Theoretical bases of nano-scale devices

Recent topics on theoretical studies for the nano-scale structures connected between the electrodes are presented. The first-principles recursion transfer matrix method and non-equilibrium Green´s function technique are utilized for the analyses of atom wires and molecular bridges. A very large effect of the terminal structures is demonstrated for both the systems. If the transport is caused by the resonant tunneling, a large loop current inside the molecule is induced near the degenerate levels. Its relationship with the magnetically induced intra-molecular current is discussed for the case of triangular graphene.