A new multiresolution scheme based on interpolating scaling function(ISF) on adaptive gridding(AG) shows promising in the first principle calculation. We also use ISFs on solving Poisson equation(PE), and find good approximations on the expansions of the second derivatives of ISFs. It is simpler than the wavelet scheme and fully implements the fast wavelet transformation so that the method is very suitable to problems with frequently updating charge density such as the first-principle calculation in electronic structures in atoms, molecules, and solids. Although the scheme is similar to the AG scheme on real space, the ISFs can represent fields more effectively and it needs less grids than the scheme of real space does. This simple and effective method provides an alternative to both the real space and the wavelet methods in the first principle calculation. Also, The method can be easily parallelized due to the block structure of the grid layout.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24616号 / 工博第5122号 / 新制||工||1979(附属図書館) / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 田中 功, 教授 奥田 浩司, 教授 中村 裕之 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Multicomponent high-entropy and amorphous alloys represent relatively new classes of structural materials with complex atomic configurations and exceptional mechanical properties. However, there are several knowledge gaps in the relationships between their atomic structure and mechanical properties. Understanding these critical relationships will enable novel alloy design and tailoring of their mechanical properties for desired engineering applications. In this dissertation, first-principles calculations and molecular dynamics simulations are applied to investigate the local atomic configurations and ordering in high-entropy and amorphous alloys. Our findings suggest that fluctuations in local atomic configurations for high- entropy alloys result in significant changes in stacking fault energy, twin energy, dislocation behavior, dislocation-twin interactions, and critical shear stress. For amorphous alloys or metallic glasses, the short-range order (SRO) and medium-range order (MRO) were found to play decisive roles in determination of their mechanical properties. Structural relaxation was found to lead to shear localization, which was attributed to free volume change and evolution of SRO and MRO to more brittle nature. In contrast, rejuvenated metallic glasses had relatively large and uniform free volume distribution giving rise to homogeneous flow and increased plasticity.

Made available in DSpace on 2016-08-18T18:19:27Z (GMT). No. of bitstreams: 1 Edson Nunes Costa Paura.pdf: 4371864 bytes, checksum: eb38ecee742cbbf15a438597d2ab23de (MD5) Previous issue date: 2010-03-10 / In this work the structural and energetic properties of C60@(17,0) carbon peapods bundle were studied under hydrostatic pressure. To study such properties we use ab initio quantum calculations based on the density functional theory in the approach of the generalized gradient approximation. All simulations were performed using the SIESTA code. The results indicate that the bundles in the study present two phase transitions, the first transitions occurring in range 2.0 GPa - 3.0 GPa and the second occurring around 15.0 GPa, in good agreement with the literature. The analysis of electronics properties through energy bands indicates that the ( it Peapods) from P < 3.0 GPa are semiconductor with visible reduction in the energy gap, while above 3.0 GPa the systems become metallic. Also the energy levels of the band are changed according to the hydrostatic pressure is being applied, such as breaking the degeneracy of the levels of valence bands and conduction bands. To each interval of pressure applied we also calculated the relative volume percentual and cohesive energy as a function of pressure. / Neste trabalho foram estudadas as propriedades estruturais, energéticas e eletrônicas de bundles de peapods de carbono C60@(17,0) submetidos à variação de pressão hidrostática. Para estudar tais propriedades, utilizamos cálculos quânticos de primeiros princípios baseados na teoria do funcional da densidade com a aproximação do gradiente generalizado. Todas as simulações foram realizadas com a utilização do código SIESTA. Os resultados encontrados indicam que os bundles em estudo sofrem duas transiçõesde fase, a primeira ocorrendo no intervalo de pressão 2,0 - 3,0 GPa e a segunda ocorrendo entre 15 - 20.0 GPa, em perfeito acordo com a literatura.A análise das propriedades eletrônicas via estrutura de bandas de energia, indica que os peapods para P < 3,0 GPa são semicondutor com visível diminuição do gap de energia, enquanto que acima de 3,0 GPa os sistemas passam a ser metálico. Também os níveis de energia da banda são alterados conforme a pressão hidrostática está sendo aplicada, como por exemplo, a quebra na degenerecencia dos níveis das bandas de valência e condução. Para cada intervalo de pressão aplicada calculamos o percentual do volume relativo e a energia coesiva do sistema.

Made available in DSpace on 2016-08-18T18:19:29Z (GMT). No. of bitstreams: 1 Samir Silva.pdf: 2648726 bytes, checksum: c089ee5506a5e19afed5dafba9cbc09f (MD5) Previous issue date: 2007-08-21 / In this work were studied the electronic, vibrations and structural properties of boron nitride nanotube bundles (16,0), (12,0) and (8,0), when submitted to the hydrostatic pressure changes. To study such properties, we used the ab initio method employing density functional theory in the approach of the generalized gradient approximation. All the simulations were performed using of the siesta code. The obtained results showed that the circular cross section of each one of the studied bundles undergoes a deformation (elliptic) when applied pressure reaches the value of P > 1,0 GPa for the bundle (16,0), P > 2,0 GPa for the bundle (12,0) and for values greater then 6,5 GPa for the bundle (8,0). For each pressure interval it was calculated the percent relative volume, cohesive energy, modes of vibrations and the band structures. The analysis of the electronic properties, through the band structures, indicates that the characteristics semiconducting of boron nitride nanotubes is preserved during the pressure increasing. / Neste trabalho foram estudadas as propriedades eletrõnicas, vibracionais e estruturais de bundles de nanotubos de nitreto de boro (16,0), (12,0) e (8,0) submetidos à variação de pressão hidrostástica. Para estudar tais propriedades, utilizamos o método ab initio com uso da teoria do funcional da densidade na aproximação do gradiente generalizado. Todas simulações foram realizadas com a utilização do código siesta. Com os resultados encontrados foi observado que a seção transversal circular de cada um dos bundles estudados sofre uma deformação (elíptica) quando a pressão aplicada atinge o valor de P > 1,0 GPa para o bundles (16,0), P > 2,0 GPa para o bundles (12,0) e P > 6,5 GPa para os bundles (8,0). Para cada intervalo de pressão aplicada calculamos o percentual do volume relativo, energia coesiva, modos vibracionais e a estrutura de bandas. A análise das propriedades eletrônicas, através da estrutura de bandas, indica que as características semicondutoras dos nanotubos de nitreto de boro são preservadas durante o aumento da pressão.