Development of efficient and low-scaling methods to compute molecular properties at MP2 and double-hybrid DFT levels

This thesis introduces new methods to compute molecular properties at the level of second-order Møller-Plesset perturbation theory (MP2) and double-hybrid density functional theory, building on a reformulation in atomic orbitals and exploiting the rank deficiency of the (pseudo-)density matrices, thus reducing the scaling behavior with respect to the size of the basis set. By furthermore employing the resolution-of-the-identity approximation, low-scaling and efficient MP2 energy gradients are presented, where significant two-electron integrals are screened using a distance-including integral estimation technique. With this, the forces and the hyperfine coupling constants of systems larger than previously computable at the MP2-level are obtained. In the second part of this thesis, the locality of the spin density in many molecular systems is exploited in the computation of the hyperfine coupling constants, leading to further speed-ups and allowing for a thorough investigation of the effect of the protein environment on the hyperfine coupling within the core region of a pyruvate formate lyase. With this efficient method, studying the effect of nuclear motion on the accuracy of the computed hyperfine coupling constants is possible. The study presented in this thesis demonstrates that both electron correlation and vibrational motion are crucial for an accurate theoretical description. When calculating magnetic properties, the dependence on the choice of gauge origins needs to be considered. This effect is studied systematically, and in detail, in a fourth project of this thesis for the computation of electronic g-tensors, for which it was previously assumed that the computation is largely independent of the choice of the gauge-origin. The study clearly contradicts this assumption and motivates the use of gauge including atomic orbitals in future work on electronic g-tensors. In a last part, this work transfers the algorithmic developments on the computation of analytic gradients to the computation of nuclear magnetic resonance (NMR) shieldings at the MP2-level. Though a sublinear scaling ansatz to compute the NMR shielding tensor per nucleus is available, the lack of an efficient implementation and the large dependency on the size of the basis sets prohibits the accurate computation of the shielding tensor of medium- to large-sized molecules. Furthermore, while this ansatz in theory scales linearly when all nuclei in a system are computed, it is inefficient due to the dependence of the rate-determining steps on the nuclear magnetic moments. This thesis therefore presents a new all-nuclei ansatz and introduces the methodology for the efficient computation of the energy gradients developed in this thesis, highlighting significant computational savings

TURBOMOLE: Today and Tomorrow

TURBOMOLE is a highly optimized software suite for large-scale quantum-chemical and materials science simulations of molecules, clusters, extended systems, and periodic solids. TURBOMOLE uses Gaussian basis sets and has been designed with robust and fast quantum-chemical applications in mind, ranging from homogeneous and heterogeneous catalysis to inorganic and organic chemistry and various types of spectroscopy, light–matter interactions, and biochemistry. This Perspective briefly surveys TURBOMOLE’s functionality and highlights recent developments that have taken place between 2020 and 2023, comprising new electronic structure methods for molecules and solids, previously unavailable molecular properties, embedding, and molecular dynamics approaches. Select features under development are reviewed to illustrate the continuous growth of the program suite, including nuclear electronic orbital methods, Hartree–Fock-based adiabatic connection models, simplified time-dependent density functional theory, relativistic effects and magnetic properties, and multiscale modeling of optical properties

Commemorative Issue in Honor of Professor Karlheinz Schwarz on the Occasion of His 80th Birthday

A collection of 18 scientific papers written in honor of Professor Karlheinz Schwarz's 80th birthday. The main topics include spectroscopy, excited states, DFT developments, results analysis, solid states, and surfaces

56th Annual Rocky Mountain Conference on Magnetic Resonance

Final program, abstracts, and information about the 56th annual meeting of the Rocky Mountain Conference on Magnetic Resonance, co-endorsed by the Colorado Section of the American Chemical Society and the Society for Applied Spectroscopy. Held in Copper Mountain, Colorado, July 13-17, 2014

Under the influence: Understanding the thermodynamic and optical properties of stimuli-responsive complex organic systems

A solid understanding of the optical and thermodynamic features of a chemical system is indispensable for the development and optimisation of new materials. Stimuli-responsive substances may be incorporated into optoelectronic devices, such as organic light-emitting diodes or sensory systems. Especially in recent years, photo-sensitive molecular aggregates and redox-switchable supramolecular architectures have proven their merit. Due to their flexible components, these noncovalently bound systems often exhibit perplexing behaviour when submitted to external stimuli, such as light or electric potential. Examples addressed in this thesis include substitution-pattern controlled fluorescence quantum yields and redox-induced switchable spectroscopic responses. While there are plenty of powerful experimental techniques around to examine the underlying mechanisms, high-level quantum-chemical approaches are often crucial for a final and conclusive interpretation of one’s experimental results. The aim of this thesis is to examine the broad scope of stimuli-responsive molecular aggregates and demonstrate the versatility of quantum-chemical methods to study their optical and thermodynamic properties. To this end, I will present six different publications separated into two parts, A and B, each contributing three papers. Due to the variety of the molecules studied in this work, computational protocols effectively tailored for each project had to be developed. The applied methods are used to study electronic as well as molecular structures and include solvent and finite-temperature effects for comparison to experiment. A major emphasis is put on the evaluation of excited states. In addition to the valuable knowledge we could gain about the underlying chemistry of the investigated systems, these protocols serve as a potent tool for the examination of similar problems. All papers include combined approaches of theory and experiment and, hence, showcase the efficient collaboration of experimental and theoretical groups. In part A, I will present a new class of fluorescent dyes: Diaminodicyanoquinones (DADQs). Owing to a large dipole moment, redox-activity, and tailorable fluorescence, DADQs are promising candidates for a variety of applications in the context of molecular electronics. Papers A1-A3 effectively follow a bottom-up approach examining monomers, aggregates in solution, and the solid state with a focus on their absorption and emission features. In all three publications, remarkable experimental observations are made including notably high quantum yields and counterintuitive concentration-dependent absorption peaks. In each case, a combination of multiple high-level state-of-the-art quantum-chemical approaches including DFT/MRCI (density functional theory/multi-reference configuration interaction) is utilised to thoroughly investigate the chemical systems and find explanations for the often unexpected experimental results. Part B presents three different redox-responsive supramolecular systems, each displaying intriguing thermodynamic or optical properties, which could only be fully unravelled by rigorous theoretical studies. Redox-responsiveness is induced either by incorporation of the organosulfur compound tetrathiafulvalene (TTF) or by complexation with a redox-active molecule such as cobaltocene. A variety of different quantum-chemical methods based on DFT and time-dependent DFT (TD-DFT) is employed in the course of part B to study switching mechanisms and rationalise thermodynamic features. In this way, the examined supramolecular structures are now equipped with an in-depth understanding of their often non-trivial chemical behaviour which paves the way towards applications in novel optoelectronic technologies.Ein klares Verständnis der optischen und thermodynamischen Eigenschaften chemischer Systeme ist unabdingbar für die Entwicklung und Optimierung neuer Materialien. Substanzen, die sich von äußeren Einflüssen steuern lassen, können in optoelektronische Geräte wie organische Leuchtdioden oder Sensorsysteme eingebaut werden. Besonders in den vergangenen Jahren haben photo-sensitive molekulare Aggregate und redox-schaltbare supramolekulare Architekturen ihren Wert unter Beweis gestellt. Aufgrund ihrer flexiblen Einzelkomponenten zeigen diese nichtkovalent gebundenen Systeme oftmals ein verblüffendes Verhalten, wenn sie durch äußere Reize wie Licht oder ein elektrisches Potenzial beeinflusst werden. Beispiele, die in dieser Dissertation adressiert werden, sind Substitutionsmuster-kontrollierte Fluoreszenzquantenausbeuten und redox-induzierte schaltbare spektroskopische Signale. Während es eine große Anzahl an vielseitigen experimentellen Methoden gibt, um die zugrundeliegenden Mechanismen zu studieren, ist oftmals die Verwendung anspruchsvoller quantenchemischer Ansätze vonnöten, um eine endgültige und schlüssige Interpretation der experimentellen Ergebnisse zu erhalten. Diese Arbeit ist darauf ausgerichtet, die Vielseitigkeit von durch äußere Reize steuerbare (eng. stimuli-responsive) molekulare Aggregate zu analysieren und die Flexibilität von quantenchemischen Methoden aufzuzeigen, die zur Untersuchung ihrer optischen und thermodynamischen Eigenschaften genutzt werden. Zu diesem Zweck werde ich sechs Publikationen vorstellen, aufgeteilt in zwei Teile, A und B, die jeweils drei Arbeiten beitragen. Aufgrund der Vielfältigkeit der untersuchten Moleküle wurden Berechnungsverfahren entwickelt, die im wesentlichen für jedes Projekt aufs Neue maßgeschneidert werden mussten. Die angewandten Methoden sind darauf ausgelegt, sowohl elektronische als auch molekulare Strukturen zu beschreiben und Solvatations- und Temperatureinflüsse für den Vergleich zu Experimenten mit einzubeziehen. Ein großes Augenmerk liegt auf der Analyse von angeregten Zuständen. Abgesehen von den wertvollen Erkenntnissen, die wir über die zugrundeliegende Chemie der untersuchten Systeme erhalten konnten, dienen die entwickelten Berechnungsansätze als leistungsfähiges Werkzeug für das Herangehen an ähnliche Probleme. Alle Publikationen beinhalten aus Theorie und Experiment kombinierte Ansätze und illustrieren damit die effiziente Zusammenarbeit von theoretisch und experimentell arbeitenden Forschungsgruppen. In Teil A werde ich eine neuartige Klasse von fluoreszierenden Farbstoffen vorstellen: Diaminodicyanochinone (DADQs). Aufgrund ihrer hohen Dipolmomente, Redoxaktivität und einstellbaren Fluoreszenz sind DADQs vielversprechende Kandidaten für eine Vielzahl von Anwendungen im Kontext der molekularen Elektronik. Publikationen A1-A3 folgen im wesentlichen einem Bottom-up-Ansatz, bei dem es um die Untersuchung von Monomeren, Aggregaten in Lösung und Festkörperstoffen geht, wobei ein Fokus auf deren Absorptions- und Emissionseigenschaften liegt. In allen drei Arbeiten sind erstaunliche experimentelle Beobachtungen gemacht worden wie beispielsweise extrem hohe Fluoreszenzquantenausbeuten oder kontraintuitive konzentrationsabhängige Absorptionsbanden. In jeder Untersuchung wurde eine Vielzahl an hochmodernen quantenchemischen Methoden inklusive des DFT/MRCI (Dichtefunktionaltheorie/Multireferenz-Konfigurationswechselwirkung) Ansatzes genutzt, um eine ausführliche Analyse der chemischen Systeme zu gewährleisten und Erklärungen für die unerwarteten experimentellen Beobachtungen zu finden. In Teil B werden drei verschiedene redox-stimulierbare supramolekulare Systeme präsentiert, die alle interessante thermodynamische und optische Eigenschaften aufzeigen, welche nur durch den sorgfältigen Einsatz von theoretischen Methoden vollkommen verstanden werden konnten. Redox-Stimulierbarkeit wurde entweder durch die Eingliederung der schwefelorganischen Verbindung Tetrathiafulvalen (TTF) oder durch Komplexierung mit einem redox-aktiven Molekül wie Cobaltocen induziert. Verschiedene quantenchemische auf DFT und zeitabhängiger DFT (TD-DFT) basierende Ansätze wurden in Teil B benutzt, um Schaltmechanismen zu untersuchen und thermodynamische Eigenschaften zu rationalisieren. Dadurch erhielten wir ein tiefes Verständnis der oftmals alles andere als trivialen chemischen Verhaltensweisen der supramolekularen Strukturen, was den Weg zur Anwendung in neuartigen, optoelektronischen Technologien ebnet

48th Rocky Mountain Conference on Analytical Chemistry

Final program, abstracts, and information about the 48th annual meeting of the Rocky Mountain Conference on Analytical Chemistry, co-endorsed by the Colorado Section of the American Chemical Society and the Rocky Mountain Section of the Society for Applied Spectroscopy. Held in Breckenridge, Colorado, July 23-27, 2006

Atomic Electrons as Sensitive Probes of Nuclear Properties and Astrophysical Plasma Environments : A Computational Approach

This thesis deals with the relativistic modeling of atoms and ions. To interpret the stellar spectra and gain more insight from astrophysical observations, the underlying processes that generate the spectra need to be well understood and described. Examples of such processes are the interactions of atomic electrons with internal and external electromagnetic fields and with the nucleus.By exploring different computational methodologies, Paper I analyzes how the transition probabilities, of transitions involving high Rydberg states, depend on the gauge and the orbital set that is used in the calculations. Papers II and III contain large homogeneous data sets of parameters related to atomic radiative processes, namely transition energies, transition probabilities, weighted oscillator strengths, and lifetimes of excited states, for carbon and aluminium systems. These parameters are essential in astrophysical applications, e.g., in abundance and plasma analyses of stars. In addition, Paper IV presents extended data of Landé g-factors, used to characterize the response of spectral lines to a given value of an external magnetic field. The description of effects arising from the interplay between atomic electrons and nuclei, such as hyperfine structure splittings and isotope shifts, requires that the nuclear structure properties giving rise to these effects are well determined. This is, however, not always the case; as we move away from the valley of stability, data of nuclear structure observables are scarce. High-resolution measurements of hyperfine structures and isotope shifts, combined with first-principles atomic structure calculations, are commonly used to probe the structures of nuclei, including short-lived and radioactive systems. In Papers V and VI, measurements of the hyperfine structure in neutral tin were combined with atomic structure calculations to extract the electric quadrupole moments of tin isotopes. Paper VII presents a novel method that combines experimental isotope shifts and calculations of atomic parameters to probe details of nuclear charge density distributions, other than charge radii