Alexander K. H. Weiss
University of Innsbruck
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Alexander K. H. Weiss.
RSC Advances | 2013
Alexander K. H. Weiss; Thomas S. Hofer
Solvation phenomena have been the focus of experimental and theoretical research for many decades. While the determination of solvation properties of mono-atomic, ionic species is already a challenging task, the associated difficulties are amplified in the case of molecular compounds. Theoretical approaches have the ability to yield manifold information of the investigated systems, providing that a reliable description of the interatomic energies and forces is employed. Hybrid quantum mechanical/molecular mechanical simulations constitute a particularly successful approach for the study of solvation phenomena, and have been employed in investigations of a variety of molecular compounds in aqueous solution. While an accurate description of these systems depends on the application of reliable, theoretical approaches, the analysis of the resulting dataset is a challenge of its own. It is outlined that standard means of analysis via pair correlation functions may yield an unspecific picture of hydration phenomena, and in some cases wrong conclusions on the hydration may be drawn. More advanced means of structural analysis are thus required as they yield manifold information on solvation phenomena since pair correlations are not sufficiently responsive in such cases. The theoretical approaches required to obtain a reliable description of the investigated systems as well as increasingly complex means of structural analysis ranging from two- and three-body correlations via angular-radial distributions and two-dimensional particle mapping to the so-called SLICE projections are discussed. The application of these analysis schemes is demonstrated for a variety of systems including mono- and polyatomic ionic solutes as well as molecular organic compounds, highlighting various aspects of the hydration of these species.
Journal of Physical Chemistry B | 2013
Andreas O. Tirler; Alexander K. H. Weiss; Thomas S. Hofer
A theoretical study of the structure and dynamics of the uranyl mono- and dicarbonate species in aqueous solution employing the quantum mechanical charge field-molecular dynamics (QMCF-MD) method is presented. The obtained structural and dynamical data were found to be in good agreement with several experimental data and theoretical investigations available in the literature. The five-fold coordination pattern observed for the equatorially bounded ligands of the uranyl ion was found to deviate from the results of a number of previous studies based on quantum chemical cluster calculations and classical molecular dynamics studies, however. The reason for the different description of the system can be seen on the one hand in the capability of QM/MM-type simulations to take charge transfer, polarization, and many-body effects into account, while the presence of a large number of MM solvent molecules ensures that the simulation system mimics the environment in the bulk of a liquid. In addition to pair, three-body and angular distributions, the use of spatial density data enabled a detailed characterization of the three-dimensional arrangement of ligands in the vicinity of the complex. Further analysis of dynamical data such as hydrogen-bond correlation functions and mean lifetime analysis enabled a detailed characterization of the properties of the complexes in aqueous solution. It could be shown that the bulk-oriented oxygen atoms of the carbonate ions form strong hydrogen bonds with bulk molecules, while the tendency of the oxygen atoms of the uranyl(VI) show decreasing tendency to form hydrogen bonds upon complexation.
Inorganic Chemistry | 2012
Oliver M. D. Lutz; Thomas S. Hofer; Bernhard R. Randolf; Alexander K. H. Weiss; Bernd M. Rode
A quantum-mechanical charge-field molecular dynamics simulation has been performed for a tetravalent Ce ion in aqueous solution. In this framework, the complete first and second hydration spheres are treated by ab initio quantum mechanics supplemented by an electrostatic embedding technique, making the construction of non-Coulombic solute-solvent potentials unnecessary. During the 10 ps of simulation time, the structural aspects of the solution were analyzed by various methods. Experimental results such as the mean Ce-O bond distance and the predicted first-shell coordination number were compared to the results obtained from the simulation resolving some ambiguities in the literature. The dynamics of the system were characterized by mean ligand residence times and frequency/force constant calculations. Furthermore, Ce-O and Ce-H angular radial distribution plots were employed, yielding deeper insight into the structural and dynamical aspects of the system.
Journal of Chemical Physics | 2013
Manuel Hitzenberger; Thomas S. Hofer; Alexander K. H. Weiss
This work presents the first ab initio molecular dynamics study of trivalent lutetium in aqueous solution. The hybrid quantum and molecular mechanics simulation has been carried out on Hartree-Fock level and the results were compared to extended X-ray absorption fine structure and X-ray diffraction data. In addition to the structural characterisation via radial and angular distribution functions, the influence of the ion on the surrounding solvent was further investigated by local-density-corrected three-body distribution functions and frequency calculations. The obtained results for the mean Lu-O bond distance and force constant were in very good agreement with the literature. Furthermore, deeper insight into the dynamics and geometry of the solvation shell and the number of involved solvent molecules was obtained.
Neuroreport | 1999
Marianne Dieterich; Reto Zink; Alexander K. H. Weiss; Thomas Brandt
Bilateral galvanic vestibular stimulation (GVS) with current intensity of 3 mA was applied at mastoid level in 11 patients with chronic bilateral vestibular failure, in order to determine ocular motor responses by 3-D video-oculography. The following abnormal features were found: (1) a predominantly torsional or mixed torsional-horizontal nystagmus at the onset of stimulation with lower current intensities (1.0-3.0 mA) in nine patients; (2) a reduced amplitude of tonic ocular torsion by about 50% in nine patients (1.3 +/- 0.6 degrees at 3 mA); (3) a nystagmus in the opposite direction at stimulation offset in five patients (rebound); (4) no eye movements at all in a patient with bilateral nerve failure. GVS stimulates the vestibular nerve, thus allowing differentiation of nerve failure from labyrinthine failure. The low thresholds for initiating nystagmus and the rebound, which appear to be the most typical features of bilateral labyrinthine failure, can be explained by central compensation mechanisms.
Journal of Chemical Physics | 2013
Syed Tarique Moin; Thomas S. Hofer; Alexander K. H. Weiss; Bernd M. Rode
Ab initio quantum mechanical charge field molecular dynamics (QMCF-MD) were successfully applied to Cu(II) embedded in water to elucidate structure and to understand dynamics of ligand exchange mechanism. From the simulation studies, it was found that using an extended large quantum mechanical region including two shells of hydration is required for a better description of the dynamics of exchanging water molecules. The structural features characterized by radial distribution function, angular distribution function and other analytical parameters were consistent with experimental data. The major outcome of this study was the dynamics of exchange mechanism and reactions in the first hydration shell that could not be studied so far. The dynamical data such as mean residence time of the first shell water molecules and other relevant data from the simulations are close to the results determined experimentally. Another major characteristic of hydrated Cu(II) is the Jahn-Teller distortion which was also successfully reproduced, leading to the final conclusion that the dominating aqua complex is a 6-coordinated species. The ab initio QMCF-MD formalism proved again its capabilities of unraveling even ambiguous properties of hydrated species that are far difficult to explore by any conventional quantum mechanics/molecular mechanics (QM/MM) approach or experiment.
Inorganic Chemistry | 2010
Ernst Hinteregger; Andreas B. Pribil; Thomas S. Hofer; Bernhard R. Randolf; Alexander K. H. Weiss; Bernd M. Rode
An ab initio quantum-mechanical charge-field molecular-dynamics (QMCF-MD) simulation of the chromate ion in aqueous solution at ambient temperature was performed to study the structure and dynamics of this ion and its hydration shell. In contrast to conventional quantum-mechanical molecular-mechanics molecular-dynamics (QM/MM-MD) simulations, the QMCF-MD approach offers the possibility of investigating composite systems with the accuracy of a QM/MM method but without the time-consuming construction of solute-solvent potential functions. The data of the simulation give a clear picture of the first hydration shell of the chromate anion, which consists of 14 water molecules. The mean distance between the oxygen atoms of the chromate and the hydrogen atoms of water is 1.82 A. Each chromate oxygen atom is in average coordinated to 2.6 water molecules. The first-shell mean ligand residence time was evalulated as 2.2 ps; the vibrational frequency of the nu(OH) mode was found to be 185 cm(-1). Several structural parameters such as the radial distribution functions, angular distribution functions, and coordination number distributions enable a full characterization of the embedding of the chromate ion in the solvent water. The dynamics of the hydration structure are described by mean residence times of the water molecules in the first hydration shell, distance plots, and velocity autocorrelation functions.
Journal of Physical Chemistry A | 2012
Ajmal Khan; Alexander K. H. Weiss; Reaz Uddin; Bernhard R. Randolf; Bernd M. Rode; Thomas S. Hofer
The hydration of the Bi(III) ion was determined via an ab initio quantum mechanical charge field molecular dynamics (QMCF-MD) simulation. Ten picosecond sampling was carried out to determine structural and dynamical properties of the Bi(III) ion in aqueous solution. In the first hydration shell, the ion is 9-fold coordinated with a maximum probability of the Bi-O distance at 2.51 Å. In total, 11 exchanges were observed in the first-shell showing associative, dissociative, and interexchange character. As with the dominant existence of 9-fold coordination, the geometry of the Bi(III) ion is in between the tricapped trigonal prism and the capped square antiprism.
Journal of Physical Chemistry B | 2014
Anirban Bhattacharjee; Alexander K. H. Weiss; Vincent Artero; Martin J. Field; Thomas S. Hofer
In this work we have studied two hydridotetraminecobalt(III) complexes using a mixture of computational techniques. These species were chosen as simple and computationally tractable models of the Co(III)-hydrido compounds that are known to be important intermediates in the catalytic cycles of hydrogen evolution mediated by the cobaloxime complexes. We have performed both static density functional theory (DFT) calculations of the complexes in implicit solvent and adaptive hybrid DFT/molecular mechanical (MM) molecular dynamics (MD) simulations in explicit solvent and compared our results to the experimental structural and spectral data that are available for one of the compounds. A principal aim of the study has been to provide a benchmark for future work on cobaloxime and other hydrogen-evolving catalysts using adaptive DFT/MM MD methods.
Physical Chemistry Chemical Physics | 2014
Martin J. Wiedemair; Alexander K. H. Weiss; Bernd M. Rode
A single sodium chloride molecule in aqueous solution was simulated by the ab initio quantum mechanical charge field-molecular dynamics (QMCF-MD) approach. During a series of simulations the solvated molecule (CIP), dissociated solvated ions and - most noticeably - a solvent separated ion pair (SSIP) were observed and the structural and dynamical characteristics of these systems were investigated. In addition to a detailed structural analysis of the observed species, vibrational spectra and charge distributions were calculated to elucidate the mechanism of the NaCl dissociation.