Dissertations / Theses on the topic 'NLO Calculations'

Les théories supersymétriques, telles que le Modèle Standard Supersymétrique Minimal, constituent des extensions très populaires du Modèle Standard de physique des particules, et sont activement recherchées au Large Hadron Collider (LHC). Dans cette thèse, nous nous concentrons sur deux aspects de la phénoménologie des théories supersymétriques aux collisionneurs hadroniques de haute-énergie, à savoir les collisions polarisées, et les calculs de précision. Dans un premier temps, nous réalisons une étude au Leading Order (LO), dans laquelle nous montrons comment la présence de faisceaux polarisés (longitudinalement) pourrait nous aider à différencier des modèles de Nouvelle Physique présentant la même signature à l'état final. A titre d'exemple, nous considérons le cas d'une classe particulière de scénarios, menant à la production de monotops, qui correspondent à la production d'un quark top en association avec de l'énergie transverse manquante. Nous présentons nos résultats pour un LHC polarisé à 14 TeV, et pour le récemment proposé Futur Collisionneur Circulaire (FCC), supposé opérer à 100 TeV. Par la suite, nous nous concentrons sur la réalisation de prédictions de précisions pour la production de paires de particules supersymétriques colorées au next-to-leading order (NLO) en QCD supersymétrique, avec ou sans violation non-minimale de saveur, et avec ou sans Parton Shower (PS). Plus particulièrement, nous fournissons les premiers résultats (préliminaires) pour la production de squark-antisquark au NLO en SUSY-QCD avec violation non-minimale de saveur, dans le cas d'un calcul à ordre perturbatif fixe, et considérons dans le contexte de modèles simplifiés la production par paires de particules colorées de type scalaire et Majorana au NLO avec PS
Supersymmetric theories, such as the Minimal Supersymmetric Standard Model (MSSM), constitute very popular extensions of the Standard Model of particle physics that are extensively searched for at the Large Hadron Collider (LHC). In this thesis, we focus on two specific aspects of the phenomenology of supersymmetric theories at high-energy hadron colliders, namely polarized collisions and precision calculations. First, we perform a Leading Order (LO) study, in which we show how the availability of (longitudinally) polarized proton beams could us help us to disentangle various Beyond the Standard Model (BSM) scenarios exhibiting the same final-state signature. For the sake of illustration, we focus on the case of one particular class of scenarios leading to monotop production, which corresponds to the production of a top quark in association with missing transverse energy. We present our results for a polarized LHC at 14 TeV, and for the recently proposed Future Circular Collider (FCC), supposed to operate at 100 TeV. Then, we concentrate on precise predictions for the pair production of coloured supersymmetric particles at next-to-leading order (NLO) in supersymmetric QCD, with or without Non-Minimal Flavour Violations (NMFV), and with or without matching those predictions with Parton Showers (PS). More specifically, we provide the first preliminary results for squark-antisquark pair production at NLO in SUSY-QCD with NMFV, in the case of a fixed order calculation, and consider in the context of simplified models the pair production of coloured scalar and coloured Majorana particles at NLO matched with PS

Cette thèse a pour objet l'étude de divers sujets liés à la physique du LHC et à ses prédictions. Nous nous sommes dans un premier temps intéressés à la recherche au LHC d'un boson de Higgs léger ($M_H\simeq 120$ GeV) et boosté ($p_{t,H}>200$ GeV) dans le canal $pp\rightarrow WH$ et $pp\rightarrow ZH$ avec $H\rightarrow b\bar b$. Nous avons montré comment, à partir d'une analyse de la sous-structure des jets en deux étapes respectivement appelées ``mass-drop'' et ``filtering'', il est possible de réduire de manière significative les divers backgrounds (mass-drop) et d'améliorer la résolution en masse lors de la reconstruction du Higgs (filtering). Cela nous a permis de rendre prometteur ce canal de recherche au LHC, longtemps considéré comme trop difficile. A partir de là nous nous sommes concentrés plus particulièrement sur la procédure du ``filtering'', qui permet de supprimer autant que possible l'effet du bruit de fond diffus que constituent l'underlying-event et le pile-up, en majeur partie responsable de la dégradation de la résolution. Nous avons optimisé ses paramètres à partir d'une analyse semi-analytique, ce qui nous a conduits à l'étude de la structure des ``non-global'' logarithms qui interviennent lors du calcul de la distribution en masse du Higgs. Finalement, nous nous sommes penchés sur les processus dont la série perturbative présente une mauvaise convergence au next-to-leading (NLO) order pour certaines observables, une caractéristique que nous avions en particulier remarquée pour les processus Z+jet et W+jet à grand $p_t$ lors de notre première étude sur le Higgs. Cet aspect est important car cette mauvaise convergence induit une perte de confiance sur les prédictions résultant des calculs perturbatifs. Il devient donc nécessaire d'examiner les ordres supérieurs, ce que permet de façon approximative un nouvel outil que nous avons élaboré, appelé ``LoopSim'', qui combine divers ordres de la théorie des perturbations de manière à annuler les divergences molles et collinéaires qui apparaissent inévitablement.

In the past years, next-to-leading order (NLO) QCD computations have become standard tools for phenomenological studies at lepton and hadron colliders. On the experimental side, instead, general purpose Shower Monte Carlo (SMC) programs have become the main tools used in the analysis. These programs perform a resummation of all order leading logarithmic contributions in soft and collinear approximation. The whole process is thus represented as a parton shower, in which subsequent emissions are strongly ordered. Being fully exclusive, it is easy to interface them with phenomenological hadronization models, enabling the comparison with experimental data. However, they do not enforce NLO accuracy. In view of increasing precision required to disentangle signals from backgrounds, at present and future colliders, it has become clear that SMC programs should be improved, when possible, with NLO results. In this way a large amount of the acquired knowledge on QCD corrections would be made directly available to the experimentalists, in a flexible form that they could easily use for simulations. The problem of merging NLO calculations with parton shower simulations is basically that of avoiding overcounting, since the SMC programs already implement approximate NLO corrections. Several proposals have appeared in the literature during past years to overcome this problem. However, the first general solution to the overcounting was the MC@NLO proposal. The basic idea of MC@NLO is that of avoiding the overcounting by subtracting from the exact NLO cross section its approximation, as implemented in the SMC program to which the NLO computation is then matched. Such approximated cross section is computed analytically, and is SMC dependent. On the other hand, the MC subtraction terms are process-independent, and thus, for a given SMC, can be computed once and for all. In the current version of the MC@NLO code, the MC subtraction terms have been computed for the HERWIG SMC. In turns out, however, that in general, the exact NLO cross section minus the MC subtraction terms does not need to be positive. Therefore MC@NLO can generate events with negative weights. For the processes implemented so far, negative-weighted events may reach about 10--15% of the total. More recently, a method, named POWHEG (Positive Weight Hardest Emission Generator), was proposed that overcomes the problem of negative weighted events, and that is not SMC specific. In the POWHEG method the hardest radiation is generated first, with a technique that yields only positive-weighted events using the exact NLO matrix elements. The POWHEG output can then be interfaced to any SMC program that is either pt-ordered, or allows the implementation of a pt veto. The POWHEG method has been successfully tested in several production processes, both at leptonic and hadronic colliders. Among these we list: $ZZ$, $Q\bar{Q}$ hadroproduction, $ q\bar{q}$ and top pairs production and decay from $e^+e^-$ annihilation, Drell-Yan vector boson production, $W'$ production, Higgs boson production via gluon fusion, Higgs boson production associated with a vector boson (Higgs-strahlung) and single top, both in the $s$- and $t$-channel production mechanism. Detailed comparisons have been carried out between the POWHEG and MCatNLO results, and reasonable agreement has been found, which nicely confirms the validity of both approaches. In the present work we give a detailed description of the POWHEG method and an overview of two specific applications: single vector boson and Higgs boson production via gluon fusion. We first present the features of a general subtraction scheme. Then, we illustrate in detail two such schemes, which we adopted in calculations appearing in this thesis: the Catani and Seymour (CS) and the Frixione, Kunszt and Signer (FKS) one. Next we concentrate on the application of the POWHEG method to the process of single vector boson production, where, in the POWHEG framework, the Catani-Seymour subtraction approach was employed for the first time. We also introduced a generalization of the method in order to deal with vanishing Born cross sections, as in the case of $W^\pm$ production. Matrix elements were evaluated from scratch using helicity amplitude methods, including finite width effects, $Z/\gamma$ interference and angular correlations of decay products. Our program has been interfaced both with HERWIG and with PYTHIA, two of the most popular Shower Monte Carlo used in simulations. Results were found in remarkable agreement both with Tevatron data and with the MC@NLO program. We also discuss results at the LHC collider. Higgs boson production via gluon fusion process is then presented, with applications to both Tevatron and LHC colliders. Gluon fusion is the predominant Higgs boson production channel over a wide range of masses. Matrix elements were evaluated analytically and regularized according to the FKS subtraction formalism. In this case, results show agreement with MC@NLO distributions up to next-to-next-to-leading order (NNLO) contributions. However, we fully understand the origin of these discrepancies and show that the POWHEG framework allows enough flexibility to get rid of them, if it is needed. Our results were also checked against NNLO and $q_T$ resummed available calculations, giving expected results.

La tesi si occupa delle correzioni di potenza calcolate su un parametro-soglia di momento trasverso che interessano calcoli perturbativi di ordine superiore nella costante di accoppiamento forte. In particolare, si impone un parametro-soglia di momento trasverso, qt_cut, su uno stato finale bianco e si calcolano le correzioni di potenza sul parametro-soglia, fino alla quarta potenza, per la sezione d'urto inclusiva al primo ordine sottodominante in QCD. Inoltre, si considera lo stesso processo al secondo ordine sottodominante in QCD, limitandosi al contributo reale-virtuale, e si calcolano le correzioni di potenza per la sezione d'urto inclusiva sino alla seconda potenza sul parametro-soglia. Lo studio della dipendenza della sezione d'urto dal parametro-soglia permette di approfondire il comportamento della prima nei limiti dello spazio delle fasi, dando indizi sulla struttura a tutti gli ordini nella costante di accoppiamento forte e sull'identificazione di caratteristiche universali. La conoscenza delle correzioni di potenza è poi un ingrediente fondamentale per ridurre la dipendenza delle sezioni d'urto di QCD dal parametro-soglia quando viene applicato un metodo slicing come la sottrazione-qt. Si presentano, quindi, risultati analitici per la produzione di un bosone vettore e per la produzione di un bosone di Higgs al primo ordine sottodominante in QCD, e per la parte reale-virtuale del canale qg per la produzione di un bosone vettore al secondo ordine. Nel dettaglio, si illustra una procedura generale per il calcolo delle correzioni di potenza sul parametro-soglia. Per mostrare l'impatto numerico di tali correzioni, si presentano dei risultati numerici e si discute di come la dipendenza residuale da qt_cut interessi la sezione d'urto totale della produzione di un bosone Z o di un bosone di Higgs presso LHC. La seconda parte della tesi, complementare alla prima, è dedicata allo sviluppo di un'interfaccia tra MadGraph5_aMC@NLO e POWHEG BOX, al fine di coniugare la flessibilità di MadGraph quando genera gli elementi di matrice per processi del Modello Standard o di sue estensioni, con tutte le caratteristiche di POWHEG BOX. Tra di esse, la possibilità di generare eventi con peso positivo è fondamentale e rende POWHEG uno dei metodi più usati quando sono necessari campioni molto numerosi. Al fine di testare l'interfaccia, si studia la produzione di un bosone di spin 0 assieme a due getti, con accoppiamenti che violano CP. Si discutono delle distribuzioni che caratterizzano le proprietà del bosone e alcuni risultati ottenuti con la funzione di ripesamento di POWHEG BOX. Infine, si presentano alcune distribuzioni ottenute con il metodo MiNLO.
The thesis deals with the power corrections in a transverse-momentum cutoff that affect perturbative calculations at higher orders in the strong coupling constant. In particular, we impose a transverse-momentum cutoff, qt_cut, on a colourless final state and we compute the power corrections for the inclusive QCD next-to-leading-order cross section in the cutoff, up to the fourth power. We also consider the same production process at next-to-next-to-leading order in QCD, restricting ourselves to the real-virtual contribution, and we compute the power corrections up to the second power in the cutoff for the inclusive cross section. The study of the dependence of the cross section on qt_cut allows for an understanding of its behaviour at the boundaries of the phase space, giving hints on the structure at all orders in the strong coupling constant and on the identification of universal patterns. The knowledge of such power corrections is also a required ingredient in order to reduce the dependence on the transverse-momentum cutoff of the QCD cross sections at higher orders, when the qt-subtraction method, i.e. a slicing scheme, is applied. We present analytic results for both Drell-Yan vector-boson and Higgs-boson production in gluon fusion at next-to-leading order in QCD, and for the real-virtual part of the qg-initiated channel of vector-boson production at NNLO in QCD. In particular, we illustrate a process-independent procedure for the calculation of the all-order power corrections in the cutoff. In order to show the impact of the power-correction terms, we present selected numerical results and discuss how the residual dependence on qt_cut affects the total cross section for Drell-Yan Z production and Higgs boson production via gluon fusion at the Large Hadron Collider. A second and complementary part of the thesis is devoted to the development of an interface between MadGraph5_aMC@NLO and the POWHEG BOX framework, in order to match the flexibility of MadGraph for the generation of matrix elements for Standard-Model processes and for several of its extensions, to all features of the POWHEG BOX framework. Among those, it is essential the possibility, via the POWHEG method, to generate events with positive weights, which makes it the method of choice when large samples of events are needed. As a proof of concept, we provide a phenomenological study for the production of a spin-0 Higgs-like boson, in association with up to two jets, with CP-violating couplings. We discuss a few distributions able to characterise the spin-0 boson CP properties, and discuss a few results obtained using the POWHEG BOX reweighting feature. We also present a few distributions obtained with the MiNLO method.

In this thesis the task of computing higher order corrections to QCD scattering processes for the LHC is considered, specifically Next-to Leading Order (NLO) and Next-toNext-to Leading Order (NNLO) perturbative QCD corrections. The infrared (IR) divergent behaviour of the cross section is isolated using the antenna subtrac- tion formalism. This method has previously been used at NNLO in the calculation of jet production in the context of e+e− annihilation and for the leading colour contribution to dijet production via pure gluon scattering. The research presented in this thesis extends the formalism to include scattering processes involving quarks with initial-state partons. General formulae, including sub-leading colour contributions, are presented for the isolation and cancellation of IR and singularities when calculating the production of colourless final-states at the LHC at NLO and NNLO accuracy. The leading colour NNLO correction to the sub-process qq ̄ → gg is calculated and numerical results are presented to demonstrate the convergence of the physical cross section and the subtraction terms in the various unresolved limits. The calculations are organised with the aid of convenient quantities, referred to as integrated antenna strings. Using these quantities, the full calculation displays a clear and predictive structure, in particular at the double virtual level where the structures presented are new.

The study of scattering amplitudes beyond one loop is necessary for precision phenomenology for the Large Hadron Collider and may also provide deeper insights into the theoretical foundations of quantum field theory. In this thesis we develop a new method for computing two-loop amplitudes, based on unitarity rather than Feynman diagrams. In this approach, the two-loop amplitude is first expanded in a linearly independent basis of integrals. The process dependence thereby resides in the coefficients of the integrals. These expansion coefficients are then the object of calculation. Our main results include explicit formulas for a subset of the integral coefficients, expressing them as products of tree-level amplitudes integrated over specific contours in the complex plane. We give a general selection principle for determining these contours. This principle is then applied to obtain the coefficients of integrals with the topology of a double box. We show that, for four-particle scattering, each double-box integral in the two-loop basis is associated with a uniquely defined complex contour, referred to as its master contour. We provide a classification of the solutions to setting all propagators of the general double-box integral on-shell. Depending on the number of external momenta at the vertices of the graph, these solutions are given as a chain of pointwise intersecting Riemann spheres, or a torus. This classification is needed to define master contours for amplitudes with arbitrary multiplicities. We point out that a basis of two-loop integrals with as many infrared finite elements as possible allows substantial technical simplications, in terms of obtaining the coefficients of the integrals, as well as for the analytic evaluation of the integrals themselves. We compute two such integrals at four points, obtaining remarkably compact expressions. Finally, we provide a check on a recently developed recursion relation for the all-loop integrand of the amplitudes of N=4 supersymmetric Yang-Mills theory, examining the two-loop six-gluon MHV amplitude and finding agreement. The validity of the approach to two-loop amplitudes developed in this thesis extends to all four-dimensional gauge theories, in particular QCD. The approach is suited for obtaining compact analytical expressions as well as for numerical implementations.

In this thesis we consider the phenomenology of the theory of strong interactions, Quantum Chromodynamics (QCD), with particular reference to the ongoing experimental program at the Large Hadron Collider in CERN. The current progress in precision measurement of Standard Model processes at the LHC experiments must be matched with corresponding precision in theoretical predictions, and to this end we present calculations at next-to-next-to-leading order in perturbation theory of observable quantities involving quarks and gluons, the strongly interacting particles of the SM. Such calculations form the most important class of corrections to observables and are vital if we are to untangle signals of New Physics from LHC data. We consider in particular the amplitudes for five parton interactions at 1- and 2-loop order and present full (in the 1-loop case) and partial (in the 2-loop case) analytic results in terms of rational functions of kinematic invariants multiplying a basis of master integrals. We address the problem of the solution of a system of integration-by-parts identities for Feynman integrals and demonstrate how some current difficulties may be overcome. We consider also the properties of the top quark, and present the NNLO, real-virtual contributions to the calculation of its decay rate. The results are presented as helicity amplitudes so that the full behaviour of the top spin is retained. These amplitudes constitute a necessary ingredient in the complete calculation of top quark pair production and decay at NNLO which will be an important theoretical input to many experimental analyses. Turning to a more phenomenological study, we consider the extraction of two important SM parameters, the top mass and the strong coupling constant, from measurements of top pair production at the ATLAS and CMS experiments. We compare with NNLO theory predictions and use a least-squares method to extract the values of the parameters simultaneously. We find best fit values of the parameters which are compatible with previous extractions performed using top data with the current world averages published by the Particle Data Group. We consider the issue of PDF choice and the circumstances in which a heavy quark can be considered a constituent of the proton. In particular, we look at the production of a Higgs boson in association with bottom quarks in four and five flavour schemes, in which the b may or may not be included in the initial state. We show that theoretical predictions in both schemes are well-motivated and appropriate in different scenarios, and moreover that results in the schemes are consistent provided a judicious choice of the renormalisation and factorisation scales is made. We suggest a typical scale choice motivated by considerations of consistency and find it to be somewhat lower than the typical hard scale of the process.

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O presente trabalho trata do estudo conformacional de S-nitrosotióis com potencial atividade biológica, 2–acetamido-3-metil-3-nitrosossulfanil-N-arilbutanamidas, e de seus tióis precursores, 2–acetamido-3-mercapto-3-metil-N-arilbutanamidas. As conformações de menor energia dos S-nitrosotióis e tióis em estudo são estabilizadas por ligações de hidrogênio intramoleculares que promovem uma maior estabilidade dos confôrmeros. A análise geométrica do grupo R-SNO mostra que esses compostos preferem a conformação trans. O cálculo das interações orbitalares pelo método NBO (Natural Bond Orbital) para as 2–acetamido-3-mercapto-3-metil-N-arilbutanamidas mostrou que as mesmas são estabilizadas pelas seguintes interações: no (N2) →  (C3-O4) e no(N10) → (C11-O12). Os resultados de NBO para os S-nitrosotíois mostraram que a interação hiperconjugativa é bastante efetiva nas conformações estáveis desses compostos, enfraquecendo a ligação que resulta no aumento do comprimento da ligação S-N em S-Nitrosotióis. A forte delocalização , induz caráter parcial a ligação S-N. A fraca ligação S-N indica uma forte delocalização do par de elétrons do O(NO) devido a interação, que é responsável pelo alongamento da ligação S-N, aumentando e a potencial capacidade do óxido nítrico ser liberado.
We carried out a conformational study on the S-nitrosothiols (R-SNO), 2-acetamido-3-methyl-3-(nitrososulfanyl)-N-arylbutanamides and their thiol precursors 2-acetamido-3-mercapto-3-methyl-N-arylbutanamides. The lowest energy conformation for both compounds is stabilized by intramolecular hydrogen bonds. Trans conformation was determined as the predominant conformation after geometrical analysis of R-SNO. Orbital interactions for 2-acetamido-3-mercapto-3-methyl-N-arylbutanamides were calculated using Natural Bond Orbital (NBO) methodology. Calculations indicated that orbital interactions for these compounds are stabilized by the following interactions: no (N2) →  (C3-O4) and no(N10) → (C11-O12). NBO results showed that the hyperconjugative interaction is very effective, weakening the σ bond and resulting in increasing length of the S-N bond in R-SNO. The strong delocalization induces partial character to the S-N bond. The bond S-N indicates a strong delocalization of the electron pair of O(NO) due to interaction. This interaction is responsible for the elongation of the S-N bond which increases the ability of the compound to release nitric oxide (NO). Based on the enhanced capacity to release NO by these compounds, our findings suggest that both compounds may display biological activity.
TEDE
BV UNIFESP: Teses e dissertações

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
This study presents a theoretical and experimental analysis of the conformational equilibrium of phenylacetic acid and its derivatives, namely: o-fluorophenylacetic, ochlorophenylacetic, o-bromophenylacetic, o-nitrophenylacetic, hydroxyphenylacetic, m-fluorophenylacetic, p-fluorophenylacetic, p-nitrophenylacetic, p-hydroxyphenylacetic, p-mercaptophenylacetic and p-aminophenylacetic. Thetechniques used were computational calculations and nuclear magnetic resonance and infrared spectroscopy.The study made it possible to verify the conformational preference of each compound, determined by their energies and geometries, which were evaluated both for the isolated molecule, at distinct theory levels, and in different solvents, with the IEF-PCM solvation model. By using natural bond orbital calculations, it was possible to identify the main orbital interactions for each conformation. With the total deletion calculations, it was verified that there was a balance between the steric and hyperconjugative effects in the stabilization of the most stable structures. The majority conformers of halogenated compounds in ortho revealed the same spatial orientation between the carbonyl and the benzene ring, similar to that of the phenylacetic acid. In the derivatives, nitro and hydroxylated in ortho, there was the presence of an intramolecular hydrogen bond, but in none of these cases the interaction referred to one of the main conformers. The infrared experiments in solvents of different polarities, allowed the identification of more than one band, enabling the attribution of conformers present in the equilibrium as well as the observation of the same tendency as the one obtained theoretically. The coupling constant 1JCH was evaluated through nuclear magnetic resonance. No significant variation of this constant was observed, showing that the major contribution to the equilibrium is related to the majoritarian conformer, which prevails even with the change in the polarity of the medium, for each compound under evaluation.
Neste trabalho foi apresentado uma análise teórica e experimental do equilíbrio conformacional do ácido fenilacético e seus derivados, sendo eles: ofluorofenilacético, o-clorofenilacético, o-bromofenilacético, o-nitrofenilacético, ohidróxifenilacético, m-fluorofenilacético, p-fluorofenilacético, p-nitrofenilacético, phidróxifenilacético,p-mercaptofenilacético e p-aminofenilacético. As técnicas utilizadas foram os cálculos computacionais e as espectroscopias de ressonância magnética nuclear e infravermelho. Com este estudo foi possível verificar a preferência conformacional de cada composto, determinadas pelas suas energias e geometrias, as quais foram avaliadas tanto para a molécula isolada, em distintos níveis de teoria, quanto em diferentes solventes, com o modelo de solvatação IEFPCM. Através dos cálculos dos orbitais naturais de ligação foi possível identificar as principais interações orbitais para cada conformação. Com os cálculos de deleção total, verificou-se que houve um balanço entre os efeitos estérico e hiperconjugativo na estabilização das estruturas mais estáveis. Os confôrmeros majoritários dos compostos halogenados em orto mostraram a mesma orientação espacial entre a carbonila e o anel benzênico, semelhante ao ácido fenilacético. Nos derivados,nitrado e hidroxilado em orto, houve a presença de uma ligação de hidrogênio intramolecular, em nenhum dos casos esta interação era referente a um dos confôrmeros principais. Utilizando a técnica de infravermelho na região do fundamental da carbonila, em solventes de diferentes polaridades, permitiram identificar a presença de mais de uma banda, sendo possível a atribuição dos confôrmeros presentes no equilíbrio, bem como observar a mesma tendência obtida teoricamente. Com a espectroscopia de ressonância magnética nuclear foi avaliada a constante de acoplamento 1JCH. Não houve uma variação significativa desta constante, mostrando que a maior contribuição no equilíbrio está relacionada com o confôrmero majoritário, que prevalece mesmo com a mudança da polaridade do meio, de cada composto avaliado.

Title: Molecular crystals for NLO applications - compounds of 1H-pyrazole-carboxamidine Author: Bc. Soňa Kohúteková Department: Department of Inorganic Chemistry Supervisor: prof. RNDr. Ivan Němec, Ph.D. Abstract: The aim of this diploma thesis is preparation and characterisation of novel compounds of 1H-pyrazole-carboxamidine in consideration of their potential application in the field of nonlinear optics. This thesis is focused on preparation of crystalline salts or adducts combining 1H-pyrazole-carboxamidine with selected inorganic and organic acids. Prepared materials were characterised mainly by the means of vibrational spectroscopy and X-ray diffraction analysis. Quantum-chemical calculations were used for a prediction of nonlinear optical properties as well as for interpretation of measured vibrational spectra. Four different approaches of calculations were used for an optimisation of computing time together with accuracy of the fit of calculated and measured spectra. Finally, measurements of second harmonic generation efficiency of two powder samples with non-centrosymmetric crystal structures were performed. Key words: NLO, vibrational spectroscopy, crystal structure, quantum-chemical calculations

This thesis is focused on preparation and study of new compounds of chosen organic bases with potential use in nonlinear optics. 2-amino-5-nitropyrimidine, 2-amino-4-methylpyrimidine and their salts with inorganic and organic acids are compounds of the main interest. Diffraction and vibrational-spectroscopic methods of characterization were used in combination with quantum chemical calculation methods. Another aim of this thesis was preparation of new salts of chosen pyrimidine derivates with the use of methylsulphonic acid. Part of this section is devoted to completion of pyridinium methylsulphonate phase transition and nonlinear optical property studies.

碩士
淡江大學
物理學系碩士班
99
In my thesis, I will first introduce CASTEP, a first principle calculation program. Then I will describe how I learned the relation between the equation of second harmonic generation (SHG) and the tool SHG code, and how to use it to obtain the SHG coefficients form a CASTEP optics calculation result. Finally, I use this experience to implement the equation of the third harmonic generation (THG) into a computer code. I will introduce the approximate or conversion formulas that I use in my code, and compare my results with them from other research groups.