Current-carrying molecules: a real space picture
  An approach is presented to calculate characteristic current vs voltage curves for isolated molecules without explicit description of leads. The Hamiltonian for current-carrying molecules is defined by making resort to Lagrange multipliers, while the potential drop needed to sustain the current is calculated from the dissipated electrical work. Continuity constraints for steady-state DC current result in non-linear potential profiles across the molecule leading, in the adopted real-space picture, to a suggestive analogy between the molecule and an electrical circuit. 
Anna Painelli