Charge transfer through single molecule contacts: How reliable are rate descriptions?

Area of Science:

• Molecular electronics
• Condensed matter physics
• Quantum transport

Background:

• Nanoscale electrical circuit fabrication drives molecular electronics progress.
• Theoretical models for molecular contacts must integrate Fermi liquid properties with molecular charge and phonon dynamics.
• Generic models, particularly transfer rate descriptions, are valuable for understanding transport processes.

Purpose of the Study:

• To analyze the accuracy of transfer rate descriptions for molecular contacts compared to numerically exact solutions.
• To investigate the applicability of transfer rate models in parameter regimes where they are not expected to succeed, such as low temperatures.
• To develop and validate an extended master equation for accurate charge-phonon complex modeling.

Main Methods:

• Formulation of charge transport using transfer rates.
• Comparison with numerically exact solutions.
• Extension of a master equation to include off-diagonal elements of the reduced density matrix for charge-phonon dynamics.

Main Results:

• Transfer rate formulations provide quantitatively accurate descriptions, even at lower temperatures.
• An extended master equation accurately captures charge-phonon interactions, including voltage-driven steady states and strong electron-phonon coupling.
• The proposed methods are computationally orders of magnitude less expensive than exact numerical simulations.

Conclusions:

• Rate descriptions and master equations provide a versatile and computationally efficient model for charge transfer in molecular junctions.
• These methods offer conceptual simplicity and flexibility for extensions, making them practical for various applications.
• Accurate results are achievable as long as strong quantum correlations do not significantly alter subunit properties.