The First-principles Study on the Rectification of Molecular Junctions Based on the Alkyl-chain-modified[2,5?]Bipyrimidinyl(biphenyl isocyanide)gold(Ⅰ)

Using density functional theory(DFT)combined with nonequilibrium Green?s function investigates the electron-transport properties of several molecular junctions based on the[2,5?]bipyrimidinyl(biphenyl isocyanide)gold(Ⅰ)molecule(BPM-Au(Ⅰ)CN-BP),which is modified by one to three alkyl groups forming BPM-Au(Ⅰ)CN-BP(CH2)n.The asymmetric current-voltage characteristics have been obtained for the molecular junctions.Rectifying performance of Au/S-BPM-Au(I)CN-BP-S/Au molecular junction can be regulated by introducing alkyl chain.The M1 molecular junction exhibits the best rectifying effect.Its maximum rectifying ratio is 2109,which is about 150 times more than that of the molecular junction based on the original M.Moreover,all the systems modified by alkyl group have obvious negative differential resistance behavior(NDR).The current-voltage(Ⅰ-Ⅴ)curves of all the systems in this work are illustrated by transmission spectra.