Coherent infrared multidimensional spectra of the OH stretching band in liquid water simulated by direct nonlinear exciton propagation

Abstract

The two-dimensional vibrational response of the disordered strongly fluctuating OH exciton band in liquid water is investigated using a new simulation protocol. The direct nonlinear exciton propagation generalizes the nonlinear exciton equations to include nonadiabatic time dependent Hamiltonian and transition dipole fluctuations. The excitonic picture is retained and the large cancellation between Liouville pathways is built-in from the outset. The sensitivity of the photon echo and double-quantum-coherence techniques to frequency fluctuations, molecular reorientation, intermolecular coupling, and the two-exciton coherence is investigated. The photon echo is particularly sensitive to the frequency fluctuations and molecular reorientation, whereas the double-quantum coherence provides a unique probe for intermolecular couplings and two-exciton coherence.

Frequency Distribution of the Amide-I Vibration Sorted by Residues in Amyloid Fibrils Revealed by 2D-IR Measurements and Simulations

“…In order to establish a link between structure fluctuations and the frequencies, DFT maps were recently introduced by combining ab-initio calculations and MD simulated trajectories. 43–55 Several parameterization schemes have been employed for the amide I mode in peptides. 43–49,51,52 We have used the CHO4 parameterization.…”

“…For each trajectory, the signal was generated following the simulation protocol in Ref. 55. The signal S ( t 1 .…”

Two-Dimensional Double-Quantum Spectra Reveal Collective Resonances in an Atomic Vapor

“…The intra-atomic elements of K mn are set to large numbers to ensure that each atom cannot be excited twice, while the interatomic elements of K mn are set to zero since the interatomic two-exciton couplings are ignored. As the last step, 2D spectra are generated using the SPECTRON package [24]. The double-quantum coherence spectrum, S III ( τ, T, t ), is $$\begin{array}{ccc}left{S}_{\mathrm{III}}false(\tau ,T,tfalse)& =& 2{\left(\frac{\iota }{\hslash }\right)}^4\sum _{t_s}\sum _{n_4}{\overrightarrow{\mu }}_{n_4}false(\tau +T+t+t_{s}false)\\ & & \times R_{n_4}^{S_{\mathrm{III}}}false(\tau +T+t+t_s,T+t+t_s,t+t_s,t_{s}false).\end{array}$$…”

Time-averaging approximation in the interaction picture: Absorption line shapes for coupled chromophores with application to liquid water

“…Calculation of nonlinear response functions for a coupled system is a demanding job because two-exciton states are involved in the spectroscopy. 53,66,67 For N coupled twostate chromophores, the dimensionality of the two-exciton states grows as N (N − 1)/2, and therefore, a direct numerical integration of the Schrödinger equation for the two-exciton manifold, which is required to calculate exact response functions, is often a difficult task for a large system. We hope that the present approximate method will be particularly useful when it is extended to nonlinear spectroscopies.…”