Rushan Han

First-principles calculation of the conductance of a single 4,4 bipyridine molecule.

The conductance of a single 4,4 bipyridine (44BPD) molecule connected to two gold electrodes is calculated using a density functional theory based Green function method. The atomic geometry of such a molecular junction is constructed from the optimized structure of a gold trimer-44BPD-gold trimer complex. Resonant conduction is the main feature of its transport properties. The magnitude of the transmission coefficient at the Fermi level is determined to be T = 1.01 × 10(-2), which is in excellent agreement with the experimental value. The dependence of the transmission on the Au-N bond length and the torsion angle is also discussed.

An accurate and efficient self-consistent approach for calculating electron transport through molecular electronic devices: including the corrections of electrodes

A self-consistent ab initio approach for calculating electron transport through molecular electronic devices is developed. It is based on density functional theory (DFT) calculations and the Greens function technique employing a finite basis of local orbitals. The device is rigorously separated into the extended molecule region and the electrode region. In the DFT part calculating the Hamiltonian matrix of the extended molecule from its density matrix, the electrostatic correction induced by electrodes and the exchange?correlation correction due to the spatial diffuseness of localized basis functions are included. Our approach is efficient and accurate, with a controllable error to deal with such open systems. A one-dimensional infinite gold monatomic chain, whose electronic structure can be known from conventional DFT calculations with periodic boundary conditions (PBCs), is employed to validate the accuracy of our approach. With both corrections, our result for the gold chain at equilibrium is in excellent agreement with the PBC DFT result. We find that, for the gold chain, the exchange?correlation correction is more significant than the electrostatic correction.

First-principles calculation of the transport properties of molecular wires between Au clusters under equilibrium

Based on the matrix Greens function method combined with hybrid tight-binding\char21{}density-functional theory, we calculate the conductances of a series of gold-dithiol molecule-gold junctions including benzenedithiol, benzenedimethanethiol, hexanedithiol, octanedithiol, and decanedithiol. An atomically contacted extended molecule model is used in our calculation. As an important procedure, we determine the position of the Fermi level by the energy reference according to the results from ultraviolet photoelectron spectroscopy (UPS) experiments. After considering the experimental uncertainty in UPS measurement, the calculated results of molecular conductances near the Fermi level qualitatively agree with the experimental values measured by Tao et al. [Science 301, 1221 (2003); J. Am. Chem. Soc. 125, 16164 (2003); Nano. Lett. 4, 267 (2004)].

Electronic properties of C28 and Hf@C28 clusters

Abstract The structure and electronic properties of C28 and Hf@C28 clusters are studied using the DV-SCM method in the local density approximation. The C28 cluster has an open electronic structure with four unpaired electrons. A tetravalent Hf atom could stabilize the cluster with an exceptional LUMO—HOMO gap of 2.3 eV and binding energy of 6.7 eV/atom, when it is put at the center of the C28 fullerene. Different calculation procedures were used to assess the accuracy of the calculation.