This thesis would not have attained such a scientific level without the generous assistance of a large number of people. Thus, I feel indebted to those who have assisted me and I would like to thank them for their support during the last years.

First and foremost I want to express my deep gratitude to my adviser Prof. Grasser for providing me the opportunity to join his research group. Furthermore, he was always eager to create a stimulating atmosphere and never missed an opportunity to offer a few encouraging words. Furthermore, it has been a pleasure to see how a small scientific group, that started from scratch, has achieved considerable progress in its field, and gained international importance over the years.

I want to thank Prof. Selberherr and Prof. Langer for providing excellent working conditions, for the possibility to work at such a prestigious place, and for the opportunity to attend several international scientific conferences. Furthermore, I owe gratitude to Prof. Süss, who is willing to serve on my examination committee.

I am thankful to my numerous colleagues, named individually in the following. First, I want to thank Franz Schanovsky, who always took the time to discuss highly challenging and lengthy topics about theoretical physics and let me participate in his knowledge about first principles codes and numerical algorithms. Furthermore, I value Paul Wagner’s elaborate comments on linguistic issues and enjoyed conversations with him about swimming techniques. I have to thank Oliver Triebl for his altruistic attitude in several situations. In particular, he assisted me with my operating system and happily joined in philosophical debates during lunch time. Furthermore, it was a pleasure to work with Philipp Hehenberger who frequently entered into debates about recent football games. Special thanks go to Markus Karner, who patiently introduced me to numerous versions of the Vienna-Schrödinger-Poisson solver. I acknowledge Oskar Baumgartner and Zlatan Stanojevic for their support during complicated implementations in the Vienna-Schrödinger-Poisson solver as well as for their help in preparing programming lectures. Furthermore, I am grateful to Robert Entner, Martin Wagner, Markus Bina, and Johann Cervenka for their sustained efforts in complicated computer affairs. I further thank Victor Sverdlov, who shared his comprehensive knowledge and valuable wisdom to help resolve some lengthy derivations. Last but not least, I want to name my long-lasting roommates Martin Vasicek and Stanislav Tyaginov, who never lost their sense of humor — even when imminent submission deadlines were looming.

I very much appreciate Prof. Pantelides’ kind offer of a research visit at the Vanderbilt University in Nashville to gain knowledge about first-principles simulations in his group. Furthermore, I want to thank Dr. Mittendorfer for his patient introduction into density functional calculations at the center of computational material science.

Above all, I want to express my deep gratitude to my family, in particular to my parents, who gave me the possibility to attend a university. They continuously encouraged me during my education and my whole life — even supporting my crazy triathlon ambitions. I also want to thank my friends, especially Johannes Csmarits, who accompanied me during my student days and curiously followed my life as a researcher.