<p>Time-dependent density functional theory calculations have been carried out to determine the complex first-order hyperpolarizability in the two-photon resonance region of the molecule IDS-Cab. Calculations show that three strongly absorbing states, in the ultraviolet region, are separated to the extent that no significant interference of the imaginary parts of the tensor elements of the first-order hyper-polarizability occurs. Consequently, and in contrast to experimental findings [27], no reduced imaginary parts of the first-order hyperpolarizability in the two-photon resonant region can be seen.</p>

L'intérêt de la recherche fondamentale pour les morceaux nanométriques de métaux nobles est principalement dû à la résonance localisée des plasmons de surface (LSPR) dans l'absorption optique. Différents aspects, liés à la compréhension théorique de la LSPR dans le cas de clusters de métaux nobles de taille dite intermédiaire, sont étudiés dans ce manuscrit. Afin d'avoir une vision plus large nous utilisons deux approches : l'approche électromagnétique classique et le formalisme ab initio en temps réel de la théorie de la fonctionnelle de la densité dépendant du temps (RT-TDDFT). Une comparaison systématique et détaillée de ces deux approches souligne et quantifie les limitations de l'approche électromagnétique lorsqu'elle est appliquée à des systèmes de taille quantique. Les différences entre les excitations plasmoniques collectives et celles impliquant les électrons d, ainsi que leurs interactions, sont étudiées grâce au comportement spatial des densités correspondantes. Ces densités sont obtenues en appliquant une transformée de Fourier dans l'espace à la densité obtenue par les simulations DFT utilisant une perturbation delta-kick. Dans ce manuscrit, des clusters de métaux nobles nus et protégés par des ligands sont étudiés. En particulier, motivé par de récents travaux sur les phénomènes d'émergence de plasmon, l'étude par TD-DFT de nano-alliages Au-Cu de taille tout juste inférieure à 2nm à fourni de subtiles connaissances sur les effets d'alliages sur la réponse optique de tels systèmes. / The fundamental research interest in nanometric pieces of noble metals is mainly due to the localized surface-plasmon resonance (LSPR) in the optical absorption. Different aspects related to the theoretical understanding of LSPRs in `intermediate-size' noble-metal clusters are studied in this thesis. To gain a broader perspective both the real-time \ai formalism of \td density-functional theory (RT-TDDFT) and the classical electromagnetics approach are employed. A systematic and detailed comparison of these two approaches highlights and quantifies the limitations of the electromagnetics approach when applied to quantum-sized systems. The differences between collective plasmonic excitations and the excitations involving $d$-electrons, as well as the interplay between them are explored in the spatial behaviour of the corresponding induced densities by performing the spatially resolved Fourier transform of the time-dependent induced density obtained from a RT-TDDFT simulation using a $\delta$-kick perturbation. In this thesis, both bare and ligand-protected noble-metal clusters were studied. In particular, motivated by recent experiments on plasmon emergence phenomena, the TDDFT study of Au-Cu nanoalloys in the size range just below 2~nm produced subtle insights into the general effects of alloying on the optical response of these systems.

L'interaction entre la matière et le rayonnement est un domaine bien établi de la physique. Pour un physico-chimiste, cette interaction peut être utilisée comme une sonde (spectroscopie) ou pour provoquer des réactions chimiques (photo-chimie). Les mécanismes des réactions photochimiques sont difficiles à étudier expérimentalement et même les études les plus sophistiquées de spectroscopies femtosecondes peuvent bénéficier énormément des simulations théoriques.Les résultats spectroscopiques d'ailleurs ont souvent besoin des calculs théoriques pour l'analyse de leurs spectres. Les méthodes théoriques pour décrire les processus photochimiques ont été principalement développées en utilisant le concept de la fonction d'onde à N corps et ont eu des succès remarquables. Cependant de telles approches sont généralement limitées à des petites ou moyennes molécules. Heureusement la théorie de la fonctionnelle de la densité dépendant du temps (TD-DFT) a émergé comme une méthode simple de calcul pouvant être appliquée à des molécules plus grandes, avec une précision qui est souvent, mais pas toujours, semblable à la précision provenant des méthodes basés sur la fonction d'onde à N électrons. Une partie de cette thèse consiste à surmonter les difficultés des approximations utilisées de nos jours en TD-DFT. En particulier, nous avons examiné la qualité des intersections coniques quand l'approche du retournement de spin non collinéaire de Ziegler-Wang est utilisée et nous avons montré que l'approche du retournement de spin, parfois ,améliore dans des cas particuliers, mais que c'est n'est pas une solution générale pour mieux décrire les intersections coniques dans les simulations photochimiques basées sur la TD-DFT. La plupart des parties de cette thèse traite d'améliorations algorithmiques, soit pour améliorer l'analyse des résultats de la TD-DFT, soit pour étendre les calculs de TD-DFT à de grandes molécules. L'implémentation de l'analyse automatique des symétries des orbitales moléculaires dans deMon2k est une contribution pour améliorer l'analyse des résultats de la TD-DFT. Cela a aussi servi comme une introduction au projet de programmation majeur. La contribution méthodologique principale dans cette thèse est l'implémentation des équations de Casida dans le code BigDFT fondé sur le formalisme des ondelettes. Cette implémentation a aussi permis une analyse détaillée des arguments positifs et négatifs de l'utilisation de la TD-DFT fondée sur les ondelettes. On montre qu'il est plus facile d'obtenir des orbitales moléculaires précises qu'avec deMon2k. Par contre, la contribution des orbitales inoccupées est plus problématiques qu'avec un code de gaussienne comme deMon2k. Finalement, les équations de base des gradients analytiques des états excités sont dérivées pour la TD-DFT. La thèse se termine avec quelques perspectives de travaux futurs. / The interaction of light with matter is a well-established domain of physical science. For a chemical physicist, this interaction may be used as a probe (spectroscopy) or to induce chemical reactions (photo- chemistry.) Photochemical reaction mechanisms are difficult to study experimentally and even the most sophisticated modern femtosecond spectroscopic studies can benefit enormously from the light of theoret- ical simulations. Spectroscopic assignments often also require theoreti- cal calculations. Theoretical methods for describing photoprocesses have been developed based upon wave-function theory and show remarkable success when going to sophisticated higher-order approxi- mations. However such approaches are typically limited to small or at best medium-sized molecules. Fortunately time-dependent density- functional theory (TD-DFT) has emerged as a computationally-simpler method which can be applied to larger molecules with an accuracy which is often, but not always, similar to high-quality wave-function calculations. Part of this thesis concerns overcoming difficulties in- volving the approximate functionals used in present-day TD-DFT. In particular, we have examined the quality of conical intersections when the Ziegler-Wang noncollinear spin-flip approach is used and have shown that the spin-flip approach has merit as a particular solution in particular cases but is not a general solution to improving the de- scription of conical intersections in photochemical simulations based upon TD-DFT. Most of this thesis concerns algorithmic improvements aimed at either improving the analysis of TD-DFT results or extending practical TD-DFT calculations to larger molecules. The implementa- tion of automatic molecular orbital symmetry analysis in deMon2k is one contribution to improving the analysis of TD-DFT results. It also served as an introduction to a major programming project. The major methodological contribution in this thesis is the implementation of Casida's equations in the wavelet-based code BigDFT and the subse- quent analysis of the pros and cons of wavelet-based TD-DFT where it is shown that accurate molecular orbitals are more easily obtained in BigDFT than with deMon2k but that handling the contribution of unoccupied orbitals in wavelet-based TD-DFT is potentially more problematic than it is in a gaussian-based TD-DFT code such as de- Mon2k. Finally the basic equations for TD-DFT excited state gradients are derived. The thesis concludes with some perspectives about future work.

No description available.

No description available.

Warm dense matter (WDM) is an extreme state of matter induced by extreme conditions and characterized as an intermediary state between (high-pressure) condensed matter and plasma. It has sparked a lot of attention in recent years as a result of current innovations in experiments and theoretical methods for modeling such complex systems. Such conditions naturally occur in astrophysical objects such as the interiors of the planets, and in white and brown dwarfs. WDM can be created in the laboratory via various methods such as laser compression, Z-pinches and heated diamond anvil cells. This thesis describes the results obtained for many such systems across a range of conditions modeled using ab-initio simulation methods. The first testbed concerns the electronic structure and linear response of the carbon phases under high-pressure and warm dense matter conditions. The focus is on modeling inelastic x-ray scattering spectra across a range of conditions useful for the analysis and interpretation of x-ray Thomson scattering (XRTS) experiments. Another major goal is to improve the existing models to compute static properties such as the equation of state, density of states with the inclusion of highly accurate data from quantum Monte Carlo (QMC) simulations relevant at finite-temperatures. This approach improves the accuracy and is also computationally inexpensive compared to path integral Monte Carlo (PIMC) methods. Lastly, improvements in linear response theory relevant for XRTS are incorporated with the inclusion of local field corrections (LFC) and finite-temperature local field corrections (T-LFC) using data from QMC simulations.

O câncer de pele se apresenta como um sério problema de saúde pública mundial, sendo incidente nos cinco continentes. As ações relacionadas à prevenção dessa doença envolvem, entre outras coisas, a utilização de protetores solares e a educação em saúde. Em virtude do aumento do número de indivíduos com câncer de pele a cada ano, é de grande valor estudos de entendimento e desenvolvimento de filtros solares melhores e mais seguros. Os produtos utilizados com a finalidade de proteger a pele dos raios solares ultravioletas (UV) possuem em sua composição filtros solares, que podem ter ação física, refletindo e dissipando a radiação UV; ou ação química, absorvendo a radiação UV. Os filtros químicos podem apresentar absorção em UVB (290-320 nm), UVA (320-400 nm) ou em ambas as faixas, sendo considerados de amplo espectro. . Dentre as várias classes de compostos com perfil de filtro solar UVB, os cinamatos destacam-se por apresentarem boa eficácia e excelente custo-benefício. A aplicação de cálculos teóricos tornou-se indispensável no planejamento de fármacos e nos estudos de mecanismo de ação de moléculas bioativas, visto a diminuição de tempo e custos em pesquisa e desenvolvimento. O desenvolvimento de métodos quânticos robustos, como o TD-DFT, permitiu a simulação de propriedades experimentais in silico, tais como espectros de RMN e UV. Diante deste panorama, aplicamos tal método na simulação de espectros UV para os cinamatos com perfil de filtros solares. Realizou-se uma busca do melhor funcional para simulação dos espectros, na qual se determinou que os funcionais B3LYP e B3P86 apresentaram melhores resultados quando comparados ao espectro experimental do composto p-metoxicinamato de etilexila determinado em metanol. Foram simulados os espectros de UV para sete compostos derivados do ácido cinâmico, os quais apresentaram &#955; máximo próximo a 310 nm, como descrito na literatura. Observou-se que a energia média para que ocorra a principal transição eletrônica, de HOMO para LUMO, é de 3,95 eV. O método mostrou-se adequado para a determinação de espectros UV para a classe dos cinamatos e pode ser utilizado na busca de novos compostos dessa classe a serem empregados como filtros solares. / Skin cancer presents itself as a very serious world public health problem, being incident all over the five continents. Using sunscreen and receiving health education, among other factors, are related to prevent the disease. The number of people with skin cancer increases every year, therefore, studies for better knowledge and development for better and safer sunscreens are crucial. Products used with the intention to protect the skin from ultraviolet sunrays (UV) are partially composed by sunscreen, which may lead to two different reactions, a physical reaction, that reflects and ceases the UV radiation; or a chemical reaction, that absorbs the UV radiation. Chemical filters may present absorption in UVB (290-320 nm), UVA (320 400 nm) or in both, which is considered as broad spectrum. Among the various types of compound forms with sunscreen UVB profile, cinnamates stand out for presenting good efficiency and excellent cost-benefit. The application of theoretical calculations became essential for drug design and bioactive molecules action mechanism studies, considering time saving and costs in research and development. The development of robust quantum method, such as TD-DFT allowed the simulation of experimental properties in silico, like RMN and UV spectra. Given this overview, this method was applied to simulate UV spectra of cinnamates with sunscreen profile. A search was done to define the best functional to simulate all spectrum, where the functionals B3LYP and B3P86 showed the best results when compared to experimental spectra of the compound ethylhexyl methoxycinnamate determined in methanol. An UV spectrum simulation for seven compounds derived from cinnamic acid showed maximum wavelength around to 310 nm, as described in the literature. It was observed that the average energy for the main electronic transition, HOMO to LUMO, is 3,95 eV. The method proved to be adequate for the determination of UV spectra for cinnamate class and it can be used as a tool on the search for new compounds from this class to be used as sunscreen.

In the first part of the dissertation, we develop a theoretical approach to analyze nonlinear spectroscopy experiments based on the formalism of quantum state (QST) and process tomography (QPT). In it, a quantum system is regarded as a black box which can be systematically tested in its performance, very much like an electric circuit is tested by sending a series of inputs and measuring the corresponding outputs, but in the quantum sense. We show how to collect a series of pump-probe or photon-echo experiments, and by varying polarizations and frequency components of the perturbations, reconstruct the quantum state (density matrix) of the probed system for a set of different initial conditions, hence simultaneously achieving QST and QPT. Furthermore, we establish the conditions under which a set of two-dimensional optical spectra also yield the desired results. Simulations of noisy experiments with inhomogeneous broadening show the feasibility of the protocol. A spin-off of this work is our suggestion of a witness that distinguishes between spectroscopic time-oscillations corresponding to vibronic only coherences against their electronic counterparts. We conclude by noting that the QST/QPT approach to nonlinear spectroscopy sheds light on the amount of quantum information contained in the output of an experiment, and hence, is a convenient theoretical and experimental paradigm even when the goal is not to perform a full QPT. In the second part of the thesis, we discuss a methodology to study the electronic dynamics of complex molecular systems, such as photosynthetic units, in the framework of time-dependent density functional theory (TD-DFT). By treating the electronic degrees of freedom as the system and the nuclear ones as the bath, we develop an open quantum systems (OQS) approach to TD-DFT. We formally extend the theoretical backbone of TD-DFT to OQS, and suggest a Markovian bath functional which can be readily included in electronic structure codes.

The nature of the ground state and the first (lowest) singlet excited state geometrical conformations and electronic transitions in the aromatic five-membered heterocyclic oligomers &ndash / oligothiophenes (nT), oligofurans (nF), and oligopyrroles (nP)- containing up to six monomer units (total of 18 molecules) were explored using several computational methodologies. Geometry optimizations were carried out at Austin Model 1 (AM1), Restricted Hartree-Fock (RHF/6-31G*), and Density Functional Theory (DFT, B3LYP/6-31G*) levels for the ground-state conformations of these structurally well-defined heterocyclic oligomers. The Configuration Interaction Singles (CIS) method with the 6-31G* basis set was chosen in computation of the optimal geometry of the lowest singlet excited state. Lowest singlet excitation S1&szlig / S0 energies were calculated using the Zerner&rsquo / s Intermediate Neglect of Differential Overlap for Spectroscopy (ZINDO/S), CIS (CIS/6-31G*), and Time-Dependent DFT (TDDFT/6-31G* and TDDFT/6-31+G*) methods. In computation of the emission S1&agrave / S0 energies, we have employed all methods above except ZINDO/S. In investigation of geometries of the ground and lowest singlet excited state, we compared the bond length alternation (BLA) parameters, Dri in the conjugated backbone of the oligomers. Saturation of the geometrical parameters at the center of oligomers was observed after a certain chain length. Among all methodologies used in computation of excitation (S1&szlig / S0) and emission (S1&agrave / S0) energies, TDDFT results showed the best agreement with experimental data. Fits of computed and experimental excitation energies to an exponential function using the least squares method enabled us to predict Effective Conjugation Length (ECL) values. We obtained the ECLs of 17 (17), 16 (15), and 14 (13) monomer units for polythiophene (PTh), polyfuran (PFu), and polypyrrole (PPr), which have very good agreement with the results obtained from the fits of experimental data (the values in parentheses).

O câncer de pele se apresenta como um sério problema de saúde pública mundial, sendo incidente nos cinco continentes. As ações relacionadas à prevenção dessa doença envolvem, entre outras coisas, a utilização de protetores solares e a educação em saúde. Em virtude do aumento do número de indivíduos com câncer de pele a cada ano, é de grande valor estudos de entendimento e desenvolvimento de filtros solares melhores e mais seguros. Os produtos utilizados com a finalidade de proteger a pele dos raios solares ultravioletas (UV) possuem em sua composição filtros solares, que podem ter ação física, refletindo e dissipando a radiação UV; ou ação química, absorvendo a radiação UV. Os filtros químicos podem apresentar absorção em UVB (290-320 nm), UVA (320-400 nm) ou em ambas as faixas, sendo considerados de amplo espectro. . Dentre as várias classes de compostos com perfil de filtro solar UVB, os cinamatos destacam-se por apresentarem boa eficácia e excelente custo-benefício. A aplicação de cálculos teóricos tornou-se indispensável no planejamento de fármacos e nos estudos de mecanismo de ação de moléculas bioativas, visto a diminuição de tempo e custos em pesquisa e desenvolvimento. O desenvolvimento de métodos quânticos robustos, como o TD-DFT, permitiu a simulação de propriedades experimentais in silico, tais como espectros de RMN e UV. Diante deste panorama, aplicamos tal método na simulação de espectros UV para os cinamatos com perfil de filtros solares. Realizou-se uma busca do melhor funcional para simulação dos espectros, na qual se determinou que os funcionais B3LYP e B3P86 apresentaram melhores resultados quando comparados ao espectro experimental do composto p-metoxicinamato de etilexila determinado em metanol. Foram simulados os espectros de UV para sete compostos derivados do ácido cinâmico, os quais apresentaram &#955; máximo próximo a 310 nm, como descrito na literatura. Observou-se que a energia média para que ocorra a principal transição eletrônica, de HOMO para LUMO, é de 3,95 eV. O método mostrou-se adequado para a determinação de espectros UV para a classe dos cinamatos e pode ser utilizado na busca de novos compostos dessa classe a serem empregados como filtros solares. / Skin cancer presents itself as a very serious world public health problem, being incident all over the five continents. Using sunscreen and receiving health education, among other factors, are related to prevent the disease. The number of people with skin cancer increases every year, therefore, studies for better knowledge and development for better and safer sunscreens are crucial. Products used with the intention to protect the skin from ultraviolet sunrays (UV) are partially composed by sunscreen, which may lead to two different reactions, a physical reaction, that reflects and ceases the UV radiation; or a chemical reaction, that absorbs the UV radiation. Chemical filters may present absorption in UVB (290-320 nm), UVA (320 400 nm) or in both, which is considered as broad spectrum. Among the various types of compound forms with sunscreen UVB profile, cinnamates stand out for presenting good efficiency and excellent cost-benefit. The application of theoretical calculations became essential for drug design and bioactive molecules action mechanism studies, considering time saving and costs in research and development. The development of robust quantum method, such as TD-DFT allowed the simulation of experimental properties in silico, like RMN and UV spectra. Given this overview, this method was applied to simulate UV spectra of cinnamates with sunscreen profile. A search was done to define the best functional to simulate all spectrum, where the functionals B3LYP and B3P86 showed the best results when compared to experimental spectra of the compound ethylhexyl methoxycinnamate determined in methanol. An UV spectrum simulation for seven compounds derived from cinnamic acid showed maximum wavelength around to 310 nm, as described in the literature. It was observed that the average energy for the main electronic transition, HOMO to LUMO, is 3,95 eV. The method proved to be adequate for the determination of UV spectra for cinnamate class and it can be used as a tool on the search for new compounds from this class to be used as sunscreen.