ECAMP 15

To access the natural timescale of electronic motion in molecules, attosecond resolution is needed. But triggering such ultrafast dynamics in excited molecules requires UV/Vis ultrashort pulses, of just a few femtoseconds. These pulses, that are becoming increasingly available in recent years [1], have a broad energy bandwidth, which creates a superposition of electronic excited states, followed by coupled electron-nuclear non-adiabatic dynamics that can affect the initial electronic coherences. The development of an appropriate framework to model such dynamics is crucial to correctly interpret hypothetical pump probe experiments capable of monitoring those electronic coherences in real time. Because of that, we are currently working on a modified version of Ab Initio Multiple Spawning (AIMS) methodology [2], that propagates the dynamics through frozen gaussian functions following classical trajectories. This choice is justified because AIMS has a much lower computational cost than fully quantum methods (such as multi-configuration time-dependent Hartree), but it is still able to accurately describe electronic coherences from the very beginning with some improvements of the standard program [3], in contrast to more classical methods such as Trajectory Surface Hopping. In this work, we implement for the first time the AIMS methodology to model electronic coherences between multiple excited states in multielectronic diatomic and small polyatomic molecules, where quantum approaches are also at hand. It is worth highlighting that we took advantage of the software TeraChem to carry out the electronic structure calculations due to its capability to run on GPUs, which are considerably faster than the usual CPUs [4]. We also analyze the sensibility of these coherences to different parameters of the simulation, such as the initial basis set of coupled gaussian functions, the spawning threshold, the order of approximation of Hamiltonian matrix elements and the explicit inclusion of the laser pulse (XFAIMS [5]).
[1] M. Reduzzi et al., Optics Express 31, 16 (2023)
[2] B. Curchod and T. Martínez, Chem. Rev. 118, 7 (2018)
[3] B. Mignolet and B. Curchod, J. Chem. Phys. 148, 134110 (2018)
[4] I. Ufimtsev and T. Martínez, J. Chem. Theory Comput. 5, 10 (2009)
[5] B. Mignolet, B. Curchod and T. Martínez, J. Chem. Phys. 145, 19 (2016)

TOMATTO project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 951224).