electron energy loss spectrum. Specifically, why these spectra have the shape and form that they do; what the significance of the material is in determining the shape and form of these spectra; what can be done with plasmon excited electrons; and how all of this fits in with the current theory of plasmon excitation. In particular, the concept of plasmon scattering being an energy transfer process of a coupled wave in the material is explored. This gives rise to slightly different explanations of the plasmon scattering process to the status quo. Multiple scattering is typically pictured as a combination of separate and independent, elastic and inelastic scattering events interactively contributing to a final exit wave function. However, this investigation explores the idea of the elastic and inelastic components being a coupled event, and what the consequences of this idea are from a conceptual point of view. The energy transfer process itself, does not deviate from a virtual particle exchange description that is consistent with the standard model. However, the two significant points made throughout the chapters are one: that the elastic and inelastic scattering events are coupled rather than separate, and two: that each succussive higher order scattering event in multiple scattering scenarios, are dependant and connecte d rather than independent.
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Ritschel, Tobias. "Electronic self-organization in layered transition metal dichalcogenides." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-188265.
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The interplay between different self-organized electronically ordered states and their relation to unconventional electronic properties like superconductivity constitutes one of the most exciting challenges of modern condensed matter physics. In the present thesis this issue is thoroughly investigated for the prototypical layered material 1T-TaS2 both experimentally and theoretically.
At first the static charge density wave order in 1T-TaS2 is investigated as a function of pressure and temperature by means of X-ray diffraction. These data indeed reveal that the superconductivity in this material coexists with an inhomogeneous charge density wave on a macroscopic scale in real space. This result is fundamentally different from a previously proposed separation of superconducting and insulating regions in real space. Furthermore, the X-ray diffraction data uncover the important role of interlayer correlations in 1T-TaS2.
Based on the detailed insights into the charge density wave structure obtained by the X-ray diffraction experiments, density functional theory models are deduced in order to describe the electronic structure of 1T-TaS2 in the second part of this thesis. As opposed to most previous studies, these calculations take the three-dimensional character of the charge density wave into account. Indeed the electronic structure calculations uncover complex orbital textures, which are interwoven with the charge density wave order and cause dramatic differences in the electronic structure depending on the alignment of the orbitals between neighboring layers. Furthermore, it is demonstrated that these orbital-mediated effects provide a route to drive semiconductor-to-metal transitions with technologically pertinent gaps and on ultrafast timescales.
These results are particularly relevant for the ongoing development of novel, miniaturized and ultrafast devices based on layered transition metal dichalcogenides. The discovery of orbital textures also helps to explain a number of long-standing puzzles concerning the electronic self-organization in 1T-TaS2 : the ultrafast response to optical excitations, the high sensitivity to pressure as well as a mysterious commensurate phase that is commonly thought to be a special phase a so-called “Mott phase” and that is not found in any other isostructural modification.
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El, Khatib Muammar. "Characterization of metallic and insulating properties of low-dimensional systems." Thesis, Toulouse 3, 2015. http://www.theses.fr/2015TOU30198/document.
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Dans cette thèse nous avons étudié des indicateurs visant à caractériser les propriétés métalliques ou isolantes de systèmes de basse dimensionnalité à partir de calculs théoriques basés sur la fonction d'onde. Ces systèmes sont intéressants car ils permettent une compréhension en profondeur des phénomènes physiques qui peuvent ensuite être extrapolés à des systèmes plus étendus. Afin de réaliser cette étude nous avons utilisé un nouvel outil basé sur la théorie de la conductivité de Kohn : le tenseur de délocalisation total ou total position spread-tensor (TPS). Ce tenseur est défini comme le second cumulant de l'opérateur position : ? = - 2. Divisé par le numéro des électrons, il diverge quand la fonction d'onde est fortement délocalisée (forte fluctuation de la position des électrons) et converge vers une valeur finie dans le cas contraire. Ainsi, la conductivité est relié à la délocalisation de la fonction d'onde. Dans ce travail, deux définitions du TPS ont été abordées : une quantité sommée sur le spin (spin-summed TPS, SS-TPS) d'une part, et une décomposition selon le spin (spin-partitioned TPS, SSP-TSP) d'autre part. Cette dernière s'est avérée être un outil très efficace pour l'étude de systèmes fortement corrélés. Au cours de la thèse, nous avons commencé par étudier plusieurs systèmes diatomiques présentant des liaisons de natures différentes à l'aide de calculs d'interaction de configurations totale (FCI). Le TPS présente alors un maximum dans une zone précédant la rupture de liaison avant de converger asymptotiquement vers les valeurs atomiques, comme la consistance de taille du tenseur le laissait présager. Dans le cas de systèmes pour lesquels l'état électronique présente un croisement évité, le TPS diverge, mettant ainsi en évidence la forte délocalisation de la fonction d'onde. Le SS-TPS est donc un indicateur de choix pour suivre la nature de la liaison chimique. Nous avons ensuite considéré des systèmes à valence mixte de type II pour lesquels l'état fondamental présente un double-puits de potentiel avec un croisement évité avec le premier état excité. Il est donc nécessaire ici d'utiliser un traitement multi-configurationnel. Deux systèmes modèles ont ainsi été étudiés : i) deux di- mères H2 en interaction faible au niveau FCI et ii) un composé du type spiro au niveau CAS-SCF (à l'aide d'un code que nous avons implémenté dans Molpro). Dans les deux cas, le TPS présentait un maximum très marqué dans la région du croisement évité, signature d'une forte mobilité électronique. Nous nous sommes également intéressés à trois types de chaines d'atomes d'hydrogène : i atomes équidistants ii) chaines dimérisées à longueur de liaison H2 fixée et iii) chaines dimérisées. Tant le SS-TPS que le SP-TPS montrent des comportements différents selon le type de chaine considérée. Les premières ont un caractère métallique et une délocalisation de spin prononcée dans le régime fortement corrélé. Les secondes sont de nature isolante avec une délocalisation limitée. Les chaines dimérisées, quant à elle, dissocient très rapidement vers un état isolant mais avec une forte délocalisation de spin. Ces chaines demi-remplies ont aussi été traitées à l'aide d'hamiltonien de Hubbard et de Heisenberg. Nous avons ainsi pu rationaliser le comportement des SS-TPS et SP-TPS en variant le rapport de l'intégrale de saut et de la répulsion électron- électron (-t/U) entre sites adjacents. Le caractère ferromagnétique/anti-ferromagnétique a également pu être suivi en modifiant la valeur de la constante de couplage J dans le cas fortement corrélé. Finalement, ces indicateurs ont été mis en oeuvre pour des polyacenes cycliques. Dans ce cas, le TPS a permis de comprendre la nature des fonctions d'onde de l'état fondamental obtenues au niveau CAS-SCF et NEVPT2I carried out a theoretical study to characterize metallic and insulating properties of low-dimensional systems using wave function methods. Low-dimensional systems are particularly important because they allow an understanding that can be extrapolated to higher dimensional systems. We have employed a new tool based on the theory of conductivity of Kohn that we have named: total position-spread tensor (TPS). The TPS is defined as the second moment cumulant of the total position operator: ? = - 2 . The tensor divided by the number of electrons diverges when the wave function is delocalized (high fluctuation of electrons' positions), and it takes finite values for localized ones. In this way, the electrical conductivity is related to the proper delocalization of the wave function. In addition, the tensor can be divided in spin-summed (SS-TPS) and spin-partitioned tensors (SP-TPS). The latter one becomes a powerful tool to the study of strongly correlated systems. In this dissertation, we started to investigate at full configuration interaction (FCI) level diatomic molecules showing different types of bond. The TPS presented a marked maximum before the bond was broken and in the asymptotic limit one recovers the TPS values of isolated atoms (size consistency). For the case of diatomic systems showing avoided-crossing electronic states, the TPS diverges evidencing the high delocalization of the wave function. Therefore, the SS-TPS is capable of monitoring and characterizing molecular wave functions. We considered mixed-valence systems that are often distinguished by a double-well potential energy surface presenting an avoided-crossing. Thus, such a configuration possesses a strongly multireference nature involving at least two states of the same symmetry. Two different systems were investigated: i) two weakly interacting hydrogen dimers that were investigated at Full CI level, and ii) a spiro like molecule where the TPS tensor was evaluated in a CAS-SCF state-averaged wave function using our implementation of the SS- TPS formalism in MOLPRO. We found that the tensor's component in the direction of the electron transfer (ET) shows a marked maximum in the avoided-crossing region, evidencing the presence of a high electron mobility. The formalisms of the SS- and SP-TPS was applied to one dimensional systems composed by three types of half-filled hydrogen chains: i) equally-spaced chains, ii) fixed-bond dimerized chains, and iii) homothetic dimerized chains. Both the SS- and SP-TPS showed different signatures associated to the three types of systems. Equally-spaced chains have metallic wave functions and a high spin delocalization in the strongly correlated regime. In contrast, fixed-bond dimerized chains have an insulating character and a restricted spin delocalization. Finally, homothetic dimerized chains dissociate very quickly which renders them in the insulating state but with a high spin delocalization. We also studied half-filled chains by using the Hubbard and the Heisenberg Hamiltonians. On the one hand, we were able to depict the response of the SS- and SP-TPS by varying the ratio between the hopping and electron-electron repulsion (-t/U parameter) of topological connected sites. On the other hand, the ferromagnetic and anti-ferromagnetic character of the wave functions were evaluated by varying the coupling constant (J) in the strongly correlated systems. A theoretical study of closed polyacenes (PAH) structures was performed at CAS-SCF and NEVPT2 level. Our methodology for choosing the active space using the Hückel Hamiltonian was able to characterize the ground state of the systems that indeed fulfilled the Ovchinnikov rule. Finally, we applied the SS-TPS to understand the nature of the wave functions of these PAHs
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Michalicek, Gregor [Verfasser], Stefan [Akademischer Betreuer] Blügel, Eugene [Akademischer Betreuer] Krasovskii, and Stefan [Akademischer Betreuer] Weßel. "Extending the precision and efficiency of the all-electron full-potential linearized augmented plane-wave density-functional theory method / Gregor Michalicek ; Stefan Blügel, Eugene Krasovskii, Stefan Weßel." Aachen : Universitätsbibliothek der RWTH Aachen, 2015. http://d-nb.info/112612396X/34.
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Azizoglu, Suha Alp. "Time Domain Scattering From Single And Multiple Objects." Phd thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609413/index.pdf.
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The importance of the T-matrix method is well-known when frequency domain scattering problems are of interest. With the relatively recent and wide-spread interest in time domain scattering problems, similar applications of the T-matrix method are expected to be useful in the time domain. In this thesis, the time domain spherical scalar wave functions are introduced, translational addition theorems for the time domain spherical scalar wave functions necessary for the solution of multiple scattering problems are given, and the formulation of time domain scattering of scalar waves by two spheres and by two scatterers of arbitrary shape is presented. The whole analysis is performed in the time domain requiring no inverse Fourier integrals to be evaluated. Scattering examples are studied in order to check the numerical accuracy, and demonstrate the utility of the expressions.
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Skubic, Björn. "Spin Dynamics and Magnetic Multilayers." Doctoral thesis, Uppsala University, Department of Physics, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8168.
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Theoretical studies based on first-principles theory are presented for a number of different magnetic systems. The first part of the thesis concerns spin dynamics and the second part concerns properties of magnetic multilayers. The theoretical treatment is based on electronic structure calculations performed by means of density functional theory.
A method is developed for simulating atomistic spin dynamics at finite temperatures, which is based on solving the equations of motion for the atomic spins by means of Langevin dynamics. The method relies on a mapping of the interatomic exchange interactions from density functional theory to a Heisenberg Hamiltonian. Simulations are performed for various magnetic systems and processes beyond the reach of conventional micromagnetism. As an example, magnetization dynamics in the limit of large magnetic and anisotropy fields is explored. Moreover, the method is applied to studying the dynamics of systems with complex atomic order such as the diluted magnetic semiconductor MnGaAs and the spin glass alloy CuMn. The method is also applied to a Fe thin film and a Fe/Cr/Fe trilayer system, where the limits of ultrafast switching are explored. Current induced magnetization dynamics is investigated by calculating the current induced spin-transfer torque by means of density functional theory combined with the relaxation time approximation and semi-classical Boltzmann theory. The current induced torque is calculated for the helical spin-density waves in Er and fcc Fe, where the current is found to promote a rigid rotation of the magnetic order.
Properties of magnetic multilayers composed of magnetic and nonmagnetic layers are investigated by means of the Korringa-Kohn-Rostocker interface Green's function method. Multilayer properties such as magnetic moments, interlayer exchange coupling and ordering temperatures are calculated and compared with experiments, with focus on understanding the influence of interface quality. Moreover, the influence on the interlayer exchange coupling of alloying the nonmagnetic spacer layers with small amounts of a magnetic impurity is investigated.
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Typovský, Viktor. "Definice parametru pro dekonvoluci obrazu z elektronového mikroskopu." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2018. http://www.nusl.cz/ntk/nusl-377767.
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Tato diplomová práce se zabývá modelováním bodové rozptylové funkce (point spread function, PSF) u skenovacího transmisního elektronového mikroskopu (STEM). Nejprve je provedena teoretická rešerše, kde jsou popsány všechny důležitě aspekty, potřebné k následnému modelování. Je tedy proveden základní popis konstrukce přístroje a určeny jeho klíčové komponenty, které mají hlavní vliv na tvar výsledné PSF. Následně jsou popsány hlavní zobrazovací vady, které ovlivňují výslednou PSF. Ty jsou popsány z hlediska vlnové optiky. Na základě toho je pak navržen a zrealizován poměrně přesný model PSF u mikroskopu STEM. Poté je vytvořeno GUI, které umožňuje plné využití daného vytvořeného modelu. Na závěr je získaný model otestován na modelových a reálných datech, pomocí metody Lucy-Richardson.
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Chergui, Mohammed. "Étude numérique de l'absorption et de l'émission d'ondes à la fréquence cyclotron électronique par un plasma de tokamak soutenu par radio-fréquence." Nancy 1, 1988. http://www.theses.fr/1988NAN10259.
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L'équation de dispersion est résolue en y injectant un modèle particulier de fonction de distribution des quantités de mouvement d'un plasma de tokamak. Les résultats obtenus sont en complet désaccord avec le modèle maxwellien, en particulier pour la disposition de l'énergie dans le cas de l'absorption, la température radiative dans le cas de l'émission et la fréquence d'intéraction onde-particule, qui est inférieure à la fréquence cyclotron électronique, ce qui présente plusieurs avantages techniques et une voie prometteuse pour le chauffage des plasmas de fusion
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AL, SALEH-MAHROUSSEH SALOUA. "Calcul relativiste, en electrodynamique quantique, de la diffusion compton sur un electron lie." Clermont-Ferrand 2, 1988. http://www.theses.fr/1988CLF21098.
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Pour expliquer le deplacement et l'elargissement du pic compton,lorsque l'energie du photon est voisine de l'energie de liaison de l'electron, il est necessaire d'introduire non seulement la liaison et le mouvement de l'electron, mais aussi le recul du mnoyau. On donne un calcul relativiste de la valeur quadratique moyenne de l'impulsion de l'electron et une expression generale des fonctions d'onde radiales. Pour le calcul analytique covariant de l'element de matrice ou utilise un propagateur pour un electron lie dans le schema de furry et determine la secton efficace, sans aucune integration
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Perez, Thomas. "Problèmes d'algèbre extérieure liés au calcul de fonctions d'ondes électroniques produits de géminales." Thesis, Université Côte d'Azur, 2020. http://www.theses.fr/2020COAZ4060.
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En chimie quantique, les fonctions d'ondes électroniques peuvent être vues comme des multivecteurs ; les problèmes se traduisent par conséquent en langage mathématique grâce à l'algèbre extérieure.Nous rappelons en premier lieu certains résultats sur l'algèbre extérieure d'un espace de Hilbert concernant les produits extérieur et intérieur qui s'avèrent utiles pour la chimie quantique. Dans cette même partie, une méthode pour trouver l'idéal annulateur d'un multivecteur, correspondant en physique à l'espace d'exclusion par le principe de Pauli, est présentée et cette technique sera employée dans un chapitre ultérieur.Dans un deuxième temps, nous faisons un résumé des notions clés du formalisme quantique des systèmes fermioniques et de leur expression du point de vue de l'algèbre extérieure. Nous rappelons également les principales méthodes d'approximation basées sur les fonctions d'ondes en chimie quantique. Nous introduisons par la suite des versions généralisées des concepts de séniorité et d'ionicité. Ces nombres généralisés comptent de façon respective les couches partiellement et entièrement occupées pour toute partition en couches de l'espace des orbitales. Nous construisons ensuite les opérateurs hermitiens dont les espaces propres correspondent aux fonctions d'ondes associées aux différentes valeurs de séniorité généralisée ou d'ionicité généralisée. Les nombres de séniorité généralisée permettent d'établir des hiérarchies plus fines des espaces d'interaction de configuration à l'intérieur d'une séniorité ordinaire donnée.Dans le troisième et principal chapitre, nous présentons le cheminement qui nous a conduit à proposer un nouvel ansatz de fonctions d'ondes produits de géminales où les géminales ne sont pas fortement orthogonales mais satisfont à des contraintes géométriques plus faibles pour réduire l'effort de calcul sans sacrifier l'indiscernabilité des électrons. Nos contraintes géométriques se traduisent par des équations simples impliquant les traces de produits de matrices de géminales. Dans le modèle non trivial le plus basique, un ensemble de solutions est donné par des matrices diagonales par blocs où chaque bloc est de taille 2x2 et se compose d'une matrice de Pauli ou d'une matrice diagonale, multipliée par un paramètre complexe qui est à optimiser. Avec cet ansatz simplifié pour les géminales, le nombre de termes dans le calcul des éléments matriciels des observables quantiques, comme l'hamiltonien de l'équation de Schrödinger électronique, est considérablement réduit.Enfin, dans la dernière partie, nous explicitons la programmation de notre modèle de produits de géminales dans le code “Tonto”, qui est un programme et une librairie pour la cristallographie quantique et la chimie quantique écrits dans le langage “Foo”. La validité de notre code a été testée sur le calcul de l'énergie électronique de chaînes d'hydrogène. De plus, une preuve de principe que notre ansatz donne des résultats significativement plus précis que la méthode des géminales fortement orthogonales a été établieIn quantum chemistry, the electronic wave functions can be viewed as multivectors, therefore all problems translate into mathematical language thanks to the exterior algebra.We first recall some results related to the exterior and the interior products of the exterior algebra of a Hilbert space, which prove useful for quantum chemistry. We follow by presenting a method to find the annihilator ideal of a multivector, corresponding in physics to the excluded space by the Pauli principle, and this technique will be used in a later chapter.In a second step, we provide a summary of the key notions of the quantum formalism of fermionic systems and their counterpart from the point of view of the exterior algebra. We also recall the main approximation methods based on wave functions in quantum chemistry. We then introduce generalized versions of the concepts of seniority number and ionicity. These generalized numbers count respectively the partially occupied and fully occupied shells for any partition of the orbital space into shells. The Hermitian operators whose eigenspaces correspond to wave functions of definite generalized seniority or ionicity values are built. The generalized seniority numbers afford to establish refined hierarchies of configuration interaction spaces within those of fixed ordinary seniority.In the third and main chapter, we present the way that has led us to propose a new geminal product wave function ansatz where the geminals are not strongly orthogonal but satisfy weaker geometrical constraints to lower the computational effort without sacrificing the indistinguishability of the electrons. Our geometrical constraints translate into simple equations involving the traces of products of geminal matrices. In the simplest non-trivial model, a set of solutions is given by block-diagonal matrices where each block is of size 2x2 and consists of a Pauli matrix or a diagonal matrix, multiplied by a complex parameter to be optimized. With this simplified ansatz for geminals, the number of terms in the calculation of the matrix elements of quantum observables, like the Hamiltonian of the Schrödinger electronic equation, is considerably reduced.Finally, in the last part, we explain the implementation of our geminal product model in the computer code “Tonto”, which is a program and library for quantum crystallography and quantum chemistry written in the “Foo” language. The validity of our code has been tested on the calculation of the electronic energy of hydrogen chains. Moreover, a proof of principle that our ansatz gives significantly more accurate results than the strongly orthogonal geminal method has been established
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Lange, Malte. "Wave function-based electronic structure theory for solids." Thesis, 2021. https://doi.org/10.7916/d8-ssjn-5h38.
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This thesis describes the application of wave function-based and perturbative methods to extended systems, primarily semiconductors.
In Chapter 1, I introduce the quantum chemistry problem along with current progress in the field. I then provide some requisite fundamental theory associated with the wave function-based methods and periodic boundary conditions.
In Chapter 2, I describe the relationship between the traditional extended system GW method and the traditionally molecular coupled-cluster formalism through diagrammatic analysis. We find that the popular coupled cluster singles and doubles (CCSD) method contains most of the diagrams in GW theory and more, and the more accurate coupled cluster singles and doubles with perturbative triples (CCSD(T)) method contains all GW diagrams and more. Benchmarking on the GW100 test set indicates that CCSD and a number of its approximations are more accurate than GW theory.
In Chapter 3, I evaluate the potential for using composite schemes to reduce the computational cost of the CCSD method. We use focal point and downfolding techniques for excited state results for the GW100 along with some sample solids. Using composite methods reduces the cost of CCSD by reducing the number of orbitals treated at a higher level of theory, which is very similar to the active space methods used in single- and multi-reference calculations.
In Chapters 4 and 5, I describe how to best treat finite size effects for wave function-based methods, including the impact of including terms like the Madelung constant and which extrapolation form to use. After establishing this, we use the prescribed procedure to compare the equation-of-motion second-order M{\o}ller-Plesset (EOM-MP2) method to the MP2 method of Gr\"{u}neis and the GW method for a standard test set of 11 solid-state systems. We find that the MP2 method performs qualitatively and quantitatively poorly for extended systems, but EOM-MP2 and GW perform qualitatively well, with quantitative MAEs of 0.40 and 0.68eV, respectively relative to a zero-point corrected electronic band gap.
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Gilka, Natalie [Verfasser]. "Electron spin-spin coupling from multireference CI wave functions / vorgelegt von Natalie Gilka." 2008. http://d-nb.info/989721078/34.
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Shabadi, Prasad. "Towards Logic Functions as the Device using Spin Wave Functions Nanofabric." 2012. https://scholarworks.umass.edu/theses/850.
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As CMOS technology scaling is fast approaching its fundamental limits, several new nano-electronic devices have been proposed as possible alternatives to MOSFETs. Research on emerging devices mainly focusses on improving the intrinsic characteristics of these single devices keeping the overall integration approach fairly conventional. However, due to high logic complexity and wiring requirements, the overall system-level power, performance and area do not scale proportional to that of individual devices.
Thereby, we propose a fundamental shift in mindset, to make the devices themselves more functional than simple switches. Our goal in this thesis is to develop a new nanoscale fabric paradigm that enables realization of arbitrary logic functions (with high fan-in/fan-out) more efficiently. We leverage on non-equilibrium spin wave physical phenomenon and wave interference to realize these elementary functions called Spin Wave Functions (SPWFs).
In the proposed fabric, computation is based on the principle of wave superposition. Information is encoded both in the phase and amplitude of spin waves; thereby providing an opportunity for compressed data representation. Moreover, spin wave propagation does not involve any physical movement of charge particles. This provides a fundamental advantage over conventional charge based electronics and opens new horizons for novel nano-scale architectures.
We show several variants of the SPWFs based on topology, signal weights, control inputs and wave frequencies. SPWF based designs of arithmetic circuits like adders and parallel counters are presented. Our efforts towards developing new architectures using SPWFs places strong emphasis on integrated fabric-circuit exploration methodology. With different topologies and circuit styles we have explored how capabilities at individual fabric components level can affect design and vice versa. Our estimates on benefits vs. 45nm CMOS implementation show that, for a 1-bit adder, up to 40x reduction in area and 228x reduction in power is possible. For the 2-bit adder, results show that up to 33x area reduction and 222x reduction in power may be possible.
Building large scale SPWF-based systems, requires mechanisms for synchronization and data streaming. In this thesis, we present data streaming approaches based on Asynchronous SPWFs (A-SPWFs). As an example, a 32-bit Carry Completion Sensing Adder (CCSA) is shown based on the A-SPWF approach with preliminary power, performance and area evaluations.
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Bajdich, Michal. "Generalized pairing wave functions and nodal properties for electronic structure quantum Monte Carlo." 2007. http://www.lib.ncsu.edu/theses/available/etd-03232007-095532/unrestricted/etd.pdf.
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CAI, WEN-REN, and 蔡文仁. "Electron-He atom elastic scattering using correlated wave function for the ground state of the atom." Thesis, 1990. http://ndltd.ncl.edu.tw/handle/12034631765557201792.
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Maltezopoulos, Theophilos [Verfasser]. "Wave-function mapping of electronic states in nanostructures by scanning tunneling spectroscopy / vorgelegt von Theophilos Maltezopoulos." 2004. http://d-nb.info/971435375/34.
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Fleig, Timo [Verfasser]. "Wave function based relativistic multi-reference electron correlation methods : development and application to atomic and molecular properties / Timo Fleig." 2007. http://d-nb.info/984672672/34.
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Li, Zong-Yan, and 李宗諺. "The effects of boundaries and electric fields on the donor electron wave function in the Kane quantum computing scheme." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/78030315923734232130.
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碩士臺灣大學
物理研究所
98
The silicon-based donor spin quantum computer, also known as the Kane quantum computer, is one of the most promising solid-state quantum computing proposals. In this Kane scheme, P donor atoms are placed in an array embedded in a pure 28Si crystal. The spin of either the extra electron or the extra proton of the P donor atom can be defined as quantum bits (qubits). By applying electric fields (voltage) and magnetic fields, the donor wave function can be deformed and manipulated. As a result, the hyperfine interaction between the nuclear spin and electron spin as well as the exchange interaction between two neighboring electron spins may be controlled to construct logical quantum gate operations. In this thesis, we investigate the effect of boundaries and electric fields on the donor electron wave function in the Kane quantum computer scheme. The device that we consider has a donor atom embedded in a silicon crystal, and the electric field is generated by two parallel conducting plates sandwiching the silicon crystal with a silicon-dioxide (SiO2) insulator layer in between on each side. At low temperature the donor electron wave function can be approximately expanded by the Bloch states of six conduction band minima (valleys) of the silicon lattice as silicon is an indirect band-gap semiconductor. We use the anisotropic effective mass theory to calculate the donor electron wave function and consider the single-valley case and six-valley case. Because SiO2 is an insulator, the donor electron wave function and donor electron density are expected to be zero at SiO2-Si boundary. The deformed hydrogen wave functions multiplied by a term which vanishes at the boundary are thus used as our trial envelope wave functions. The effects of image charges of the donor electron and nucleus are also investigated. We calculate the values of the characteristic electric field, Fc, at which the donor electron is about to be ionized to the interface region , for different donor depths. We also calculate the tunneling time and the hyperfine interaction as a function of the electric field strength.
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Yi, Zhijun. "Ab-initio Study of Semi-conductor and Metallic Systems: from Density Functional Theory to Many Body Perturbation Theory." Doctoral thesis, 2010. https://repositorium.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-201002115394.
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Substitutional dopants in III-V semi-conductors, such as Si atoms in GaAs, are of great interest for the applications in transistors, Schottky diodes, and doping super-lattices which have been widely employed to control the electrical properties of semi-conductors. Although Si doped GaAs systems have been intensively investigated theoretically and experimentally in the last
several decades, some properties are still debated. In order to give a further explanation of Si
doped GaAs systems, we systematically studied DX center in bulk GaAs and in GaAs(110), as
well as the relative stabilities of different charged systems for Si atom replacing Ga atom at the substitutional site near GaAs(110) surface from first principles ground state
method. We show that DX centre is a metastable state in bulk GaAs and completely unstable in
the top few layers of GaAs(110). When Si atom replaces Ga atom at the surface, Charge states have an important influence on the stability of the system, and the additional charge is mainly concentrated on the Si atom for charged system. In addition, we studied the STM images of clean GaAs(110) and
charged Si:GaAs(110) by employing Tersoff-Hamann approximation. The calculated STM
images are in good agreement with experimental results. We show that at the positive bias
voltage the positively charged Si atom presents a bright feature while the negatively charged Si
atom shows a dark feature. In a semi-conductor, all bands are either completely full or completely empty. It is well known that DFT underestimates the band gaps of semi-conductors, a simple rigid shift can be used to
correct the band energies of semi-conductors. Unlike semi-conductor, the fermi energies of
metals lie in some bands. Furthermore, it turned out that some noble metals such as Cu and Ag
depend on the considered band and k point , therefore, the so-called scissors operator can not be
used for the metallic systems. The most successful approach within theoretical method for these
metals is the many body perturbation theory. On the other hand, an interesting study for metals is quasi-particle excitations, which play an important role in a rich variety of physical and
chemical phenomena such as energy transfer in photochemical reaction, desorption and
oxidation of molecules at surfaces, spin transport within bulk metals, across interfaces, and at
surfaces. One of the crucial properties of quasi-particle excitation is their lifetimes which
determine the duration of these excitations. We carried out the calculations of quasi-particle
band-structures and lifetimes for noble metals Cu and Ag within the GW approximation. For
Cu, both the calculated positions of the d bands and the width of the d bands is within 0.1 eV
compared to the experimental results. For Ag, partial core correction should be included in the
pseudo-potential to get reliable positions of the d bands. The calculated lifetime agree with the
experiment in the energy region away from the Fermi level, but deviates from the experimental
results near the Fermi level where short range interactions which GW approach fails to describe
play an important role. For a better description of the lifetime near the Fermi level, higher terms
beyond the GW approximation in the many body perturbation theory need to be considered. In
addition, the image potential state lifetimes in Cu(100) have been calculated using GW
approximation based on the localized Gaussian basis set, and the calculated n=1, 2 imagepotential
state lifetimes are in good agreement with experimental results.