Hybridization and covalency in the Group 2 and Group 12 metal cation/rare gas complexes

We provide a consistent set of interaction energy curves for the Group 2 (IIA) and Group 12 (IIB) metal cation/rare gas complexes, M+-RG, where M+= Be+–Ra+ and Zn+–Hg+; and RG = He–Rn. We report spectroscopic constants derived from these, compare them with available data, and discuss trends in the values. We gain insight into the interactions that occur using a range of approaches: reduced potential energy curves; charge and population analyses; molecular orbital diagrams and contour plots; and Birge-Sponer plots. Although sp hybridization occurs in the Be+-RG, Mg+-Rg and Group 12 M+-RG complexes, this appears to be minimal and covalency is the main aspect of the interaction. However, major sd hybridization occurs in the heavier Group 2 M+-RG systems, which increases their interaction energies but there is minimal covalency. Examination of Birge-Sponer plots reveals significant curvature in many cases, which we ascribe to the changing amounts of hybridization or covalency as a function of internuclear separation. This suggests why the use of a simple electrostatics-based model potential to describe the interactions is inadequate

Complexes of Zn(II)–Triazoles with CO2 and H2O: Structures, Energetics, and Applications

Using a first-principle methodology, we investigate the stable structures of the nonreactive and reactive clusters formed between Zn2+–triazoles ([Zn2+-Tz]) clusters and CO2 and/or H2O. In sum, we characterized two modes of bonding of [Zn2+-Tz] with CO2/H2O: the interaction is established through (i) a covalent bond between Zn2+ of [Zn2+-Tz] and oxygen atoms of CO2 or H2O and (ii) hydrogen bonds through N–H or C–H of [Zn2+-Tz] and oxygen atoms of H2O or CO2, N–H···O. We also identified intramolecular proton transfer processes induced by complexation. Indeed, water drastically changes the shape of the energy profiles of the tautomeric phenomena through strong lowering of the potential barriers to tautomerism. The comparison to [Zn2+-Im] subunits formed with Zn2+ and imidazole shows that the efficiency of Tz-based compounds for CO2 capture and uptake is due to the incorporation of more accessible nitrogen donor sites in Tzs compared to imidazoles. Since [Zn2+-Tz] clusters are subunits of an organometallic nanoporous materials and Zn–proteins, our data are useful for deriving force fields for macromolecular simulations of these materials. Our work also suggests the consideration of traces of water to better model the CO2 sequestration and reactivity on macromolecular entities such as pores or active sites.This is the peer-reviewed version of the article: J. Phys. Chem. A 2019, 123, 26, 5555-5565, [https://doi.org/10.1021/acs.jpca.9b03228]Published version: [http://cer.ihtm.bg.ac.rs/handle/123456789/3270

Ab initio and force field investigations of physical hydrogen adsorption in Zeolitic Imidazole Frameworks

Recent theoretical calculations and experiments have considered that metal-organic frameworks are promising for storing molecular hydrogen (H2). Optimizing the geometry and the interaction energy of storing for enormous H2 storage is of great current interest. In this work, we used specific category of MOFs, Zeolitic Imidazole Frameworks (ZIFs). We carried out calculations through high-accuracy electronic structure calculations (MP2, CCSD and CCSD(T)) levels of theory, with controlled errors. Also we established and calibrated a computational protocol for accurately predicting the binding energy and structure of weakly bound complexes. Then, we applied the protocol to a number of models for metal-organic frameworks. For example, we have built many systems of noncovalently bound complexes [H2…benzene, H2….imidazole, CO…. imidazole, N2… imidazole, NH3…imidazole and H2O …imidazole] and we have optimized geometries of these systems through calculating numerical gradients at MP2/CP level and LMP2 level of theory and extrapolated from aug-cc-PVTZ and aug-cc-PVQZ basis set to evaluate the binding energy by using Hobza's scheme to obtain correct interaction energies. We found that NH3 and H2O with imidazole prefer to form hydrogen bonds rather than physical adsorption (London dispersion force). Also, the perpendicular position of hydrogen has the lowest potential energy surface, while the parallel hydrogen position has the highest potential energy surface. We have confirmed that by using a high level of basis set at MP2 such as ccpVXZ (x= Q, 5, 6) and aug-cc-pVXZ (x=D, T, Q, 5, 6), and by using the same basis sets at CCSD and CCSD(T) as the high level of theory. Also, it is clear from these results that the binding energies are sensitive to improvement of the size of basis sets. In terms of applying Hobza's scheme to obtain correct interaction energies, we found that this scheme CCSD(T)/ [34] = MP2/ [34] + (CCSD(T)/ [23] – MP2 [23]) achieved the highest accurate of interaction energy for CO...imidazole. On the other hand, this scheme CCSD(T)/ [34] = MP2/ [34] + [CCSD(T)/AVDZ– MP2/AVDZ] produced the highest accurate of interaction energy for H2...imi, N2…imi and H2…Benzene. Regarding to Basis Set Superposition Error (BSSE) and counterpoise examination (CP), Ab initio and Force field investigations of physical hydrogen adsorption in Zeolitic Imidazole Frameworks we found that the MP2/CP and LMP2 methods yield very similar results at the basis set limit and the convergence of MP2 and LMP2 with increasing size of basis sets is different since the BSSE in LMP2 is reduced. Furthermore, we found that the extrapolation to the CBS limit cannot offer an alternative to the counterpoise correction where the differences in the values of bending energies are large so we need to use both techniques together to overcome the BSSE problem. Then to confirm our result regard to the potential energy surface, we calculated corresponding potential energy surfaces using several popular force fields potential, and compare critically with best ab initio results, where we focused on the adsorption of H2 on imidazole as the organic linker in ZIFs. We carried out ab initio calculations at the MP2/CCSD(T) levels with different basis sets, basis set extrapolation and Lennard-Jones potential for the three directions X, Y and Z for 294 positions of H2. Also, we have fitted ab initio binding energy at the MP2/CCSD(T) levels with different basis set and basis set extrapolation to Lennard-Jones (12-6 LJ) binding energy by applying the nonlinear least squares method. Then we estimated the fitted binding energy using Hobza’s schemes to reduce the errors. We found that the 12-6 LJ formula produced unreasonable fit for ab initio calculated potential energy surface PES, for both the equilibrium and attractive regions, to improve this fitting, we found the good fit is only achieved by the exponential formula of repulsion region. It is hoped that this study could facilitate the search for a “good” application to store the H2 molecule conveniently and safely

Estudo local de ad-átomos no grafeno usando espectrocopia de correlação angular perturbada

The interest in understanding the interaction between graphene and atoms and molecules that are adsorbed on its surface (adatoms and admolecules) spans a wide range of research fields and applications, for example, to controllably change the properties of graphene in electronic devices or to detect those changes in graphene-based sensors. Since the properties of graphene+adsorbent systems are strongly dependent on the adsorption configuration (e.g. isolated versus clusters, their geometry and coordination), it is important to not only understand these effects from a theoretical point of view, but also to be able to probe them experimentally. This thesis focuses on the interaction between graphene and adatoms (model cases: Hg, Cd, In and Ag) and admolecules (model case: HgO2), in terms of structural and electronic properties. The theoretical part of the research was based on density functional theory (DFT) calculations for different heavy elements adsorbed on graphene (Hg, Ag, Cd and In). The binding energy and the electronic structure were calculated for various high-symmetry atomic configurations, from isolated adatoms to a continuous monolayer. Detailed studies were carried out for Hg-graphene, as a model system, i.e. testing various functionals and covering a wide range of nominal concentration. For Ag, Cd, In, we carried out more targeted studies, based on the extensive calculations for Hg. It was demonstrate that the binding energy depends on adatom concentration and as well on adsorption site (H, T, or B). All studied elements are predicted to be more stable as isolated adatoms than as a continuous monolayer. For each element, we calculated the electric field gradient (EFG) parameters (Vzz and asymmetry parameter η). The EFG exhibits some variation when comparing different high-symmetry sites, and also depends on the nominal concentration of the adatom relative to C atoms. Furthermore, the EFG is found to be sensitive to the local atomic structure, distinguishing isolated from monolayer configurations, and for some cases, varying significantly with small variations in adatom position (at the sub-Å scale). Based on these calculations, we propose that the electric field gradient, which can be measured using hyperfine techniques, can be used as an experimental observable providing insight on the local atomic configuration and bonding stability of adatoms and admolecules on graphene. In particular, our calculations indicate that the level of detail that can be addressed via the EFG parameters (e.g. positional precision) increases with the stability (binding energy). In other words, the more stable the graphene-adatom system (i.e. more relevant in a application scenario), the more it lends itself to be studied using hyperfine techniques. Finally, adsorption of Hg on graphene in ambient conditions was experimentally studied using perturbed angular correlation (PAC) spectroscopy and 199mHg as probe nuclei. The combination of PAC measurements and DFT calculations allowed us to conclude that the majority of the Hg probes were adsorbed in the form of linear HgO2 molecules, which are adsorbed with higher binding energies (exceeding 1 eV) than isolated Hg adatoms (below 0.2 meV), i.e. oxygen plays a crucial role in stabilizing Hg adsorption on graphene. This work constitutes a proof-of-principle for the use of hyperfine techniques to study the interaction between graphene and adsorbed atoms and molecules, at the atomic scale. We also reported the first PAC experiment based on the decay of 68mCu (6−,721 keV,3.75 min) and demonstrated the feasibility of using this Cu isotope as a probe nuclei for PAC for applications in the fields of solid state physics in particular in the context of graphene research. Since Cu is the most widely employed catalyst for obtaining graphene monolayers with reasonable quality, establishing 68mCu as a suitable PAC probe enables the use to study the influence of the Cu substrate, e.g. on grain size and orientation, number of layers and quality of the grown graphene. Our findings open the way for a wide range of applications of hyperfine techniques, including other 2-dimensional materials and other types of adatoms and phenomena. For example, the magnetic properties of transition elements can also be addressed, via the magnetic hyperfine interaction. In addition to the ability to probe multiple adatom properties and phenomena (e.g. structural and magnetic), such an experimental approach based on hyperfine techniques is generally compatible with applied electric or magnetic fields (often used to investigate basic and functional properties), ultra-high vacuum (typically necessary when studying surfaces, to minimize contamination), and low temperature operation (typically necessary when studying isolated adatoms, due to their high surface mobility).A interacção de átomos e moléculas adsorbidos na superfície do grafeno (adátomos e ad-moléculas) constitui um tópico de intensa pesquisa no contexto de vários domínios científicos, demonstrando em certos casos a possibilidade do desenvolvimento de novas aplicações tecnológicas. Tendo em conta que as propriedades do sistema grafeno+ad-átomo/ad-molécula são dependentes da configuração de adsorção (ad-átomo isolado, organizado em cluster com diversas geometrias e coordenações) é importante compreender os seus efeitos do ponto de vista teórico mas também desenvolver métodos que permitam o seu estudo a nível experimental. A presente tese centra-se no estudo da interacção de ad-átomos (Hg, Cd, In e Ag) e ad-moléculas (HgO2) no grafeno, em termos estruturais e das propriedades electrónicas do sistema conjunto. O estudo teórico, baseado na teoria de funcional de densidade (DFT), focou-se num conjunto de cálculos e simulações para diferentes elementos adsorbidos na superfície do grafeno (Hg, Ag, Cd e In). A energia de ligação e a estrutura electrónica foram obtidas para diferentes posições atómicas (simétricas), desde ad-átomos isolados até arranjos do tipo mono-camada contínua. Um estudo detalhadofoirealizadoparaografeno-Hg,comosistemamodelo,usandodiversos funcionais e testando diferentes concentrações do ád-atomo no grafeno. Para os ad-átomos de Ag, Cd e In, foram realizados estudos mais direccionados, com enfâse em configurações de maior interesse tendo por base o estudo exaustivo realizado para o Hg. Os resultados permitiram perceber que a energia de ligação depende da concentração do ad-átomo no grafeno bem com da posição simétrica de adsorção (H, T, ou B). Todos os elementos estudados são mais estáveis na configuração de ad-átomo isolado, sendo preferêncial relativamente à configuração de mono-camada contínua. Para cada um dos elementos em estudo, calculou-se o gradiente de campo eléctrico (EFG) (componente Vzz e parâmetro de simetria η). Mostrou-se que o EFG é sensível à posição de adsorção bem como à concentração do ad-átomo em relaçãoaonúmerodeátomosdecarbonodarede. Alémdisso,ficoudemonstrada a capacidade de usar o EFG como parâmetro experimental capaz de distinguir o regime de ad-átomos isolados e o regime de mono-camadas contínuas, sendo que em certos casos com variações significativas com a distância ao grafeno e entre diferentes posições simétricas. Com base nos cálculos realizados, é proposto a utilização do gradiente de campo eléctrico (que pode ser obtido experimentalmente recorrendo a técnicas hiperfinas) como parâmetro de estudo da estabilidade e configuração de ad-átomos e ad-moléculas no grafeno. Em particular, demonstrou-se que a sensibilidade do EFG é tanto maior quanto maior a energia de ligação do ad-átomo ao grafeno. Porúltimo,foirealizadooestudoexperimentaldaadsorçãodeHgnografeno,nas condições normais de temperatura e pressão, recorrendo à técnica de correlações angularesperturbadas(PAC)usando 199mHgcomoátomosonda. Acombinação das medidas experimentais e DFT permitiu identificar a coordenação do Hg na surperfíciedegrafenonaformadamoléculalinearHgO2, comelevadaenergiade ligação (superior a 1 ev) em comparação com ad-átomos de Hg isolados (inferior a 0.2 eV). Os resultados permitem ainda concluir o papel crucial do oxigénio na forte ligação entre a ad-molécula e o grafeno. Este trabalho representa a demonstração da possibilidade do uso de técnicas hiperfinas para estudar à escala atómica a interacção de átomos ou moléculas adsorbidos na superfície do grafeno. Foi ainda reportada a primeira experiência de PAC realizada no isótopo de 68mCu para o decaimento 68mCu (6−,721 keV,3.75 min), demonstrando-se a possibilidade de usar este isótopo de cobre como sonda de PAC para aplicações em diversos campos da física do estado sólido em particular no contexto da investigação do grafeno. Tendo em conta que o Cu constitui um dos catalizadores mais amplamente usados na obtenção de monocamadas de grafeno, a caracterização do 68mCu como nova sonda disponível para PAC permitirá, por exemplo, um estudo à escala atómica da influência do substrato de Cu, ao nível do tamanho de grão e orientação, na qualidade do grafeno obtido. O presente estudo permitiu encontrar novas direcções de pesquisa com recurso a técnicas hiperfinas para investigação do grafeno e outros materiais 2-D, não apenas para ad-átomos de metais pesados mas para outros elementos. Por exemplo, o estudo de propriedades magnéticas de elementos de transição em grafeno poderá ser estudado por via de uma medida experimental com recurso a técnicas hiperfinas. Diferentes cenários experimentais podem ser idealizados, comdiferentescondiçõesdetemperaturaepressão,compossiblidadedeaplicação de campo eléctrico ou magnético, permitindo a realização de estudos mais detalhados do processo de estabilidade/adsorção de ad-átomos e ad-moléculas no grafeno.Programa Doutoral em Engenharia Físic

Modelování interakce proteinů a peptidů s kovovými ionty

Modelling of interactions of proteins and peptides with metal ions Ondrej Gutten - Diploma thesis Keywords: Metalloproteins, metal ion selectivity, in silico prediction Abstract: An approach for in silico prediction and estimation of selectivity properties of metal-binding peptides is suggested. An in-depth analysis is performed to disclose the justifiability and limitations of this approach. The study is divided into three parts. First part investigates the soundness of two quantum chemical methods (MP2 and DFT) for their use in the set-up quest. The testing includes comparison with CCSD(T), effect of basis selection, performance of the two methods in geometry optimizations and effect of implicit solvent model. Second part foreshadows the approach of searching for a metal selective peptide by thoroughly investigating the ability of simple representative systems, derived from their metalloprotein templates, to retain the property of interest. Final part describes the initial step of extensive combinatorial approach towards examination of vast number of simple systems that represent metal-binding sites, and which are to be used for prediction of metal-selectivity through exploitation of the described approach and, ultimately, to the de novo design of metalloproteins with desired properties.Modelování interakce proteinů a peptidů s kovovými ionty. Ondrej Gutten - Diplomová práce Klíčová slova: Metaloproteiny, selektivita pro ionty kovů, in silico predikce Abstrakt: Byla navržena metoda pro in silico predikci a odhad schopnosti vybraných peptidů selektivně vázat ionty kovů. Dále byly důkladně otestovány použitelnost a omezení navržené metody. Studie je rozdělena do tří částí. První část se zabývá použitelností dvou kvantově- chemických metod (DFT, MP2) pro navržený přístup. Testování zahrnuje porovnání s referenčními výsledky získanými metodou CCSD(T), analýzu vlivu použité báze atomových orbitalů, porovnání obou metod při optimalizaci geometrie a analýzu použitého modelu reprezentujícího vodní prostředí. Ve druhé části jsou porovnávány výsledky predikce selektivity vazby iontů kovů v modelových peptidech a v jednoduchých systémech z nich odvozených. Poslední část diplomové práce popisuje první krok v rozsáhlé snaze prozkoumat obrovské množství jednoduchých modelových systémů, která povede k návrhu metaloproteinů s definovanými vlastnostmi.Department of BiochemistryKatedra biochemieFaculty of SciencePřírodovědecká fakult

Ab initio molecular dynamics simulations of lanthanide coordination structures in water and in faujasite

Atomic and molecular resolution can provide unique insights into the ambiguous mechanisms by which lanthanum increases the hydrothermal stability of faujasite in cracking catalysts, as well as in cation exchange in faujasite. The structures of the lanthanide aqua ions were resolved with density functional theory calculations and ab initio molecular dynamics (AIMD) simulations within ~0.05 Å of experimental results. Reaction energies were quantified by predicting the first hydrolysis constant of lanthanide aqua ions within ~1.1 pKa units using AIMD with rare event simulation techniques and electronic structure calculations. The capture of structural and reaction trends in the lanthanide aqua ion served as a benchmark for implementing similar methods in lanthanum-exchanged faujasite. In faujasite, AIMD simulation identified the preferred binding site of lanthanum. AIMD with a rare event simulation technique was used to quantity the free energy of faujasite aluminum tetrahedra deprotonation, with and without lanthanum exchanged in faujasite. The presence of lanthanum makes faujasite deprotonation energetically more favorable, thus making faujasite less hydrophilic. The local structure of water confined in faujasite was simulated with AIMD. The model faujasite structure was modified to produce a series of systems to study the influence of confinement, hydrophilicity, and cation exchanged on the local structure of water as quantified from radial distribution functions. Increases in hydrophilicity in hydrogen-exchanged faujasite disrupts the confined water structure. While lanthanum ions compensate for a larger magnitude of charge, equivalent number of sodium ions have a higher probability of occupying sites interacting with the supercage and thus disrupt the local structure of water more significantly than lanthanum

Understanding and Tuning Magnetism in van der Waals Magnetic Compounds

The recently discovered two-dimensional (2D) magnetism has attracted intensive attention due to possible magnetic phenomenon arising from 2D magnetism and their promising potential for spintronics applications. The advances in 2D magnetism have motivated the study of layered magnetic materials, and further enhanced our ability to tune their magnetic properties. Among various layered magnets, tunable magnetism has been widely investigated in metal thiophosphates MPX3. It is a class of magnetic van der Waals (vdW) materials with antiferromagnetic ordering persisting down to atomically thin limit. Their magnetism originates from the localized moments due to 3d electrons in transition metal ions. So, their magnetic properties are strongly dependent on the choice of M. With this motivation, we synthesized metal-substituted MPX3 compounds such as Ni1-xMnxPS3 (0 ≤ x ≤ 1), Ni1-xCrxPS3 (0 ≤ x ≤ 0.09), and Fe1-xMnxPSe3 (0 ≤ x ≤ 1). The magnetic properties have been found to be very tunable with metal substitutions. Furthermore, we performed previously unexplored non-magnetic X substitution in MnPS3-xSex (0 ≤ x ≤ 3), FePS3-xSex (0 ≤ x ≤ 3), and NiPS3-xSex (0 ≤ x ≤ 1.3). Interestingly, such non-magnetic S-Se substitution also effectively modifies the magnetic exchange and anisotropy in MPX3¬. In addition to M and X substitutions, we conducted electrochemical intercalation of Li into NiPS3. We found the emergence of ferrimagnetism at low temperature in Li-intercalated NiPS3, which has never been observed due to substitution technique. Such efficient engineering of magnetism provides a suitable platform to understand low-dimensional magnetism and design future magnetic devices

Understanding and Tuning Magnetism in van der Waals Magnetic Compounds

The recently discovered two-dimensional (2D) magnetism has attracted intensive attention due to possible magnetic phenomenon arising from 2D magnetism and their promising potential for spintronics applications. The advances in 2D magnetism have motivated the study of layered magnetic materials, and further enhanced our ability to tune their magnetic properties. Among various layered magnets, tunable magnetism has been widely investigated in metal thiophosphates MPX3. It is a class of magnetic van der Waals (vdW) materials with antiferromagnetic ordering persisting down to atomically thin limit. Their magnetism originates from the localized moments due to 3d electrons in transition metal ions. So, their magnetic properties are strongly dependent on the choice of M. With this motivation, we synthesized metal-substituted MPX3 compounds such as Ni1-xMnxPS3 (0 ≤ x ≤ 1), Ni1-xCrxPS3 (0 ≤ x ≤ 0.09), and Fe1-xMnxPSe3 (0 ≤ x ≤ 1). The magnetic properties have been found to be very tunable with metal substitutions. Furthermore, we performed previously unexplored non-magnetic X substitution in MnPS3-xSex (0 ≤ x ≤ 3), FePS3-xSex (0 ≤ x ≤ 3), and NiPS3-xSex (0 ≤ x ≤ 1.3). Interestingly, such non-magnetic S-Se substitution also effectively modifies the magnetic exchange and anisotropy in MPX3¬. In addition to M and X substitutions, we conducted electrochemical intercalation of Li into NiPS3. We found the emergence of ferrimagnetism at low temperature in Li-intercalated NiPS3, which has never been observed due to substitution technique. Such efficient engineering of magnetism provides a suitable platform to understand low-dimensional magnetism and design future magnetic devices

Azadipyrromethenes as near-infrared absorber materials for organic solar cells: Synthesis and characterization of structure-property relationships

Organic solar cells have the potential to become a low-cost photovoltaic technology. One approach to further increase the device efficiency aimsvto cover the near-infrared region of the sunvspectrum. However, suitable absorber materials are rare. This thesis focuses on the material class of aza-bodipy and dibenzo-aza-bodipy as near-infrared absorber materials for organic solar cells. Besides the synthesis of novel thiophene-substituted aza-bodipys, azadiisoindomethenes were prepared by the addition of Grignard reagents to phthalodinitrile an subsequent reduction with formamide. Starting from these azadiisoindomethenes as precursors, complexes with borondifluoride, boroncatechole and transition metals were synthesized. The optical and electrochemical properties of all compounds prepared were investigated by experimental and theoretical methods. The (dibenzo-)aza-bodipys are characterized by their electronic structure, comprising a central electron acceptor core and peripheral electron donor units. The substituents at the donor units offer a stronger impact on the HOMO energy than on the LUMO energy. Electron donating substituents at the donor units result in an overall decreased HOMO-LUMO gap. This allows to redshift the absorption maximum up to 800 nm. The corresponding dibenzo-analogues already demonstrate a bathochromic shift of the absorption compared to the (non-annulated) aza-bodipys. Yet, the central acceptor is weakened and a further redshift by substituents is less distinct. The compounds can be thermally evaporated in high vacuum. The required thermal stability is increased in some cases by boroncatechol compared to borondifluoride complexes, without significant influence on the optical and electrochemical properties. Besides the characterization of the molecular properties, promising materials were evaluated in thin fifilms and solar cell devices. The charge carrier mobility in the measured compounds were found to be between 10E-6 and 10E-4 cm2V-1s-1. The charge transport parameters were calculated on the basis of obtained single crystal structures. It was found that a high charge carrier mobility may be attributed to a better molecular overlap and a short intermolecular distance in the corresponding solid state structure. Selected materials were characterized in organic solar cells. In solution processed devices, the dibenzo-aza-bodipys reached efficiencies of 1.6 % and 2.1 %, as donor materials in combination with PC61BM and PC71BM as acceptor. The main limiting factor in these devices turned out to be the low fill factor of 30 %. From a series of vacuum processed devices with aza-bodipys and dibenzo-aza-bodipys, increased voltages were obtained with decreasing HOMO energy of the bodipy derivatives. A suitable near-infrared absorbing dibenzo-aza-bodipy exhibited a contribution to the photocurrent from 750 - 950 nm.Die organische Photovoltaik hat das Potential eine kostengünstige Solarzellentechnologie zu werden. Ein Ansatz die Effizienz weiter zu steigern besteht darin den aktiven Spektralbereich in den nahen Infrarotbereich zu erweitern. Bisher gibt es jedoch nur wenige geeignete Materialien. In dieser Arbeit werden Verbindungen aus der Materialklasse der Aza-Bodipy und Dibenzo-Aza-Bodipy als Absorbermaterialien für den nahen Infrarotbereich zur Verwendung in organischen Solarzellen untersucht. Neben der Synthese von neuen Thiophen-substituierten Aza-Bodipys wurden Azadiisoindomethine durch die Addition von Grignardverbindungen an Phthalodinitril und anschließender Reduktion mit Formamid dargestellt. Ausgehend von den Azadiisoindomethinen sind neue Bordifluorid, Borbrenzcatechin und Übergangsmetallkomplexe synthetisiert worden. Alle Substanzen sind mit experimentellen und theoretischen Methoden auf ihre optischen und elektrochemischen Eigenschaften hin untersucht worden. Die elektronische Struktur der (Dibenzo-)Aza-Bodipys ist charakterisiert durch periphere Elektronendonoreinheiten um einen zentralen Elektronenakzeptor. Die langwelligste Absorptionsbande kann in beiden Systemen durch Elektronen schiebende Gruppen an den Donoreinheiten bathochrom, auf über 800 nm verschoben werden. Die Ursache liegt in einem stärkeren Einfluss der Substituenten auf das HOMO als auf das LUMO und einem damit einhergehenden stärkeren Anstieg der HOMO-Energie woraus eine verkleinerte HOMO-LUMO Lücke resultiert. Die Dibenzo-Aza-Bodipys zeichnen sich durch eine rotverschobene Absorption gegenüber den (nicht benzannulierten) Aza-Bodipys aus. Jedoch ist der Akzeptor in den Dibenzo-Aza-Bodipys abgeschwächt, so dass die Rotverschiebung durch die selben Substituenten weniger stark ausgeprägt ist und die Energieniveaus tendenziell höher liegen. Die Verbindungen lassen sich thermisch im Vakuum verdampfen. Die für das Verdampfen wichtige thermische Stabilität, kann durch Austausch von Bordifluorid mit Borbrenzcatechol erhöht werden, ohne die optischen und elektronischen Eigenschaften wesentlich zu beeinflussen. Neben der Charakterisierung der molekularen Eigenschaften, sind einige Verbindungen im Dünnfifilm auf ihre elektrischen Eigenschaften und in Solarzellen untersucht worden. Die Ladungsträgerbeweglichkeit liegt bei den gemessenen Verbindungen zwischen 10E-6 und 10E-4 cm2V-1s-1. Durch Berechnung der Ladungstransportparameter auf Basis erhaltener Kristallstrukturen ist eine höhere Beweglichkeit auf eine günstigere Packung und einen geringeren intermolekularen Abstand zurückgeführt worden. Ausgewählte Verbindungen sind als Donormaterialien in organischen Solarzellen charakterisiert worden. Aus Lösungsmittel prozessierte Solarzellen mit Dibenzo-Aza-Bodipys erreichen eine Effifizienz von 1.6 % mit PC61BM, und 2.1 % mit PC71BM als Akzeptor. Der Effizienz limitierende Faktor ist hierbei der niedrige Füllfaktor von ca. 30 %. In vakuumprozessierten Solarzellen mit planarem Dono-Akzeptor-Übergang von Aza-Bodipys und Dibenzo-Aza-Bodipys hat sich gezeigt, dass die erhaltene Spannung mit abnehmender HOMO Energie der Materialien gesteigert wird. Ein geeignetes Dibenzo-Aza-Bodipy Material ist mit einen Beitrag zum Photostrom im nahen Infrarotbereich, von 750 - 950 nm, gezeigt worden

Oxidation Resistance Enhancement of Metallic Materials in Nuclear Reactors Environment

The research in my dissertation aims at a better understanding of the corrosion mechanism of alloys applied in nuclear reactors and potential methods to enhance their corrosion resistance based on reliable computational simulations. First-principles based calculations and density functional theory (DFT) simulations are taken to investigate the chemical reaction between nuclear structural materials and corrosive coolants. Zirconium (Zr) based cladding materials are widely used in commercial light water nuclear reactors and it is essential to prevent them from water oxidation to avoid serious safety issues in nuclear power plants such as Fukushima nuclear accident. To provide guidelines to design novel Zr alloys with enhanced water oxidation resistance, we performed a first-principles high-throughput screening (HTS) search that is based on the water dissociation mechanism over Zr basal plane. 53 metal dopants, including transition and non-transition metals, were selected to determine the promising dopants in Zr-X binary alloys with significantly improved resistance of water oxidation. Firstly, the adsorption and dissociation mechanisms of water molecules on the zirconium basal (0001) surface are determined using the density functional theory (DFT) calculations. Then the water dissociation barrier is used as a descriptor for the HTS approach. Next, the neutron cross-section is considered for the realistic applications of Zr-X alloys as cladding materials in nuclear reactions. Finally, the stability is checked for the possibility of processing these binary Zr-X alloys experimentally. Al, Zn, Ge, As, Sn, Sb, Pb, and Bi are singled out as promising dopants that could improve the corrosion resistance of zirconium alloys. In fact, aluminum alloys have already been used as fuel cladding, and Zr alloys such as Zircaloy, ZIRLO, which contain 1% ~ 1.5% Sn, have been used as fuel cladding for PWRs and BWRs for decades. Eutectic LiCl-KCl molten salt is often used in molten salt reactors as the primary coolant due to its high thermal capacity and high solubility of fission products. Thermophysical properties, such as density, heat capacity, and viscosity, are important parameters for engineering applications of molten salts, but may be significantly influenced by metal solute from corrosion of metallic structural materials. The behavior of the LiCl-KCl eutectic composition is well-researched, yet the effects on these properties due to chlorocomplex formation from metals dissolved in the salt are less well known. These properties are often difficult to accurately measure from experimental methods due to issues arising from the dissolved species such as volatility. Here we applied a combination of quantum mechanics molecular dynamics (QM-MD) and deep machine learning force field (DP-FF) molecular dynamics simulations to investigate the structure and thermophysical properties of LiCl-KCl eutectic as well as the influence of dissolved transition metal chlorocomplexes NiCl2 and CrCl3 at low concentrations. We find that the dissolution of Ni and Cr in the LiCl-KCl system forms the local tetrahedral (NiCl4)2- and octahedral (CrCl6)3- chlorocomplexes, respectively, which do not have a significant impact on the overall liquid salt structures. In addition, the thermodynamic properties including diffusion constant and specific heat capacity are not significantly affected by these chlorocomplexes. However, the viscosity is significantly changed in the temperature range of 673 ~ 773 K. This study thus provides essential information for evaluating the effects of dissolved metals on the thermophysical and transport properties of molten salts