CAREER: Quantum-mechanical methods for electronic excited states in complex systems

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Professor Eugene DePrince of Florida State University is funded by the Chemical Theory, Models, and Computational Methods program of the Chemistry Division to develop new theories and computer algorithms to aid in the description of the electronic structure of complex molecules and materials. Dr. DePrince and his group are developing techniques that describe a system with many electrons using an approach (two-electron reduced-density matrix: 2-RDM) that reduces the problem to two electrons, rather than the more familiar and complicated many-electron techniques. Because the 2-RDM approach is more compact than the many-electron wave function, these methods enable large computations on complex systems that are not possible using conventional approaches. The theories and algorithms being developed facilitate the discovery and characterization of novel molecules and materials relevant energy conversion, catalysis, and advanced energy storage technologies. Professor DePrince is also developing Chemical Physics courses, a lecture series, and online educational content with the goal of establishing a Chemical Physics PhD track in the Department of Chemistry and Biochemistry at Florida State University.The project aims to develop a theoretical and computational framework for the description of electronically excited states in complex systems. Here, the term complex refers to systems that fall into one of two categories: (i) molecules whose electronic wave functions cannot be described qualitatively by a single electronic configuration (i.e. strongly correlated systems) or (ii) molecules embedded in extreme environments, such as those in the vicinity of a plasmonic nanoparticle, where intense external electric fields can significantly perturb the electron density for the molecule. For the former category, frequency- and time-domain methods are being developed to extract excited-state information from variational two-electron reduced-density matrix (2-RDM)-driven complete active space self-consistent field computations. For the latter category, the investigator and his group are developing fully-quantum mechanical approaches that simulate plasmon-molecule interactions in the time domain. Because the plasmon is modeled in a quantum-mechanical way, such an approach captures quantum-mechanical effects, such as entanglement and coherences between plasmon excitations. Professor DePrince places the codes developed as part of this research effort in the public domain in either free or commercial electronic structure packages. Making these codes available to the public facilitates the discovery of novel materials and the advancement of the numerical methods developed throughout the project.