Orientador: Roy Edward Bruns / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-09T10:57:29Z (GMT). No. of bitstreams: 1 SilvaJunior_JoaoVicozo_M.pdf: 455136 bytes, checksum: d8cb42bcd5d75c3d6dd417771ba11425 (MD5) Previous issue date: 2007 / Resumo: O momento dipolar molecular, suas derivadas e as intensidades fundamentais no espectro infravermelho dos fluoroclorometanos são determinados a partir de cargas e dipolos atômicos QTAIM, e de seus fluxos no nível MP2/6-311++G(3d,3p). A comparação dos momentos dipolares e das intensidades fundamentais no infravermelho calculados usando parâmetros QTAIM com aqueles obtidos diretamente a partir de cálculos MP2/6-311++G(3d,3p) mostra erros rms (root mean square) de 0,01 D e 5,6 km mol, e erros de 0,04 D e 23,1 km mol quando comparados com valores experimentais. As contribuições de carga, fluxo de carga e fluxo de dipolo são calculadas para todos os modos normais de vibração destas moléculas. Uma correlação negativa significativa (-0,92) é observada entre as contribuições de fluxo de carga e de fluxo de dipolo e indica que a transferência de carga de um lado para outro da molécula durante as vibrações é acompanhada por uma relaxação da densidade eletrônica que se polariza na direção oposta. Os modos normais de estiramento CF, CCl e CH destas moléculas mostram ter conjuntos de valores característicos de contribuições de carga, fluxo de carga e fluxo de dipolo. Embora as deformações FCF e ClCCl também possam ser diferenciadas umas das outras a partir dos tamanhos e sinais destas contribuições, algumas deformações HCH têm contribuições que são parecidas com aquelas das deformações ClCCl / Abstract: The molecular dipole moments, their derivatives and the fundamental infrared intensities of the fluorochloromethanes are determined from QTAIM atomic charges and dipoles and their fluxes at the MP2/6- 311++G(3d,3p) level. Root-mean-square (rms) errors of 0.01 D and 5.6 km mol are found for the dipole moments and fundamental infrared intensities calculated using QTAIM parameters when compared with those obtained directly from the MP2/6-311++(3d,3p) calculations and 0.04 D and 23.1 km mol when compared to the experimental values. Charge, charge flux and dipole flux contributions are calculated for all the normal vibrations of these molecules. A large negative correlation coefficient of -0.92 is calculated between the charge flux and dipole flux contributions and indicates that charge transfer from one side of the molecule to the other during vibrations is accompanied by relaxation with electron density polarization in the opposite direction. The CF, CCl and CH stretching normal modes of these molecules are shown to have characteristic sets of charge, charge flux and dipole flux contributions. Although the FCF and ClCCl deformation normal modes can also be discriminated from one another based on their sizes and signs of these contributions some HCH deformations have contributions that are similar to those for some of the ClCCl deformations / Mestrado / Físico-Química / Mestre em Química

Modern solid state chemistry is inconceivable without theoretical treatment of solids thanks to the availability of efficient and accurate computational methods. Being developed mainly by physicist's community and deeply rooted in the formalism of reciprocal space, they often lack connections to familiar chemical concepts, indispensable for the chemical understanding of matter. Quantum chemical topology approach is a powerful theory able to efficiently recover chemical entities from the abstract description of a system given by its density matrices. It can be used to partition any many-electron system into the atoms, using the topology of electron density or for instance into atomic shells, using the topology of ELI-D field. Various characteristics of interactions between these chemical building blocks can be obtained applying bonding indicators, e.g. from the analysis of domain-averaged properties. Quantum chemical topology methods have been extended in the current work for the applications on the diversity of theoretical methods widely used for the description of solids nowadays – from the mean field Kohn-Sham density functional theory to the reduced one-electron density matrices functional theory or from the scalar-relativistic methods to the many-component formalisms employing spinor wavefunctions. It has been shown, that they provide chemically meaningful description of the bonding which is universally applicable to any class of extended systems, be it ionic insulator, covalent solid or metal. It has been shown, that the relativistic effects on the chemical bonding can be easily revealed using extensions of bonding indicators developed in the current work. Classical chemical concepts like Zintl-Klemm concept can be easily recovered with these descriptions. Intimate connection between the class of the material and the degree of chemical bonding delocalization has been also established. All these methods have been successfully applied to the various classes of solids and delivered novel insights on their crystal structure, properties, solid state transitions and reactivity.

Orientador: Roy Edward Bruns / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-27T17:55:48Z (GMT). No. of bitstreams: 1 SilvaFilho_ArnaldoFernandesda_D.pdf: 3082631 bytes, checksum: e9ba02a9f689d66f518049735ac3117b (MD5) Previous issue date: 2015 / Resumo: No que diz respeito aos clorofluorometanos, os estiramentos e deformações C-F têm cargas atômicas que fornecem as contribuições dominantes para as intensidades totais, ainda que as suas interações com os fluxos de carga e de dipolo sejam importantes. A soma das contribuições de carga com estas interações permite estimativas muito precisas para as intensidades dos estiramentos C-F. Para os estiramentos e deformações C-H e C-Cl as contribuições de carga não são dominantes. Para os estiramentos e deformações C-H as contribuições de carga são diminuídas pelas contribuições fluxo de carga e fluxo de dipolo, bem como por suas interações. Isto é também o caso para o acetileno, que possui um dos hidrogênios mais ácidos entre todos os hidrocarbonetos. O fenômeno de transferência de carga - contrapolarização foi utilizado para determinar com precisão a intensidade de 30 vibrações (estiramentos e deformações C-H) para átomos de carbono hibridizados sp3 e sp2. A carga de equilíbrio deve ser levada em consideração para descrever intensidades envolvendo hidrogênios ligados aos carbonos hibridizados sp, ainda que efeitos de transferência de carga ¿ contrapolarização ainda sejam importantes. Para os complexos de ligação de hidrogênio, a diminuição do fluxo de carga causa um aumento na intensidade de absorção devido às interações entre termos cruzados. Para os estiramentos simétrico e antissimétrico para a água o fluxo de dipolo é determinante para o aumento de intensidade, porque os termos de carga e fluxo de carga se cancelam quase inteiramente com sua interação. Os estudos QTAIM sugerem que para as intensidades dos trímeros, dímeros e monômeros de água e HF existem funções muito complexas de parâmetros eletrônicos, mas que essas funções podem ser representadas de maneira simplificada por contribuições CCFDF do hidrogênio "ponte", responsável por maior parte das flutuações eletrônicas / Abstract: Atomic charges are dominant to the C-F stretches and bendings to total intensity, even though the interactions with charge fluxes and dipole fluxes are also important. The sum of the charge contributions with these interactions enable a very precise estimate to the intensities . For C-H and C-Cl stretches and bending charge contributions are not dominant. For the C-H stretches and bendings charge contributions are reduced by the charge flux and dipole flux interactions. This is also the case for acetylene, which has one of the most acidic hydrogens among all hydrocarbons. The charge transfer ¿ counter polarization model was used to accurately determine the intensity of 30 C-H vibrations for both sp3 and sp2 carbon atoms. The the charge contributions must be taken into account to describe intensities involving hydrogens attached to sp hybridized carbons, even though charge transfer ¿ counter polarization effects are still important. For hydrogen bonding complexes, the decrease in charge flux causes an increase in absorption intensity due to the cross interactions terms. For the symmetric and antisymmetric stretches of the water dimer the dipole flux is crucial to the intensity increase, since the terms of charge and charge flux cancel each other almost entirely .The infrared intensities for complexes can be represented in a simplified manner by the CCFDF contributions of the "bridge" hydrogen , responsible for most electronic fluctuations. / Doutorado / Físico-Química / Doutor em Ciências

Ces travaux de thèse ont pour but l’étude théorique et la caractérisation d’interactions non-covalentes par des méthodes QCT (Quantum Chemical Topology), qui sont des outils interprétatifs de chimie quantique. Plusieurs interactions furent étudiées du point de vue de la densité électronique (calculs DFT), notamment des interactions intramoléculaires entre atomes halogènes ainsi que des liaisons halogène inter- et intramoléculaires. L’analyse topologique QTAIM complétée par la décomposition énergétique IQA (Interacting Quantum Atoms) nous a permis de dévoiler la nature physique des interactions étudiées, i.e. la part d’interaction électrostatique et la part d’échange (covalence). Il a été montré que l’échange tient un rôle majeur dans la stabilisation de telles interactions et permet de rationnaliser les différentes topologies observées en terme de compétition entre canaux d’échange primaires et secondaires. Aussi, la formation et la rupture d’une liaison hydrogène au cours de transferts de protons a été étudiée grâce à la décomposition de grandeurs globales (de DFTConceptuelle) en contributions monoatomiques ; le schéma de décomposition proposé se base sur la partition QTAIM et la décomposition énergétique IQA. Cette approche permet de suivre l’évolution, le long d’un chemin réactionnel, de la contribution de chaque atome à la réactivité du système. Une nouvelle façon de caractériser les barrières d’énergie potentielle et les états de transition a ainsi été proposée. / This work aims to theoretically investigate and characterize non-covalent interactions by means of Quantum Chemical Topology (QCT) methods, which are quantum chemistry interpretative tools. Several interactions were studied from the point of view of the electron density (DFT calculations), including intramolecular interactions between halogen atoms as well as inter- and intramolecular halogen bonds. The QTAIM topological analysis complemented by the Interacting Quantum Atoms (IQA) energy decomposition revealed the physical nature of those interactions, i. e. the part of electrostatics and the part of exchange (covalency). It has been shown that exchange plays a significant role in stabilizing such interactions and enables rationalizing the different topologies observed in terms of competition between primary and secondary exchange channels. Also, the formation and breaking of a hydrogen bond during proton transfer reactions has been analyzed by utilizing an atomic decomposition of global quantities (from Conceptual DFT), the new decompositionscheme being based on the QTAIM partition and the IQA energy decomposition. This approach allows following the contribution of every atom to the reactivity of the whole system along a reaction path, introducing a new way of characterizing energy barriers and transition.

Submitted by Maike Costa (maiksebas@gmail.com) on 2017-06-20T14:41:46Z No. of bitstreams: 1 arquivototal.pdf: 4206052 bytes, checksum: 763f7d238671bd04ad2fa14a2f8e48c0 (MD5) / Made available in DSpace on 2017-06-20T14:41:46Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 4206052 bytes, checksum: 763f7d238671bd04ad2fa14a2f8e48c0 (MD5) Previous issue date: 2017-07-08 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The mesoionic compounds comprise a class of heterocycles with wide range of biological and technological applications. Despite many theoretical and experimental studies, some of their properties are still controversial or poorly understood; in particular: charge distribution, the nature of the chemical bonds in the mesoionic ring and the noncovalent interactions in mesoionic complexes. In this work, we sought to clarify these issues through the theoreticalcomputational study of 54 mesoionic compounds and 12 combinations of dimers. Compounds belonging to the 1,3-oxazol-5-one; 1,3-diazole-4-thione and 1,3-thiazole-5-thione rings have been evaluated by a combination of topological methods and charge models. Atomic, bond and ring properties and interactions in mesoionic dimers have been assessed. Results showed that the ring electron density and ring Laplacian were restricted to characteristic range of values for each group studied, which allows us the ring identification using those properties. The bond properties confirmed a prevalance of shared interactions in the mesoionic ring bonds, but with important charge transfers and significant and heterogeous π contribution. When individual atoms were considered, the different charge models exhibited similar qualitative results, but none of them agreed with existing mesoionic definitions. On the other hand, when net charges were considered in rings and fragments, the different models showed large differences and only one of them (QTAIM) agreed with one of the mesoionic definitions. Hence, it is unclear which of the charge models is the most suitable for these compounds. The assessment of mesoionic complexes revealed that interactions in dimers are favored at antiparallel orientations and in the presence of aromatic substituents, that suggests that charge separation and the groups bonded to the ring are paramount in those interactions. Finally, it is concluded that classical mesoionic models do not satisfactorily describe either the charge distribution or the π character of bonds in mesoionic rings. / Os compostos mesoiônicos constituem uma classe de heterociclos com ampla variedade de aplicações biológicas e tecnológicas. Apesar dos vários estudos teóricos e experimentais, algumas de suas propriedades são controversas ou mal compreendidas; em particular: a distribuição de carga, a natureza das ligações químicas no anel mesoiônico e as interações não covalentes em complexos de mesoiônicos. Neste trabalho, buscou-se elucidar esses pontos através do estudo teórico-computacional de 54 compostos mesoiônicos e 12 combinações de dímeros. Compostos das classes 1,3-oxazólio-5-ona; 1,3-diazólio-4-tiona e 1,3-tiazólio-5- tiona foram avaliados através de uma combinação de métodos topológicos e modelos de carga. Propriedades atômicas, de ligação, de anel e interações em dímeros de mesoiônicos foram avaliadas. Os resultados mostraram que a densidade eletrônica e o laplaciano de anel restringiram-se a faixas de valores características para cada grupo estudado, permitindo a identificação do tipo de anel através dessas propriedades. As propriedades de ligação apontaram uma prevalência de interações compartilhadas nas ligações do anel mesoiônico, mas com importante transferência de carga e uma contribuição significativa e heterogênea de caráter π. Considerando átomos individuais, os diferentes modelos de carga apresentaram resultados qualitativos similares, mas nenhum dos modelos corroborou as definições existentes de mesoiônicos quanto à carga. Por outro lado, quando cargas líquidas de anel e de fragmentos foram consideradas, os diferentes modelos apresentaram grandes discrepâncias e apenas um deles (QTAIM) mostrou-se de acordo com uma das definições de mesoiônicos. A avaliação dos complexos de mesoiônicos revelou que as interações em dímeros são favorecidas em orientações antiparalelas e na presença de substituintes aromáticos, sugerindo que a separação de cargas e os grupos ligados ao anel são fundamentais nessas interações. Por fim, conclui-se que os modelos clássicos de mesoiônico não descrevem de forma satisfatória nem a distribuição de carga nem o caráter π das ligações dos anéis mesoiônicos.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-07-03T12:42:00Z No. of bitstreams: 1 AcassioRochaSantos_DISSERT.pdf: 9390259 bytes, checksum: d25d8e92963faba78cb36774741179e4 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-07-06T11:41:22Z (GMT) No. of bitstreams: 1 AcassioRochaSantos_DISSERT.pdf: 9390259 bytes, checksum: d25d8e92963faba78cb36774741179e4 (MD5) / Made available in DSpace on 2017-07-06T11:41:22Z (GMT). No. of bitstreams: 1 AcassioRochaSantos_DISSERT.pdf: 9390259 bytes, checksum: d25d8e92963faba78cb36774741179e4 (MD5) Previous issue date: 2017-02-21 / O estudo te?rico de clusters met?licos tem despertado um interesse consider?vel, devido ? possibilidade de criar novas ligas de materiais em nanoescala, as chamadas "nanoligas". Pesquisas sobre nanoligas desempenham papel significativo na Ci?ncia de Materiais, pois, entre seus objetivos mais importantes, est?o o de prever a estabilidade das estruturas, seus modos de crescimento, bem como o de auxiliar a interpreta??o de medidas espectrosc?picas e outras medi??es experimentais. Nesse contexto, um grande n?mero de m?todos foi relatado nos ?ltimos anos para a otimiza??o do m?nimo global de grupos at?micos e moleculares, sendo um dos mais utilizados atualmente o do Algoritmo Gen?tico (doravante, GA), o qual baseia-se em princ?pios relacionados a processos evolutivos, em operadores inspirados na Teoria da Evolu??o e na Gen?tica, isto ?, na recombina??o, muta??o e sele??o natural. Particularmente, o GA com a implementa??o do potencial Gupta tem se mostrado eficiente na busca de solu??es ??timas? em problemas de otimiza??o de clusters met?licos. Esta disserta??o ? composta por cap?tulos de introdu??o, de metodologia, de abordagem te?rica (Cap. 1, 2 e 3); e tamb?m por cap?tulos que cont?m artigos sobre o tema proposto (Cap. 4, 5 e 6). No primeiro artigo (Cap. 4), analisaram-se clusters bimet?licos AlxNay (x+y?55) por meio da aplica??o do GA com a implementa??o do potencial Gupta. Com base tamb?m na aplica??o do GA, no segundo cap?tulo (Cap. 5) foram estudados clusters de AlxLiy e AlxKy (x+y ? 55). Em ambos os trabalhos, para elevar a efici?ncia do GA, introduziu-se mais dois operadores: o Aniquilador e o Hist?ria. Ao serem comparadas as estruturas obtidas por meio do GA com potencial Gupta para clusters de alum?nio puro, l?tio puro e alum?nio-l?tio com resultados recentes da literatura, verificou-se que para os sistemas Al2, Al3, Al6, Al8, Al9, Li5, Li6, Li7, Al1Li5, Al1Li7 e Al1Li8 as geometrias obtidas foram muito semelhantes ?quelas resultantes de c?lculos de funcional de densidade e ab initio[como CCSD(T)]. No terceiro artigo (Cap. 6), analisou-se um novo algoritmo gen?tico qu?ntico (Q-GA) para pequenos sistemas de clusters NaxLiy com (x+y ? 10). Constatou-se que o Q-GA apresenta maior efici?ncia na busca do m?nimo global em rela??o ao GA com o potencial Gupta. Isso porque o primeiro utiliza m?todo qu?ntico, enquanto o segundo usa um m?todo cl?ssico. Por ser mais preciso, o Q-GA possui uma abrang?ncia menor. Neste artigo, al?m de c?lculos ab inito, tamb?m foram realizados c?lculos topol?gicos a partir da Teoria Qu?ntica de ?tomos em Mol?culas (QTAIM) para as estruturas Na1Li5, Na2Li4, Na3Li3, Na4Li2 e Na5Li1, obtidas pelo Q-GA. Nessas estruturas, chama a aten??o o fato de n?o haver caminho de liga??o envolvendo diretamente os metais, sendo unidos por pseudo?tomos, com exce??o do Na5Li1. Algumas intera??es at?micas n?o foram indicadas pelo caminho de liga??o e sua an?lise foi feita pelo ?ndice de deslocaliza??o (DI). No sistema Na1Li5, os pares at?micos Na1-Li2 e Na1-Li6 t?m as intera??es mais fortes (e equivalentes ? do sistema NaLi) de todos os pares Na-Li de todos clusters NaxLiy(x+y=6); ao mesmo tempo, os outros pares Na-Li t?m intera??es dez vezes mais fracas do que aquelas do sistema NaLi. As intera??es Na-Na dos clusters Na4Li2 e Na5Li1 s?o as mais fortes quando comparadas com sistemas puros. Por fim, verificou-se que a f?rmula do grau de degeneresc?ncia do ?ndice de aromaticidade D3BIA e a carga at?mica indicaram que os ?tomos de l?tio mais pr?ximo ao ?tomo de s?dio transferem carga para esse ?ltimo. / The theoretical study of metal clusters has drawn considerable interest due to the possibility of creating new alloys from materials in nanoscale, the so-called "nanoalloys". Research on nanoalloys has had an important role in materials science, since, among some of its most relevant objectives, we may find the prediction of stability in structures, their manners of growth and further assistance in the interpretation of spectroscopic and other experimental measures. In this context, several methods have been reported in the last few years towards the global minimum optimization of atomic and molecular groups, where the Genetic Algorithm (henceforth GA) is currently considered one of the most used methods, whilst based on principles related to evolutionary processes as well as operators inspired by the Theory of Evolution and Genetics, i. e., by recombination, mutation and natural selection. The GA method in particular, and altogether with the implementation of the Gupta potential, has become efficient in the search for ?optimal? solutions for optimization problems in metallic clusters. The present dissertation is composed of chapters consisting of introduction, methodology and theoretical considerations (Chap. 1, 2 and 3), as well as of chapters containing articles on the proposed subject (Chap. 4, 5 and 6). In the first article (Chap. 4), we may find the analysis of AlxNay (x + y ? 55) bimetallic clusters through the Genetic Algorithm method with the implementation of the Gupta potential. Also based on the GA application, in the following chapter (Chap. 5) we may find a study regarding AlxLiy e AlxKy (x+y ? 55) clusters. In both works, in order to improve GA efficiency, two additional operators have been introduced: Annihilator and History. By being compared to structures obtained by means of GA with Gupta potential for pure aluminum, pure lithium and aluminum-lithium clusters in recent results from literature, it has been verified that, regarding systems Al2, Al3, Al6, Al8, Al9, Li5, Li6, Li7, Al1Li5, Al1Li7 e Al1Li8, the obtained geometries were very similar to those resulting from density functional and ab initio calculations [such as CCSD(T)]. In the third chapter (Chap. 6), we analyzed a new quantum genetic algorithm (QGA) for small cluster systems NaxLiy with (x+y ? 10). It has been observed that Q-GA presents an improved efficiency towards a global minimum regarding the GA with the Gupta potential. That has been the case since the former uses the quantum method, while the latter uses a classic method. More specifically, the Q-GA has a narrower scope. In this article, besides ab initio calculations, topological calculations were performed as well, grounded on the Quantum Theory of Atoms in Molecules (QTAIM) for the structures Na1Li5, Na2Li4, Na3Li3, Na4Li2 e Na5Li1 obtained by the Q-GA. In these structures, it is evident that there is no bonding path between the metals, since they are bonded by pseudo atoms, with the exception of the Na5Li1. Some of the atomic interactions have not been suggested by the bonding path, being their analysis performed according to the delocalization index (DI). In the Na5Li1 system, the atomic pairs Na1-Li2 and Na1-Li6 have the strongest interactions (equivalent to the NaLi system) of all Na-Li pairs in all of the NaxLiy (x+y=6) clusters; concurrently, other Na-Li pairs bear interactions ten times weaker than those from the NaLi system. The Na-Na interactions from the clusters Na4Li2 e Na5Li1 are stronger when compared to pure systems. Finally, it has been verified that the degree of degeneracy formula of the aromaticity index D3BIA and the atomic charge suggest that the lithium atoms that are closer to the sodium atom transfer charge to the latter.

The main focus of this work was to investigate substitution effects on the chemical bonding in compounds of AlB 2 -type and related structure types. Delocalization indices within the QTAIM approach and the topological analysis of the ELI functionals were used as tools to describe the bonding situation in digallides and diborides. Digallides of AlB 2 -type were found only within group I and II; for CaGa 2 (meta-stable phase), SrGa 2 , BaGa 2 , YGa 2 and LaGa 2 compounds. Within these compounds, QTAIM analysis showed similar trend as previously found in diborides. That is, along the period in the Periodic Table, metal-triel interactions increase at the expense of in-plane (triel-triel) ab interactions (Tr=triel). However, transition metal diborides adopt the AlB 2 -type up to group VI. To understand this difference, we simulated transition metal (TM) digallides and diborides up to group VI in the AlB 2 -type. Additionally, the puckered variants diborides ReB 2 and OsB 2 were also simulated in the AlB 2 -type. With filling of d shell, there is a delicate balance between increase of TM–Tr and decrease of in-plane (Tr–Tr) ab electron sharing. This balance is maintained as long as interlayer interactions in the c direction (Tr–Tr ) c and (TM–TM ) c are not relatively too high in comparison to in-plane electron sharing. In contrast to TM B 2 of AlB 2 -type, digallides in the same structure type build up strong interlayer interactions for early transition metal elements. Our results showed that within digallides, a relatively strong increase in interlayer electron sharing (Ga–Ga) c and (TM–TM ) c takes place. Such increase occurs already for ScGa 2 and TiGa 2 . On the other hand, diborides show a steady increase in electron sharing of TM –B and (TM–TM ) c , but not of (B–B) c . Therefore, it is reasonable to suggest that diborides will tend to adopt a 3D network composed of boron and transition metal atoms (ReB 2 and RuB 2 types). The additional high (Ga–Ga) c interlayer interactions indicate a tendency for digallides to form 3D networks composed only by gallium atoms, characteristic of CaGa 2 (CaIn 2 -type) and ScGa 2 (KHg 2 -type). The counterbalancing bonding effects of in-plane and out-of-plane interactions that give the chemical flexibility of the AlB 2 -type in diborides is thus disrupted in AlB 2 -type digallides by a further enhanced degree of interlayer interactions (Ga–Ga) c and (TM –TM ) c . This results in a smaller number of digallides than that of diborides in AlB 2 -type. The most conspicuous difference between diborides and digallides of AlB 2 -type is in the representation of the B – B and Ga – Ga bonds revealed by the ELI- D topology. Whereas AlB 2 -type diborides exhibit one ELI-D attractor at the B – B midpoint, AlB 2 -type digallides exhibit two ELI-D attractors symmetrically opposite around the Ga – Ga bond midpoint. We utilized the E 2 H 4 (E=triel, tetrel ) molecular series in the D 2h point group symmetry as model systems for solid state calculations. In particular, we addressed the appearance of ELI- D double maxima for Ga – Ga, by using orbital decomposition within the ELI framework. The ELI-D topology changes along the 13th group T r 2 H 4 series. Whereas B 2 H 4 and Al 2 H 4 exhibit one ELI-D attractor representing the Tr–Tr bond, Ga 2 H 4 and In 2 H 4 give rise to two ELI-D attractors. Partial ELI-D allows the orbital decomposition of the electron density. Partial ELI-q gives access to the decomposition of a two-particle property, which is given by the Fermi-hole curvature. We have found that the d-orbitals enable the formation of the two ELI-D attractors through pairing contributions. This has a net effect of lowering electron localizability at the Ga – Ga bond midpoint. Namely, the different ELI-D topology of Ga – Ga and B – B bonds stems from the contributions of d-orbitals to orbital pairing. We have also investigated the bonding situation in transition metal diborides of ReB 2 -type (MnB 2 , TcB 2 , ReB 2) and RuB 2 -type (OsB 2 , RuB 2). One can consider these two structure types as an extension of the trend found in TM B 2 of AlB 2 -type: an increase in TM –B interactions and an enhanced three-center bonding. The change in the structure type results in a puckered layer of boron atoms with electrons equally shared between B – B and TM –B. However, TM –B bonds exhibit a high three-center character. The ELI-D/QTAIM intersection technique also revealed a high participation of TM in the B – B bonding basin population. Moreover, ELI-D topology in the ReB 2 -type also discloses a seemingly important Re 3 three-center interaction along the flat layer of Re atoms. Such basin is absent in MnB 2 , which coincides with the fact that MnB 2 was only observed in the AlB 2 -type. In this regard, we concluded that the 3D network consists not only of covalent B – B bonds, but also of TM –B bonds.

Orientadores: Pedro Antonio Muniz Vazquez, Roy Edward Bruns / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-13T13:18:26Z (GMT). No. of bitstreams: 1 Gomes_ThiagoCostaFerreira_M.pdf: 1436397 bytes, checksum: e5805c97c30c379a63a433cea23ec055 (MD5) Previous issue date: 2008 / Resumo: Neste trabalho investigamos se as cargas e dipolos atômicos ajustados ao potencial eletrostático (ChelpG) são adequados para aplicação em estudos de contribuições de carga, fluxo-de-carga e fluxo-de-dipolo (CCFDF) de movimentos vibracionais moleculares. O método ChelpG é não iterativo, computacionalmente barato e largamente utilizado, fatores que geraram interesse em avaliar seu desempenho no contexto do modelo CCFDF. Foi estudado um conjunto de doze moléculas da família dos clorofluormetanos, que compreende moléculas totalmente apolares e altamente polares. Os resultados, obtidos no nível de teoria MP2/6-311G++(3d,3p), sugerem que as cargas e dipolos atômicos ChelpG não são adequados para aplicação em estudos CCFDF, mesmo que as intensidades fundamentais de absorção no infravermelho obtidas segundo o modelo CCFDF/ChelpG reproduzam muito bem as intensidades analíticas. Este último resultado é atribuido a uma das equações de vínculo utilizadas no método ChelpG. Entretanto, o método foi considerado inadequado para a aplicação proposta pois fornece valores demasiadamente elevados para as contribuições de carga, fluxo-decarga e fluxo-de-dipolo (definidas pelo modelo CCFDF). O fato dos valores calculados para estas contribuições serem fisicamente irreais é o problema mais grave e há outros que, em conjunto com este, levam a reprovar as cargas e dipolos atômicos ChelpG para aplicações CCFDF; estes problemas são avaliados e discutidos / Abstract: In this work we investigate whether atomic charges and dipoles obtained from the electrostatic potential (ChelpG) are appropriate for application in studies on charge, charge-flux and dipole-flux contribuitions (CCFDF) occurring during molecular vibrations. ChelpG is a non-iterative, low-computational-effort-demanding method which has been largely employed. These features made worthwhile to assess it¿s performance within the CCFDF model. We studied twelve molecules from the flourochloromethanes family, which includes non-polar and highly polar molecules. The results, obtained at the MP2/6-311G++(3d,3p) theory level, suggest that ChelpG atomic charges and dipoles do not fit for application in CCFDF studies, even if the fundamental infra-red absorption intensities obtained from the CCFDF/ChelpG model approach the analytic intensities to a good extent. This last result is due to one of the restriction equations of the ChelpG method. Nevertheless we consider the ChelpG method inappropriate for use in CCFDF studies, mainly because it yields excessively large charge, charge-flux and dipole-flux contributions (which the CCFDF model defines). The fact of the calculated values for these contributions being physically unreal is the worst problem but there are others that, altogether, made us refuse ChelpG atomic charges and dipoles for CCFDF applications; we assess and discuss these problems / Mestrado / Físico-Química / Mestre em Química

2,2′-Bipyridine (BPy), one of the most widely used ligands in coordination chemistry, exists naturally in the s-trans conformation but must preorganize to the s-cis conformer in order to form chelating complexes. Lower stability of the s-cis conformer was mainly attributed to steric 3,3′-hydrogen clashes and nitrogen lone pair-lone pair interactions, but recent trends in the literature suggest that these clashes might be bonding interactions in similar molecules. These close contacts are also present in metal complexes with BPy and are often used as “steric repulsions” in order to explain trends in formation constants. In the present work we investigate the CH•••HC interaction in the free ligand as well as in ZnII(BPy)n(OH2)6-2n and NiII(BPy)n(OH2)6-2n complexes. We use multiple distinct advances in theoretical chemistry in order to arrive at a consistent and coherent model describing these interactions. The Quantum Theory of Atoms in Molecules (QTAIM) reveals the presence of an atomic interaction line (a bond path) for the CH•••HC interaction. Using the Interacting Quantum Atoms (IQA) energy decomposition scheme we show that the CH•••HC interaction is attractive and quantum mechanical in nature. The Extended Transition State coupled with Natural Orbitals for Chemical Valence (ETS-NOCV) energy decomposition scheme show favorable orbital mixing, and Non-Covalent Interaction (NCI) analysis reveals that no steric (Pauli) strain exists in the valence (overlap) regions of the interaction - electron density is concentrated rather than depleted in the bonding region. We also studied various other interactions, ranging from purely repulsive (N--N interaction in the s-cis conformer of BPy), purely electrostatic (CH•••N interaction in s-trans conformer of BPy), H-bonding (CH–N and CH–O bonds in complexes) to coordination bonds and covalent bonds. Using a comparative approach, we show the similarities and differences among the interactions, and conclude that the CH•••HC interaction cannot be classified as a “steric repulsion” - the interaction is similar in properties to every studied known bonding interaction and opposite in nature to the studied known repulsions. Finally, we suggest novel interpretations and understanding of the nature of intramolecular interactions and the field of theoretical chemistry, as well as representing the first work to combine and corroborate QTAIM, IQA, NCI and ETS-NOCV findings. / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Chemistry / unrestricted

Yes / The optimisation of a peptide-capped glycine using the novel force field FFLUX is presented. FFLUX is a force field based on the machine-learning method kriging and the topological energy partitioning method called Interacting Quantum Atoms. FFLUX has a completely different architecture to that of traditional force fields, avoiding (harmonic) potentials for bonded, valence and torsion angles. In this study, FFLUX performs an optimisation on a glycine molecule and successfully recovers the target density-functional theory energy with an error of 0.89 ± 0.03 kJ mol−1. It also recovers the structure of the global minimum with a root-mean-squared deviation of 0.05 Å (excluding hydrogen atoms). We also show that the geometry of the intra-molecular hydrogen bond in glycine is recovered accurately. / EPSRC Established Career Fellowship [grant number EP/K005472]