First Principles Investigations Of The Electronic Transport Properties Of Chain Type Organic Molecules

As the decreasing of the scale of electronic device, molecular electronic componentsdevelop rapidly. The detail of experimental method and the outside conditions have a stronginfluence on the conclusion. Combining the theoretical simulation and experimentalmeasurement, we can explore the transport properties of molecular electronic deviceseffectively. Using the first-principles density functional theory (DFT) and nonequilibriumGreen’s function formalism, we focused on the effluence of contact mode ofdipyrimidinyl–diphenyl，and the effects of modified the S-bridge to tetrapyrimidinyl.First, the electron transport properties dipyrimidinyl-diphenyl (DD) with differentcontact mode and the saturated hydrogen atom have been investgated. Result show that thereare low-bias NDR behaviors of DD molecule without saturated H atom. We also examinationDD molecule with saturated H, it shows switching and rectifying behaviors. In addition, NDRbehavior can be eliminate by change the contact sites. By the way, the possible contact modeof the molecule in the experiment [Díez-Pérez et.al, Nat. Chem.11(2009)392] is identifiedthrough examining the roles of both the molecular adsorption sites on gold electrodes and thesaturated hydrogen atom on the conductance. The mechanism of the properties are explainedby the HOMO, LUMO and the transmission spectra.Second, we investigate the effect of modified sulfur bridge on the two-probe system withtetrapyrimidinyl molecule and Au electrodes.Using five modified treats on the sulfur bridgewith H, N or O atom, we obtained various current-voltage curves of the two-probe systemwith tetrapyrimidinyl molecule. The two-probe system shows switching behavior when themodified atom is H, the conduction direction depends on the position of the modify H atom. Itshows negative differential resistance behavior when the modified atom is N or O. When themodify atom is N, the NDR behavior is more obvious than the modify atom is O. We alsogive the HOMO, LUMO and the transmission spectra to explain the properties.