Excitons with time-dependent density-functional theory

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NONTECHNICAL SUMMARYThis award supports theoretical and computational research and education to develop new approaches for computing and visualizing optical properties of inorganic and organic materials. An accurate and computationally efficient approach to simulate the optical properties of these materials will provide important assistance for understanding and designing novel solar cell and optoelectronic devices.The scientific part of this project will pursue two objectives. The first goal will be to develop methodologies that yield accurate predictions related to the absorption of light by bulk insulators, semiconductors and novel organic materials. The second goal will be to develop a computational tool, which will allow a visualization of the charged particle dynamics following light absorption in complex organic molecules.The educational component of this award consists of the training and mentoring of undergraduate and graduate students in theoretical and computational condensed-matter research, the curricular developments in undergraduate condensed-matter physics and materials science, and the preparation of future faculty in the Science, Technology, Engineering, and Mathematics disciplines via engagement in the Center for the Integration of Research, Teaching and Learning network.TECHNICAL SUMMARYThis award supports theoretical and computational research and education to develop time-dependent density-functional theory based approaches for computing and visualizing excitonic properties in inorganic and organic materials. Time-dependent density-functional theory offers computationally efficient approaches for calculating the optical properties of complex systems from first principles. However, extended systems pose many challenges, in particular, local and gradient-corrected exchange-correlation functionals cannot describe excitonic effects. Excitons require exchange-correlation functionals with a long spatial range, and so far only a few of these have been available for solids. The primary research goal will be to develop and test new functionals which capture excitonic binding in insulators and semiconductors.Two interrelated research objectives will be pursued. The first objective is to use linear-response time-dependent density-functional theory to calculate singlet and triplet exciton binding energies in bulk semiconductors and insulators. A variety of exchange-correlation functionals will be implemented and tested; the influence of the ground-state band structure will be studied; and nonadiabatic functionals will be developed. Calculations will be carried out for a variety of inorganic and organic bulk crystalline materials and low-dimensional systems.The second research objective is to investigate real-time exciton dynamics in organic molecules. A new computational tool to visualize exciton dynamics, the time-dependent particle-hole map, will be developed and interfaced with existing computer codes. The particle-hole map will be mainly applied to study photoexcited organic donor-acceptor molecules and charge-transfer systems that are of interest for application in photovoltaics. In addition, exciton radiative lifetimes, intersystem crossing rates, and nonradiative lifetimes will be computed.The educational component of this award consists of the training and mentoring of undergraduate and graduate students in theoretical and computational condensed-matter research, the curricular developments in undergraduate condensed-matter physics and materials science, and the preparation of future faculty in the Science, Technology, Engineering, and Mathematics disciplines via engagement in the Center for the Integration of Research, Teaching and Learning network.