Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2014-12-22T13:03:07Z No. of bitstreams: 1 Dissertação - Idney Resplandes Brandão Leite - 2014.pdf: 1973206 bytes, checksum: 4d3a96660c36dd1cef5779f1835a09e8 (MD5) / Approved for entry into archive by Cláudia Bueno (claudiamoura18@gmail.com) on 2014-12-23T13:22:42Z (GMT) No. of bitstreams: 1 Dissertação - Idney Resplandes Brandão Leite - 2014.pdf: 1973206 bytes, checksum: 4d3a96660c36dd1cef5779f1835a09e8 (MD5) / Made available in DSpace on 2014-12-23T13:22:42Z (GMT). No. of bitstreams: 1 Dissertação - Idney Resplandes Brandão Leite - 2014.pdf: 1973206 bytes, checksum: 4d3a96660c36dd1cef5779f1835a09e8 (MD5) Previous issue date: 2014-04-10 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / Using Hartree-Fock (HF) and the second-order Møller-Plesset perturbation theory (MP2) methods with the 6-311++G(2d,2p) basis set, we have determined the dipole moment (𝜇), static linear polarizability ( 𝛼) and first hyperpolarizability (𝛽𝑡𝑜𝑡 and 𝛽𝐻𝑅𝑆) of the following linear chains : (HCN)𝑁, (HNC)𝑁, (LiCN)𝑁′ and (LiNC)𝑁′ (for 𝑁=1-10 and 𝑁′ = 1−15). The asymptotic MP2/6-311++G(2d,2p) values of 𝜇, 𝛼, 𝛽𝑡𝑜𝑡 and 𝛽𝐻𝑅𝑆 per unit ( 𝜇, 𝛼, 𝛽𝑡𝑜𝑡 and 𝛽𝐻𝑅𝑆) of the chains of HCN, HNC and LiNC have been estimated. For the chains of LiCN, at the same calculation level, we have estimated only the polymeric values (infinite chain values) of 𝜇 and 𝛼. For the chains of HCN and HNC, the obtained results shows that the effect of the structural isomerization on the polymeric values of 𝜇, 𝛼, 𝛽𝑡𝑜𝑡 and 𝛽𝐻𝑅𝑆 is significant, principally for these two latter properties. In the case of chains of LiCN and LiNC, the isomeric change practically does not affect the asymptotic values of 𝜇 and 𝛼. In the polymeric limit, the presented results also show that the effect of substitution of hydrogen atoms in linear chains of HCN and HNC for lithium atoms is an expressive increase of 𝜇 and 𝛼 and a substantial reduction of 𝛽𝑡𝑜𝑡 and 𝛽𝐻𝑅𝑆. / Utilizando os métodos ab initio de Hartree-Fock (HF) e de Møller-Plesset em segunda ordem (MP2) com o conjunto de funções-base 6-311++G(2d,2p), determinamos o momento de dipolo (𝜇), a polarizabilidade linear ( 𝛼) e a primeira hiperpolarizabilidade estática (𝛽𝑡𝑜𝑡 e 𝛽𝐻𝑅𝑆) das seguintes cadeias lineares: (HCN)𝑁, (HNC)𝑁, (LiCN)𝑁′ e (LiNC)𝑁′ (para 𝑁=1-10 e 𝑁′ = 1−15). Os valores assintóticos MP2/6-311++G(2d,2p) de 𝜇, 𝛼, 𝛽𝑡𝑜𝑡 e 𝛽𝐻𝑅𝑆 por unidade ( 𝜇, 𝛼, 𝛽𝑡𝑜𝑡 e 𝛽𝐻𝑅𝑆) das cadeias de HCN, HNC e LiNC foram estimados. Para as cadeias de LiCN, neste mesmo nível de cálculo, só foi possível estimar os valores poliméricos (valores para cadeias infinitas) de 𝜇 e 𝛼. Para as cadeias de HCN e HNC, os resultados obtidos mostram que o efeito da isomerização estrutural sobre os valores poliméricos de 𝜇, 𝛼, 𝛽𝑡𝑜𝑡 e 𝛽𝐻𝑅𝑆 é significativo, principalmente para estas duas últimas propriedades. No caso das cadeias de LiCN e LiNC, a mudança isomérica praticamente não afeta os valores poliméricos de 𝜇 e 𝛼. No limite polimérico, os resultados apresentados também mostram que o efeito da substituição dos átomos de hidrogênio das cadeias de HCN e HNC por átomos de lítio é um aumento expressivo dos valores de 𝜇 e 𝛼 e uma redução substancial de 𝛽𝑡𝑜𝑡 e 𝛽𝐻𝑅𝑆.

This work presents first-principles calculations of long-range intermolecular dispersion energies between two atoms or molecules as expressed in terms of the C6 dipole-dipole dispersion coefficients. In a series of publications, it has been shown by us that the complex linear polarization propagator method provides accurate ab initio and first-principles density functional theory values of the C6 dispersion coefficients in comparison with those reported in the literature. The selected samples for the investigation of dispersion interactions in the electronic ground state are the noble gases, n-alkanes, polyacenes, azabenzenes, and C60. It has been shown that the proposed method can also be used to determine dispersion energies for species in their respective excited electronic states. The C6 dispersion coefficients for the first π → π* excited state of the azabenzene molecules have been obtained with the adopted method in the multiconfiguration self-consistent field approximation. The dispersion energy of the π → π* excited state is smaller r than that of the ground state. It is found that the characteristic frequencies ω1 defined in the London approximation of n-alkanes vary in a narrow range and that makes it possible to construct a simple structure-to-property relation based on the number of -bonds for the dispersion interaction in these saturated compounds. However, this simple approach is not applicable for the interactions of the π-conjugated systems since their characteristic frequencies ω1 vary strongly depending on the systems. / <p>Report code: LIU-TEK-LIC-2006:2</p>

A combination of quantum chemical calculation and molecular dynamics simulation is applied to compute refractive indices of liquid-forming silicon oils. The densities of these species are obtained from molecular dynamics simulations based on the NPT ensemble while the molecular polarizabilities are evaluated by density functional theory. This procedure is shown to yield results well compatible with available experimental data, suggesting that it represents a robust and economic route for determining the refractive indices of liquid-forming organic complexes containing silicon.

High performance natural materials typically employ highly tuned structures spanning the nanoscopic to macroscopic length scales. Synthetically recapitulating this degree of complexity has become a unifying goal connecting the fields of chemistry, nanoscience, biology, and materials science. One common strategy is to direct the bottom up assembly of nanoparticle building blocks into hierarchical structures using stimuli such as electric fields. Despite the promise and great versatility of electric fields, there are many knowledge gaps surrounding their use to assemble highly complex structures. In this thesis, we explore the assembly of nanoparticles into hierarchical structures through dielectrophoresis (DEP), or the motion of polarizable objects in non-uniform electric fields. Critically, through a systematic approach, we study the fundamental polarizability of individual particles, the assembly of particle dimers, and finally the emergence of macroscopic structure from nanoscopic particles. Interweaving these explorations are instrumentation advances that broaden our ability to measure fundamental particle properties and explore hierarchical structures. Initially, we measure the polarizability of nanoparticles in solution using fluorescence microscopy. Specifically, we quantify the polarizability of solution-phase semiconductor quantum dots (QDs) for the first time. Through analyzing the thermodynamic distribution of particles in a microfluidic device with a non-uniform electric field profile, we identify a striking 30-fold increase in polarizability in the presence of low salt conditions due to the Debye screening length being commensurate with the particle size. This increase in polarizability indicates that nanoparticles assemble far more rapidly and easily than previously predicted. Next, we study the assembly of nanoparticles in the vicinity of anisotropic template particles as a path to realizing hierarchical structures. Specifically, we explore eight particle geometries using finite element analysis and find a >10-fold local field enhancement near some shapes, potentially promoting hierarchical assembly. We subsequently introduce a framework for predicting the assembly outcome of particles with multiple distinct sizes and shapes that includes thermodynamic and kinetic considerations. Then, we perform experiments demonstrating the hierarchical assembly of QDs into macroscopic structures. Despite theory predicting the formation of chains, we observe a macroscopic foam-like cellular phase when the QDs experience a combination of alternating current (AC) and direct current (DC) voltages. The resulting materials are both highly hierarchical in that they are 200 µm thick materials comprised of 20 nm particles, but they also represent extremely low-density materials. Finally, we report the invention of a novel instrument for imaging hierarchical materials. Specifically, we describe a massively parallel atomic force microscope with >1000 probes that is made possible through the combination of a new cantilever-free probe architecture and a scalable optical method for detecting probe-sample contact that provides sub-10 nm vertical precision. / 2022-09-28T00:00:00Z

One of the most intriguing properties of light-matter interaction is the ability of an electromagnetic field to exert mechanical forces on polarizable objects. This phenomenon is a direct consequence of the fact that light carries momentum, which in turn can be transferred to matter. Mediated by scattering, this interaction usually manifests itself as a “pushing force” in the direction of beam propagation. However, it is possible to judiciously engineer these optical forces, either by tailoring particle polarizability, and/or by structuring the incident light field. As a simple example, a tightly focused laser beam demonstrates strong gradient forces, which may attract and even trap particles with positive polarizability in the focal volume. The opposite occurs in the regime of negative polarizability, where particles are expelled from the regions of highest intensity. Based on this fundamental principle, one can actively shape the beam using spatial light modulators to manipulate individual objects as well as ensembles of particles suspended in a liquid. In the latter case, a modulation of the local particle concentration is associated with changes of the effective refractive index. The result is an artificial nonlinear medium, whose Kerr-type response can be readily tuned by the parameters of its constituent particles. In the course of this work, we introduce a new class of synthetic colloidal suspensions exhibiting negative polarizabilities, and observe for the first time robust propagation and enhanced transmission of self-trapped light over long distances. Such light penetration in strongly scattering environments is enabled by the interplay between optical forces and self-activated transparency effects. We explore various approaches to the design of negative-polarizability arrangements, including purely dielectric as well as metallic and hybrid nanoparticles. In particular, we find that plasmonic resonances allow for extremely high and spectrally tunable polarizabilities, leading to unique nonlinear light-matter interactions. Here, for the first time we were able to observe plasmonic resonant solitons over more than 25 diffraction lengths, in colloidal nanosuspensions.

Molecular nonlinear optical (NLO) properties are extensively studied using both theory and experiment because of their use in myriad applications. Experimental measurements of the most interesting molecules’ NLO properties are difficult, so experimental data for molecules with desirable NLO properties is scarce. Theoretical tools don’t suffer from the same limitations and can provide significant insights into the physico-chemical phenomena underlying the nonlinear responses, can help in interpreting response behaviour of molecules, and can guide design the materials with desirable response properties. Here, I present my work on developing methods for accurately calculating the NLO properties of molecules using the finite field (FF) approach. The first chapter provides a background for the finite field and electronic structure methods used in this dissertation. Chapter two is a thorough investigation of the finite field method. The limitations of the method are highlighted and the optimal conditions for overcoming its drawbacks and obtaining meaningful and accurate results are described. Chapter three presents the first systematic study of the dependence of optimal field strengths on molecular descriptors. The first protocol for predicting the optimal field for the second hyperpolarizability is presented and successfully tested, and the dependence of the optimal field strength for the first hyperpolarizability on the molecular structure is investigated. Chapter four is an assessment of various DFT functionals in calculating the second hyperpolarizabilities of organic molecules and oligomers. This study shows the limitations of conventional DFT methods and the importance of electron correlation to response properties. In chapter five we present a new method of calculating NLO properties using a rational function model that is shown to be more robust and have lower computational cost than the traditional Taylor expansion. Finally, chapter six includes a summary of the thesis and an overview of future work. / Thesis / Doctor of Philosophy (PhD)

Van der Waals-Wechselwirkungen (vdW) sind allgegenwärtig und spielen eine zentrale Rolle in einer großen Anzahl biologischer und moderner synthetischer Materialien. Die am weitesten verbreitete theoretische Methode zur Berechnung von Materialeigenschaften, die Dichtefunktionaltheorie (DFT) in semilokaler Näherung, vernachlässigt diese Wechselwirkungen jedoch größtenteils, was zur Entwicklung vieler verschiedener vdW-Modelle führte. Die hier vorgestellte Arbeit ebnet den Weg hin zu einem vereinheitlichten vdW-Modell welches die besten Elemente der unterschiedlichen Klassen von vdW-Modellen vereint. Zu diesem Zweck haben wir einen vereinheitlichten theoretischen Rahmen geschaffen, der auf dem Reichweite-separierten Adiabatischer-Zusammenhang-Fluktuations-Dissipations-Theorem aufbaut und die meisten existierenden vdW-Modelle umfasst. Wir analysieren die MBD-korrelierte Wellenfunktion am prototypischen Beispiel von π–π-Wechselwirkungen in supramolekularen Komplexen und stellen fest, dass diese Wechselwirkungen größtenteils durch delokalisierte kollektive Ladungsfluktuationen entstehen. Um zu dem langreichweitigen vdW-Modell ein ausgewogenes kurzreichweitiges Dichtefunktional zu identifizieren, präsentieren wir eine umfassende Untersuchung zum Zusammenspiel der kurz- und langreichweitigen Energiebeiträge in acht semilokalen Funktionalen und drei vdW-Modellen für eine große Spanne von Systemen. Die Bindungsenergieprofile vieler der DFT+vdW-Kombinationen unterscheiden sich sowohl quantitativ als auch qualitativ stark voneinander. Schließlich untersuchen wir die Performance des Vydrov–Van Voorhis-Polarisierbarkeitsfunktionals über das Periodensystem der Elemente hinweg und identifizieren eine systematische Unterschätzung der Polarisierbarkeiten und vdW-C₆-Koeffizienten für s- und d-Block-Elemente. Als Lösung entwickeln wir eine orbitalabhängige Verallgemeinerung des Funktionals. / The ubiquitous long-range van der Waals interactions play a central role in nearly all biological and modern synthetic materials. Yet the most widely used theoretical method for calculating material properties, the density functional theory (DFT) in semilocal approximation, largely neglects these interactions, which motivated the development of many different vdW models. The work in this thesis paves way towards a unified vdW model that combines best elements from the different classes of the vdW models. To this end, we developed a unified theoretical framework based on the range-separated adiabatic-connection fluctuation--dissipation theorem that encompasses most existing vdW models. We analyze the MBD correlated wave function on the prototypical case of π–π interactions in supramolecular complexes and find that these interactions are largely driven by delocalized collective charge fluctuations. To identify a balanced short-range density functional to accompany the long-range vdW model, we present a comprehensive study of the interplay between the short-range and long-range energy contributions in eight semilocal functionals and three vdW models on a wide range of systems. The binding-energy profiles of many of the DFT+vdW combinations differ both quantitatively and qualitatively, and some of the qualitative differences are independent of the choice of the vdW model. Finally, we investigate the performance of the Vydrov—Van Voorhis polarizability functional across the periodic table, identify systematic underestimation of the polarizabilities and vdW C₆ coefficients for s- and d-block elements, and develop an orbital-dependent generalization of this functional to resolve the issue.

Submitted by Jaqueline Silva (jtas29@gmail.com) on 2014-09-16T17:01:54Z No. of bitstreams: 2 Naves, Emílio Santiago-2014-tese.pdf: 587232 bytes, checksum: 384bbcad6790ecde844af07f4c8deed9 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Jaqueline Silva (jtas29@gmail.com) on 2014-09-16T17:02:18Z (GMT) No. of bitstreams: 2 Naves, Emílio Santiago-2014-tese.pdf: 587232 bytes, checksum: 384bbcad6790ecde844af07f4c8deed9 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2014-09-16T17:02:18Z (GMT). No. of bitstreams: 2 Naves, Emílio Santiago-2014-tese.pdf: 587232 bytes, checksum: 384bbcad6790ecde844af07f4c8deed9 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2013-11-08 / This work presents results for the dynamic (hyper)polarizabilities of ozone, sulfur dioxide, nitrous oxide and carbon dioxide molecules, with inclusion of vibrational corrections. The electronic contributions for the properties of interest were computed analytically at the single and double coupled cluster level through response theory. Ozone and sulfur dioxide were studied separately. For both systems, contributions of connected triple excitations were also estimated by the multiplicative correction scheme. The vibrational corrections were calculated by the perturbation theoretical method (PT). The zero-point vibrational average correction, calculated only for ozone and sulfur dioxide, proved to be small. Results also show that the pure vibrational correction is relevant for the following nonlinear optical processes: dc-Pockels effect, intensity dependent refractive index, and dc-Kerr effect. For the ozone molecule the dc-second harmonic generation effect also had a significant pure vibrational correction. In addition, pure vibrational correction was calculated according to a variational methodology proposed by our research group (VAR) for the four systems, and the results were compared with the corresponding PT results. A comparison between PT and VAR results shows that ozone is the system most sensitive to the method, while sulfur dioxide and carbon dioxide are the most well behaved. / Neste trabalho são apresentados resultados para as (hiper)polarizabilidades dinâmicas das moléculas de ozônio, dióxido de enxofre, óxido nitroso e dióxido de carbono, com inclusão de correções vibracionais. As contribuições eletrônicas das propriedades de interesse foram computadas analiticamente através da teoria de resposta no nível coupled cluster com substituições simples e duplas. O ozônio e o dióxido de enxofre foram estudados separadamente. Para ambos os sistemas, as contribuições das substituições triplas conexas também foram estimadas através do esquema de correção multiplicativa. As correções vibracionais foram calculadas por meio dométodo de perturbação teórica (PT). A correção da média vibracional de ponto zero, calculada apenas para o ozônio e o dióxido de enxofre, revelou-se pequena. Os resultados também mostram que a correção vibracional pura é relevante para os seguintes processos ópticos não lineares: efeito dc-Pockels, índice de refração dependente da intensidade e efeito dc-Kerr. Para a molécula de ozônio o efeito de geração de segundo harmônico dc também teve uma correção vibracional pura significativa. Em adição, a correção vibracional pura foi calculada segundo uma metologia variacional proposta pelo nosso grupo de pesquisa (VAR) para os quatro sistemas, e os resultados foram comparados com os respectivos resultados PT. Uma comparação entre os resultados PT e VAR mostra que o ozônio é o sistema mais sensível ao método, ao passo que o dióxido de enxofre e o dióxido de carbono são os mais bem comportados.

<p>The basic building blocks in molecular electronics often correspond to conjugated molecules. A compound class consisting of rigid rod-like staffane molecules with the heavier Group 14 elements Si, Ge, Sn and Pb at their bridgehead positions has now been investigated. Herein these oligomers are called heavy-core or Si-, Ge-, Sn- or Pb-core staffanes. These compounds benefit from interaction through their bicyclo[1.1.1]pentane monomer units. Quantum chemical calculations were performed to probe their geometries, stabilities and electronic properties associated with conjugation.</p><p>The stabilities of the bicyclo[<i>n.n.n</i>]alkane and [<i>n.n.n</i>]propellanes (1 ≤ <i>n</i> ≤ 3) with C, Si, Ge and Sn at the bridgehead positions were studied by calculation of homodesmotic ring strain energies. The bicyclic compounds with <i>n</i> = 1 and Si, Ge or Sn at bridgehead positions have lower strain than the all-carbon compound.</p><p>A gradually higher polarizability exaltation is found as the bridgehead element is changed from C to Si, Ge, Sn or Pb. The ratio between longitudinal and average polarizability also increases gradually as Group 14 is descended, consistent with enhanced conjugation in the heavier oligomers.</p><p>The localization of polarons in C-, Si- and Sn-core staffane radical cations was calculated along with internal reorganization energies. The polaron is less localized in Si- and Sn-core than in C-core staffane radical cation. The reorganization energies are also lower for the heavier staffanes, facilitating hole mobility when compared to the C-core staffanes.</p><p>The effect of the bicyclic structure on the low valence excitations in the UV-spectra of compounds with two connected disilyl segments was also investigated. MS-CASPT2 calculations of 1,4-disilyl- and 1,4-bis(trimethylsilyl)-1,4-disilabicyclo[2.2.1]heptanes and 1,4-disilyl- and 1,4-bis(trimethylsilyl)-1,4-disilabicyclo[2.1.1]hexanes revealed that although the bicyclic cage separates the two disilyl chromophores, there is a strong red-shift of the lowest valence excitations when compared to an isolated disilane.</p>

The basic building blocks in molecular electronics often correspond to conjugated molecules. A compound class consisting of rigid rod-like staffane molecules with the heavier Group 14 elements Si, Ge, Sn and Pb at their bridgehead positions has now been investigated. Herein these oligomers are called heavy-core or Si-, Ge-, Sn- or Pb-core staffanes. These compounds benefit from interaction through their bicyclo[1.1.1]pentane monomer units. Quantum chemical calculations were performed to probe their geometries, stabilities and electronic properties associated with conjugation. The stabilities of the bicyclo[n.n.n]alkane and [n.n.n]propellanes (1 ≤ n ≤ 3) with C, Si, Ge and Sn at the bridgehead positions were studied by calculation of homodesmotic ring strain energies. The bicyclic compounds with n = 1 and Si, Ge or Sn at bridgehead positions have lower strain than the all-carbon compound. A gradually higher polarizability exaltation is found as the bridgehead element is changed from C to Si, Ge, Sn or Pb. The ratio between longitudinal and average polarizability also increases gradually as Group 14 is descended, consistent with enhanced conjugation in the heavier oligomers. The localization of polarons in C-, Si- and Sn-core staffane radical cations was calculated along with internal reorganization energies. The polaron is less localized in Si- and Sn-core than in C-core staffane radical cation. The reorganization energies are also lower for the heavier staffanes, facilitating hole mobility when compared to the C-core staffanes. The effect of the bicyclic structure on the low valence excitations in the UV-spectra of compounds with two connected disilyl segments was also investigated. MS-CASPT2 calculations of 1,4-disilyl- and 1,4-bis(trimethylsilyl)-1,4-disilabicyclo[2.2.1]heptanes and 1,4-disilyl- and 1,4-bis(trimethylsilyl)-1,4-disilabicyclo[2.1.1]hexanes revealed that although the bicyclic cage separates the two disilyl chromophores, there is a strong red-shift of the lowest valence excitations when compared to an isolated disilane.