A theoretical study of molecular conduction: IV. A three-terminal molecular device

We discuss the features of a three-terminal molecular device and the control of electric current using a gate terminal. We introduce a capacitance model to investigate the effect of the gate terminal that could reduce to a two-terminal molecule for a very small gate capacitance. Therefore, this capacitance model can be used in the framework of ordinary ab initio quantum chemical methods. We show the effect of the gate terminal analytically using a simple Huckel method. Moreover, we used our capacitance model with a nonequilibrium Green's function (NEGF)-based Hartree-Fock (HF) approach to study the gate control features of the benzenedithiolate molecule, and we show that the current through the molecule can be modulated by the gate voltage in the case of a high gate control parameter. We also discuss the molecule's response to the applied bias voltage. It is found that the molecular charging effect has a strong influence on the behavior of molecular-based electronic devices.