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The first-principles calculations based on the density functional theory are applied to investigate the effect of a chemical group coadsorbed on one electrode surface on the electronic transport of a molecular device. We find that the types of the coadsorbed groups and their sites on one electrode surface affect the electronic transport significantly, and the resulting shift of the molecular levels upon coadsorption depends jointly on various effects, such as the electrostatic interaction, shift of the Fermi level of the electrode, the chemical interaction, and so on. Among these factors, the chemical interaction-induced the charge transfer across metal-molecule interface is identified as a determining factor resulting in the variation of transport properties. Our findings suggest that the coadsorption may offer the novel possibility to modify the transport behaviors of a molecular device in a controlled way and can improve/add some particular functionalities or should be avoided in order to keep a stable transport for a molecular device. [ABSTRACT FROM AUTHOR]

Molecular devices are constructed based on a molecule connected into both electrodes with different metal materials, and their transport properties are investigated by the first-principles method. The result shows that such devices can generate two asymmetrical Schottky barriers at contacts; the current rectification thus is created. This rectification is also fully rationalized by the calculated transmission spectra and the spatial distribution of the lowest unoccupied molecular orbital and highest occupied molecular orbital states. Our study suggests that it might be a very important way for both electrodes using different materials to realize a molecular rectification. [ABSTRACT FROM AUTHOR]