The Theoretical Simulation On Porphyrin Molecular Electronic Devices

As the conventional silicon based electronic devices is approaching to Nano-scale dimension, it will face tremendous challenges aroused from quantum effect. Therefore, to develop molecular electronic devices will be an promising way to solve the above problem. Though the research on molecular electronic devices has gained some important progress, the electron transport mechanism of molecular electronic devices is still not clear. Hence, it's very necessary to do some investigations for these problems.The geometric structures of porphyrin (PH2) and metalloporphyrin (ZnP, MgP, MnP, FeP, CoP, NiP, CuP, PdP, SnP) are investigated by B3LYP method with the 6-31G* (for C, H, N) and LanL2DZ (for mental) basis sets. It demonstrate that the porphyrin is not a strict symmetry molecule, but the metalloporphyrins are strict symmetry plane structure molecules.The electron transport properties of single porphyrin molecule have been studied by density functional theory calculations combined with non-equilibrium Green's function technique. In particular, the joint mode (flat and diagonal) between porphyrin molecules and Au(111) electrode surface is compared, showing that the flat mode is much more conductive. The electron transport properties of porphyrin and mentalloporphyrins (ZnP, NiP, PdP, PtP) are studied as well. The results reveal that the conductance of the porphyrin and four types of metalloporphyrin are similar and their conductance follow the order of: PH2>ZnP>PdP>PtP>NiP. Moreover, the chain length dependence of the electron transport properties of porphyrin oligomer has also been studied.Based on the conduction property of porphyrin molecules, three types of porphyrin-X molecule are designed: porphyrin-alkyl, porphyrin-phenyl and porphyrin-alkyne. Density functional theory calculations combined with non-equilibrium Green's function technique are performed to study the effect of the functional groups on the electron transport property. Among these three model molecules, the porphyrin-alkyne molecule has the strongest electron transport ability, porphyrin-phenyl is next, and porphyrin-alkyl is weakest. However, porphyrin-alkyl and porphyrin-phenyl have obvious rectification character, while the porphyrin-alkyne almost shows no rectification. The above results will benefit the design and rationalization of novel molecular electronics, such as molecular diode, molecular switches and molecular storage devices.