Development and Applications of Electronic Structure Methods for Open-shell and Electronically Excited Species with Strongly Interacting States of Different Character

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Anna Krylov of the University of Southern California is supported by the Theoretical and Computational Chemistry Program to develop electronic structure methodology for open-shell and electronically excited species, in particular for those with strongly interacting electronic states of different nature. The proposed program capitalizes on the PI's recent advances in developing new equation-of-motion (EOM) coupled-cluster (CC) methods, which extend this robust and efficient technique to treat diradicals, triradicals, and bond-breaking. The following methodological developments are planned: (i) exploring higher sectors of the Fock space (e.g., double spin-flip, spin-flip - (double) ionization, etc.) to extend EOM to situations with more extensive degeneracies encountered upon multiple bond-breaking, in transition metals and polyradicals; (ii) including higher excitations to achieve chemical accuracy; (iii) spin-adaptation of open-shell CC and EOM wave functions to improve accuracy in problematic cases such as spin-contaminated or unstable references. The new methodology will be applied to study electronic structure of open-shell species involved in combustion and atmospheric chemistry as well as practically relevant radical anionic reactions (i.e., benzyne and fulvene anions), in continuing collaborations with experimental groups. This research is expected to lead to new insights into problems of environmental and technological importance, for example chemical reaction systems that are relevant to atmospheric and synthetic chemistry. This research also includes a strong component of computer code design and implementation, and will help prepare students for careers in high-tech industries where the ability to solve complex problems using sophisticated computational tools is highly valued. New computer software will be integrated into widely available electronic structure programs, making these results available to the broad chemistry community.