Theoretical Studies On I-v Properties Of Organic Molecular Junctions

Great development of the study on molecular electronics and molecular devices has taken place in theoretical regions as well as in experimental regions in recent years. Comparing to the traditional solid electronics, organic electronics has many advantages than traditional materials, for example, low cost, large-area fabrication and et al. Therefore molecular devices have began to play an important role in switches rectifiers, photovoltaic devices and so forth.Organic materials are of various kinds, as well as functional variety. It has also proved that some organic material such as benzene and polythiophene may conduct current as molecular wires. They possess the similar properties to the traditional devices such as NDR. However, majority of organic compounds have little electronic current. For this reason, the search for molecular devices which can easily transport electrons is of paramount importance in this field. In this thesis we mainly study the I-V properties of organic molecular junctions which are consist of 4,4BPD and the series of molecular wires which have different numbers of benzene between the two molecular (pyridine) by using smeagol. This program package is based on the density functional theory and nonequilibrium green's function approach. The leads are the faces of Au (100). The results show that this has a superior electrical property and can be easily controlled on experiments when contacting the new ideal configuration. The LUMO contributes to transport current and has the similar I-V properties. The number of benzene has little influence on the I-V properties. Besides, with the increasing of the chain's length, the current becomes less.Besides we have studied the molecular junctions made of oligothiophene with the number is one, three and five. We find that HOMO contributes to the transport, and with the chain's length increasing the current becomes less. We have found the negative differential resistance (NDR) effect.