Silicon germanium nanostructures (SiGe NSs) have acquired today a prominent role in several cutting-edge research topics in nanoscience, thanks to the most recent advances in synthesis, processing and characterization [1-4]. The physical properties of such nanosystems are strictly related not solely to the size of the system (as in pure Si and Ge NSs), but also to the relative composition of Si and Ge atoms as well as to the geometry of Si/Ge interface. The investigation of these materials with experimental techniques is, however, complicated by several factors not always well controlled which can hide the right comprehension of the fundamental properties. In this context first principles theoretical modeling is extraordinarily important as it can complement or augment experimental observations.

Here, I will present an overview of the ab initio computational modeling of various types of SiGe nanosystems (nanowires [5], nanodots [6] and slabs [7-8]). I will outline how by bringing together two similar elements –Si and Ge, neighbors in the periodic table–, a broad variety of new chemical and physical properties emerge, stimulating both fundamental and application-driven research in nanoscience. Indeed, I will show that substituting some of the atoms of a pure Si NS with Ge in configurations of distinct compositions and dimensionalities, can strongly affect some fundamental properties such as band gap, band offsets, work function and impurity doping levels.

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