1. Molecular Electronics

In order to describe the quantum mechanical properties of the systems NanoDCAL uses a detailed description of the chemical species of the constituent atoms [TGJ01]. A chemical species in NanoDCAL is characterized by the wavefunctions of valence electrons (s, p, d, f) and by pseudopotentials that define the atomic core (see DFT in NanoDCAL). This separation between the valence orbitals and the atomic core is known as the pseudopotential approximation, which is widely used in solid state physics and is the only feasible approach for the complex systems NanoDCAL is designed to model [WHL06]. The wavefunction, and thus quantum mechanical state, of the entire system is described as a linear combination of atomic orbitals (LCAO). The orbital functions are derived from properties of an isolated atom but, for best results, the parameters describing the orbital functions must be tuned to the chemical environment of the nanostructure. The atomic positions of the device structure must be specified. A two-probe device structure will consist of two ideal lead structures and an interface or scattering region for a detailed discussion on this point [WLG07]. Moreover, the scattering region can be composed of single-molecule, ribbons, rings, rough cavities, two-dimensional material (with single or multi-layer), quantum dot, biologic systems, etc.