Besides accurate quantum chemical estimate of energetics, studies on the dynamics of electrons within and in between molecules grows more and more crucial after about 95 years of establishment of the Born-Oppenheimer paradigm. There are very good experimental reasons for this such as ultrafast spectroscopy and many more, yet it is essential to recognize that chemical changes like reactions are primarily dominated by the time propagation of electronic states. In the time-domain of electronic states, there will appear many phenomena one can newly explore and actually we have been doing. These include, for example, a) Real-time track of electron flow (flux) in molecules induced by chemical reactions. Unknown quantum mechanical mechanism of electronic motion in reactions can be revealed. Coupled proton and electron-wavepacket transfer for charge separation dynamics such as one in water splitting is particularly interesting in this aspect. b) Symmetry problems arising from coupling between electrons and nuclei can be discussed. Control of chemical reactions can be achieved by breaking symmetry in this aspect. A quantum mechanical origin to break molecular optical symmetry can be found in the Schroedinger dynamics. c) Manifolds, in which electronic states are densely quasi-degenerate with each other, appear to be a new chemical target. Due to very frequent nonadiabatic mixing among the states, the notion of potential energy surface (PES) loses its physical sense, let alone the meaning of the individual adiabatic states. d) Dynamics of electronic motion in molecules induced by photo-excitation in laser fields, autoionization, molecular collision can be tracked. Nonadiabatic coupling can pump electrons into ionization manifold. e) Only in the space-time domain, relativistic theory for electronic states can be well addressed to the conservation of the Lorentz invariance. My talk begins with some basic material about the Born-Oppenheimer approximation and proceed to selected topics.

From energy-domain to time-domain in quantum chemistry: Nonadiabatic electron dynamics

ACS Fall 2021

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