Electron transport through single conjugated organic molecules: Basis set effects in ab initio calculations

TL;DR

This study examines how basis set choices in ab initio calculations influence electron transport predictions in single conjugated molecules, revealing significant effects on conductance especially for longer molecules, with implications for theoretical modeling accuracy.

Contribution

It highlights the importance of basis set selection in ab initio transport calculations and demonstrates its impact on conductance predictions for different molecular lengths.

Findings

Basis set size affects Fermi energy position and conductance.

Long molecules show orders-of-magnitude conductance changes due to basis set.

Resonances can stabilize Fermi energy positioning.

Abstract

We investigate electron transport through single conjugated molecules - including benzenedithiol, oligo-phenylene-ethynylenes of different lengths, and a ferrocene-containing molecule sandwiched between two gold electrodes with different contact structures - by using a single-particle Green function method combined with density functional theory calculation. We focus on the effect of the basis set in the ab initio calculation. It is shown that the position of the Fermi energy in the transport gap is sensitive to the molecule-lead charge transfer which is affected by the size of basis set. This can dramatically change, by orders of magnitude, the conductance for long molecules, though the effect is only minor for short ones. A resonance around the Fermi energy tends to pin the position of the Fermi energy and suppress this effect. The result is discussed in comparison with experimental data.