RUI: Exciton-Phonon Interactions in Solids based on Time-Dependent Density Functional Perturbation Theory

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NONTECHNICAL SUMMARYThis award supports computational research and educational activities to advance the understanding of interactions between excited electrons and lattice vibrations in semiconductors and insulators. When an electron is excited to a higher-energy state, it leaves an empty spot with a positive charge known as a hole. The electron and the hole can be strongly bound to each other in an excitonic state. The interactions between phonons (quantization of lattice vibrations) and excitons play a crucial role in many chemical and materials problems. The goal of this research is to develop an accurate, versatile, and efficient first-principles approach to compute exciton-phonon interactions in extended and condensed-matter systems. The method will have applications in energy conversion and storage, ranging from photovoltaics to photocatalysis, photodetectors, photo-synthesis, optoelectronics, light-emitting diodes, and biosensors. In this project, the PI will apply the method to study the exciton-phonon interactions in two-dimensional van der Waals heterostructures, which are the new frontier for novel optoelectronic and photovoltaic device applications.The project will also provide cutting-edge educational and training opportunities to undergraduate and graduate students as well as postdoctoral scholars, who will gain valuable experience in computational materials science. The PI is fully committed to broadening participation and enhancing diversity in materials research and education by strengthening opportunities for underrepresented groups. A graduate course on the first-principles method will be developed to prepare the students for the research activities. The PI will also reach out to local high schools and community colleges through targeted recruitment, workshops, summer camps for high-school teachers, and curriculum development in community colleges.TECHNICAL SUMMARYThis award supports computational research and educational activities to develop a novel computational methodology for the study of coupled electron-ion dynamics with electronic excited states in semiconductors and insulators. Understanding, predicting, and ultimately controlling exciton behavior and coupled exciton-ion dynamics are central to diverse chemical and materials problems. Accurate and efficient first-principles methods are highly desired for quantitatively computing exciton-phonon interactions in real materials applications. The project goal is to develop an accurate, efficient, and robust first-principles approach to capture exciton-phonon interactions in semiconductors and insulators based on time-dependent density functional perturbation theory. The method developed will allow calculations of the exciton band structure, charge density, and ionic forces associated with the exciton state, non-adiabatic couplings between exciton states, the exciton-phonon coupling matrix, and exciton dynamical processes in extended solid systems. Fully unconstrained noncollinear magnetism will be implemented to determine excitonic properties in materials with a prominent spin-orbital coupling effect. Several levels of parallelization will be exploited, rendering computational codes amenable to massively parallel platforms. In this project, the method will be used to study the phonon-assisted interfacial charge and energy transfer in two-dimensional transition-metal dichalcogenide-based van der Waals heterostructures, unraveling the momentum transfer between excitons and phonons as well as intra/interlayer exciton-phonon interactions during interfacial exciton dynamics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.