Assessing Spin-flip Time-Dependent Density-Functional Based Tight-Binding For Describing Photoisomerisation Reactions

Photoisomerisation of molecular systems are important as building blocks for light driven molecular motors. Understanding the effect of chemical substitution on the underlying mechanisms and the isomerisation quantum yields is crucial for optimizing their functionality. In this study, we develop, implement and evaluate the performance of the spin-flip time-dependent density-functional based tight-binding (SF-TDDFTB) as a cost-effective approach for simulating the excited-state potential energy surfaces of several photoisomerising chromophores. By comparing the results with SF-TDDFTB with all-electron MRSF-TDDFT, we investigate the accuracy of the tight-binding formalism in capturing the correct potential energy surface leading to the photoisomerization pathways for well-known photoisomerisation reactions of a protonated Schiff base, an oxidondole molecular motor, the green fluorescent protein chromophore and a photodrug. Our findings demonstrate that the SF-TDDFTB method offers a balanced trade-off between computational efficiency and accuracy. These results pave the way for more efficient computational models for studying the photoisomerisation reactions of complex molecular systems.