Theoretical Investigations Of Nanoscale Single Molecular Rectifiers And Multifunction Molecular Device Based On Fused Benzene-substituted Oligothiophenes Rings

Theoretical quantum calculations were carried out to study the anchor and donor/acceptorposition effects in fused benzene substitute oligotheophene. Using B3LYP/6-31(d,p) withGaussian09to optimize the thiol free (SH) group and using Atomistix ToolKit (ATK)11.8.2package to formulate devices with periodic boundary conditions. Utilizing non-equilibrium-functional theory to theoretically explore thetransport properties of molecular devices based on fused benzene-substituted oligothiophenesusing Landauer Bütiker formula to calculate nonlinear current through the device. The deviceshave a suffix H for those at hollow position and T for those at top position.The results showed that the anchor position and donor/acceptor position of functional groupscan affect the rectifying behaviors significantly, and the rectification direction can be tuned bybias, i.e., at low bias, the devices show forward rectification, but a reversal of the rectificationdirection can occur at high bias.The anchor position has effects on both forward and reverse rectification. Devices at hollowposition have a higher forward rectification but a lower reverse rectification compared to thosethan those at top position which have rectification a high reverse and low forward rectification.Donor/acceptor position was also found to have adverse on both current and rectification.Devices with donor and accept is located on the same side of central molecule show the highestforward rectification ratio at hollow position, and the highest reverse rectification ratio at top siteThe first-principles calculations demonstrate that the asymmetric shift of transmission peakswhich is derived from the HOMO state and the Fermi level of electrodes under low bias is theprimary reason for the forward rectification, while the asymmetric localization of HOMO statesunder high bias result in the reverse rectification behaviors, and show the tunable of rectificationdirection by applied bias.