First-Principles Simulation of Quantized Charge Transport in Extended Systems

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Professor Yosuke Kanai of the University of North Carolina at Chapel Hill is supported by an award from the Chemical Theory, Models and Computational Methods Program of the Division of Chemistry and the Condensed Matter and Materials Theory Program of the Division of Materials Research to study the electron transport in extended chemical systems. His research advances computational methodologies and simulates electron motion using of a large number of processors (or separate computers) to perform a set of coordinated computations in parallel (simultaneously) - this is called massively parallel computing. They are using this technique to study microscopic details of how electrons move in materials i.e., how materials carry electrical current. This research may enable modern electronics to continue to decrease in size, while increasing in speed and complexity. A new class of materials called topological materials represents a great opportunity to improve electronics if scientists can exploit their unique electrical conductivity properties. Current scientific understanding of how chemical features in topological insulators control the unique electron transport behavior is largely lacking. By developing novel computational methods, new simulations will enable a microscopic understanding of how electron transport properties are governed at the molecular scale. The research activities will also promote science education at the undergraduate level for underrepresented minority students with interests in computational sciences, Professor Kanai engages students through summer hands-on workshops where the students build a parallel computer and learn about both hardware and software development. The student will be taught to perform electronic structure calculations and program simple code on the computers they build.The large-scale, real-time time-dependent density functional theory (TDDFT) method is formulated in the maximally-localized Wannier function (MLWF) gauge. It is used to develop a fundamental understanding of quantized charge transport in extended systems at the molecular level. Topological Floquet theory is studied beyond the typical adiabatic evolution limit by simulating quantum-mechanical electron dynamics in real chemical systems. In particular, the quantized charge transport behavior is investigated and how chemical moieties can potentially be used to control the quantized transport is studied. The work further explores the novel concept of optically gated transistors that exhibits quantized conductance. Improving the real-time TDDFT code by incorporating advanced exchange-correlation approximations via time-dependent MLWFs is an important aspect of this investigation. Professor Kanai also provides hands-on tutorials on TDDFT methodologies at workshops.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.