Ab initio modeling of open systems: Charge transfer, electron conduction, and molecular switching of a ${\mathrm{C}}_{60}$ device

We present an ab initio analysis of electron conduction through a ${\mathrm{C}}_{60}$ molecular device. Charge transfer from the device electrodes to the molecular region is found to play a crucial role in aligning the lowest unoccupied molecular orbital of the ${\mathrm{C}}_{60}$ to the Fermi level of the electrodes. This alignment induces a substantial device conductance of $\sim 2.2\times {(2e}^2/h).\mathrm{}$ A gate potential can inhibit charge transfer, and introduce a conductance gap near $E_F,$ changing the current-voltage characteristics from metallic to semiconducting, thereby producing a field-effect molecular current switch.