Calculamos a estrutura eletrônica de heteroestruturas semicondutoras III-V e II-VI na aproximação da função envelope, usando o método k.p, na presença de campos elétricos e magnéticos externos. Para isso desenvolvemos um método numérico baseado na técnica das diferenças finitas e no método da potência inversa para resolvermos a equação de massa efetiva. As principais características desse método são a estabilidade, a rápida convergência e a possibilidade de calcular os estados ligados de poços quânticos com formas arbitrárias na presença de campos elétricos e magnéticos. Investigamos inicialmente o tunelamento ressonante de portadores em um poço quântico duplo assimétrico de GaAs/GaAlAs na presença de um campo elétrico aplicado na direção de crescimento e de um campo magnético aplicado no plano perpendicular. Mostramos como as relações de dispersão de um poço quântico simples podem ser obtidas experimentalmente da curva do campo elétrico versus campo magnético ressonante e como, para determinadas intensidades desses campos, podemos colocar os estados eletrônicos e de buracos em ressonância simultaneamente, isto é, mostramos a possibilidade de termos o tunelamento ressonante de éxcitons. Investigamos também o tunelamento ressonante de portadores em um poço quântico duplo assimétrico de CdTe/CdMnTe na presença de um campo elétrico e de um campo magnético aplicados na direção de crescimento. Mostramos então como podemos obter o tunelamento ressonante de elétrons, buracos e também de éxcitons. Outro problema estudado foi a anisotropia do efeito Zeeman com a direção do campo magnético aplicado em um poço quântico simples de CdTe/CdMnTe. Calculamos os níveis de energia e as transições eletrônicas desse sistema em função da intensidade e da direção do campo magnético. Em todos os casos fazemos uma comparação dos nossos resultados com dados experimentais apresentados na literatura. / The electronic structure of III-V and II-VI semiconductor heterostructures has been calculated in the envelope function approximation using the k.p method in the presence of external electric and magnetic fields. A numerical method based on the technique of the finite differences and in the inverse power method has been developed to solve the effective-mass equation. The main features of this method are stability, fast convergence and ability to calculate bound states of quantum wells with arbitrary shapes including electric and magnetic fields. We investigate the resonant tunneling of carriers in an GaAs/GaAlAs asymmetric double quantum well in the presence of an electric field applied in the growth direction and a magnetic field applied in the perpendicular plane. We show how the dispersion relation of a quantum well can be experimentally determined from the electric versus resonant magnetic fields curves. For certain intensities of these fields, we can make both electrons and holes resonate simultaneously, which leads to resonant tunneling of excitons. The resonant tunneling of carriers has also been investigated in a CdTe/CdMnTe asymmetric double quantum well in the presence of an electric field and a magnetic field applied both in the growth direction. For this system we show that how we can obtain resonant tunneling of electrons, holes and excitons. Finally, we have studied the anisotropy of the Zeeman Effect as a function of the direction of the magnetic field for a CdTe/CdMnTe quantum well. We calculated the energy levels and the electronic transitions of this system as a function of the intensity and the direction of the magnetic field. In all the cases we compare our results with available experimental data.

As interações intermoleculares em meio líquido foram estudadas através do uso de uma metodologia sequencial que combina simulações clássicas com cálculos de mecânica quântica. Estudamos, em ordem crescente de complexidade, os efeitos de uma carga em meio líquido, o sódio em hélio líquido e moléculas complexas (benzotriazol e aminonopurina) em meio aquoso. As estruturas do líquido foram geradas usando simulações clássicas de Monte Carlo. Os efeitos das interações soluto-solvente foram obtidos através do cálculo de propriedades eletrônicas em meio líquido. Valores médios para a energia de ligação, energia de transição eletrônica e momento de dipolo de estados eletrônico fundamental e excitados foram calculados para estruturas descorrelacionadas obtidas na simulação. A variação das propriedades dos níveis eletrônicos pode ser correlacionada com o deslocamento solvatocrômico medido diretamente para a molécula em meio líquido e em fase gasosa. Esta metodologia vem sendo usada com a combinação do método de Monte Carlo com cálculos semiempíricos. Um passo adicional dado nesta tese é a combinação do método Monte Carlo com métodos quânticos de primeiros princípios, multiconfiguracionais e baseados em teoria do funcional da densidade. Dentre as interações intermoleculares foram consideradas também as ligações de hidrogênio formadas na interação soluto-solvente. O caso específico estudado foi a hidratação do par de bases guanina-citosina. / Molecular interactions in liquid environment were studied by a sequential methodology combining classical simulations with quantum mechanical calculations. We studied, an increase of difficulty, the effects of a charge in aqueous environment, the sodium atomem liquid helium and complex molecules like benzotriazole and aminopurine in aqueous environment. The structures of the liquid were generated with classical Monte Carlo simulations. The effects of the solute-solvent interactions were obtained by electronic proprieties in liquid environment. Averaged values for interaction energies, electronic transition energies and dipole moments in fundamental and excited states were calculated with uncorrelated configurations obtained during the simulations. The change of the proprieties can be correlated with the solvatocromic shift which can be directly measured for molecules in liquid and in gas phase. This methodology was used in combination of Monte Carlo method with semi-empirical calculations. An additional step implemented in this thesis is the combination of Monte Carlo simulation with first principle calculations like multiconfigurational and density functional theory based calculations. Among the intermolecular interactions, the hydrogen bond interactions formed in the solute-solvent interaction. An specific case studied was the hydration of the guanine-cytosine base pair.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第14639号 / 工博第3107号 / 新制||工||1462(附属図書館) / 26991 / UT51-2009-D351 / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 榊 茂好, 教授 田中 庸裕, 教授 村上 正浩 / 学位規則第4条第1項該当

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第15396号 / 工博第3275号 / 新制||工||1493(附属図書館) / 27874 / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 榊 茂好, 教授 白川 昌宏, 教授 北川 進 / 学位規則第4条第1項該当

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第17162号 / 工博第3652号 / 新制||工||1555(附属図書館) / 29901 / 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 横尾 俊信, 教授 梶 弘典 / 学位規則第4条第1項該当

M.Sc. (Physics) / The way we live has been fundamentally changed by technological innovations based on optical, electronic and magnetic materials. Without the continuous increase of scienti c understanding on phenomena that occur in materials, together with the processing and synthesis of materials, these technological revolutions would be impossible. Thus, the search of new materials is still the key driving force for the continuous blooming of modern technology...

Relativistic effects are extremely important for heavy atoms and heavy atom containing molecules. Therefore, a relativistic treatment is needed when calculating molecular properties of these species. The fully- relativistic Dirac treatment involves electronic and positronic wavefunctions and a very large basis set is required. This leads to calculations that are too costly and time-consuming for larger molecules. The Zeroth-Order Regular Approximation (ZORA) is an approximation to the Dirac approach, which only deals with the electronic wavefunction. However, unfortunately this method is plagued by the gauge-dependence problem. The gauge-independent ZORA (ZORA-GI) and strictly atomic ZORA approaches provide solutions to this problem.In this work, the ZORA-GI and strictly atomic ZORA codes have been successfully implemented into the Gaussian 09 program. They have been used to calculate the bond lengths, harmonic vibrational frequencies and dissociation energies of the I2, Au2 and Pt2 diatomic molecules. The results show good agreement with experiment and previous theoretical studies. The non-relativistic, ZORA-GI, strictly atomic ZORA and pseudopotential approximations have been used to investigate the electronic structure of the actinide monoxides, AnO, and actinide monoxide cations, AnO+ (An = Th – Cm). It was found that the ground state configurations were dependent on the relativistic approximation chosen. The bond lengths, harmonic vibrational frequencies and dissociation energies were also calculated, with the ZORA methods generally outperforming the pseudopotential approximation. The first theoretical g-tensor study of the organouranium(V) complexes [U(C7H7)2]-, [U(η8-C8H8)(NEt2)(THF)]+, [U(η5-C5H5)(NMe2)3(THF)]+, [U(η8-C8H8)(NEt2)3], [U(η5-C5H5)2(NEt2)2]+ and [U(η8-C8H8)(η5-C5H5)(NEt2)2] has been carried out. It was demonstrated that the choice of density functional affects the way in which the g-tensor axes are assigned. The ground state spin density and SOMO are also sensitive to the choice of density functional. It is these factors that determine the value of the g-tensor.

Organic semiconductor interfaces are promising materials for use in next-generation electronic and optoelectronic devices. Current models for metal-organic interfacial electronic structure and dynamics are inadequate for strongly hybridized systems. This work aims to address this issue by identifying the factors most important for understanding chemisorbed interfaces with an eye towards tuning the interfacial properties. Here, I present the results of my research on chemisorbed interfaces formed between thin-films of phthalocyanine molecules grown on monocrystalline Cu(110). Using atomically-resolved nanoscale imaging in combination with surface-sensitive photoemission techniques, I show that single-molecule level interactions control the structural and electronic properties of the interface. I then demonstrate that surface modifications aimed at controlling interfacial interactions are an effective way to tailor the physical and electronic structure of the interface. This dissertation details a systematic investigation of the effect of molecular and surface functionalization on interfacial interactions. To understand the role of molecular structure, two types of phthalocyanine (Pc) molecules are studied: non-planar, dipolar molecules (TiOPc), and planar, non-polar molecules (H2Pc and CuPc). Multiple adsorption configurations for TiOPc lead to configuration-dependent self-assembly, Kondo screening, and electronic energy-level alignment. To understand the role of surface structure, the Cu(110) surface is textured and passivated by oxygen chemisorption prior to molecular deposition, which gives control over thin-film growth and interfacial electronic structure in H2Pc and CuPc films. Overall, the work presented here demonstrates a method for understanding interfacial electronic structure of strongly hybridized interfaces, an important first step towards developing more robust models for metal-organic interfaces, and reliable, predictive tuning of interfacial properties.

The main objective of the thesis is to carry out structural bioinformatics study along with usage of advanced quantum chemical methods to look at the structural stability and energetics of RNA building blocks. The main focus of the work described here lies on understanding the reasons behind the intrinsic stability of key interactions in nucleic acids. Crystal structures of RNA molecules exhibit fascinating variety of non-covalent interactions, which play an important role in maintaining the three dimensional structures. An accurate atomic level description of these interactions in the structural building blocks of RNA is a key to understand the structure-function relationship in these molecules. An effort has been made to link the conclusions drawn from quantum chemical computations on RNA base pairs in wide biochemical context of their occurrence in RNA structures. The initial attention was on the impact of natural and non-natural modifications of the nucleic acid bases on the structure and stability of base pairs that they are involved in. In the remaining sections we cover other molecular interactions shaping nucleic acids, as the interaction between ribose and the bases, and the fluoride sensing riboswitch system in order to investigate structure and dynamics of nucleic acids at the atomic level and to gain insight into the physical chemistry behind.

This dissertation contains four projects: transforming electronic structure Hamiltonian to approximating Ising-type Hamiltonian to enable electronic structure calculations by quantum annealing, quantum-assisted restricted Boltzmann machine for electronic structure calculations, hybrid quantum classical neural network for calculating ground state energies of molecules and qubit coupled cluster single and double excitations variational quantum eigensolver for electronic structure. In chapter 1 we present a general introduction of quantum computer, including a brief introduction of two quantum computing model: gate model and quantum annealing model. We also give a general review about electronic structure calculations on quantum computer. In chapter 2, we show an approximating mapping between the electronic structure Hamiltonian and the Ising Hamiltonian. The whole mapping is enabled by first enlarging the qubits space to transform the electronic structure Hamiltonian to a diagonal Hamiltonian. Then introduce ancilla qubits to transform the diagonal Hamiltonian to an Ising-type Hamiltonian. We also design an algorithm to use the transformed Hamiltonian to obtain the approximating ground energy of the original Hamiltonian. The numerical simulation results of the transformed Hamiltonian for H₂, He₂, HeH⁺, and LiH molecules match the exact numerical calculations of the original Hamiltonian. This demonstrates that one can map the molecular Hamiltonian to an Ising-type Hamiltonian which could easily be implemented on currently available quantum hardware. In chapter 3, we report a hybrid quantum algorithm employing a restricted Boltzmann machine to obtain accurate molecular potential energy surfaces. By exploiting a quantum algorithm to help optimize the underlying objective function, we obtained an efficient procedure for the calculation of the electronic ground state energy for a small molecule system. Our approach achieves high accuracy for the ground state energy for H₂, LiH, H₂O at a specific location on its potential energy surface with a finite basis set. With the future availability of larger-scale quantum computers, quantum machine learning techniques are set to become powerful tools to obtain accurate values for electronic structures. In chapter 4, we present a hybrid quantum classical neural network that can be trained to perform electronic structure calculation and generate potential energy curves of simple molecules. The method is based on the combination of parameterized quantum circuit and measurements. With unsupervised training, the neural network can generate electronic potential energy curves based on training at certain bond lengths. To demonstrate the power of the proposed new method, we present results of using the quantum-classical hybrid neural network to calculate ground state potential energy curves of simple molecules such as H₂, LiH and BeH₂. The results are very accurate and the approach could potentially be used to generate complex molecular potential energy surfaces. In chapter 5, we introduce a new variational quantum eigensolver (VQE) ansatz based on the particle preserving exchange gate to achieve qubit excitations. The proposed VQE ansatz has gate complexity up-bounded to O(<i>n</i>⁴) where <i>n</i> is the number of qubits of the Hamiltonian. Numerical results of simple molecular systems such as BeH₂, H₂O, N₂, H₄ and H₆ using the proposed VQE ansatz gives very accurate results within errors about 10^-3 Hartree.