At the dawn of quantum physics, RE Peierls proposed to combine the concept of quanta of lattice vibration, i.e. phonons, with the particle Boltzmann Transport Equation (BTE) theory to describe thermal transport processes at the microscopic level. Since then, the phonon gas (PG) model has served as the theoretical foundation to calculate and interpret thermal transport properties of solids. In this talk, I will present some of our recent work of implantation and further development of atom-scale computational methodologies for lattice thermal conductivity calculations. First, I will discuss the strengths and weaknesses of three commonly adopted computational methods, namely, (1) the non-equilibrium molecular dynamics simulation method, (2) the equilibrium fluctuation-dissipation theory, such as Green-Kubo formalism, and (3) the phonon BTE theory. Then, I will highlight some of our newly discovered heat transfer mechanisms, including the phonon-polariton effects on bulk lattice thermal conductivity at high temperatures, and the coupling-decoupling mechanism for interfacial heat transfer cross weakly bonded molecular interfaces. Finally, I will discuss the breakdown conditions of the PG model based on our newly proposed vibration Fokker-Planck Equation (FPE) theory, and the implications to calculations of thermal conductivity at high temperatures and/or of solids with strongly localized vibrational modes.

References:
Yi Zeng, Jianjun Dong, and Jay M. Khodadadi, “Theory and simulations of thermal conductance of flexible molecular interfaces”, under review.
Yi Zeng and Jianjun Dong, “Fokker-Planck equation for lattice vibration: Stochastic dynamics and thermal conductivity", Phys. Rev. B 99, 014306 (2019).
A.M. Hofmeister, Jianjun Dong, and J. Branlund, “Thermal diffusivity of electrical insulators at high temperatures: evidence for diffusion of bulk phonon-polaritons at infrared frequencies augmenting phonon heat conduction”, J. Appl. Phys. 115, 163517 (2014).
Xiaoli Tang and Jianjun Dong, "Lattice thermal conductivity of MgO at conditions of Earth's interior", Proc. Natl. Acad. Sci. U.S.A. 107, 4935-4954 (2010)