Ab Initio Multiple Spawning (AIMS) is a method that allows for accurate yet efficient excited-state molecular dynamics. It portrays nuclear wavepackets as linear combinations of coupled Gaussian functions that follow classical trajectories. (See our recent review for a detailed discussion on this method.)
AIMS emerges from the (formally-exact) Full Multiple Spawning framework by invoking two central approximations related to the coupling between Gaussian functions. While AIMS has been successfully employed to simulate the photochemistry of numerous molecules, a detailed analysis of the strengths and weaknesses of its underlying approximations was missing in the literature.
Together with Dr. Benoît Mignolet (University of Liège), we investigated in great details the approximations in AIMS using a model molecule, LiH, photoexcited by an external electric field to generate interfering nuclear wavepackets. Interestingly, AIMS could capture the behavior of properties like electronic state populations and the more challenging time-dependent molecular dipole moment, even if this low-dimensional system constitutes one of the worst-case scenarios for the AIMS approximations. We furthermore proposed and validated strategies, compatible with the simulation of larger molecular systems, to overcome some potential shortcomings of these approximations.
This Symposium was directly followed by the first TeraChem/FMS developer meeting. TeraChem is a GPU-accelerated quantum chemical package that can be interfaced with the nonadiabatic dynamics method Full Multiple Spawning (FMS). Both codes are used in the ISP group and this developer meeting was an exciting opportunity to discuss their future directions and developments.
From February 26 to March 2, Basile co-organized a CECAM School entitled “Nonadiabatic Molecular Dynamics in Three Different Flavors” with Todd Martínez (Stanford University), Graham Worth (University College London), and Ivano Tavernelli (IBM Zürich). The School took place at the CECAM Headquarter in Lausanne (Switzerland).
The central idea of this School was to introduce the 40 participants to general concepts of computational photochemistry as well as three distinct methods for nonadiabatic molecular dynamics: Multiconfiguration Time-Dependent Hartree (MCTDH), Ab Initio Multiple Spawning (AIMS), and Trajectory Surface Hopping (TSH). The morning was dedicated to lectures for each method, and exercises on the computer were organized each afternoon. The main goal of these exercises was for the participants to play with each technique and to be able to use them, maybe, in their own research.
What happens to a molecule after it absorbs light? Have a look at our review freshly published in Chemical Reviews to discover different theoretical approaches that aim to answer this question. We focus our attention on nonadiabatic frameworks that can be derived from the time-dependent molecular Schrödinger equation and employ traveling Gaussian functions to describe nuclear wavefunctions. We discuss in details the different approximations used to produce methods that are compatible with an on-the-fly propagation of the Schrödinger equation for molecules in their full configuration space, such as Ab Initio Multiple Spawning (AIMS), MultiConfigurational Ehrenfest (MCE), or variational Multi-Configurational Gaussian (vMCG).
Basile gave an invited talk during the Kick Off meeting of the CHAMPS (Chemistry and Mathematics in Phase Space) programme in Bristol. You can learn more about this 6 year EPSRC-sponsored Programme Grant here.
Basile organized with Petr Slavíček, Eva Muchova, and Jean-Hugues Fillion, a workshop entitled “Formation and destruction of molecules by UV and X-ray radiation”, in the context of the COST Action “Our Astro-Chemical History“. This workshop took place at the University of Bristol and triggered very stimulating discussions between theoretical and experimental chemists on the effect of UV and X-ray radiations on molecules in interstellar space.