Quantum chemical methods for studying photon and electron driven processes

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Professor Spiridoula Matsika of Temple University is supported by an award from the Chemical Theory, Models and Computational Methods program in the Chemistry Division to develop and apply theoretical methods to better understand electron-driven processes. Heat, light (photons), and electrons provide different routes to initiate chemical reactions. While heat- and photon-driven chemical processes are well studied, electron-driven processes are not well understood, even though electrons are ubiquitous in nature. Electrons are generated by radiation, and their collisions with atoms and molecules are essential in biology and chemistry, as well as in technology. Examples of electron-driven phenomena can be found in interstellar chemistry, radiation chemistry, environmental chemistry, stability of waste repositories, plasma processing of materials for microelectronic devices, and other applications. A major complication in electron-driven processes is that the states that are involved are metastable. Matsika and her research group develop computational and theoretical approaches to treat metastable states and their chemical reactivity. They specifically apply these methods to better understand DNA damage by radiation as well as formation of prebiotic molecules in interstellar medium. The research is expected to provide valuable insights into the understanding of important electron-driven phenomena in many areas of chemistry, specifically biological systems and formation of prebiotic molecules. This research is carried out by a research team involving collaboration of undergraduate and graduate students with postdoctoral associates. The involvement of high school students in research activities inspires students to be involved in science. This involvement has a very positive effect in their education and future career prospects.Conventional quantum chemical methods cannot be applied to study metastable states (or resonances), and several approaches have been developed to treat this problem. The Matsika group is developing appropriate methods that can treat metastable states and their chemical reactivity taking advantage of the knowledge of excited state reactivity. Specific goals of this work are to develop and test of efficient multireference methods for resonances. The complex absorbing potential approach is used in combination with multireference configuration interaction (MRCI) to obtain both the energies and lifetimes of these states. The performance of the complex absorbing potential method (CAP) is compared with that of orbital stabilization methods for medium sized molecules in combination with various electronic structure methods. Gradients and nonadiabatic couplings for CAP/MRCI are developed. These methods are used to explore complex potential energy surfaces and conical intersections between complex surfaces. The developed methods are used to study electron-driven processes related to radiation damage in nucleobases and the formation of organic molecules in the interstellar medium. The methodology is being implemented in publicly available computational software. Students with a range of backgrounds and levels of academic preparation contribute to this work.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.