Evaluating the accuracy of DFT functionals applying for determining geometries of coumarin derivatives using the averaged Cartesian atomic coordinates.

This study reports a new approximate method to create reference data for evaluating the accuracy of density functional theory (DFT) functionals in predicting optimized geometries of ground states (GSs) and excited states (ESs), as an alternative to the limited reference data from high‐accuracy theoretical levels. This method utilized atomic coordinates within molecules to assess accuracy in predicting optimized geometries, rather than relying solely on individual parameters such as bond lengths, bond angles, and dihedral angles. Additionally, the method used the averaged Cartesian atomic coordinates within molecules obtained from multiple DFT functionals as reference values, instead of the atomic coordinates derived from high‐accuracy theoretical levels. This approach was demonstrated to yield reliable results based on comparative evaluation with a reference dataset of optimized geometries for GSs and ESs obtained at CC3/CCSDR(3) and EOM‐CCSD. These new findings opened opportunities for assessing the accuracy of DFT functions in predicting optimized geometries, particularly for medium‐to‐large organic molecules, where reference structures are challenging to obtain. This method was applied to evaluate the accuracy of 10 DFT functionals in predicting optimized geometries of the GS and ES of 25 coumarin derivatives. The results showed that the PBE0, APFD, and CAM‐B3LYP functionals provided the safest and most reliable accuracy. In contrast, the PBE and BP86 functionals provided the least safe and least reliable accuracy for optimized geometries of the GS and ES. These findings were obtained from the results of research conducted on a limited number of coumarin derivatives (25 compounds) and a restricted set of DFT functionals (10 functionals). Therefore, further similar studies are needed to expand the applicability of these research results. [ABSTRACT FROM AUTHOR]