Physical Chemistry Seminar: Professor Nancy Makri, University of Illinois at Urbana-Champaign

Physical Chemistry Seminar: Professor Nancy Makri, University of Illinois at Urbana-Champaign
Date
Tue March 12th 2019, 4:30 - 5:30pm
Location
Sapp Center Lecture Hall

Physical Chemistry Seminar: Professor Nancy Makri, University of Illinois at Urbana-Champaign (Host: Tom Markland)

About the Seminar

“Interference, decoherence, and quantum-classical path integral simulations with thousands of atoms”

The wavefunction – the central object of quantum mechanics – requires storage which grows exponentially with system size.  This scaling severely impacts the feasibility of accurate calculations, restricting them to systems of only a few particles. Feynman’s path integral formulation offers an attractive alternative for calculating time-dependent observables without propagating wavefunctions. Instead, the quantum mechanical amplitude is obtained by summing the amplitudes along all possible paths. Unfortunately, the path sum typically involves astronomical numbers of terms, and stochastic methods are unable to deal with the rapidly oscillating quantum mechanical phase.
Phase interference is responsible for intriguing quantum mechanical phenomena, but can also lead to decoherence and dissipative effects. Exploiting the latter offers a promising strategy for devising rigorous and robust algorithms for quantum dynamics. This approach led to a fully quantum mechanical real-time path integral methodology for simulating the dynamics of a quantum system interacting with a bath of harmonic oscillators, which allowed a deeper understanding of tunneling on condensed phase chemical reactions and shed light on the early steps of photosynthetic charge separation.  
Understanding the physics of decoherence, which emerges from phase cancellation, has allowed progress beyond the harmonic bath simplification. The most prominent, “classical decoherence” mechanism, is associated with phonon absorption and induced emission and is dominant at high temperature. A second, nonlocal in time, “quantum decoherence” process, becomes important at low temperatures; this is associated with spontaneous phonon emission and is responsible for detailed balance.   Quantum-classical treatments offer a pragmatic approach for simulating processes in solution or in complex biological environments containing thousands of atoms. While traditional quantum-classical methods, which are based on wavefunctions, are based on severe assumptions, the quantum-classical path integral is a rigorous, yet efficient approach that enables all-atom simulations of electron transfer reactions with unprecedented accuracy.  

 

About the Speaker

Nancy Makri obtained a B.S. from the University of Athens in 1985 and a Ph.D. from the University of California at Berkeley in 1989.  After spending two years as a Junior Fellow at Harvard, she joined the University of Illinois, where she is currently the Edward William and Jane Marr Gutgsell Professor and holds faculty appointments in Chemistry and Physics.  Makri’s research focuses on the development of theoretical methods for simulating the quantum dynamics of condensed phase processes.  She has pioneered the development of rigorous real-time path integral methods, which have helped quantify quantum mechanical effects in chemical kinetics.  Makri is the recipient of Packard, Beckman and Sloan research awards, Cottrell and Dreyfus scholar awards, and the Bodossaki Academic Prize in Physical Sciences.  She is also a Medalist and a member of the International Academy of Quantum Molecular Science.