Chemistry, Light and Dynamics Mini Symposium

New and old challenges in spectroscopy modeling - Prof. Anna Krylov

Spectroscopy is a powerful tool for interrogating the matter, but decoding the message delivered by the spectra is far from trivial. How do we convert the spectra into what the nuclei and electrons are doing? The theoretical modeling provides a way to do so. This lecture will discuss new and old challenges faced by the theory in the context of modeling electronic structure in strong fields, high-energy, and non-linear regimes and highlight recent progress in many-body methodology in treating spectroscopic signatures of core-level states.

[1] S. Gozem and A. I. Krylov, The ezSpectra suite: An easy-to-use toolkit for spectroscopy modeling WIRES Comp. Mol. Sci., e1546 (2021)
[2]L. Kjellsson, K. Nanda, J.-E. Rubensson, G. Doumy, S. H. Southworth, P. J. Ho, A. M. March, A. Al Haddad, Y. Kumagai, M.-F. Tu, T. Debnath, M. S. Bin Mohd Yusof, C. Arnold, W. F. Schlotter, S. Moeller, G. Coslovich, J. D. Koralek, M. P. Minitti, M. L. Vidal, M. Simon, R. Santra, Z.-H. Loh, S. Coriani, A. I. Krylov, and L. Young, Resonant inelastic x-ray scattering reveals hidden local transitions of the aqueous OH radical, Phys. Rev. Lett. 124, 236001 (2020)

[3] Z.-H. Loh, G. Doumy, C. Arnold, L. Kjellsson, S. H. Southworth, A. Al Haddad, Y. Kumagai, M.-F. Tu, P. J. Ho, A. M. March, R. D. Schaller, M. S. Bin Mohd Yusof, T. Debnath, M. Simon, R. Welsch, L. Inhester, K. Khalili, K. Nanda, A. I. Krylov, S. Moeller, G. Coslovich, J. Koralek, M. P. Minitti, W. F. Schlotter, J.-E. Rubensson, R. Santra, and L. Young, Observation of the fastest chemical processes in the radiolysis of water, Science 367, 179 – 182 (2020)

Dynamics near a conical intersection – a diabolical compromise for ab initio multiple spawning - Lea Ibele

Full multiple spawning describes the nonadiabatic dynamics of a system in principle exactly, expressing nuclear wavefunctions by coupled classically-moving trajectory basis functions (TBFs). For molecular systems, the couplings between TBFs can approximated, leading to the more tractable ab initio multiple spawning (AIMS), which provides an accurate description of the photochemistry of larger molecules in full dimensionality. While these approximations have recently been validated for a 1D system, no detailed tests of AIMS have been conducted for dynamics approaching conical intersections [1].

In this work, we investigated the implications of the AIMS approximations on the dynamics of a molecule through a conical intersection by using a two state 2D-linear vibronic coupling model, parametrised to reproduce the nonadiabatic dynamics of the molecules bis(methylene)adamantyl, butatriene cation and pyrazine [2] We analysed the AIMS dynamics in comparison with exact quantum dynamics, for the predicted population decay and the time-evolution of the wavepackets [3].
Additionally, we looked at the influence of the neglected contributions to the matrix elements, highlighting the challenges of including second-order couplings and geometric phase effects within the AIMS-framework.

[1] B. Mignolet and B. F. E. Curchod, J. Chem. Phys., 148, 134110 (2018)
[2] I. G. Ryabinkin et al., J. Chem. Phys., 140, 214116 (2014) [3] L. M. Ibele and B. F. E. Curchod, J. Chem. Phys, accepted (2021)