Simulation of Impulsive Vibrational Spectroscopy

Abstract

In the present work we applied a fully atomistic electron−nuclear real-time propagation protocol to compute the impulsive vibrational spectroscopy of the five DNA/RNA nucleobases in order to study the very first steps (subpicosecond) of their energy distribution after UV excitation. We observed that after the pump pulse absorption the system is prepared in a coherent superposition of the ground and the pumped electronic excited states in the equilibrium geometry of the ground state. Furthermore, for relatively low fluency values of the pump pulse, the dominant contribution to the electronic wave function of the coherent state is of the ground state and the mean potential energy surface within the Ehrenfest approximation is similar to that of the ground state. As a consequence, the molecular displacements are better correlated with ground-state normal modes. On the other hand, when the pump fluency is increased the excited-state contribution to the electronic wave function becomes more important and the mean potential energy surface resembles more that of the excited state, producing a better correlation between the molecular displacements and the excited-state normal modes. Finally, it has been observed that the impulsive activation of several vibrational modes upon electronic excitation is triggered by the development of excited-state forces which accelerate the nuclei from their equilibrium positions causing a distribution of the absorbed electronic energy on the nuclear degrees of freedom and could be closely related to the driving force of the ultrafast nonradiative deactivation observed in these systems.

Photoinduced charge-transfer in chromophore-labeled gold nanoclusters: quantum evidence of the critical role of ligands and vibronic couplings

“…Regarding this point, the implementation of the semiclassical Ehrenfest method for nuclear-electron dynamics in DFTB+ allow us to consider the nuclei motion within the TD-DFTB approach. This method has already been successfully used to study coherent breathing oscillations on metal nanoparticles, 45 transient absorption spectra in organic molecules, 46 impulsive vibrational spectroscopy on biological systems, 47 and photoinduced charge transfer in sensitized nanodiamonds. 22 In a experimental work of M.S.…”

A real-time time-dependent density functional tight-binding implementation for semiclassical excited state electron-nuclear dynamics and pump-probe spectroscopy simulations

“…We have studied the good correlation between the IV spectrum and the PED in previous works. 21,88 What is different in this case, as shown in figure 7, is the drop in intensity in both the IV spectrum and the PED for the peaks centered in 448 and 1830 cm −1 . We have observed that these modes are the most coupled with the Soret transition, 21 in a partial agreement with experimental evidence.…”

“…In previous works, 21,88 we have proposed interpreting the IV spectrum along with the potential energy distributed (PED) on ground-state normal modes after the pulse. The PED is obtained from the pump-only trajectory projecting the nuclear displacements onto normal modes coordinates as follows: 98…”

Ab initio simulation of laser-induced electronic and vibrational coherence

“…Compared to other methods for computing non-adiabatic dynamics, the focus is shifted away from potential-energy surfaces (PES) towards a real-space representation based on the charge density. Further conclusions can be drawn from direct simulations of third-order spectroscopy, which is fairly straightforward with RT-TDDFT or related real-time methods [38][39][40][41][42].…”