Photochrome molecules are widely studied for their many potential applications. It exists a considerable chemical space to explore for the optimization of the required properties and a necessity to understand their incorporation in devices. Thus, cheap and reliable computational methods can be powerful tools to steer synthetic developments. As DFT methods remain costly for any extensive studies, semi-empirical methods like Density Functional Tight-Binding (TB) could offer a good compromise between accuracy computational cost. However, these approaches necessitate benchmarking on the families of compounds of interest. Thus, the aim of the present study is to evaluate the accuracy of key features calculated with TB methods (DFTB2, DFTB3, GFN2-xTB, and LC-DFTB2) for three sets of photochromic molecules: azobenzene (AZO), norbornadiene/quadricyclane (NBD/QC) and dithienylethene (DTE) derivatives. The features considered are the optimized geometries, the difference in energy between the two isomers (ΔE), and the energies of the first relevant excited states. All the TB results are compared to those obtained with DFT methods and state-of-the-art electronic structure calculation methods: DLPNO-CCSD(T) for ground states and DLPNO-STEOM-CCSD for excited states. Our results show that, overall, DFTB3 is the TB method leading to the best results for the geometries and the ΔE values and can be use alone for these purposes for NBD/QC and DTE derivatives. Single point calculations using r2SCAN-3c with TB geometries allow circumvent the deficiencies of the TB methods in the AZO series. For the electronic transitions, the range-separated LC-DFTB2 method is the most accurate TB method tested for AZO and NBD/QC derivatives.

Providing tools to understand the physical mechanisms governing magnetic properties in transition metal-based compounds is still of great interest. Here, the magnetic exchange coupling in a series of heterodinuclear complexes...