Stochastic simulation of nonequilibrium heat conduction in extended molecular junctions

Area of Science:

• Nanoscale science
• Condensed matter physics
• Computational chemistry

Background:

• Phononic heat transport in molecular junctions is crucial for nanoscale heat conduction.
• Understanding these processes is key to developing new thermal management strategies.
• Existing models often operate within the linear response regime.

Purpose of the Study:

• To present a Langevin dynamics simulation framework for investigating heat transport in molecular junctions.
• To analyze heat transport in saturated and unsaturated linear hydrocarbon chains connecting gold substrates.
• To compare classical and quantum simulation methods for nanoscale heat conduction.

Main Methods:

• Utilized a Langevin dynamics simulation framework with filtered Markovian noise and damping.
• Applied the framework to alkanedithiol and polyyne molecular junctions connected to gold substrates.
• Compared classical simulations (full universal force field) with quantum calculations (harmonic approximation).

Main Results:

• Classical and quantum simulations showed close agreement at room temperature, suggesting classical mechanics adequately describes low-frequency vibrations governing heat transport.
• Simulations for alkanedithiols matched previous quantum calculations and experimental measurements (approx. 20 pW/K thermal conductance).
• Simulations on polyynes revealed effects of molecular conjugation, with differences from alkanes correlating to polyyne rigidity and mode localization.

Conclusions:

• The developed simulation framework is effective for studying nanoscale heat transport beyond the linear response regime.
• Classical simulations are reliable for predicting heat transport in molecular junctions at room temperature.
• The study provides insights into the influence of molecular structure, such as conjugation and rigidity, on thermal transport properties.