somewhere in time

Chem.Phys.Lett. 400,336

Jun Jiang

We have applied the elastic-scattering Green
s function theory to study the coherent electron transportation processes in both metal–alkanedithiol–metal (gold–[S(CH2)nS]–gold, n = 8–14) and metal–alkanemonothiol–metal (gold–[H(CH2)nS]–gold, n = 8–14) at the hybrid density functional theory level. It is shown that the current decreases exponentially with the molecular length. At the low temperature limit the electron decay rate, b, for alkanedithiol junction is found to be around 0.30/CH2 at 1.0 V bias, much smaller than the calculated value of 0.60/CH2 for alkanemonothiol junction. The decay rate for alkanedithiol junction at the room temperature is neither sensitive to the activation of the Au–S stretching vibrational mode nor to the external bias. The calculated current–voltage characteristics and decay rates for both junctions are in excellent agreement with the corresponding experimental results.

Phys.Rev.B 71,165316

Z.Crljen

We theoretically study the electronic transport in the monolayer of dithiolated phenylene vinylene oligomeres coupled to the s111d surfaces of gold electrodes. We use nequilibrium Green’s functions and densityfunctional theory implemented in the TranSIESTA package to obtain a full ab initio self-consistent description of the transport current through the molecular nanostructure with different electrochemical bias potentials. The
calculated current-voltage characteristics of the systems for the same contact geometry have shown a systematic decrease of the conductivity with the increased length of the molecules. We analyze the results in terms of transmission eigenchannels and find that besides the delocalization of molecular orbitals the distance between gold electrodes also determines the transport properties.

Phys.Rev.B 75,245407:

Y.Zhou

In recent experiment it was found that for a quantum length dependence of conductance of oligothiophene-CH2 molecules under low bias [Xu et al., Nano Lett.5,1491],the longer molecule has larger conductance. Due to the experimental motivation, we calculated the conductance of a similar organic compound, oligothiophene, by means of the first-rinciples method. Our calculations show a similar quantum length dependence of conductance in the low bias region and an oscillated length dependence of conductance in the high bias region. The transport behaviors are determined by the distinct electronic structures of the molecular compounds. The length dependencies of conductance for several other oligomers are calculated to show the diversity in the transport behaviors of molecular wires. The results show that Ohm’s law is not valid for the molecular conductance anymore, and for the low bias region, Magoga’s law is not applicable for some
molecular wires, for example, oligothiophene dithiolates.

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