First Principles Investigaitons Of The Electronic Transport Properties Of C₂₄, C₁₆S₄and C₃₇H₃₀S₂N₂

The researches of molecular nano-device have become a hotspot, and manyexperimentalists have synthetized various function nano-device, for example, amplifier,photosensitive switch and steadying resistance. The structural property of molecule cannot bedetermined by experiment, and the changing of external condition or different experimentmethod will lead to different conclusion. Therefore, we should combine theory andexperiment to investigate the electrical properties of molecular devices. In order to providetheoretical reference for designing molecule device, we investigate the effect of moleculeorientation, electrode orientation and atom substitution to molecular transport propertiesbased on first-principle density functional theory and nonequilibrium Green’s function.First, we investigate the orientation effect on the electronic transport properties of C₂₄fullerene molecule. We optimize the molecular structures by DMol³package based onfirst-principle density functional theory, and verify the stability by frequency analysis. Wecalculate electronic transport properties of different orientated C₂₄fullerene molecule by ATKsoftware. The effects of k-point sampling on the Brillouin zone and the relation betweenenergy and interelectrode distance are explored. The zero bias transmission spectrum,transmission spectrum and I-V characteristic under bias voltage are determined. Our resultsshow that the negative differential resistance of C₂₄molecule is found in such a system. Thesefindings suggest that molecule orientation place a very important role in designing moleculenano-device.Then we investigate the effects of crystallographic orientations of electrode and bias onthe switch behavior of C₃₇H₃₀S₂N₂photosensitive molecules. We optimize the two differentforms of the molecular structures by DMol³package, and verify the stability by frequencyanalysis. The zero bias transmission spectrum, transmission spectrum and I-V characteristicunder bias voltage are explored. The on-off conduction ratios under bias voltage and differentelectrode are determined. We find that on-off conduction ratios are different when themolecules are between different electrodes or under a different bias voltage. Electrode andbias voltage will significantly affect transport properties of photosensitive molecules.Therefore, both of the factors should be considered in designing photosensitive moleculeswitch. Last, we study four S atoms instead four C atoms of C₂₀molecules. We optimize themolecular structures by DMol³package, and verify the stability by frequency analysis. Thezero bias transmission spectrum, transmission spectrum and I-V characteristic under biasvoltage are determined by ATK software. Our results show that the C₂₀molecular can be astability constant resistance device by S replacement. It has enlightening effort to design orselect special functional electronic devices.