All-Electric Single-Molecule Motor modeled with ADF

In the November 2010 issue of ACS Nano, Jos Seldenthuis and coworkers at the Delft University of Technology published a design for an all-electric single-molecule motor which has drawn worldwide interest. The rotating moiety of the molecule exhibits a large dipole moment, which enables it to be driven by an external electric field. The molecule is conjugated when planar. During rotation the conjugation breaks, which enables the detection of the rotation through the modulation of the low-bias conductance. Advantages of this design over light- or thermally driven motors include full control over the speed of rotation through the frequency of the oscillating external field.

All relevant properties of the proposed molecular motors (dipole moment, rotational barrier potential and zero-bias off-resonance conductance as a function of the rotation angle) have been calculated with ADF. The fragment-based approach of ADF and the provided Python tools were particularly helpful in constructing the Green’s function and made the implementation of the post-DFT transport calculations almost trivial.

At the moment the proposed motor exists only on paper. However, certain aspects of the design have already been verified experimentally, and the ADF calculations show that it should be possible to drive and measure the motor in current electromigrated break-junction setups. The group of Herre van der Zant is already talking to chemists who have expressed an interest in synthesizing the molecules and hopes to start measuring them sometime next year.

Left: Design of an all-electric single-molecule motor. Right: Rotational barrier potential and zero-bias off-resonance conductance as a function of the rotation angle.

J. S. Seldenthuis, F. Prins, J. M. Thijssen, and H. S. J. van der Zant, An All-Electric Single-Molecule Motor. ACS Nano,4, 6681 (2010).