Approximate Quantum Mechanical Methods for Excited State Potential Energy Surface Exploration

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With this award, the Chemical Theory, Models and Computational Methods program in the Division of Chemistry is supporting Dr. Christine Aikens of Kansas State University (KSU) to develop quantum mechanical methods that will enable the study of photochemical processes in large biological molecules and nanoparticles. There are broad potential applications of these studies to the fields of biomedical imaging, photochemistry, and solar energy conversion. Without these methods, it is currently not feasible to study excited state processes in large systems with hundreds of atoms accurately. The methods being developed in this work will enable excited state potential energy exploration of large biological molecules and nanoparticles for the first time. This will allow the examination of energy transfer pathways and light emission in these systems. Outreach efforts through the GROW (Girls Researching Our World, 6th-8th grade) and EXCITE! (EXploring sCIence, Technology, and Engineering, 9th-12th grade) programs at KSU for middle and high school girls will foster a continuing interest in STEM, particularly computational chemistry, among the participants. This work will also be presented at Science Cafés at a level aimed at a general audience.Dr. Christine Aikens and her research group are developing a suite of approximate methods based on time-dependent density functional theory (TDDFT) that will enable the calculation of excited state energies and gradients at about 50 to 60 times lower computational cost compared to current TDDFT methods. These methods will include open-shell versions that are expected to be effective for radicals and triplet states, as well as versions that include Hartree-Fock exchange that are designed to accurately treat charge-transfer excitations. Methods that include fractional occupation numbers will also be developed, which will be beneficial for systems such as large metal nanoparticles that have a very small HOMO-LUMO gap. These computational methods are expected to have broader scientific impacts on biological imaging methods development, photochemistry studies, and upon solar energy conversion research, endeavors in which nuclear relaxation and dynamics on excited state potential energy surfaces are critical for predicting luminescence emission wavelengths,reactive pathways, and energy transfer pathways.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.