FCE - Trabajos de Titulación Post-Grado

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Análisis de la capacidad predictiva del concepto Zintl-Klemm en clusters del grupo 13 y 14 de la tabla periódica : diseño y aplicaciones
(2016) Vásquez Espinal, Alejandro; Tiznado, William,
La química de los elementos del grupo principal se ha estudiado principalmente a través de comparaciones con la química de sus homólogos más ligeros, es decir, con la química orgánica. Sin embargo, durante las dos últimas décadas del siglo pasado y, hasta el día de hoy, el número de compuestos basados en estos elementos que han sido sintetizados, se ha incrementado. Las similitudes en la estequiometría y la estructura de estos compuestos con sus análogos, como ocurre en las fases de Zintl, enmascaran algunas diferencias fundamentales en sus propiedades electrónicas y químicas, por lo que es de interés estudiar la química de estos nuevos compuestos y establecer nuevas reglas para racionalizar su comportamiento. Un área particular que involucra a estos elementos y atrae una atención especial, es el diseño y estudio de los diferentes clusters homoatómicos y heteroatómicos (por ejemplo, los clusters de Zintl) que pueden formar. Este interés se debe principalmente a las potenciales aplicaciones tecnológicas de estos clusters, como en catálisis, almacenamiento de hidrógeno y otras aplicaciones energéticas, tales como su uso en baterías. Por otra parte, desde un punto de vista químico, son de gran interés, ya que sus propiedades dependen en gran medida de su tamaño, por lo que su estudio debe realizarse de manera específica para cada sistema, lo cual, teniendo en cuenta el gran número de posibles combinaciones, hace el estudio de estos sistemas un terreno aun por explorar. Además, estos estudios proporcionan una base para la comprensión de la química de sistemas moleculares más complejas. En esta tesis, es de interés primordial el estudio de la química de compuestos basados en elementos del grupo principal, sus clusters atómicos análogos en fase gaseosa y el análisis de su relación con sistemas isoelectrónicos clásicos o con sistemas similares formados por elementos de grupos vecinos en la tabla periódica. Por otro lado, se estudia la reactividad de algunos de estos clusters, con especial interés en reacciones con H2, a fin de explorar la capacidad catalítica de estos sistemas.
Estudio teórico de las interacciones entre tinturas orgánicas derivadas de fenotiazinas y superficies de TiO2-anatasa
(2015) Urzúa Leiva, Rodrigo Antonio; Arratia Pérez, Ramiro
Entre los dispositivos diseñados para recolectar luz solar y transformarla en energía eléctrica, las celdas solares sensibilizadas por tinturas (DSSC) son las que presentan un mayor crecimiento en cuanto a eficiencia e investigación durante las últimas décadas. Dentro de este grupo de dispositivos, las DSSC orgánicas han ganado gran atención debido al bajo costo, simplicidad de diseño y síntesis, sumado al amplio conocimiento químico de algunas familias de tinturas orgánicas. Sin embargo, la complejidad de este tipo de celdas plantean aún grandes incógnitas en cuanto a su funcionamiento y eficiencia. En este contexto, el siguiente trabajo presenta un estudio teórico-computacional de las interacciones entre tinturas orgánicas derivadas de fenotiazinas (PTZ) y superficies de TiO2 en su morfología anatasa, que comúnmente son usados en DSSC. El estudio consiste en una detallada descripción de las superficies de anatasa a partir de su estructura cristalina fundamental, para posteriormente adsorber sobre dichas superficies dos conjuntos de PTZ funcionalizadas con los grupos de anclaje ácido cianoacrílico y ácido acético rodanina-3. Además, a partir de las diferencias encontradas en las geometrías de adsorción de estos dos conjuntos de PTZ, se realizó un estudio dinámico del mecanismo de trasferencia de energía resonante de Forster (FRET) cuando se utiliza como grupo antena dador de electrones el carbazol (CZ). En la primera etapa de este trabajo, se realizó un estudio del rendimiento de varios funcionales de la densidad (LDA, PW91 , PBE, HSE, PBE0 y B3L YP) en reproducir los parámetros de la red cristalina, el módulo de compresibilidad y el band- gap de la morfología anatasa, con la finalidad de establecer el(los) funcional( es) que mejor reproduce(n) la estructura geométrica y electrónica de los cristales de anatasa que serán usados para construir las superficies. Los resultados mostraron que la combinación de los funcionales PBE y HSE resultan en el mejor acuerdo entre exactitud y desempeño para determinar la morfología anatasa. De este modo, a partir de las estructuras cristalinas establecidas, se estudió la estabilidad teórica de las superficies de anatasa exponiendo las caras ( 1 O 1 ), ( 100) y (O 1 O), resultando la cara ( 1 O 1) como la más estable y en claro acuerdo con resultados experimentales. En la segunda etapa, se estudiaron ocho tinturas orgánicas derivadas de PTZ adsorbidas sobre superficies perfectas de anatasa (101). Dos tipos PTZ fueron consideradas: PTZl y PTZ2, ambas funcionalizadas con los grupos de anclaje ácido cianoacrílico o ácido acético rodanina-3. Además, se estudiaron tres tipos de sustituyentes en las PTZ tipo 1 (PTZ 1) con la finalidad de evaluar sus efectos en las propiedades de adsorción. En cada sistema estudiado se evaluaron detalladamente las energías de adsorción, la transferencia de carga (análisis de cargas de Bader) y las densidades de estado proyectadas (pDOS) sobre los átomos. Los resultados mostraron que el grupo de PTZ funcionalizadas con ácido cianoacrílico se adsorbe en una forma cercana a la perpendicular respecto de la superficie, a diferencia del grupo de PTZ funcionalizadas con el ácido acético rodanina- 3, que lo hacen en una forma más paralela a la superficie. Esta diferencia incide en el efecto que ejerce el sustituyente en las energías de adsorción de las PTZl, mostrado tendencias opuestas en cada subconjunto. Por otra parte las energías de adsorción y cargas de Bader indican que todas las PTZ se adsorben favorablemente sobre superficies de anatasa ( 1 O 1) y que ocurre una transferencia de carga desde la superficie hacia el adsorbato. Junto con esto, un análisis de las pDOS que componen la superficie y el adsorbato en el grupo de PTZ funcionalizadas con ácido cianoacrílico, mostraron que nuestro modelo de orbitales frontera HOMO-LUMO en la superficie y el adsorbato presentan un buen acuerdo con resultados experimentales acerca de las energías de excitación fundamental en estas tinturas. Finalmente, en un estudio dinámico de la tasa FRET sobre dos PTZ funcionalizadas con ácido cianoacrílico o ácido acético rodanina- 3, y sustituida con el grupo antena CZ, se estableció que en este tipo de sistemas resulta indispensable incluir las fluctuaciones térmicas cuando se intenta predecir teóricamente la tasa FRET. Además se mostró que la aproximación de esta tasa mediante los modelos estáticos e isotrópicos es inadecuada cuando se trata de reproducir resultados de FRET en DSSC funcionalizadas con derivados de CZ- PTZ.
Theoretical study of magnetic anisotropy in mono and polynuclear lanthanide complexes
(2018) Solis Céspedes, Eduardo; Páez Hernández, Dayán
The development of new lanthanide materials with special magnetic properties has been in the last decades a tapie with a vertiginous advance. The high chemical modifiability of the constituting molecules makes such materials highly versatile, and the small size of the building blocks leads to the rise of various quantum mechanical phenomena. This work describes the computational and theoretical studies in the field of molecular magnetism using state-of-the-art quantum chemical methods based on ab-initio multireference approaches. In a first step the methodology is proposed and applied to describe the role of the ligand environment on the Kramers doublets derived from the 6H1s12 ground configuration of the Dysprosium (Dy3+) ion in its complexes; concluding that in the case of lanthanides whose electron distributions are oblate (squashed along the axial direction), such as terbium, dysprosium and holmium, an axial position of the ligand electrons is particularly favorable for generating a sizeable magnetic anisotropy. In the second work a theoretical model is proposed to model the electronic states and magnetic properties derived from the f1 configuration. This model was applied to lanthanocene and actinocene compounds, showing the important role of the symmetry in the study of the magnetic properties. Finally, a theoretical insight in the superexchange mechanism of coupling in a f1 -f1 system is presented for Ce2(COT)3 compound; an altemative mechanism for the superexchange between the two f1 lanthanide centers is presented considering the 5dz 2 orbitals. In ali cases the computational tools offer more insight into the electronic structure and chemical properties of the systems, giving rise a better understanding of the causes of the various observed magnetic phenomena. The results contribute to our understanding of magnetically interesting molecular systems and suggest new details to take into account in the fíeld.
Metallacycles capabilities in host-guest chemistry
(2014) Ponce Vargas, Miguel Armando; Muñoz Castro, Álvaro
Metallacycles offer structural diversity and interesting properties based on their highly symmetric frameworks and host-guest chemistry. They can be used as molecular recognition agents, photochromic devices, catalysts, and surface patterning structures, just to mention a few applications. The aim of this work is to gain a deeper understanding into the coupling forces within metallacycle complexes possessing metal centers acting as binding sites, by using density functional calculations. We focus on the electrostatic contribution to total interaction energy, which can be divided in ion-dipole, ion-quadrupole, dipole-dipole, dipolequadrupole, etc., according to the multipole expansion of the electrostatic potential. We choice two representative case studies: halide-centered hexanuclear copper(II) pyrazolate- and di-halide cyclic pentameric perfluoroisopropylidenemercury complexes, due to the presence of metal centers capable of interacting directly with the guest entities. The current approach, allows us to determine the role of certain Coulombic terms in the electrostatic nature of the coupling forces, leading to a clear rationalization of the soft-soft or hard-soft preferences into the formation of the host-guest entities. The non-covalent forces involving the hexanuclear copper(II) pyrazolate complexes and a halide guest [trans-Cu6{μ -3 ,5-(CF3)2pz}6(μ-OH)6X]- (X = F, Cl, Br, 1), describe an electrostatic character (about 70% of the stabilizing terms) where the ion-dipole and ionquadrupole contributions to the electrostatic term range from 95.0% to 77.0%, going from f - to r-, describing the increasing role of higher arder interactions, such as quadrupoledipole and quadrupole-quadrupole into the coupling as the guest becomes softer. In di-halide cyclic pentameric perfl uoroisopropylidenemercury complexes, [(HgC(Cf3)2)s2X]2- (X = Cl, Br, 1), our results revea! an interesting case where the expected soft acid-soft base pair is not the more stable situation. Instead, a surprising hardsoft pair arises as the preferred species, with stronger forces towards Cl- than those corresponding to J- by about 24 kcal/mol. The almost linear mercury local geometry and the Dsh molecular symmetry determine the shape of the local quadrupole moments at the binding sites leading to an in-plane distribution, preventing the arise of a significant quadrupole component perpendicular to the Hgs plane, that could contribute to higher order electrostatic terms such as quadrupole-quadrupole, which is related to the soft-soft preference. In summary, the results here presented suggest that metallacycles hosts with metal centers acting as binding sites, can offer great advantages in comparison to their organic counterparts, prompted by the versatility of such centers, which can modulate their electron density according to the incoming guest. This work was made possible by the CONICYT 63130036 Doctoral fellowship, and the financia! support of UNAB-DI-403-13/I Interna! Project, 1140358 FONDECYT Grant and RCl20001 MILLENNIUM Project.
The globular cluster systems of the milky way and the Sagittarius dwarf galaxy
(Universidad Andrés Bello, 2023) Garro, Elisa Rita; Minniti, D.; Fernández Trincado, Jose Gregorio; Gómez, Matías; Alonso García, Javier; Ripepi, Vincenzo; Facultad de Ciencias Exactas
The VISTA Variables in the Via Lactea Survey (VVV) and its Extension (VVVX) allow us to probe ´ previously unexplored regions of the inner Milky Way (MW), especially those that are affected by stellar crowding and strong extinction. My long-term goal is to identify new star clusters and investigate them to reveal their true nature. In particular, I am looking for new candidate globular clusters (GCs) located in the Galactic bulge and disk, with the aim of completing the census of the MW GC system. I searched and characterized new star clusters, using a combination of the near-infrared (IR) VVV-VVVX survey and Two Micron All Sky survey (2MASS) datasets, and the optical Gaia Data Releases (DR2, EDR3 and DR3) photometry and its precise astrometry and proper motions (PMs). Performing a PM-decontamination procedure, I built final catalogues with high-likely cluster members, on which I carried out a detailed photometric analysis. I estimated the main physical parameters, such as reddenings and extinction, heliocentric and Galactocentric distances, mean cluster PMs, metallicities, ages, integrated luminosities, and structural parameters (core and tidal radii). I analysed 34 new GC candidates in the MW and 21 in the Sagittarius dwarf galaxies, confirming (photometrically) the GC nature for 17 of them, and 4 are old open clusters in the MW bulge and disk, whereas other 17 GCs belonging to the Sagittarius dwarf galaxy. Finally, for 11 bound systems, I collected radial velocity informations (from H-/K-band spectra and/or Gaia DR3 datasets) in order to reconstruct their orbital history for the first time, thus associating these clusters to the relative Galactic components and understand their (in-situ or ex-situ) origin.
Search for hypervelocity stras in the central regions of the galaxy
(Universidad Andrés Bello, 2023) Ruiz Fernández, Alonso Luna; Minniti, D.; Rejkuba, Marina; Marchetti, Tommaso; Alonso García, Javier; Leigh, Nathan; Facultad de Ciencias Exactas
In this thesis, I propose a new approach to search for hypervelocity stars in the inner part of our Galaxy. Hypervelocity stars are moving at velocities around 1000 km s−1 , acquiring such velocity after an interaction with the supermassive black hole at the centre of the Milky Way: Sgr A*. Hence, these stars inform us about i) dynamical stellar interactions with Sgr A*, ii) phenomena in regions with high stellar density, iii) the stellar content in the inner part of the Galaxy, and iv) the presence of massive objects, such as intermediate and stellar-mass black holes. Hypervelocity stars are extremely rare, to identify them it was necessary to characterise the proper motions of the stars in the used catalogues: Gaia , VVV and VIRAC2, which contain hundreds of millions of sources. I explore also different approaches to identify and validate the reliable data in such catalogues, that result in being able to identify the unique objects in these catalogues, in this case, hypervelocity stars. The results of this work are the characterisation of the astrometric data of Gaia DR3 and VIRAC2 with respect to data from the Hubble Space Telescope (HST) in observations towards the Galactic bulge. On one hand, the uncertainties in the proper motions of Gaia DR3 are underestimated with respect to the HST proper motions, thus the need for an inflation factor to bring them into a 1σ consistency. On the other hand, VIRAC2 proper motions are in agreement with HST proper motions. For this reason, I used VIRAC2 proper motions to search for hypervelocity stars. With the developed method, I identified 139 candidate hypervelocity stars in the inner 60 sqdeg. around the Galactic centre. These stars appear to be ejected after an interaction with Sgr A *. Besides that, we identified more than 1000 high-velocity stars (> 600 km s−1 ), probably produced in the Galactic disc, although their origin is uncertain.
Sulfur abundances in the milky way major components
(Universidad Andrés Bello, 2023) Lucertini, Francesca; Monaco, Lorenzo; Caffau, Elisabetta; Sbordone, Luca; Bonifacio, Piercarlo; Francois, Patrick; Facultad de Ciencias Exactas
The measurements of chemical abundances and their ratios are a powerful diagnostic to put con straints on both stellar nucleosynthesis and galaxy formation history. For instance, the ratio between elements produced on different timescales, such as α-elements (produced by Supernovae Type-II after ∼30 Myr) and iron (produced by Supernovae Type-Ia on longer timescales), can be used as cosmic clocks. Sulfur is an α-element produced in the final stage of the evolution of massive stars by oxygen convective shell burning and explosive oxygen burning. Moreover, it is moderately volatile so, unlike other α-elements, its abundance measured in stars in the Local Group galaxies can be directly compared to the abundance measured in the gaseous phase in the far Universe, as extra-galactic H II regions or damped Ly-α systems. For these reasons sulfur abundances provide clues on star forma tion history and properties of the interstellar medium, connecting the local and distant Universe. Despite the great potential of this element, most of the available stellar abundances of sulfur come from Galactic stars. Only in the latest years, this analysis was expanded to stars outside the Milky Way. Our view of the behavior of Sulphur in the Milky Way and its satellite is, thus, far from complete. I ran a series of experiments to define the top level requirements needed to measure sulfur abun dances, and I explored the ESO archive looking for available data in a setup adequate for my goal. I identified several interesting public datasets. I focused on the Milky Way major components and, in particular, I found useful data for the Galactic bulge and disk, and a few clusters likely residual of accretion events in the Milky Way (like ω Cen, M 54 and Rup 106). Furthermore, the collaboration with the MINCE project gave me access to high-quality spectra of giant stars at intermediate metallicities in the Milky Way halo. The analysis of this dataset provides important clues about the evolution of Sulphur within the Milky Way. It provides a homogeneous database useful to compare the Milky Way major components with distant systems.
Galactic archaeology in the 21st century : unveiling accretion in the MW disc
(Universidad Andrés Bello, 2022) Tronrud, Thorold; Tissera, Patricia; Gómez, Facundo A.; Gómez, Matías; Bignone, Lucas; Facultad de Ciencias Exactas
The evolution of large galaxies such as the Milky Way (MW) in Λ Cold Dark Matter (ΛCDM) cosmology is driven by interactions with other galaxies. These interactions affect the structure of the galaxy in long-lasting ways, not only forming the stellar halo, and modifying the size and characteristics of the stellar disc, but also contributing gas that fuels star formation and depositing stars directly into the galaxy. This stellar debris, formed outside the galaxy in which they now reside (a.k.a. ex-situ), retain the chemical fingerprint of the environment in which they formed, leaving them distinct from the stars that were formed within the primary galaxy (a.k.a. in-situ). If these ex-situ stars are located beyond the disc, in the stellar halo, the distributions they occupy in space — based on the kinematics of their progenitor object — may be readily apparent as streams or great circles surrounding the primary galaxy. A population of ex-situ stars are also expected to reside in the stellar disc, even at high circularities. These stars have been found in simulations to be deposited by relatively few massive mergers, but finding them poses a challenge in this dense region. I propose a method, based on training and utilizing neural networks, to classify disc stars as in- or ex-situ based on their chemical parameters. The use of this method is motivated by my research into the effects mergers and accretion have on the galactic stellar disc of a suite of simulated MW-like galaxies, in which I demonstrate that accretion events and accreted stars cause observable changes to calculated metallicity gradients, and can cause disagreements in correlations between observed parameters based on the ages of the stars being used. Galactic discs form inside-out, starting small and slowly expanding with new star formation at the outer edges. This imparts a natural negative age gradient. Stars that have been deposited onto the disc will not necessarily follow this age gradient, which is one of the primary drivers of the stellar disc’s metallicity gradient. These ex-situ stars drive several age-specific correlations between metallicity gradient and 𝑅 −1 eff and 𝜆 ★ gal that vanish entirely once these contaminants are removed. A chemistry-based method for flagging potentially-accreted stars will allow researchers to remove the bulk of these from their samples, which will allow them to examine the evolution of the galactic disc more finely. Furthermore, these flagged, ex-situ stars can be grouped by their characteristics, for attempts to discern early progenitors of the primary galaxy with significantly less noise from stars formed in-situ. I demonstrate that the Galactic Archaeology Neural Network (GANN) recovers usable fractions of nearly every contributor to the suite of simulated stellar discs. Thus, a catalogue of stars flagged by GANN will contain most of the merger information that is present in the stellar disc of a galaxy. Future applications of this method could aid in the discovery of many ancient remnants, and broaden our understanding of how our galaxy formed.
Description of the optical and molecular properties in lanthanide macrocyclic complexes using quantum chemical relativistic methods
(Universidad Andrés Bello, 2015) Rabanal León, Walter A; Arratia Pérez, Ramiro; Facultad de Ciencias Exactas
The lanthanides or most commonly known as .. rare earths" have attracted the interest of thc scic11tific comrnunity i11 thc last 30 ycars, duc to their uniquc and appealing characteristics. Probably, one of the most interesting is their f-f inherent spectroscopic properties in thc nea.r infra-red rcgion of the spectra prescnting charactcristic narrow "line-like" emission bands. Additionally, these f-f transitions are parity (and sornetimes also spin) forbidclen, rcsulting in vcry long livcd excited states. Unfortunately, as another consequence of the parity (Laporte) forbidden nature of the 4f transitions, the direct absorption of Ln(III) cations is quite poor, and they hence have very low molar absorption coefficients which limits their practical usage. For that reason, the use of molecular antennas, which absorbed highly effi.ciently the light and then promete a charge/energy transfer to the lanthanide center (populating their excited states), was proposed as a simple and useful way to sensitize and enhance the lanthanide luminescence. In this way, this doctoral dissertation entitled: "Description of the Optical and Molecular Properties in Lanthanide ::Ylacrocyclic Complexes Using Quantum Chemical Relativistic Methods", is a study based on the relativistic density functional and the wave-function theory of a series of poly-aza and poly-oxo lanthanide macrocyclic complexes, whose purpose is to characterize: i) the ground and excited states, ii) the lanthanide-macrocycle interaction, and iii) the nature of the main electronic transitions involved in optical applications. During the development of this work, we found interesting results on the characterization of the bond interaction, energetics and optical properties, that show the potential use of 1r-conjugated macrocyclic systems as molecular antennas which could sensitize the lanthanide luminescence throughout a charge transfer phcnomena, which is favoured by a dativc covalcnt intcraction betwccn thc macrocyclic ligand and the lanthanide center. Moreover, it was achieved an extensivc knowledge of thc clectronic structurc, cspecially the multi-coufigurational naturc of the ground and excited states, as a consequence of the low-lying character of the lanthanidc 4f-shcll ancl thc strong statc rnixiug possibility due to the low sy111rnetry and the spin-orbit coupling effect.
Caracterización teórica de catalizadores de Rutenio con potencial actividad en reacciones de metátesis
(Universidad Andrés Bello, 2014) Paredes Gil, Katerine; Jaque, Pablo
La metátesis de olefinas o reorganización de dobles enlaces C-C es una de las transformaciones químicas más utilizadas en las últimas dos décadas para la generación de numerosos compuestos dentro de la química fina, farmacológica, y ciencia de los materiales. Esta reacción ocurre a través de un catalizador metálico el cual está basado principalmente en complejos de rutenio tipo carbeno. Diversos estudios experimentales y computacionales han permitido comprender las características generales de este proceso, tal como es descrito en el Capítulo 1. Sin embargo, algunos aspectos de tipo electrónico, cinético y termodinámico podrían ser abordados desde el punto de vista computacional con el propósito de profundizar en el comportamiento químico de esta reacción. n esta dirección, un eje principal de discusión dentro de la metátesis de olefinas es la diferenciación de la reactividad de la 1 ra y 2dª generación de catalizadores de Grubbs. Múltiples estudios han abordado este tema a partir de los cambios energéticos que ocurren tanto en la reacción de disociación del ligando PR3 como en la interconversión de las especies catalíticas de 14e-. Sin embargo, el cambio en la reactividad de estos catalizadores en la etapa de formación del rutenaciclobutano no ha sido explorado, y es el tema central del Capítulo 4. Por otra parte, la identificación de las diferencias de los enlaces principales que participan en la etapa de iniciación, son descritas en el Capítulo 5. Ambos aspectos permitieron proponer que la mayor reactividad de la segunda generación en las reacciones de metátesis de olefinas debe entenderse como la suma de diferentes efectos dentro de la etapa de iniciación: cambios en la transferencia de carga, polarización y deslocalización electrónica, principalmente.
Optical and magnetic properties of organoactinide complexes an application of relativistic density functional theory
(Universidad Andrés Bello, 2012) Páez Hernández, Dayán
The discovery of slow magnetic relaxation in certain transition metal-oxo clusters revealed a new family of magnetic materia Is known as single-molecule magnets. Such molecules possess a high-spin ground state (with total spin S) for which spin-orbit coupling results in a zero-field splitting of the (2S + 1 )-fold degeneracy in a manner that creates a thermal relaxation barrier and gives rise to magnetic bistability at low temperature. Two major goals of research in this area are generating new molecules with larger relaxation barriers and understanding the quantum tunneling processes that can sho1tcut the ban-ier. The greater radial extension of the 5/ valence orbitals of actinides can potentially provide increased overlap with bridging ligand orbitals, thereby enhancing the concerted magnetic behavior between bridged metal centers within a single cluster unit. Researchers have confronted the intricacies of the magnetic exchange in a number of interesting ways, often with the goal of identifying and, to the extent possible, quantifying ferro- or antife1TOmagnetic exchange coupling. Understanding these exchange interactions not only is essential to the development of models for the basic electronic stmcture of the Velements but also may represent the key to producing the first actinide-based SMMs. In this work we present the theoretical investigation about the magnetic and optical properties for a group of organoactinide complexes. Our calculations reveal that the electron mobility (delocalization) and relativistic effect pa1ticularly spin-orbit coupling have a principal role for a good description of these properties in this kind of molecule. Also we propose sorne molecular models with desirable structural parameters when the optical and magnetic properties detennined should open the door to the design of new materials with potential technological applications.
Understanding quasar microlensing light curves in the context of large area surveys
(Universidad Andrés Bello, 2022) Neira, Favio; Anguita Timo; Facultad de Ciencias Exactas
The accretion disc around the super massive black hole (SMBH) of quasars, and active galactic nuclei (AGN) in general, is believed to be the central engine of the optical and UV continuum we observe. AGN and their host galaxy are tightly connected in their evolution, thus a detailed understanding of the accretion disc is required for a coherent picture of not only their evolution, but also of their environment and the large scale universe. However, due to how typically far away these objects are (z∼2), as well as how compact the are, we have not been able to directly resolve in detail its structure. One such method to indirectly probe these accretion discs relies on observing microlensing high magnification events (HME) in strongly lensed quasars. These kinds of studies usually consist of comparing observations with simulations in order to infer the properties of the accretion disc. However, these simulations are computationally expensive, especially due to the large range of parameters that needs to be explored. Furthermore, we expect to increase the number of lensed quasars from hundreds to the order of thousands. The few HME studies that have been been done are relegated to a few selected systems with specific parameters, this in part due to how few of them we had known and how hard it is to obtain suitable data for these studies. Because of this, preparation for the new systems is timely, however, there are not quantitative results that could allow us to prepare for this. In this thesis we provide a simulation framework from where microlensing light curves of lensed quasars can be generated and facilitate the study of high magnification events (HME). Motivated by the, yet to be fully unveiled, potential of HME at constraining the inner structure of quasar, the main goal of this work is to develop tools and methods to prepare for the forthcoming large area surveys. Specifically, we have built a tool that can generate simulated quasar microlensing light curves and serve as the foundation for qualitative and quantitative HME studies. To highlight the capabilities of i this tool to enable HME studies, we generated of the order of billions (109) simulated light curves and analyzed them to statistically study and understand the nature of HME. We studied three lensed quasar known to have microlensing, and show that, depending on their location on the sky, the lens and source redshift, and the caustic network density, the microlensing variability time scales may deviate from theoretical estimations. We estimate that 300 HME with Δm > 1 could potentially be observed by The Vera Rubin Observatory Legacy Survey of Space and Time (LSST) each year. We show that depending on the observing strategy adopted, in the best scenario only 20% of these events would be missed. We generated microlensing light curves for thousands of simulated lensed quasars. We estimate that about 55 HME with delta mag Δm > 0.3 could be observed each year in the southern (or northern) sky by most telescopes. We observe a broad range in frequency, duration and amplitude of these events. We show that this can be better understood by classifying these events by the parity of the image from which they were identified (i.e. minimum or saddle) and whether or not the center of the quasar accretion disc crosses a caustic during the event (caustic crossing). We assess the usefulness of the simulated lensed quasar images for HME studies and show that the top 20% can have 50% of the total expected number of events. The tool that has enabled these studies is publicly available at https://gerlumph.swin.edu. au/tools/lsst_generator/. There are many issues to address regarding HME studies, which the tool presented here could help to. We have shown how this tool can help push forward our understanding of HME, bringing us a step closer to developing the tools and methods that will allow us to make the most out of the forthcoming large area surveys.
Desarrollo e implementación de algoritmos híbridos para la exploración de la superficie de energía potencial en clusters atómicos y moleculares
(Universidad Andrés Bello, 2018) Yáñez Osses, Osvaldo Andrés; Tiznado, William; Garza Olguín, Jorge; Facultad de Ciencias Exactas
los cúmulos atómicos (clusters en este escrito) son entidades químicas con propiedades, físicas y químicas, particulares y dependientes de su tamaño. la química teórica, enmarcada en la mecánica cuántica y clásica, cumple un rol fundamental en el estudio de estos sistemas, ya que éstos se sintetizan mediante la atomización del material (a altas temperaturas) y las propiedades que se logran medir son en estado gaseoso. Por este motivo la forma práctica de asignación estructural se basa en medir la propiedad experimental con su contraparte teórica. Por ejemplo, se utilizan los espectros fotoelectrónicos para estas asignaciones, siendo éstos característicos de cada isómero (la estructura electrónica es muy dependiente de la estructura geométrica). la predicción conformacional de clusters atómicos tiene implicaciones relevantes en campos tan variados como el diseño de nanomateriales, nanobiomedicina, catálisis, entre otros, por lo tanto es necesario contar con un método confiable o una combinación de varios métodos para la exploración de las superficie de energía potencial (SEP) de clusters atómicos y moleculares. En consecuencia, la determinación de la estructura y de las propiedades físicas de un sistema molecular está íntimamente relacionada con el mínimo global en su SEP.
Compuestos metal-orgánicos con propiedades multifuncionales
(Universidad Andrés Bello, 2018) Baldo Hurtado, Bianca; Paredes García, Verónica; Facultad de Ciencias Exactas
RESUMEN El hecho que un compuesto metal-orgánico contenga tanto una parte orgánica como una inorgánica, hace que estos sistemas sean altamente modulables, desde la dimensionalidad de su estructura hasta las propiedades que se obtienen. Es así como durante el último tiempo, la química de coordinación ha estado enfocada en la síntesis de nuevos materiales basados en cationes 3d y 4f, enlazados a través de ligantes orgánicos con grupos funcionales de diferente naturaleza química, lo que hace posible encontrar en este tipo de materiales propiedades interesantes como luminiscencia, óptica no lineal y magnetismo, entre otras. Por otra paite, la síntesis de compuestos metal-orgánicos de mayor dimensionalidad se ha visto dominada por tiempos largos de reacción, además de la utilización de solventes orgánicos expuestos a condiciones de temperatura y presión mayores a las utilizadas en métodos de síntesis tradicionales. Sin embargo, en los últ imos años ha crecido el interés por el desarrollo de nuevas técnicas sintéticas con menores tiempos de reacción y más amigables con el medio ambiente, como son la mecanoquímica y sonoquímica.
Calculated optical properties of polypyridine complexes and its possible use in solar cells
(Universidad Andrés Bello, 2013) Schott Verdugo, Eduardo; Arratia Pérez, Ramiro; Facultad de Ciencias Exactas
A senes of polypyridyl complexes with tris-(2,2'-Bipyridine) and 2,2':6',2"-terpyridine substituted dyes and Ru(II) or Os(II) as central metal were studied. The influence on the variation of the substituents over the composition of the molecular orbitals, electronic transitions and reactivity of these compounds was studied. A good agreement with tbe previously reported experimental data, of the geometrical parameters and of the UV-Vis transitions, was found for the complexes which have previous experimental reports. In these theoretical calculations the -COOH anchor group to get attached to the semiconductor surface was included. Using the charge transfer analysis and the orbitals that are involved in the transitions, it was observed that the complexes that have electron-donor substituents might be more efficient to donate electrons when they are attached to a semiconductor surface than those complexes that have electron-acceptor substituents. Therefore the results suggest that these dyes with electron-donor substituents will give better yields in photocurrent generation. Also, the localization of the LUMO over the ligand that has the anchor will help to improve electron injections into the TiO2 nanoparticles. We propase here severa! not yet synthetized dyes, which could be used in this kind of devices, due to their interesting molecular properties. l
First-order Lagrangian of Lovelock gravity and applications
(Universidad Andrés Bello, 2022) Guilleminot Arellano, Pablo; Olea, Rodrigo; Merino, Nelson; Faraggi, Alberto; Miskovic, Olivera; Aros, Rodrigo; Corral, Cristóbal; Facultad de Ciencias Exactas
En este trabajo, se analizan, analíticamente, aspectos de evolución espacial en gravedad de Lovelock. Se muestra que la adición de términos de Myers a la acción elimina las derivadas de segundo orden respecto a la variable de evolución. Así, la conexión entre el problema de Dirichlet y Lagrangianos de primer orden es establecida. Luego, se exhibe como la transformada de Legendre de este último permite calcular directamente el Hamiltoniano del sistema para la misma variable de evolución. Con estos resultados, se analiza el comportamiento de cáscaras delgadas con masa en el contexto de gravedad de Lovelock. Para esto, se trabaja el principio variacional escrito en un set adaptado de coordenadas válido cerca de la cáscara. Se concluye que la cantidad que es discontínua en la cáscara es el momentum canónico. Finalmente se obtienen algunas expresiones explicitas para configuraciones con simetría esférica.
Desarrollo e implementación de métodos de cómputo para densidades de estados, usando ensambles generalizados
(Universidad Andrés Bello, 2022) Moreno Muñoz, Felipe Eduardo; Peralta, Joaquín; Davis, Sergio; Faraggi, Alberto; Gutiérrez, Gonzalo; Molina, Francisco; Poblete, Simón; Facultad de Ciencias Exactas
El presente trabajo se enfoca en el desarrollo e implementación de algoritmos de simulación que permitan calcular la Densidad de Estados (DOS) de sistemas de muchas partículas interactuantes usando ensambles generalizados. Métodos para obtener las propiedades de un sistema que se basan en el uso de ensambles canónicos o microcanónicos—como el popular algoritmo de Metropolis—se han usado durante ya un largo tiempo. Sin embargo, el empleo de ensambles generalizados muestra ser una alternativa que permite generar curvas más suaves con menor número de simulaciones, además de evitar ciertos problemas típicos de esos métodos como el tener dificultades para muestrear correctamente sistemas con muchos mínimos locales. En este trabajo se presenta una implementación flexible y modular del algoritmo de Wang–Landau, además de un novedoso algoritmo basado en un método Bayesiano para el cálculo directo de la DOS, los cuales puede ser usados para obtener las propiedades termodinámicas de un sistema con una superficie de energía potencial compleja. Nuestros resultados muestran que los algoritmos son capaces de calcular la DOS con razonable precisión. Hemos estudiado, como aplicación de los métodos anteriormente mencionados, las propiedades termodinámicas de un modelo de Potts de 3 estados modificado, en el contexto de la aproximación de “lattice gas” para partículas cargadas confinadas en un volumen.
DFT study of the optical properties and substituent effects in macrocyclic systems formed by metalloporphyrins for their potential application in solar cells
(Universidad Andrés Bello, 2012) Zárate Bonilla, Ximena del Pilar.; Arratia Pérez, Ramiro; Facultad de Ciencias Exactas.
Dye-sensitized solar cells (DSCs) were designed by Michael Griitzel. They have become as a promising inexpensive alternative to light-current conversion. Basically, DSCs are constituted by nanocrystalline films of a semiconductor oxide, a !ayer of dye adsorbed to the oxide surface, solution of iodide/triiodide redox couple that by its reduction regenerates the dye after the electron-injection to the semiconductor. Nowadays, continuous researches are being carried out because of the variety of elementary components present in these cells. The process of current generation starts with the photo-excitation of the dye molecules, being this, the most important topic that has attracted a considerable experimental and theoretical interest. Studies point to different kind of dyes that allow tuning the properties and then to optimize their overall performance in assembled devices. The dyes show interesting properties useful in the design of a DSC, namely light absorption in the UV-Visible region of the electromagnetic spectrum, chemical stability, sensitization, effective adsorption on the semiconductor surface, electron-separated states, etc. Among the wide amount of dyes employed, porphyrinic systems have shown to be efficient lightharvesting. In this sense, properties of different families constituted by monomers, dimers and trimers of porphyrinic macrocycles coordinated to metals like Ti, Ni and Zn were studied. The structural modification consists in changing the peripheral 13-substituents in the rings with the proposal to predict the geometrical and electronic properties of new complexes which can be good candidates as sensitizers in solar cells. In addition, the study of electron-injection mechanisms from dyes to a TiO2 nanoparticle was performed since a theoretical point of view. In general, the results show that complexes with electron donor peripheral substituents are very promising to provide good performances as sensitizers and they could act as light-harvesting for DSCs. On the other hand, it was found a theoretical tool which allows differentiation of the direct and indirect photo electron-injection mechanisms in a DSC.
Phenomenological chemical reactivity theory for mobile electrons
(Universidad Andrés Bello, 2009) González Suárez, José Mauricio.; Renato Contreras.; Facultad de Ciencias Exactas.
We present herein a model to
Relativistic study of the luminescent properties in systems containing lanthanide and actinide ions : a view of the antenna effect
(Universidad Andrés Bello, 2017) Cantero López, Plinio de los Santos Plinio de los Santos.; Arratia Pérez, Ramiro; Facultad de Ciencias Exactas.
In the recent decades, the synthesis and the theoretical study of new compounds containing Lanthanide and Actinide ions have become in a very interesting topic of research. Ali this due to the potential use ofthis systems as materials for biological immunoassays, lasers, cathode ray tubes, lighting systems, electroluminescent devices, sensors, dosimeters, imaging agents, display applications, decoration purposes and light-emitting diodes (LEDs). These unique spectroscopic properties are attributed to the characteristic f-f transitions in their inner ( 4f/5f) shell, which is shielded from the influence of the environment by the outer (5s,5p/6d,7s) shells. These transitions are Laporte-forbidden with low absorption coefficient, which makes the direct excitation of the Ln/ An ion inefficient. For this purpose, over the years have been preved that the complexation by certain organic and organometallic ligands favored and enhances the luminescence intensity ofthese ions (Antenna effect), due to the ligand absorb highly efficiently the light in the ultraviolet region and transfers energy from its excited level to the resonant level of the Ln/An center (charge/energy transfer process), which can ernit light or decay nonradiatively. In this context, this doctoral thesis entitled: "Relativistic Study of the Luminescent Properties in Systems Containing Lanthanide Ions and Actinide" we study the Antenna effect and the electronic structure of the Ln/An systems using quantum chemical relativistic methods (relativistic density functional). In a first step, we investigated heterobimetallic systems of Actinide and transition metals unsupported by bridging ligands. Our aim was to research the role of the [CpM(C0)2r (M= Fe, Ru, Os) chromophore in the optical properties of the [Cp2ThMCp(C0)2]+ complexes. In the next stage, was shown the possibility of tuning the molecular antenna effect in these molecules by means of structural modifications in the peripheral ligands. Finally, were synthesized new luminescent Eu(III) complexes, based on dypiridophenazine (dppz) derivatives ligands. Apart from the Relativistic DFT, these compounds were also theoretically studied by means of ab initio methods that allows excited states in Lanthanide complexes to be analyzed, and energy transfer pathways from the antenna to Lanthanide ion.

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