Thermal transport through GaN-AlN interfaces with mass and force variance from first-principles*

We present thermal conductance calculations of a GaN-AlN interface using a Landauer formalism with all interatomic force constants (IFCs), including those relaxed at the interface, computed from density functional theory. A thorough convergence study of the conductance value is outlined, focusing on the effects of truncating long-range IFCs from polar materials and properly enforcing various symmetries and invariances. For example, enforcing the simple acoustic sum rule instead of using more advanced methods overestimates the conductance by 7% with a 35% overestimation of the optical phonon contributions. We compare our fully first-principles conductance with those using empirical mixing rules to define interfacial IFCs. Moreover, we contrast our calculations with values inferred from thermal conductivity measurements of GaN-AlN superlattices. Our calculations constitute initial steps towards a fully predictive framework of interfacial thermal conductance.