Implementing the Keldysh formalism intoab initiomethods for the calculation of quantum transport: Application to metallic nanocontacts

We discuss the key steps that have to be followed to calculate quantum transport out of equilibrium by means of the ab initio Gaussian embedded-cluster method recently developed by the authors. Our main aim is to emphasize that, if a sufficiently large portion of the electrodes is included in the ab initio calculation, there is no need to impose an electrostatic potential V drop across the system. The electrochemical-potential difference μL-μR=eV (where μL and μR are the electrochemical potentials well into the left and right electrodes), which is also incorporated in the method, suffices to induce a charge redistribution that creates an electrostatic drop across the constriction. The discussion is illustrated by means of quantum transport calculations through aluminum and gold nanocontacts.