Atomistic Models of Nanosystems

Nanoscopic systems contain, in essence, a finite number of atoms. Description of nanosystems with first principles methods of quantum mechanics is still a cumbersome process, hence simpler models are rather used in the process of modeling. In this communication we analyze atomistic approaches like the empirical tight-binding (ETB) method that can be used with many flavors of sophistication to calculate both electronic structure and transport properties of nanosystems of various sizes ranging from tens and hundreds to millions of atoms. In contrast, the ab-initio methods deal with smaller systems, yet they provide reliable information, like equilibrium geometry and charge distribution, which are not fully captured by ETB methods. Several examples of relevant nanosystems that uses either ETB or ab-initio methods are provided.