Assessment of Newest Meta-GGA Hybrids for Late Transition Metal Reactivity: Fractional Charge and Fractional Spin Perspective

In recent years there has been a significant interest of DFT community in the development of new (hybrid) meta-generalized gradient approximations (meta-GGAs), including range-separated hybrids. The new DFT methods, e.g., SCAN, SCAN0, omega B97M-V, and our own LC-PBETPSS-D3 promise an improvement over well-established models, such as, PBE, PBEO, omega B97X-D, and the M06-type functionals. However, the tests published to date cover only main-group chemistry. This work fills this gap by examining reactivity of model systems, such as gold-ligand complexes, Pd and Ni insertion reactions into covalent bonds, and the pathway for olefin metathesis by a model Grubbs system, all of which include late transition metals. In the attempt to rationalize the performance of functionals, we study the fractional charge and fractional spin errors of the Au atom and the Au-7 cluster. While we find the main qualitative issues of DFT are not yet solved, the introduction of meta-GGA ingredients yields a notable improvement makeing the new meta-GGAs the preferred choice for transition-metal chemistry.