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Phonon transmission across interfaces of dissimilar materials has beenstudied intensively in the recent years by using atomistic simulation toolsowing to its importance in determining the effective thermal conductivity ofnanostructured materials. Atomistic Green's function (AGF) method withinteratomic force constants from the first-principles (FP) calculations hasevolved to be a promising approach to study phonon transmission in many notwell-studied material systems. However, the direct FP calculation forinteratomic force constants becomes infeasible when the system involves atomicdisorder. Mass approximation is usually used, but its validity has not beentested. In this paper, we employ the higher-order force constant model toextract harmonic force constants from the FP calculations, which originatesfrom the virtual crystal approximation but considers the local force-fielddifference. As a feasibility demonstration of the proposed method thatintegrates higher-order force constant model from the FP calculations with theAGF, we study the phonon transmission in the Mg2Si/Mg2Si1-xSnx systems. Whenintegrated with the AGF, the widely-used mass approximation is found tooverpredict phonon transmission across Mg2Si/Mg2Sn interface. The differencecan be attributed to the absence of local strain field-induced scattering inthe mass approximation, which makes the high-frequency phonons less scattered.The frequency-dependent phonon transmission across an interface between acrystal and an alloy, which often appears in high efficiency "nanoparticle inalloy" thermoelectric materials, is studied. The interfacial thermal resistanceacross Mg2Si/Mg2Si1-xSnx interface is found to be weakly dependent on thecomposition of Sn when the composition x is less than 40%, but increasesrapidly when it is larger than 40% due to the transition of high-frequencyphonon DOS in Mg2Si1-xSnx alloys.

Phonon transmission across Mg2Si/Mg2Si1-xSnx interfaces: A first-principles-based atomistic Green's function study