A ‘molecular ’ description of current flow

Abstract — We present a unified formalis m for describing current flow through any small 'molecule '. The formalis m can be translated into 'first princip les ' simulat ions towards predictive properties with no adjustable parameters. Three case studies are presented – electron spectroscopy in buckyballs on silicon, spin currents and torques in an Fe-MgO-Fe tunnel junction, and thermal currents in graphene nanoribbons. In each case, a ‘molecular ’ description is crit ical to the underlying physics. Modern day electronics is rapidly reaching nanometer dimensions where atomistic, quantum and many-body effects dominate. The non-equilibrium Green’s function (NEGF) approach provides a systematic way to handle these effects. The channel bands are described by a Hamiltonian H and potential U, while the contact thermal reservoirs are described by self-energy matrices 1,2 (Fig. 1). Dephasing is described by additional self-energies s. By solving the resulting Schrodinger equation with open non-equilibrium boundary conditions set by the contact Fermi functions (with unequal electrochemical potentials 1,2), we can arrive at a rigorou