Study of electric conductance of atomic or molecular wire in terms of the phase-shift

A simple expression of the electric conductance through a nanostructure connected to 2 electrodes is obtained by using the phase-shift analysis. The phase-shifts are given by solving the characteristic equation obtained by extending the method applied to the single impurity problem in the metal. It is shown the importance of the effect due to multiple orbitals in nanostructures. Concrete examples of the conductance through some bridge systems are given.