An effective semiclassical approach to IR spectroscopy

Micciarelli, Marco; Gabas, F.; Conte, Riccardo; Ceotto, Michele

doi:10.1063/1.5096968

Cited by 37 publications

(43 citation statements)

References 73 publications

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“…MC SCIVR can be rigorously derived from the stationary phase approximation of the exact Feynman’s path integral, and expresses the quantum time-evolution propagator in terms of a few classical trajectories, whose energy is close to the vibrational eigenvalues of the system (see Supplementary Methods). Moreover, MC SCIVR is also able to recover a reliable approximation of the vibrational ground and excited eigenstates by expanding the eigenfunction of each vibrational eigenvalue as a combination of harmonic eigenfunctions 50 – 52 . The combination coefficients are calculated by Fourier transforming the semiclassical approximate quantum mechanical time correlation function of each harmonic eigenfunction at the vibrational eigenvalue obtained from a preliminary MC SCIVR power spectrum calculation (see Supplementary Methods).…”

Section: Introductionmentioning

confidence: 99%

Anharmonic quantum nuclear densities from full dimensional vibrational eigenfunctions with application to protonated glycine

et al. 2020

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The interpretation of molecular vibrational spectroscopic signals in terms of atomic motion is essential to understand molecular mechanisms and for chemical characterization. The signals are usually assigned after harmonic normal mode analysis, even if molecular vibrations are known to be anharmonic. Here we obtain the quantum anharmonic vibrational eigenfunctions of the 11-atom protonated glycine molecule and we calculate the density distribution of its nuclei and its geometry parameters, for both the ground and the O-H stretch excited states, using our semiclassical method based on ab initio molecular dynamics trajectories. Our quantum mechanical results describe a molecule elongated and more flexible with respect to what previously thought. More importantly, our method is able to assign each spectral peak in vibrational spectroscopy by showing quantitatively how normal modes involving different functional groups cooperate to originate that spectroscopic signal. The method will possibly allow for a better rationalization of experimental spectroscopy.

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Section: Introductionmentioning

confidence: 99%

Anharmonic quantum nuclear densities from full dimensional vibrational eigenfunctions with application to protonated glycine

et al. 2020

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“…33, the evaluation of the full absorption spectrum should be feasible. 108,112 √ ω lql + i √ w lp l and…”

Section: Discussionmentioning

confidence: 99%

Reduced rovibrational coupling Cartesian dynamics for semiclassical calculations: Application to the spectrum of the Zundel cation

Bertaina

Liberto

Ceotto

2019

The Journal of Chemical Physics

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We study the vibrational spectrum of the protonated water dimer, by means of a divide-and-conquer semiclassical initial value representation of the quantum propagator, as a first step in the study of larger protonated water clusters. We use the potential energy surface from [Huang et al., J. Chem. Phys. 122, 044308 (2005)]. To tackle such an anharmonic and floppy molecule, we employ fully Cartesian dynamics and carefully reduce the coupling to global rotations in the definition of normal modes. We apply the time-averaging filter and obtain clean power spectra relative to suitable reference states, that highlight the spectral peaks corresponding to the fundamental excitations of the system. Our trajectory-based approach allows us for physical interpretation of the very challenging proton transfer modes. We find that it is important, for such a floppy molecule, to selectively avoid to initially excite lower energy modes, in order to obtain cleaner spectra. The estimated vibrational energies display a mean absolute error (MAE) of ∼ 29cm −1 with respect to available Multi-Configuration time-dependent Hartree calculations and MAE ∼ 14cm −1 when compared to the optically active experimental excitations of the Ne-tagged Zundel cation. The reasonable scaling in the number of trajectories for Monte Carlo convergence is promising for applications to higher dimensional protonated cluster systems.The Zundel cation is the most representative member of the family of protonated water clusters, towards which many computational efforts are being devoted, mainly motivated by a flourishing of experimental results, 11-16 and the request for higher accuracy. [17][18][19][20][21] In this respect, this molecule is a prototypical example that has been tackled by various approaches, given the great biological relevance of the charge transport mechanism in aqueous solutions. [22][23][24][25][26][27] On the experimental side, the vibrational spectrum of the Zundel cation has been investigated by infrared multiphoton photodissociation spectroscopy 28,29 and noble gases predissociation spectroscopy, in particular Argon and Neon. [30][31][32] The theoretical literature about the vibrational spectrum of the Zundel cation is quite vast, since its strong anharmonicity provides the ideal test-bed for theoretical methods. The PES computed at the level of coupled cluster theory and devised in Ref. 33, has been employed by a plethora of methods for vibrational calculations, such as vibrational configuration interaction (VCI), 34 diffusion Monte Carlo, 32,35 classical molecu-

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“…This can become rather costly for accurate ab initio calculations of large molecules. 36,60,[69][70][71][72][73][74][75][76][77][78][79][80] For this reason, two of us have proposed the single-Hessian thawed Gaussian approximation, 39 where…”

Section: Evaluating Spectra Beyond Condon and Harmonic Approximationsmentioning

confidence: 99%

Semiclassical Approach to Photophysics Beyond Kasha’s Rule and Vibronic Spectroscopy Beyond the Condon Approximation. The Case of Azulene

Prlj

Begušić

Zhang

et al. 2020

J. Chem. Theory Comput.

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Azulene is a prototypical molecule with an anomalous fluorescence from the second excited electronic state, thus violating Kasha's rule, and with an emission spectrum that cannot be understood within the Condon approximation. To better understand photophysics and spectroscopy of azulene and other non-conventional molecules, we develop a systematic, general, and efficient computational approach combining semiclassical dynamics of nuclei with ab initio electronic structure. First, to analyze the nonadiabatic effects, we complement the standard population dynamics by a rigorous 1 arXiv:2001.08414v2 [physics.chem-ph] measure of adiabaticity, estimated with the multiple-surface dephasing representation.Second, we propose a new semiclassical method for simulating non-Condon spectra, which combines the extended thawed Gaussian approximation with the efficient single-Hessian approach. S 1 ← S 0 and S 2 ← S 0 absorption and S 2 → S 0 emission spectra of azulene, recorded in a new set of experiments, agree very well with our calculations. We find that accuracy of the evaluated spectra requires the treatment of anharmonicity, Herzberg-Teller, and mode-mixing effects.

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An effective semiclassical approach to IR spectroscopy

Cited by 37 publications

References 73 publications

Anharmonic quantum nuclear densities from full dimensional vibrational eigenfunctions with application to protonated glycine

Anharmonic quantum nuclear densities from full dimensional vibrational eigenfunctions with application to protonated glycine

Reduced rovibrational coupling Cartesian dynamics for semiclassical calculations: Application to the spectrum of the Zundel cation

Semiclassical Approach to Photophysics Beyond Kasha’s Rule and Vibronic Spectroscopy Beyond the Condon Approximation. The Case of Azulene

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