Optimized atomic structures of the LML systems investigated, obtained by relaxing fully the molecule, the first two atomic layers of the two lead surfaces, and the molecule-lead separation. (a), (b), and (c): The Au leads are in the (001) direction, and there are 0, 2, and 1 additional Au atoms at the contacts, respectively. (d), (e), and (f): The Au leads are in (111) direction, and there are 0, 2, and 1 additional Au atoms at the contacts, respectively. The dashed line indicates the interface between the device region and the left or right lead ( or ). The in-plane adsorption site of the molecule is indicated by a dark-colored ball in (g) for (001) and in (h) for (111).
Comparison between the transmission functions of the unrelaxed (dashed line) and the relaxed (solid line) systems. Different systems are indicated by their structure labels as defined in the text. (a), (b), (c), and (d) correspond to the atomic structures of (a), (b), (d), (e) in Fig. 1, respectively.
Local density of states within the energy window around the Fermi energy for the systems (001)̱0Au (upper) and (001)̱2Au (lower). Note the channel with LUMO-like character in the latter which is absent in the former.
Equilibrium conductance and lead-to-molecule electron transfer as functions of the change in Au–S distance , for (a) unrelaxed (001)̱2Au system, (b) unrelaxed (001)̱0Au system, and (c) relaxed (001)̱1Au system. In (a) and (b) of the two contacts is rigidly and symmetrically changed, while in (c) only of the contact without the additional Au is rigidly changed. The transmission function for point is shown in (d), while those for points and are already shown in Figs. 2(b) and 2(a), respectively. Note the large resonance conductance peak in panels (a)–(c) accompanied by significant electron transfer to the molecule. The similarity of (d) to Fig. 2(b) shows that increased Au–S separation has an effect comparable to that of the extra Au atoms.
Contour plots of transmission as a function of both energy and for (a) unrelaxed (001)̱2Au system, (b) unrelaxed (001)̱0Au system, and (c) relaxed (001)̱1Au system. The meaning of is the same as in Fig. 4. The contributions from the HOMO and LUMO orbitals of the isolated molecule are indicated in (a) and (b).
curve of the smaller (001)̱2Au system shown in the upper inset, whose transmission function under zero bias is shown in the lower inset. Note that there is a large resonance peak in around the Fermi energy which causes a large negative differential conductance in the curve around .
Calculated equilibrium conductance (, in units of ) and molecule-lead electron transfer (, in units of electron, a positive value means that electrons are transferred from lead to molecule). Note the large effect of adding additional Au atoms.
Equilibrium conductance (in units of ) calculated by using the wider leads and the smaller basis set as mentioned in the text. For a consistent comparison, we also list the results from the small-bais-set calculation for the small leads. Note the same effect of adding additional Au atoms, as shown in Table I.
Calculated equilibrium conductance (, in units of ) and molecule-lead electron transfer (, in units of electron) for the Se- and Te-anchored systems. (The notations are the same as those in Table I). All the trends seen in the S anchored systems are also evident here.
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