Abstract
Capturing nuclear dynamics through conical intersections is pivotal to understand the fate of photoexcited molecules. The concept of a conical intersection, however, belongs to a specific definition of the electronic states, within a Born–Huang representation of the molecular wavefunction. How would these ultrafast funneling processes be translated if an exact factorization of the molecular wavefunction were to be used? In this article, we build upon our recent analysis [B.F.E. Curchod, F. Agostini, J. Phys. Chem. Lett. 8, 831 (2017)] and address this question in a broader perspective by studying the dynamics of a nuclear wavepacket through two types of conical intersections, differing by the strength of their underlying diabatic coupling. Our results generalize our previous findings by (i) showing that the time-dependent potential energy surface smoothly varies, both in time and in position, between the corresponding diabatic and adiabatic potentials, with sometimes more complex features if interferences are observed, (ii) highlighting the non-trivial behavior of the time-dependent vector potential and the fact that it cannot be gauged away in general, and (iii) justifying some approximations employed in the derivation of a mixed quantum/classical scheme based on the exact factorization.
Highlights
Conical intersections (CIs) [1,2,3,4,5,6,7,8] are often invoked to interpret relaxation processes undergone by photoexcited molecules
The theoretical framework of the exact factorization of the electron-nuclear wavefunction has been employed to investigate the nuclear dynamics at conical intersections
The time-dependent potential energy surface and the time-dependent vector potential have been analyzed as indicators of the nonadiabatic effects influencing nuclear relaxation through a region of strong coupling between electronic states
Summary
Conical intersections (CIs) [1,2,3,4,5,6,7,8] are often invoked to interpret relaxation processes undergone by photoexcited molecules. CIs are prototypical examples of the breakdown of the Born–Oppenheimer (BO) approximation, as they represent efficient funnels [9,10,11] for population transfer between electronic states, mediated by nuclear motion They are regions of configuration space where the adiabatic potential energy surfaces (PESs) are degenerate and exhibit, within the so-called branching place, a typical double-cone shape. These curious features of adiabatic PESs have been widely studied in the chemical physics literature, for their role in nonadiabatic processes and for the effect that the related Berry phase (a topological phase) has on adiabatic phenomena, for instance occurring purely in the electronic ground state [2,3,4,5,6,7,8,11,12,13,14,15,16,17,18,19,20].
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