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Ab initio calculation [Basis choice]

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Die Raman-Schwingungsspektroskopie ist eine der führenden Charakterisierungsmethoden für chemische Konstitution und liefert wertvolle Beiträge zur Strukturaufklärung großer Moleküle. Die Interpretation experimenteller Raman-Spektren wird durch den Vergleich der theoretischen Vorhersagen für Schwingungsfrequenzen und Raman-Intensitäten mit experimentellen Daten ermöglicht. Diese Arbeit umfasst die Entwicklung, Implementierung und Validierung effizienter Verfahren zur Berechnung der Raman-Intensitäten im Rahmen der zeitabhängigen Dichtefunktionaltheorie (TDDFT). Die Verwendung analytischer Gradientenmethoden eröffnet den Weg zur simultanen Berechnung der Raman-Intensitäten aller Schwingungsmoden eines Moleküls innerhalb der Polarisierbarkeitstheorie. Die entwickelten Verfahren werden hinsichtlich ihrer Genauigkeit und ihres Rechenaufwandes untersucht und zur Interpretation der Raman-Spektren von Fullerenen eingesetzt.

Lagrange-Funktional --- Resonanz-Raman-Effekt --- Dichtefunktionalformalismus --- analytische Ableitungsmethoden --- Raman-Spektrum --- Polarisierbarkeit --- Ab-initio-Rechnung

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The QM/MM method, short for quantum mechanical/molecular mechanical, is a highly versatile approach for the study of chemical phenomena, combining the accuracy of quantum chemistry to describe the region of interest with the efficiency of molecular mechanical potentials to represent the remaining part of the system. Originally conceived in the 1970s by the influential work of the the Nobel laureates Martin Karplus, Michael Levitt and Arieh Warshel, QM/MM techniques have evolved into one of the most accurate and general approaches to investigate the properties of chemical systems via computational methods. Whereas the first applications have been focused on studies of organic and biomolecular systems, a large variety of QM/MM implementations have been developed over the last decades, extending the range of applicability to address research questions relevant for both solution and solid-state chemistry as well. Despite approaching their 50th anniversary in 2022, the formulation of improved QM/MM methods is still an active field of research, with the aim to (i) extend the applicability to address an even broader range of research questions in chemistry and related disciplines, and (ii) further push the accuracy achieved in the QM/MM description beyond that of established formulations. While being a highly successful approach on its own, the combination of the QM/MM strategy with other established theoretical techniques greatly extends the capabilities of the computational approaches. For instance the integration of a suitable QM/MM technique into the highly successful Monte-Carlo and molecular dynamics simulation protocols enables the description of the chemical systems on the basis of an ensemble that is in part constructed on a quantum-mechanical basis. This eBook presents the contributions of a recent Research Topic published in Frontiers in Chemistry, that highlight novel approaches as well as advanced applications of QM/MM method to a broad variety of targets. In total 2 review articles and 10 original research contributions from 48 authors are presented, covering 12 different countries on four continents. The range of research questions addressed by the individual contributions provide a lucid overview on the versatility of the QM/MM method, and demonstrate the general applicability and accuracy that can be achieved for different problems in chemical sciences. Together with the development of improved algorithms to enhance the capabilities of quantum chemical methods and the continuous advancement in the capacities of computational resources, it can be expected that the impact of QM/MM methods in chemical sciences will be further increased already in the near future.

Quantum Chemistry --- Hybrid Quantum Mechanical/Molecular Mechanical --- Density Functional Theory --- Ab initio/First Principles --- QM/MM --- Empirical Potentials --- Molecular Mechanics --- Force Field

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The QM/MM method, short for quantum mechanical/molecular mechanical, is a highly versatile approach for the study of chemical phenomena, combining the accuracy of quantum chemistry to describe the region of interest with the efficiency of molecular mechanical potentials to represent the remaining part of the system. Originally conceived in the 1970s by the influential work of the the Nobel laureates Martin Karplus, Michael Levitt and Arieh Warshel, QM/MM techniques have evolved into one of the most accurate and general approaches to investigate the properties of chemical systems via computational methods. Whereas the first applications have been focused on studies of organic and biomolecular systems, a large variety of QM/MM implementations have been developed over the last decades, extending the range of applicability to address research questions relevant for both solution and solid-state chemistry as well. Despite approaching their 50th anniversary in 2022, the formulation of improved QM/MM methods is still an active field of research, with the aim to (i) extend the applicability to address an even broader range of research questions in chemistry and related disciplines, and (ii) further push the accuracy achieved in the QM/MM description beyond that of established formulations. While being a highly successful approach on its own, the combination of the QM/MM strategy with other established theoretical techniques greatly extends the capabilities of the computational approaches. For instance the integration of a suitable QM/MM technique into the highly successful Monte-Carlo and molecular dynamics simulation protocols enables the description of the chemical systems on the basis of an ensemble that is in part constructed on a quantum-mechanical basis. This eBook presents the contributions of a recent Research Topic published in Frontiers in Chemistry, that highlight novel approaches as well as advanced applications of QM/MM method to a broad variety of targets. In total 2 review articles and 10 original research contributions from 48 authors are presented, covering 12 different countries on four continents. The range of research questions addressed by the individual contributions provide a lucid overview on the versatility of the QM/MM method, and demonstrate the general applicability and accuracy that can be achieved for different problems in chemical sciences. Together with the development of improved algorithms to enhance the capabilities of quantum chemical methods and the continuous advancement in the capacities of computational resources, it can be expected that the impact of QM/MM methods in chemical sciences will be further increased already in the near future.

Quantum Chemistry --- Hybrid Quantum Mechanical/Molecular Mechanical --- Density Functional Theory --- Ab initio/First Principles --- QM/MM --- Empirical Potentials --- Molecular Mechanics --- Force Field --- Quantum Chemistry --- Hybrid Quantum Mechanical/Molecular Mechanical --- Density Functional Theory --- Ab initio/First Principles --- QM/MM --- Empirical Potentials --- Molecular Mechanics --- Force Field

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Atomistic simulations, based on ab-initio and semi-empirical approaches, are nowadays widespread in many areas of physics, chemistry and, more recently, biology. Improved algorithms and increased computational power widened the areas of application of these computational methods to extended materials of technological interest, in particular allowing unprecedented access to the first-principles investigation of their electronic, optical, thermodynamical and mechanical properties, even where experiments are not available. However, for a big impact on the society, this rapidly growing field of computational approaches to materials science has to face the unfavourable scaling with the system size, and to beat the time-scale bottleneck. Indeed, many phenomena, such as crystal growth or protein folding for example, occur in a space/time scale which is normally out of reach of present simulations. Multi-scale approaches try to combine different scale algorithms along with matching procedures in order to bridge the gap between first-principles and continuum-level simulations. This Research Topic aims at the description of recent advances and applications in these two emerging fields of ab-inito and multi-scale materials modelling for both ground and excited states. A variety of theoretical and computational techniques are included along with the application of these methods to systems at increasing level of complexity, from nano to micro. Crossing the borders between several computational, theoretical and experimental techniques, this Research Topic aims to be of interest to a broad community, including experimental and theoretical physicists, chemists and engineers interested in materials research in a broad sense.

molecular dynamics simulations --- Classical and Quantum Monte Carlo methods --- ab-initio --- macromolecular complex --- Materials characterization --- Multiscale and Hierarchical modeling --- mechanical --- Electronic and optical properties of solids --- Carbon-based systems --- materials growth --- Density-functional