# Guest Student Programme 2009

## Proceedings

Speck, Robert (Ed.) (2009)

Technical Report IB-2009-04, 2009

## Abstracts

### Parallel Monte Carlo for Condensed Polymers

**Jonathan Groß, Universität Leipzig**

**Adviser: Thomas Neuhaus, Marcus Richter, Binh Trieu**

A simple model of a condensed polymer was simulated using the parallel tempering algorithm. The implementation makes use of multiple cores in modern workstations utilizing POSIX threads. Also there is an outlook to porting the parallel tempering algorithm to GPGPUs using NVIDIA's CUDA.

### Threshold Determination for the Fault-Tolerant Implementation

**Ricardo Kennedy, Universität zu Köln**

**Adviser: Stefan Dürr**

The controlled-NOT (CNOT) gate is implemented fault-tolerantly using the Juelich Massively Parallel Ideal Quantum Computer Simulator (JUMPIQCS) and its performance is tested under the influence of two different error sources: For decoherence errors, we find that the threshold for effective error correction (10^{-6} < pthr< 10^{-5}) is comparable to the single qubit threshold found in [1]. In the case of operational errors, we find that the threshold is of the same order of magnitude as in the single qubit case, but dependent on the initial state. It is determined to be σ_{thr1}=(5.5±0.3)*10^{-2} for a separable initial state |11> and σ_{thr2}=(2.0±0.3)*10^{-2} for the maximally entangled state 1/√2*(|01>-|10>)

### Algorithmic optimization issues in quenched lattice gauge theory

**Malik Kirchner, Humboldt University Berlin**

**Adviser: Stefan Dürr**

Calculations in lattice are very time consuming and need an enormous amount of memory and computing power. Inverting the Dirac-operator is very costly. Many architectures compute faster in single than double precision. It is possible to speed up the inversion of the Dirac-operator by iterative ``mixed precision'' solvers by a factor of almost two. The Monte-Carlo integration is done by a multi-hit Metropolis algorithm based on random uniformly distributed (N)

### I/O Problems in Massively Parallel Applications

**Lukasz Kucharski, Adam Mickiewicz University Poznan**

**Adviser: Jan Meinke, Sandipan Mohanty, Wolfgang Frings**

Recently ProFASi application has encountered the problem of excessive file usage on massively parallel systems. This became a real concern in terms of performance degradation and the file number quota limits. This work focuses on integrating SIONlib into ProFASi by introducing a new middle layer library called SFFS. SFFS aims to extend SIONlib capabilities to make it a general parallel I/O replacement for standard C/C++ paradigms. This paper introduces SFFS concepts and discusses ProFASi performance gains and the integration process.

### Simulation of Drift-Kinetic Dynamics of Charged Particles in Magnetized Plasmas

**Stilianos Louca, Friedrich Schiller Universität Jena**

**Adviser: Paul Gibbon, Benjamin Berberich**

In particle codes for fusion plasma simulations, an upper bound for the integration time-step is set by the high frequency gyro-motions (∼ THz) of electrons. A method for replacing the exact electron positions by their guiding centers is discussed and tested on single particle simulations. It is shown, that for typical electromagnetic fields found in fusion experiments as the TOKAMAK, the time-step can be increased by a factor of up to 100, while still maintaining deviations of the guiding centers in the order of 10^{-2} gyro-radii.

Moreover, a divergence-free interpolation method is introduced for cylinder-symmetric magnetic fields defined on triangular meshes, which results in an almost everywhere smooth field. The interpolation is reduced to 1-dimensional interpolations and can include an arbitrary number of base-points.

### Electronic Structure of Transition Metal Complexes with Phthalocyanines

**Stefan Maintz, RWTH Aachen University**

**Adviser: Thomas Müller**

Density functional theory (DFT) calculations have become an elemental tool for various natural sciences over the past decades. In this work calculations on 3d-transition metal complexes with Phthalocyanine ligands have been carried out using the B3-LYP hybrid functional, in order to evaluate the performance of DFT applied to open-shell complexes that contain many electronic excited states in the vincinity of the ground state. The results have been compared with predictions and expectations arising from ligand field theory (LFT). It was found that DFT apparently has inherent errors as not even expected trends within

### Analysis of a parallel preconditioner

**Hendrik Rittich, Bergische Universität Wuppertal**

**Adviser: Bernhard Steffen**

In this report we will analyse the quality and performance of the library Hypre, a library wich provides highly parallel preconditioners and solvers for large sparse systems of linear equations. First we will give a short introduction into a certain class of iterative methods and preconditioners. Afterwards we will present results from different experiments analysing different parts of Hypre.

### Simulation of NMR signal formation

**Martin Rückl, Julius-Maximilians-Universität Würzburg**

**Adviser: Walter Nadler**

Constrictions of heart arteries called stenosis can be detected by analysing the configuration of capillaries in myocardium using nuclear magnetic resonance (NMR). In this work a simulation model for the NMR signal formation was developed to check influence of capillary configuration on transversal relaxation processes. It has been found that faster diffusion strongly reinforces geometric influence.

### Domain-Force-Decomposition

**Theodros Zelleke, Ruhr-Universität Bochum**

**Adviser: Godehard Sutmann**

A new parallel algorithm for classical Molecular Dynamics is presented. The algorithm is an extension to a common domain decomposition algorithm and is suitable for simulation systems with short range forces and an inhomogenous distribution of the particles and for low density systems. The implementation is presented in the context of the combined Molecular Dynamics/ Multiparticle Collision Dynamics program MP2C.

## Group Photo

Persons on the photo, left to right, front to back:

*1. row:* Stefan Maintz, Theodros Zelleke, Robert Speck, Benjamin Berberich, Bernhard Steffen, Malik Kirchner

*2. row:* Lukasz Kucharski, Hendrik Rittich, Jonathan Groß

*3. row:* Sandipan Mohanty, Martin Rückl, Stilianos Louca, Ricardo Kennedy, Thomas Neuhaus, Walter Nadler