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京都大学 / 新制・課程博士 / 博士(工学) / 甲第23918号 / 工博第5005号 / 新制||工||1781(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 作花 哲夫, 教授 佐藤 徹 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

<p>Approximating the exchange-correlation energy in density functional theory (DFT) is a crucial task. As the only missing element in the Kohn-Sham DFT, the search for better exchange-correlation functionals has been an active field of research for fifty years. Many models and approximations are known and they can be summarized in what is known as the Jacob’s ladder. All the functionals in that ladder are local in the sense that they rely on the information of only one electronic coordinate. That is, even though the exchange-correlation hole, the cornerstone in density functional theory, is a two-electron coordinate quantity, one of the coordinates is averaged over in “Jacob’s ladder functionals.” This makes the calculations considerably more efficient. On the other hand, some of the important constraints on the form of the exchange-correlation functional become inaccessible in the one-point forms. The violation of these constraints leads to functionals plagued by systematic errors, leading to qualitatively incorrect descriptions of some chemical and physical processes.</p> <p>In this thesis the idea of a weighted density approximation (WDA) is explored. More specifically, a symmetric and normalized two-point functional is proposed for the exchange-correlation energy functional. The functional is based entirely on the hole for the uniform electron gas. By construction, these functionals fulfill two of the most important constraints: the normalization of the exchange-correlation hole and the uniform electron gas limit. The findings suggest that we should pursue a whole new generation of “new Jacob’s ladder” functionals.</p> <p>A further step was considered. Given the relevance of the long-range behavior of the exchange-correlation hole, a study of the electronic direct correlation function was performed. The idea was to build up the long-range character of the hole as convoluted pieces of the simple and short-ranged direct correlation function. This direct correlation function provides better results, at least for the correlation energy in the spin-polarized uniform electron gas.</p> <p>The advantage of one-point functionals is their computational efficiency. We therefore attempted to develop new methods that mitigate the relative computational inefficiency of two-point functionals. This led to new methods for evaluating the six-dimensional integrals that are inherent to the exchange-correlation energy.</p> / Doctor of Philosophy (PhD)

It has been 10 years since the first hybrid halide perovskite photovoltaics was fabricated. Power conversion efficiency increases from the initial 3.8% to the current 25.2%. Fabrication method envolves from spin-coating to printable technology, and we deeply experience the drastic development of hybrid halide perovskite photovoltaics. Although hybrid halide photovoltaics render a variety of advantages over traditional photovoltaics, we still cannot find any practical application of these hybrid halide photovoltaics. There exist a few issues which hinder the commercialization of this type of solar cell. Among these issues, the long-term instability of hybrid halide perovskite is the main concern for the next development. This thesis expands on investigating the instability of hybrid halide perovskites from first principles. In Chapter 1, two computational methods employed in the thesis: density functional theory and Ab initio molecular dynamics are introduced. Theoretical investigations of the instability of CH3NH3PbI3 using density functional theory method are mainly conducted at 0 K. The finite temperature effect on this instability of CH3NH3PbI3 is usually neglected. In Chapter 2 of this thesis, we combined density functional calculations and additional thermodynamic data to explain the intrinsic instability of CH3NH3PbI3 under finite temperature conditions. We also analyzed the stability under humid conditions. It is shown that the aqueous solubilities of reactants play an important role in the products’ stabilities. The Born–Haber cycle of NaCl splits the enthalpy change into several components which will give a better understanding of the origin of the corresponding enthalpy change. In Chapter 3, with the extension of the Born–Haber cycle to the hybrid halide perovskites, the reaction enthalpies which govern the intrinsic instability of ionic compounds were analyzed. We proposed a criterion that helps to filter the hybrid halide perovskites with improved stability aimed for photovoltaics. Since the instability of CH3NH3PbI3 is intrinsic. The long-term instability can be settled by discovering alternative perovskite absorber. In Chapter 4, based on literature research, we propose a three-membered ring cation which has a suitable size to fit into the Pb-I framework, leading to optimal band gap for photovoltaics. Besides, the cation has a good ionization energy which will potentially render better stability. Whereas, a comprehensive study of this cyclic ring based perovskite indicates that the instability of the three-membered ring cation will make it impossible to synthesize this theoretical structure. Moisture degradation mechanisms of CH3NH3PbI3 are investigated intensively. More importantly, for practical photovoltaics, we have to imagine different situations the modules will encounter, e.g. after a couple of years, cracks appearing on the modules are inevitable, at this stage, understanding of the degradation mechanism of CH3NH3PbI3 according to liquid water becomes important. Chapter 6 elaborately describes a comprehensive degradation mechanism of CH3NH3PbI3 under liquid water. We investigate the energy barrier for the first dissolution event of CH3NH3PbI3 in water. Furthermore, thermodynamic analyses of CH3NH3PbI3 dissolution in water clearly explain the spontaneity of CH3NH3PbI3 degradation in water. Besides, different mechanisms of CH3NH3PbI3 and CsPbI3 dissolution in water are discussed. / Dissertation / Doctor of Philosophy (PhD)

First-principle calculations is a key ingredient for us to understand, improve and design new materials. Density functional theory (DFT) [1] has proven to be a very powerful tool and a number of different versions exist depending on the problem at hand. A crucial perspective brought by DFT, thanks to the Hohenberg-Kohn theorems, is that all the information needed is contained in the ground state electronic density and that the density that minimizes the energy functional is the true density. This shift the problem from solving a many-body Schrödinger equation to an easier problem of solving single-particle Kohn-Sham equations where each electron interacts with the electronic density. One can then solve the problem self-consistently, iterating until the global minimum is reached. The most expensive part computationally is the inversion of a large Hamiltonian, with the help of the Recursion Method [4]. The goal of the project was to skip this step in some of the iterations by solving the Dyson equation to get a new Green's function from the old one and the parameters used to construct the Hamiltonian. The implemented Dyson recursion algorithm, into the self-consistent process of the RS-LMTO-ASA code, indicates that we in some cases do improve convergence time of the studied systems, showing a great decrease of the number of regular Hamiltonian inversions, using linear mixing, needed to get to a low moment difference.

Acetylcholinesterase (AChE) terminates cholinergic neurotransmission by catalyzing the hydrolysis of the neurotransmitter acetylcholine (ACh). Inhibition of AChE has proven an effective treatment for the memory loss exhibited by early stage Alzheimer's disease (AD) patients; four AChE inhibitors (AChEI) have been approved by the FDA for this purpose. The first AChEI approved for the palliative treatment of AD-related memory loss was 9-amino-1,2,3,4-tetrahydroacridine (tacrine). Inhibition of AChE may present either therapeutic or toxic effects depending upon the dose administered. With the goal of discovering safe and effective pesticides to control the population of Anopheles gambiae, a malaria-transmitting mosquito indigenous to Sub-Saharan Africa, the reoptimization of the tacrine pharmacophore was undertaken. Because the optimized drug would necessarily be a poor inhibitor for human AChE (hAChE), initial ligand design focused on modification to tacrine known to negatively impact the inhibition potency for hAChE. Ultimately, an AChEI was discovered, which exhibited micromolar inhibition of Anopheles gambiae AChE (AgAChE) and essentially no potency for hAChE. Two units of this lead compound were tethered through an alkyl chain to yield a nanomolar inhibitor of AgAChE that was more than 1,100-fold selective for the mosquito enzyme over hAChE. Dimerization of an active inhibitor is an effective strategy to increase the potency and selectivity of AChEI, and many examples of tacrine hetero- and homodimers complexed to AChE can be found in the RCSB Protein Data Bank (PDB). The bond formed between the exocyclic amine moiety and the heterocyclic ring system of tacrine is analogous to an amide bond when tacrine is protonated. Therefore, the rotational profile of protonated N-alkyltacrine should exhibit a conformational profile in which dihedral angles significantly out of the plane formed by the ring system are associated with high energies relative to those when the dihedral angles are nearly coplanar with the ring system. The barrier of rotation (ΔG^‡) produced by this phenomenon in two tacrine derivatives and two quinoline derivatives was experimentally determined using dynamic 1H NMR. These values were compared to density functional theory (DFT) derived values for the same phenomenon. Furthermore, since the ΔG^‡ proved to be impossible to experimentally determine for the optimal model compound for the active site portion of tacrine dimers, N-methyltacrine, the DFT method employed for modeling the ΔG^‡ of the tacrine and quinoline analogs was used to computationally derive the entire rotational conformation diagram of N-methyltacrine. The calculated values were then used to comment on the relative energies of adopting certain conformations found in the X-ray crystal structures of dimer/AChE complexes. / Ph. D.