Antiresonances in Molecular Wires

TL;DR

This paper analytically and numerically investigates conductance antiresonances in molecular wires, emphasizing the importance of non-orthogonality effects and identifying mechanisms for antiresonance occurrence, with implications for experimental observation.

Contribution

The study provides an exact analytic solution for antiresonances considering non-orthogonality and extends the analysis to complex systems with numerical simulations.

Findings

Antiresonances occur at specific energies predicted by the derived expression.

Non-orthogonality effects are crucial for accurate antiresonance predictions.

Numerical simulations confirm the analytic results in more complex, realistic systems.

Abstract

We present analytic and numerical studies based on Landauer theory of conductance antiresonances of molecular wires. Our analytic treatment is a solution of the Lippmann-Schwinger equation for the wire that includes the effects of the non-orthogonality of the atomic orbitals on different atoms exactly. The problem of non-orthogonality is treated by solving the transport problem in a new Hilbert space which is spanned by an orthogonal basis. An expression is derived for the energies at which antiresonances should occur for a molecular wire connected to a pair of single-channel 1D leads. From this expression we identify two distinct mechanisms that give rise to antiresonances under different circumstances. The exact treatment of non-orthogonality in the theory is found to be necessary to obtain reliable results. Our numerical simulations extend this work to multichannel leads and to molecular wires connected to 3D metallic nanocontacts. They demonstrate that our analytic results also provide a good description of these more complicated systems provided that certain well-defined conditions are met. These calculations suggest that antiresonances should be experimentally observable in the differential conductance of molecular wires of certain types.