Abstract
Knowledge about the electronic motion in molecules is essential for our understanding of chemical reactions and biological processes. The advent of attosecond techniques opens up the possibility to induce electronic motion, observe it in real time, and potentially steer it. A fundamental question remains the factors influencing electronic decoherence and the role played by nuclear motion in this process. Here, we simulate the dynamics upon ionization of the polyatomic molecules paraxylene and modified bismethylene-adamantane, with a quantum mechanical treatment of both electron and nuclear dynamics using the direct dynamics variational multiconfigurational Gaussian method. Our simulations give new important physical insights about the expected decoherence process. We have shown that the decoherence of electron dynamics happens on the time scale of a few femtoseconds, with the interplay of different mechanisms: the dephasing is responsible for the fast decoherence while the nuclear overlap decay may actually help maintain it and is responsible for small revivals.
Highlights
Knowledge about the electronic motion in molecules is essential for our understanding of chemical reactions and biological processes
We have shown that the decoherence of electron dynamics happens on the time scale of a few femtoseconds, with the interplay of different mechanisms: the dephasing is responsible for the fast decoherence while the nuclear overlap decay may help maintain it and is responsible for small revivals
Electronic motion initiates specific rearrangements of atoms in molecules that are responsible for chemical reactions and biological processes
Summary
Previous works showed that the nuclear motion treated classically with the Ehrenfest method does not destroy electron dynamics [13,14,15,19,21,22,23] but that the intrinsic distribution of geometries in a nuclear wave packet leads to a fast dephasing of the oscillations in the electronic density [16,18,19] The latter prediction was obtained using an ensemble of independent trajectories. The effect of the nuclear motion may be underestimated with a mean-field approach [24] and the quantum behavior of the nuclei will not be described by independent trajectories These methods do not allow the nuclear wave packets on different electronic states to move in different ways; the mechanism (ii) has been completely omitted so far in the theoretical description of electron dynamics upon molecular ionization.
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