Charging of molecules during transport

The possibility that a single molecule can acquire charge during steady-state transport is an open issue. We report first-principles calculations in a range of configurations of certain molecules and conclude the following. When a molecule is strongly coupled to the electrodes, charging is not sustainable. On the other hand, by using variable-length tunnel barriers (insulating tethers) one can enable and control charging. In particular, by using different combinations of tethers, we demonstrate the possibility of charging by a single electron, sustainable over a wide bias range, and also the possibility of continuous linear charging when a gate voltage is applied.