Projects
Light metal tetrahydroboranes: Theory, Modelling, Structure and Properties.
by Riccarda Caputo (Empa, Abt 138 Division Hydrogen & Energy, Theory and modeling group)Alkali and alkaline-earth metal tetrahydroboranes represent promising compounds for solid-state hydrogen storage materials. We apply first-principles calculations to study structure and electronic properties.
Metal borides: Are they intermediates or precursor materials for hydrogen storage?
by Riccarda Caputo (Empa, Hydrogen and Storage laboratory, Theory and modeling)The complex borohydrides release hydrogen by thermal decomposition, which, at the experimental (p,T) conditions, most likely passes through intermediates of reaction constituted by the corresponding metal borides. Their exact stechiometry depends on the particular pressure-composition conditions, according to the corresponding binary phase diagram of metal/boron systems. The metal borides could play an important role in making reversible the hydrogenation and de-hydrogenation processes of complex borohydrides. Ab-initio phase diagram calculations are used to search for the most stable binary phase Metal/Boron.
Large scale railway noise calculations
by Kurt Heutschi (Empa, Acoustics laboratory)
The figure shows a section of the propagation of noise from a running train
[2D simulation, 40x25 meters]
The aim of the calculations is to determine railway noise for a corridor along the major north-south transversal from Basel to Chiasso. The calculations will account for all known sound propagation effects, in particular reflections in urban areas and meteorological phenomena. For the first time such calculations will be done on such a large scale. We will use mostly serial jobs in a Delphi environment or its Linux emulator Lazarus.
Ag overlayers on Pt surfaces
by Daniele Passerone (Empa, nanotech@surfaces)
The figure shows the alternating fcc and hcp regions in a triangular network, appearing upon deposition of 2 monolayers of Ag on Pt(111) [about 15x15 nanometers]
Mixed DFT and empirical potential approach for molecules at metal surfaces
by Carlo Pignedoli (Empa, nanotech@surfaces)
people involved: Teodoro Laino (IBM Zuerich), Daniele Passerone (Empa), Roman Fasel (Empa) Matthias Treier (Empa)
In this project we simulate the geometric and electronic porperties of molecules on metal surfaces with the aid of a mixed DFT and empirical potentials approach. If the metal surface does not play an active role in the chemistry of the adsorbed molecules, the Van der Waals interaction between the molecules and the metal substrate acn be modeled with an empirical potential and the metal substrate can be described via Embedded Atom Method. The example below shows the initial configuration of a molecule that undergoes dehydrogenation upon anealing on a Cu(111) surface. The computer code in use is cp2k, for the system showed in the example 16-32 cores are the ideal request for resources on ipazia.
Dipole moment at metal stepped surfaces
by Carlo Pignedoli (Empa, nanotech@surfaces)
people involved: Daniele Passerone (Empa), Roman Fasel (Empa) Matthias Treier (Empa)
Experimentally it is evident that absorption of particular organic molecules on vicinal gold surfaces result in the alignment of the molecules along the surface steps allowing for the realization of self-assembled periodic wires.
We interpret recent experimental findings [1] for hexa-peri-hexabenzocoronene (HBC, C42H18) on gold as the interaction between the dipole of the steps [2] of the surface and the molecule.
The calculation of spontaneous surface polarization is a problem of fundamental interest and several methods have been proposed in the literature to solve it [3–6]. For a symmetric metallic slab it is not obvious how to obtain the surface dipole moment from a computer simulation.
The aim of the project is to get insight the electrostatics of stepped metal surfaces through a decomposition on single atomic contributions obtained partitioning the charge density in atomic basins according to Bader’s QTAIM [7].
In the picture below, a Au(788) surface is modelled with a slab containing 230 atoms. The geometry is fully relaxed with the q-espresso code. Bader basins for selected atoms are superimposed together with the dipole moment (centered on atoms) of the charge basins.
Each charge basin can deviate from neutrality (charge -11) by a small value as indicated in the colorcode in the second image.
The relaxation of the Au slab was done on the IBM PW5 in Manno but is also now affordable on the IB nodes of ipathya. Postprocessing was done on ipathia.
[1] P.Ruffieux et al., J. Am. Chem. Soc. 129, 5007, (2007)
[2] R. Smoluchowski: Phys. Rev 60, 661 (1941).
[3] A. Baldereschi, S. Baroni, R. Resta: Phys. Rev. Lett. 61, 734 (1988).
[4] C. J. Fall, N. Binggeli, A. Baldereschi: Phys. Rev. B. 66 (2002).
[5] X. Wu, O. Dieguez, K. M. Rabe, O. Vanderbilt: Phys. Rev. Lett 97, 107602 (2006).
[6] G. P. Brandino, et al.: Phys. Rev. B 76, 85322 (2007).
[7] R. F. Bader: Atoms in Molecules: A Quantum Theory (Oxford University Press Oxford, 1994).
[8] S. Baroni, A. Dal Corso, S. de Gironcoli, and P. Giannozzi, PWSCF package, http://www.pwscf.org
Imaging disordered media with Time Reversal Processing
by Michele Griffa (Empa, Building technologies laboratory)people involved: Jan Carmeliet (EMPA), Paul A. Johnson (Los Alamos National Laboratory, USA), Marco Scalerandi (Polytechnic Institute of Torino, Italy)
It derives from the field of Time Reversal Acoustics, mainly developed by M. Fink's group at Laboratoire Ondes et Acoustique of the École Supérieure de Physique et de Chimie Industrielles de la Ville de Paris/Université Paris 7, and it is of interest for applications and basic studies in Ocean Acoustics and Communications, Wireless Communications, Non Destructive Evaluation via Ultrasounds, Biomedical Ultrasound Imaging, Remote Sensing and Geophysics.
Focusing is at the basis of many imaging techniques relying on electromagnetic or elastic waves.
The aim of this project is to use Time Reversal Processing for solving inverse source and scattering problems in Imaging of complex disordered solid media by ultrasound and seismic waves.
Time Reversal Processing relies on the simple fact that classical waves travel from the receiver to the source point exactly as they travel from the source point to the receiver but with reversed direction, as if time was reversed.
Actual and scattering source location, i.e. imaging, is possible by constructing an approximate “reverse movie” of the propagating wavefield by sending from the receivers the reversed-in-time recorded signals produced by the propagated waves. Compared to most of other methods for solving inverse source/scattering problems, based on heuristic and partial descriptions of the source and/or the wavefields and on complicated analytical descriptions, direct full modeling of the wave propagation is the core of Imaging by Time Reversal Processing.
In order to address real world problems, we have to deal with complex reverberant and highly heterogeneous 3D media that require accurate and complete numerical solutions requiring High Performance Computing resources.
This project is in collaboration with the Nonlinear Elasticity/Time Reversal Imaging Team of the Los Alamos National Laboratory (LANL), USA, and with the Dept. of Physics of the Polytechnic Institute of Torino, Italy.
For more information, please have a look at this review paper about Time Reversal Acoustics in solid media and respective applications and at the LANL project Web site.
LOng RAnge Transport (LORAT) of atmospheric methane and carbon monoxide
by Stephan Henne (Empa, Air Pollution/Environmental Technology)
People involved: Dominik Brunner, Jörg Klausen (Empa)
To improve our understanding of the impact and the time-scales of atmospheric pollution transport and to understand the mixing ratios of non- or weakly reactive gases observed within monitoring programmes such as the Global Atmosphere Watch (GAW) programme global scale atmospheric transport models provide valuable and requisite information. Atmospheric transport described in a Lagrangian framework, contrary to the Eulerian approach, does not suffer from numerical diffusion. In addition, information on transport times of newly released emissions is easily accessible in the Lagragian concept. Therefore, Lagrangian models are the ideal tool to answer the questions raised above.
To this end the Lagrangian particle dispersion model FLEXPART (Version 8.0) was extended and set up on the global domain with 3 million particles that are permanently transported based on ECMWF wind fields. All particles carry 9 different counters that indicate times since certain atmospheric regions were left: 1 counter for each of the 6 WMO regions keeping track of atmospheric boundary layer contact, 2 counters for inter-hemispheric transport, and 1 counter for stratosphere-troposphere exchange. Thirteen different species are represented with each particle: 1 atmospheric air tracer, 6 carbon monoxide (CO) and 6 methane (CH4) tracers according to emissions from the 6 WMO regions. Global monthly mean fields for each species, each clock and 11 age-classes are produced by the model and offer detailed insight into the time-scales of transport and the contributions from different source regions. Furthermore, receptor concentrations (daily temporal resolution) are produced for selected GAW sites and
allow for model inter-comparison and interpretation of observations.
The figure shows the December 2001 monthly mean field of carbon
monoxide, (upper left) total mixing ratios, (others) mixing ratios
by source region.
Atmospheric transport towards GAW monitoring sites
by Stephan Henne (Empa, Air Pollution/Environmental Technology)
People involved: Jörg Klausen (Empa)
The Global Atmosphere Watch (GAW) programme of the World Meteorological Organization (WMO) focuses on the observation of long term atmospheric composition changes. It incorporates measurements from a world wide network of ground based in-situ monitoring sites.
These observatories are usually placed at location away from emission sources and therefore focus on the atmospheric background. However, pollutants from distant sources (for example biomass burning plumes) are often advected for several days and might still cause a clear observable signal at a remote monitoring site. A simple, qualitative tool to distinguish such signals from local pollution events is the use of air mass backward trajectories to identify potential source regions. Operational trajectory calculations using the FLEXTRA model are performed once daily for a set of 30 Global (core site) GAW sites. Results are made available to the public in form of a web based trajectory browser.
The figure shows the backward air trajectories that arrive at the Swiss Global GAW station Jungfraujoch on 2009-03-06 20:00 UTC. Different colours indicate different arrival heights.
Representativeness of air pollution monitoring sites
by Stephan Henne (Empa, Air Pollution/Environmental Technology)People involved: Dominik Brunner (Empa)
As contribution to the EC FP6 project GEOmon the atmospheric transport towards 34 air pollution monitoring sites within Europe was analysed applying the Lagrangian Particle Dispersion Model (LPDM) FLEXPART in the receptor oriented backward mode. For an investigation period of one year an individual calculation was initialized every 3 hours for each station. For each run 50000 particles were released at the receptor site and traced back 120 hour in time considering large
scale flow and sub-grid scale turbulent mixing. These calculations result in source-receptor sensitivity maps (footprints) that indicate area in which a surface flux (emissions or deposition) of
an atmospheric trace gas would cause a signal at the monitoring site. Combining the information from the whole year an average "catchment" area of a can be defined and a site can be characterized by emission or deposition fluxes (as taken from inventories) within this catchment area.
(footprint) for the arrival time 2005-01-01 00:00 and all 34
investigated sites (white dots).
First principles study of molecular networks on metal surfaces
by Manh Thuong Nguyen (Empa, nanotech@surfaces)
People involved: Carlo A. Pignedoli, Daniele Passerone, Roman Fasel, Matthias Treier
A typical molecular network on a flat gold surface