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Two-channel conduction through polyacenes—Extension of the source–sink potential method to multichannel coupling to leads
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View: Figures


Image of FIG. 1.
FIG. 1.

A two-channel molecular wire constructed from tetracene. Other polyacenes or derivatized polyacenes could also be used. Portions of the leads and molecule are labeled according to the partitioning of the lead–molecule introduced in Sec. II. The j,k indices are shown for the atoms in L´ and L´´.

Image of FIG. 2.
FIG. 2.

Hückel parameters on the left for a two-channel molecular wire. Analogous parameters apply to the right side of the wire.

Image of FIG. 3.
FIG. 3.

Probability of symmetric reflection (red solid lines) and transmission (blue dotted lines) through benzene. Antisymmetric transmission and reflection probabilities are identically zero because of the top–bottom mirror symmetry of benzene. The molecule Hückel parameters are α = −6.5 eV and β = −2.7 eV. The lead parameters are , , , while lead–molecule couplings are (top panel) and −3 eV (bottom panel).

Image of FIG. 4.
FIG. 4.

Reflection and transmission through ethenylbenzene. Symmetric channels are depicted as in Fig. 3, while antisymmetric reflection and transmission probabilities are denoted by magenta-dashed and cyan-dotted-dashed lines, respectively. The latter two probabilities are equal because of the left-right mirror symmetry of ethenylbenzene. Hückel parameters are as in Fig. 3.

Image of FIG. 5.
FIG. 5.

Molecular portion of MED wavefunctions (on the left) at resonance peak energies for the lowest (top panel) and third lowest energy resonances (bottom panel). Corresponding (i.e., associated eigenvalues close to the resonance energies) isolated molecule eigenvectors are shown on the right. The parameters are those of the top panel of Fig. 4 (i.e., the weak coupling case of ethenylbenzene). Each circle radius indicates the relative size of the modulus of the coefficient for that atomic orbital. The phase of each coefficient is indicated (only for the MED molecular wavefunctions) by the direction of the straight line from the circle center—e.g., a line to the right indicates a real positive coefficient. Green solid circles indicate phase closest to real positive, while red dotted circles indicate phase closest to real negative.

Image of FIG. 6.
FIG. 6.

As in Fig. 5, except these molecular wavefunctions correspond to the second lowest (top panel) and fourth lowest energy (bottom panel) resonances. Also, note that cyan-dotted-dashed and magenta-dashed circles indicate orbital coefficients closest to the positive and negative imaginary axes, respectively.

Image of FIG. 7.
FIG. 7.

Three resonances seen in the reflection and transmission probabilities of the top panel of Fig. 4, compared with weak-coupling model lineshapes—indicated by truncation to neighborhoods of the three resonances.

Image of FIG. 8.
FIG. 8.

As in the bottom panel of Fig. 4, except these data are for 1-ethenylnaphthalene.

Image of FIG. 9.
FIG. 9.

Four independent leads attached to benzene. As in the top panel of Fig. 3, except . Symmetric and antisymmetric channels are replaced by bottom and top channels, respectively. The incoming wave is in the bottom channel. Here, we use. Otherwise, parameters are as in other figures.

Image of FIG. 10.
FIG. 10.

The resonance, seen in Fig. 9, associated with the lower degenerate eigenvalue of benzene, compared with weak-coupling model lineshapes (see Appendix A). The model lineshapes are very close to the complete lineshapes here—they are not discernable as separate lines.

Image of FIG. 11.
FIG. 11.

The molecular portions of the MED wavefunction (on the left) at three energies near the resonance depicted in Fig. 10, E = −9.4, −9.2, and −9.0 eV. Orbital coefficients are depicted as in Fig. 5. Also shown (on the right) are the projections of these molecular wavefunctions onto the two-dimensional eigenspace of isolated benzene with eigenvalue = −9.2 eV.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Two-channel conduction through polyacenes—Extension of the source–sink potential method to multichannel coupling to leads