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Materials Modelling Seminar

Zhun-Yong Ong, Institute of High Performance Computing Singapore

Thursday 23rd Nov, 11:00

Goldsmiths 1 (0_017), Department of Materials Science & Metallurgy

Title: Modelling phonon scattering and thermal transport with the

extended Atomistic Green's Function method

The diffusion of heat across the boundary between two insulating
crystalline solids is controlled by its Kapitsa (thermal) resistance,
which is determined at the microscopic level by the reflection and
transmission of quantised lattice vibrations (i.e. phonons), and depends
strongly on the crystallographic microstructure of the interface.
However, our conceptualisation of phonon scattering by the interface
relies heavily on analogies from wave optics and acoustics, and remains
limited by the lack of computationally efficient methods for quantifying
the transmission and reflection of individual phonons, constraining our
ability to analyse the theoretical connection between phonon scattering
and interfacial microstructure.

In this talk, I discuss how these difficulties can be overcome by
extending the Atomistic Green's Function method that is commonly used to
study ballistic phonon transport. I first show how the Kapitsa
resistance phenomenon can be treated as a scattering (S-matrix) problem
within the familiar conceptual framework of conventional quantum
mechanics. This approach allows us to employ existing theoretical
machinery, originally developed for studying quantum transport in open
systems, as the basis for our extension of the Atomistic Green's
Function (AGF) method.Our extension of the AGF method enables the
precise calculation of transition amplitudes between phonon channels
(i.e. the individual elements of the S-matrix) and yields insights into
the dependence of the transmission and reflection coefficients on
interfacial microstructure as well as phonon frequency, momentum and
polarisation. Other possible applications of our extended AGF approach
include the lattice defect and edge scattering of phonons. To illustrate
the utility of this method, we present some simulation results and
analysis, obtained using inputs from ab initio calculations, for the
MoS2/WS2 interface and isotopically non-uniform graphene. The concepts
and numerical techniques developed in our approach may be potentially
useful for analogous scattering problems in other areas such as
tight-binding models, photonics and acoustics.

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