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Mestdagh, J. - M., Barreau, L., & Poisson, L. (2024). Real-time dynamics of vibronic wavepackets within Rydberg and ion-pair states of molecular iodine. Phys Chem Chem Phys, .
Résumé: Real-time dynamics of vibrationally and electronically excited I_2 molecules has been investigated experimentally using the pump-probe technique. A 2-photon excitation was performed either at 269 nm or 266 nm. An electronic and vibrational wavepacket was built as coherent superposition of a few (269 nm excitation) or many (266 nm excitation) Rydberg states of the and series partly coupled with ion-pair states. The probe operated by ionisation or photodetachement. The energy and angular distribution of the resulting photoelectrons, I(+) photocations and I(-) photoanions were monitored. During the dynamics that is turned on by the pump excitation, the wavepacket splits and explores a variety of electronic states of Rydberg and ion-pair character. The experimental results were complemented by molecular dynamics calculations. This provided invaluable information to identify wavepacket motion along ion-pair potential energy curves.
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Attal, L., Falvo, C., Calvo, F., & Parneix, P. (2024). Modeling the dynamics of quantum systems coupled to large-dimensional baths using effective energy states. J. Chem. Phys., 16011(4), 04410700.
Résumé: The quantum dynamics of a low-dimensional system in contact with a large but finite harmonic bath is theoretically investigated by coarse-graining the bath into a reduced set of effective energy states. In this model, the couplings between the system and the bath are obtained from statistically averaging over the discrete, degenerate effective states. Our model is aimed at intermediate bath sizes in which non-Markovian processes and energy transfer between the bath and the main system are important. The method is applied to a model system of a Morse oscillator coupled to 40 harmonic modes. The results are found to be in excellent agreement with the direct quantum dynamics simulations presented in the work of Bouakline et al. [J. Phys. Chem. A 116, 11118–11127 (2012)], but at a much lower computational cost. Extension to larger baths is discussed in comparison to the time-convolutionless method. We also extend this study to the case of a microcanonical bath with finite initial internal energies. The computational efficiency and convergence properties of the effective bath states model with respect to relevant parameters are also discussed.
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Attal, L., Calvo, F., Falvo, C., & Parneix, P. (2024). Coherent state switching using vibrational polaritons in an asymmetric double-well potential. Phys. Chem. Chem. Phys., 2622(9), 753477–754477.
Résumé: The quantum dynamics of vibrational polaritonic states arising from the interaction of a bistable molecule with the quantized mode of a Fabry–Perot microcavity is investigated using a generic asymmetric double-well potential as a simplified one-dimensional model of a reactive molecule. After discussing the role of the light–matter coupling strength in the emergence of avoided crossings between polaritonic states, we investigate the possibility of using these crossings to trigger a dynamical switching of these states from one potential well to the other. Two schemes are proposed to achieve this coherent state switching, either by preparing the molecule in an appropriate vibrational excited state before inserting it into the cavity, or by applying a short laser pulse inside the cavity to obtain a coherent superposition of polaritonic states. The respective influences of dipole moment amplitude and potential asymmetry on the coherent switching process are also discussed.
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Panadés-Barrueta, R. L., Nadoveza, N., Gatti, F., & Peláez, D. (2023). On the sum-of-products to product-of-sums transformation between analytical low-rank approximations in finite basis representation. Eur. Phys. J. Spec. Top., 2322(121), 18971–19041.
Résumé: In this work, we analyze and compare different possible strategies for the transformations among low-rank (i.e., few number of terms) tensor approximations. The motivation behind this is to achieve compact yet accurate representations of potential-like operators (scalar fields) in symbolic or analytical form. We do this analysis from a formal and from a numerical perspective. Specifically, we concentrate on Tucker and Canonic Polyadic ansätze. We introduce the sum-of-product finite basis representations (SOP-FBR) for both. Here, the factor matrices (aka single-particle functions) are approximated through a set of auxiliary basis functions, specific to the system. In this way, analytical, grid-independent, low-rank expressions can be obtained. We illustrate how finite-precision arithmetic hinders transformations among all these forms. The solution to this issue seems to adapt current algorithms to high-precision arithmetic at the expense of an increase in CPU times.
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Tajouo Tela, H., Quintas-Sanchez, E., Dubernet, M. - L., Scribano, Y., Dawes, R., Gatti, F., & Ndengue, S. (2023). Rovibrational states calculations of the H(2)O-HCN heterodimer with the multiconfiguration time dependent Hartree method. Phys Chem Chem Phys, 2522(4644), 3181333–3182433.
Résumé: Water and hydrogen cyanide are two of the most common species in space and the atmosphere with the ability of binding to form dimers such as H(2)O-HCN. In the literature, while calculations characterizing various properties of the H(2)O-HCN cluster (equilibrium distance, vibrational frequencies and rotational constants) have been done in the past, extensive calculations of the rovibrational states of this system using a reliable quantum dynamical approach have yet to be reported. In this work, we intend to mend that by performing the first calculation of the rovibrational states of the H(2)O-HCN van der Waals complex on a recently developed potential energy surface. We use the block improved relaxation procedure implemented in the Heidelberg MultiConfiguration Time-Dependent Hartree (MCTDH) package to compute the states of the H(2)O-HCN isomer, from which we extract the transition frequencies and rotational constants of the complex. We further adapt an approach first suggested by Wang and Carrington-and supported here by analysis routines of the Heidelberg MCTDH package-to properly characterize the computed rovibrational states. The subsequent assignment of rovibrational states was done by theoretical analysis and visual inspection of the wavefunctions. Our simulations provide a Zero Point Energy (ZPE) and intermolecular vibrational frequencies in good agreement with past ab initio calculations. The transition frequencies and rotational constants obtained from our simulations match well with the available experimental data. This work has the broad aim to propose the MCTDH approach as a reliable option to compute and characterize rovibrational states of van der Waals complexes such as the current one.
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