2, University of California, Riverside, Riverside, California, United States
Encompassing diffusive, quasi-ballistic and ballistic regimes, heat conduction is inherently a multiscale problem. At the atomistic level, the phonon mean-free-path (MFP) distribution is typically obtained by density functional theory. On the other side, phonon-boundary interaction is conveniently captured by continuum models, such as the Boltzmann transport equation (BTE). Finally, short-MFP phonons will mostly travel diffusively, so they can be accounted for by a standard diffusive solver. OpenBTE  attempts bridging these three regimes. Specifically, the MFP distribution, computed by first-principles, is used as input to the MFP-BTE , a recently introduced version of the BTE that uses the phonon MFP as a control variable. Then, using a parameter-free multiscale approach, the BTE solver integrates a modified diffusive model that calculates heat carried by short-MFP phonons. After a brief introduction to the software architecture, we will show example applications, including thin films, nanoporous materials, Graphene nanoribbons, Si serpentines, phonon focusing and large-scale screening of nanostructured materials for thermoelectric applications. Conclusions and final remarks will conclude the talk.
 G. Romano and J. C. Grossman. "Heat conduction in nanostructured materials predicted by phonon bulk mean free path distribution." Journal of Heat Transfer, 137.7 (2015): 071302.