Computational Physical and Polymer Chemistry:
Mesoscopic and Atomistic Modelling of Systems and Processes

Computational simulation and modelling of systems and modelling of processes is a very modern field, the importance of which increases strongly. This is due to the enormous progress in computer technology as well as in the progress of theoretical concepts and models. In quite a few cases, computational simulations are on the same level of accuracy and reliabilty as experiment. The advantage of computational simulations is that all the parameters are well defined and their influence on the results can be analyzed. By that, computational-theoretical modelling becomes a powerful tool for predicting yet unknown properties, and suggesting experiments. Therefore, strong collaborations with experimental groups are a natural consequence, which offers the student and scientist the almost unique opportunity to get experience with both technqiues, the experiment and the computer simulation.

In our group, two basic concepts are pursued. One concept consists in truly atomistic simulations by solving the Schrödinger equation for a many body quantum system of atoms, which interact in terms of chemical bonding. No empirical information is needed, every property - which can be derived from the wave functions solving the Schrödinger equation - is calculated directly on the computer in a truly ab initio way. The crucial point is the treatment of the many body interactions which reflect all the quantum properties, such as Pauli's principle and quantized states. We do this in terms of density functional theory (DFT) which is the fundamental theory most widely used nowadays in many simulations of solid state science and materials science.

The other basic concept is the modelling of polymer systems. Quantum mechanical calculations from first principles are too exhaustive in this case, as length scales of structural properties as well as time scales of dynamic properties are spread over several orders of magnitude. Thus, mesoscale simulation techniques (combining several atoms or monomers to segments and using more simple potentials) are used as well as force field based atomistic classical dynamics for smaller systems.




In the subgroup of G. Zifferer numerical investigations comprising simulations of polymer systems as well as theoretical and numerical investigations of polymerization processes are performed. Thus, the projects may be divided into two main areas, i.e. (1) modeling of polymer and oligomer systems based on atomistic molecular dynamics and mesoscale simulation techniques and (2) theoretical and numerical aspects of the kinetics of polymer processes. A further project, not connected to polymers, refers to the atomistic simulation of amorphous ice phases under high pressure.
Detailed investigations of the concentration dependence of characteristic polymer properties have been undertaken supplemented by analytical models. An important feature was the calculation of the thermodynamic shielding factor of termination reactions between polymer radicals, which served as the basis of investigations on free radical polymerization considering a chain-length dependent termination rate coefficient. Recently, the shielding concept has been extended to various types of reactions including Z-RAFT star polymerization and surface initiated polymerization (part of FWF Projects P20124 and P23142)
Numerical and analytical modeling of pseudostationary polymerization processes yielded a sound theoretical basis for the pulsed laser polymerization method which in the meantime is used all over the world and is an IUPAC recommended benchmark method for the determination of kinetic coefficients; nevertheless, further improvements are still in progress.
A lot of efforts have also been made to study the properties of a variety of polymer systems by use of Monte Carlo methods: linear as well as branched and ring shaped chains have been examined. Isolated chains, pairs of chains, fundamental bulk properties, surface and interface properties have been investigated for homo- and copolymers.
In recent time we extended our interest to off-lattice mesoscale simulations and to fully atomistic simulations, e.g. glass transitions of polymers, small polymer chains in solution, adsorption of oligomers at metal oxide surfaces and super cooled water. For these latter (atomistic) investigations the commercial program package Materials Studio (© Accelrys) and the open source program GROMACS (http://www.gromacs.org) is used, while for the other cases the necessary programs have been developed by ourselves.
For details see homepage.univie.ac.at/gerhard.zifferer. As an example a snapshot of a star-branched polymer (with different colors for segments of different arms) is shown.




The subgroups of P. Herzig and R. Podloucky, see www.tssc.univie.ac.at, homepage.univie.ac.at/peter.herzig and homepage.univie.ac.at/renate.eibler apply DFT approaches for solving materials properties.
P. Herzig works on transition metal and rare earth hydrides which show interesting physical properties, like metal-insulator transitions depending on hydrogen concentration ("switchable mirrors"). Our investigations reveal how the structural properties (hydrogen vacancies and the huge atomic relaxations induced by them) are related to the electronic and optical properties (band gaps) of these hydrides.
In the figure the electron density for a particular state in an exceptionally stable hydrogen double vacancy in almost stoichiometric LaH3 is shown. Further work is done in boride systems where NMR spectra are simulated and compared to single-crystal measurements by Prof. Zogal in Wroclaw and in Li-transition metal nitrides which are remarkable for their fast Li+ ion diffusion.


In the group of R. Podloucky several scientific and technological aspects are under considerations as can be seen from the funded projects, which deal with e.g. nanoscience on surfaces (oxide surfaces and nanostructure), surface and adsorption properties (complex adsorption of atomic layers), precipitations in metals and alloys, nanocoating of materials (hardening of materials), properties of compounds (magnetism, bonding, phase stabilities, superconductivity).
As an example, the figure (by courtesy of C. Franchini) shows the results of a simulation of thin films of manganese oxide as grown on a palladium substrate with different coverages. The top row in grey shows calculated scanning-tunneling microscopy (STM) images which can be compared to the experimental STM image coloured in brown (in the center). The middle row is a topview of the calculated atomic geometry (with oxygen in red and manganese in blue), the bottom row is a sideview cutting through the film with the top layer being the surface. By closer inspection with an experienced eye, all the shown calculated structures are found in the experimental STM image, which indicates how sensitive the manganese oxide layer is to small changes of physical parameters. In this particular case for both, theory as well as experiment it is difficult to get well-defined structures, and both need each other to derive conclusive results.




The research of R. Stadler and his co-workers focuses on single-molecule electronics, which has become a vibrant area of nano-electronics, because the predictions of Moore's law of a continuous rise in the performance of digital devices due to their ongoing miniaturisation, cannot be upheld down to the atomic scale based on Silicon devices. For realising the potential of this field, it is necessary to design realistic devices by theoretical means, where the active part of the circuit would be performed by a single molecule junction, i.e. a single molecule sandwhiched between two metal electrodes. Ideally one would like to combine two things: i) A device scheme developed and justified by theoreticians should be so simple that it can be applied by experimentalists without significant theoretical knowledge; ii) the device scheme should be reliable enough, which means that its validity has to be derived from and assessed by first principles calculations. Both i) and ii) have been achieved recently, where a graphical scheme has been established, which can predict the occurrence or absence of quantum interference (QI) effects in relation to the molecular structure. The findings have been verified by density functional theory (DFT) calculations and provide an important tool for the design of data storage elements as well as logic gates based on single molecules. This work has been published in Nano Lett. 10, 4260 (2010) and highlighted in a recent Uni:View contribution. Another aspect of this field is that in spite of the recent progress in experimental and theoretical research on single molecule conductivity in a ultra-high vacuum setup at cryogenic temperatures, the latter two conditions impose severe limits on any practical applications. Experimental studies in an electrochemical environment offer a new perspective notably at room temperature but for a better understanding of electron transport in such an environment it is essential to arrive at a clear theoretical picture of its mechanism based on first principles calculations. This is a formidable task. Not only are the transition metal complexes which need to be investigated rather large and potentially problematic in terms of an accurate description of the localization of charges, but also the influence of solvent and substrate further complicates the picture. A comprehensive approach within the framework of the semi-classical Marcus theory needs to be developed for electron transfer based on vibrationally induced electron hopping but also the theoretical description of the competing coherent tunneling mechanism requires an adjustment of the oxidation state of the central redox system, which poses significant methodological challenges for DFT. This research is embedded in close collaborations with experimentalists at IBM Zurich and Imperial College London.




Our group member I. Schnöll-Bitai passed away in December, 2008. An obituary may be found in dieUniversitaet-online. Her research interests were focused on two main topics, namely polymerization kinetics and analysis of polymers which were carried out in national and international cooperations and in the frame of IUPAC projects. The method of pulsed laser polymerization was developed experimentally, backed up by the corresponding theoretical calculations and its versatile applicability was demonstrated for polymerization in homogenous (bulk, solution) and heterogeneous (microemulsion) systems for some monomer and comonomer systems. Several methods based on the concepts of pseudostationary and quenched instationary polymerization were developed as well. For the analysis of the molecular weight distribution (MWD) obtained by size-exclusion chromatography (SEC) it is necessary to take into account the phenomenon of band broadening (BB), thus several methods to determine its extent were developed and tested experimentally. The ultimate goal of correcting for the deviations from the true MWD due to BB was achieved (at least partially) for some selected types of information deduced from chromatograms with the aid of equations based on theoretical considerations and simulations. Lately, Irene was engaged in the use of matrix assisted laser desorption / ionization mass spectroscopy as a complementary technique (to SEC) which offers an alternative route to gain insight into BB phenomena of SEC.





Equipment

  • Inhouse Cluster: Login server, file server (9TB) and cluster based on infiniband connected nodes; 3 Queues (8x2 Xeon X5650, 15x2 Xeon X5550 and 25 quadcore nodes)
  • Project based usage of the Vienna Scienticic Cluster VSC

  • Recent Projects

  • G. Zifferer, FWF P20124, Properties of star-branched (co)polymers, 1.3.2008-31.12.2011
  • G. Zifferer, FWF P23142, Simulation of Polymer Nanocomposites, 1.9.2011-31.12.2015
  • G. Zifferer, member of IUPAC Project 2013-051-1-400
  • G. Zifferer, partner institution of International PhD Progamme of UW and WUT (Warsaw)

  • R. Stadler, FWF P20267, Interference effects in molecular electronics 1.3.2008-28.2.2011
  • R. Stadler, FWF P22548, Electrochemical charge transport 1.3.2011-31.10.2014

  • P. Herzig, FWF P19205, First-principles investigations of the La-H system, 1.11.2006-28.2.2010
  • P. Herzig, FWF P22252, First-principles investigation of the lutetium-hydrogen system, 16.2.2010-15.8.2012

  • Current Cooperations

    G. Zifferer:

  • T. Lörting and M. Seidl, Universität Innsbruck, Institut für Physikalische Chemie, Austria
  • A. Sikorski, Department of Chemistry, University of Warsaw, Warsaw, Poland
  • P. Vana, Universität Göttingen, Institut für Physikalische Chemie, Göttingen, Germany

  • R. Stadler:

  • Tim Albrecht, Imperial College London
  • Emanuel Loertscher, IBM Zurich
  • Karsten W. Jacobsen, Kristian Thygesen, Technical University of Denmark (DTU)
  • Victor Geskin, Jerome Cornil, Université de Mons


  • Recent Theses

  • Markus Seidl (GZ), Der Glasübergang in hochdichtem amorphen Eis, Diploma thesis, 2009, GOECH award for best diploma theses
  • Michael Nardai (GZ), Simulation sternförmig verknüpfter Polymerer mittels Dissipative Particle Dynamics, Diploma thesis, 2009, GOECH award for best diploma theses
  • Ingo Füreder (GZ), Simulation verdünnter Lösungen ringförmiger Makromoleküle, Diploma thesis, 2010
  • Georg Kastlunger (RP), First principles study of ternary alloys: Investigation on the Fe-rich FexNiyAl1-y-x system on a bcc lattice, Diploma thesis, 2011
  • Rene Moser (RP), First-principle studies of the Seebeck coefficient of clathrate compounds Ba8ZnxGe46-x, Diploma thesis, 2011
  • Ferenc Karsai (PH), First-principles investigations of the dihydrides of scandium, yttrium, lanthanum, and lutetium, Master thesis, 2011
  • Stephan Eisenhaber (GZ), Numerische Untersuchung von Wechselwirkungseffekten zwischen (sternförmigen) Makromolekülen und Oberflächen, Master thesis, 2012
  • Elisabeth Durstberger (RP), First-principles model study of clathrates as thermoelectric materials, Diploma thesis, 2014
  • Zeynep Ergönenc (RP), Density functional theory study of oxygen vacancy formation in LaFeO3, SrFe3, Sr0.5La0.5Fe3, Master thesis, 2014
  • Martin Jehser (GZ), Simulation amorpher Eisphasen, Master thesis, 2014


  • Markus Stöhr (RP), First Principles Investigations of Adsorption on a Transition Metal Surface: Oxygen and Indium on the (110) Tungsten Surface, Doctoral thesis, 2009
  • Gunther Schöllhammer (PH), First-principles studies of the binary hydrogen system of lanthanum and other selected rare-earth metals, Doctoral thesis, 2010
  • David Reith (RP), Vibrational properties and Thermodynamical Stabilities of Alloys and Compounds: a first principles study, Doctoral thesis, 2011
  • Mingxing Chen (RP), First-principles Modeling of Thermoelectric Materials, Doctoral thesis, 2012
  • Markus Gerd Fröhlich (GZ), Systematic Investigation of Shielding Effects in Reactions between Star-Branched Polymers, Doctoral thesis, 2011
  • Michael Nardai (GZ), Investigations of Polymer Systems by Atomistic Molecular Dynamics and Dissipative Particle Dynamics, Doctoral thesis, 2014
  • Georg Kastlunger (RS), Electrochemical charge transport: A comparison of coherent and hopping charge transfer, Doctoral thesis, in progress
  • Stephan Eisenhaber (GZ), Numerical Study of Polymer Chains and Polymer-Polymer Reactions close to a Surface, Doctoral thesis, in progress
  • Martin Jehser (GZ), Mesoscopic and Atomistic Simulations of (macro)molecular Systems of special Designs and/or special Confinements, Doctoral thesis, in progress


  • Memberships and Awards

    G. Zifferer:

  • Member of the International Advisory Board of the journal Macromolecular Theory and Simulations
  • Member of GOECH, GDCH, Bunsengesellschaft
  • Awards: Theodor Körner Price 1995, Kardinal Innitzer Price 1996






  • Offenlegung nach MedienG §25:
    Medieninhaber: Universität Wien / Fakultät für Chemie / Institut für Physikalische Chemie
    1090 Wien, Währinger Straße 42

    Gerhard Zifferer © modified: 17.06.14 / 18:09