[Paper Review] A New Formalism for Calculating Modal Contributions to Thermal Interface Conductance from Molecular Dynamics Simulations

Kiarash Gordiz, Asegun Henry|arXiv (Cornell University)|Jul 24, 2014

Thermal properties of materials71 references3 citations

TL;DR

This paper introduces a novel formalism to calculate modal contributions to thermal interface conductance in molecular dynamics simulations, explicitly accounting for anharmonicity. It reveals that interfacial modes—especially localized ones—dominate conductance per mode, and inelastic scattering due to anharmonicity contributes 20% of total conductance even at 10 K.

ABSTRACT

A new formalism for extracting the modal contributions to thermal interface conductance with full inclusion of anharmonicity is presented. The results indicate that when two materials are joined a new set of vibrational modes are required to correctly describe the transport across the interface. Among these new modes, certain classifications emerge, as most modes extend at least partially into the other material. Localized interfacial modes are also present and exhibit the highest conductance contributions on a per mode basis. The results also show that anharmonicity enables inelastic scattering at temperatures as low as 10K and inelastic processes contribute 20% of the conductance for the system studied.

Motivation & Objective

• To develop a formalism that accurately extracts modal contributions to thermal interface conductance from molecular dynamics simulations.
• To account for the full effects of anharmonicity in interfacial thermal transport.
• To identify and classify vibrational modes that contribute most significantly to conductance across material interfaces.
• To quantify the role of inelastic scattering in thermal conductance at low temperatures.
• To reveal the emergence of new interfacial modes not present in bulk materials.

Proposed method

• The formalism uses time-series data from molecular dynamics simulations to compute the vibrational density of states and mode-specific energy fluxes.
• It decomposes the total interfacial conductance into contributions from individual vibrational modes, including interfacial and bulk-like modes.
• Anharmonic effects are included through the full time evolution of atomic displacements and energy transfer dynamics.
• The method identifies localized interfacial modes by analyzing spatial extent and coupling across the interface.
• Inelastic scattering contributions are quantified by tracking non-conservative energy transfer between modes.
• Conductance is calculated by integrating mode-specific energy fluxes weighted by the appropriate distribution functions.

Experimental results

Research questions

• RQ1 What vibrational modes dominate thermal conductance across a material interface, and how do they differ from bulk modes?
• RQ2 How does anharmonicity influence the contribution of inelastic scattering to interfacial conductance at low temperatures?
• RQ3 To what extent do new interfacial modes emerge upon contact between two materials?
• RQ4 Which mode types—localized or delocalized—contribute most to conductance per mode?
• RQ5 What is the quantitative contribution of inelastic scattering to total conductance in the presence of anharmonicity?

Key findings

• A new set of vibrational modes emerges at the interface, which are essential for accurate description of interfacial thermal transport.
• Localized interfacial modes contribute the highest conductance per mode, indicating their dominant role in energy transfer.
• Anharmonicity enables inelastic scattering processes that contribute 20% of the total thermal conductance in the studied system.
• Inelastic scattering is significant even at 10 K, demonstrating that anharmonic effects are non-negligible at low temperatures.
• Delocalized modes extending into both materials also contribute substantially, but less per mode than localized interfacial modes.
• The formalism successfully captures the full anharmonic behavior of interfacial phonons, resolving limitations of harmonic approximations.