Research in the Kim Group

Theoretical chemistry. Nonequilibrium statistical mechanics and chemical reaction dynamics in condensed phase; development of a time correlation function approach to chemical reactions and computer simulations for reactive and nonreactive systems in liquids. Quantum chemistry for equilibrium and nonequilibrium solvation.

Our main research goal is to understand the mechanisms and controlling factors of chemical reactions in solution. To this end, we are developing various theoretical tools by employing both analytical and computational methods. Recent efforts have been focused on developing a simple quantum mechanical description to study the interplay and competition between the solute molecule and the solvent environment, and their influence on the reaction energetics. These aspects are essential to understand a wide range of charge transfer and shift processes in solution, e.g., electron and proton transfers, SN1, SN2, ion-pair recombination and electronic spectroscopy. By using a coherent state description for solvent electrons, a nonlinear Schrodinger equation approach to the solute electronic structure has been developed for both equilibrium and nonequilibrium solvent nuclear configurations. Its application to a classic SN1 ionization of tert-butyl chloride in a polar solvent has revealed a rather unconventional origin for activation tree energies, which is in marked contrast with traditional Hughes- lngold perspectives.

A current theoretical thrust is I ) to implement the large basis set quantum chemistry algorithms for the solute and solvent electrons, and 2) to incorporate the microscopic aspects of the solvent molecules for equilibrium and nonequilibrium solvation via computer simulations. While these two arenas -- ab initio calculations for the solute electronic structure and molecular dynamics (MD) algorithms for solvent nuclear motion -- are being explored separately, our ultimate goal is to combine the two in a consistent way to simulate a realistic reaction system in solution. Through this marriage of the two computational techniques, we hope to provide an accurate (both qualitatively and quantitatively), molecular-level theoretical description to understand the (free) energetics and dynamics of various solution-phase reactions.

Other research projects currently under way include: free energetic and dynamic studies of ultrafast excited-state electron transfer and subsequent relaxation processes in twisted intramolecular charge transfer complexes, hydride transfer in biological redox systems and dissociative electron attachments (both homogeneous and electrochemical) for alkyl and aryl halides, and MD simulation studies of dielectric friction.