Phonon-mediated thermal transport is inherently multiscale, for example , the phonon wave length (λ) is at nanometer scale, the typical phonon wave packet size (η) is tens of nanometers, and the phonon mean free path (Λ) can be microns. To simulate the multiscale thermal transport behavior in materials, we further developed the coarse-grained (CG) atomistic model to reproduce a complete phonon spectrum (figures above), and in turn, to predict the thermal conductivity of polyatomic materials as following. 
