Based on ab initio theory, the interfacial spin polarization of a benzene-dithiolate molecule vertically adsorbed on a nickel surface is investigated by adopting different microscopic contact configurations. The results demonstrate a strong dependence of the interfacial spin polarization on the contact configuration, where the sign of spin polarization may vary from positive to negative with the change of contact configuration. By analyzing the projected density of states, an interfacial orbital hybridization between the 3d orbital of the nickel atom and the sp 3 hybridized orbital of the sulfur atom is observed. We also simulated the interfacial adsorption in mechanically controllable break junction experiments. The magnetoresistance obtained from Julliere model is about 27% based on the calculated interfacial spin polarization, which is consistent with experimental measurement.

Using nonequilibrium Green’s function method combined with density functional theory, we theoretically investigate the influences of alkaline and acid solutions on electronic transport properties in oligophenyleneethynylene molecular junctions with amino and carboxylic groups. The numerical results show that comparing with the case of neutral state, the conductance of the molecular junction is double improved and the rectifying direction is inverted when carboxylic group is deprotonated in the alkaline environment. On the other hand, the rectification ratio is enhanced trebly and the rectifying direction is inverted similarly when amino group is protonated in the acid environment. This theoretical work presents a chemically controllable method of manipulating conductance and rectification of molecular junctions.