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PREVIOUS Computational Physics Seminars

                 

Computational Physics Seminar

20th May 2015, Professor Robin Seligman,
ANNOUNCEMENT.

Check this webpage at http://phycomp.technion.ac.il/~phr76ja/CPsem.html or the noticeboards outside Rm 603 or Rm 315 for updates and changes. View previous seminars in this series.

Wednesday, 23rd October, 2013

11:00AM, Rm. 620, Lidow Physics Building

                 

Title: The Electronic Structure of Dye-Sensitized TiO2 Clusters

Speaker: Noa Marom, Department of Physics and Engineering Physics, Tulane University, New Orleans, LA 70118

Abstract

The development of solar cells is driven by the need for clean and sustainable energy. Organic and dye sensitized cells (DSC) are considered as promising alternatives for traditional single crystal silicon cells, particularly for large area, low cost applications. However, the efficiency of such cells is still far from the theoretical limit. First-principles quantum mechanical simulations may be used for computer-aided design of new materials, material combinations, and nano-structures for more efficient organic and dye-sensitized cells. To this end, it is important to obtain an accurate description of the electronic structure, including the fundamental gaps and energy level alignment at interfaces. This requires a treatment beyond ground-state density functional theory (DFT). Within the framework of many-body perturbation theory (MBPT), these properties may be calculated using the GW approximation, where G is the one-particle Green's function and W is the dynamically screened Coulomb potential.

In this talk I will provide an introduction to GW methods and demonstrate their applications to the components of organic and dye-sensitized solar cells: TiO2 clusters [1], organic semiconductors [2,3], dyes [4,5], and dye-sensitized TiO2 clusters [6,7].

References:

  1. N. Marom, M. Kim, and J. R. Chelikowsky, Phys. Rev. Lett. 108, 106801 (2012)
  2. T. Korzdorfer and N. Marom, PRB 86, 041110(R) (2012)
  3. N. Marom, F. Caruso, X. Ren, O. Hofmann, T. K?rzd?rfer, J. R. Chelikowsky, A. Rubio, M. Scheffler, and P. Rinke, PRB 86 245127 (2012)
  4. N. Marom, X. Ren, J. E. Moussa, J. R. Chelikowsky, and L. Kronik, Phys. Rev. B 84, 195143 (2011)
  5. E. Salomon, P. Amsalem, N. Marom, M. Vondracek, L. Kronik, N. Koch, and T. Angot, Phys. Rev. B 87 075407 (2013)
  6. N. Marom, J. E. Moussa, X. Ren, A. Tkatchenko, and J. R. Chelikowsky, Phys. Rev. B 84, 245115 (2011)
  7. N. Marom, T. K?rzd?rfer, X. Ren, A. Tkatchenko, and J.R. Chelikowsky, to be published

Wednesday, 19th June , 2013

10:30AM, Rm. 620, Lidow Physics Building

                 

Title: Simulated annealing of multiple-aperture telescopes

Speaker: Irina Paykin, Physics Department, Technion

MSc seminar (In Hebrew): Supervisors: Drs Erez Ribak and Joan Adler.

Abstract

A model based on the crystal roughening transition is applied to solve the phasing of a multi-aperture telescope. The quest for finer angular resolution in astronomy leads to larger apertures. But high resolution imaging from space telescopes is currently limited by launch vehicle constrains and system cost. The concept of segmented and multi-aperture systems has attracted more interest in the next generation of the space telescopes, because such systems have the advantage of low cost, light weight, and can reach the demanded angular resolution. A multi-aperture system can combine the light from smaller sub-apertures to capture a higher angular resolution image than is possible from any of the individual sub-apertures. In order to achieve high resolution image we have to phase the sub-apertures to within a fraction of the wavelength. Relatively short optical wavelengths require high positioning accuracy for alignment of each sub-aperture.

This study concentrates on an approach for aligning multi-aperture optical systems by using information available only in the image plane itself, thereby correcting the image without any information on the wave-front. Previous theoretical work and simulations have shown that the optical problem can be mapped onto a model for crystal roughening that has served as a motivation to implement the simulated annealing algorithm in adaptive optical systems.

We present the first simulations which are carried out in tandem with a hardware realization of a simulated annealing algorithm by Dr. E. Ribak and Lee Yacobi in a specially designed multi-aperture active optical system. The results of both simulations and laboratory experiments demonstrate the ability of the simulated annealing algorithm to correct a piston and tip/tilt errors. In addition we explored image restoration techniques, required for multi-aperture systems. We implemented and investigated several classic deconvolution algorithms, such as Wiener-Helstrom, Lucy-Richardson and blind deconvolution. Finally, we analyzed diffraction and aberration effects related to specific multi-aperture pupil configurations.


Wednesday, 31st October, 2012

11:00AM, Rm. 620, Lidow Physics Building

Title: No. 2 on the TOP 500 - K-Computer, Kobe, Japan

Speaker: Joan Adler

Affiliation: Physics, Technion

Report and (hopefully movie) about the no. 2 computer in the world.

Completely different architecture to other top 500 machines.


SPECIAL SEMINAR, Tuesday 14th August, 2012

11:00AM, Rm. 724, Lidow Physics Building

Title: Modeling and simulation of solid-solid and solid-liquid interfaces

Speaker: Dr Adham Hashibon

Affiliation: Fraunhofer Institute for Mechanics of Materials IWM, Wöhlerstr. 11, 79108 Freiburg

Heterophase interfaces between solids or between solids and liquids play a decisive role in numerous technological applications, such as corrosion and diffusion barriers, brazing and lubrication. Predicting the structure and properties of interfaces in solids is paramount for the understanding of the mechanical and thermal properties of materials. Nonetheless, determining the atomistic structure of interfaces remains one of the most intriguing problems in material science, presenting challenges to both experimental characterization and theoretical atomic scale modeling. Molecular dynamics and static energy minimization methods are used to investigate a model heterophase boundary in metals. It is demonstrated that the equilibrium interface structure may be found by considering vacancy formation energy profiles on both sides of the interface in combination with simulated anneals. Investigation of heterophase interfaces between a solid and a liquid presents an even greater challenge to material science, since it is more difficult to characterize the interface in situ. Molecular dynamics simulations of interfaces formed by depositing liquid Cu on Ta free surfaces are used to investigate the wetting and spreading on the atomic scale. It is found that Cu dewets from Ta leaving behind a thermodynamically stable monolayer of Cu. Finally, specific aspects of multi scale modeling of solid liquid interfaces and wetting behavior from the atomistic to the macro scales will be presented, in particular in the contexts of reactive wetting and microfluidic applications.

Date                        

Speaker                

Topic                        

16th May, 2012

Grzegorz Kamieniarz

Nanomagnetism en route from molecules to materials

Computational Physics Group, Poznan, University of Poland

ABSTRACT: Some aspects of magnetism and magnetic materials are described and their importance in science, medicine and technology is indicated. Molecular nanomagnets in the form of polynuclear clusters and zigzag chains as well as their unique characteristics are discussed, using the accurate computer simulation results based on the quantum spin models. Some known and well understood phenomena are reviewed, emphasizing their possible applications and focusing on state-of-the-art investigations in the field of quantum information processing, addressing individual molecules and quantum modelling.


Special Seminar - Thursday 28th July, 2011- 11:00AM, Rm 620, Lidow Physics Building


Title:    Electronic Structure and Electron Transport in Nanoscale Systems

Speaker:  Professor Jerry Bernholc, Drexel Professor of Physics and Director
          Center for High Performance Simulation
          North Carolina State University, Raleigh, NC 27695-7518

Date:     Thursday 28th July, 2011
 
Abstract: Nanoscale and molecular electronics promise to revolutionize 
computing, sensing, and harvesting of solar energy. However, molecular-scale 
control and manufacturing are difficult tasks, which require major advances to 
become practical in large-scale applications. The development of molecular 
scale devices and circuits can be greatly enhanced by predictive simulation 
of their components and by formulating design principles that will make 
molecular circuitry smaller, more efficient and more reliable. This talk 
will discuss two recent applications: (i) We show that the celebrated 
Negative Differential Resistance (NDR) effects in molecular electronics 
can be expected for a wide range of organic molecules attached to 
semiconductor and metallic leads. In particular, the NDR position and 
strength can be made tunable both by simple atomic substitutions and by 
doping of the leads. In multi-terminal structures, NDR can also emerge 
through quantum interference effects, which open new avenues for device 
design and logic. (ii) In the second part of the talk we will discuss the 
electronic structure and spin polarization of nitrogen-doped carbon 
nanoribbons, which are candidate materials for ultrahigh speed nanodevices. 
While the ground state of zigzag ribbons (ZR) is spin polarized, 
defects at the edges destroy the polarization and lead to a non-magnetic 
ground state. We also find enhanced N segregation in ZR, due to interplay 
between impurity states in the valence bands and the edge states.
Spin distribution is significantly affected, even at edges that are 
quite far from the dopant. Turning to armchair nanoribbons (AR), the 
three AR families, defined by mod (n, 3), behave differently in doping, with 
family 1 AR being the most attractive for n-type semiconductor applications. 

Last Fall 2010/11 seminar - Sunday 11:00 in Rm 620, Lidow Physics Building


Title:  GPUs as a computational engine - basic ideas

Speaker: Mark Silberstein, EE, Technion

Date: Sunday January 9th, 2011
 
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This is the last seminar for this semester. Seminar restarts next semester at 10:30 on Tuesdays.
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Title : Effects of disorder in microscopic models of heat conduction in one 
dimensional dielectrics

Speaker: Tal Kachman Aviv

Date: November 28, 2010

Abstract:

Understanding transport phenomena in the micro scale is of interest
from both the fundamental theoretical point of view as well as the practical
one. The problem of classical heat conduction in 1D system is a well known
one. The problem regards the validity of Fourier law in this setting. In
our research we investigate the heat transfer in broader context, taking
into account the non-stationary processes.
In this talk we will report the investigation of the phenomena of non-
stationary heat conduction in one-dimensional linear and nonlinear chains
(classical models of dielectrics), by combining molecular dynamics simu-
lations and analytic investigation. Two main aspects of our research were
the transport of kinetic energy through periodic chains (both integrable
and non-integrable) and through disordered chains. We also investigate
how the effects of disorder affect the transport mechanism




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Speaker: Dr Dan Mordehai

Affiliation: Materials, Technion

Topic: Size Effect in trength of Microparticles: A combined Experimental/FEM/Molecular Dynamics Study

Date: 2010-11-14
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Speaker: Joan Adler

Date: 7th November

Title: Visualization of electron density in general and in carbon allotropes 

ABSTRACT: Quantum mechanics tells us that electrons don't run in circles 
around nuclei, they have a probablity of being somewhere at sometime. 
This is a concept that we try to explain in Modern Physics courses, 
but its hard to ``see''.

The distribution of  electron density around the carbon atoms of allotropes, 
including diamond, amorphous carbon and  nanotubes, turns out to 
be very important for understanding their properties.

I will describe the AViz  approach to visualizing electron density with 
examples from both Modern Physics courses and research projects in the 
Computational Physics group.

The talk will be based on slides from  my recent conference presentations:

Hydrogen atom visualization - 

http://phycomp.technion.ac.il/~phr76ja/TW/talkindex.html

and carbon allotrope visualization - 

http://phycomp.technion.ac.il/~phr76ja/CCP2010/talktitle.html

and will present results obtained in collaboration with Joey Fox, Or Cohen 
David Saada, Anastassia Sorkin, Rafi Kalish, Jeremie Zaffran, Amihai 
Silverman and Polina Pine. 




Speaker: Oleg Gendelman

Affiliation: Mechanical Engineering, Technion

Title: Peculiarities of heat conduction in nanosystems

Date: 24-Oct-2010, Sunday

Time: 11:00 (note change from earliest announcement)

Place: Lidow Complex, room 620

Remarks: Coffee/tea at 10:45

The presentation is devoted to applicability of Fourier law of heat conduction in at nanoscale and in low – dimensional systems. Two main aspects of this problem will be discussed, with brief review of existing analytic, numeric and experimental results.

The first aspect is existence (size independence) of the heat conduction coefficient for the case of stationary conduction. Numeric simulations, supported by some analytic evidence, suggest crucial effect of dimensionality – only for 3D systems the heat conduction coefficient reveals size independence.

The other aspect is related to the nonstationary heat conduction. In this case, one can demonstrate that for extremely small times or extremely small space scales, the parabolic equation of the heat conduction is no more applicable and hyperbolic models should be used instead. Such models use even more empiric coefficients than the common Fourier law. Applicability of popular hyperbolic extensions of Fourier law (Cattaneo – Vernotte and some others) will be discussed quantitatively and qualitatively.

Last semester's talks

Monday 4th October at 11:00 in rm 620

Jonathan Gross, Juelich

Massively parallelized computer simulations on GPUs with CUDA.

We discuss the advantages of parallelization on graphics processing
units (GPUs) for parallel tempering Monte Carlo computer simulations of
an exemplified bead-spring model for homopolymers. Since the sampling of
a large ensemble of conformations is a prerequisite for the precise
estimation of statistical quantities such as typical indicators for
conformational transitions like the peak structure of the specific heat,
the advantage of a strong increase in performance in Monte Carlo
simulations cannot be overestimated. Employing multithreading and
utilizing the massive power of the large number of cores on GPUs,
available in modern but standard graphics cards, we find a noticeable
increase of efficiency when porting parts of the code to the GPU. Not
only is it possible to simulate multiple replica simultaneously, but
also to parallelize important parts of a single simulation itself. With
a deeper understanding of the GPU architecture and different memory
layers further optimizations can be done.

Date

Speaker

Topic

Abstract

March 8th
 
 

François Sausset
Physics,
Technion

Molecular Dynamics in a curved space:
physical motivations, methods, and parallel implementation

 

March 22nd

Or Cohen
Weizmann Institute

Approximation free approach to dual-scale problems:
calculating the electronic structure of
molecules using multigrid techniques

March 29th
April 5th

Pesach Holidays

Moedim LeSimcha

 

April 12th
THIS TIME ONLY
seminar starts at 11:30

Michael Bachmann
Juelich

Statistical analyses of conformational transitions in small molecular systems

April 26th

Simon Brandon
Chem. Engineering,
Technion

Computational analysis of transport phenomena and solidification:
reconciling computations with experiments

May 3rd

Jeremie Zaffran
Physics,
Technion

Density Functional Theory applied to the
solid state… An introduction to VASP

Date
to be
determined
 
 

Vladimir Privman
Clarkson University,
Potsdam, New York, USA

Models of Novel Materials
and Surfaces for Nanotechnology

Check this webpage at http://phycomp.technion.ac.il/~phr76ja/CPsem.html or the noticeboards outside Rm 603 or Rm 315 for updates and changes.

  • Mini-Symposium
  • Previous seminars and another previous seminar
  • Recent Computational Events with links to abstracts and slides - LinkSceem meeting, Computational Nanotechnology 2 Computational Nanotechnology 1