Giuseppe Romano1 2 Jackson Harter3 Ali Ramazani1 Alexie Kolpak1 Todd Palmer3 Alex Greaney2

1, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
2, University of California, Riverside, Riverside, California, United States
3, Oregon State University, Corvallis, Oregon, United States

When phonons encounter a region of crystal containing a gradient in the properties that dictate equilibrium phonon radiance, there must exist additional phonon collision processes in order to satisfy the principle of detailed balance [1]. Despite much research in this area, there is no widely accepted heat transport model across dissimilar materials. Here we introduce a simple form for this additional collision operator for use in Boltzmann transport simulations (BTE) of phonons using the relaxation time approximation. In particular, we develop a partially diffuse boundary condition that leads to zero boundary resistance in the case of imaginary interfaces, i.e. between two identical materials, and to complete diffuse scattering in the case of a hard wall. The method has been developed within OpenBTE [2], a recently introduced platform for multiscale phonon size effects in materials with complex geometries. Molecular dynamics (MD) simulations based on the Green-Kubo relation are also employed to study phonon transport across interfaces at the atomic level. Based on MD simulation findings, phonon-phonon scattering, phonon mean free paths, phonon lifetimes and transmission coefficients across the interfaces are calculated. We will also discuss possible routes for coupling MD simulations with the BTE.

[1] E. S. Landry and A. J. H. McGaughey. Physical Review B 80.16 (2009): 165304.