Abstract
Photo-initiated processes in molecules often involve complex situations where the induced dynamics is characterized by the interplay of nuclear and electronic degrees of freedom. The interaction of the molecule with an ultrashort laser pulse or the coupling at a conical intersection (CoIn) induces coherent electron dynamics which is subsequently modified by the nuclear motion. The nuclear dynamics typically leads to a fast electronic decoherence but also, depending on the system, enables the reappearance of the coherent electron dynamics. We study this situation for the photo-induced nuclear and electron dynamics in the nucleobase uracil. The simulations are performed with our ansatz for the coupled description of the nuclear and electron dynamics in molecular systems (NEMol). After photo-excitation uracil exhibits an ultrafast relaxation mechanism mediated by CoIn's. Both processes, the excitation by a laser pulse and the non-adiabatic relaxation, are explicitly simulated and the coherent electron dynamics is monitored using our quantum mechanical NEMol approach. The electronic coherence induced by the CoIn is observable for a long time scale due to the delocalized nature of the nuclear wavepacket.
Highlights
The interaction of molecular systems with light induces numerous chemical processes which can be natural, such as vision [1,2,3] and photosynthesis [4,5,6,7], or artificial like organic photovoltaics [8,9,10,11,12] and photocatalysis [13, 14]
The necessary non-adiabatic couplings (NACs) between the states involved are only present in the vicinity of a conical intersection (CoIn) [16,17,18] or an avoided crossing
In this work we investigate the photo-induced nuclear and electron dynamics of the nucleobase uracil with nuclear and electron dynamics in molecular systems (NEMol)
Summary
The interaction of molecular systems with light induces numerous chemical processes which can be natural, such as vision [1,2,3] and photosynthesis [4,5,6,7], or artificial like organic photovoltaics [8,9,10,11,12] and photocatalysis [13, 14]. The second summation defines the coherent contribution to the coupled electron density and consists of the time-dependent overlap Ajk(t), the oneelectron transition density ρjk(r; R (t)) and its pure electronic phase ξjk(t) defined by the energy difference Ejk between the electronic states involved This coherent part of the density can be induced by an interaction with a laser pulse or by non-adiabatic coupling events. For non-dissociative molecular dynamics like in uracil the time-dependent overlap determines the disappearance and especially the potential reappearance of the coherent electron dynamics To go beyond this single geometry approximation we introduced the NEMol-grid [32] where the full nuclear coordinate space is split up into segments for which partial densities are calculated. The third term denotes the coherence between the states characterized by the product of the two orbitals
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