Introduction

Ab initio molecular dynamics has been called a “virtual matter laboratory” [510] and even a “virtual laboratory” [934]. This notion is justified in view of the obvious parallels to experiments, being performed typically in the real laboratory. In the virtual lab, ideally, a system is prepared in some initial state and then evolves according to the basic laws of (quantum-statistical) physics – without the need for experimental input. The trajectory thus generated by ab initio molecular dynamics can be analyzed in arbitrary detail, including the dynamics of the electronic structure, which hence offers deep insights into the occuring processes. As a third step, the initial state and/or the external conditions such as for instance the temperature or composition of the system can be varied, but the system can also be exposed to light, electrical current, hydrostatic pressure, or uniaxial mechanical forces. Thus, not only the investigated matter as such is virtual, but also the apparatus used to manipulate matter, for instance a laser beam or an atomic force microscope, is fully represented “in silico”. It is clear to every practitioner that this viewpoint is highly idealistic for more than one reason, but still this philosophy allows one to compute observables with predictive power and is at the same time the reason behind the broad application range and versatility of ab initio simulations. Furthermore, progress in the general availability of powerful computer hardware makes it easier as time goes on to follow the “virtual lab avenue” to achieve scientific progress.