Simulation of Multi-Dimensional Signals in the Optical Domain: Quantum-Classical Feedback in Nonlinear Exciton Propagation

Abstract

We present an algorithm for the simulation of nonlinear 2D spectra of molecular systems in the UV-vis spectral region from atomistic molecular dynamics trajectories subject to nonadiabatic relaxation. We combine the nonlinear exciton propagation (NEP) protocol, that relies on a quasiparticle approach with the surface hopping methodology to account for quantum-classical feedback during the dynamics. Phenomena, such as dynamic Stokes shift due to nuclear relaxation, spectral diffusion, and population transfer among electronic states, are thus naturally included and benchmarked on a model of two electronic states coupled to a harmonic coordinate and a classical heatbath. The capabilities of the algorithm are further demonstrated for the bichromophore diphenylmethane that is described in a fully microscopic fashion including all 69 classical nuclear degrees of freedom. We demonstrate that simulated 2D signals are especially sensitive to the applied theoretical approximations (i.e., choice of active space in the CASSCF method) where population dynamics appears comparable.

Nonadiabatic dynamics: The SHARC approach

“…Related works using SHARC for nucleobases were focused on uracil (Richter & Fingerhut, ; Richter, Mai, Marquetand, & González, ) and thymine (Mai, Richter, Marquetand, & González, , ), where also a low but non‐negligible population of triplet states was observed in gas phase. Generally speaking, these works show that in the isolated pyrimidine nucleobases the triplet states can potentially be relevant to understand its excited‐state relaxation dynamics, and that they should not be neglected a priori.…”

Ultrafast and radiationless electronic excited state decay of uracil and thymine cations: computing the effects of dynamic electron correlation

“…56,57 Our simulations of these spectral signals assume that excited state absorptions of the individual 2 n + O and 2 π + states are dominated by the electronic structure at their corresponding minima, 58,59 thus neglecting the time-evolution of the system and its lineshape as their simulation requires more sophisticated approaches that are out of the scope of the present study. [60][61][62][63] The CAS state interaction method 64 was employed to evaluate transition dipole moments and oscillator strengths and the energies were corrected with the standard (single-state) CASPT2 formulation with an IPEA shift of 0.0.…”

Two-dimensional electronic spectroscopy as a tool for tracking molecular conformations in DNA/RNA aggregates

“…Effectively, the spectra of the individual snapshots are subject to a constant line broadening of 1000 cm -1 , which has been set so that the broadenings along Ω 1 for the total ApA spectrum mimic the experimental broadening recently measured in 2DUV experiments for adenine. 17 Although several computational approaches have been devised recently to consider spectral diffusion and non-adiabatic effects on the simulated 2DES, [45][46][47][48][49] the size of the current system prevents the usage of more sophisticated approaches. Quasi-absorptive signals were simulated for the condition of a collinear pump pulse pair (thus recording simultaneously rephrasing and non-rephasing contributions).…”