Post-doctoral project

Electronic absorption spectra simulations with nuclear quantum effects in condensed phase

Background

UV-Visible spectroscopy is a powerful tool to characterize and identify molecules while numerical simulations are crucial to interpret electronic spectra from the microscopic point of view. However, simulating electronic spectra in condensed phase from first principles and accurately capturing the band positions but also the band shapes remain a challenging task. One of the most common methods is to use quantum electronic structure computations associated with sampling of the molecule configuration space in order to explore and determine the most probable geometries of the molecule and its environment. Usually, classical molecular dynamics (MD) simulations perform this sampling. However, accounting for nuclear quantum effects during the sampling proves to be crucial 1 in order to correctly reproduce experimental band positions and lineshapes. Nuclear quantum effects (NQE) are phenomena stemming from the quantum delocalization of light nuclei such as protons.

Job description

The aim of this post-doctoral research project is to develop, implement and apply methods to simulate electronic absorption spectra of molecular systems in condensed phase, while taking into account nuclear quantum effects. In particular, the researcher will simulate the spectrum of a small organic molecule in solution, acrolein in water, with several standard methods and compare the results to those given by a method currently developed in our laboratory. Once this initial benchmarking has been performed, the methods will be extended to dynamical approaches, notably to simulate 2D absorption spectra.
We propose to use a quantum thermostat, the adaptive quantum thermal bath 2,3 (adQTB) to correctly account for NQE. Quantum thermostats offer the advantage of a low computational cost, similar to classical MD simulations. The adQTB also includes a systematic adaptation procedure that automatically corrects for zero-point energy leakage, an issue that affects other quantum thermostats methods but is essentially suppressed in the adQTB framework.
The hired researcher will use the adQTB method to sample the configuration space of a small organic molecule in solution, acrolein in water, in its ground state and compare the results to classical (MD) or quantum sampling with path integral methods (PIMD). Absorption spectra will be calculated with vertical transitions with multiconfigurational and DFT quantum chemistry methods. After this initial benchmarking step with acrolein, the adQTB method will be extended to sample initial conditions for surface-hopping algorithms. This new method adQTB-SH will be tested on model systems for which the dynamics can be determined with a numerically exact quantum method (HEOM 4 ). Lastly, the new adQTB-SH code will be extended to simulate 2D absorption spectra and test on model and realistic systems, such as pyrene in ethanol.

References

(1) Borrego-Sánchez, A.; Zemmouche, M.; Carmona-García, J.; Francés-Monerris, A.; Mulet, P.;
Navizet, I.; Roca-Sanjuán, D. Multiconfigurational Quantum Chemistry Determinations of Absorption Cross Sections (σ) in the Gas Phase and Molar Extinction Coefficients (ε) in Aqueous Solution and Air–Water Interface. J. Chem. Theory Comput. 2021, 17 (6), 3571–3582. https://doi.org/10.1021/acs.jctc.0c01083.
(2) Mangaud, E.; Huppert, S.; Plé, T.; Depondt, P.; Bonella, S.; Finocchi, F. The Fluctuation–
Dissipation Theorem as a Diagnosis and Cure for Zero-Point Energy Leakage in Quantum Thermal Bath Simulations. J. Chem. Theory Comput. 2019, 15 (5), 2863–2880. https://doi.org/10.1021/acs.jctc.8b01164.
(3) Mauger, N.; Plé, T.; Lagardère, L.; Bonella, S.; Mangaud, É.; Piquemal, J.-P.; Huppert, S. Nuclear Quantum Effects in Liquid Water at Near Classical Computational Cost Using the Adaptive Quantum Thermal Bath. J. Phys. Chem. Lett. 2021, 12 (34), 8285–8291. https://doi.org/10.1021/acs.jpclett.1c01722.
(4) Mangaud, E.; Jaouadi, A.; Chin, A.; Desouter-Lecomte, M. Survey of the Hierarchical Equations of Motion in Tensor-Train Format for Non-Markovian Quantum Dynamics. Eur. Phys. J. Spec. Top. 2023, 232 (12), 1847–1869. https://doi.org/10.1140/epjs/s11734-023-00919-0.

Estimated dates: 06/2024-12/2025

How to apply: Please send your application before May 3rd by email to:

Etienne Mangaud ([email protected])

Isabelle Navizet ([email protected])

Simon Huppert ([email protected])