In 2012, a new functional form called N12 was developed that pushes the limits of local functionals, providing simultaneous accuracy on energetic and structural properties of both solids and molecules 171 . Unlike traditional GGAs, the N12 functional is a non-separable approximation (NGA) between the density and its (reduced) gradient that embodies both exchange and correlation effects, and can be seen as a generalization of the dualrange M11-L. By adding a dependence on the kinetic energy density, and the M08/M11 correlation term, Peverati and Truhlar designed the MN12-L meta-non-separable gradient approximation to obtain even broader accuracy with a local functional. With the inclusion of 25% of short-range exact exchange (that is screened at large distances), the MN12-SX functional yields better results than MN12-L for most chemical properties, and is notably more successful in calculating semiconductor band gaps 149 . Finally, re-optimization of MN12-L using a larger training database and additional smoothness restraints on the functional form resulted in the most recent MN15-L local meta-NGA functional. This latter shows better performance for transition metals and is generally recommended over MN12-L . Its hybrid version, called MN15, was trained using a combination of single-reference chemical data (barrier heights), as well as diverse multi-reference transitionmetal bond energies and atomic excitation energies that are challenging to describe with KS-DFT. As a result, it provides broad accuracy for both multi-reference and single-reference systems, and at the same time has demonstrated outstanding performance in describing noncovalent interactions . Note that we include NGAs in the category of GGAs in the rest of the text for simplicity's sake.