Neste trabalho, foram caracterizados os estados eletrônicos fundamental e excitados de mais baixa energia dos sistemas 1;3[H,C,As]. Para isso, foram empregados vários métodos ab initio de estrutura eletrônica (MP2, CCSD(T), CCSD(T)-F12b e MRCISD) aliados a extensos conjuntos de funções de base consistentes na correlação (aug-cc-pVnZ, em que n = D, T, Q e 5). Buscando uma acurácia ainda maior, os resultados obtidos foram extrapolados para o limite do conjunto de base completa (CBS). O estado X1Σ+ da molécula HCAs e o estado eletrônico fundamental do sistema 1[H,C,As], com as seguintes distâncias internucleares: rHC=1,0748 Å e rCAs=1,6602 Å; para as frequências harmônicas, obtivemos ω1(&#963)=1068 cm-1, ω2(π)/ω3(&#960)= 626 cm-1 e ω4(σ)=3310 cm-1 no nível de teoria CCSD(T)-F12-CBS. A espécie 1Σ+ HAsC e um ponto de sela de segunda ordem sobre a superfície de energia potencial (localizado a 75,24 kcal.mol-1 do X1Σ+ HCAs), ou seja, chegamos a conclusão que esta espécie, neste estado eletrônico, em fase gasosa, não existe. Já para os estados tripletos, ha isomerização, sendo que o 13A\' HCAs e o 13A\' HAsC foram caracterizados como mínimos com uma energia relativa ao mínimo global de 59,27 kcal.mol-1 e 88,22 kcal.mol-1, respectivamente. Além disso, exploramos os canais de dissociação destas espécies no nível de teoria CCSD(T). Foram ainda calculadas as frequências fundamentais para os estados do HCAs e do HAsC, como também investigada a inclusão da correlação dos elétrons do caroço nos parâmetros estruturais, vibracionais e energéticos. Estimamos o calor de formação (ΔH0f) a 0 e 298,15 K para as espécies CH, AsH, CAs e HCAs, sendo que a maioria desses valores ainda não e conhecida na literatura. Para o X1Σ+ HCAs, obtivemos um valor de ΔH0f igual a 71,22 kcal.mol-1 a 0 K e 70,38 kcal.mol-1 a 298,15 K. Calculamos o potencial de ionização da molécula HCAs utilizando varias metodologias teóricas, obtendo valores muito próximos aos experimentais, por exemplo, o CCSD(T)-aVTZ forneceu 9,90 eV frente ao valor experimental de 9,8 eV. Os estados eletrônicos excitados singleto e tripleto das espécies HCAs e HAsC foram também caracterizados com a obtenção de dados estruturais, vibracionais e energéticos. A maioria dos dados das espécies HCAs e HAsC nesta dissertação são inéditos na literatura química. / In this work, the ground state and low-lying excited electronic states of system 1;3[H,C,As] were investigated theoretically. Several ab initio molecular electronic structure theory were employed (MP2, CCSD(T), CCSD(T)-F12b e MRCISD) along with extensive correlation-consistent basis sets (aug-cc-pVnZ, n= T, Q e 5). Seeking increasing accuracy, further extrapolation of the results to the complete-basis-set (CBS) limit were carried out. The ground electronic state of 1[H,C,As] is the 1Σ+ HCAs specie, with internuclear distances of rHC=1.0748 Å and rCAs=1.6602 Å, and with harmonic vibrational frequencies ω1(&#963)=1068 cm-1, ω2(π)/ω3(&#960)= 626 cm-1 ω4(σ)=3310 cm-1, at the CCSD(T)-F12-CBS level theory. The electronic state 1Σ+ HAsC is a second-order saddle point on the potential energy surface (located at 75.24 kcal.mol-1 above HCAs), thus providing evidence that this species does not exist in gas phase. However, there is isomerization for triplet electronic states 13A\' HCAs to 13A\' HAsC, with energy relative to global minimum of 59,27 kcal.mol-1 e 88,22 kcal.mol-1, respectively. Fundamental frequencies and the effects of correlation of core electrons in structural, vibrational, and energetic parameters were also evaluated for HCAs and HAsC. Furthermore, the dissociation channels of these species were also evaluated at the CCSD(T)-CBS level theory. The heats of formations (ΔH0f), at 0 and 298,15 K, for the species CH, AsH, CAs and HCAs, were estimated; for most of them these results are inexistent in the literature. For X1Σ+ HCAs, we obtained 71.22 kcal.mol-1 at 0 K and 70.38 kcal.mol-1 at 298.15 K for ΔH0f. The ionization potential was also calculated by several theoretical methodologies, and the results are close to the experimental data; using CCSD(T)-aVTZ, we predicted a value of 9,9 eV, in close agreement with experimental value of 9,8 eV. The singlet and triplet electronic excited states of HCAs and HAsC were investigated and their structural, vibrational and energetic properties evaluated. Most of the results of this work are new in the chemistry literature.

Chien Siu-Hung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references. / Abstracts in English and Chinese. / Abstract (English) / Abstract (Chinese) / Acknowledgements / Table of Contents / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- The Gaussian-2 Method / Chapter 1.2 --- The Gaussian-3 Method / Chapter 1.3 --- The G3 Method with Reduced Moller-Plesset Order and Basis Set / Chapter 1.4 --- Calculated Thermochemical Data / Chapter 1.5 --- Remark on the Location of Transition State / Chapter 1.6 --- Scope of the Thesis / Chapter 1.7 --- References / Chapter Chapter 2 --- "Energetics and Structures of the Carbonyl Chloride Radical, Oxalyl Chloride, and Their Cations" --- p.6 / Chapter 2.1 --- Introduction / Chapter 2.2 --- Computational Methods / Chapter 2.3 --- Results and Discussion / Chapter 2.3.1 --- Carbonyl Chloride and Its Cation / Chapter 2.3.2 --- The anti and syn Conformers of Oxalyl Chloride and Oxalyl Chloride Cation / Chapter 3.3.3 --- The anti and gauche Conformers of (ClCO) 2 and the TS Linking Them / Chapter 2.4 --- Conclusions / Chapter 2.5 --- Publication Note / Chapter 2.6 --- References / Chapter Chapter 3 --- "An Isomeric Study of N5, N5+，and N5- : A Gaussian-3 Investigation" --- p.17 / Chapter 3.1 --- Introduction / Chapter 3.2 --- Computational Methods / Chapter 3.3 --- Results and Discussion / Chapter 3.3.1 --- "The N5 Isomers """ / Chapter 3.3.2 --- The N5+ Isomers / Chapter 3.3.3 --- The N5- Isomers / Chapter 3.3.4 --- Comparison of the G3 and G3(MP2) Results / Chapter 3.4 --- Conclusions / Chapter 3.5 --- Publication Note / Chapter 3.6 --- References / Chapter Chapter 4 --- Thermochemistry of Hydrochlorofluorosilanes : An Ab Initio Gaussian-3 Study --- p.28 / Chapter 4.1 --- Introduction / Chapter 4.2 --- Computational Methods / Chapter 4.3 --- Results and Discussion / Chapter 4.3.1 --- Heats of Formation for Neutral HCFSis / Chapter 4.3.2 --- Ionization Energies / Chapter 4.3.3 --- Electron Affinities / Chapter 4.3.4 --- Proton Affinities / Chapter 4.3.5 --- Acidities / Chapter 4.3.6 --- G3 versus G3(MP2) / Chapter 4.4 --- Conclusions / Chapter 4.5 --- Publication Note / Chapter 4.6 --- References / Chapter Chapter 5 --- A Gaussian-3 Study of the Photodissociation Channels of Thiirane --- p.48 / Chapter 5.1 --- Introduction / Chapter 5.2 --- Computational Methods / Chapter 5.3 --- Results and Discussion / Chapter 5.3.1 --- The Heats of Reactions / Chapter 5.3.2 --- The Dissociation Channels Taking Place at the Ground State / Chapter 5.3.3 --- The Dissociation Channels Taking Place at Excited States / Chapter 5.4 --- Conclusions / Chapter 5.5 --- References / Chapter Chapter 6 --- A Gaussian-3 Study of the VUV Photoionization and Photodissociation of Chloropropylene Oxide --- p.59 / Chapter 6.1 --- Introduction / Chapter 6.2 --- Computational Methods / Chapter 6.3 --- Results and Discussion / Chapter 6.3.1 --- Ionization Energy / Chapter 6.3.2 --- Dissociation Channels / Chapter 6.4 --- Conclusions / Chapter 6.5 --- Publication Note / Chapter 6.6 --- References / Chapter Chapter 7 --- Conclusions --- p.69 / Appendix A The Gaussian-n (n=l-3) Theoretical Models --- p.71 / Chapter A.1 --- The G1 and G2 Theories / Chapter A.2 --- The G3 Theory / Chapter A.3 --- The G3(MP2) Theory / "Appendix B Calculation of Enthalpy at 298 K,H298" --- p.74

Li Chi-Lun. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references. / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgements --- p.iii / Table of Contents --- p.iv / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Remark on the Location of Transition Structures --- p.1 / Chapter 1.2 --- Scope of the Thesis --- p.1 / Chapter 1.3 --- References --- p.2 / Chapter Chapter 2 --- "A Gaussian-3 Study on the Photodissociation of Phenylacetylene and Formation of 1,3,5-Hexatriyne" --- p.5 / Chapter 2.1 --- Introduction --- p.6 / Chapter 2.2 --- Computational Method --- p.7 / Chapter 2.3 --- Results and Discussion --- p.8 / Chapter 2.3.1 --- Phenylacetylene → Acetylene + Benzyne --- p.8 / Chapter 2.3.2 --- "Phenylacetylene → Acetylene + (Z)-3 -Hexene- 1,5-diyne" --- p.9 / Chapter 2.3.3 --- "(Z)-3-Hexene-l,5-diyne / (E)-3 -Hexene-1,5-diyne → 1,3,5-Hexatriyne and Molecular Hydrogen" --- p.9 / Chapter 2.3.4 --- Evaluation of Thermochemical Data --- p.10 / Chapter 2.3.5 --- Evaluation of Ion Energetics Data --- p.10 / Chapter 2.4 --- Conclusions --- p.10 / Chapter 2.5 --- References --- p.11 / Chapter Chapter 3 --- A Gaussian-3 Study of the Photoionization and Dissociative Photoionization Channels of Cyanoethylene --- p.21 / Chapter 3.1 --- Introduction --- p.22 / Chapter 3.2 --- Computational Method --- p.22 / Chapter 3.3 --- Results and Discussion --- p.23 / Chapter 3.3.1 --- Bond Cleavage Reactions --- p.23 / Chapter 3.3.2 --- Dissociation Channels Involving Transition Structures --- p.25 / Chapter 3.4 --- Conclusions --- p.25 / Chapter 3.5 --- References --- p.26 / Chapter Chapter 4 --- "A Gaussian´ؤ2 Study of Structures, Energetics, and Reactions of C2H3S- Anions" --- p.34 / Chapter 4.1 --- Introduction --- p.35 / Chapter 4.2 --- Computational Method --- p.35 / Chapter 4.3 --- Results and Discussion --- p.36 / Chapter 4.3.1 --- Thioformylmethyl Anion --- p.37 / Chapter 4.3.2 --- Thioacetyl Anion --- p.37 / Chapter 4.3.3 --- Cyclic C2H3S- Ions --- p.37 / Chapter 4.3.4 --- CH2SCH- --- p.38 / Chapter 4.3.5 --- 2-Thiovinyl Anion --- p.38 / Chapter 4.3.6 --- 1-Thiovinyl Anion --- p.39 / Chapter 4.3.7 --- Intramolecular Rearrangements of 1- --- p.39 / Chapter 4.3.8 --- Intramolecular Rearrangements of Cyclic C2H3S- ions and 1´ؤThiovinyl Anion --- p.39 / Chapter 4.4 --- Conclusions --- p.40 / Chapter 4.5 --- References --- p.40 / Chapter Chapter 5 --- "Theoretical Studies of Transition Metal Complexes: Bond Energies for Fe+-D, Fe+-H2O, and Fe+-CO" --- p.51 / Chapter 5.1 --- Introduction --- p.52 / Chapter 5.2 --- Computational Method --- p.53 / Chapter 5.3 --- Results and Discussion --- p.54 / Chapter 5.3.1 --- Fe+-D --- p.54 / Chapter 5.3.2 --- Fe+-CO --- p.54 / Chapter 5.3.3 --- Fe+-H2O --- p.55 / Chapter 5.4 --- Conclusions --- p.56 / Chapter 5.5 --- References --- p.57 / Chapter Chapter 6 --- Ab Initio Study of the Charge-Delocalized and -Localized Form of the Rhodizonate Dianion --- p.61 / Chapter 6.1 --- Introduction --- p.62 / Chapter 6.2 --- Computational Method --- p.63 / Chapter 6.3 --- Results and Discussion --- p.64 / Chapter 6.3.1 --- Charge-Localized C6062- --- p.64 / Chapter 6.3.2 --- Charge-Delocalized C6062- --- p.64 / Chapter 6.4 --- Conclusions --- p.65 / Chapter 6.5 --- References --- p.66 / Chapter Chapter 7 --- "Franck-Condon Factor Simulated Spectra of the Cations of cis-2-Butene,trans-2-Butene, Isobutene, cis-Dichloroethene, and trans-Dichloroethene" --- p.71 / Chapter 7.1 --- Introduction --- p.72 / Chapter 7.2 --- Computational Method --- p.72 / Chapter 7.3 --- Results and Discussion --- p.73 / Chapter 7.3.1 --- cis-2-Butene Cation --- p.73 / Chapter 7.3.2 --- trans-2-Butene Cation --- p.74 / Chapter 7.3.3 --- cis-Dichloroethene Cation --- p.75 / Chapter 7.3.4 --- trans-Dichloroethene Cation --- p.76 / Chapter 7.3.5 --- Isobutene --- p.76 / Chapter 7.4 --- Conclusions --- p.77 / Chapter 7.5 --- References --- p.77 / Chapter Chapter 8 --- Conclusions --- p.88 / Appendix A --- p.89 / Appendix B --- p.91 / Appendix C --- p.92

本論文主要研究了磁性雜質在三種不同的石墨烯體系中的性質。這三個體系分別是：伯爾納堆垛（Bernal stacked）結構的雙層石墨烯(bilayer graphene)，包含空位的雙層石墨烯和zigzag 型石墨烯納米帶(graphene nanoribbon)。本文中主要運用的數值方法為Hirsch-Fye 量子蒙特卡羅方法 （quantum Monte Carlo method）和貝葉斯最大熵方法（Bayesian Maximum Entropy method）。 / 在論文的第二章會詳細介紹這兩種方法。 我們用量子蒙特卡羅方法得到的結果是準確的，因為原則上我們可以計算無窮大的體系， 並且不需要采用任何近似去處理多體問題。 / 第三章，我們討論磁性雜質在伯爾納堆垛結構的雙層石墨烯中的性質。我們主要考慮兩種情況：磁性雜質分別位於A 亞晶格和B 亞晶格上。我們發現類似于單層石墨烯中的情況，隨著化學勢的變化，雜質原子的磁矩在一定的能量範圍內可調。但是由於雙層石墨烯中的兩套亞晶格不等價，雜質的性質很大程度上取決於雜質的位置，並且其區別隨著s-d 混合強度的增加和d 電子的關聯能的減少而變得更加明顯。我們也討論了雜質原子的譜密度和s-d 電子之間的關聯函數。我們的所有結果都體現雜質性質對空間位置的相同依賴關係。 / 在第四章，我們研究在伯爾納堆垛結構的雙層石墨烯中磁性原子在空位附近的性質。在雙層石墨烯系統中，空位引起的局域態的性質依舊取決於空位所屬的亞晶格。這也是由於兩套晶格的不等價性。我們討論雜質在空位周圍時雜質性質對空位所屬亞晶格的依賴關係，以及兩種缺陷之間的相對位移對雜質磁性的影響。當磁性原子附著在空位的最近鄰格點上時，A 亞晶格上的空位會對雜質原子的磁矩有更強的抑制。而隨著磁性原子和空位之間的距離增加，局域態對磁性原子的影響迅速衰減，並且B 亞晶格上的空位對雜質的影響相對長程一些。 / 在第五章，我們討論兩個磁性雜質在zigzag 型石墨烯納米帶邊緣上的間接互作用隨化學式的變化。由於在zigzag 型石墨烯納米帶邊緣有局域的零能態，雜質的磁矩被嚴重抑制，兩個雜質原子之間的自旋-自旋關聯函數也與石墨烯中的行為有很大區別。有趣的是，當兩個雜質附著在兩個最近鄰的碳原子上時，隨著化學式的降低，雜質之間的反鐵磁關聯會有一個顯著增強再降低的過程。我們也討論了自旋關聯隨著距離的變化，并發現關聯強度隨著距離的變化迅速衰減。 / 最後再第六章，我們會本論文中的內容進行總結和討論。 / In this research thesis, we study the magnetic properties of Anderson impurities in three different graphene based systems: pure Bernal stacked bilayer graphene, Bernal stacked bilayer graphene with a vacancy and graphene ribbon with zigzag edges. Quantum Monte Carlo method based on the Hirsch-Fye algorithms are used to obtain the basic thermodynamic quantities, and the Bayesian maximum entropy method is used to obtain the spectral densities of the impurity sites. We discuss the numerical methods in chapter 2. / In chapter 3, we investigate the local moment formation of a magnetic impurity in Bernal stacked bilayer graphene. In the two cases we study, impurity is placed on top of the two different sublattices in bilayer system. We find that similar to the monolayer case, magnet moment of the impurity could still be tuned in a wide range through changing the chemical potential. However, the property of the impurity depends strongly on its location due to the broken symmetry between the two sublattices. This difference becomes more apparent with the increase in the hybridization and decrease in the on-site Coulomb repulsion. Additionally, we calculate the impurity spectral densities and the correlation functions between the impurity and the conduction-band electrons. All the computational results show the same spatial dependence on the location of the impurity. / In chapter 4, we address the issue of single magnetic adatom located in the vicinity of a vacancy in bilayer graphene with Bernal stacking. In bilayer system, the property of vacancy induced localized states depends on whether the vacancy belongs to A or B sublattice. The magnetic impurity is placed in the vicinity of the vacancy, and the dependence of its magnetic property on the location of the vacancy is discussed. We switch the values of the chemical potential and study the basic thermodynamic quantities and the correlation functions between the magnetic adatom and the carbon sites. When the magnetic adatom is located on the nearest site of the vacancy, the local moment is more strongly suppressed if the vacancy belongs to the sublattice A. The influence of the zero-energy localized states decays fast as the displacement between the two defects increases, and the effect of B vacancy on the local moment of magnetic adatom is relatively long ranged. / In chapter 5, we examine the behavior of the indirect magnetic interactions of two magnetic impurities on the zigzag edge of graphene ribbon as a function of chemical potential. We find that the spin-spin correlation between two adatoms located on the nearest sites are drastically suppressed at the Dirac energy, and as we lower the chemical potential, the antiferromagnetic correlation is first enhanced and then decreased in values. If the two adatoms are adsorbed on the sites belong to the same sublattice, we find similar behavior of spin-spin correlation except for a cross over from ferromagnetic to antiferromagentic correlation in the vicinity of zero-energy. We also calculated the weight of the wave functions and basic thermodynamic quantities for various values of parameters, and compare the results with their counterpart in bulk graphene. / Finally in chapter 6, we summarize our results. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Sun, Jinhua = 石墨烯體系中磁性雜質的量子蒙特卡羅研究 / 孫金華. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 92-[100]). / Abstract also in Chinese. / Sun, Jinhua = Shi mo xi ti xi zhong ci xing za zhi de liang zi Mengte Kaluo yan jiu / Sun Jinhua. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Electronic properties of graphene --- p.1 / Chapter 1.1.1 --- Band structure --- p.1 / Chapter 1.1.2 --- Dirac fermions --- p.4 / Chapter 1.1.3 --- Mesoscopic effects --- p.4 / Chapter 1.1.4 --- Superconductivity in graphene --- p.6 / Chapter 1.2 --- Potential applications --- p.7 / Chapter 1.2.1 --- In semiconductors --- p.8 / Chapter 1.2.2 --- In spintronics --- p.10 / Chapter 1.3 --- Magnetic impurities in graphene based systems --- p.11 / Chapter 1.4 --- Outline of this thesis --- p.13 / Chapter 2 --- Numerical method --- p.15 / Chapter 2.1 --- Quantum Monte Carlo method based on Hirsch-Fye algorithm . --- p.15 / Chapter 2.1.1 --- Anderson impurity model Hamiltonian --- p.16 / Chapter 2.1.2 --- Key steps of Hirsch-Fye algorithm --- p.16 / Chapter 2.1.3 --- Basic thermodynamic quantities --- p.23 / Chapter 2.1.4 --- Extended Hirsch-Fye algorithm --- p.24 / Chapter 2.1.5 --- Two-impurity case --- p.25 / Chapter 2.1.6 --- Relation to the determinant quantum Monte Carlo method based on BSS algorithm --- p.27 / Chapter 2.2 --- Bayesian maximum entropy method --- p.30 / Chapter 2.2.1 --- Bayesian inference --- p.31 / Chapter 2.2.2 --- Maximum entropy analysis --- p.34 / Chapter 3 --- Magnetic impurity in Bernal stacked bilayer graphene --- p.37 / Chapter 3.1 --- Introduction --- p.37 / Chapter 3.2 --- Density of states and local density of states --- p.38 / Chapter 3.3 --- Results --- p.43 / Chapter 3.3.1 --- Basic thermodynamic quantities --- p.43 / Chapter 3.3.2 --- Spectral densities --- p.48 / Chapter 3.3.3 --- Correlation functions --- p.50 / Chapter 3.4 --- Summary --- p.52 / Chapter 4 --- Magnetic impurity in the vicinity of a vacancy in bilayer graphene --- p.54 / Chapter 4.1 --- Introduction --- p.54 / Chapter 4.2 --- Zero-energy localized states in the vicinity of vacancy --- p.56 / Chapter 4.2.1 --- Monolayer graphene with a vacancy --- p.57 / Chapter 4.2.2 --- Bilayer graphene with vacancy --- p.58 / Chapter 4.3 --- Results --- p.60 / Chapter 4.3.1 --- Basic thermodynamic quantities --- p.61 / Chapter 4.3.2 --- Spin-spin and charge-charge correlations --- p.68 / Chapter 4.4 --- Summary --- p.69 / Chapter 5 --- Indirect exchange of magnetic impurities in zigzag graphene ribbon --- p.71 / Chapter 5.1 --- Introduction --- p.71 / Chapter 5.2 --- Density of states and local density of states --- p.73 / Chapter 5.3 --- Results --- p.76 / Chapter 5.3.1 --- Basic thermodynamic quantities --- p.77 / Chapter 5.3.2 --- Spin-spin correlation --- p.80 / Chapter 5.3.3 --- Weight of different components of the d electron wave function --- p.84 / Chapter 5.3.4 --- Comparison : two magnetic impurities in bulk graphene sheet --- p.85 / Chapter 5.4 --- Summary --- p.88 / Chapter 6 --- Summary and discussions --- p.89 / Bibliography --- p.92 / Chapter A --- Derivation of the input Green’s function G0(τ ) in Bernal stacked bilayer graphene --- p.101 / Chapter B --- Input Green’s function for U = 0 in bilayer graphene in the presence of a vacancy --- p.106

Lam Chow Shing. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references. / Abstracts in English and Chinese. / Thesis Examination Committee --- p.i / Abstract --- p.ii / Acknowledgements --- p.iv / Table of Contents --- p.v / List of Tables --- p.vii / List of Figures --- p.viii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- The Gaussian-3 Method --- p.1 / Chapter 1.2 --- The G3 Method with Reduced MΦller- Plesset Order and Basis Set --- p.2 / Chapter 1.3 --- Density Functional Theory (DFT) --- p.3 / Chapter 1.4 --- Calculation of Thermodynamical Data --- p.3 / Chapter 1.5 --- Remark on the Location of Transition Structures --- p.3 / Chapter 1.6 --- Natural Bond Orbital (NBO) Analysis --- p.4 / Chapter 1.7 --- Scope of the Thesis --- p.4 / Chapter 1.8 --- References --- p.5 / Chapter Chapter 2 --- Theoretical Study of Tri-s-triazine and Its Derivatives --- p.7 / Chapter 2.1 --- Introduction --- p.7 / Chapter 2.2 --- Methods of Calculation --- p.9 / Chapter 2.3 --- Results and Discussion --- p.9 / Chapter 2.3.1. --- Property of Tri-s-triazine --- p.9 / Chapter 2.3.2. --- Substituent Effects on the Properties of the Tri-s-triazine Parent Molecule --- p.10 / Chapter 2.3.3. --- Heats of Formation of Derivatives of Tri-s-triazine --- p.20 / Chapter 2.4 --- Conclusion --- p.22 / Chapter 2.5 --- References --- p.22 / Chapter Chapter 3 --- A Gaussian-3 Study of the Dissociative Photoionization of Acetone --- p.25 / Chapter 3.1 --- Introduction --- p.25 / Chapter 3.2 --- Methods of Calculation --- p.26 / Chapter 3.3 --- Results and Discussion --- p.26 / Chapter 3.3.1. --- "Formation of m/z = 42 (CH2CO+.),43 (CH3CO+) Ions" --- p.31 / Chapter 3.3.2. --- Formation of m/z = 43 (c-CH2CHO+) and m/z = 15 (CH3+) Ions --- p.32 / Chapter 3.3.3. --- Formation of m/z = 57 (CH3COCH2+) Ions --- p.37 / Chapter 3.3.4. --- Formation of m/z = 39 (C3H3+) Ions --- p.38 / Chapter 3.4 --- Conclusion --- p.40 / Chapter 3.5 --- Publication Note --- p.40 / Chapter 3.6 --- References --- p.40 / Chapter Chapter 4 --- "A G3(MP2) Study of the C3H60+. Isomers Fragmented from l,4-Dioxane+" --- p.42 / Chapter 4.1 --- Introduction --- p.42 / Chapter 4.2 --- Methods of Calculation --- p.43 / Chapter 4.3 --- Results and Discussion --- p.44 / Chapter 4.3.1. --- "Formation of C3H60+. Isomers 1 and 2 via Fragmentation of 1,4-Dioxane+" --- p.44 / Chapter 4.3.2. --- Reaction with Acetonitrile --- p.55 / Chapter 4.3.3. --- Reaction with Formaldehyde --- p.57 / Chapter 4.3.4. --- Reaction with Ethylene --- p.61 / Chapter 4.3.5. --- Reaction with Propene --- p.63 / Chapter 4.4 --- Conclusion --- p.67 / Chapter 4.5 --- Publication Note --- p.68 / Chapter 4.6 --- References --- p.68 / Chapter Chapter 5 --- A Computational Study of the Photodissociation Channels of Chloroiodomethane --- p.71 / Chapter 5.1 --- Introduction --- p.71 / Chapter 5.2 --- Methods of Calculation --- p.73 / Chapter 5.3 --- Results and Discussion --- p.74 / Chapter 5.3.1 --- CH2C1 + I(2P1/2) and CH2C1 + I(2P3/2) Channels --- p.77 / Chapter 5.3.2 --- "CH2I + C1(2P3/2,1/2) Channel" --- p.78 / Chapter 5.3.3 --- CHI + HC1 Channel --- p.80 / Chapter 5.3.4 --- CH2 + IC1 Channel --- p.81 / Chapter 5.4 --- Conclusion --- p.82 / Chapter 5.5 --- Publication Note --- p.83 / Chapter 5.6 --- References --- p.83 / Chapter Chapter 6 --- Conclusion --- p.86 / Appendix A --- p.87 / Appendix B --- p.89

Le domaine des senseurs chimiques et biochimiques est en pleine expansion, tant au niveau de la recherche fondamentale que du design et de la fabrication de nouveaux « nez artificiels ». Les recherches actuelles visent à la mise au point de dispositifs de taille réduite permettant l’identification et la quantification d’espèces multiples, avec une réponse rapide et réversible, une détection sensible et sélective, le tout intégré dans une technologie simple et peu coûteuse. Les composantes actives des nez artificiels dont il est question ici reposent sur l’utilisation en tant que composante active de polymères et molécules conjugués. Les polymères conjugués sont attractifs pour leur grande sensibilité (tributaire du processus de diffusion efficace des excitations électroniques le long des chaînes) tandis que les molécules conjuguées répondent généralement favorablement au cahier des charges imposé à un senseur, dont les interactions fortes et spécifiques entre le senseur et la molécule à détecter ou encore une grande stabilité chimique et photochimique. Dans ce contexte, le but de cette thèse est d’associer polymères et molécules conjugués pour mettre au point un dispositif hybride combinant les avantages des deux composantes. Afin de caractériser ces dispositifs et de les optimiser, nous nous sommes focalisés dans un premier temps sur l’étude des propriétés géométriques, électroniques et optiques des entités séparées, que nous avons étudiées par le biais de méthodes issues de la chimie quantique. D’une part, nous avons considéré les améliorations pouvant être apportées aux détecteurs moléculaires tant au niveau des limites de détection que de ses propriétés spectroscopiques. D’autre part, nous avons mené une étude mécanistique des processus de transfert d’énergie le long de chaînes de polymères conjugués rigides, en apportant une attention particulière sur les différentes approches envisageables pour en améliorer l’efficacité (effets conformationnels, introduction d’unités à longues durées de vie, écart énergétique donneur-accepteur). Enfin, sur base des résultats obtenus pour les constituants séparés, nous avons proposé des structures chimiques de systèmes ‘hybrides’, constitués de polymères conjugués substitués en bouts de chaîne par des groupements ionophores. Ces études ont été menées en étroite collaboration avec le groupe du Prof. Noël Boens à la KULeuven, où les molécules et polymères conjuguées étudiés théoriquement dans le cadre de ce travail ont été synthétisés et caractérisés d’un point de vue spectroscopique.

The quantum chemical investigations presented in this thesis use hybrid density functional theory to shed light on the catalytic mechanisms of mononuclear non-heme iron oxygenases, accommodating a ferrous ion in their active sites. More specifically, the dioxygen activation process and the subsequent oxidative reactions in the following enzymes were studied: tetrahydrobiopterin-dependent hydroxylases, naphthalene 1,2-dioxygenase and α-ketoglutarate-dependent enzymes. In light of many experimental efforts devoted to the functional mimics of non-heme iron oxygenases, the reactivity of functional analogues was also examined. The computed energetics and the available experimental data served to assess the feasibility of the reaction mechanisms investigated. Dioxygen activation in tetrahydrobiopterin- and α-ketoglutarate-dependent enzymes were found to involve a high-valent iron-oxo species, which was then capable of substrate hydroxylation. In the case of naphthalene 1,2-dioxygenase, the reactivity of an iron(III)-hydroxperoxo species toward the substrate was investigated and compared to the biomimetic counterpart.

Direct, gas phase propylene epoxidation reactions are carried out on model slabs representing Ru-Cu(111) bimetallic and Cu(111) metallic catalyst surfaces with periodic Density Functional Theory (DFT) calculations. Ru-Cu(111) surface is modelled as a Cu(111) monolayer totally covering the surface of Ru(0001) surface underneath. The catalytic activity is evaluated following the generally accepted oxametallacycle mechanism. It is shown that the Ru-Cu(111) surface has a lower energy barrier (0.48 eV) for the stripping of the allylic hydrogen of propylene and a higher energy barrier (0.92 eV) towards propylene oxametallacycle (OMMP) formation compared to 0.75 eV barrier for OMMP formation and 0.83 eV barrier for allylic hydrogen stripping on Cu(111), and thus ineffective for propylene oxide production based on the investigated models and mechanism. In order to analyze the observed inability of the Ru-Cu(111) surface to selectively catalyze propylene oxide formation, a Lewis acid probe, SO2, was adsorbed on the oxygenated Cu(111) and Ru-Cu(111) surfaces and the binding energies, a measure of the basicity of the chemisorbed oxygen on the surfaces, on two systems are compared. As a conclusion, the reason behind this ineffectiveness of the Ru-Cu(111) surface for selectively catalyzing propylene epoxidation is related to the higher basicity of the atomic oxygen adsorbed on Ru-Cu(111) compared to the oxygen on Cu(111). The results are consistent both with recent publications about propylene epoxidation and previous studies performed about the structure of Ru-Cu catalysts.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 115-124).

Computational modelling of chemical systems is most easily carried out in the vacuum for single molecules. Accounting for environmental effects accurately in quantum chemical calculations, however, is often necessary for computational predictions of chemical systems to have any relevance to experiment. This PhD thesis focuses on accounting for environmental effects in quantum chemical calculations by quantum mechanics/ molecular mechanics (QM/MM) approaches, taking on diverse examples from the solid state, the liquid phase and the protein environment. The methods are applied to compute a variety of properties from transition metal NMR properties of molecular crystals and enzymes, via conformational properties of zwitterions in aqueous solution, to an intramolecular amidation reaction in peptides. Chapter 3 concerns QM/MM calculations of molecular properties in the solid state, both molecular crystals and metalloenzymes, with a focus on transition metal chemical shift and EFG properties. We demonstrate that solid-state effects on such properties in molecular crystals can be accounted for by a simple general black-box QM/MM approach. We also describe preliminary QM/MM calculations of 51V anisotropic NMR properties for a vanadium-dependent enzyme. In Chapter 4 the focus is on solvent effects on the conformational preference of a small zwitterionic molecule, 3F-γ-aminobutyric acid (3F-GABA), calculated using QM/MM molecular dynamics simulations. NMR spin-spin coupling constants in solution are also calculated. Our simulations highlight the difficulty of accounting for solvation effects well enough to achieve agreement with experimental observations. Chapter 5 concerns the reaction mechanism of an intramolecular amidation reaction in a bacterial peptide, predicted by QM/MM calculations. We predict a reaction mechanism that accounts well for the experimental observations both for the wild-type and mutants. We demonstrate that environmental effects can often be satisfactorily accounted for by QM/MM approaches, thus helping to bridge the gap between theory and experiment.