A new method of obtaining a self-consistent surface electronic structure for a finite electric field and current within the local density functional formalism is presented. In the method, two different chemical potentials are assigned to the left and right electrodes, and the scattering waves are calculated by the step-by-step recursion matrix method. This method is applied to the Na bimetallic planar junction. Effective potential, electric current, and charge density distribution are presented for given values of the separation and the bias voltage.