#### Computational Theoretical Physics

# Oliver Melchert

| Institut für Physik |

### A Brief ...

#### ... paragraph to introduce our group:

Research activities in our group "Computational Theoretical Physics" are interdisciplinary, linking physics and computer science. Our main interests are problems from molecular biology, theoretical computer science and disordered systems from solid-state physics. In our group, computer simulations play a pivotal role to gain insight to systems where no analytic treatment is possible. So as to answer open questions in the aforementioned disciplines, we perform numerical experiments using up to date algorithmic techniques.

#### ... resume:

I was born on Monday 16.06.1980 in Herborn (Hessen). From August 2000 to December 2005 I studied Physics at the Justus-Liebig University Giessen. There I wrote my diploma thesis in the Group of Prof. Scheid on the quantum mechanical inverse scattering problem.

In Mai 2006, I joined Alexander K. Hartmanns Junior research group ``Complex Ground States of Disordered Systems'' at the Georg-August University Göttingen as PhD-student. Since June 2007 I'm part of the group ``Computational Theoretical Physics'' at the Carl-von-Ossietzky University Oldenburg where I complete my PhD-thesis under the supervision of Prof. Hartmann. My work on disordered systems is related to 2d Ising spin glasses, shortest (at least in some way :) ) paths and percolation phenomena.

### Publications:

- Biased and greedy random walks on two-dimensional lattices with quenched randomness: the "greedy" ant within a disordered environment

T. L. Mitran, O. Melchert, A.K. Hartmann, preprint arXiv:1308.4269 - Typical and large-deviation properties of minimum-energy paths on disordered hierarchical lattices

O. Melchert and A.K. Hartmann, Eur. Phys. J. B**86**, 323 (2013),

see arXiv:1302.6487 - Percolation thresholds on planar Euclidean relative neighborhood graphs,

O. Melchert, Phys. Rev. E**87**, 042106 (2013),

see arXiv:1301.6967 - Information theoretic approach to ground-state phase transitions for two and three-dimensional frustrated spin systems,

O. Melchert and A. K. Hartmann, Phys. Rev. E**87**, 022107 (2013),

summary at papercore database under ID Melchert2012,

see arXiv:1211.4434 - Universality class of the two-dimensional randomly distributed growing-cluster percolation model

O. Melchert, Phys. Rev. E**87**, 022115 (2013),

see arXiv:1211.0478 - Minimum weight spanning trees of weighted scale free networks,

O. Melchert, Lecture Notes MCS 2012 - Optimization,

see arXiv:1209.4493**Note:****not**contained in the official volume of Lecture Notes, since the class was given on short notice! The example programs can be downloaded here - Basic Data Analysis and More - A Guided Tour Using Python,

O. Melchert, Lecture Notes MCS 2012 - Optimization,

see also arXiv:1207.6002**Note:**the example programs can be downloaded here - Analysis of the loop length distribution for the negative weight percolation problem in dimensions d=2 through 6,

G. Claussen, L. Apolo, O. Melchert, and A.K. Hartmann, Phys. Rev. E**86**, 056708 (2012),

summary at papercore database under ID Claussen2012,

see also arXiv:1207.2893 - A computational mechanics approach to estimate entropy and (approximate) complexity for the dynamics of the 2D Ising Ferromagnet,

O. Melchert and A.K. Hartmann,

summary at papercore database under ID Melchert2011b,

see also arXiv:1206.7032, - Is negative-weight percolation compatible with SLE?

C. Norrenbrock, O. Melchert, and A.K. Hartmann,

summary at papercore database under ID Norrenbrock2012,

see also arXiv:1205.1412, - Mean-field behavior of the negative-weight percolation model on random regular graphs

O. Melchert, A.K. Hartmann, and M. Mezard, Phys. Rev. E**84**, 041106 (2011),

summary at papercore database under ID Melchert2011,

see also arXiv:1107.1742 - A dedicated algorithm for calculating ground states for the triangular random bond Ising model,

O. Melchert and A.K. Hartmann, Comp. Phys. Comm. 182, 1828-1832 (2011),

see also arXiv:1007.5463v1 - Configurational statistics of densely and fully packed loops in the negative-weight percolation model,

O. Melchert and A.K. Hartmann, Eur. Phys. J. B 80, 155-165 (2011),

see also arXiv:1005.5637v1 - The upper critical dimension of the negative-weight percolation problem,

O. Melchert, L. Apolo, and A.K. Hartmann, Phys. Rev. E**81**, 051108 (2010),

see also arXiv:1003.1591v1 - autoScale.py - A program for automatic finite-size scaling analyses: A user's guide,

O. Melchert, arXiv:0910.5403v1**Note**: The source-code of the Python program autoScale.py and the raw-data for an illustrative example can be downloaded together with the source-files of the preprint at http://arxiv.org/abs/0910.5403 by choosing the download-option 'Other formats'. Alternatively, the supplementary material that comes together with the source-files of the preprint can be downloaded here. - Finite-temperature local protein sequence alignment: percolation and free-energy distribution,

S. Wolfsheimer, O. Melchert and A.K. Hartmann, Phys. Rev. E**80**, 061913(2009),

see also arXiv:0907.2187v1 - Scaling behavior of domain walls at the T=0 ferromagnet to spin-glass transition,

O. Melchert and A.K. Hartmann, Phys. Rev. B**79**, 184402 (2009),

see also arXiv:0902.2938v2**Note:**After submission of our manuscript to Phys. Rev. B, we received correspondence from R. Fisch and E. Vicari containing valuable suggestions and comments that enabled us to improve the manuscript further. The article was accepted without a request for amendments. Hence and to our regret, these improvements do not appear in the published version [Phys. Rev. B 79, 184402 (2009)] of the article. - Phase transitions in diluted negative-weight percolation models,

L. Apolo, O. Melchert and A.K. Hartmann, Phys. Rev. E**79**, 031103 (2009),

see also arXiv:0812.2230v1 - Ground states of 2d +-J Ising spin glasses via stationary Fokker-Planck sampling,

O. Melchert and A.K. Hartmann, J. Stat. Mech. P10019 (2008),

see also arXiv:0808.3869v2**Note:**After submission of our manuscript to J. Stat. Mech. and right before it was accepted for publication, we received correspondence from A. Berrones containing valuable comments. We amended the preprint accordingly, so as to improve the manuscript further. To our regret, these amendments do not appear in the published version [J. Stat. Mech. P10019 (2008)] of the article. - Negative-weight percolation,

O. Melchert and A.K. Hartmann, New J. Phys.**10**, 043039 (2008),

see also arXiv:0711.4069v2 - Fractal dimension of domain walls in two-dimensional Ising spin glasses,

O. Melchert and A.K. Hartmann, Phys. Rev. B**76**, 174411 (2007),

see also arXiv:0704.2004v2**Note:**One of the figures contained in the article was graded*visually attractive*and made its way to the PRB Kaleidoscope images of November 2007, look here. - Effective Rb–Rb inter-atomic potential from ultracold Bose-gas collisions,

D. Schumayer, O. Melchert, W. Scheid and B. Apagyi, J. Phys. B: At. Mol. Opt. Phys.**41**035302,

see also arXiv:cond-mat/0702568v1 - Inversion of real and complex phase shifts to potentials by the generalized Cox-Thompson inverse scattering method at fixed energy,

O. Melchert, B. Apagyi and W. Scheid, J. Phys. G: Nucl. Part. Phys.**32**(2006) 849

### 10th Granada Seminar:

I had the possibility to join the 10th Granada Seminar on Computational and Statistical Physics, held in Granada, Spain, from 15-19 September 2008. There, I presented a talk on the "Scaling behavior of domain walls at the T=0 ferromagnet to spin glass transition".

Left: A nice palm tree.

Right: Me giving a talk. Thanks to Tapati Dutta for taking the picture.

### Group Workshop 2008:

We spent our Group Workshop from 8-12 September 2008 at Norderney, a small Island at the North Sea coast in Northwest Germany. During that week we learned to improve on our communication skills. In particular I learned that my voice is focused on vocals and as a remedy I got some tips that will help me putting some emphasis on the consonants. I will do my very best :)

Left: Me, exposed to crosswind.

Right: That's a sight.

### DAAD RISE scholarship program 2008:

In June 2008, Luis Apolo made his way from the Big Apple to Oldenburg to support us on a project focusing on critical phenomena in disordered systems, related to negative weight percolation. Among other things, Luis investigated the impact of dilution on the percolation properties of string-like objects on lattices.

Left: Luis and me in the Office.

Right: The things we worked out and experiences we gained during the 10 weeks of our scientific team work surely don't fit onto one black board, however I think the picture is quite fancy.

### 72nd spring conference of the DPG 2008:

In February 2008, Alex, Stefan, Taha and me joined the 72nd spring conference of the DPG held in Berlin. I had the possibility to present a talk on "Negative weight percolation" and a poster on the "Scaling behavior of domain walls at the T=0 ferromagnet to spin-glass transition".

Left: Taha and me on a sightseeing trip in Berlin.

Right: The Quadriga, unimpressed by any kind of weather.

### Statphys23:

From 9-13 July 2007, we joined the Statphys23 conference on Statistical Physics held in Genova, Italy. I was lucky and excited that I had the possibilty to present a talk on the "Fractal dimension of domain walls in two-dimensional Ising spin glasses".

Left: Palm trees along a promenade.

Right: Border to the sea close to the conference centre.

### Summerschool "Interfaces between Physics and Computer Science":

From 11-22 June 2007 we joined the Heraeus International Summer School "Interfaces between Physics and Computer Science" at the Jacobs University Bremen. This is where I met Gregor Pardella, a computer scientist from the university of Cologne who devotes his time to the calculation of Exact Ground States of Huge Two-Dimensional Planar Ising Spin Glasses.

Left: Gregor and me standing arround.

Right: Part of the campus.