Quantum Mechanical Effects in Complex Systems

Donald Truhlar of the University of Minnesota is supported by the Theoretical and Computational Chemistry Program to develop new methods for simulating complex, reactive dynamical systems in chemistry, and to apply these methods to chemical reactions in complex systems. Two areas of development are singled out: reactions catalyzed by enzymes and electronically nonadiabatic reactions (photochemical reactions). The research will incorporate quantum mechanical effects in systems that are too large to be treated by brute force converged quantum mechanical structural and dynamical calculations, and work at the interface of electronic structure theory and dynamics. Project efforts include (1) QM/MM methods for modeling enzyme/coenzyme/substrate potential energies functions, (2) new methods for modeling the participation of enzyme coordinates in the reaction coordinate for catalyzed reactions, (3) new methods for diabatic representations of electronic states, (4) new approaches to including decoherence in semiclassical Ehrenfest calculations in coupled-state dynamics, (5) new approaches to fitting coupled potential energy surfaces, and (6) new methods for rare event sampling in collisions of systems with weakly coupled potential energy surfaces. A special effort involves the use of experimental data and accurate quantum dynamics to validate the accuracy of semiclassical methods designed to be applicable in a practical way to complex systems.

This research will impact our molecular level understanding of photochemical dynamics and enzyme mechanisms, which in turn will have implications in areas such as biochemistry and atmospheric chemistry. Broader impacts include strong efforts in student mentoring, as well as free distribution of computer codes accessible from the PI's web site.