  During the past decades, quantum mechanical methods have undergone an amazing
transition from pioneering investigations of experts into a wide range of
practical applications, made by a vast community of researchers. First
principles calculations of systems containing up to a few hundred atoms have
become a standard in many branches of science. The sizes of the systems which
can be simulated have increased even further during recent years, and
quantum-mechanical calculations of systems up to many thousands of atoms are
nowadays possible. This opens up new appealing possibilities, in particular for
interdisciplinary work, bridging together communities of different needs and
sensibilities. In this review we will present the current status of this topic,
and will also give an outlook on the vast multitude of applications, challenges
and opportunities stimulated by electronic structure calculations, making this
field an important working tool and bringing together researchers of many
different domains.
