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\chapter*{Acknowledgment}

First of all, I would like to thank my official advisers Prof. Dr. Bernd Stritzker and Prof. Dr. Kai Nordlund for accepting me as a doctoral candidate at their chairs at the University of Augsburg and the University of Helsinki.
I am grateful to Prof. Dr. Bernd Stritzker who, although being an experimental scientist, gave me the opportunity to work on a rather theoretical field.
The working environment providing insight on problems dealt with in this thesis from the point of view of an experimentalist were of great importance contributing to the success of this work.
Furthermore, I would like to thank Prof. Dr. Kai Nordlund for his expertise in the field of atomistic simulations and the possibility to repeatedly visit his group in Helsinki.
Much progress of this study is owed to the regrettably few but fruitful discussions and explanations by electronic mail, within short meetings on conferences and, of course, during my long-term stays in the nice capital of Finland.

Due to the official supervising of both of them, participation in a special research fellowship of the Bayerische Forschungsstiftung was enabled providing financial support for the first three years.
Next to living costs, travel expenses for scientific conferences as well as my stays in Helsinki were unbureaucratically taken over by the research foundation.

I owe my deepest gratitude to Prof. Dr. J\"org K. N. Lindner guiding me through my first time of scientific working already beginning with the diploma thesis.
I am heartily thankful for his frequent encouragements and the confidence he has shown enabling a greatly independent research and the improvement of respective skills.
Furthermore, his experiences in the materials system covered in this study and fine grasp with regard to scientific routines were of great help for this work.

Getting appointed to a professorship at the University of Paderborn, it was also him, who initiated a collaboration with the local theory group under the direction of Prof. Dr. Wolf Gero Schmidt.
I would like to thank him for six month of financial support, which allowed me to extend my research period, as well as for his helpful contributions to common articles and respective publishing procedures.
More importantly, the collaboration involved further investigations based on first-principles calculations, which improved the quality of this work to a great extent.
At this point, I would like to express special thanks to Dr. Eva Rauls.
The present thesis would not have been possible without her assistance and mentoring with respect to the utilized methods required by the new approach of investigation as well as her expertise in the materials system.
I am greatly thankful for the possibility to repeatedly visit the theory group in Paderborn.
In this context, Dr. Simone Sanna is acknowledged for respective technical support and Michael Weinl, doctoral student of Prof. J\"org K. N. Lindner back then, for accommodation.

I am grateful to Priv.-Doz. Dr. habil. Volker Eyert for writing one of the certificates of this work.
Furthermore, his lectures on computational physics and the electronic structure of materials, which I attended during my academic studies, influenced me to pursue scientific research in the field of computational physics.

One more time, I would like to thank Prof. Dr. Bernd Stritzker for another two-month position as a member of his research staff and various long-term employments as a research assistant, which not only ensured a minimum of financial supply but also involved tutorships in the field of solid state physics that could be carried out in a more or less free and autonomous way.

I am grateful to Ralf Utermann, responsible for the computing infrastructure in the physics department, for providing access and support with the excellently maintained high performance units available in the Augsburg Linux Compute Cluster.
Furthermore, being employed as an assistant under his direction during the first times of my studies, he provided insight into modern computing technology and, in doing so, sparked my interest in computational physics.

I would like to show my gratitude to Rolf Anders.
Similarly situated, performing numerical investigations at another experimental physics division, he was always interested in discussing, both, specific and general problems related to physics as well as to scientific computing.

Residing in the office of the undergraduates, I would like to thank all of the many fellow students I met during this time.
Interesting and not necessarily scientific discussions appeared on the daily agenda.
It was a great time of lively exchange of ideas and excellent coffee that I will keep in good memory.
I am likewise thankful to all the other members of the division for the distinctive and pleasant working environment and the permanent willingness to discuss, which very often happened on Fridays burning the midnight oil.

For discussions aside from natural science, I am grateful to the small but fine reading group formed on the fringes of the temporary student protests in 2009.
I would like to thank Meta Schnell, Berthold Arlt, Michael Lippok, Erika Rempel, Leo Sellinger, Michaela Strattner, Katja Teich and Matthias Link for the numerous sessions reviewing elements of the critical theory of society.

I am grateful to Melanie Lenk for moral support during my time as a diploma and doctoral student.
For the nice time we had and, in particular, for her patience and care in stressful times as well as for encouraging internet telephony calls during my stays abroad, I will always be thankful.
Dear Mali, you will always be in my mind, wherever life as a teacher may take you.

I would like to thank Stefanie Rajkay accompanying me during the last stages of this work.
Although there cannot be a right life amidst wrongs\footnote[1]{Theodor W. Adorno, {\em Minima Moralia: Reflexionen aus dem besch\"adigten Leben}, Suhrkamp 1994, p. 19.}, I am glad for our joint effort trying to organize and anticipate a way of (private) life that would be the actual right one in a free society.
Dear Stoffl, somehow, we will manage!

Last but not least, I would like to express my gratitude to my parents Wilfriede and Karl Zirkelbach, who contributed to a great extent to pursue a scientific career without major difficulties.
My brother Till Zirkelbach is greatly acknowledged for backup of any kind of concern.
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Thanks!

