Notes on simulating two-dimensional Raman and terahertz-Raman signals with a full molecular dynamics simulation approach

Ito, Hironobu; Jo, Ju Yeon; Tanimura, Yoshitaka

doi:10.1063/1.4932597

Cited by 28 publications

(34 citation statements)

References 80 publications

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“…This observation is in stark contrast to results from recent MD work, which revealed an echo for the TRT pulse sequence. 28,44,45 That echo originated from the hindered rotation band around 600 cm −1 , which we however do not observe in the experiment due to the limited bandwidth. A large nonlinearity in the polarizability for that mode can be understood from the fact that a strict ∆J = 2 selection rule would apply for a Raman interaction, together with a ∆J = 1 selection rule for a THz interaction, in the limiting case of a free rather than hindered rotor.…”

Section: Discussionmentioning

confidence: 54%

Feynman diagram description of 2D-Raman-THz spectroscopy applied to water

Sidler

Hamm

2019

The Journal of Chemical Physics

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2D-Raman-THz spectroscopy of liquid water, which has been presented recently (Proc. Natl. Acad. Sci. USA 110, 20402 (2013)), directly probes the intermolecular degrees of freedom of the hydrogen-bond network. However, being a relatively new technique, its information content is not fully explored as to date. While the spectroscopic signal can be simulated based on molecular dynamics simulation in connection with a water force field, it is difficult to relate spectroscopic signatures to the underlying microscopic features of the force field. Here, a completely different approach is taken that starts from an as simple as possible model, i.e., a single vibrational mode with electrical and mechanical anharmonicity augmented with homogeneous and inhomogeneous broadening. An intuitive Feynman diagram picture is developed for all possible pulse sequences of hybrid 2D-Raman-THz spectroscopy. It is shown that the model can explain the experimental data essentially quantitatively with a very small set of parameters, and it is tentatively concluded that the experimental signal originates from the hydrogen-bond stretching vibration around 170 cm −1 . Furthermore, the echo observed in the experimental data can be quantified by fitting the model. A dominant fraction of its linewidth is attributed to quasi-inhomogeneous broadening in the slowmodulation limit with a correlation time of 370 fs, reflecting the lifetime of the hydrogen-bond networks giving rise the absorption band.

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Section: Discussionmentioning

confidence: 54%

Feynman diagram description of 2D-Raman-THz spectroscopy applied to water

Sidler

Hamm

2019

The Journal of Chemical Physics

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“…[47][48][49] For example, whenÂ =B =Ĉ =Π, withΠ being a component of the polarizability tensor, the response R(t, t ) is relevant to two-dimensional Raman spectroscopy. 12,15,47,[53][54][55][56][57][58][59] If, on the other hand,Â =Π andB =Ĉ =μ (μ being a component of the dipole operator), then Eq. 14reduces to a particular scheme of two-dimensional terahertz-Raman spectroscopy.…”

Section: B Double Kubo Transform and Second-order Responsementioning

confidence: 99%

“…14reduces to a particular scheme of two-dimensional terahertz-Raman spectroscopy. [47][48][49]60 Expanding the commutators of Eq. 14, we find that R(t, t ) involves a linear combination of four two-time standard correlation functions.…”

Section: B Double Kubo Transform and Second-order Responsementioning

confidence: 99%

“…II B), 3 which are relevant to vibrational spectroscopy such as 2D-Raman and 2D-THz-Raman spectroscopy. [47][48][49] By expressing the response functions in the frequency domain, it is possible to rewrite them in terms of the real (symmetric) and imaginary (asymmetric) parts of the corresponding double Kubo transformed (DKT) correlation functions. The main contribution to the response can be expressed only in terms of the symmetric DKT, invoking a harmonic reference potential with operators expanded to second order in the harmonic variable.…”

Section: Introductionmentioning

confidence: 99%

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Inclusion of nuclear quantum effects for simulations of nonlinear spectroscopy

Jung

Videla

Batista

2018

The Journal of Chemical Physics

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The computation and interpretation of nonlinear vibrational spectroscopy is of vital importance for understanding a wide range of dynamical processes in molecular systems. Here, we introduce an approach to evaluate multi-time response functions in terms of multi-time double symmetrized Kubo transformed thermal correlation functions. Furthermore, we introduce a multi-time extension of ring polymer molecular dynamics to evaluate these Kubo transforms. Benchmark calculations show that the approximations are useful for short times even for nonlinear operators, providing a consistent improvement over classical simulations of multi-time correlation functions. The introduced methodology thus provides a practical way of including nuclear quantum effects in multi-time response functions of non-linear optical spectroscopy.

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“…However, this information is encoded in complex, threepoint correlation functions that must be disentangled with the aid of theoretical and computational methods. 30,31,[34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] This problem of interpretation is further complicated by the number of vibrational states that need to be considered. Whereas infrared-active modes are usually in their vibrational ground state at room temperature and typically only involve single excitations upon illumination, THz-active modes can be thermally excited at room temperature, and multiple transitions between the different states are possible.…”

Section: Introductionmentioning

confidence: 99%

Interpretation of the THz-THz-Raman Spectrum of Bromoform

et al. 2019

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Nonlinear THz-THz-Raman (TTR) liquid spectroscopy offers new possibilities for studying and understanding condensed-phase chemical dynamics. Although TTR spectra carry rich information about the systems under study, the response is encoded in a three-point correlation function comprising of both dipole and polarizability elements. Theoretical methods are necessary for the interpretation of the experimental results. In this work, we study the liquid-phase dynamics of bromoform, a polarizable molecule with a strong TTR response. Previous work based on reduced density matrix (RDM) simulations suggests that unusually large multi-quanta dipole matrix elements are needed to understand the measured spectrum of bromoform. Here, we demonstrate that a self-consistent definition of the time coordinates with respect to the reference pulse leads to a simplified experimental spectrum. Furthermore, we analytically derive a parametrization for the RDM model by integrating the dipole and polarizability elements to the 4 th order in the normal modes, and we enforce inversion symmetry in the calculations by numerically cancelling the components of the response that are even with respect to the field. The resulting analysis eliminates the need to invoke large multi-quanta dipole matrix elements to fit the experimental spectrum; instead, the experimental spectrum is recovered using RDM simulations with dipole matrix parameters that are in agreement with independent ab initio calculations. The fundamental interpretation of the TTR signatures in terms of coupled intramolecular vibrational modes remains unchanged from the previous work.

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Notes on simulating two-dimensional Raman and terahertz-Raman signals with a full molecular dynamics simulation approach

Cited by 28 publications

References 80 publications

Feynman diagram description of 2D-Raman-THz spectroscopy applied to water

Feynman diagram description of 2D-Raman-THz spectroscopy applied to water

Inclusion of nuclear quantum effects for simulations of nonlinear spectroscopy

Interpretation of the THz-THz-Raman Spectrum of Bromoform

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