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Aplicação do modelo carga-fluxo de dipolo para calcular e interpretar as intensidades no espectro infravermelho dos fluoroclorometanos / Application of the charge-charge flux-dipole model to calculate and interpret the infrared intensities of the fluorochlorolethanesSilva Junior, João Viçozo 07 December 2006 (has links)
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
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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
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Chemical Bonding Analysis of Solids in Position SpaceBaranov, Alexey 02 October 2015 (has links) (PDF)
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.
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Aprimoramento do modelo QTAIM/CCFDF : como descrever a vibração de moléculas / Improving the QTAIM/CCFDF : describing molecular vibrationsSilva Filho, Arnaldo Fernandes da, 1987- 25 February 2015 (has links)
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
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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
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Caractérisation topologique d'interactions non-covalentes inter- et intramoléculaires / Topological characterization of inter-and intramolecular non-covalent interactionYahia-Ouahmed, Meziane 29 May 2017 (has links)
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.
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Avaliação topológica da estrutura Eletrônica de compostos mesoiônicosAnjos, Italo Curvelo dos 08 July 2017 (has links)
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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.
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Estudo de clusters met?licos de alum?nio-s?dio, alum?niopot?ssio, alum?nio-l?tio e s?dio-l?tio pelas abordagens de algoritmos gen?ticos, c?lculos qu?nticos e an?lise topol?gicaSantos, Acassio Rocha 21 February 2017 (has links)
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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.
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A Position-Space View on Chemical Bonding in Metal Digallides with AlB2 Type of Structure and Related CompoundsQuaresma Faria, Joao Rodolfo 26 March 2018 (has links) (PDF)
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.
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Calculo e interpretação de intensidades de bandas de transições fundamentais no infravermelho de clorofluormetanos utilizando o modelo CCFDF e cargas e dipolos atomicos ChelpG / Calculation and interpretation of infrared fundamental intensities for the chlorofluoromethanes using the CCFDF model and ChelpGGomes, Thiago Costa Ferreira, 1983- 13 August 2018 (has links)
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
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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
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Theoretical investigation of CH,HC contacts and other intramolecular interactions in 2,2′-Bipyridine and itscomplexes with metal ionsDe Lange, Jurgens Hendrik January 2013 (has links)
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
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Structural Characteristics and Thermophysical Properties of Molten Salts From Ab Initio Molecular Dynamics SimulationsClark, Austin David 09 August 2021 (has links)
This work 1) draws insights on molten salt structure and properties directly from ab initio molecular dynamics (AIMD) simulations, 2) demonstrates the advantageous symbiosis of computational and experimental collaborations on molten salt research, and 3) simultaneously generates ab initio data sets for fitting an interatomic potential model for classical molecular dynamics (MD) simulations. This work discusses the motivations for AIMD simulations of molten salts, thermophysical properties and structural characteristics of interest, advanced methodologies for AIMD simulations, and several completed AIMD studies on molten salts. Of import are the methodological contributions of this work to AIMD simulations, primarily the radical increase in generalized gradient planewave energy cutoff used to more accurately model the electron distribution across a highly-polarizable molten salt. Cutoffs of up to 2500 Rydbergs are used in this work, but 2000 Rydbergs is found to be sufficient for most AIMD NpT modelling of molten fluorides. The equilibrium liquid density of eutectic FLiNaK as a function of temperature is found to agree with the experimental density reported by Chrenkova et al. to within 0.2%, and the equilibrium liquid density of eutectic FMgNaK is found to agree with experimental measurements reported herein to within 4%. Self-diffusion coefficients in FMgNaK are also considered, with applicability to other halide salts. Molybdenum, Cesium, iodide, nickel, hydrogen, oxide, and uranium complexation are examined. It is found that solvation strength can be qualitatively determine via AIMD simulations, and that poorly solvated solutes will minimize the surface area of interaction with the salt solution. Cesium in particular is shown to be volatile or retainable in FLiBe at 500, 650, and 800 ËšC based on complexation and validated experimentally. It is shown that the chemical potential of an anion varies between melts as influenced by the different cations present in each melt. Hence, attempts to use a common electrochemical reference reaction for different salt mixtures are at best an approximation.
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