Non-Born-Oppenheimer Effects in the Framework of Multicomponent Time-Dependent Density Functional Theory

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Professor Sharon Hammes-Schiffer of Yale University is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry to develop computational methods for describing the role of electrons and protons in chemical processes. The interaction or coupling of electrons and protons plays a vital role in a wide range of biological and chemical processes, including photosynthesis, respiration, and energy production in solar cells. The development of computational methods that accurately describe this coupling is challenging because electrons and protons are so light that they must be treated specially, which is computationally expensive. Professor Hammes-Schiffer is developing methods that describe electrons and protons in a computationally practical manner. She is applying these methods to specific processes of biological and chemical relevance to elucidate the fundamental principles of these processes. In addition, she and her research group are incorporating these computational methods into established quantum chemistry software packages to benefit the general scientific community. Professor Hammes-Schiffer is also maintaining and enhancing a website containing software and educational tools including computer programs, tools, demonstrations, and tutorials. This research facilitates technological and biomedical advances in more effective solar cells and other renewable energy sources as well as improved understanding of enzymes. Professor Hammes-Schiffer is developing new theoretical and computational approaches that provide insight into the underlying fundamental principles of photoinduced proton transfer and proton-coupled electron transfer (PCET) reactions, which play a vital role in a broad range of biological and chemical processes. These approaches are designed to include nuclear quantum effects, such as proton delocalization and zero-point energy, as well as non-Born-Oppenheimer effects, in a computationally practical manner. Hammes-Schiffer is developing these methods within the framework of the nuclear-electronic orbital density functional theory (NEO-DFT) approach, which treats key nuclei, such as the transferring proton(s), quantum mechanically on the same level as the electrons within the framework of DFT. The multicomponent time-dependent DFT (NEO-TDDFT) approach enables the calculation of excited electronic, proton vibrational, and electron-proton vibronic states. Hammes-Schiffer is developing NEO methods for computing minimum energy paths and tunneling splittings for proton transfer and PCET reactions, as well as mixed electron-proton vibronic excited states for photoinduced reactions. She is also developing real-time NEO-TDDFT methods and other nonadiabatic dynamics methods for the simulation of ultrafast electronic and nuclear dynamics, targeting applications to photoinduced PCET reactions. She is incorporating these approaches into well-established quantum chemistry software packages and is creating tutorials to explain how to perform NEO calculations and highlight the unique capabilities of this approach. Furthermore, she is maintaining and enhancing a web site on PCET to convey useful information to the community and to provide valuable tools, scripts, and programs relevant to studying PCET.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.