京都大学 / 新制・課程博士 / 博士(工学) / 甲第24634号 / 工博第5140号 / 新制||工||1982(附属図書館) / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 佐藤 啓文, 教授 佐藤 徹, 教授 松田 建児 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Kohn-Sham density functional theory is a rigorous formulation of many-electron quantum mechanics which, for practical purposes, requires approximation of one term in its total energy expression: the exchange-correlation energy. This work elucidates systematic methods for constructing approximations to the exchange-correlation energy solely from first-principles physics. We review the constraints that can be built into approximate density functionals, and use thermochemical data to argue that satisfaction of these constraints permits a more general description of electronic matter. Contact with semiclassical physics is made by studying the turning surfaces of Kohn-Sham potentials in solids. Perfect metals and covalently-bound, narrow-gap insulators do not have turning surfaces at equilibrium, but do under expansive strain. Wide-gap insulators, ionic crystals, and layered solids tend to have turning surfaces at equilibrium. Chemical bonds in solids are classified using the turning surface radii of its constituent atoms. Depletion of the charge density, such as near a monovacancy in platinum, is shown to produce a turning surface. Further, this work demonstrates why generalized gradient approximations (GGAs) are often able to describe some properties of sp-bonded narrow-gap insulators well. A Laplacian-level pure-density functional is developed with the goal of describing metallic condensed matter. This functional is derived from the r2SCAN orbital-dependent meta-GGA, and reduces its tendency to over-magnetize ferromagnets; improves its description of the equation of state properties of alkali metals; and improves its description of intermetallic thermodynamics. It is constructed to enforce the fourth-order exchange gradient expansion constraint (not satisfied by r2SCAN), and a few free parameters are fitted to paradigmatic metallic systems: jellium surfaces and closed-shell jellium clusters. Last, we modify an exchange-correlation kernel that describes the density-density response of jellium to better satisfy known frequency sum rules. We also constrain the kernel to reproduce the correlation energies of jellium, and compare it to a wide variety of common kernels in use for linear response, time-dependent density functional theory calculations. / Physics

Electronic structure methods aim to accurately describe the behaviour of the electrons in molecules and materials. To be applicable to arbitrary systems, these methods cannot depend on observations of specific chemical phenomena and must be derived solely from the fundamental physical constants and laws that govern all electrons. Such methods are called ab initio methods. Ab initio methods directly solve the electronic Schrödinger equation to obtain the electronic energy and wavefunction. For more than one electron, solving the electronic Schrödinger equation is impossible, so it is imperative to develop approximate methods that cater to the needs of their users, which can vary depending on the chemical systems under study, the available computational resources and time, and the desired level of accuracy. The most accessible ab initio approaches, including Hartree-Fock methods and Kohn-Sham density functional theory methods, assume that only one electronic configuration is needed to describe the system. While these single-reference methods are successful when describing systems where a single electron configuration dominates, like most closed-shell ground-state organic molecules in their equilibrium geometries, single-reference methods are unreliable for molecules in nonequilibrium geometries (e.g., transition states) and molecules containing unpaired electrons (e.g., transition metal complexes and radicals). For these types of multireference systems, accurate results can only be obtained if multiple electronic configurations are accounted for. Wavefunctions that incorporate many electronic configurations are called multideterminant wavefunctions. This thesis presents a systematic approach to developing multideterminant wavefunctions. First, we establish a framework that outlines the structural components of a multideterminant wavefunction and propose several novel wavefunction ansätze. Then, we present a software package that is designed to aid the development of new wavefunctions and algorithms. Using this approach, we develop an algorithm for evaluating the geminal wavefunctions, a class of multideterminant wavefunctions that are expressed with respect to electron pairs. Finally, we explore using machine learning to solve the Schrödinger equation by presenting a neural network wavefunction ansatz and optimizing its parameters using stochastic gradient descent. / Thesis / Doctor of Science (PhD)

Accurate correlated electronic structure methods involve a significant amount of computations and can be only employed to small molecular systems. For example, the coupled-cluster singles, doubles, and perturbative triples model (CCSD(T)), which is known as the ``gold standard" of quantum chemistry for its accuracy, usually can treat molecules with 20-30 atoms. To extend the reach of accurate correlated electronic structure methods to larger molecular systems, we work towards two directions: parallel computing and reduced-cost/scaling approaches. Parallel computing can utilize more computational resources to handle systems that demand more substantial computational efforts. Reduced-cost/scaling approaches, which introduce approximations to the existing electronic structure methods, can significantly reduce the amount of computation and storage requirements. In this work, we introduce a new distributed-memory massively parallel implementation of standard and explicitly correlated (F12) coupled-cluster singles and doubles (CCSD) with canonical bigO{N^6} computational complexity ( C. Peng, J. A. Calvin, F. Pavov{s}evi'c, J. Zhang, and E. F. Valeev, textit{J. Phys. Chem. A} 2016, textbf{120}, 10231.), based on the TiledArray tensor framework. Excellent strong scaling is demonstrated on a multi-core shared-memory computer, a commodity distributed-memory computer, and a national-scale supercomputer. We also present a distributed-memory implementation of the density-fitting (DF) based CCSD(T) method. (C. Peng, J. A. Calvin, and E. F. Valeev, textit{in preparation for submission}) An improved parallel DF-CCSD is presented utilizing lazy evaluation for tensors with more than two unoccupied indices, which makes the DF-CCSD storage requirements always smaller than those of the non-iterative triples correction (T). Excellent strong scaling is observed on both shared-memory and distributed-memory computers equipped with conventional Intel Xeon processors and the Intel Xeon Phi (Knights Landing) processors. With the new implementation, the CCSD(T) energies can be evaluated for systems containing 200 electrons and 1000 basis functions in a few days using a small size commodity cluster, with even more massive computations possible on leadership-class computing resources. The inclusion of F12 correction to the CCSD(T) method makes it converge to basis set limit much more rapidly. The large-scale parallel explicitly correlated coupled-cluster program makes the accurate estimation of the coupled-cluster basis set limit for molecules with 20 or more atoms a routine. Thus, it can be used rigorously to test the emerging reduced-scaling coupled-cluster approaches. Moreover, we extend the pair natural orbital (PNO) approach to excited states through the equation-of-motion coupled cluster singles and doubles (EOM-CCSD) method. (C. Peng, M. C. Clement, and E. F. Valeev, textit{submitted}) We simulate the PNO-EOM-CCSD method using an existing massively parallel canonical EOM-CCSD program. We propose the use of state-averaged PNOs, which are generated from the average of the pair density of excited states, to span the PNO space of all the excited states. The doubles amplitudes in the CIS(D) method are used to compute the state-averaged pair density of excited states. The issue of incorrect states in the state-averaged pair density, caused by an energy reordering of excited states between the CIS(D) and EOM-CCSD, is resolved by simply computing more states than desired. We find that with a truncation threshold of $10^{-7}$, the truncation error for the excitation energy is already below 0.02 eV for the systems tested, while the average number of PNOs is reduced to 50-70 per pair. The accuracy of the PNO-EOM-CCSD method on local, Rydberg and charge transfer states is also investigated. / Ph. D.

Submitted by William Justo Figueiro (williamjf) on 2015-07-09T22:47:34Z No. of bitstreams: 1 28b.pdf: 928828 bytes, checksum: 03bf0090fd6d0473043b76c6366d0c61 (MD5) / Made available in DSpace on 2015-07-09T22:47:34Z (GMT). No. of bitstreams: 1 28b.pdf: 928828 bytes, checksum: 03bf0090fd6d0473043b76c6366d0c61 (MD5) Previous issue date: 2014-12-22 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O presente estudo busca investigar as relações retóricas que emergem do encaixe de segmentos narrativos na organização macroestrutural de notícias de divulgação científica (DC) dirigidas aos públicos infantil e adulto. A organização narrativa é analisada segundo os postulados de Adam (2011) e Charaudeau (2008b); a organização retórica macroestrutural dos textos, por sua vez, é estudada de acordo com a Rhetorical Structure Theory – RST. (MANN; THOMPSON, 1988). O corpus do estudo é composto de 15 notícias de DC voltadas ao público infantil, publicadas na revista Ciência Hoje das Crianças entre dezembro de 2004 e setembro de 2010, e de 15 notícias de DC direcionadas ao público adulto, veiculadas na revista Ciência Hoje, entre agosto de 2005 e julho de 2012. A metodologia empregada consiste na análise quantitativa da emergência de relações retóricas entre os segmentos narrativos encontrados nos corpora (infantil e adulto) e as demais porções textuais, bem como na análise qualitativa de alguns textos selecionados para exemplificar cada uma das relações retóricas encontradas. Em seguida, é realizada uma análise comparativa entre os dados quantitativos provenientes das análises dos textos para crianças e dos textos para adultos. Assume-se que a esquematização de um texto é um processo de coconstrução, no qual o produtor, ao organizar seu plano textual, leva em consideração as características e conhecimentos de seu possível leitor e, a partir disso, lança mão de estratégias variadas para alcançar o fim discursivo pretendido e causar os efeitos desejados sobre o leitor. Dessa forma, conclui-se que a emergência recorrente de determinadas relações retóricas entre as narrativas encaixadas e as outras partes do texto revela estratégias do produtor textual para orientar a leitura e compreensão da notícia, tanto nos textos escritos para crianças quanto nos escritos para adultos. / This research aims to investigate the rhetorical relations which emerge from the insertion of narrative segments in the macrostructural organization of scientific popularization news directed to children and adults. The narrative organization is analyzed according to Adam’s (2011) and Charaudeau’s (2008b) postulates; the rhetorical organization of the texts, in turn, is studied according to Rhetorical Structure Theory – RST. (MANN; THOMPSON, 1988). The research corpus is composed of 15 scientific popularization news intended for children, published in the magazine Ciência Hoje das Crianças, and of 15 scientific popularization news directed to adults, issued in the magazine Ciência Hoje. The methodology consists of a quantitative analysis of the emergency of rhetorical relations between the narrative segments found in the corpora (texts for children and texts for adults) and other textual portions, as well as of a qualitative analysis of some selected texts in order to exemplify each one of the rhetorical relations found. Then, a comparative analysis is done between the quantitative data resultant from the analysis of the texts for children and of the texts for adults. We assume that the schematization of a text is a process of co-construction, in which the producer, when organizes the text plan, takes into consideration the characteristics and knowledge of his/her possible reader and, from this, resorts to different strategies in order to achieve the discursive aim intended and cause the desired effect over the reader. Thus, we conclude that the recurrent emergency of certain rhetorical relations between the inserted narratives and the other portions of the text reveals strategies of the textual producer in order to guide the reading and comprehension of the new, both in texts written forchildren and in texts written for adults.

This thesis investigates the relationship between creative potential and the rhetorical structure of children&rsquo / s narratives. 44 middle school children (aged 12-15) were given a set of paper-pen activities including one divergent thinking test, one convergent thinking test and a story to be completed. Results of the divergent and convergent thinking tests were taken as the predictors to estimate the potential for creative thinking. Children were examined in terms of how they encode rhetorical relations in their writings. Whether a creative potential made a difference in children&rsquo / s writings in terms of rhetorical relations they used, and whether children within the same creative potential group used the same rhetorical relations in common were investigated. Rhetorical Structure Theory (RST) (Marcu, 2000 and Carlson and Marcu, 2001) was used in coding children&rsquo / s writings. It was found that children in the study interpreted story writing as an act of attribution. This result is contrary to Marcu et.al (1999b), who found the elaboration-additional relation as the most frequent relation in their corpora. The study also found that there was an inverse relationship between the convergent thinking scores and the number of satellites (an EDU (elementary discourse unit) playing an auxilliary role for a text in question) for the 7th graders. Finally, it was found that high quartile (highest scorers in the study, top 25%) convergent thinkers were able to construct a narrative element with few number of EDUs and few number of discourse relation types.

ITSs (Intelligent Tutoring Systems) provide a way of addressing some of the issues that the more traditional CAI (Computer Aided Instruction) systems do not address - the individual learning needs and individual learning abilities and levels of users - so that the user is in control of their learning experience. An ITS needs to be able to provide an explanation, for a real world situation, that successfully meets the needs of the user. To ensure relevant explanation content requires the ITS be based on sound planning principles and tutoring knowledge as well as knowledge of the domain and the user. To ensure a coherent explanation structure requires that the tutoring knowledge be applied with full recognition of the knowledge of the domain and the user. For a model of the user's knowledge to be effective, the system should be able to use it to enhance the flexibility and responsiveness of explanations generated. A user model should guide the generation of explanations so they are pitched at the correct level of the user's existing knowledge; models should be able to actively support the needs of the user so that the user's efforts in seeking out information are minimised. The aim of this research is to generate effective, flexible and responsive explanations, in educational software systems, through developing better explanation facilities than exist in currently available ITS software. In achieving this aim, I am advancing research into dialogue planning and user modelling. The explanation facilities described meet the requirements of an explanation that is tailored to the user's needs, a sound theory from which particular explanations are constructed, and a user model that can accurately represent the behaviour and beliefs of the user. My research contributions include explicitly and formally representing discourse planning / reasoning, from both the user's view and the tutor's view so that they can be clearly understood and represented in the ITS. More recent planners have adopted approaches that can be characterised as using adaptations of the classical planning approach, with informally specified planning algorithms and planning languages. Without clear, explicit and full descriptions of actions and the planning algorithm we can not be certain of the plans that such planners produce. I adopt a theoretically rigorous approach based on classical planning theory - the actions available to the planner, the planning language and algorithm should be explicitly represented to ensure that plans are complete and consistent. Classical regression planning uses dynamic planning thus enabling the system to be flexible in a variety of situations and providing the responsiveness required for an ITS. I take a theoretically rigorous approach in constructing a well specified model of discourse, building upon existing research in the area. I present a tutoring module that is able to find a way to motivate the user to take a recommended action, by relating the action to the user's goals, and that is able to reason about the text structure to generate an effective explanation - putting together several clauses of text whilst maintaining coherency. As part of developing such constructs for motivating, enabling and recommending, as well as constructs for structuring text, I use a pedagogic model based on the principled approach of (i) advising the user to take an action (ii) motivating the user to want to take the action and (iii) ensuring the user knows how to do the action. I take a clear and realistic approach to user modelling, making explicit models of the user's behaviour and beliefs. I adopt a theoretically rigorous approach, formally distinguishing between the user's reasoning and their actions, so they can be focused on separately. Formally making this distinction, more easily enables models of the user's reasoning to be tailored to the individual user. To enable the tutor to consider the full impact on the user, of the information to be delivered to the user, I use different plan spaces. I explicitly identify the different perspectives of the user and the tutor so that they can be focused on separately to generate an explanation that is tailored to the user. In my approach, reasoning about the user's skills, rules and knowledge is independent from reasoning about those of the tutor.

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This paper aims to investigate the change in corporate debt levels in South Africa from 1994 to 2016, included is an analysis of factors that firms take into consideration when determining the company’s capital structure. This study uses data from firms in the Real Estate and REIT, Travel and Leisure and Construction and Materials sectors listed on the Johannesburg Stock Exchange (JSE). Four different leverage measures are used to determine the change in capital structure for the period under review, as well as six of the most commonly used determinants of capital structure. A high level interpretation of the results reflected the following; an increase in the use of debt in the Travel and Leisure and Construction and Materials Sectors, however a significant decrease in the use of debt relative to equity was seen in the Real Estate and REIT Sector thus skewing the Total Sample findings considerably. An increase in the use of long term debt relative to short term was also found. Results from the analysis of the capital structure determinants varied, with some determinants showing statistical significance. The following determinants were positively related to debt; firm size, asset tangibility and growth while the determinants; cost of debt and tax had a negative relationship. The relationship between profitability and leverage was varied.

Accurate energetic modeling of large molecular systems is always desired by chemists. For example, ligand-protein binding simulations and enzymatic catalysis studies all involve with a small energy difference. The energetic accuracy depends largely on a proper handling of electronic correlations. Molecular mechanics (MM) methods deliver a parameterized Newtonian treatment to these problems. They show great capability in handling large calculations but give only qualitatively good results. Quantum mechanics (QM) methods solve Schrödinger equations and exhibit much better energy accuracy, though the computational cost can be prohibitive if directly applied to very large systems. Fragment-based methods have been developed to decompose large QM calculations into fragment calculations. However, most current schemes use a self- consistent field (SCF) method on fragments, in which no electronic correlation is accounted for. The super-system energy is computed as a sum of fragment energies plus two-body corrections and, possibly, three-body corrections (a "body" is a fragment). Higher order corrections can be added. Nevertheless, many problems require the treatment of high order electronic correlations. The coupled-cluster (CC) theory is the state-of-the-art QM method for handling electronic correlations. The CC wavefunction contains correlated excitations up to a given truncated level and coincidental excitations for all possible electronic excitations. It is a brilliant way of including more electronic correlations while maintaining a low-order scaling. In the proposed excitonic coupled-cluster (X-CC) theory, substantial modifications have been made to allow CC algorithms to act on the collective coordinates of fragment fluctuations to obtain super-system energy. The X-CC theory is designed to achieve accurate energetic modeling results for large chemical systems with much improved affordability and systematic improvability. The test system used in this work is a chain of beryllium atoms. A 30-fragment X-CCSD(2) calculation delivered matching accuracy with traditional CCSD method. An X-CCSD(2) calculation on a chain of 100 bonded fragments finished in 7 hours on a single 2.2 GHz CPU core. The X-CC scheme also demonstrates the ability in handling charge transfer problems. Due to the use of fluctuation basis in the test cases, the excitonic algorithms can be easily generalized to inhomogeneous systems. This will be investigated in future work.