  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.

Materials Science