Hi all,
John Tully of Yale, developer of the famous surface hopping method used in *ab
initio* molecular dynamics simulations, will be giving today's theoretical
chemistry seminar. The seminar will be held in *4-163 from 4-6 PM* with a
short break between the two halves of the talk. The title and abstract of
the talk are below.
Title: *Quantum-Classical Dynamics: Issues and Applications*
Abstract:
Conventional Molecular Dynamics (MD) rests on two fundamental assumptions:
1. Nuclear motion evolves by classical mechanics. 2. The forces on the
nuclei derive from a single electronic potential energy surface (the
Born-Oppenheimer Approximation). There are hosts of chemical processes for
which one or both of these assumptions are not adequate. Nuclear motion can
exhibit pronounced quantum mechanical effects associated with tunneling,
zero-point motion and quantized energy levels. Transitions among multiple
electronic states can play a dominant role in processes such as
nonradiative transitions, electron transfer, photochemistry, and chemistry
at semiconductor and metal surfaces. Mixed quantum-classical dynamics
(MQCD) has been an at least partially successful strategy for introducing
quantum effects into molecular dynamics simulations, as well as providing a
procedure to treat open systems. A crucial concern in MQCD is feedback
between the classical and quantum motions. The time-dependent motion of the
classical nuclei induces transitions among quantum states. Quantum
mechanical transitions, in turn, alter the forces that govern the motion of
the classical particles. Proper treatment of this “quantum back reaction”
has been a subject of controversy for more than 40 years. Aspects of this
issue will be examined, both at a fundamental level and by example. Among
the applications presented are the quantum dynamics of proton transfer in
solution and inelastic scattering of molecules from metal surfaces. Because
metal surfaces exhibit a continuum of infinitesimally spaced conduction
electron levels, the latter is an extreme example of anticipated inadequacy
of the Born-Oppenheimer Approximation.
--
Michael Mavros
Department of Chemistry, Massachusetts Institute of Technology
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