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We have investigated the optical excitation of solitons and charge transfer excitons in polymer chains by solving the equations of motion for the reduced density matrix and the lattice displacement simultaneously in time. Electron-phonon coupling leads to polaron-exciton formation which can be identified in transient pump-probe signals.
We introduce a concept which allows to study the nonlinear optical response of conjugated polymers taking into account many-body effects of the excitation process. The formation of charge transfer excitons and the creation of lattice distortions are studied in short polymer chains by solving the self consistent equations of motion for the reduced single electron density matrix and the lattice displacement. The coupling of electronic motions to lattice dynamics gives rise to the formation of excitonic polarons, which can be identified in the femtosecond pump-probe signal.
We analyze risks and crises for healthcare providers and discuss the impact of cloud computing in such scenarios. The analysis is conducted in a holistic way, taking into account organizational and human aspects, clinical, IT-related, and utilities-related risks as well as incorporating the view of the overall risk management.
The complexity of providing medical care in a high-tech environment with a highly specialized, limited labour force makes hospitals more crisis-prone than other industries. An effective defence against crises is only possible if the organizational resilience and the capacity to handle crises become part of the hospitals’ organizational culture. To become more resilient to crises, a raised awareness — especially in the area of human resource (HR) — is necessary. The aim of this paper is to contribute to the process robustness against crises through the identification and evaluation of relevant HR crises and their causations in hospitals.
Qualitative and quantitative methods were combined to identify and evaluate crises in hospitals in the HR sector. A structured workshop with experts was conducted to identify HR crises and their descriptions, as well as causes and consequences for patients and hospitals. To evaluate the findings, an online survey was carried out to rate the occurrence (past, future) and dangerousness of each crisis.
Six HR crises were identified in this study: staff shortages, acute loss of personnel following a pandemic, damage to reputation, insufficient communication during restructuring, bullying, and misuse of drugs. The highest occurrence probability in the future was seen in staff shortages, followed by acute loss of personnel following a pandemic. Staff shortages, damage to reputation, and acute loss of personnel following a pandemic were seen as the most dangerous crises.
The study concludes that coping with HR crises in hospitals is existential for hospitals and requires increased awareness. The six HR crises identified occurred regularly in German hospitals in the past, and their occurrence probability for the future was rated as high.
In German hospitals there is a need for optimized crisis- and risk management. About one third of all hospital-acquired patient damages are due to medication errors. The aim of our interdisciplinary project “Risk Management in Hospitals” is to analyze the behavior of the various key players in the fields of medical care, human resources, supply and IT-systems in the context of various simulated risk scenarios as well as to develop adequate risk management tools. In this abstract, the first Results on medication errors are presented.
The first three-dimensional quantum-dynamical ab initio simulation of the large amplitude vibrational dynamics of an Ag3 cluster initiated from its linear transition state is presented. This can be monitored by femtosecond pump-probe negative-ion to neutral-to-positive-ion spectroscopy with zero electron kinetic energy (NeNePo-ZEKE). The time evolution of the representative wavepacket confirms the dynamical effects which have been discovered previously by Wigner-type semiclassical simulations: the initial coherent bending and stretching from linear to near equilateral triangular configuration, followed by intracluster collision and intracluster vibrational relaxation with a weak fractional revival. In addition, the quantum wavepacket shows interferences and spreading.
Theoretical study of femtosecond pump–probe signals of nonstoichiometric alkali halide clusters
(1999)
We present the outline of the ab–initio molecular dynamics method for adiabatic excited states which is suitable to treat the involved excited electronic states simultaneously with the motion of the nuclei. The method allows the simulation of time–resolved pump–probe signals and the analysis of the signals in terms of the underlying nuclear dynamics. Moreover, the timescales of the structural relaxation in excited electronic states vs. intramolecular vibrational relaxation processes can be estimated and the influence of the initial temperature of the cluster can be determined.
The method is applied to the analysis of the timescales as well as of the dynamics of localized/delocalized electronic excitations in the Na2F molecule which represents a test example for nonstoichiometric alkali–halides with one excess electron. The aim is to develop a method for the investigation of time–dependent laser induced processes in clusters which is capable to extract the leading physical effects responsible for the controlled excitation dynamics and for the evolution of the non–equilibrium states.
We present a theoretical study of the multistate dynamics of the Ag3-/Ag3/Ag3+ system on the time scale of nuclear motion, as explored by femtosecond pump−probe negative ion-to neutral-to positive ion (NENEPO) spectroscopy. The dynamics of the Ag3 cluster initiated from its linear transition state involves configurational relaxation, intracluster collision, and onset of IVR, resonant and dissipative IVR and vibrational equilibration, whose time scales were determined. Our analysis reveals that theory is essential for the elucidation of the rich dynamic information regarding geometrical change, completion of IVR, and vibrational coherence effects in the NENEPO femtosecond signals.
Stationary spectra offer information on the interplay between the structures and the nature of electronic excitations reflecting bonding properties, as shown by comparing Sin with Agn (n=4-6) clusters. In order to study the dynamical properties, simulations and analysis of femtosecond (fs) time-resolved pump–probe or pump–dump signals have been carried out, which allows us to determine the timescales and the nature of configurational changes versus internal vibrational relaxation (IVR) in electronic ground or excited states. For this purpose we have developed a multi-state ab initio molecular dynamics (involving ground as well as adiabatic or non-adiabatic excited electronic states) on the timescale of the nuclear motion, using the time evolution of a thermal ensemble in the Wigner representation. The combination of ab initio quantum-chemical methods used for the molecular dynamics ‘on the fly’ and the Wigner-distribution approach for the description of the motion of the nuclei also allowed the accurate determination of pump–probe and pump–dump signals under temperature-dependent initial conditions. We use this novel combination of methods to investigate the dynamics in excited states of non-stoichiometric NanFn-1 clusters with a single excess electron. The timescales of the structural relaxation in excited states versus intramolecular vibrational relaxation processes have been determined, as illustrated for the example of Na4F3. This is the first study of the system with 15 degrees of freedom for which the dynamics in the excited states has been carried out without the precalculation of the energy surfaces.
The central issue in femtosecond (fs) time resolved spectroscopy of clusters is the investigation of geometric relaxation and internal vibrational redistribution (IVR) after optical excitation in a nonequilibrium configuration of nuclei by laser photoelectron excitation, and corresponding time delayed probing by multiphoton-ionization. For this purpose, we have developed multistate ab initio molecular dynamics involving adiabatic ground and excited electronic states, as well as nonadiabatic coupling between them, using the time evolution of initial thermal ensemble in Wigner representation. The combination of ab initio quantum chemical methods, used for the adiabatic and nonadiabatic molecular dynamics “on the fly,” and the Wigner distribution approach for the description of the motion of the nuclei allowed us the accurate determination of pump-probe and pump-dump signals also under temperature dependent initial conditions. The connection between simulated pump-probe signals and the underlying dynamics of nuclei involving adiabatic electronic ground states has been first established for the example of the Agequation image/Ag3/Agequation image systems, and compared with experimental negative-to-neutral-to-positive NeNePo pump-probe signals. Our simulations reproduced the experimental NeNePo results and determined, in addition to the timescales of geometric relaxation, the conditions under which the resonant or dissipative IVR, as well as vibrational coherence, should be found in the experimental pump-probe signals. This can be realized in the zero electron kinetic energy NeNePo-ZEKE experiments, which are in progress. The above combination of methods has been recently extended to the analysis of the timescales as well as of the dynamics in excited electronic states of the nonstoichiometric NanFn−1 (n=2–4) clusters with the single excess valence electron. Our approach allows the simulation of femtosecond NeExPo-pump-probe and NeExNe-pump-dump signals, based on an analytic formulation which utilizes temperature dependent ground state initial conditions of neutral system (Ne); an ensemble of trajectories carried out either on the adiabatic electronic excited state (Ex), or on both the excited and the ground states through nonadiabatic coupling in connection with the fewest switching hopping algorithm for the investigation of the dynamics of the system; and either the cationic (Po) or the neutral ground state (Ne) for the probing step. The choice of the systems has been made in order to determine the timescales of processes involving (1) fast geometric relaxation leaving the bonding frame intact versus IVR, as during the adiabatic dynamics in the first excited state of Na4F3, being the smallest prototype of F-colored centers in the bulk; and (2) the photo-isomerization process through the conical intersection during nonadiabatic dynamics due to the long amplitude motion, as in the Na3F2 cluster after breaking of one metallic and one ionic bond, representing the first example of a five atomic cluster in the gas phase exhibiting conical intersection between the ground and the first excited state. In both cases, full complexity of the problem has been considered taking into account all degrees of freedom. The investigated systems represent important test cases for providing the conceptual framework of ultrafast dynamics in finite systems.
We investigate ultrafast multi-state nuclear dynamics in a triatomic cluster. In particular, we explore how the intracluster nuclear dynamics of the Ag−3/Ag3/Ag+3 system is reflected in the femtosecond pump-probe negative ion-to neutral-to positive ion (NENEPO) signals. The nuclear dynamics is based on classical trajectories on the ground electronic adiabatic state potential hypersurfaces obtained from accurate ab initio quantum chemistry calculations. The nuclear dynamics of Ag3 initiated from the linear transition state involves distinct sequential processes of configurational relaxation to the triangular configuration, intracluster collisions, and the onset of IVR, resonant, and dissipative IVR, and vibrational equilibration. We determined the timescales for these processes and discussed their dependence on the initial cluster temperature. The Wigner representation of the density matrix was utilized to simulate the NENEPO-zero kinetic energy (NENEPO-ZEKE) signal and the total (integrated over the photoelectron energy) NENEPO signal. We show how geometrical change, completion of IVR and vibrational coherenceeffects can be identified in the NENEPO signals. A comparison of the calculated NENEPO signals with the available experimental data is presented.
Ab-initio study of structural and optical properties of nonstoichiometric alkalimetal- oxides
(1997)
Structural and optical properties of nonstoichiometric LinO and NanO (n = 3, 4) clusters containing one and two excess electrons are studied using ab-initio methods accounting for electron correlation. We show that calculated absorption patterns are excellent fingerprints of structural and bonding properties. The optical response of Li4O and Na4O clusters with the most stable tetrahedral type structures is characterized by a common feature, that is the appearance of a dominant intense transition in infrared regime although excess of electrons are not localized, as it is the case for small alkali-halide clusters, with cuboid corner vacancy (surface F-center in finite systems).
We present an exactly diagonalizable model Hamiltonian for the large polaron derived by analyzing the variational ansatz by Haga-Larsen (HL) for the Fröhlich Hamiltonian. The lowest energy eigenvalue of the model Hamiltonian for fixed wave numbers reproduces the energy of the variational ansatz by Haga-Larsen and is, therefore, an upper bound with respect to the corresponding energy eigenvalue of the Fröhlich Hamiltonian. This is valid for any momentum which is proven by extending the Haga-Larsen approach. Furthermore, since all integrations can be performed analytically, the model Hamiltonian is easily tractable. The energy eigenvalue spectrum of the model Hamiltonian is studied below and above the phonon-emission threshold. The quality of the model Hamiltonian is determined by the variational ansatz of Haga and Larsen. Incorporating an improved energy-momentum relation, a generalized model Hamiltonian is derived possessing a larger validity range with respect to the coupling strength. Furthermore, a second exactly diagonalizable model Hamiltonian based on improved Wigner-Brillouin perturbation theory due to Warmenbol, Peeters, and Devreese (WPD) is presented. It is briefly demonstrated that one is able to construct all mentioned model Hamiltonians also in the 2D polaron problem. In contrast to the 3D case, where the HL-type model Hamiltonian possesses the higher quality for any momentum, in the 2D case, it works well only for small momenta. For large momenta, only the WPD-type model Hamiltonian describes the energy-momentum relation correctly. We demonstrate the usefulness of the model Hamiltonian concept by exactly calculating the one-electron Green’s function for all mentioned model Hamiltonians and comment why significant advantages of the model Hamilton concept for the treating of low-dimensional systems (planar semiconducting quantum-well structures) can be expected.
The optical response of conjugated polymers is calculated using a one-dimensional tight-binding model with Coulomb interactions, and adopting the multipolar form for the electromagnetic field Hamiltonian. By formulating the problem using the reduced single-electron density matrix and its evolution in Liouville space, we obtain a real-space description for the elementary electronic excitations. A unified expression for the linear response including radiative decay, which is valid for arbitrary chain size compared with the optical wavelength, is described. For small sizes it shows exciton confinement effects on the radiative decay and for larger sizes it fully incorporates polariton effects.
Portals are called web sites which are designed to offer services and/or an outline of special subjects. They have been developed as fast as information data bases and electronic communication facilities were extended. Recently, portals with geographically referenced information became important and popular for different fields like geo information systems of cities (see e. or the presentation of economically relevant data in the context of regional marketing, foreign direct investment or tourism by indicating important objects like public institutions, companies, hotels, sights, etc. on maps. In this manner they may contribute to the improvement of industrial structure and the marketing of a region. For representing geographical data on maps, applications with special client-server-architecture have to be developed. There are different solutions for the Internet using HTML and JavaScript, Flash or Java Applets. In our contribution we discuss currently available solutions and show an alternative approach. Our solution is based on the Java Applet technology and Asynchronous JavaScript and XML (Ajax). This technology is part of the web solutions known as Web 2.0 which is strongly discussed and developed in the present. Our results are demonstrated as a user-friendly web application with data of the Slovakian region Špis (Zips). An extended version of this web solution could be nicely incorporated into a modern concept for tourism of the Špis region.