High-frequency light-matter interaction in atoms and molecules

The field of attosecond science is a novel and fast-evolving research area that aims at unravelling the motion of particles in atoms, molecules, and solids. Therein, attochemistry thrives to understand, monitor, and one-day control the movement of electrons in molecules, which will open a new path to steer nuclear dynamics and photochemical reactions. In order to observe the motion of electrons, attosecond resolution and, thus, attosecond light pulses are needed. These attosecond pulses are inherently rooted in the high-frequency regime, ranging from XUV to soft and hard x-ray radiation. Depending on the energy, intensity, and aimed-at observable, different light-matter interactions can be studied. In this work, we tackle three different kinds of high-frequency light-matter interaction that originate in three different energy regimes and allow us to gain novel insight into the dynamics of molecules. In the XUV regime, the ionisation dynamics of correlated, multi-particle systems is studied together with few-cycle effects. In the soft x-ray regime, attosecond x-ray absorption is introduced as a novel tool to observe coupled electron and nuclear dynamics in a neutral molecule. In the hard x-ray regime, we focus on ultrafast, non-resonant x-ray scattering, which can be transformed into a future technology capable of observing electron dynamics. We are confident that this work will benefit the general understanding of high-frequency light-matter interaction in atoms and molecules, as well as aid and initiate new experiments in the field of attochemistry using XUV ionisation, x-ray absorption, and x-ray scattering

Nuclear–Electron Correlation Effects and Their Photoelectron Imprint in Molecular XUV Ionisation

The ionisation of molecules by attosecond XUV pulses is accompanied by complex correlated dynamics, such as the creation of coherent electron wave packets in the parent ion, their interplay with nuclear wave packets, and a correlated photoelectron moving in a multi-centred potential. Additionally, these processes are influenced by the dynamics prior to and during the ionisation. To fully understand and subsequently control the ionisation process on different time scales, a profound understanding of electron and nuclear correlation is needed. Here, we investigate the effect of nuclear–electron correlation in a correlated two-electron and one-nucleus quantum model system. Solving the time-dependent Schrödinger equation allows to monitor the correlation impact pre, during, and post-XUV ionisation. We show how an initial nuclear wave packet displaced from equilibrium influences the post-ionisation dynamics by means of momentum conservation between the target and parent ion, whilst the attosecond electron population remains largely unaffected. We calculate time-resolved photoelectron spectra and their asymmetries and demonstrate how the coupled electron–nuclear dynamics are imprinted on top of electron–electron correlation on the photoelectron properties. Finally, our findings give guidelines towards when correlation resulting effects have to be incorporated and in which instances the exact correlation treatment can be neglected

LOGISTIK: LEHRE UND FORSCHUNG IN MAGDEBURG

Die Logistik ist als Begriff und Handlungsfeld uralt, dennoch als Wirtschafts- und Wissenschaftsfeld recht jung und an der Otto-von-Guericke-Universität mit Lehrstühlen in der Fakultät für Maschinenbau seit 1992 und in der Fakultät für Wirtschaftswissenschaft seit 1994 vertreten. In diesen zwei einander ergänzenden wissenschaftlichen Sichtweisen wird hier das breite Lehr- und Forschungsgebiet der Logistik behandelt. Für die Ver- und Entsorgungsaufgaben in der Wirtschaft ist die Logistik von existenzieller Bedeutung. Die zunehmende Arbeitsteilung der Produktion und die Globalisierung des Warenaustauschs schafft größere räumliche und engere zeitliche Bedingungen sowie intensivere Vernetzungen und Abhängigkeiten, die es theoretisch und praktisch zu beherrschen gilt. Die Informations- und Kommunikationstechnologie als Innovationstreiber fördert die zunehmende Integration, so dass die Logistik heute die Stoff-, Informations- und Geldflüsse als Einheit sieht, die es bezüglich der Infrastrukturen, des Ressourceneinsatzes und der organisatorischen Ablaufplanung effizient zu gestalten gilt. Für diese Querschnittsaufgaben entwickelt der grundständige Studiengang Wirtschaftsingenieurwesen Logistik die erforderlichen Fähigkeiten und Kompetenzen. Die Forschung bedient sich mathematischer und experimenteller Modelle, um die zunehmende Komplexität der logistischen Systeme und Prozesse in technischer, organisatorischer und betriebswirtschaftlicher Hinsicht immer besser zu beherrschen

Unraveling the Light-Activated Reaction Mechanism in a Catalytically Competent Key Intermediate of a Multifunctional Molecular Catalyst for Artificial Photosynthesis

Understanding photodriven multielectron reaction pathways requires the identification and spectroscopic characterization of intermediates and their excited-state dynamics, which is very challenging due to their short lifetimes. To the best of our knowledge, this manuscript reports for the first time on in situ spectroelectrochemistry as an alternative approach to study the excited-state properties of reactive intermediates of photocatalytic cycles. UV/Vis, resonance-Raman, and transient-absorption spectroscopy have been employed to characterize the catalytically competent intermediate [(tbbpy)2RuII(tpphz)RhICp*] of [(tbbpy)2Ru(tpphz)Rh(Cp*)Cl]Cl(PF6)2 (Ru(tpphz)RhCp*), a photocatalyst for the hydrogenation of nicotinamide (NAD-analogue) and proton reduction, generated by electrochemical and chemical reduction. Electronic transitions shifting electron density from the activated catalytic center to the bridging tpphz ligand significantly reduce the catalytic activity upon visible-light irradiation. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Photo-Induced Charge Separation vs. Degradation of a BODIPY-Based Photosensitizer Assessed by TDDFT and RASPT2

A meso-mesityl-2,6-iodine substituted boron dipyrromethene (BODIPY) dye is investigated using a suite of computational methods addressing its functionality as photosensitizer, i.e., in the scope of light-driven hydrogen evolution in a two-component approach. Earlier reports on the performance of the present iodinated BODIPY dye proposed a significantly improved catalytic turn-over compared to its unsubstituted parent compound based on the population of long-lived charge-separated triplet states, accessible due to an enhanced spin-orbit coupling (SOC) introduced by the iodine atoms. The present quantum chemical study aims at elucidating the mechanisms of both the higher catalytic performance and the degradation pathways. Time-dependent density functional theory (TDDFT) and multi-state restricted active space perturbation theory through second-order (MS-RASPT2) simulations allowed identifying excited-state channels correlated to iodine dissociation. No evidence for an improved catalytic activity via enhanced SOCs among the low-lying states could be determined. However, the computational analysis reveals that the activation of the dye proceeds via pathways of the (prior chemically) singly-reduced species, featuring a pronounced stabilization of charge-separated species, while low barriers for carbon-iodine bond breaking determine the photostability of the BODIPY dye

Post-Ionization Interaction of OCS in Phase-Locked Two- Color Laser Fields

The control of fragment ejection direction and selective bond breaking of OCS are demonstrated by using a simple pulse shaping technique, two-color phase-locked two-color laser fields. The important roles of post-ionization interaction of polar molecules during dissociation are discussed using state-of-the-art numerical simulations.International Conference on Ultrafast Phenomen

Quantum Equation of Motion with Orbital Optimization for Computing Molecular Properties in Near-Term Quantum Computing

Determining the properties of molecules and materials is one of the premier applications of quantum computing. A major question in the field is how to use imperfect near-term quantum computers to solve problems of practical value. Inspired by the recently developed variants of the quantum counterpart of the equation-of-motion (qEOM) approach and the orbital-optimized variational quantum eigensolver (oo-VQE), we present a quantum algorithm (oo-VQE-qEOM) for the calculation of molecular properties by computing expectation values on a quantum computer. We perform noise-free quantum simulations of BeH2 in the series of STO-3G/6-31G/6-31G* basis sets and of H4 and H2O in 6-31G using an active space of four electrons and four spatial orbitals (8 qubits) to evaluate excitation energies, electronic absorption, and, for twisted H4, circular dichroism spectra. We demonstrate that the proposed algorithm can reproduce the results of conventional classical CASSCF calculations for these molecular systems.</p

Subspace Methods for the Simulation of Molecular Response Properties on a Quantum Computer

We explore Davidson methods for obtaining excitation energies and other linear response properties within the recently developed quantum self-consistent linear response (q-sc-LR) method. Davidson-type methods allow for obtaining only a few selected excitation energies without explicitly constructing the electronic Hessian since they only require the ability to perform Hessian-vector multiplications. We apply the Davidson method to calculate the excitation energies of hydrogen chains (up to H10) and analyze aspects of statistical noise for computing excitation energies on quantum simulators. Additionally, we apply Davidson methods for computing linear response properties such as static polarizabilities for H2, LiH, H2O, OH-, and NH3, and show that unitary coupled cluster outperforms classical projected coupled cluster for molecular systems with strong correlation.</p

Which Options Exist for NISQ-Friendly Linear Response Formulations?

Linear response (LR) theory is a powerful tool in classic quantum chemistry crucial to understanding photoinduced processes in chemistry and biology. However, performing simulations for large systems and in the case of strong electron correlation remains challenging. Quantum computers are poised to facilitate the simulation of such systems, and recently, a quantum linear response formulation (qLR) was introduced [Kumar et al., J. Chem. Theory Comput. 2023, 19, 9136-9150]. To apply qLR to near-term quantum computers beyond a minimal basis set, we here introduce a resource-efficient qLR theory, using a truncated active-space version of the multiconfigurational self-consistent field LR ansatz. Therein, we investigate eight different near-term qLR formalisms that utilize novel operator transformations that allow the qLR equations to be performed on near-term hardware. Simulating excited state potential energy curves and absorption spectra for various test cases, we identify two promising candidates, dubbed "proj LRSD" and "all-proj LRSD"