First-principles calculation of the electronic structure for a bielectrode junction system under strong field and current

We present a method for the first-principles calculation of the electronic states under strong field and current, which is effective for the bielectrode system with atomic structures around the surface regions. A microscopic electron distribution is calculated self-consistently together with the field and current distributions. In our method the scattering waves are calculated by the step-by-step recursion-matrix method and two different Fermi levels are assigned to each jellium electrode in accord with a given applied bias voltage. The method is applied to the Na/vacuum/Na junction system with a tip structure to mimic the scanning tunneling microscopy (STM). The tip-surface chemical interaction induced by the electric field is clarified and shown to provide a clue for the extreme site specificity of atom extraction by STM.