In an effort to examine the intricacies of electronic nanodevices, we present an atomistic description of the electronic transport properties of an isolated benzene molecule. We have carried out ab initio calculations to understand the modulation of the molecular orbitals (MOs) and their energy spectra under the external electric field, and conducting behavior of the benzene molecule. Our study shows that with an increase in the applied electric field, the energy of the third lowest unoccupied molecular orbital (LUMO) of benzene decreases, while the first and second LUMO energies are not affected. Above a certain threshold of the external electric field, the third LUMO is lowered below the original LUMO and becomes the real LUMO. Since the transport through a molecule is to a large extent mediated by the molecular orbitals, the change in MOs can lead to a dramatic increase in the current passing through the benzene molecule. Thus, in the course of this study, we show that the modulation of the molecular orbitals in the presence of a tuning parameter(s) such as the external electric field can play important roles in the operation of molecular devices. We believe that this understanding would be helpful in the design of electronic nanodevices.

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In this geometrical setup, the system is mirror symmetric. Although the two leads are simply assumed to be coupled to the para positions of the benzene, the model parameters used actually consider the cases (such as the systems including S atoms instead of H atoms) which are well connected to metal electrodes. Thus, the present system would be applicable to phenylene-based systems. The contact problem is an important issue to be solved in future, but not a current issue in this communication.

16.

Egap of benzene is 6.59 eV, while Au-s-benzene-s-Au has smaller Egap(2.12eV).

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