2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/118718Calculating an exact self energy for ab initio transport calculations relevant to ``Molecular Electronics'' can be troublesome. Errors or insufficient approximations made at this step are often the reason why many molecular transport studies become inconclusive. We propose a simple and efficient approximation scheme, that follows from interpreting the self energy as an absorbing boundary condition of an effective Schroedinger equation. In order to explain the basic idea, a broad introduction into the physics incorporated in these self energies is given. The method is further illustrated using a tight binding wire as a toy model. Finally, also more realistic applications for transport calculations based on the density functional theory are included.Lecture notes summerschool ``Nano-Electronics'', Bad Herrenalb September 1-4 2005; to appear in CFN Lectures on Functional Nanostructures, Vol. II, ``Nano-Electronics'', Springer Lecture Notes in Physics (2006)Mesoscale and Nanoscale Physicstext