QMHP: Nonequilibrium Green function modeling of coupled electron and phonon transport in nanoscale thermoelectric devices

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This project will help us understand the fundamental barriers to higher efficiency in chips used as energy sources, in hopes that we can achieve future breakthroughs in energy by harnessing that understanding.More specifically, the project will develop a quantum transport framework, implemented via massively parallel computation, to study coupled electron and phonon (i.e., vibrations of atoms) propagation in realistic nanostructures. The recent experimental and nanofabrication advances have ignited the exploration of heat flow and thermoelectricity in nanowires and molecular junctions. However, the theoretical and computational studies of such systems are lagging behind by considering electron and phonon currents independently. The approach is nonequilibrium Green function formalism combined with either first-principles methodology in the case of molecular junctions or with sermi-empirical models in the case of nanowires.Intellectual Merit:The nonequilibrium quantum many-body problem posed by the inelastic coupling between electrons and phonons has enormous computational complexity which has prevented microscopic consistent treatment of both charge transport and energy transport on an equal footing. The proposed novel algorithm development to tackle this challenging problem has a potential to be the first of its kind.Broader Impact:Thermoelectrics transform temperature gradients into electric voltage and vice versa. The optimization of the thermoelectric figure of merit for the proposed devices combining graphene nanoribbons or silicon nanowires with small molecules or nanopores could lead to commercially viable technologies for generation of electricity from waste heat or solid-state coolers for electronic circuits. The proposed research will offer excellent training for graduate students in advanced techniques of nonequilibrium quantum statistical mechanics, nanoscale device engineering, and high-performance computing. The outreach activities will include organization of workshops on "Nanoscience and nanotechnology for high school teachers and students," lecturing at summer schools, and organization of international workshops on computational electronics.