Simulating Attochemistry: Which Dynamics Method to Use?

Abstract

Attochemistry aims to exploit the properties of coherent electronic wavepackets excited via attosecond pulses to control the formation of photoproducts. Such molecular processes can, in principle, be simulated with various nonadiabatic dynamics methods, yet the impact of the approximations underlying the methods is rarely assessed. The performances of widely used mixed quantum-classical approaches, Tully surface hopping, and classical Ehrenfest methods are evaluated against the high-accuracy DD-vMCG quantum dynamics. This comparison is conducted for the valence ionization of fluorobenzene. Analyzing the nuclear motion induced in the branching space of the nearby conical intersection, the results show that the mixed quantum-classical methods reproduce quantitatively the average motion of a quantum wavepacket when initiated on a single electronic state. However, they fail to properly capture the nuclear motion induced by an electronic wavepacket along the derivative coupling, the latter originating from the quantum electronic coherence property, key to attochemistry.

Controlling Electronic Coherences and the Curvature Induced by the Derivative Coupling at a Conical Intersection: A Quantum Ehrenfest (QuEh) Protocol for Reaction Path Following Application to “Channel 3” Benzene Photochemistry

“…In the time period between 10 and 16 fs both the S 0 and S 1 are populated, and we have a coherent superposition of the two states. (In attochemistry ,, this coherent superposition is created with a laser pulse). This effect comes from the coupling with nm 24.…”

“…Of course, the second-order Ehrenfest method ignores the effect of the derivative coupling between other possible trajectories/normal modes, which partly diverts the reaction path parallel to the derivative coupling (see Figure b–e). This idea has been reviewed recently . This effect requires the explicit computation of interaction/coupling of several trajectories and normal modes that occur in the quantum dynamics approach .…”

“…This idea has been reviewed recently. 19 This effect requires the explicit computation of interaction/coupling of several trajectories and normal modes that occur in the quantum dynamics approach. 20 Various approaches are available to transcend this limitation: One approach is to add the effect of the derivative coupling in the surface hop method.…”