PhD Defense : Isabella MERRITT

Isabella MERRITT, PhD student in CEISAM MODES team, will defend his thesis untitled “Modelling of photochemical reactions through non-adiabatic dynamics simulations” on November 14th 2023 at 9h30 in CEISAM’s conference room « Marie Curie ».


This thesis is concerned with the modelling of photochemical reactions, especially of the popular azobenzene (AZB) photochrome. Photochromes are molecules which can be switched between two different meta-stable forms, using light for at least one direction. The photochemical reactions studied are non-adiabatic (NA), meaning that relaxation to the electronic ground state occurs without release of a photon.
In this thesis, two NA dynamics methods are used to model photoswitching. The first, trajectory surface hopping (TSH), is mixed quantum classical while the second, Multi-Configuration Time Dependent Hartree (MCTDH) is fully quantum mechanical.
We first used TSH to describe the cis-to-trans switching of AZB. Simulations of the opposite trans-to-cis direction then led to identification and correction of a flawed approximation within the TSH implementation in OpenMOLCAS used. Five popular TSH schemes were then benchmarked on a representative set of reactions, to identify which schemes provide reliable results at lower cost.
MCTDH has also been used to model the trans-to-cis photoswitching of AZB. First, static investigations were carried out into the photoswitching process, leading to construction of a reduced dimensionality 3-mode 4-state model Hamiltonian. Using this model, we then simulated using MCTDH the photoreaction, before critically analysing the value and accuracy of our model.


Photochemistry, ab initio calculations, non-adiabatic dynamics, azobenzene, TSH, MCTDH

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